Thermal Characteristics of Conventional and Flat Miniature Axially Grooved Heat Pipes

1995 ◽  
Vol 117 (4) ◽  
pp. 1048-1054 ◽  
Author(s):  
D. Khrustalev ◽  
A. Faghri
Keyword(s):  
Thermal Characteristics ◽  
Heat Pipes ◽  
Heat Fluxes ◽  
Vertical Position ◽  
Maximum Heat ◽  
Evaporation And Condensation ◽  
Maximum Heat Transfer ◽  
Mass Transfer Processes ◽  
Grooved Surface ◽  
Heat Transfer Capacity

A detailed mathematical model of low-temperature axially grooved heat pipes (AGHP) is developed in which the fluid circulation is considered along with the heat and mass transfer processes during evaporation and condensation. The results obtained are compared to existing experimental data. Both capillary and boiling limitations are found to be important for the flat miniature copper-water heat pipe, which is capable of withstanding heat fluxes on the order of 40 W/cm2 applied to the evaporator wall in the vertical position. The influence of the geometry of the grooved surface on the maximum heat transfer capacity of the miniature AGHP is demonstrated.

Thermal Analysis of a Micro Heat Pipe

1994 ◽  
Vol 116 (1) ◽  
pp. 189-198 ◽  
Author(s):  
D. Khrustalev ◽  
A. Faghri
Keyword(s):  
Heat Pipe ◽  
Thermal Characteristics ◽  
Shear Stresses ◽  
Maximum Heat ◽  
Micro Heat Pipe ◽  
Wetting Contact Angle ◽  
Maximum Heat Transfer ◽  
Mass Transfer Processes ◽  
Heat Transfer Capacity ◽  
Liquid Vapor

A detailed mathematical model is developed in which the heat and mass transfer processes in a micro heat pipe (MHP) are examined. The model describes the distribution of the liquid in a MHP and its thermal characteristics depending upon the liquid charge and the applied heat load. The liquid flow in the triangular-shaped corners of a MHP with polygonal cross section is considered by accounting for the variation of the curvature of the free liquid surface and the interfacial shear stresses due to a liquid-vapor frictional interaction. The predicted results obtained are compared to existing experimental data. The importance of the liquid fill, minimum wetting contact angle, and the shear stresses at the liquid-vapor interface in predicting the maximum heat transfer capacity and thermal resistance of the MHP is demonstrated.

Numerical and Experimental Investigation of Heat Transfer Enhancement Using Heat Pipes for Electronic Cooling

2018 ◽  
Author(s):  
Ning Zhang ◽  
Pankaj R. Chandra ◽  
Ryan Robledo ◽  
Sree Harsha Balijepalli
Keyword(s):  
Heat Transfer ◽  
Heat Pipes ◽  
Copper Plate ◽  
Heat Sinks ◽  
Modern World ◽  
Processing Unit ◽  
Maximum Heat ◽  
Central Processing ◽  
Load Combination ◽  
Maximum Heat Transfer

Computers are crucial to nearly every endeavor in the modern world. Some computers, particularly those used in military applications, are required to endure extreme conditions with limited maintenance and few parts. Units such as these will hereafter be referred to as “rugged computers.” This series of experiments aims to produce improvements to rugged computers currently in service. Using heat pipes and finned heat sinks on an enclosed box, a computer’s Central Processing Unit (CPU) is able to reject heat without suffering contamination from unforgiving environments. A modular prototype was designed to allow for three distinct cases; a case with no heat pipes and fins, a cast with heat-pipes mounted internally with exterior fins and a case with heat-pipes extended externally with exterior fins. Each case was tested at three different heat loads, with a copper plate heated by a silicone heat strip simulating the heat load generated by a CPU. Each case/load combination was run many times to check for repeatability. The aim of this research is to discover the ideal case for maximum heat transfer from the CPU to the external environment. In addition to the experiments, numerical simulation of these modular prototypes with different designs of heat pipes were conducted in this research. Creating an accurate model for computer simulations will provide validation for the experiments and will prove useful in testing cases not represented by the modular prototype. The flow and heat transfer simulations were conducted using Autodesk CFD. The aim here is to create a model that accurately reflects the experimentally-verified results from the modular prototype’s cases and loads, thereby providing a base from whence further designs can branch off and be simulated with a fair degree of accuracy.

