Numerical Study on the Performance Characteristics of Cylindrical Heat Pipes With Differing Wick Type

2018 ◽  
Author(s):  
Mahboobe Mahdavi ◽  
Saeed Tiari ◽  
Ajaysinh Solanki ◽  
Vivek Pawar
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Operating Temperature ◽  
Numerical Study ◽  
Operating Conditions ◽  
Liquid Sodium ◽  
Working Fluid ◽  
Liquid Pressure ◽  
Pressure Drops ◽  
Sintered Powder

In the current study, the performance of a high temperature, cylindrical heat pipe under various operating conditions is investigated numerically. To find the appropriate geometrical and working parameters of the heat pipe, a two-dimensional axisymmetric model is developed to describe the vapor and liquid flows and heat transfers in the vapor core, the wick, and the wall regions. Sodium and stainless steel are selected as the working fluid, the wick material, and the container material. The compressibility of the vapor and viscous dissipation are taken into account. In the wick region, the Darcy–Brinkman–Forchheimer model is applied to simulate the liquid sodium characteristics. The effect of wick type, heat input, and operating temperature are studied on the overall performance of the heat pipe as well as vapor and liquid pressure drops. Screen wick, sintered powder wick and felt wick are selected. The results showed that, for the selected wick types, the sintered powder wick resulted in the largest liquid pressure drop and the felt wick resulted in the lowest thermal resistance. In addition, the influence of operating temperature on thermal resistance diminishes with increasing temperature.

scholarly journals Integration of a Pulsating Heat Pipe in a Flat Plate Heat Sink

2014 ◽  
Author(s):  
Mitchell P. Hoesing ◽  
Gregory J. Michna
Keyword(s):  
Thermal Resistance ◽  
Flat Plate ◽  
Heat Pipe ◽  
Heat Sink ◽  
New Technologies ◽  
Operating Conditions ◽  
Working Fluid ◽  
High Heat Flux ◽  
Pulsating Heat Pipe ◽  
Plate Heat

The ongoing development of faster and smaller electronic components has led to a need for new technologies to effectively dissipate waste thermal energy. The pulsating heat pipe (PHP) shows potential to meet this need, due to its high heat flux capacity, simplicity, and low cost. A 20-turn flat plate PHP was integrated into an aluminum flat plate heat sink with a simulated electronic load. The PHP heat sink used water as the working fluid and had 20 parallel channels with dimensions 2 mm × 2 mm × 119 mm. Experiments were run under various operating conditions, and thermal resistance of the PHP was calculated. The performance enhancement provided by the PHP was assessed by comparing the thermal resistance of the heat sink with no working fluid to that of it charged with water. Uncharged, the PHP was found to have a resistance of 1.97 K/W. Charged to a fill ratio of approximately 75% and oriented vertically, the PHP achieved a resistance of .49 K/W and .53 K/W when the condenser temperature was set to 20°C and 30°C, respectively. When the PHP was tilted to 45° above horizontal the PHP had a resistance of .76 K/W and .59 K/W when the condenser was set 20°C and 30°C, respectively. The PHP greatly improves the heat transfer properties of the heat sink compared to the aluminum plate alone. Additional considerations regarding flat plate PHP design are also presented.

scholarly journals Problems of sodium using in pulsating heat pipe made from fused silica

2018 ◽  
Vol 207 ◽  
pp. 04004
Author(s):  
Radovan Nosek ◽  
Tatiana Liptáková ◽  
Libor Trško ◽  
Zuzana Kolková ◽  
Milan Malcho ◽  
...  
Keyword(s):  
High Temperature ◽  
Heat Pipe ◽  
Alkali Metals ◽  
High Efficiency ◽  
Fused Silica ◽  
Operating Conditions ◽  
Liquid Sodium ◽  
Working Fluid ◽  
Pulsating Heat Pipe ◽  
High Temperature Reaction

You Heat pipe is a high efficiency heat transfer element, depends on the evaporation, condensation and circulation of inside working fluid. The working fluid of a high temperature pulsating heat pipe is generally alkali metals, and sodium heat pipe can operate in range of 500-1100°C. In order to investigate terminal velocity of working fluid, the glass pulsating heat pipe was produced for experimental purposes. The experiment was carried out, in order to simulate real operating conditions in range of 500-1100°C. Sudden boiling of liquid sodium (b.p. = 883°C at 1 atm) inside the all quartz-made heat pipe results in high-temperature reaction of sodium vapour with the inner wall surface. The reaction became more aggressive with increasing vapour temperature and resulted in heat pipe explosion. The evaluation of damage character is analysed in this paper.

scholarly journals Numerical Investigation on the Dielectric Working Fluid Effect on the Flow and Thermal Parameters of an Electrohydrodynamic Flat Heat Pipe

2020 ◽  
Vol 79 (1) ◽  
pp. 128-152
Author(s):  
Imène Saad ◽  
Samah Maalej ◽  
Mohamed Chaker Zaghdoudi
Keyword(s):  
Pressure Drop ◽  
Vapor Pressure ◽  
Electric Field ◽  
Heat Pipe ◽  
Liquid Velocity ◽  
Thermal Parameters ◽  
Working Fluid ◽  
Liquid Pressure ◽  
Pressure Drops ◽  
Capillary Limit

The present work highlights the impact of the working dielectric fluid on the flow and the thermal parameters of an axially grooved flat mini heat pipe (FMHP) submitted to Electrohydrodynamic (EHD) effects. Three dielectric working fluids are considered: pentane, R123, and R141b. A model is developed by considering the Laplace-Young, mass, momentum, and energy balance equations. The numerical results show that the electric field affects the liquid distribution along the heat pipe and helps the condensate to flow back to the evaporator section. Moreover, under the electric field conditions, the vapor pressure drop increases, however, the liquid pressure drop decreases. The effect of the electric field on the liquid velocity depends on the FMHP zone, and the vapor velocity is hardly affected by the EHD effects. Furthermore, lower capillary driving pressures are required to provide the necessary capillary pumping under EHD conditions. Besides, pentane allows for higher vapor pressure drops compared to those obtained with R123 and R141b, while the liquid pressure drops are highest for R123. It is found that with R123, the liquid velocity is higher than that reached with R141b and pentane. It is also demonstrated that the capillary limit increases under EHD conditions, and for R141b, the capillary limit is the highest either in zero-field and EHD conditions. Best heat pipe thermal performances are observed for wide and deep grooves with R141b. Finally, the optimum fill charge allowing the maximum heat transfer capacity is determined for each working fluid and different groove dimensions. It is shown that the optimum fill charge is hardly affected by the electric field whatever the working fluid. R123 requires the highest optimum fill charge, however, the heat transport capacity of the FMHP is the lowest when using this working fluid.

Experimental Performance of a Nanofluid Pulsating Heat Pipe

2008 ◽  
Author(s):  
Wei Qu ◽  
Chong Qu ◽  
Jianchao Feng
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Operating Temperature ◽  
Nano Particles ◽  
Working Fluid ◽  
Pulsating Heat Pipe ◽  
Operation Temperature ◽  
Heating Section ◽  
Inclination Angles

The startup and operating performances of a nanofluid pulsating heat pipe are experimented. When the working fluid is selected as nanofluid instead of the base working fluid, the pulsating heat pipe can work at lower heating loads and start up more quickly and the thermal resistance between the heating section and the cooling section significantly decreases. For the nanofluid and base working fluid, the operating temperature increases with the heating load, the thermal resistance of pulsating heat pipe decreases with the operating temperature. The inclination angles of pulsating heat pipe as 30°, 60°, or 90°, have little effects on heat transfer performance. Under a vertical bottom heating mode of 100 watts and at the operation temperature of 110 °C, the thermal resistance of TiO2/H2O nanofluid pulsating heat pipe can be 0.11 °C/W, while it is 0.23 °C/W for the base working fluid. The mechanisms that the nanofluid pulsating heat pipe has better performance are tentatively explained as, the nano particles can form many micro nuclear centers for the boiling, and can lead to several heat transfer enhancement.

