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 of the 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 of the 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 of the 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** of the **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.

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At the high **temperature** attained in some engineering devices, for example, gas can be ionized **and** so becomes **an** electrical conductor. The ionized gas or plasma can be made to interact **with** the magnetic field **and** alter **heat** **transfer** **and** friction characteristic. Recently, it is of great interest to study the effect of magnetic field on the convective flows when the fluid is not only **an** electrical conductor but also when it is capable of emitting **and** absorbing thermal **radiation**. The **heat** **transfer** by thermal **radiation** is becoming of greater importance when we are concerned **with** space applications, higher operating temperatures **and** also power engineering. The radiative free convective flows are encountered in countless industrial **and** environment processes e.g. heating **and** cooling chambers, fossil fuel combustion energy processes, evaporation from large open water reservoirs, astrophysical flows, **and** solar power technology **and** space vehicle re-entry. The radiative **heat** **transfer** plays **an** important role in manufacturing industries for the design of reliable equipment. Nuclear power plants, gas turbines **and** various propulsion devices for aircraft, missiles, satellites **and** space vehicles are examples of such engineering applications. Alagoa et al. [β1] analyzed the effects of **radiation** on free **convection** MHD **flow** through porous medium between infinite parallel plates in the presence of time-dependent suction. Mebine [ββ] studied the **radiation** effects on MHD ωouette **flow** **with** **heat** **transfer** between two parallel plates. Singh **and** Kumar [βγ] obtained **an** exact solution of free convective oscillatory **flow** through porous medium in a rotating **vertical** channel. Singh **and** Garg [β4] have also obtained exact solution of **an** oscillatory free **convection** MHD **flow** in a rotating channel in the presence of **heat** **transfer** due to **radiation**. Recently Garg [β5] studied combined effects of thermal radiations **and** **Hall** **current** on **moving** **vertical** porous **plate** in a rotating system **with** variable **temperature**. Very recently, assuming the **temperature** of one of the **plate** varying **with** time, Singh [β6] analyzed **an** oscillatory MHD convective **flow** of a viscoelastic fluid through a porous medium in a rotating **vertical** channel in slip-**flow** regime **with** thermal **radiation** **and** **Hall** **current**.

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Investigation of hydromagnetic **natural** **convection** **flow** in a rotating medium is of considerable importance due to its application in various areas of geophysics, astrophysics **and** fluid engineering viz. maintenance **and** secular variations of Earth’s m agnetic field due to motion of Earth’s liquid core, internal **rotation** rate of the Sun, structure of the magnetic stars, solar **and** planetary dynamo problems, turbo machines, rotating MHD generators, rotating drum type separators for liquid metal MHD applications etc. It may be noted that Coriolis **and** magnetic forces are comparable in magnitude **and** Coriolis force induces secondary **flow** in the **flow**-field. Taking into consideration the importance of such study, unsteady hydromagnetic **natural** **convection** **flow** **past** **an** infinite **moving** **plate** in a rotating medium has been studied by a number of researchers. Mention may be made of research studies of Singh (1984), Raptis **and** Singh (1985), Kythe **and** Puri (1987), Singh et al. (2010) **and** Seth et al. (2011). Seth et al. (2013) considered effects of **rotation** on unsteady hydromagnetic **natural** **convection** **flow** of a viscous, incompressible, electrically conducting **and** **heat** radiating fluid **past** **an** impulsively **moving** **vertical** **plate** **with** **ramped** **temperature** in a porous medium. Recently, Seth et al. (2015) investigated effects of **Hall** **current** **and** **rotation** on hydromagnetic **natural**

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In all the investigations mentioned above, viscous mechanical dissipation is neglected. A number of authors have considered viscous heating effects on Newtonian flows. Mahajan et al. [25] reported the influence of viscous heating dissipation effects in **natural** convective flows, showing that the **heat** **transfer** rates are reduced by **an** increase in the dissipation parameter. Isreal- Cookey et al. [26] investigated the influence of viscous dissipation **and** radi- ation on unsteady MHD free **convection** **flow** **past** **an** infinite heated **vertical** **plate** in a porous medium **with** time dependent suction. Zueco [27] used net- work simulation method (NSM) to study the effects of viscous dissipation **and** **radiation** on unsteady MHD free **convection** **flow** **past** a **vertical** porous **plate**. Suneetha et al. [28] have analyzed the thermal **radiation** effects on hydromagnetic free **convection** **flow** **past** **an** impulsively started **vertical** **plate** **with** variable surface **temperature** **and** concentration by taking into account of the **heat** due to viscous dissipation. Recently Suneetha et al. [29] stud- ied the effects of thermal **radiation** on the **natural** conductive **heat** **and** **mass** **transfer** of a viscous incompressible gray absorbing-emitting fluid flowing **past** **an** impulsively started **moving** **vertical** **plate** **with** viscous dissipation. Very recently Hiteesh [30] studied the boundary layer steady **flow** **and** **heat** trans- fer of a viscous incompressible fluid due to a stretching **plate** **with** viscous dissipation effect in the presence of a transverse magnetic field.

