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This research aims to the effect of evaporator section lengths and working fluids on operational limit of closed loop oscillating heat pipes with check valves (CLOHP/CV) with R123 Ethanol and Water were used as the working fluids. A set of CLOHP/CV was made of copper tubes in combination of following dimension: 1.77 mm inside diameter: 10 turns: 5, 10 and 15 cm equal lengths for evaporator, adiabatic and condenser sections. The working fluid was filled in the tube at the filling ratio of 50%. The evaporator section was given heat by heater while the condenser section was cooled by volume water in a cold bath. The adiabatic section was properly insulated. In the test operation. Which the temperature at the adiabatic section was controlled at 60[degrees]C in steady-state condition. From The obtained results obtained, it could be concluded as follows. When the evaporator lengths increased from 5 cm to 10 and 15 cm the critical heat transfer flux decreased. There was working fluids change from R123 to Ethanol and water the critical heat flux decreased. Key words: Closed-looped oscillating heat-pipe, check valves, operational limit, critical heat flux, INTRODUCTION The CLOHP/CV is a very effective heat transfer device Akachi et al. (1): it has a simple structure and fast thermal- response. The CLOHP/CV consists of a long capillary [...]

The transient behavior of the microgrooved heat pipe is presented by a mathematical model and utilizing a macroscopic approach. The time needed for the onset of dry out at the hot end and for the micro heat pipe to reach a steady state is predicted by results.

The thermal performance of solar heating systems is strongly influenced by the thermal stratification in the heat storage. The higher the degree of thermal stratification is, the higher the thermal performance of the solar heating systems. Thermal stratification in water storage can for instance be achieved by use of inlet stratifiers combined with low flow operation in the solar collector loop. In this paper, investigation of a number of different fabric stratification pipes is presented and compared to a non-flexible inlet stratifier. Additional, detailed investigation of the flow structure close to two fabric stratification pipes is presented for one set of operating conditions by means of the optical PIV (Particle Image Velocimetry) method. Keywords: Solar heating systems; Inlet stratifiers; PIV measurements

The pulsating heat pipe (PHP) heat transfer characteristic versus its operating temperature is discussed. Results reveal that single phase cooling in PHP causes a large total temperature differences fluctuation, and phase change proportion increases at the optimal operating temperature.

A novel flat heat pipe fabricated by bonding an array of parallel wires between two layers of screen mesh and enclosing this in a solid case are developed to assist in meeting the high thermal design requirements in high power microelectronics, power converting systems, laptop computers and spacecraft thermal control systems. Two different prototypes, each measuring 152.4 mm by 25.4 mm, are constructed and evaluated experimentally.

Thermal performance characteristics of a eutectic mixture of lauric and stearic acids as phase change material (PCM) during the melting and solidification processes were determined experimentally in a vertical two concentric pipe-energy storage system. This study deals with three important subjects: The first one is to determine the eutectic composition ratio of the lauric acid (LA) and stearic acid (SA) binary system, and to measure its thermophysical properties by DSC. The second one is to establish the thermal characteristics of the mixture such as total melting and solidification times, the heat transfer modes in melted and solidified PCM, and the effect of Reynolds and Stefan numbers as inlet heat transfer fluid (HTF) conditions on the phase transition behaviors. The final one includes the calculations of the heat transfer coefficients between the outside wall of the HTF pipe and the PCM, and heat fractions during the melting and solidification processes of the mixture, and also the discussion of the effect of inlet HTF parameters on these characteristics. The LA-SA binary system in the mixture ratio of 75.5:24.5 wt % forms a eutectic, which melts at 37[degrees]C and has a latent heat of 182.7 J [g.sup.-1], and, thus, these properties make it an attractive phase change material used for passive solar space heating applications such as building and greenhouse heating with respect to the climate conditions. The experimental results indicated that the mixture encapsulated in the annulus of two concentric pipes has good thermal and heat transfer characteristics during the melting and solidification processes, and it has potential for heat storage in passive solar space heating systems.

The performance of a new solar hot water system with an integrated heat-pipe is investigated theoretically and experimentally. The new system uses a wickless gravity assisted loop heat-pipe for the heat transfer from the collector--evaporator to the tank through a heat exchanger--condenser. A detailed heat transfer experimental study is performed, focused on the thermal behaviour of the different parts of the system. The results show that the system can reach satisfactory efficiencies which, in combination with manufacturing simplicity, absence of moving parts and good behaviour under freeze conditions, make it an interesting technological solution. Furthermore, a theoretical model for the collector is proposed and comparison with experimental results is performed. This model can be used for the optimisation of the system design. [C] 2002 Published by Elsevier Science Ltd.

Transition of chaotic flow is discussed relative to a radially heated Taylor-Couette system. The effect of a radial temperature gradient quantified by the Grashof number and the acceleration ratio has been studied. It was found that dynamics of temperature variations can be inferred from the dynamics of the velocity variations.

A study on the effective cooling of electric components using micro heat pipes presents a mathematical model to predict temperature variations and heat transport capacity that contribute to the overall axial temperature drop as a function of heat transfer. Results obtained from this model show that the temperature drop occurring in the evaporator is considerably larger than those occurring in the condenser. Both temperature drops increase with increases in the input power.

Research is conducted to examine the one-dimensional and two-dimensional approaches in the analysis of the fin as a means of controlling the temperature of a piece of equipment. The objective is to illustrate two-dimensional effects by comparing the results of one-dimensional and two-dimensional investigations of a rectangular fin on a pipe with convection from the tip as a function of the Biot number and relative fin size. Results indicate the existence of similar effectiveness relationships for both approaches with the one-dimensional method being less restrictive.

Research is conducted to examine the performance of a helically grooved revolving heat pipe for different working temperatures, rotational speeds and adverse tilt angles. A mathematical model was formulated for the measurement of capillary limit which was hindered by the variation of the body-force field along the length of the groove and around the heat pipe circumference. Results demonstrate that the capillary limit significantly increased with rotational speed caused by the helical geometry of the heat pipe wick structure.

The maximum heat transfer capabilities of two copper-water flat miniature heat pipes (FMHPs) with diagonal trapezoidal micro capillary grooves and one copper-water FMHPs with axial rectangular micro capillary grooves are studied. The objective is to extensively manufacture investigate and model a variety of flat miniature heat pipes. Experimental results are in good agreement with the theoretical prediction of the capillary limitation int he horizontal orientation.

A study was conducted to analyze the approximate analytical approach developed by T.P. Cotter for determining the maximum heat transport capacity in micro heat pipes. A semi-empirical correlate was developed that integrated the effects of the temporal intrusion of the evaporating region into the heat pipe's adiabatic region. Results indicated that the approach integrated a fixed evaporator length that failed to accommodate the growth of the evaporator region resulting from conduction through the heat pipe's wall.

Fundamental heat transfer experiments were carried out for three kinds of heat pipes that may be applied to turbine cooling in future aero-engines. In the turbine cooling system with a heat pipe, heat transfer rate and start-up time of the heat pipe are the most important performance criteria to evaluate and compare with conventional cooling methods. Three heat pipes are considered, called heat pipe A, B, and C, respectively. All heat pipes have a stainless steel shell and nickel sintered powder metal wick. Sodium (Na) was the working fluid for heat pipes A and B; heat pipe C used eutectic sodium-potassium (NaK). Heat pipes B and C included noncondensible gas for rapid start-up. There were fins on the cooling section of heat pipes. In the experiments, an infrared image furnace supplied heat to the heat pipe simulating turbine blade surface conditions. In the results, heat pipe B demonstrated the highest heat flux of 17 to 20 W/[cm.sup.2]. The start-up time was about 6 minutes for heat pipe B and about 16 minutes for heat pipe A. Thus, adding noncondensible gas effectively reduced start-up time. Although NaK is a liquid phase at room temperature, the startup time of heat pipe C (about 7 to 8 minutes) was not shorter than the heat pipe B. The effect of a gravitational force on heat pipe performance was also estimated by inclining the heat pipe at an angle of 90 deg. There was no significant gravitational dependence on heat transport for heat pipes including noncondensible gas.

A study was conducted to analyze the influence of transverse acceleration-induced body forces on the capillary limit of copper-ethanol heat pipes supporting helical groove wick structures. A rotameter and digital flow meter was utilized to express the mass flow rate of coolant through the calorimeter. Results showed that increases in the transverse body force helped in returning the working fluid back to the evaporator area of the heat pipe.

This paper presents a comparative study between theoretical predictions and experimental results of a flat-plate solar collector with heat pipes. The theoretical model for the heat pipe solar collector is based upon the method by Duffie and Beckman (1980), modified to use heat pipes for energy transport. The methanol filled heat pipes are self-contained devices whose evaporators are inserted under pressure in the fiat plate of the solar collector and the heat exchange is carried out at their condensers. The evaporators contain a wick of one mesh layer to ensure a better distribution of the working fluid. The condensers are wickless and inclined 15 deg more than the inclination of the evaporators to facilitate the return of the condensate to the evaporators. The time constant of the heat pipe solar collector was calculated and found to be about 23 minutes. Also presented in this paper are comparative experimental results of the proposed solar collector and a conventional commercial solar collector. The two collectors were tested simultaneously. The instantaneous efficiencies of the heat pipe solar collector are lower than the conventional collector in the morning and higher when the heat pipes reach their operating temperatures.

At the DLR a second generation sodium heat pipe receiver for the Schlaich Bergermann und Partner (SBP) 9-k[W.sub.e] dish/Stirling system has been developed and constructed. Long-term operation occurred from Oct. 1992 until Aug. 1993 at the Plataforma Solar de Almeria (PSA) in Spain, accumulating 950 operating hours. The performance of the SBP 9-k[W.sub.e] system with a sodium heat pipe receiver is evaluated according to the guidelines for dish/Stirling performance evaluation by Stine and Powel, as proposed to the International Energy Agency (IEA). Tests were stopped due to a leak in the receiver absorber surface. The analysis of this damage are reported.

In this article the validity of the utilisability method for evacuated heat pipe solar panels was tested, through a comparison of expected useful energy and that measured in an experimental plant. The panels used are distinctive for the working of the heat pipes, which for collection, require a threshold irradiance value higher than the critical, used in quantification of heat losses. Working limits were identified and the basal utilisability calculation hypotheses tested by using a calculation code that simulates heat pipe behaviour. Dynamic phenomena linked to inertia during collection were studied with a mathematical model constructed from results provided by the collector's field at stepped variation to solar irradiance. The numerical and experimental results enable a critical comparison between calculated and measured energy.

Solar heating systems often employ conduits to carry cool fluid to the collector array and to carry the heated fluid back to the storage tank. In systems in which these two conduits are bundled together in one cover (in what has come to be known as the 'life-line') there is a thermal performance penalty caused by heat transfer from the hot conduit to the cold conduit. This cross heat transfer results in a penalty in system performance, and this paper is about evaluating this penalty. We show that the standard Hottel-Whillier-Bliss (HWB) equation can be modified to simultaneously take into account both the pipe heat losses to the ambient environment and the cross heat transfer between the hot and cold streams. Parameters in these equations are the thermal resistances between the fluids and between each fluid and the ambient. Methods are presented for both calculating and measuring these thermal resistances. We carry out sample calculations of the parameters in the modified HWB equation for a representative solar DHW system equipped with either of two different life-lines of commercial design. System simulations using these parameters reveal that the thermal effects of these life-lines are to reduce the net delivered solar energy by 6-14%, and that heat loss to the ambient is more detrimental to the system performance than heat transfer from the hot to the cold conduit.

The heat transport capacity of micro heat pipes depends upon the apex channel angle of the liquid arteries, the contact angle of the liquid flow, the length of the heat pipe, the vapor flow velocity and characteristics, and the tilt angle. Effects of the frictional interaction between the liquid and vapor flow also need to be considered for accurate predictions. The maximum heat transport capacity has been calculated using the theoretical expression for the minimum meniscus radius. The flow characteristics of the micro heat pipes have been determined using a control volume technique.

The thermal behavior of tape carrier package (TCP) in the reference notebook and sub-notebook are characterized thermal solutions for the use of Pentium processors. Solutions for the notebook include the heat sink and the aluminium plate solution, the heat pipe connected to the outside aluminium plate solution, the heat pipe connected to the keyboard solution, and the fan/heat sink solution. The solutions for the sub-notebook include the heat pipe on the bottom chassis solution and the heat pipe connected to keyboard solution.

A mathematical model describes the thermal properties of the conventional and flat miniature axially grooved heat pipes (AGHP). The model accounts for fluid circulation in the AGHP. The evaporator thermal resistance decreases and the condenser thermal resistance increases with an increase of the heat load. The maximum heat flux in the evaporator of copper-water flat AGHP is 25 and 50 watts/cm squared for horizontal orientation and vertical orientations. The capillary and boiling limitations check this maximum heat flux in the operating temperature range of 90 to 120 degrees celsius.

A thermally permeable wall affects the longitudinal heat transfer by fluid pulsation in a pipe. The mean temperature distribution is a quadratic curve, when the heat loss through the wall over a cycle of fluid pulsation is uniform over the pipe. The amplitude of the curve decreases with the decrease in temperature. The rate of longitudinal heat transfer is directly proportional to temperature. The effect of the Womersley number on temperature distribution is discussed.

A combined experimental and analytical investigation was conducted to evaluate a heat pipe convective cooling device consisting of sixteen small copper/water heat pipes mounted vertically in a 4 x 4 array which was 25.4 mm square. The analytical portion of the investigation focused on determination of the maximum heat transport capacity and the resistance of the individual heat pipes. The resistance of each heat pipe was found to be 2.51 K/Watt, or more than 3 times smaller than the resistance produced by a solid copper rod with the same dimensions. The maximum predicted heat rejection for the module was over 50 Watts, or a power density in excess of 7.75 Watts/[cm.sup.2]. In the experimental portion of the investigation, two different modules were tested. The first module utilized ten circular aluminum fins mounted on the condenser end of each heat pipe to enhance heat rejection, while the second contained only the sixteen copper/water heat pipes. The effects of flow velocity, input power, and base plate temperature on the overall thermal resistance and the heat rejection capacity were determined, as well as the pressure drop resulting from each module. The tinned heat pipe array was found to have a lower overall thermal resistance and thus, a higher heat rejection capacity, but also resulted in a significantly larger pressure drop than the array without fins. The results of the heat pipe array experiments were also compared with experimental and empirical results obtained from flow over a flat plate 25.4 mm square.

A mathematical model suitably explains the heat transfer of thin liquid films in heat pipes' capillary-grooved evaporators. The heat transfer coefficient can reduce by 30% due to the solid surface roughness in thin evaporating film area. Grooved evaporators can hold high heat fluxes because the major portion of the heat flow is shifted to the meniscus region. The local evaporative heat transfer coefficient does not depend on the heat flux.

The transient thermal response of vapor deposited micro heat pipe arrays fabricated as an integral part of silicon wafers was measured to determine if these arrays could be used to reduce the local temperature gradients and improve the reliability of semiconductor devices. Wafers with arrays of 34 and 66 micro heat pipes were evaluated using an IR thermal imaging system in conjunction with a VHS video recorder. These arrays occupied 0.75 and 1.45 percent, of the wafer cross-sectional area, respectively. The wafers with micro heat pipe arrays demonstrated a 30 to 45 percent reduction in the thermal time constant when compared to that obtained for plain silicon wafers. This reduction in response time was shown to lead to a significant reduction in the maximum wafer temperature, due to the increased effective thermal conductivity caused by the vaporization and condensation occurring in the individual micro heat pipes. The experimental results were then used to validate a transient numerical model, capable of accurately predicting the transient temperature profile and thermal time constant of the wafer/heat pipe combinations.

An experimental investigation of vapor deposited micro heat pipe arrays was conducted using arrays of 34 and 66 micro heat pipes occupying 0.75 and 1.45 percent of the cross-sectional area, respectively. The performance of wafers containing the arrays was compared with that of a plain silicon wafer. All of the wafers had 8 X 8 mm thermofoil heaters located on the bottom surface to simulate the active devices in an actual application. The temperature distributions across the wafers were obtained using a Hughes Probeye TVS Infrared Thermal Imaging System and a standard VHS video recorder. For wafers containing arrays of 34 vapor deposited micro heat pipes, the steady-state experimental data indicated a reduction in the maximum surface temperature and temperature gradients of 24.4 and 27.4 percent, respectively, coupled with an improvement in the effective thermal conductivity of 41.7 percent. For wafers containing arrays of 66 vapor deposited micro heat pipes, the corresponding reductions in the surface temperature and temperature gradients were 29.0 and 41.7 percent, respectively, and the effective thermal conductivity increased 47.1 percent, for input heat fluxes of 4.70 W/[cm.sup.2]. The experimental results were compared with the results of a previously developed numerical model, which was shown to predict the temperature distribution with a high degree of accuracy, for wafers both with and without the heat pipe arrays.

A comparative study of the efficiencies of disk-shaped heat pipe and flat-plate heat pipe reveals that heat transfer capability is higher for disk-shaped heat pipe than flat-plate heat pipe. The performance of both types of heat pipes is influenced by changes in wick thickness, the overall thickness of the heat pipe and the vapor channel thickness. An integral analysis helps determine the overall pressure distribution and velocity profiles for both liquid and vapor phases.

A newly developed thermodynamic model, which includes Marangoni surface effects, changes in local interface curvature and disjoining pressure, helps explain the vapor-liquid interface characteristics in micro heat pipes. Examination of vapor-liquid interface as an intrinsic meniscus reveals the significant dependence of the rate of heat transfer on the magnitude of the evaporator capillary radius. Increase in the wall superheat increases the value of the mean curvature in the evaporator.

Examination of a rotating heat pipe using a transient two-dimensional model indicates that vapor density and operating temperature influence the complex vapor flow patterns in a rotating heat pipe. Modification in the vapor temperature due to vapor flow pattern influences the performance of the heat pipe. Vapor velocity field of rotating heat pipe is different from that of heat pipes without rotation.

A study of flow of hot water through a pipe reveals that the delay in flow is due to thermal coupling between the fluid and the pipe. Hot water from the water tank does not flow out as soon as the tap is opened, which may be due to the presence of cold water in the pipe between the hot water tank and the tap. Cold pipe also reduces the speed of the flowing hot water in the initial stages of flow.

Transient two-dimensional simulation of gas-loaded heat pipes includes diffusion and variable heat pipe properties, and involves the use of a conjugate solution scheme to combine vapor flow with unsteady wall-based heat transfer. The pipe operating temperature and the vapor-gas interface location are influenced by the boundary conditions. Heat pipe operation depends on gas mass, which influences pipe operating temperature and transient time period.

Experimental studies of film condensation heat transfer by R-152a vapor, condensing on a single horizontal smooth tube and three enhanced tubes, reveal agreement within 15% of the predicted data from Nusselt theory. The high heat transfer performance of R-152a results from its higher latent heat and heat conductivity and lower liquid viscosity. Use of enhanced tubes such as the integral bind and the sawtooth-type tube enhance the heat transfer coefficient of R-152a.

A mathematical model to analyze heat and mass transfer process in a micro heat pipe (MHP) defines liquid distribution in and thermal features of MHP. The thermal features are influenced by liquid charge and applied heat load. The model highlights the significance of liquid fill, minimum wetting contact angle and shear stresses at the liquid-vapor interface in predicting maximum heat transfer capacity and thermal resistance of the MHP.

This article presents a theoretical model for the determination of the efficiency, the heat removal factor, and the outlet water temperature of a single collector and an array of flat-pipe heat-pipe collectors. The model is validated by on-site testing of 16 heat-pipe collectors under the typical weather conditions in Singapore. Within the operational range of interest of the hot water temperatures, the results show that the proposed model is sufficient to describe the steady-state performance of the collector array.

Results of an experimental study are reported which demonstrate the ability of heat pipes to simultaneously dissipate high heat fluxes and high total power at low surface temperatures. The application is to cooling high power density (and high total power) semiconductor chip modules. The two designs studied incorporate air or liquid cooling in the condenser sections. The air-cooled design consisted of a manifold base plate with a series of holes drilled in it each of which was lined with sintered copper powder which served as the wick. An array of wick lined tubes was attached normal to the plate and served as the condenser section. The other heat pipe was disk shaped and also had a sintered wick structure. Cooling water channels were placed over the entire periphery of the housing except in the region of heat input. Reported steady heat fluxes are up to 31 W/cm squared corresponding to total power dissipation of up to 1400 W for the water cooled heat pipe and up to 47 W/cm squared (900 W total power) for the air cooled heat pipe with surface temperatures under 100 degrees C.

A study was conducted to evaluate the development of a two-region model for analyzing high-temperature heat pipe startup. The model assumes that vapor flow is characterized by Navier-Stokes equations and focuses on a simulation by a self-diffusion model. Results show that high-temperature heat pipe startup process is conditioned by a moving hot zone with relatively steep fronts.

A study was conducted to evaluate the heat pipe startup process. The study presents a physical description and divides the process into five periods for analytical convenience. Results show that earlier research which developed numerical simulations of the process were unsuccessful because they failed to include the pipe's rarefied vapor flow. Thus, a rarefied vapor self-diffusion model is constructed which adopt numerical simulations lacking in previous research.