Optimization of Wettability Gradient for Enhancement of Thermal Performance of Micro Heat Pipes

2018 ◽  
Author(s):  
Manjinder Singh ◽  
Naresh Varma Datla ◽  
Supreet Singh Bahga ◽  
Sasidhar Kondaraju
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Variable Mass ◽  
Working Fluid ◽  
Maximum Heat ◽  
Continuous Increase ◽  
Maximum Heat Transfer ◽  
Integration Density ◽  
Heat Transfer Capacity ◽  
Micro Heat Pipes

Continuous increase in the integration density of microelectronic units necessitates the use of MHPs with enhanced thermal performance. Recently, the use of wettability gradients have been shown to enhance the heat transfer capacity of MHPs. In this paper, we present an optimization of axial wettability gradient to maximize the heat transfer capacity of the MHP. We use an experimentally validated mathematical model and interior point method to optimize the wettability gradient. For our analysis, we consider two cases wherein (i) the mass of working fluid is constrained, (ii) mass of working fluid is a design variable. Compared to MHP with uniform high wettability and filled with a fixed mass of working fluid, optimization of the wettability gradient leads to 65% enhancement in heat transfer capacity. Similar comparisons for MHP filled with variable mass of working fluid shows more than 90% increase in the maximum heat transfer capacity due to optimization of wettability gradient.

scholarly journals Влияние наножидкостей на теплопередающую способность миниатюрных термосифонов для охлаждения электроники

2019 ◽  
Vol 45 (6) ◽  
pp. 54
Author(s):  
Б.И. Бондаренко ◽  
В.Н. Морару ◽  
В.Ю. Кравец ◽  
Г. Бехмард
Keyword(s):  
Thermal Resistance ◽  
Closed Loop ◽  
Electronics Cooling ◽  
Sharp Decrease ◽  
Vapor Film ◽  
Two Phase ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Boiling Process ◽  
Heat Transfer Capacity

AbstractStable nanofluids based on DG-100 grade carbon black and carbon nanotubes have been prepared, and their influence on the maximum heat-transfer capacity and thermal resistance of closed-loop two-phase thermosyphons (TPTs) intended for electronics cooling have been studied. A more than twofold increase in the critical heat flux of these TPTs as compared to those filled with water has been obtained along with a sharp decrease in their thermal resistance. It is suggested that this effect is not only due to the high thermal conductivity of the proposed nanofluids, but is also related to the formation of a specific porous structure hindering the appearance of a vapor film and enhancing the boiling process.

scholarly journals Enhancing Heat Transfer in Tube Heat Exchanger by Inserting Discrete Twisting Tapes with Different Positions

2019 ◽  
Vol 25 (8) ◽  
pp. 39-51
Author(s):  
Nassr Fadhil Hussein ◽  
Abdulrahman Shakir Mahmood
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Constant Heat Flux ◽  
Vertical Position ◽  
Maximum Heat ◽  
Tube Heat Exchanger ◽  
Twisted Tapes ◽  
Maximum Heat Transfer

Enhancement of heat transfer in the tube heat exchanger is studied experimentally by using discrete twisted tapes. Three different positions were selected for inserting turbulators along tube section (horizontal position by α= 00, inclined position by α= 45 0 and vertical position by α= 900). The space between turbulators was fixed by distributing 5 pieces of these turbulators with pitch ratio    PR = (0.44). Also, the factor of constant heat flux was applied as a boundary condition around the tube test section for all experiments of this investigation, while the flow rates were selected as a variable factor (Reynolds number values vary from 5000 to 15000). The results show that using discrete twisted tapes enhances the heat transfer rate by about 60.7-103.7 % compared with plane tube case. Also, inserting turbulators with inclined position offers maximum heat transfer rate by 103.7%.  