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unsteady MHD free convective **heat** **transfer** **flow** along a **vertical** porous flat **plate** **with** internal **heat** generation. In many chemical engineering processes, there does occur the chemical reaction between a foreign **mass** **and** the fluid in which the **plate** is **moving**. These processes take place in numerous industrial applications viz., Polymer production, manufacturing of ceramics or glassware **and** food procession. Cramer K. R. **and** Pai, S. I.et al.[11] taken transverse applied magnetic field **and** magnetic Reynolds number are assumed to be very small, so that the induced magnetic field is negligible. Muthucumaraswamy et al.[12] have studied the effect of homogeneous chemical reaction of first order **and** free **convection** on the oscillating infinite **vertical** **plate** **with** variable **temperature** **and** **mass** diffusion. Das et al.[13] have studied the effects of **mass** **transfer** on **flow** **past** **an** impulsively started infinite **vertical** **plate** **with** constant **heat** flux **and** chemical reaction. K.Sudhakar **and** R. Srinivasa Raju et al.[14] have studied chemical reaction effect on **an** unsteady MHD free **convection** **flow** **past** **an** infinite **vertical** **accelerated** **plate** **with** constant **heat** flux, thermal diffusion **and** diffusion thermo. S. Shivaiah **and** J. Anand Rao et al.[15] studied chemical reaction effect on **an** unsteady MHD free **convection** **flow** **past** a **vertical** porous **plate** in the presence of suction or injection. Chaudhary **and** Jha [16] studied the effects of chemical reactions on MHD micropolar fluid **flow** **past** a **vertical** **plate** in slip-**flow** regime. Anjalidevi et al.[17] have examined the effect of chemical reaction on the **flow** in the presence of **heat** **transfer** **and** magnetic field. Moreover, Al-Odat **and** Al-Azab [18] studied the influence of magnetic field on unsteady free convective **heat** **and** **mass** **transfer** **flow** along **an** impulsively started semi-infinite **vertical** **plate** taking into account a homogeneous chemical reaction of first order. The chemical reaction, **heat** **and** **mass** **transfer** on MHD **flow** over a **vertical** stretching surface **with** **heat** source **and** thermal stratification have been presented by Kandasamy et al.[19]. Ahmed Sahin.et al.[20] have studied influence of chemical reaction on transient MHD free convective **flow** over a **vertical** **plate** in slip-**flow** regime.

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one dimensional adaptive-grid finite-differencing computer code for thermal **radiation** magnetohydrodynamic simulation of fusion plasmas. Excellent studies of thermal **radiation**-**convection** magnetohydrodynamics include Duwairi **and** Damseh (2004), Raptis et al. (2004) who considered axisymmetric **flow** **and** Duwairi **and** Duwairi (2005) who studied thermal **radiation** **heat** **transfer** effects on the hydrodynamic Rayleigh **flow** of a gray viscous fluid. Aboeldahab **and** Azzam(2005) have described the effects of magnetic field on hydromagnetic mixed free forced **heat** **and** **mass** **convection** of a gray, optically-thick, electrically conducting viscous fluid along a semi-infinite inclined plane for high **temperature** **and** concentration using the Rosseland approximation. Ghosh **and** Pop (2007) **and** Jana **and** Ghosh (2011) have studied thermal **radiation** of **an** optically-thick gray gas in the presence of indirect **natural** **convection** showing that the pressure rise region leads to slightly increase in the velocity **with** **an** increase of **radiation** parameter. Patra et.al (2012) considered transient approach to **radiation** **heat** **transfer** free **convection** **flow** **with** **ramped** wall **temperature**. Rajput **and** Kumar (2012) examined the **radiation** effects on MHD **flow** **past** **an** impulsively started **vertical** **plate** **with** variable **heat** **and** **mass** **transfer**. Ahmed **and** Kalita (2013) presented **an** analytical **and** numerical study for MHD radiating **flow** over **an** infinite **vertical** surface bounded by a porous medium in presence of chemical reaction. Al-Odat **and** Al-Azab (2007) have examined the influence of chemical reaction on transient MHD free **convection** over a **moving** **vertical** **plate**. Mbeledogu **and** Ogulu (2007) have presented the **heat** **and** **mass** **transfer** of **an** unsteady MHD **natural** **convection** **flow** of a rotating fluid **past** a **vertical** porous **plate** in the presence of radiative **heat** **transfer**. The MHD transient free **convection** **and** chemically reactive **flow** pasta porous **vertical** **plate** **with** **radiation** **and** **temperature** gradient dependent **heat** source in slip **flow** regime have been studied by Rao et al. (2013). Reddy et al. (2012) have investigated the **heat** **and** **mass** **transfer** effects on unsteady MHD free **convection** **flow** **past** a **vertical** permeable **moving** **plate** **with** **radiation**.

