Improve the Performance of Micro Heat Pipe by Surface Modification

2017 ◽  
Vol 868 ◽  
pp. 21-26
Author(s):  
Yi Luo ◽  
Si Di Li ◽  
Zi Cheng Yu ◽  
Xiao Dong Wang
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
High Power ◽  
High Heat ◽  
Cover Plate ◽  
Working Fluid ◽  
High Heat Flux ◽  
Glass Cover ◽  
Micro Heat Pipe ◽  
High Power Led

The appearance of high power LED has put forward higher requirements for thermal management. The micro heat pipe (MHP) has high heat transfer ability and plays an important role in high power LED and other high heat flux device cooling. In this paper, we designed and fabricated a micro heat pipe with fluoroalkyl silane (FAS) surface modified glass cover. The contact angle of the working area of glass cover reached 95.49° and made working fluid drops fall back to micro groove of silicon substrate more quickly. Thus the new glass cover can speed up the circulation of working fluid and enhance the heat transfer. The experimental results also proved that hydrophobic glass cover has a better heat transfer capability. Besides, this novel MHP reached the stable working status faster. When the input heat power was 10 W, the balance temperature of MHP with hydrophobic glass cover was 22 oC lower than traditional MHP, while the balance time is 58 seconds less. The work presented in this paper provides a new direction for optimize the MHP, not only the wick structure in substrate, but also the wettability of cover plate.

Working Fluid Inventory Effect on Heat Transfer Performance of a Grooved Micro Heat Pipe

2013 ◽  
Vol 589-590 ◽  
pp. 559-564
Author(s):  
Xi Bing Li ◽  
Yun Shi Ma ◽  
Xun Wang ◽  
Ming Li
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Pipe ◽  
Heat Transfer Performance ◽  
Mathematic Model ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Transfer Performance ◽  
Flux Concentration

As a highly efficient heat transfer component, a micro heat pipe (MHP) has been widely applied to the situations with high heat flux concentration. However, a MHPs heat transfer performance is affected by many factors, among which, working fluid inventory has great influence on the security, reliability and frost resistance of its heat transfer performance. In order to determine the appropriate working fluid inventory for grooved MHPs, this paper first analyzed the working principle, major heat transfer limits and heat flux distribution law of grooved MHPs in electronic chips with high heat flux concentration, then established a mathematic model for the working fluid inventory in grooved MHPs. Finally, with distilled water being the working fluid, a series of experimental investigations were conducted at different temperatures to test the heat transfer performances of grooved MHPs, which were perfused with different inventories and with different adiabatic section lengths. The experimental results show that when the value of α is roughly within 0.40±0.05, a grooved MHP can acquire its best heat transfer performance, and the working fluid inventory can be determined by the proposed mathematic model. Therefore this study solves the complicated problem of determining appropriate working fluid inventory for grooved MHPs.

A Mathematical Modeling Method for Capillary Limit of Micro Heat Pipe with Sintered Wick

2011 ◽  
Vol 175 ◽  
pp. 335-341
Author(s):  
Xi Bing Li ◽  
Chang Long Yang ◽  
Gong Di Xu ◽  
Wen Yuan ◽  
Shi Gang Wang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Pipe ◽  
Heat Dissipation ◽  
High Heat ◽  
Experimental Investigations ◽  
High Heat Flux ◽  
Micro Heat Pipe ◽  
Copper Powders ◽  
Capillary Limit

With heat flux increasing and cooling space decreasing in microelectronic and chemical products, micro heat pipe has become an ideal heat dissipation device in high heat-flux products. Through the analysis of its working principle, the factors that affect its heat transfer limits and the patterns in which copper powders are arrayed in circular cavity, this paper first established a mathematical model for the crucial factors in affecting heat transfer limits in a circular micro heat pipe with a sintered wick, i.e. a theoretical model for capillary limit, and then verified its validity through experimental investigations. The study lays a powerful theoretical foundation for designing and manufacturing circular micro heat pipes with sintered wicks.

Circulation Effectiveness of Working Fluid in Inclined Micro Heat Pipes

2015 ◽  
Vol 789-790 ◽  
pp. 422-425
Author(s):  
Fun Liang Chang ◽  
Yew Mun Hung
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Thermal Performance ◽  
Heat Pipes ◽  
Operating Conditions ◽  
Circulation Rate ◽  
Working Fluid ◽  
High Heat Flux ◽  
Micro Heat Pipe ◽  
Micro Heat Pipes

Micro heat pipe is a two-phase heat transfer device offering effective high heat-flux removal in electronics cooling. Essentially, micro heat pipe relies on the phase change processes, namely evaporation and condensation, and the circulation of working fluid to function as heat transfer equipment. The vast applications of micro heat pipe in portable appliances necessitate its functionality under different orientations with respect to gravity. Therefore, its thermal performance is strongly related to its orientation. By incorporating solid wall conduction, together with the continuity, momentum, and energy equations of the working fluid, a mathematical model is developed to investigate the heat and fluid flow characteristics of inclined micro heat pipes. We investigate both the favorable and adverse effects of gravity on the circulation rate which is intimately related to the thermal performance of micro heat pipes. The effects of gravity, through the angle of inclination, on the circulation strength and heat transport capacity are analysed. This study serves as a useful analytical tool in the micro heat pipe design and performance analysis, associated with different inclinations and operating conditions.

