Showing papers on "Heat pipe published in 2008"
TL;DR: Pulsating (or oscillating) heat pipes (PHP or OHP) are new two-phase heat transfer devices that rely on the oscillatory flow of liquid slug and vapor plug in a long miniature tube bent into many turns.
Abstract: Pulsating (or oscillating) heat pipes (PHP or OHP) are new two-phase heat transfer devices that rely on the oscillatory flow of liquid slug and vapor plug in a long miniature tube bent into many turns. The unique feature of PHPs, compared with conventional heat pipes, is that there is no wick structure to return the condensate to the heating section; thus, there is no countercurrent flow between the liquid and vapor. Significant experimental and theoretical efforts have been made related to PHPs in the last decade. While experimental studies have focused on either visualizing the flow pattern in PHPs or characterizing the heat transfer capability of PHPs, theoretical examinations attempt to analytically and numerically model the fluid dynamics and/or heat transfer associated with the oscillating two-phase flow. The existing experimental and theoretical research, including important features and parameters, is summarized in tabular form. Progresses in flow visualization, heat transfer characteristics, and ...
368 citations
TL;DR: In this article, an experimental study on the operational limitation of closed loop pulsating heat pipes (CLPHPs), which consist of a total of 40 copper tubes with 1mm and 2mm inner diameter, respectively, was presented.
239 citations
TL;DR: In this paper, a heat pipe with de-ionic water, alcohol, and nanofluids (alcohol and nanoparticles) was fabricated from the straight copper tube with the outer diameter and length of 15, 600 mm, respectively.
230 citations
TL;DR: In this article, preliminary experimental results on using copper tube having internal and external diameter with 2.4mm and 3mm, respectively, to carry out the experimental pulsating heat pipe were presented.
225 citations
TL;DR: A short review on the micro and miniature heat pipes is presented in this paper, where the authors present a short review of the heat pipe design, definition and prediction of most simple cases, but even today heat pipes are not completely understood and solution strategies still contain significant simplifications.
202 citations
TL;DR: In this paper, a mathematical model is developed for predicting the thermal performance of a flat micro heat pipe with a rectangular grooved wick structure, and the results obtained from the proposed model are in close agreement with several existing experimental data in terms of the wall temperatures and the maximum heat transport rate.
160 citations
TL;DR: In this article, a theoretical model based on effectiveness-NTU method was developed for evaluating the thermal efficiency of the collector, the inlet, outlet water temperatures and heat pipe temperature.
149 citations
TL;DR: It is demonstrated that the traditional way of calculating evaporative heat loss of a clothed person can lead to substantial errors, especially for clothing with low permeability, which can be positive or negative, depending on the climate and clothing type.
Abstract: Investigating claims that a clothed person's mass loss does not always represent their evaporative heat loss (EVAP), a thermal manikin study was performed measuring heat balance components in more ...
144 citations
TL;DR: A discussion of the current status of spray cooling technology as well as NASA's goals, current direction, and challenges associated with the implementation and practice of this technology in the micro-gravity environment is provided in this article.
138 citations
TL;DR: In this paper, the authors investigated the thermal performance of a horizontal closed-loop oscillating heat pipe (HCLOHP) at normal operating condition, where the working fluids used within the HCLOHPs were distilled water and absolute ethanol, which were added into the tubes to various filling ratios.
135 citations
Patent•
15 Apr 2008
TL;DR: In this paper, the authors present methods for cooling components contained in enclosures that reject 500 or more Watts employing two phase passive heat transfer devices including Loop Heat Pipes and devices referred to as LHPLs.
Abstract: Disclosed in the present invention are methods for cooling components contained in enclosures that reject 500 or more Watts employing two phase passive heat transfer devices including Loop Heat Pipes and devices we refer to as LHPLs. The methods minimize the amount of energy employed in cooling while at the same time maximizing the quality of heat rejected to the secondary cooling loops that transmit the heat to the outside world. Where data centers provide direct access to chilled water it becomes possible to reject heat directly to cooling towers in locations as hot and humid as Atlanta Ga. eliminating 40% or more of the total energy consumed. The key advances that make this energy efficient performance possible employ LHPLs that have the smallest possible total thermal resistance, methods that maximize their effectiveness and ancillary devices that minimize the energy consumed in cooling with air.
TL;DR: It has been realized that the physical properties of nan ofluids such as surface tension, liquid thermal conductivity, viscosity and density have significant effects on the nanofluid two-phase flow and heat transfer characteristics but the lack of the accurate knowledge of these physical properties has greatly limited the study in this interdisciplinary field.
Abstract: Nanofluids are a new class of fluids engineered by dispersing nanometer-size solid particles in base fluids. As a new research frontier, nanofluid two-phase flow and thermal physics have the potential to improve heat transfer and energy efficiency in thermal management systems for many applications, such as microelectronics, power electronics, transportation, nuclear engineering, heat pipes, refrigeration, air-conditioning and heat pump systems. So far, the study of nanofluid two-phase flow and thermal physics is still in its infancy. This field of research provides many opportunities to study new frontiers but also poses great challenges. To summarize the current status of research in this newly developing interdisciplinary field and to identify the future research needs as well, this paper focuses on presenting a comprehensive review of nucleate pool boiling, flow boiling, critical heat flux, condensation and two-phase flow of nanofluids. Even for the limited studies done so far, there are some controversies. Conclusions and contradictions on the available nanofluid studies on physical properties, two-phase flow, heat transfer and critical heat flux (CHF) are presented. Based on a comprehensive analysis, it has been realized that the physical properties of nanofluids such as surface tension, liquid thermal conductivity, viscosity and density have significant effects on the nanofluid two-phase flow and heat transfer characteristics but the lack of the accurate knowledge of these physical properties has greatly limited the study in this interdisciplinary field. Therefore, effort should be made to contribute to the physical property database of nanofluids as a first priority. Secondly, in particular, research on nanofluid two-phase flow and heat transfer in microchannels should be emphasized in the future.
TL;DR: In this article, the authors studied the thermal characteristics of the miniature Loop Heat Pipe (mLHP) with the flat disk shaped evaporator, 10 mm thick and 30 mm in diameter, for thermal control of the compact electronic equipments.
11 May 2008
TL;DR: In this paper, a cooling design that uses a copper/water heat pipe with aluminum fins to cool a concentrated photovoltaic cell by natural convection was discussed, with a cell level waste heat flux of 40 W/cm2.
Abstract: Concentrating photovoltaic systems (CPV) utilize low cost optical elements such as Fresnel lens or mini-reflecting mirrors to concentrate the solar intensity to 200 to 1000 suns. The concentrated solar energy is delivered to the solar cell at up to 20 to 100 W/cm2. A portion of the energy is converted to electricity, while the portion that is not converted to electricity must be dissipated as waste heat. Solar cell cooling must be an integral part of the CPV design, since lower cell temperatures result in higher conversion efficiencies. Heat pipes can be used to passively remove the high heat flux waste heat at the CPV cell level, and reject the heat to ambient through natural convection. This paper discusses a cooling design that uses a copper/water heat pipe with aluminum fins to cool a CPV cell by natural convection. With a cell level waste heat flux of 40 W/cm2, the heat pipe heat sink rejected the heat to the environment by natural convection, with a total cell-to-ambient temperature rise of only 40°C.
TL;DR: In this article, a mathematical model predicting the oscillating motion in an oscillating heat pipe is developed, where the model considers the vapor bubble as the gas spring for oscillating motions including effects of operating temperature, nonlinear vapor bulk modulus, and temperature difference between the evaporator and the condenser.
Abstract: A mathematical model predicting the oscillating motion in an oscillating heat pipe is developed. The model considers the vapor bubble as the gas spring for the oscillating motions including effects of operating temperature, nonlinear vapor bulk modulus, and temperature difference between the evaporator and the condenser. Combining the oscillating motion predicted by the model, a mathematical model predicting the temperature difference between the evaporator and the condenser is developed including the effects of the forced convection heat transfer due to the oscillating motion, the confined evaporating heat transfer in the evaporating section, and the thin film condensation in the condensing section. In order to verify the mathematical model, an experimental investigation was conducted on a copper oscillating heat pipe with eight turns. Experimental results indicate that there exists an onset power input for the excitation of oscillating motions in an oscillating heat pipe, i.e., when the input power or the temperature difference from the evaporating section to the condensing section was higher than this onset value the oscillating motion started, resulting in an enhancement of the heat transfer in the oscillating heat pipe. Results of the combined theoretical and experimental investigation will assist in optimizing the heat transfer performance and provide a better understanding of heat transfer mechanisms occurring in the oscillating heat pipe.
TL;DR: In this article, the authors studied the performance of a horizontal micro-grooved heat pipe using CuO nanofluid as the working fluid and found that the average diameter of CuO nanoparticles varied from 0.5 wt% to 2.0 wt%.
Abstract: An experiment was carried out to study the heat transfer performance of a horizontal micro-grooved heat pipe using CuO nanofluid as the working fluid. CuO nanofluid was a uniform suspension of CuO nanoparticles and deionized water. The average diameter of CuO nanoparticles was 50 nm. Mass concentration of CuO nanoparticles varied from 0.5 wt% to 2.0 wt%. The experiment was performed at three steady operating pressures of 7.45 kPa, 12.38 kPa and 19.97 kPa, respectively. Effects of the mass concentration of CuO nanoparticles and the operating pressure on both the heat transfer coefficients of the evaporator and the condenser sections, the critical heat flux (CHF) and the total heat resistance of the heat pipe were discussed. Experimental results show that CuO nanofluid can improve the thermal performance of the heat pipe and there is an optimal mass concentration which is estimated to be 1.0 wt% to achieve the maximum heat transfer enhancement. Operating pressure has apparent influences on both the heat transfer coefficients and the CHF of nanofluids. The minimum pressure corresponds to the maximum heat transfer enhancement. Under an operating pressure of 7.45 kPa, the heat transfer coefficients of the evaporator can be averagely enhanced by 46% and the CHF can be maximally enhanced by 30% when substituting CuO nanofluids for water.