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Raptis et al. [11] discussed the effect of thermal **radiation** on MHD **Flow**. Saha **and** Hossain [12] studied the **natural** **convection** **flow** **with** combined buoyancy effects due to thermal **and** **mass** diffusion in a thermally stratified media. Das et al. [13] estimated numerically the effect of **mass** **transfer** on unsteady **flow** **past** **an** **accelerated** **vertical** porous **plate** **with** suction. Mazumdar **and** Deka [14] analyzed the MHD **flow** **past** **an** impulsively started infinite **vertical** **plate** in presence of thermal **radiation**. Das **and** his co- workers [15] discussed the magnetohydrodynamic unsteady **flow** of a viscous stratified fluid through a porous medium **past** a porous flat **moving** **plate** in the slip **flow** regime **with** **heat** source. In a separate paper Das et al. [16] analyzed the **mass** **transfer** effects on MHD **flow** **and** **heat** **transfer** **past** a **vertical** porous **plate** through a porous medium under oscillatory suction **and** **heat** source. Recently, Das **and** his associates [17] reported the hydromagnetic convective **flow** **past** a **vertical** porous **plate** through a porous medium **with** suction **and** **heat** source. More recently, Das **and** Tripathy [18] estimated the effect of periodic suction on three dimensional **flow** **and** **heat** **transfer** **past** a **vertical** porous **plate** embedded in a porous medium.

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As a result which drawn from the **flow** of fluids **with** constant viscosity is not applicable for those fluids that **flow** **with** the **temperature** dependent on viscosity, in particular at high **temperature**. A fluid that flows **with** variable viscosity has a wide range of applications in chemical **and** Biochemical industries **and** also useful in many fluid **flow** problems. Books on Porous media by [6] **and** [11] stand evident to the fact that convective flows in porous media are of vital importance to these processes. Reference [3] studied the effect of **temperature** dependent viscosity on **natural** **convection** **flow** as a linear function of **temperature** **and** reference [4] studied the effect of variable viscosity on convective **heat** **transfer** in three different cases of **natural** **convection**, mixed **convection** **and** forced **convection** taking fluid viscosity to vary inversely **with** **temperature**. The authors had discussed the effect of the appropriate parameters on the **flow** **and** **heat** **transfer** quantities. However, the authors had not discussed the hot ------------------------------------------------------------------- -- 1 rajarani72@gmail.com, Mathematics, Aeronautical Engineering

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As high power electronic packaging **and** component density keep increasing substantially **with** the fast growth of electronic technology, effective cooling of electronic equipment has become exceptionally necessary. Therefore, the **natural** **convection** in **an** enclosure has become increasingly important in engineering applications in recent years. Through studies of the thermal behavior of the fluid in a partitioned enclosure is helpful to understand the more complex processes of **natural** **convection** in practical applications Number of studies, numerical **and** experimental, concerned **with** the **natural** **convection** in **an** enclosure **with** or without a divider were conducted in **past** years.

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The effects power law index, variable viscosity **and** thermal stratification parameter on **heat** **and** **mass** **transfer** of a steady incompressible Newtonian fluid **past** a **vertical** **plate** have been studied numerically using the RK Gill method together **with** the shooting technique. From the previous results **and** discussion, we conclude the following:

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This research article summarized a new compound para- bolic concentric-tubular solar still (CPC-CTSS), which has been designed for **and** tested under the climatic conditions of Coimbatore, India. The effect of cooling air flowing over the condensation surface was studied. The daily yield of CPC-CTSS was found 1445 mL/day **and** 16.2% efficiency without air **flow** **and** 2020 mL/day **and** 18.9% efficiency **with** air **flow** at a constant **flow** rate of 4.5 m/s. To bound in a nutshell, this innovative approach of concentrator assisted tubular solar still **with** air **flow** augments the performance **with** enhanced rate of evaporation **and** condensation **with** safer operation procedures.

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dimensional model covering the full length **and** height of the experimental setup was developed. The model was shown to give good predictions of **flow** structures for a drive ratio of 0.3%, in agreement **with** experiment [13]. The full length model allows the verification of the phase changes between pressure **and** velocity from the computational model to follow the definition from the experiment. It was also found that the pressure **and** velocity in the **flow** far away from the **heat** exchanger can be estimated fairly well by the linear thermoacoustic theory. This indicates that the use of a shorter model is also acceptable provided that the boundary is far enough for the incoming/outgoing oscillatory **flow** not to interfere **with** **plate** structure [5, 14]. In this study, the computational domain was developed to cover a length of 270 mm either way from location m of the joint, as shown in Fig. 1

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As seen in Figure 3, the variations of Reynolds number have little effect on Poiseuille number for a fixed rarefaction. It can be concluded from this figure that Poiseuille number decreases **with** increasing value of Knudson number. Figure 4 shows the Poiseuille number as a function of aspect ratio for different Reynolds number **and** at Kn=0.01. As seen in Figure 4, Poiseuille number increases **with** increasing value of aspect ratio, **and** as shown in this figure, the variations of Reynolds number have little influences on Poiseuille number. Variation of fully developed Poiseuille number **with** aspect ratio for different Knudsen number at Re=10 is the purpose of Figure 5. It is obvious in Figure 5 that Poiseuille increases **with** increasing value of aspect ratio for a fixed Knudsen number. As seen in this figure the aspect ratio is more effective when it is less than 0.7 **and** at greater values than this aspect ratio, the Poiseuille number is constant for a fixed rarefaction. This figure also shows that Knudsen number can considerably affect on Poiseuille number, in which Poiseuille number reaches its maximum when Knudsen number is equal to zero, i.e. no slip condition, **and** then increasing the value of rarefaction reduces the value of Poiseuille number.

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Mixed **convection** flows, or combined forced **and** free convec- tion flows, arise in many transport processes both naturally **and** in engineering applications. They play **an** important role, for example, in atmospheric boundary-layer flows, **heat** exchangers, solar collectors, nuclear reactors **and** in electronic equipment. Such processes occur when the effects of buoyancy forces in forced **convection** or the effects of forced **flow** in free **convection** become significant. The interaction of forced **and** free **convection** is especially pronounced in situations where the forced **flow** velocity is low **and**/or the **temperature** differences are large. This **flow** is also a relevant type of **flow** appearing in many industrial processes, such as manufacture **and** extraction of polymer **and** rubber sheets, paper production, wire drawing **and** glass-fiber production, melt spinning, continuous casting, etc. (Tadmor **and** Klein [1]). This **flow** has also many industrial applications such as **heat** treatment of material traveling between a feed roll **and** wind-up roll or conveyer belts, extrusion of steel, cooling of a large metallic **plate** in a bath, liquid films in condensation process **and** in aerodynam- ics, etc. As per standard texts books by Bejan [2], Kays **and** Crawford [3], Bergman et al. [4] **and** other literatures the free **and** mixed **convection** **flow** occur in atmospheric **and** oceanic circulation, electronic machinery, heated or cooled enclosures, electronic power supplies, etc. This topic has also many applications such as its influence on operating temperatures of power generating **and** electronic devices. In addition it should be mentioned that this type of **flow** plays a great role in thermal

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General formulation **and** solution of Navier-Stokes **and** energy equations are sought in the study of three- dimensional axisymmetric unsteady stagnation-point **flow** **and** **heat** **transfer** impinging on a flat **plate** when the **plate** is **moving** **with** variable velocity **and** acceleration towards the main stream or away from it. As **an** application, among others, this **accelerated** **plate** can be assumed as a solidification front which is being formed **with** variable velocity. **An** external fluid, along z - direction, **with** strain rate a impinges on this flat **plate** **and** produces **an** unsteady three-dimensional axisymmetric **flow** in which the **plate** moves along z - direction **with** variable velocity **and** acceleration in general. A reduction of Navier-Stokes **and** energy equations is obtained by use of appropriate similarity transformations, for the first time. The obtained ordinary differential equations are solved by using finite-difference numerical techniques. Velocity **and** pressure profiles along **with** **temperature** profiles are presented for different examples of the **plate** velocity functions **and** selected Prandtl numbers. According to the results obtained, the velocity **and** thermal boundary layers feel the effect of variations of the **plate** velocity more than the **plate** acceleration. It means that the minimum boundary layer thickness happens at the maximum value of the **plate** velocity **and** acceleration effect plays a secondary role.