Utilization of Advanced Working Fluids With Biporous Evaporators

2011 ◽  
Vol 3 (2) ◽  
Author(s):  
Sean W. Reilly ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Operating Temperature ◽  
Temperature Drop ◽  
High Heat ◽  
Heat Fluxes ◽  
Working Fluid ◽  
High Heat Flux ◽  
Inorganic Aqueous Solution ◽  
Operating Temperature Range

A novel fluid for use as a working fluid in a heat pipe has been tested at UCLA. The fluid was discovered originally in use with a device consisting of a metal tube charged with the patented inorganic aqueous solution (IAS), which is evaporated when the tube is evacuated before use. According to the patent, this evaporation leaves a thin film that allows the tube to carry high heat flux loads with low temperature drop across the tube in a solid state mode. However, various experiments with these tubes have produced inconsistent results, and there are some questions as to whether the fluid is completely evaporated. The research on which this work is based is focused on testing whether the charging fluid will operate as the working fluid in a heat pipe, in order to determine the nature of the IAS fluid. A heat pipe apparatus was charged with a biporous wick in order to investigate if the fluid plays a role in heat transfer. There are extensive data for this experiment using water as the working fluid, which will be used to compare the two sets of results. Testing has shown a reduction of the superheat required to drive heat fluxes through a wick compared to water by approximately 40%. Some experiments have shown that the operating (temperature) range of the IAS is much larger than a standard heat pipe. It is theorized that the increase in performance of the IAS is due to an increased thermal conductivity of the wick and increased capillarity. If this fluid is proven to be effective, it would lead to more effective and tunable heat transfer devices.

A Mathematical Modeling Method on Micro Heat Pipe with a Trapezium-Grooved Wick Structure

2010 ◽  
Vol 29-32 ◽  
pp. 1686-1694
Author(s):  
Xi Bing Li ◽  
Shi Gang Wang ◽  
Jian Hua Guo ◽  
Dong Sheng Li
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Pipe ◽  
Chemical Engineering ◽  
High Heat ◽  
High Heat Flux ◽  
Micro Heat Pipe ◽  
Flow Limit ◽  
Wick Structure ◽  
Design And Manufacture

With heat flux increasing and cooling space decreasing in the products in microelectronics and chemical engineering, micro heat pipe has become an ideal heat radiator for products with high heat flux. Through analyzing the factors influencing the structure, strength and heat transfer limits of circular micro heat pipe with trapezium-grooved wick structure, the heat transfer models are established in this paper, including the models of viscous limit, sonic limit, entrainment limit, capillary limit, condensing limit, boiling limit, continuous flow limit and frozen startup limit. The study lays a powerful theoretical foundation for the design and manufacture of circular micro heat pipe with a trapezium-grooved wick structure.

Research on Thermal Resistance of Micro Heat Pipe with Sintered Wick

2013 ◽  
Vol 589-590 ◽  
pp. 552-558
Author(s):  
Xi Bing Li ◽  
Xun Wang ◽  
Yun Shi Ma ◽  
Zhong Liang Cao
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Heat Transfer Performance ◽  
High Heat ◽  
Working Fluid ◽  
Transfer Performance ◽  
Total Thermal Resistance ◽  
Vapor Cavity ◽  
Micro Heat Pipe

As a highly efficient heat dissipation unit, a micro heat pipe is widely used in high heat flux microelectronic chips, and its thermal resistance is crucial to heat transfer capacity. Through analyses of the structure and heat transfer performance of a circular heat pipe with sintered wick, the theoretical model of total thermal resistance was established on heat transfer theory, and then simplified, finally a testing platform was set up to test for total thermal resistance performance. The testing results show that when the micro heat pipe is in optimal heat transfer state, its total thermal resistance conform well with that from the theoretical model, and its actual thermal resistance is much lower than that of the rod made of the material with perfect thermal conductivity and of the same geometric size. With the increment of heat transfer capability, the total thermal resistance of a micro heat pipe with sintered wick decreases first, then increases and reaches the minimum when it is in the optimal heat transfer state. The greater total thermal resistance in low heat transfer performance is mainly caused by too much working fluid accumulating in evaporator and the lower velocity in vapor cavity, and the greater total thermal resistance in high heat transfer performance is mainly due to the working fluid drying up in condenser. Total thermal resistance is related to many factors, such as thermal conductivity of tube-shell material, wall thickness, wick thickness, copper powders grain size and porosity, the lengths of condenser and evaporator, and the diameter of vapor cavity etc.. Therefore, the structure parameters of a micro heat pipe with sintered wick should be reasonably designed according to the specific conditions to ensure its heat transfer capacity and total thermal resistance to meet the requirements.

Utilization of Advanced Working Fluids in Heat Pipes

2011 ◽  
Author(s):  
Sean W. Reilly ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Temperature Drop ◽  
High Heat ◽  
Heat Fluxes ◽  
Working Fluid ◽  
High Heat Flux ◽  
Inorganic Aqueous Solution ◽  
Positive Results ◽  
Operating Temperature Range

A novel fluid for use as a working fluid in a heat pipe has been tested at UCLA. The fluid was discovered originally in use with a device consisting of a metal tube charged with the patented inorganic aqueous solution (IAS) which is evaporated when the tube is evacuated before use. According to the patent, this evaporation leaves a thin film which allows the tube to carry high heat flux loads with low temperature drop across the tube in a solid state mode. However, various experiments with these tubes have produced inconsistent results and there is some question as to whether the fluid is completely evaporated. The research on which this work is based, is focused on testing whether the charging fluid will operate as the working fluid in a heat pipe, in order to determine the nature of the IAS fluid. We charged a heat pipe apparatus with a biporous wick in order to investigate if the fluid plays a role in heat transfer. We have extensive data for this experiment using water as the working fluid which will use to compare the two sets of results. Testing has shown positive results in the reduction of the superheat required to drive heat fluxes through a wick compared to water. