Overthe past couple of years the focus on using concavities or dimples provides enhanced heattransfer has been documented by a number of researchers. Dimples are used on thesurfaceof internal flow passages because they produce substantial heattransfer augmentation. This project work is concerned with experimentalinvestigationofthe forced convection heattransferoverthedimpledsurface. The objective ofthe experiment is to find out theheattransfer and air flow distribution on dimpled surfaces and all the results obtained are compared with those from a flat surface. The varying parameters were i) Dimple arrangement on the plate i.e. staggered and inline arrangement and ii) Heat input iii)Dimple density on the plate.
As the number of transistors increases with new generation of microprocessor chips, the power draw and heat load to dissipate during operation increases. As a result of increasing theheat loads and heat fluxes the Conventional cooling technologies such as fan, heat sinks are unable to absorb and heattransfer excess heat dissipated by these new microprocessor. So, new technologies are needed to improve theheat removal capacity. In the present work single phase liquid cooling system with mini channel is analyzed and experimentally investigated. Mini channels are chosen as to provide higher heattransfer co-efficient than conventional channel. Copper pipes of 0.36 mm diameter are taken to fabricate heat sink and heat exchanger. A pump is used to circulate the fluid through heat sink and heat exchanger. A solid heated aluminium block to simulate heat generated electronic component is used and electrical input is supplied to the heated aluminium block and cooling system is placed overthe heated block. The performance ofthe cooling system is analyzed from theexperimental data obtained. It is experimentally observed that the mini channel liquid cooling system with water as a coolant has better performance than diluted ethylene glycol as coolant at different flow rates. Thesurface temperature ofthe heated aluminium block with convective heattransfer co-efficient is observed
Experimentalinvestigationofheattransfer and friction factor characteristics of circular tube fitted with full-length square jagged twisted tape inserts of different twist ratio has been presented. Calculations and curve fitting is done and correlations are obtained. The results showed that there was an appreciable enhancement in heattransfer and that theheattransfer is more with lesser twist ratio.
The working length ofthe thermosyphon consists of three parts; a lower part of 430 mm as the evaporator section, the middle part of 160 mm as the adiabatic section, and a upper part of 410 mm as the condenser section. The 410 mm long water jacket was surrounding the condenser section. Inlet and outlet connections located obliquely across each other to introduce swirl flow. Eight Ni-Cr thermocouples were installed mechanically to thesurfaceofthe evaporator and adiabatic and condenser to monitor the temperature distribution. A personal computer and a data logger were used to show the temperatures measured by thermocouples. The two phase closed thermosyphon was surrounded by 40 mm thickness of glass wool for insulating and stopping theheattransfer to the environment. Table 1 shows the specifications of two phase closed thermosyphon for this study.
A comprehensive theoretical and experimental study was carried out on the thermal performance of a pin fin heat sink. An experimental model was shows that have the capability of predicting influence of effective surface area of pin fin on thermal heattransfer coefficient. Pin fin array are used in many applications to enhance heattransfer and also shows enhancementofheattransfer coefficient for different material of fin. Several different type of experiment test were run out with corresponding variation including the material of pin fin and different perforation on pin fin .Perforation with circular cross section are along the height of pin fin and there number varies from 1 to 3. The result indicates that the material having higher thermal conductivity with higher number of perforation gives more heattransfer coefficient. The effect of perforation on heattransfer was investigated.
The majority of electronic boards are constructed with small elements that generate considerable amount ofheat. Cooling of these electronic boards constitutes an essential part for their reliable operation and the main cooling systems deal with a flow of air through chan- nels. Nowadays, because of size reduction (i. e., board compaction), the cooling medium has become a vital part ofthe system. Optimum active cooling systems are preferred approaches for performance evaluation criteria (PEC) ofthe electronic boards [1, 2]. The active method with application of corona wind is well known owing to its ability to work with any external sources of energy. Corona is a visible luminous emission caused by the creation of photon and occurs in the vicinity of sharp edges where the intensity ofthe electric field is high. An im- portant aspect of corona discharge is the generation of corona wind, which is a gas flow in- duced by corona discharge. This phenomenon is caused by the ionization of gas molecules and formation of electrons that accelerate in strong electric fields and collide with neutral molecules, resulting in more ionization. Because the ions are heavier than electrons, they ac- celerate and drag the neighboring gas molecules. This action generates a secondary flow, known as corona wind.
Fu and Yang (2001a) observed theheattransfer phenomena induced by moving square object. The finite element method with Arbitrary Lagrangian-Eulerian (ALE) method was used to simulate the moving boundary problem. The results indicated that theheattransfer rate remarkably increased when object moved in opposition to flowing fluid. Fu and Yang (2001b) presented the new concept of cooling strategy, the swing fins. The study was conducted by finite element method with ALE. It could be seen that swing fins clearly disrupted the thermal and velocity boundary layers along the fin surface. Heattransfer would be improving when fins moved at large speed. However, when fins were swinging at low speed, the results were similar to the flow over flat plate without vibration. Fu et al. (2001) numerically investigated heattransfer rate from heat plate with jet impingement. Theheattransfer performance was improved by implementing the moving block on the plate surface. After installing moving block, thermal boundary layer was eliminated and new thermal boundary layer was formed. These phenomena clearly improved theheattransfer performance. The results indicated that increment ofheattransfer rate was approximately 200% at the highest Reynolds number. Fu and Tong (2002) used finite element method with ALE to study heattransfer characteristic from heated
Bayram Sahin, Alparslan Demir  studied theheattransferenhancement and the corresponding pressure drop over a flat surface equipped with square cross-sectional perforated pin fins in a rectangular channel. The experiments covered the following range: Reynolds number 13,500 –42,000, the clearance ratio (C/H) 0, 0.33 and 1, the inter-fin spacing ratio (Sy/D) 1.208, 1.524, 1.944 and 3.417. Correlation equations were developed for theheattransfer, friction factor and enhancement efficiency. Theexperimental results showed that the use ofthe square pin fins may lead to heattransferenhancement. Both lower clearance ratio and lower inter-fin spacing ratio and comparatively lower Reynolds numbers are suggested for higher thermal performance.
Teerapat Chompookham, Chinaruk Thianpong, Sutapat Kwankaomeng, Pongjet Promvonge have done Experimental investigations to study the effect of combined wedge ribs and winglet type vortex generators (WVGs) on heattransfer and friction loss behaviors for turbulent airflow through a constant heat flux channel. To create a reverse flow in the channel, two types of wedge (right-triangle) ribs were introduced. Wedge ribs were pointing downstream and pointing upstream. The arrangements of both rib types placed inside the opposite channel walls are in-line and staggered arrays. To generate longitudinal vortex flows through the tested section, two pairs ofthe WVGs with the attack angle of 60° were mounted on the test channel entrance. The test channel had an aspect ratio, AR=10 and height, H=30 mm with a rib height, e/H=0.2 and rib pitch, P/H=1.33. The flow rate in terms of Reynolds numbers is based on the inlet hydraulic diameter ofthe channel ranging from 5000 to 22,000. The presence ofthe combined ribs and the WVGs shown the significant increase in heattransfer rate and friction loss overthe smooth channel. The Nusselt number and friction factor values obtained from combined the ribs and the WVGs were found to be much higher than those from the ribs/WVGs alone. In conjunction with the WVGs, the in-line wedge pointing downstream provides the highest
In the next sections, flow and heattransfer inside the boundary layers of a gravity-driven liquid film along a vertical preamble plate subject to nonuniform suction flow are modeled and analyzed. Thesurface suction velocity is considered to have power-law profile distri- bution. Both momentum and energy equations ofthe developing liquid film are transformed into nonsimilar equations and solved numerically. The skin friction coefficient, Nusselt number, and different heattransferenhancement indicators are computed. The numerical solutions are validated with the asymptotic analytical ones. An extensive parametric study has been con- ducted in order to explore the influence of average sur- face suction velocity, suction velocity profile, Froude number, and Galilei number on the skin friction coeffi- cient, Nusselt number, and different heattransferenhancement indicators.
The boundary layer flow past a stretching surface in the presence of a magnetic field has much practical relevance in polymer processing and in other several industrial processes. Along with this, a new dimension is added to the study of flow and heattransfer effects over a stretching surface by considering the effect of thermal radiation. Thermal radiation effects may play an important role in controlling heattransfer in industry where the quality ofthe final product depends to a great extend on theheat controlling factors and the knowledge of radiative heattransfer in the system can perhaps lead to a desired product with sought qualities. High temperature plasmas, cooling of nuclear reactors and liquid metal fluids are some important applications of radiative heattransfer. The radiative flow of an electrically conducting fluid with high temperature in the presence of a magnetic field are encountered in electrical power generation, astrophysical flows, solar power technology, space vehicle re-entry, nuclear engineering applications and in other industrial areas.