Effect of Concentration and Loading Fluid of Nanofluids on the Thermal Resistance of Sintered Powder Wick Heat Pipe

2013 ◽  
Vol 651 ◽  
pp. 728-735 ◽  
Author(s):  
Nandy Putra ◽  
Wayan Nata Septiadi ◽  
Ridho Irwansyah
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Fluid Transport ◽  
Heat Pipes ◽  
Alternative Methods ◽  
Working Fluid ◽  
Cooling Systems ◽  
Sintered Copper ◽  
Sintered Powder ◽  
Flow Features

Heat pipes have been widely used as one of the alternative methods to absorb more heat in the cooling systems of electronic devices. One of the ways to improve the thermal performance of heat pipes is to change the fluid transport properties and flow features of working fluids using nanofluids. The purpose of this research was to investigate the effect of Al2O3-water nanofluids concentration and fluid loading to the thermal resistance between evaporator and adiabatic section of copper straight sintered copper powder wick heat pipe. In this research, sintered powder wick heat pipes were manufactured and tested to determine the thermal resistance of the sintered powder wick heat pipes which charged with water and Al2O3-water nanofluids. The concentrations of the nanoparticles were varied from 1 %, 3% and 5 % of the volume of the base fluid. The result shows that Al2O3-water nanofluids have the ability to reduce the temperature at the evaporator section and the thermal resistance of heat pipe. The increase in nanofluids concentration could give significant effect to reduce the thermal resistance of heat pipes. The amount of working fluid charged into the heat pipes also gives an effect in heat pipes thermal resistance, where the thermal resistance was lower when the heat pipe was charged with 60% of its volume. The formation of coating layer at sintered powder wick also can fixed the wick porosity and cause roughness on the surface of granular pore which the increased of capillary could give the effect for enhancement of heat pipe performance.

scholarly journals Numerical Study on the Effects of using Nanofluids in Pulsating Heat Pipe

2018 ◽  
Vol 7 (4.35) ◽  
pp. 204
Author(s):  
M. Zufar ◽  
P. Gunnasegaran ◽  
Ng K. Ching
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Thermal Performance ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Pulsating Heat Pipe ◽  
Working Fluids ◽  
Resistance Value

Pulsating Heat Pipe (PHP) is the next generation heat pipe that has a prospect in improving the heat transfer performance. The type of working fluid use in the PHP has a direct influence on the thermal performance. Incorporating nanofluid in PHP may greatly increase its thermal performance as compared to using base fluid (water). The current work focuses on the simulations of 2-dimensional flows in PHP using working fluids such as diamond, silver (Ag), silica oxide (SiO2) nanofluids and water. Constant heat flux and filling ratio of 50% were used throughout the study. From the results, it was found out that diamond nanofluid has the lowest thermal resistance value as compared to other working fluids. The effect of the number of PHP turns was studied and it was discovered that higher number of turns would produce lower thermal resistance value.

Experimental Investigation of a Flat-Plate Oscillating Heat Pipe With Groove-Enhanced Minichannels

2020 ◽  
Vol 12 (6) ◽  
Author(s):  
Matthew J. Rhodes ◽  
Scott M. Thompson
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Heat Pipe ◽  
Operating Temperature ◽  
Operating Conditions ◽  
Working Fluid ◽  
Oscillating Heat Pipe ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Wide Range

Abstract The thermal and capillary performance of a groove-enhanced, or “microchannel-embedded,” flat-plate oscillating heat pipe (MC FP-OHP) was experimentally investigated while varying heating width, orientation, working fluid and operating temperature. The copper MC FP-OHP possessed two layers of 1.02 × 1.02 mm2 square channels, with the center 14 channels possessing two embedded microchannels (0.25 × 0.13 mm2) aligned coaxially with the primary minichannels. A FP-OHP without embedded microchannels, but with deeper minichannels (DC FP-OHP), was also tested for comparison. The FP-OHPs were filled with Novec 7200 or water (both at 80% ± 2% by volume), and the heating widths were varied between full-width and localized configurations: 38.71 cm2 and 14.52 cm2, respectively. Experimental results demonstrate that the MC FP-OHP is significantly less sensitive to operating orientation and can perform with less detriment as heat flux increases. The MC FP-OHP has a lower startup heating requirement and provides more fluid wetting along the FP-OHP structure—which is advantageous for pumping liquid from the evaporator to the condenser. The MC FP-OHP has enhanced convective heat transfer during operation, as it was observed to have similar or lower thermal resistances to that of the DC FP-OHP for a wide range of operating conditions. The groove-enhanced minichannel within the MC FP-OHP also provides for enhanced heat transfer because there being more thin-film evaporation sites and vapor–liquid mixing between the minichannel and microchannels.