Effect of Gap Distance on Confined Boiling Heat Transfer Over a Saturated Porous Structure

2005 ◽  
Author(s):  
M. J. Schertzer ◽  
M. Khammar ◽  
D. Ewing ◽  
C. Y. Ching ◽  
J. S. Chang
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
High Speed ◽  
Imaging System ◽  
Porous Plate ◽  
Heat Removal ◽  
Heat Fluxes ◽  
Maximum Heat ◽  
Porous Wick ◽  
Maximum Heat Transfer

An experimental investigation was performed to study the effect that the introduction of a gap between a heated fin and a porous media would have on the heat removal characteristics of a capillary evaporator. In these experiments, a thin stainless steel resistive foil stretched between two copper electrodes was used to heat a saturated porous plate with an effective pore size of 50 microns. The temperature distribution on a 10 mm wide simulated fin was measured by a high-speed infra-red thermal imaging system. The heat removal performance was investigated for gap distances of 0.00 to 1.00 mm and for heat fluxes of 17 to 180 kW/m2. These results showed that the maximum heat transfer rate that could be achieved before persistent hot spots were observed on the surface increased with gap distance. Local temperature measurements made using thermocouples embedded in the porous media indicate that vapour penetration into the porous wick is intermittent, and that there is no stable single phase blanket of vapour. For a gap distance of 0.00 mm, this penetration is more uniformly distributed across the width of the heated fin than at a gap distance of 0.50 mm. In the latter case, the vapour distribution is much higher near the edge of the heated fin.

Guidelines for Designing Micropillar Structures for Enhanced Evaporative Heat Transfer

2021 ◽  
Author(s):  
Kidus Guye ◽  
De Dong ◽  
Yunseo Kim ◽  
Hyoungsoon Lee ◽  
Baris Dogruoz ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Interfacial Area ◽  
High Heat ◽  
Heat Fluxes ◽  
Air Cooling ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Evaporation Heat

Abstract Over the last several decades, cooling technologies have been developed to address the growing thermal challenges associated with high-powered electronics. However, within the next several years, the heat generated by these devices is predicted to exceed 1 kW/cm2, and traditional methods, such as air cooling, are limited in their capacities to dissipate such high heat fluxes. In contrast, two-phase cooling methods, such as microdroplet evaporation, are very promising due to the large latent heat of vaporization associated with the phase change process. Previous studies have shown non-axisymmetric droplets exhibit different evaporation characteristics than spherical droplets. For a droplet pinned atop a micropillar, the solid-liquid and liquid-vapor interfacial area, the volume, and thickness of the droplet are the major factors that govern the evaporation heat transport process. In this work, we develop a shape optimization tool using the particle swarm optimization algorithm to maximize evaporation from a droplet confined atop a micropillar. The tool is used to optimize the shape of a nonaxisymmetric droplet. Compared to droplets atop circular and regular equilateral triangular micropillar structures, we find that droplets confined on pseudo-triangular micropillar structures have 23.7% and 5.7% higher heat transfer coefficients, respectively. The results of this work will advance the design of microstructures that support droplets with maximum heat transfer performance.

Experimental investigation of a loop heat pipe with R245fa and R1234ze (E) as working fluids

2021 ◽  
pp. 1-17
Author(s):  
Guangming Xu ◽  
Rongjian Xie ◽  
Nanxi Li ◽  
Cheng Liu
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Characteristic Temperature ◽  
Thermal Characteristics ◽  
Heat Pipes ◽  
Loop Heat Pipe ◽  
Working Fluids ◽  
Loop Heat Pipes ◽  
Heat Transfer Capacity ◽  
Heat Loads

Abstract Two kinds of new refrigerant-R1234ze (E) and R245fa were discussed as substitutes or supplements to traditional working fluids of loop heat pipes based on their favorable thermophysical properties and characteristics such as being safe and environmentally friendly. Thermal characteristics of a loop heat pipe with sintering copper wick at different charging ratios were experimentally investigated under variable heat loads. The results showed that the optimal charging ratio in the loop heat pipe range from 65% to 70%, and at this charging level, the R1234ze(E) system had better start-up response, while the R245fa system presented a stronger heat transfer capacity. The characteristic temperature of R1234ze(E) system was below 35 °C, and the corresponding thermal resistance was 0.08 K/W ~ 1.62 K/W under heat loads ranging from 5 W to 40 W. The thermal resistance of the R245fa system was 0.18 K/W ~ 0.91 K/W under heat loads of 10 W ~ 60 W, and the operating temperature was below 60 °C. The loop heat pipes charged with the proposed new refrigerants exhibit superb performance in room temperature applications, making them beneficial for enhancing the performance of electronics, and could provide a distinctive choice for the cooling of small-sized electronics especially.

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