Now a days, the energy efficiency is an extremely important topic in view of thermal conductivity enhancement amongst the researchers. For this purpose the researchers considered the involvement of nanoparticles in the base fluid. Originally Masuda et al. (1996) reported the liquid dispersions of submicron particles or nanoparticles. After that, first time nanofluid term is used by Choi (1995). In comparison to the base fluids, thermal conductivity of nanofluid is too high that's why these have been used in many energetic systems such as cooling of nuclear systems, radiators, natural convection in enclosures etc. The model proposed by Buongiorno (2006) studies the Brownian motion and the thermophoresis on theheattransfer characteristics. Recently, the analytical solutions for the laminar axisymmetric mixed convection boundary layer nanofluid flow past a vertical cylinder is obtained by Rashidi et al. (2012a). Stagnation point flow of nanofluid near a permeable stretched surface with thermal convective condition is provided by Alseadi et al. (2012). Mustafa et al. (2013) discussed the boundary layer flow of nanofluid over an exponentially stretching sheet with convective boundary conditions. Rashidi et al. (2014b) presented the analytical solutions of transport phenomena in nanofluid adjacent to a nonlinearly porous stretching sheet. Sheikholeslami and Ganji (2013a) studied theheattransferof Cu-water nanofluid flow between the parallel plates. Turkyilmazoglu (2013) studied the unsteady mixed convection flow of nanofluids over a moving vertical flat plate with heattransfer. Sheikholeslami et al. (2013b) determined free convection flow of nanofluid. Hayat et al. (2014) presented the mixed convection peristaltic flow of magnetohydrodynamic (MHD) nanofluid in presence of Brownian motion and thermophoresis. Casson fluid model is one ofthe base fluids which exhibits yield stress. However such fluid behaves like a solid when shear stress less than the yield stress is applied and it moves if applied shear stress is greater than yield stress. Examples of Casson fluid include jelly, soup, honey, tomato sauce, concentrated fruit juices, blood and many others. In fact several substances like protein, fibrinogen and globin in an aqueous base plasma, human red cells form a chain like structure, known as aggregates or rouleaux. If the rouleaux behaves like a plastic solid then there exists a field stress that can be identified with the constant yield stress in Casson fluid by Dash et al. (1996). Recently, Mukhopadhyay (2013a) provided the boundary layer flow of Casson fluid over a non-linearly stretching sheet. Some ofthe recent studies about flow of Casson fluid are [Shehzad et al. (2013), Mukhopadhyay and Vajravelu (2013b), Hayat et al. (2012a)].
In order to verify obtained numerical results experimentalinvestigation was carried out. The experiments were conducted on theexperimental installation shown in fig. 8. The main part was the cylindrically shaped tank of about 77 dm 3 , whose internal space in this case was filled by paraffin E53 as PCM. The PCM was heated by the electric heater (EH), located in the central position ofthe TES. Four thermocouples (A1, A2, A3, and A4) were placed at the heater surface. The top thermocouple (A1) at the heater surface was used for the heating control (the switch off sensor). If the temperature ofthe heater reached 473 K the electricity was switched off, until the temperature dropped below the given range. For the measurement of temperature profile inside PCM, eight thermocouples (B1-B4 and C1-C4) were placed in- side the tank, four along the axis and two along the radius. Four thermocouples (D1-D4) were placed at the outer surfaceofthe tank. The enumeration and position are shown in fig. 8.
surface area, creating rough surface, or by changing system boundary conditions . The active technique involves increasing the thermal conductivity ofthe base luid itself is by addition of milli-sized metallic particles in the base luid for heat augmentation. However addition of these particles sufers from high sedimentation time and more low resistance, thereby requires high- er pumping power. Further, these particles cause severe clogging and deposition at the corners and in pump valves creating malfunctioning ofthe system. The latest manufacturing process produces the ultra ine nanoparticles in metallic form, which has greatly inluenced heat trans- fer methods. This forced to add further much iner grade particles, i. e. nano-sized particle to the base luid in pure as well as an oxide form for theheattransferenhancement. Such a luid is often termed as nanoluids. This was irst noted by Choi  in the year 1996 at the National Argonne Laboratory in U. S. A. The nanoparticles are produced by physical and chemical syn- thesis processes. The physical process involves mechanical grinding, mechanical milling, and inert gas condensation methods. Whereas chemical technique is associated with the chemical precipitation, chemical vapor deposition, spray pyrolysis band thermal spraying . The single step and the two step technique facilitate the simultaneous production of nanopowders in crys- talline, amorphous and disperse powders in the base luid form. The nanoluids are the colloidal dilute dispersion of nanoparticles (a billionth of a meter) in small quantity of metals, oxides, carbides, or carbon nanotubes in the conventional base luids such as water, ethylene glycol, or oil. The nanoparticle possesses superior thermal conductivity, lower speciic heat, large surface area which makes nanoluids superior in an energy transport carrier.
