Development and application of wire-mesh sensors for high-speed multiphase flow imaging

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(1)UNIVERSIDADE TECNOLÓGICA FEDERAL DO PARANÁ PROGRAMA DE PÓS GRADUAÇÃO EM ENGENHARIA ELÉTRICA E INFORMÁTICA INDUSTRIAL. EDUARDO NUNES DOS SANTOS. DEVELOPMENT AND APPLICATION OF WIRE-MESH SENSORS FOR HIGH-SPEED MULTIPHASE FLOW IMAGING. DOCTORAL THESIS. CURITIBA AUGUST 2015.

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(3) EDUARDO NUNES DOS SANTOS. DEVELOPMENT AND APPLICATION OF WIRE-MESH SENSORS FOR HIGH-SPEED MULTIPHASE FLOW IMAGING. Doctoral thesis presented to the Graduate Program. in. Electrical. and. Computer. Engineering (CPGEI) of Federal University of Technology – Paraná (UTFPR), in partial fulfilment of the requirements for the degree of Doctor in Science (D.Sc.). Advisor: Prof. Dr. Marco José da Silva.. CURITIBA AUGUST 2015.

(4) Dados Internacionais de Catalogação na Publicação. S237d 2015. Santos, Eduardo Nunes dos Development and application of wire-mesh sensors for high-speed multiphase flow imaging / Eduardo Nunes dos Santos.-- 2015. 205 p. : il.; 30 cm Tese (Doutorado) - Universidade Tecnológica Federal do Paraná. Programa de Pós-graduação em Engenharia Elétrica e Informática Industrial, Curitiba, 2015 Bibliografia: p. 133-173 1. Escoamento multifásico. 2. Detectores. 3. Malha de eletrodos. 4. Engenharia elétrica - Dissertações. I. Silva, Marco José da. II. Universidade Tecnológica Federal do Paraná Programa de Pós-Graduação em Engenharia Elétrica e Informática Industrial. III. Título. CDD 22 -- 621.3 Biblioteca Central da UTFPR, Câmpus Curitiba.

(5) UNIVERSIDADE TECNOLÓGICA FEDERAL DO PARANÁ. Câmpus Curitiba Programa de Pós-Graduação em Engenharia Elétrica e Informática Industrial. Título da Tese Nº. 121. Development and Application of Wire-Mesh Sensors for High-Speed Multiphase Flow Imaging por. Eduardo Nunes dos Santos Orientador: Prof. Dr. Marco José da Silva Esta tese foi apresentada como requisito parcial à obtenção do grau de DOUTOR EM CIÊNCIAS – Área de Concentração: Engenharia de Automação e Sistemas, pelo Programa de Pós-Graduação em Engenharia Elétrica e Informática Industrial – CPGEI – da Universidade Tecnológica Federal do Paraná – UTFPR, às 9:00h do dia 14 de agosto de 2015. O trabalho foi aprovado pela Banca Examinadora, composta pelos doutores: _____________________________________. ___________________________________. Prof. Dr. Marco José da Silva. Prof. Dr. André Augusto Mariano. (Presidente – UTFPR). (UFPR). __________________________________. ___________________________________. Prof. Dr. Sebastian Yuri Cavalcanti Catunda. Prof. Dr. Cícero Martelli. (UFRN). (UTFPR). ___________________________________ Prof. Dr. Rigoberto Eleazar Melgarejo Morales (UTFPR). __________________________________ Visto da Coordenação: Prof. Dr. Emilio Carlos Gomes Wille (Coordenador do CPGEI).

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(7) This thesis is lovingly dedicated to my parents and my family. Their continuous support, encouragement, and constant love has sustained me throughout my life..

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(9) Acknowledgements First and foremost, I would like to express my sincere gratitude to my advisor Prof. Dr.-Ing. Marco José da Silva for the continuous support of my study and research, for his patience, motivation, enthusiasm, and immense knowledge. His guidance helped me throughout during the time of this research and while writing this thesis. I could not have imagined a better advisor and mentor than him for this particular research. Besides him, I am deeply grateful to all my friends and fellow researchers working in the field of multiphase flows whose ideas helped me to complete this research. I am also indebted to my close colleagues and lab-mates, Aluísio Wrasse, Cesar Ofuchi, Frederico Aguiar, Greg dos Santos, Jean Longo, Juliana Leitzke, Leonardo Lipinski, Maína Silva, Murilo Kramar, Nikolas Libert, Rafael Dias and my co-fighter Ph.D. student Tiago Vendruscolo, each of whom who made my professional and academic life a real pleasure. I am also grateful to have worked on multiphase flow problems with a group of extremely talented students including Cristiane Cozin, Fernando Castillo, Mauren Sguario and Virgínia Baroncini from NUEM – Multiphase flow group and STG - Sensing Technology Group. I look forward to having all of you as my colleagues in the future. I take this opportunity to express my gratitude to all of the Department faculty members for their help and support, Professors: Carlos Amaral, Cicero Martell, Flávio Neves, Rigoberto Morales, Daniel Pipa and Valéria Arruda. I am extremely thankful and indebted to them for sharing expertise, their sincere and valuable guidance and encouragement extended to me. I also express my deep gratitude to the head of Experimental Thermal Fluid Dynamics Prof. Dr. Uwe Hampel, my supervisors Eckhard Schleicher and Sebastian Reinecke while working as assistant researcher during my doctoral internship at Helmholtz-Zentrum Dresden-Rossendorf in Institute of Fluid Dynamics, DresdenGermany. I also extend my thanks to Arun Selvaraj, research engineer at Fluid Flow. vii.

(10) & Reactor Engineering in Shell International Exploration and Production Inc. Houston, Texas, USA. Furthermore, I would also like to give a heartfelt, special thanks to Elisabeth Drechsel and her family for the great time in Dresden. Finally, I wish to express sincere thanks to my parents Edison e Mariza for their unceasing encouragement, support and attention throughout my life and many thanks for my brother for the support and for being truly brother when needed. Last but not the least, I express my gratitude for the financial support of Agência Nacional do Petróleo, Gás Natural e Biocombustíveis – ANP, the Financier of Studies and Projects – FINEP and the Ministry of Science and Technology – MCT through the Program of Human Resources ANP for the Oil and Gas Sector – PRH-ANP/MCT – and Training Program of Human Resources PETROBRAS - PRH10-UTFPR. Curitiba, August 2015.. Eduardo Nunes dos Santos. viii.

(11) “Mathematics is an experimental science, and definitions do not come first, but later on” — Oliver Heaviside ‡. ‡. Operators in physical mathematics, part II, Proceedings of the Royal Society of London, Volume 54,. 1893, p. 121 ix.

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(13) Abstract DOS SANTOS, Eduardo N., Development and application of wire-mesh sensors for high-speed multiphase flow imaging. 205 p. Doctoral Thesis – Graduate Program in Electrical and Computer Engineering (CPGEI), Federal University of Technology – Paraná (UTFPR). Curitiba, 2015.. Multiphase flows are present not only in nature but also are very common in industrial activities such as in exploration, production and transport of oil and gas. In oil production, the mixture of gas, oil and water is often found streaming through production columns and flow risers. A lot of progress has been made in recent years in the development and application of measurement techniques applied to multiphase flow measurement in order to accurately quantify, predict and control the flow of multiphase mixtures. Especially, high-speed imaging of multiphase flows has received much attention in recent years. Wire-mesh sensors are flow-imaging devices and allow the investigation of multiphase flows with high spatial and temporal resolution. In the past, such sensors have found widespread application in gas-liquid flows. Its operating principle is based on measurement of a single electrical property (conductivity or permittivity) of flowing mixture. The objective of this work is the application of the wire-mesh technique for high-speed multiphase flow imaging in different flow conditions as applied so far, as well as the further development of this technique by adding the capability of dual-modality (simultaneous conductive/capacitive) operation. Hence, novel routines and data processing algorithms for the investigation of two-phase flows of the type gas-liquid and solid-liquid (slurry) were developed and tested. As a step towards the further development of the wire-mesh sensor technique, a novel dualmodality electronics being able to simultaneously evaluate the conductivity and permittivity component of a fluid through vector measurements (amplitude and phase) is introduced. Further, a model-based algorithm to fuse the data of dual-modality wire. xi.