USAGE OF A DIATOMITE-CONTAINING NANOFLUID AS THE WORKING FLUID IN A WICKLESS LOOP HEAT PIPE: EXPERIMENTAL AND NUMERICAL STUDY

2018 ◽  
Vol 49 (17) ◽  
pp. 1721-1744 ◽  
Author(s):  
Adnan Sözen ◽  
Erdem Çiftçi ◽  
Selçuk Keçel ◽  
Metin Gürü ◽  
Halil Ibrahim Variyenli ◽  
...  
Keyword(s):  
Heat Pipe ◽  
Numerical Study ◽  
Working Fluid ◽  
Loop Heat Pipe

Experimental and Numerical Simulation for Thermal Investigation of Oscillating Heat Pipe Using VOF Model

2020 ◽  
Vol 38 (1A) ◽  
pp. 88-104
Author(s):  
Anwar S. Barrak ◽  
Ahmed A. M. Saleh ◽  
Zainab H. Naji
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Heat Input ◽  
Cfd Simulation ◽  
Working Fluid ◽  
Maximum Deviation ◽  
Inlet Temperature ◽  
Maximum Heat ◽  
Oscillating Heat Pipe ◽  
Vof Model

This study is investigated the thermal performance of seven turns of the oscillating heat pipe (OHP) by an experimental investigation and CFD simulation. The OHP is designed and made from a copper tube with an inner diameter 3.5 mm and thickness 0.6 mm and the condenser, evaporator, and adiabatic lengths are 300, 300, and 210 mm respectively.  Water is used as a working fluid with a filling ratio of 50% of the total volume. The evaporator part is heated by hot air (35, 40, 45, and 50) oC with various face velocity (0.5, 1, and 1.5) m/s. The condenser section is cold by air at temperature 15 oC. The CFD simulation is done by using the volume of fluid (VOF) method to model two-phase flow by conjugating a user-defined function code (UDF) to the FLUENT code. Results showed that the maximum heat input is 107.75 W while the minimum heat is 13.75 W at air inlet temperature 35 oC with air velocity 0.5m/s. The thermal resistance decreased with increasing of heat input. The results were recorded minimum thermal resistance 0.2312 oC/W at 107.75 W and maximum thermal resistance 1.036 oC/W at 13.75W. In addition, the effective thermal conductivity increased due to increasing heat input.  The numerical results showed a good agreement with experimental results with a maximum deviation of 15%.

Remote Heat Pipe Based Heat Exchanger Performance in Notebook Cooling

2005 ◽  
Author(s):  
Seyyed Khandani ◽  
Himanshu Pokharna ◽  
Sridhar Machiroutu ◽  
Eric DiStefano
Keyword(s):  
Heat Exchanger ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Cooling System ◽  
Temperature Drop ◽  
Operating Conditions ◽  
Cooling Systems ◽  
Temperature Variations ◽  
Non Linear ◽  
Condenser Temperature

Remote heat pipe based heat exchanger cooling systems are becoming increasingly popular in cooling of notebook computers. In such cooling systems, one or more heat pipes transfer the heat from the more populated area to a location with sufficient space allowing the use of a heat exchanger for removal of the heat from the system. In analsysis of such systems, the temperature drop in the condenser section of the heat pipe is assumed negligible due to the nature of the condensation process. However, in testing of various systems, non linear longitudinal temperature drops in the heat pipe in the range of 2 to 15 °C, for different processor power and heat exchanger airflow, have been measured. Such temperature drops could cause higher condenser thermal resistance and result in lower overall heat exchanger performance. In fact the application of the conventional method of estimating the thermal performance, which does not consider such a nonlinear temperature variations, results in inaccurate design of the cooling system and requires unnecessarily higher safety factors to compensate for this inaccuracy. To address the problem, this paper offers a new analytical approach for modeling the heat pipe based heat exchanger performance under various operating conditions. The method can be used with any arbitrary condenser temperature variations. The results of the model show significant increase in heat exchanger thermal resistance when considering a non linear condenser temperature drop. The experimental data also verifies the result of the model with sufficient accuracy and therefore validates the application of this model in estimating the performance of these systems.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

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