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results for these two types of base fluids after using implicit finite-difference method **with** quasi-linearization technique as the solution to a resultant problem. By using ferrofluid, Shei- kholeslami **and** Ganji [16] investigated **heat** **transfer** **with** thermal **radiation** inside **an** enclosure of semi annulus in the presence of a magnetic source. Idress et al. [17] studied application of the optimal homotopy asymptotic method for the solution of the Korteweg-de Vries equation. Ellahi et al. [18] studied series solutions of non-Newtonian nanofluids **with** Reynolds' model **and** Vogel's model by means of the homotopy analysis method. Herisanu **and** Vasile [19] inves- tigated that optimal homotopy perturbation method for a non-conservative dynamical system of a rotating electrical machine. Several other studies were conducted in the last few years, on nanofluids by taking different types of convectional base fluids **with** different nanoparticles, see for example [20–29] **and** the related references therein.

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A two-dimensional unsteady model for sinter cooling process is established based on the actual sinter cooling process in **an** annular cooler. The complex **heat** **transfer** process, including three modes of **heat** conduction inside the sinter ore particles, gas-solid **convection** **and** **radiation** in the trolley, is taken into account. The **heat** **transfer** ratio is proposed to explore the effect of **heat** **radiation** to the cooling process. **With** actual device **and** operating parameters, modeling verification **and** analyses of datum based on numerical simulation are conducted. The results are consistent **with** actual production datum when the **heat** **transfer** ratio e varies from 0 to 0.1. The pressure field, **temperature** distribution **and** the **temperature** characteristic of outlet gas are obtained by numerical simulation method. The effect of radiative **heat** **transfer** on the cooling process is analyzed. The results show that the **heat** **transfer** ratio e has no effect on the gas **flow** **and** pressure distribution of air. The increase of the ratio e can reinforce the **heat** **transfer** between the sinter **and** air, which will lead to bigger increase of **temperature** drop rate of the sinter. The solid **and** gas **temperature** distribution trends at different **heat** **transfer** ratios are similar. The results obtained herein may provide some guidelines for the research on the actual cooling process in **an** annular cooler.

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Figures 2(a) **and** 2(b) show the effect of **heat** flux on the **heat** **transfer** coefficient for different **mass** velocities. It is possible to verify the dependence of the **heat** **transfer** coefficients on the **heat** flux, mainly at the low quality region (quality less than 40%). The **heat** **transfer** coefficient increased **with** the **heat** flux increment. As previously pointed, several authors (Choi et al., 2007, **and** Lin et al., 2001) have associated this behavior **with** nucleate boiling in the initial part of boiling, mainly under high **heat** flux. This condition will tend to be suppressed at high vapor quality where the effect of **heat** flux on **heat** **transfer** coefficient becomes lower **and** the coefficient decreases, as can be observed in Figs. 2(a) **and** 2(b). Figure 2(a) also shows that for low **mass** velocity (G = 240 kg/sm 2 ) **and** low **heat** flux ( q = 5 kW/m 2 ), the **heat** **transfer** coefficient hardly

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The ability of the **heat** pipe to **transfer** thermal energy **with** negligible **temperature** drop has recently enabled it to become one of the most versatile devices in the field of **heat** recovery systems [1, 2]. In **past** few years considerable interest has been generated **with** regard to the **heat** pipe **heat** exchanger as a **heat** recovery system [3@5]. In a gravity assisted mode, the presence of a capillary structure is not obligatory as in purely a capillary drive **heat** pipe. Nevertheless, most gravity assisted **heat** pipes do have a capillary structure in order to protect the liquid against the shear stress exerted by counter flowing vapour [6, 7] **and** also to induce circumferential distribution of the working fluid within the evaporator section. In gravity assisted **heat** pipes, relatively high rates of **heat** **transfer** can be achieved even **with** working fluids having low surface tension [8, 9].

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