(14) mesh sensor is developed to obtain individual phase fraction distributions in gas-oilwater three-phase flows. Hence, this thesis’ main contribution to the field of flow measurement and investigation is the development and application of software solutions for extracting flow parameters from wire-mesh sensor data, as well as the improvement in the hardware of measuring electronics. As a result, the range of application of wire-mesh sensors is enhanced being capable to investigate two-phase gas-liquid and slurry flows as well as gas-liquid-liquid three-phase flow problems through high-speed flow imaging.. Keywords: Multiphase flow. Wire-mesh sensor. Electrical conductivity. Electrical Permittivity. Dual modality. Data fusion. Phase fraction. Flow visualization.. .. xii.

(15) Resumo DOS SANTOS, Eduardo N., Desenvolvimento e aplicação de sensores wire-mesh para visualização de escoamentos multifásicos. 205 p. Tese de doutorado – Pós-Graduação em Engenharia Elétrica e Informática Industrial (CPGEI), Universidade Tecnológica Federal do Paraná (UTFPR). Curitiba, 2015.. Escoamentos multifásicos estão presentes não somente em diversos processos da natureza, mas também são muito comuns em diversas atividades industriais, como na exploração, produção e transporte de petróleo e gás. Na produção de petróleo, a mistura multifásica de gás, petróleo e água é frequentemente encontrada fluindo através de colunas e risers de produção. Nos últimos anos muito progresso no desenvolvimento e aplicação de técnicas de medição em escoamentos multifásicos foi realizado cujo intuito é quantificar com exatidão, prever e/ou controlar o fluxo de misturas multifásicas. Em especial técnicas de imageamento do escoamento multifásico estão em foco atualmente. Sensores de malha de eletrodos (wire-mesh sensors) são dispositivos que produzem imagens da distribuição das fases na seção transversal de uma tubulação com alta resolução espacial e temporal. Em estudos anteriores a utilização desse sensor é explorada em diversas aplicações em escoamentos bifásicos (predominantemente do tipo gás-líquido). O princípio de funcionamento do sensor é baseado na medição de uma única propriedade elétrica (condutividade ou permissividade) da mistura multifásica. Portanto, o objetivo deste trabalho é a aplicação da técnica wire-mesh para visualização de escoamentos multifásicos em alta velocidade para condições de escoamentos diferentes daquelas utilizados até o momento, bem como prover a técnica com melhorias, adicionando a capacidade de operar em dupla modalidade (medição simultânea condutiva/capacitiva). Assim, novos algoritmos e rotinas de processamento de dados para a investigação de escoamentos gás-líquido e sólido-líquido (suspensão) foram desenvolvidos e testados. A fim de continuar com o aprimoramento da técnica. xiii.

(16) de medição, uma nova eletrônica capaz de medir simultaneamente a permissividade e condutividade através da medição (vetorial) de amplitude e fase é introduzido. Além disso, um algoritmo baseado em um modelo da permissividade elétrica complexa realiza a fusão dos dados de condutividade e permissividade gerados pela técnica desenvolvida. Assim, esta fusão permite obter distribuições individuais das frações de fase de misturas de óleo-água-gás. A principal contribuição deste trabalho no campo de medição e investigação de escoamentos multifásicos é, por conseguinte, o desenvolvimento e aplicação soluções em software e processamento de dados para extração de parâmetros do fluxo multifasico a partir de dados do sensor wire-mesh, bem como a melhoria no sistema de medição com adoção de medidas vetoriais. Desta forma, a gama de aplicação do sensor wire-mesh é ampliada, permitindo a investigação de escoamentos gás-líquido e gás-sólido, assim como escoamentos trifásicos gás-líquido-líquido através de visualização em alta velocidade da distribuição de fases em escoamentos.. Palavras-chave: Escoamento multifásico. Sensor Wire-mesh. Condutividade elétrica. Permissividade elétrica. Dupla modalidade. Fusão de dados. Fração de fase. Visualização de escoamentos.. xiv.

(17) Contents Acknowledgements .................................................................................................... vii Abstract ..................................................................................................................... xi Resumo ..................................................................................................................... xiii Contents .................................................................................................................... xv List of figures............................................................................................................ xix List of tables ............................................................................................................ xxv Nomenclature ........................................................................................................ xxvii Introduction ..................................................................................... 33 1.1. Motivation ................................................................................................ 33. 1.2. Objectives ................................................................................................. 35. 1.3. Thesis outline ........................................................................................... 35 Measurement techniques for multiphase flow .................................. 37. 2.1. Basic concepts and definitions of multiphase flow .................................... 37 2.1.1 Phase fraction .................................................................................. 38 2.1.2 Superficial and phase velocities ........................................................ 39. 2.2. Flow regimes ............................................................................................. 39 2.2.1 Two-phase, gas-liquid flow ............................................................... 40 2.2.2 Two-phase, liquid-liquid flow ........................................................... 43 2.2.3 Three-phase, gas-liquid-liquid flow ................................................... 44 2.2.4 Two-phase, solid-liquid flow ............................................................. 46. 2.3. Measurement techniques for multiphase flows .......................................... 47 2.3.1 Tomographic flow imaging techniques.............................................. 48. 2.4. Wire-mesh sensor ...................................................................................... 55 2.4.1 Capacitive wire-mesh sensor ............................................................. 58. xv.

(18) 2.4.2 Intrusive effects................................................................................. 59 2.4.3 Applications ...................................................................................... 61 2.5. Summary ................................................................................................... 63 Electrical impedance measurement in fluids ..................................... 65. 3.1. Electrical impedance ................................................................................. 65 3.1.1 Definitions ........................................................................................ 65. 3.2. Dielectric mixtures models ........................................................................ 68. 3.3. Impedance measurement ........................................................................... 71. 3.4. Summary ................................................................................................... 73 Three dimensional bubble shape estimation in gas-liquid flow ......... 75. 4.1. Introduction .............................................................................................. 75. 4.2. Data processing and bubble identification ................................................. 76. 4.3. Results ...................................................................................................... 78 4.3.1 Materials and methods ..................................................................... 78 4.3.2 Bubble shape .................................................................................... 80 4.3.3 Bubble volume evaluation................................................................. 85. 4.4. Conclusions ............................................................................................... 86 Visualization of hold-up distribution in slurries ............................... 87. 5.1. Introduction .............................................................................................. 87. 5.2. Experimental setup ................................................................................... 89. 5.3. Homogeneous criteria and suspension quality ........................................... 91. 5.4. Experimental results ................................................................................. 93 5.4.1 Suspension quality ............................................................................ 93 5.4.2 Phase fraction measurement ............................................................. 96 5.4.3 Solid distribution measurement ........................................................ 99 5.4.4 Three-phase flow ............................................................................. 100. 5.5. Conclusions ............................................................................................. 102 Data fusion model ........................................................................... 105. 6.1. Introduction ............................................................................................ 105. 6.2. Data fusion three-phase flow model ........................................................ 106. xvi.