The performance of a solar chemical heat pipe was studied using CO2 reforming of methane as the vehicle for storage and transport of solar energy. The endothermic reforming reaction was carried out with a reactor packed with a supported rhodium catalyst and heated by the concentrated solar flux from the Schaeffer solar furnace at the Weizmann Institute (Rehovot, Israel). The maximum absorbed power was 8.5 kW. The reforming was run under variable insolation conditions, including partly cloudy days. The flux input was regulated by opening the doors of the concentrator building. The product gas temperature followed a predetermined set point that automatically controlled the flow of reactants to ensure constant composition of the reformer products. The exothermic methanation reaction was run in a multistage methanator filled with the same Rh catalyst and fed with the products from the reformer. High conversions were achieved for both reactions. In the closed-loop mode, the products from the reformer and from the methanator were compressed into separate storage tanks. The two reactions were run consecutively, and the whole process was repeated for over 60 cycles. The overall performance of the closed loop was satisfactory; scale-up work is in progress.

Equations are formulated for the two-dimensional, anisotropic conduction of heat in space radiator fins. The transverse temperature field is obtained by the integral method, and the axial field by numerical integration. A shape factor, defined for the heat-pipe interface boundary condition, simplifies the analysis and renders the results applicable to general heat-pipe/conduction-fin designs. The thermal results are summarized in terms of the fin efficiency, a fin length parameter, and a radiation/axial-conductance number. These relations, together with those for mass distribution between fins, heat pipes, and headers are used in formulating a radiator mass/heat-rate criterion function. Minimization of the criterion function results in asymptotic solutions for the optimum radiator geometry and conditions. The effect of physical properties on the optimum design is determined; in particular, performance is found to vary with fin conductivity to the 1/3 power for large conductivity values.

The derivation of a flat-front startup model-based closed-form solution for heat pipe startup from the frozen state is discussed. Good agreement was assessed bythe comparison of the analytical solution to both experimental and numerical solutions. A quick prediction method for the heat pipe startup process was obtained from the closed-form solution. A fundamental guidance for heat pipe design is provided by this frozen startup limitation.

A chemical reactor for carbon dioxide reforming of methane was integrated into a sodium reflux heat pipe receiver and tested in the solar furnace of the Weizmann Institute of Science, Rehovot, Israel. The receiver/reactor was a heat pipe with seven tubes inside an evacuated metal box containing sodium. The catalyst, 0.5 wt% Rh on alumina, filled two of the tubes with the front surface of the box serving as the solar absorber. In operation, concentrated sunlight heated the front plate and vaporized sodium from a wire mesh wick attached to the other side. Sodium vapor condensed on the reactor tubes, releasing latent heat and returning to the wick by gravity. The receiver system performed satisfactorily in many tests under varying flow conditions. The maximum power absorbed was 7.5 kW at temperatures above 800 degrees C. The feasibility of operating a heat pipe receiver/reactor under solar conditions was proven, and the advantages of reflux devices confirmed.

An engine employing reciprocating heat pipes shows full-scale liquid impingement on the upper evaporator wall for a cranking speed near 420 rpm, and proves their suitability for engine piston cooling applications. The reciprocating motion produces a high-frequency shaking-up action. The shaking-up action is responsible for the liquid return mechanism between the evaporator and condenser sections in these pipes. The tests are conducted on copper/water reciprocating heat pipes.

The Nusselt analysis model of a vertical axis rotating condenser allows the determination of heat transfer. Fluid merit number and a simplified Nusselt number result, which are suitable for design applications. In rotating heatpipes the centrifugal effect is responsible for the transport of liquid from the condenser to the evaporator in the absence of a wick. The study involves coordinate directions which are perpendicular and tangential to a wall.

The transient conjugated heat transfer in laminar pipe flow, when the flow is hydrodynamically and thermally developed, is analyzed mathematically. Conductivity, diffusivity and radius ratios are the solid-fluid factors that influence thermal behavior. Wave heat flux increases as a result of increased thermal conductivity. An increase in conductivity and diffusivity ratios results in an increase in the thermal entrance length of the tube.

A study was conducted to investigate the effects of gravity for the case of inclined-, triangular- and trapezoidal-shaped micro heat pipes (MHPs). The results revealed that the axial distribution of the liquid phase changes qualitatively.

Two-dimensional quasi-steady conduction equation is used in the analytical study of rewetting of an infinite slab with uniform heating by Wiener-Hopf technique. The dryout caused by the heat flux has importance in measuring the decay heating of a nuclear fuel or in designing of heat pipes for thermal radiators.

One-dimensional, semi-analytical model for prediction of the wetted length supported by inclined triangular capillary grooves subject to heating from below is presented. The design curves that are concluded can be used to estimate the capillary limit in inclined heated triangular capillary grooves for a variety of operating conditions.