To reduce heat losses from theheat exchangers to the environment, insulation is installed as illustrated in Fig. 1b. The ceramic plate is used to provide a space between theheat exchangers to prevent theheat conduction between them. Each heat exchanger rests on a PTFE cylinder to avoid a thermal contact with the stainless steel case. Pieces of PE sheets with 10cm length are attached to the internal surfaceofthe stainless steel resonator pipe to reduce heat loss from the oscillating fluid to the pipe. Silicate wool is put in the cavity between heat exchangers and stainless steel case to reduce theheat loss due to natural convection in the empty volume. With these efforts, theheat losses still exist. This part ofheat loss is calculated and added to the cold side to give the approximate total heat output. Theheat imbalance between theheat input and output is used as an indication ofthe accuracy oftheexperimental data. In the present study, the average heat imbalance is 13.42%.
Rather than Brownian motion, liquid layering, phonon transport, and agglomeration, Lee et al. (2006) experimentally investigated the effect ofsurface charge state ofthe nanoparticle in suspension on the thermal conductivity. They showed that the pH value ofthe nanofluid strongly affected the thermal performance ofthe fluid. The further the pH value diverged from the isoelectric point ofthe particles, the more stable the nanoparticles in the suspension and greater the change in the thermal conductivity. That may partially explain the disparities between different experimental data since many researchers used surfactants in nanofluids, but with insufficient descriptions. By adopting a variation ofthe classical heat conduction method in porous media to the problem ofheat conduction in nanofluids, Vadasz (2006) demonstrated that the transient heat conduction process in nanofluids may provide a valid alternative explanation for the apparent heattransferenhancement.
It is noticed that when the density of an electrically conducting fluid is low and/or applied magnetic field is strong, Hall current plays a vital role in determining flow-features ofthe fluid flow problems because it induces secondary flow in the flow-field (Sutton and Sherman (1965). Taking into account of this fact, Aboeldahab and Elbarbary (2001) and Seth et al. (2012) investigated the effects of Hall current on hydromagnetic free convection boundary layer flow past a flat plate considering different aspects ofthe problem. It is noteworthy that Hall current induces secondary flow in the flow-field which is also the characteristics of Coriolis force. Therefore, it is essential to compare and contrast the effects of these two agencies and also to study their combined effects on such fluid flow problems. Narayana et al. (2013) studied the effects of Hall current and radiation- absorption on MHD natural convection heat and mass transfer flow of a micropolar fluid in a rotating frame of reference. Recently, Seth et al. (2013a) investigated the effects of Hall current and rotation on unsteady hydromagnetic natural convection flow of a viscous, incompressible, electrically conducting and heat absorbing fluid past an impulsively moving vertical plate with ramped temperature in a porous medium taking into account the effects of thermal diffusion. Aim ofthe present investigation is to study unsteady hydromagnetic natural convection heat and mass transfer flow with Hall current of a viscous, incompressible, electrically conducting, temperature dependent heat absorbing and optically thin heat radiating fluid past an accelerated moving vertical plate through fluid saturated porous medium in a rotating environment when temperature ofthe plate has a temporarily ramped profile. This problem has not yet received any attention from the researchers although natural convection heat and mass transfer flow of a heat absorbing and radiating fluid resulting from such ramped temperature profile of a plate moving with time dependent velocity may have strong bearings on numerous problems of practical interest where initial temperature profiles are of much significance in designing of so many hydromagnetic devices and in several industrial processes occurring at high temperatures where the effects of thermal radiation and heat absorption play a vital role in the fluid flow characteristics.
A three dimensional incompressible steady model has been developed to investigate the effects of Reynolds number, aspect ratio, rarefaction, Prandtl number and radiation heattransfer on Poiseuille and Nusselt number for fully developed laminar flow over a range of slip flow regime in a microchannel with rhombus cross section. Constant wall temperature, slip velocity and temperature jump boundary conditions were included. The Nusselt and Poiseuille number both decrease with decreasing the value of aspect ratio, but rarefaction has inverse effect on Poiseuille and Nusselt number in which Poiseuille and Nusselt number decreases with increasing in Kn. It is observed from the figures that Reynolds number has more effect on Nusselt number then Poiseuille number. It is concluded from the figures and results that the presence ofthe radiation augments theheattransfer rate and Nusselt number to about 3% in comparison by the absence of radiation.
The last equation corresponds to typical thermal diffusion equation for a 2D object oriented in cartesian coordinate system (but finally we find the 3D solution). It should be solved for initial condition T (x 1 , x 2 , 0) = T 0 (pouring temperature), while the
A water tank of 40 liters capacity with two numbers of electrical heaters (each 2 kW capacity) with temperature monitor is used to heat and maintain the required temperature of hot water which is flowing in the shell side ofheat exchanger. In order to measure the relative temperature of both hot and cold water, a digital temperature indicator is used. Four number of RTD were provided to measure temperature of hot and cold water. Two thermocouples measures hot water and two of them measures cold water temperatures.