(19) 6.2.1 System evaluation .......................................................................... 108 6.2.2 Three-phase mixture colour scale ................................................... 109 6.2.3 Flow application ............................................................................. 110 6.3. Conclusions ............................................................................................. 113 Dual-modality mesh electronics ..................................................... 115. 7.1. Introduction ............................................................................................ 115. 7.2. System description .................................................................................. 116. 7.3. Complex voltage measurement ............................................................... 118. 7.4. Measuring electronics .............................................................................. 119. 7.5. System evaluation ................................................................................... 120. 7.6. Permittivity and conductivity measurements ......................................... 123. 7.7. Fluid measurement ................................................................................. 126. 7.8. Conclusions ............................................................................................. 129 Conclusion ...................................................................................... 131. 8.1. Conclusions ............................................................................................. 131. 8.2. Future development ................................................................................ 132. References ............................................................................................................... 133 List of author’s publications ........................................................... 175 Capacitive WMS data processing ................................................... 179 B.1 Permittivity measurement ...................................................................... 179 B.2 Profiles of time-average and cross-sectional phase distributions ............. 181 Bubble detection algorithm ............................................................ 185 C.1 Data binarization .................................................................................... 185 C.2 Bubble identification/labelling ................................................................ 186 C.3 Bubble volume measurement .................................................................. 187 Two-phase gas-liquid results .......................................................... 189 D.1 Bubble nose velocities ............................................................................. 189 D.2 Mean and median images........................................................................ 191 Two-frequency dual-modality WMS .............................................. 201 E.1 Circuit analysis ....................................................................................... 201. xvii.

(20) E.2 Dual-modality wire-mesh electronics and data processing ....................... 202. xviii.

(21) List of figures Figure 2.1: Developing of gas-liquid two-phase flow patterns in (a) vertical (b) horizontal. ................................................................................................ 42 Figure 2.2: Gas-liquid two-phase flow maps (a) horizontal flow [7] and (b) vertical [17]. ................................................................................................................ 43 Figure 2.3: Flow regimes for oil and water based on measurements of horizontal flow plotted in logarithmic scale. The dotted line indicates the difference between forms of water-in-oil and oil-in-water flow (modified from [23])............... 44 Figure 2.4: Multiphase composition triangle (water, oil and gas) commonly found in three-phase flows. (Multiphase triangle modified from [34]). ................... 45 Figure 2.5: Flow regimes for slurry flow in a horizontal pipeline. .............................. 47 Figure 2.6: Sketch of the wire-mesh sensor for lab applications (16 ´ 16 sensitive points) [3]. ............................................................................................................ 56 Figure 2.7: Wire-mesh principle of work illustration.................................................. 56 Figure 2.8: Simplified scheme of the conductivity electrode-mesh device [3]. ............ 57 Figure 2.9: Different wire-mesh sensors in accord with the application (a) 200 mm i.d. 64 × 64 wires (b) 8 mm 16 ´ 16 wires (c) 26 mm i.d. 12 × 12 wires (d) high pressure/temperature applications (e) sensor electronics. ................ 58 Figure 2.10: (a) Schematic diagram of a simplified 4 × 4 wire-mesh sensor electronics, (b) excitation scheme. .............................................................................. 59 Figure 2.11: (a) Bubble fragmentation caused by the wire-mesh sensor, (b) Bubble reconstruction in a bubble column [143]. ................................................. 60. xix.

(22) Figure 2.12: Bubble–electrode wire interaction: (a)–(c) in stagnant liquid, (d)–(f) liquid mass flux of 100 kg/m². (a) and (d): single bubbles; (b) and (e) nose of an approaching slug; (c) and (f) film region of a slug [118]. .......................... 61 Figure 2.13: Number of publications regarding the application and development of wiremesh technology. ...................................................................................... 62 Figure 3.1: Theoretical behaviour of the mixture permittivity for oil–water mixtures according to the different described models. ............................................. 69 Figure 3.2: The model by [312] assumes a continuous phase containing small spheres of two different bulk substances. (1, 1) denotes the electrical properties of continuous phase, while (2, 2) and (3, 3) give the electrical properties of dispersed phases. ...................................................................................... 70 Figure 3.3: The relationship between impedance and component radio [312]. ............ 71 Figure 3.4: (a) Basic circuit configuration of the auto-balancing bridge impedance measuring method. (b) Practical circuit for measuring capacitive impedances formed as parallel circuit of a capacitor and a resistor. ......... 72 Figure 4.1: Two-phase intermittent flow regime and parts of the unity cell. ............. 76 Figure 4.2: (a) Colour map used to represent the void fraction value, 0% water – 100% gas, (b) A bubble image in axial cut, (c) Snap shots of cross section images of void fraction distribution...................................................................... 77 Figure 4.3: Representation of initial Ui and final position Uf and the unity cell dimensions: bubble size LB, Liquid slug size LS and unit cell size LU. ....... 78 Figure 4.4: Two-phase flow map and measuring points. ............................................ 79 Figure 4.5: Experimental two-phase flow plant facility. Superficial velocities are independently measured by means of a Coriolis flow meter for water and a rotameter for air. ...................................................................................... 80 Figure 4.6: Taylor’s bubble images of wire-mesh sensor measurement. ...................... 80. xx.

(23) Figure 4.7: Bubble size for superficial liquid velocity (jL = 1.5 m/s) and superficial gas velocity of (jG = 0.5 m/s, 0.7 m/s, 1.0 m/s and 1.5 m/s). ........................ 82 Figure 4.8: Bubble size nose velocity comparison between wire-mesh sensor technique and predictions from the Bendiken-correlation. ....................................... 83 Figure 4.9: Bubble size distribution for superficial liquid velocity (jL = 1.5 m/s). ..... 84 Figure 4.10: Liquid slug size distribution for superficial liquid velocity (jL = 1.5 m/s) ......................................................................................................... 84 Figure 4.11: Bubble shape according to chosen threshold for jL = 1.5 m/s and jG = 1.5 m/s..................................................................................................... 85 Figure 4.12: Bubble volume measurements using wire-mesh sensor technique. Dashed lines represent ±10% error boundaries. .................................................... 85 Figure 5.1: Experimental apparatus for visualization of hold-up distributions in slurries. ................................................................................................................ 90 Figure 5.2: Photography of the pitched impeller. ...................................................... 90 Figure 5.3: Wire-mesh sensor (16 ´ 16 wires, 100 mm inner diameter) displaced near the bottom of the PVC tank. ................................................................... 91 Figure 5.4: Degree of solid suspension (a) partial suspension; (b) complete suspension; (c) uniform suspension. ............................................................................ 92 Figure 5.5: Mixture index along for increasing impeller speed including the mixture conditions at 1000 – 1600 rpm. ................................................................ 94 Figure 5.6: (a) Mixture index at 1600 rpm (b) Photo of experimental test facility during the stirring process ................................................................................... 94 Figure 5.7: Radial development of mixture relative permittivity with increasing impeller velocity for different solid concentrations. ............................................... 95. xxi.