TL;DR: In this paper, the authors investigated the thermal performance of the heat pipe cooling system with the thermal resistance model and found that the evaporation resistance and the condensation resistance both grow with increasing heating power and decreasing fill ratio.
TL;DR: In this paper, a test is performed in order to determine a borehole's characteristics in layers consisting of clay, silt and sand at various analogies, and the ground thermal conductivity (λ ) was found to be 1.605 W/(m K) and the effective borehole thermal resistance (R b ) to be 0.257 K/(W/m).
TL;DR: In this article, a detailed three-dimensional model has been developed to analyze the thermal hydrodynamic behaviors of flat heat pipes without empirical correlations, and the results show that vertical wick columns in the vapor core can improve the thermal and hydrodynamic performance of the heat pipes, including thermal resistance, capillary limit, wall temperature, pressure drop, and fluid velocities due to the enhancement of the fluid/heat mechanism form the bottom condenser to the top evaporator.
TL;DR: In this article, the authors present static and dynamic energy conversion technologies for use in space reactor power systems and provide estimates of the system's net efficiency and specific power, and the specific area of the radiator.
TL;DR: Cooling technologies that address high-density and asymmetric heat dissipation in CPU packages of high-performance servers are discussed and the development of a new metallic thermal interface technology is introduced.
Abstract: Cooling technologies that address high-density and asymmetric heat dissipation in CPU packages of high-performance servers are discussed. Thermal management schemes and the development of associated technologies are reviewed from a viewpoint of industrial application. Particular attention is directed to heat conduction in the package and heat removal from the package/heat sink module. Power dissipation and package cooling characteristics of high-performance microprocessors are analyzed. The development of a new metallic thermal interface technology is introduced, where thermal and mechanical performance of an indium-silver alloy in the chip/heat spreader assembly was studied. The paper also reports on research on other thermal management materials, such as diamond composite heat-spreading materials. Some actual package designs are described to illustrate the enhanced heat spreading capability of heat pipes and vapor chambers.
TL;DR: In this article, a numerical study of flow and heat transfer characteristics is made in a double pipe heat exchanger with porous structures inserted in the annular gap in two configurations: on the inner cylinder (A) and on both the cylinders in a staggered fashion (B).
TL;DR: In this paper, a multifunctional heat pipe sandwich panel combining efficient structural load support and thermal management characteristics has been designed and experimentally assessed, which is based upon a truncated, square honeycomb sandwich structure.
TL;DR: In this paper, binary mixtures with a non-linear dependence of the surface tension with temperature were investigated as potential working fluids for wicked heat pipes to take advantage of Marangoni effect.
TL;DR: In this article, a detailed mathematical model predicting fluid flow and heat transfer through the thin film region is developed, considering the effects of inertial force, disjoining pressure, surface tension, and curvature.
Abstract: The evaporating thin film region is an extended meniscus beyond the apparent contact line at a liquid/solid interface. Thin film evaporation plays a key role in a highly efficient heat pipe. A detailed mathematical model predicting fluid flow and heat transfer through the thin film region is developed. The model considers the effects of inertial force, disjoining pressure, surface tension, and curvature. Utilizing the order analysis, the model is simplified and can be numerically solved for the thin film profile, interfacial temperature, meniscus radius, heat flux distribution, velocity distribution, and mass flow rate in the evaporating thin film region. The prediction shows that while the inertial force can affect the thin film profile, interfacial temperature, meniscus radius, heat flux distribution, velocity distribution, and mass flow rate, in particular, near the non-evaporating region, the effect can be neglected. It is found that a maximum velocity, a maximum heat flux, and a maximum curvature exist for a given superheat, but the locations for these maximum values are different.
TL;DR: In this paper, a thin planar bifacial evaporator with a Bifacial wick structure was devised, and the operating characteristics in a horizontal position for different fluid inventories were examined in detail.
TL;DR: In this article, the authors investigated the use of heat pipe vacuum tube (HPVT) collectors in a solar desiccant cooling set up and the experimentally evaluated efficiency of the HPVT collectors for one operating day varies between 0.6 and 0.7.
TL;DR: In this article, a numerical model is developed to simulate the transient performance characteristics of loop heat pipes (LHP), which satisfactorily simulates the overall dynamic behavior of an LHP unit tested under ambient and vacuum environments.
TL;DR: In this paper, a liquid and vapour flow model coupled with a thermal model is presented for a flat plate heat pipe with micro-grooves, which allows the calculation of the liquid and vapor pressures and velocities, the meniscus curvature radius in the grooves and the temperature field in the heat pipe wall from the heat source to the heat sink.
TL;DR: Capillary heat loops (CHL) are heat transfer designs with higheffectiveness, highperformance, highreliability, highflexibility, and anti-gravitation features of interest to the space community as discussed by the authors.