(24) Figure 5.8: Radial profiles for experimental data at 1600 rpm. The maximum relative deviation from the average value is -1.0629 % at 47.5 mm. ..................... 95 Figure 5.9: Average values of relative permittivity measurements. ............................ 96 Figure 5.10: Measured relative permittivity values ● and linear fit (dashed line) including wet-sand reference point ■ (εwet-sand = 43.26, αwet-sand = 55.1%). . 97 Figure 5.11: Measured solid concentration using empirical approach with deviation from the ideal value less 1%. The solid line represents the ideal function (y = x); the dashed lines show the deviation of 5% from the ideal line. ....... 98 Figure 5.12: Probability density function with a Gaussian distribution fit (ISC = Initial solid concentration, MSC = measured solid concentration). .................... 99 Figure 5.13: Cross section images showing the distribution of solid calculated by the empirical approach. ................................................................................ 100 Figure 5.14: Cross section images distribution of solid calculated by empirical approach. ............................................................................................................... 102 Figure 6.1: Mixture permittivity (a) and conductivity (b) according. It assumes w = 100 mS/cm  w = 80, oil o = 0 o = 3 and gas g = 0 g = 1. The darker surface is for water continuous and the brighter one for oil continuous mixture. The surfaces were plotted according to the continuity equation (6.9) in addition to the condition vw ≥ 0.2 for water-continuous and vo ≥ 0.2 for oil-continuous mixture. ..................................................................... 108 Figure 6.2: Mixture admittance L m for water-continuous (blue) and oil-continuous (green) mixture normalized by the conductivity of water w assuming values given in Figure 6.1. In grey are values obtained when continuous phase fraction is arbitrary, i.e. no restriction for minimum value. ................... 109 Figure 6.3: Colour scheme for three-phase fused images. ......................................... 110 Figure 6.4: Wire-mesh sensor attached to a pipe segment. ...................................... 110. xxii.

(25) Figure 6.5: Resulting images of measured permittivity (a) and conductivity (b) and phase fraction (c) for the layered three-phase experiment. .................... 111 Figure 6.6: Axial slice images of flow experiment: (a) permittivity distribution, (b) conductivity distribution and (c) fused image of phase distribution. At the bottom, three snapshot photos of initial (d), intermediate (e) and final (f) condition. An arrow in (c) indicates an intentional slight agitation of pipe segment to remove oil droplets trapped to the wires. ............................ 112 Figure 6.7: Time series of phase fraction for the flow experiment. .......................... 113 Figure 7.1: Simplified schematic diagram for wire-mesh sensor with four excitation and four receiver wires. ................................................................................. 117 Figure 7.2: Block diagram for a single excitation-receiver pair. ............................... 118 Figure 7.3: Front panel view of the 19” rack electronics box. .................................. 119 Figure 7.4: Developed circuit board ......................................................................... 120 Figure 7.5: Step response of the receiver circuit showing the normalized control, input and output voltages. .............................................................................. 121 Figure 7.6: (a) Gain variation. (b) Absolute phase variation. .................................. 122 Figure 7.7: Amplitude and phase variation for increasing the water conductivity. .. 122 Figure 7.8: (a) Comparison of the reference and measured permittivity values. (b) Relative deviation calculated for the measurements based on the reference values. .................................................................................................... 124 Figure 7.9: (a) Control of the salinity and temperature of the sample (b) magnetic stirrer (VWR Lab ™ Disc - S41) and commercial conductivity probe (Digimed DM-3P). ................................................................................. 125 Figure 7.10: Relative phase variation with increasing water conductivity by addition of sodium chloride. ..................................................................................... 125. xxiii.

(26) Figure 7.11: Sensor immersion in a container containing the substance to be investigated ............................................................................................ 126 Figure 7.12: Normalized amplitude and phase output in measuring different substances. ............................................................................................................... 127 Figure 7.13: Experimental setup for measurements in static conditions, showing the wire-mesh sensor and developed front-end electronics. ........................... 128 Figure 7.14: Results for stratified flow. (a) photography of phase layered structure with water, oil and air, (b) cross section image of measured amplitude, (c) voltage image along a central chord of the pipe, (d) cross section image of measured phase, (e) phase image along a central chord of the pipe. ...................... 128 Figure 7.15: Axial slice and images of flow experiment: (a) amplitude distribution, and (b) phase distribution. ............................................................................ 129 Figure B.1: Capacitance measuring equivalent circuit for one crossing point........... 179 Figure B.2: Weight coefficients ai,j for averaging the gas fraction in the measuring cross section .................................................................................................... 182 Figure B.3: Weight coefficients ai,j,m for calculating radial gas fraction profiles. ....... 183 Figure C.1: Representation of bubbles id’s in wire-mesh data matrix ...................... 187 Figure E.1: Asymptotic and simplified frequency response of a practical circuit for impedance measurement considering the non-ideal components. ............ 202 Figure E.2: (a) Schematic representation of 4 x 4 wire-mesh sensor in a pipe and (b) block diagram of the developed multichannel impedance measuring system. ............................................................................................................... 203 Figure E.3: Multiplexing Scheme to activation and synchronization of the transmitters channels for four excitation wires. .......................................................... 204 Figure E.4: Schematic representation of amplitude spectrum obtained via FFT analysis. ............................................................................................................... 204 xxiv.

(27) List of tables Table 2.1: A comparison of ECT, ERT and EMT (modified from [56]) .................... 55 Table 2.2: Application of typical wire-mesh technology in many flow types ............. 62 Table 4.1: 3D bubble shape estimation image results. ............................................... 81 Table 4.2: Average bubble nose velocities comparison. .............................................. 83 Table 5.1: Reference values of relative permittivity for air, water at 22 ºC, dry sand and wet-sand. ........................................................................................... 97 Table 5.2: Reference values of permittivity for air, water, dry sand and wet sand. . 101 Table 7.1: Values of capacitance and resistance related to the relative permittivity and electrical conductivity for each substance. ............................................. 121 Table 7.2: Result for the permittivity measurement with different substances. Table also presents the mean value of measured permittivity and the relative deviation. ............................................................................................... 123 Table. 7.3:. Values. of. relative. permittivity. and. conductivity. for. different. substances. ............................................................................................. 126. xxv.

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(29) Nomenclature. Roman symbols ∗. ∗. A. Area. m². a, b. Proportionality factors. -. B. Susceptance. S. C. Capacitance. F. D. Pipe diameter. DS. Distance between sensors. m. f. Frequency. Hz. G. Conductance. S. g. Gravity acceleration vector. m/s². H. Height. m. I, i. Electrical current. A. i, j. Spatial indeces. -. j. Superficial velocity. m/s. j. Imaginary unit. -. K. Position. -. k. Temporal index. -. k. Constant. -. kg. Geometric factor. m. L. Length. m. MI. Mixture index. -. Note that in this thesis the bold-faced variables such Z or  represent complex quantity or a vector. xxvii.

(30) P. Pressure. Bar. Q. Volumetric flow rate. m³/s. R. Resistance. W. r. Blade length. m. T. Temperature. º Celsius. T. Internal diameter. m. th. Threshold. -. U. Velocity. m/s. V. Voltage. V. v. Volume. m³. v. Voltage. V. X. Reactance. W. Y. Admittance. S. Z. Impedance. W. Z. Axial distance. m. L. Specific admittance. S. . Phase/Void fraction. m². . Relative deviation from a reference value. -. . Electric permittivity. -. . Conductivity. S/m. q. Angle. rad, º. . Angular frequency. rad/s. Greek symbols. xxviii.

(31) Subscripts A. Air. B, b. Bubble. a, b. Proportionality factors. a. Absolute. f. Final. f. Feedback. g. Gas. H. High. i. Initial. i. Input. L. Low. m. Mixture. O, o. Oil. o. Output. P. Phase. r. Relative. S. Slug. T. Total. u. Unit cell. W, w. Water. x. Unknown. xxix.

(32) Abbreviations AC. Alternating current. CAT. Computer-assisted tomography. CFD. Computational fluid dynamics. CT. Computer tomography. DC. Direct current. ECT. Electrical capacitance tomography. EIT. Electrical impedance tomography. EMT. Electromagnetic tomography. ERT. Electrical resistance tomography. ET. Electrical tomography. FBG. Fiber Bragg Grating. fps. Frames per scond. HSC. High-speed camera. HZDR. Helmholtz-Zentrum Dresden-Rossendorf. ISC. Initial solid concentration. LASII. Laboratório de Sensores e Instrumentação Industrial. LDA. Laser Doppler anemometry. LF. Low frequency. MFM. Multiphase flow metering. MRI. Magnetic resonant imaging. MSC. Measured solid concentrarion. NMR. Nuclear magnetic resonance. PDA. Phase Doppler anemometry. PET. Positron emission tomography. PEPT. Positron emission particle tracking. xxx.

(33) PIV. Particle image velocimetry. ppm. parts per million. ppt. parts per thousand. PRH. Programa de Recursos Humanos da ANP/Petrobras. PTS. Pressurized Thermal Shock. PWR. Pressurized water reactor. QCV. Quick closing valve. ROCOM. Rossendorf Coolant Mixing Model. rpm. Rotation per minute. RPV. Reactor Pressure Vessel. RSD. Relative standard deviation. S. Switch. SCVS. Subchannel Void Sensor. S/H. Sample-and-hold. TDS. Total dissolved solids. TMS. Thermo-resistive Mesh Sensor. UTFPR. Universidade Tecnológica Federal do Paraná. WMS. Wire-mesh Sensor. xxxi.

(34) xxxii.

(35) Introduction. This opening chapter presents the motivation and objectives of the thesis as well as summarizes the contents of further chapters.. 1.1. Motivation. Multiphase flow is defined as two or more immiscible substances having different properties concurrently flowing in a container, such as ducts, pipes, or reactors. It is commonly found in various industrial activities such as exploration and production of oil and natural gas, where it is usually confined to pipes. In oil production activities is commonly found streaming as a mixture of oil, gas and water [1]. The understanding of such phenomena helps in the design of production plants, pipelines and equipment of oil production, as well as determines the efficiency and safety of processes and equipment where they occur. The problem of measuring oil-water-gas flow has been of interest to the petroleum industry since the early 1980s [2]. Since then, many efforts have been spent to monitoring and measure parameters of interest in multiphase flow. The measurement of such parameters is important from two different points of view: •. Technical / practical: for the control and monitoring processes online and in real time, for instance the measurement of volumetric flow rate along the flow lines or production management and supervision;. 33.

(36) 34. Chapter 1 - Introduction. •. Scientific / theoretical: for understanding physical phenomena or support the development of flow models as well as providing data for validating computational fluid dynamic (CFD) codes, where pilot-plant studies are normally used for scaled-down flow simulation of large-scale circuits and components.. For the latter, advanced instrumentation and flow imaging capability is more and more required in order to produce detailed flow data and parameters. Due to such importance, several measurement techniques have been developed and tested, especially flow imaging modalities such as tomographic imaging. However, none of them has a universal application and therefore improvements in measurement technology are still required and are of great interest. The wire-mesh sensor is an intrusive imaging device, which provides flow images at high spatial and temporal resolutions (at moderate cost and simple installation in experimental loops). Such sensors have been successfully employed by a number of researchers to investigate different flow phenomena in past, having been initially applied for visualizing two-phase flow [3]. Wire-mesh sensor’s working principle is to capture differences in some electrical property - conductivity or permittivity - existing in each substance [4] from the wires stretched over the cross section of the pipe. With the passage of flow through the sensor, cross section images of phase distributions are obtained without the need for solving an inverse problem, as usual for tomographic methods. Although. widely. applied,. wire-mesh. sensor. technology. still. requires. improvements in its capability of flow investigation regarding the types of substances involved and also data processing algorithms. Such enhancements might allow achieving a broader application range. In order to perform high-speed imaging of multiphase flow, this doctoral thesis is within the context of development of data processing and hardware techniques to fill some gaps in current wire-mesh sensor technology. Consequently, it is possible to use this measurement technique as an imaging tool to extract parameters of interest in the study of multiphase flows..

(37) Chapter 1 - Introduction. 1.2. 35. Objectives. This work is divided in two main lines. (i). The use and application of currently wire-mesh sensor based on capacitance (electrical permittivity) measurements in two-phase applications: •. Investigation and experimental approach of shape of elongated bubbles in horizontal two-phase gas-liquid intermittent flow;. • (ii). Solid concentration visualization in two-phase solid-liquid slurry flow;. Improvement in the wire-mesh technology due the current presents some limitations in investigation of three-phase flow. •. Development of a data fusion algorithm to obtain individual phase fraction of gas-oil-water flow based on currently dual-modality wire-mesh technology.. •. Development of a new dual-modality technique, increasing the spatial and temporal resolution and also the substance range capability of current systems. The development includes a design of a new electronic instrumentation (receiver modules) to operate sensors up to 16 ´ 16 (16 transmission channels and 16 receiver channels) as well as the algorithms for processing and evaluation of data and measuring system.. As a result, with the development of this instrument, it is intended to contribute to a more universal application than those currently in use.. 1.3. Thesis outline. The thesis is organized as follows. The aim of Chapter 2 and Chapter 3 of this thesis is to give an overview of the multiphase flow background as well as the theory of electrical impedance of fluids and its measurement. Chapter 2 gives a short review on multiphase flow and an overview of state-of-the-art measuring techniques. Chapter 3 describes the theory of electrical properties of fluids; the concepts of impedance and complex permittivity are introduced and the current impedance measurement methods are described. The following three chapters 4 to 7 introduce the development and application for the investigation of flow phenomena. Thus, in Chapter 4 the capacitive wire-mesh.

(38) 36. Chapter 1 - Introduction. imaging technique was applied to investigate typical bubble shape of gas-liquid intermittent flow. Furthermore the qualification of the technique for the measurement of cross-sectional solid concentrations in solid–liquid mixtures is presented in Chapter 5. Chapter 6 introduces the use of a model-based method to fuse the data from the dual-modality wire-mesh sensor and to obtain individual phase fraction of gas-oil-water flow. Following the current trend for multimodality techniques, a novel dual-modality electronics for wire-mesh sensor is presented in Chapter 7. This thesis finishes in Chapter 8 with conclusions, a discussion of main results obtained and suggestions for future work. Some parts of the work described in this thesis are based on papers which were already published in international journals and conferences. Furthermore, a consistent list of these papers can be found in Appendix A..

(39) Measurement techniques for multiphase flow. This. chapter. provides. essential. knowledge. of. multiphase flow summarizing fundamental concepts with relevance to measurement techniques. It does not pretend to present a comprehensive review of the details of any one multiphase flow. Furthermore an overview. of. the. instrumentation. techniques. developed for multiphase flow analysis is described. The. chapter. will. emphasize. on. visualization. techniques focusing on oil and gas applications.. 2.1. Basic concepts and definitions of multiphase flow. Multiphase flow is defined as one in which more than one phase having different properties flow simultaneously in a way that may be in ducts, equipment and porous media, among others. The research into multiphase flow is performed in many areas for instance nuclear, chemical, petroleum, aerospace among others. The simplest case is a two-phase flow when flow in which the same component is present in two different phases (e.g. steam-water flow). In other hand, different chemical substances are referred as multicomponent (e.g. air-water flow).. 37.

(40) 38. Chapter 2 - Measurement techniques for multiphase flow. The phases present in a multiphase flow are composed of: •. Solids, which are typically in the form of relatively small particles. The solid phase is incompressible and has non-deformable interfaces with the surrounding fluids.. •. Liquids, which are also relatively incompressible, but their interfaces with the other phases are deformable.. •. Gases, where the phase is compressible and deformable.. The most common class of multiphase flows are two-phase flows: Gas–solid flows, Liquid–liquids flows, Liquid–solid flows and Gas–liquid flows, being the latter is probably the most important form of multiphase flow and is found widely in industrial applications. Examples of three-phase flows are also of practical significance: Gas– liquid–solid flows, Gas–liquid–liquid flows, Solid–liquid–liquid flows. The last two situations are often found in oil production and sometimes occurs a Gas–liquid–liquid– solid flows (Gas–oil–water–gas–sand) mixtures [1]. In particular, the disposal of offshore oil production and gas development takes place through pipes transporting fluids to operating platform at the sea surface and treatment facilities where generally, it is characterized by a multiphase flow of oil, gas and water. The spatial distributions for the constituent phases are called flow patterns and are determined by several factors involved, for example: •. property of fluids;. •. flow rate;. •. operating conditions (temperature, pressure, gravity, etc.);. •. characteristics of the environment;. These factors affect the shape and behaviour of the interfaces between phases to acquire a variety of configurations [5]. 2.1.1 Phase fraction The phase fraction of one of the phases of a multiphase flow is the cross-sectional area locally occupied by the phase P, relative to the cross-sectional area of the pipe AT at the same local position.

(41) Chapter 2 - Measurement techniques for multiphase flow. P . AP AT. 39. (2.1). .. Furthermore the sum of all contained phases in the pipe is 1  2 ...n  1. (2.2). 2.1.2 Superficial and phase velocities For multiphase flow in a pipe, the superficial velocity of each phase is the volumetric flow rate QP of that phase divided by the pipe area AT. In other words, the superficial velocity of the phase is its velocity as if the phase was flowing in the pipe without other phases. jP . QP AT. (2.3). .. The sum of these surface velocities is known as the superficial mixture velocity, which is calculated by. j  j P1  j P2 ...j Pn . 2.2. QP1  QP2 ...QPn AT. .. (2.4). Flow regimes. In oil production, oil wells often produce single-phase crude oil at first, but it is common for water and natural gas to occur after some time of production. The transport of such fluids inevitably leads to the emergence of a multiphase flow with different interfacial configurations. The understanding of flow regime in such wellbores and the pipelines is one of the fundamental parameters with important engineering significance in multiphase flow systems, and has always been an important aspect of research. Also, the knowledge in main mechanisms in both gas-liquid and liquid-liquid pipe flow is a good first step towards understanding three-phase gas-oil water flow..

(42) 40. Chapter 2 - Measurement techniques for multiphase flow. 2.2.1 Two-phase, gas-liquid flow Gas–liquid flows appear in natural and industrial processes such as chemical reactors, thermal hydraulics of nuclear reactors and are commonly present in oil industry confined in pipe flows. In dealing with such flows, the interface between the phases can undertake complicated configurations or flow regimes. This flow can occur in vertical, inclined or horizontal pipelines and some researchers classify distributions of two-phase flow based on empirical analysis (usually using air-water) and qualitative data. [6]. This type of analysis by observation is the factor that generates the variety classification, horizontal two-phase flow: [7]–[10] and vertical two-phase flow: [11]–[14]. Therefore, the classification is carried out in more a synthetic form, adopting a few standards and simplifying the phenomena. The most common vertical flow regimes, gas-liquid up-flow regimes are shown in Figure 2.1a where the flow developing is shown from the bottom to top as the gas flow rate increases. •. Bubbly flow: The gas phase is dispersed into small discrete bubbles with different sizes and shapes (usually spherical much smaller than the diameter of the tube itself) in a continuous liquid phase. The bubbles travel with a complex motion within the flow. In some situations, they coalesce forming non-uniform sizes.. •. Slug flow: This flow is characterized by large cap of bubbles where collisions between bubbles are more frequent and they coalesce often-called Taylor’s bubbles. These bubbles are followed by liquid slugs which often contain a dispersion of smaller bubbles.. •. Churn flow: A further increase in the gas flow rate causes the slugs to distort and break down into an unstable pattern in which there is a churning or oscillatory motion of liquid in the pipe.. •. Annular flow: When the gas flow rate is large enough to support a liquid film at the wall of the pipe then the annular flow regime occurs, in which a gas core flows at the centre of the pipe with some entrained liquid droplets, while liquid film flows at the pipe wall.. Unlike the vertical flow regimes, the gas-water flow regimes in a horizontal pipe are strongly affected by gravity, which causes the gas phase to flow at the upper side.

(43) Chapter 2 - Measurement techniques for multiphase flow. 41. of the horizontal pipe. The most common horizontal flow regimes in a pipe of circular cross section are illustrated in Figure 2.1b displayed from the top to bottom, left to right in order to increase the gas flow rate. •. Bubbly flow: The equivalent pattern in vertical flow consists of gas bubbles dispersed in a liquid continuum. However, due to the effect of buoyancy force on the bubbles, they tend to accumulate in the upper part of the pipe.. •. Intermittent (plug flow and slug flow): Is characterized by shaped gas bubbles called Taylor’s bubbles. However due to the gravity interaction they travel along the top of the pipe. o Plug flow: The diameter of bubbles are smaller than the tube and the liquid film becomes continuous along the bottom of the tube. Sometimes this subtype is referred to as elongated bubble flow. o Slug flow: At higher gas velocities, the diameter of elongated bubbles become similar in size to the pipe high and the liquid slugs separating the bubbles develops large amplitude waves. Due the high gas velocity, small bubbles are dispersed in the liquid slug.. •. Stratified flow: This regime occurs when the gravitational separation is complete. The liquid flows along the bottom of the tube and the gas along the top part of the tube.. •. Stratified wavy flow: An increase of gas velocity in the stratified flow causes waves to form on the phases interface.. •. Annular: Is characterized by a continuous gas core with a complete wall film of liquid with some droplets entrained in the gas core. Gravity causes the film to be thicker on the bottom of the pipe but as gas velocity is increased the film becomes circumferentially more uniform..

(44) 42. Chapter 2 - Measurement techniques for multiphase flow. Figure 2.1: Developing of gas-liquid two-phase flow patterns in (a) vertical (b) horizontal.. From a practical engineering point of view, visual observations may not always be available, and simple methods that can be used to predict flow regimes inside the pipeline for a given set of flow parameters are needed. In order to define the various flow regime transitions, flow regime maps were thus developed based upon either experimental data or mechanistic models and often display the flow patterns occurring in various parts of a parameter space defined by the component flow rates and/or dimensionless numbers. The flow rates used may be the volume fluxes, mass fluxes, momentum fluxes, or other similar quantities depending on the author. Summaries of these flow pattern studies and the various empirical laws extracted from them are a common feature in reviews of multiphase flow (see, for example, [15], [16]). The flow pattern map from [7] is the most widely used flow pattern map for horizontal two-phase flow. This map is based on a semi-theoretical method, and it is computationally more difficult to use than other flow maps. Figure 2.2 depicts flow maps describing two-phase flow patterns for flows inside horizontal [7] and vertical pipes [17]..

(45) Chapter 2 - Measurement techniques for multiphase flow. 43. Figure 2.2: Gas-liquid two-phase flow maps (a) horizontal flow [7] and (b) vertical [17].. 2.2.2 Two-phase, liquid-liquid flow Flows of two immiscible liquids for instance oil and water have not been explored to the same extent such as gas-liquid flows but is widely found in the chemical and petroleum industries. Two-phase liquid-liquid flow is not principally different from twophase gas-liquid flow, but the density and viscosity ratios tend to be closer, and they mix differently. Liquid-liquid flow shows a greater variation in flow regimes being a challenge to determine which flow characterizes a given situation. Diverse flow patterns can be observed, most of them are based on visual observations, photographic/video techniques, or on changes in the pressure drop systems. In some recent studies, these techniques are evaluated by conductivity measurements (e.g. conductivity probes, conductivity wire-mesh sensor, etc.), high frequency impedance probes or Gamma densitometers for local holdup sampling, or local pressure fluctuations and average holdup measurements [18]. The flow patterns can be classified into four basic types: •. Stratified layers with either smooth or wavy interface having oil over water.. •. Large slugs, elongated or spherical, of one liquid in the other;. •. Annular flow, where one of the liquids forms the core and the other liquid flows in the annulus;. •. A dispersion of relatively fine drops of one liquid in the other (emulsion);.

(46) 44. Chapter 2 - Measurement techniques for multiphase flow. An emulsion is a dispersion of liquid droplets in a continuous liquid that are normally immiscible (unmixable or unblendable) [19], [20]. As some other flow types, the emulsion occurs in almost all phases of oil production and processing due to several sources of mixing [21]. Its occurrence may cause several operational problems in wetcrude handling facilities and gas/oil separating plants[22]. In Figure 2.3 a somewhat simplified flow regime map shows that the flow pattern consists of a combination of these basic prototypes, furthermore that phase inversion can happen from various initial conditions and predicting them accurately is not easy [23].. Figure 2.3: Flow regimes for oil and water based on measurements of horizontal flow plotted in logarithmic scale. The dotted line indicates the difference between forms of water-in-oil and oil-in-water flow (modified from [23]).. A good review on liquid-liquid flow can be found in [18], [23] which brings more detailed information about flow regimes. 2.2.3 Three-phase, gas-liquid-liquid flow Three-phase flows are often found as a mixture of gas, oil and water where it is extensively encountered in the process of oil well production and oil-gas transport. Unlike the two-phase flow patterns, the existence of another phase makes the illustration and classification of this flow a more difficult task. Over the last few years,.

(47) Chapter 2 - Measurement techniques for multiphase flow. 45. the study of three-phase flow has grown but there is still no consensus among authors on a generic classification. [24]–[29]. The work done by [30] highlights the difficulty of flow pattern classification for three phases. As held in two-phase flow, previous studies used the observation through transparent pipes for the classification of standards. Later, filming techniques for high speed enabled a better analysis, since it deals with the evaluation of a very fast phenomenon. Some classifications can be found at: [28]–[33]. According to [12] the difficulty to predict the behaviour of a three-phase flow is to know the mix level of the liquid phases during the flowing. To simplify the representation of the patterns found in three-phase flow (water, oil and air), Figure 2.4 illustrates a multiphase triangle formed by different combinations of phases and fractions synthesizing three different patterns.. Figure 2.4: Multiphase composition triangle (water, oil and gas) commonly found in three-phase flows. (Multiphase triangle modified from [34]).. In a vertical young well, the flow will therefore, presumably, be fully developed where the flow will be single-phase, essentially oil only. As oil is removed from the well, the pressure will decrease, and the gas fraction in the well flow line will increase, and appear as gas bubbles where they will become larger with further aging. From the.

(48) 46. Chapter 2 - Measurement techniques for multiphase flow. coalescence of small bubbles and breakdown of the liquid film caused by turbulence these bubbles will result in slugs of gas that travel up the centre of the pipe leaving a slower layer of moving liquid on the wall. These slugs tend to overtake each other forming larger slugs many meters long. With increasing of water rate, droplets of water will be present forming a third phase. Considering a horizontal two-phase flow, the less-dense phase tends to migrate to the top of the pipe due to the gravity effect causing loss of asymmetry. Thus, in a gas-liquid flow, the gas will move to the top of the pipe as bubbles. Following the same effects such as vertical flow, as the gas flow increase these bubbles may become larger, slugs of gas take up regions against the top of the pipe. Eventually, a sufficient number of these will lead to stratified flow. In mixtures of two liquids (e.g., water in oil), the droplets of water will sink toward the bottom of the pipe, mirroring the behaviour of air bubbles, and will eventually drop out onto the bottom of the pipe causing a continuous layer of water. To achieve a fully developed flow (stability between the phases) it is necessary to have an equilibrium of factors involved moreover a length of straight pipe of 100 times the pipe diameter or more [35]. 2.2.4 Two-phase, solid-liquid flow As a further case, liquid-solid flow denotes the flow of a continuum liquid phase carrying dispersed solid particles suspended and conveyed by the drag and pressure forces of the liquid acting on the particles. Solid-liquid mixture (slurry) is widely used in several industries such as mineral, coal, chemical, food and water. The transport relies on higher flow velocity for these multiphase flows in order to keep the particles in suspension. In oil industries, the reliability of slurry transport pipelines is a major ongoing problem due to unexpected piping failures. Thus, making the study of multiphase gasliquid-solid is very necessary and vital for the growth of the industry. In slurry transport, different flow patterns of solids are observed, depending upon the nature of the slurry and flow condition. In [36] a classification of slurry flows based on average particle size was developed. Since then, other refined classifications have been introduced. In horizontal pipes these may suitably be classified according to the following four regimes (Figure 2.5): •. Homogeneous flow: This regime is also named as symmetric flow characterizing uniform distribution of solids about the horizontal axis of the.

(49) Chapter 2 - Measurement techniques for multiphase flow. 47. pipe, although not necessarily exactly uniform. In this regime, turbulent and other lifting forces are capable of overcoming the net body forces as well as the viscous resistance of the particles. •. Heterogeneous flow: With decrease in the slurry velocity, intensity of turbulence and lift forces are decreased. As a result there is distortion of the concentration profile of the particles, with more of the solids, particularly the larger particles, being contained in the lower part of the pipe. Thus there is a concentration gradient across the pipe cross section with a larger concentration of solids at the bottom. This flow is also called asymmetric flow.. •. Saltation flow: This type of flow takes place at low velocities and is one in which solid particles tend to accumulate on the bottom of the pipe, first in the form of separated “dunes” and then as a continuous moving bed.. •. Stationary bed flow: As the slurry velocity is further reduced, the lowermost particles of the bed become nearly stationary, the bed thickens and bed motion is limited to the uppermost particles tumbling over one another (saltation). Eventually, with continued reduction in the mixture velocity and build-up of the bed, pressure gradient increases very rapidly to maintain the flow and in the absence of an abnormally high-applied pressure, blockage of pipe occurs.. Figure 2.5: Flow regimes for slurry flow in a horizontal pipeline.. For further detail, the reader is referred to [37], [38] and [39].. 2.3. Measurement techniques for multiphase flows. The description of multiphase flow still relies to a large extent on empirical rules and correlations, which in turn are based on measurements made under conditions as relevant as possible to industrial practice. Thus, quantitative and qualitative parameters are highly desirable in many industrial and research areas and has received.

(50) 48. Chapter 2 - Measurement techniques for multiphase flow. much attention in recent years. On the one hand online flow monitoring is required in many applications, on the other hand detailed information about flow behaviour under controlled conditions is essential as a source of data for flow modelling, simulations and prediction. Furthermore, this understanding helps in the design of production plants and the design of pipelines and equipment of oil production, as well as determines the efficiency and safety of processes and equipment where they occur. In addition to the problems encountered in the measurement of a single-phase flow [35], there are other problems found in mixtures of two or more phases, where the spatial and temporal resolution of the measurement technique should be considered due to the necessity of differentiating their phases and transitions. Factors such as the condition of the flow confinement, for instance opaque metallic pipes, complex test section geometrics or even environmental conditions at high pressure and high temperature may limit the use of some measuring principle. Therefore, the robustness of the measurement system is a very important parameter for some industrial applications [40]. Despite these difficulties, improvements in instrumentation technology have fostered many advances in the research and development experimental methods for measurement of practical or fundamental parameters in multiphase flow. One of the most important parameters for the characterization of multiphase flow is the phase fraction which corresponds to a dimensionless number indicating the amount of the substance as a function of a geometric or temporal domain as discussed in section 2.1. In this section it will be presented some tomographic measuring techniques mainly focused on phase fraction distribution measurement in two- and three-phase flows. Good reviews in this field can be found in [41], [40] and [42]. An overview on multiphase flow measurement in general can be gained from the review [43] and for further details of measurement techniques specifically intended for gas-solid flow, see [44], liquid-solid (or slurry) flow, see [45], and liquid-liquid flow, see [46]. 2.3.1 Tomographic flow imaging techniques In industrial flow systems, the information on how the components are distributed is valuable to the study of the flow behaviour and accurate measurement of mass flow rate for different flow regimes. Tomographic multiphase flow imaging provides useful means for visualizing cross-sectional images of the distribution of material in a process.

(51) Chapter 2 - Measurement techniques for multiphase flow. 49. finding many applications in the imaging and measurement of industrial processes. A tomographic image is a two-dimensional representation of a slice through an object and it implies solving an inverse problem: the measurement geometry and result are known so that the assignment is to determine which spatial distribution of the imaged parameter gives these results. The use of various tomographic methods is widespread in diagnostic medicine [47] and several imaging modalities originally developed for medical imaging and are now being adapted to industrial process imaging. There are three main types of tomography systems in use today [48]: (1) nuclearbased imaging techniques using ionizing radiations: x-ray, g-ray, positron emission tomography and neutron tomography; (2) nuclear-based, but non-ionizing imaging techniques: nuclear magnetic resonance imaging and (3) non-nuclear-based imaging techniques: optical, ultrasonic, microwave and electrical tomography. The use of tomographic imaging for the investigation of multiphase flows has been reported in a few exhaustive review papers [1], [48]–[56] a) x-ray, g-ray and neutron tomography Tomography techniques using ionizing radiation such as x-ray, g-ray and neutron is the so-called “hard-field” sensing property, which means that the sensitivity of the measurement to the measured parameter is uniform and independent of the component distribution [42]. These modalities are based on the attenuation of a beam as it travels through a heterogeneous medium providing a measure of the line integral of the local density along the beam’s path. Since the components involved have different radiation attenuation characteristics, images of phase fraction distributions may be obtained by reconstructing a set of projections at different orientations generated either by rotating source and detectors around the pipe or by the use of multiple source and detectors. As automated process is known as either computer-assisted tomography (CAT) or computed tomography (CT). Tungsten and molybdenum are the most commonly used x-ray sources that generate photons of relatively low energy [48]. These non-invasive tomographic techniques have high spatial resolution, but most still have low temporal resolution, due to mechanical movement of parts of the scanner around the pipe. The use of x-ray tomography for void fraction measurements was described, for instance, by [57] and [58], while use of gamma-ray tomography was reported by [59], [60], among.

(52) 50. others.. Chapter 2 - Measurement techniques for multiphase flow. In order to investigate three-phase flow air-oil-water, x-ray technique was. developed by [61] using two different energy spectra. Attempts to increase time resolution have been reported by [62] who used a large number of sources acting directly on receptors in order to replace the moving sources and reducing the data acquisition time (100 fps), by [63] who introduced a multitube x-ray scanner achieving 2 000 fps and recently by [64], [65] who used an electron beam to generate a fast moving x-ray spot reaching 10 000 fps. x-rays and grays are of great importance in situations where metal walls are used, for example, where the use of other techniques become unworkable, however, even these solutions are relatively complex and costly. Neutrons have some advantages regarding the attenuation in matter. Organic materials or water are clearly visible in neutron radiograph due to their high hydrogen content, while materials such as aluminium or steel are nearly transparent. On the other hand, neutron tomography has some limitations considering the complex and heavy equipment for the generation of neutron, and consequently its use for investigation of multiphase flows has been limited in the past [66]. b) Positron emission tomography Positron emission tomography (PET) is based on the use of positron-emitting radionuclides. External detectors are used to measure the number of rays emerging from the system along each line of sight. This information allows the reconstruction of the tracer distribution by the standard tomographic approach [67]. However, PET system has a temporal resolution in the order of minutes being too slow for high-speed flow investigation. Positron emission particle tracking (PEPT) can be seen as an alternative method. This technique is based on introducing a single labelled tracer particle in the process, which has its trajectory tracked by using advanced algorithms [68]. The system time response is in the range of milliseconds allowing flow investigation at higher speed. c) Magnetic resonance imaging Magnetic resonant imaging (MRI) is widely used in modern medicine; however, its use in engineering and the physical sciences is much less known. Notwithstanding, it has many characteristics that make it a considerable tomography technique due to the different types of contrast and information that it can be used to measure. MRI.

(53) Chapter 2 - Measurement techniques for multiphase flow. 51. scanners use the phenomenon of nuclear magnetic resonance of hydrogen nuclei in conjunction with radio frequency and magnetic gradient pulses to map the object under investigation [69]. Essentially, MRI detects the concentration of hydrogen atoms, thus liquid water presents excellent contrast. MRI is not only able to determine the density of nuclei but also the velocity in case of moving objects. There are a number of excellent texts treating the subject in greater detail [70]–[72]. In [73] is reported some flow applications of MRI in their reviews. Some limitations of MRI are the necessity of non-magnetic, non-conducting pipes to allow the measurements, the rather low imaging frequency and the relatively high hardware cost. [74] used MRI to measure void fraction and investigate gas-liquid phase distribution and [75] applied a special MRI technique called Echo-planar Imaging to investigate slug flow. However, this technique needs even more costly hardware than conventional MRI to achieve such a frame rate. d) Optical tomography In optical tomography system, an arrangement of multiple optical emitters and receivers are photodiodes arranged on the circumference of the measuring area. It uses low energy electromagnetic radiation, either of the infrared, visible or ultraviolet wavelength range. From the measurements, image reconstruction methods are used to reconstruct the internal distribution profiles from an object or a parameter of interest by means of CT algorithms. In studies of flow, this technique is used for the investigation of single phase and multiphase flows [76]–[78]. The common characteristic of these systems is the use of low-cost light emitters and detectors. Another example of optical tomography applied to process investigation is a technique concerned with the concentration distribution of the species of interest, exploiting a specific substance absorption at near-infrared band [79]–[81]. An advantage in optical tomography is the very high temporal resolution of a few thousand frames/s. Nevertheless, regarding gasliquid flows, optical systems can only be successfully employed to flows with low void fraction (typically up to 10%) due to the fact that the flow becomes opaque for light at high void fraction. Optical systems also need transparent walls and transparent liquids to be able to investigate the flow..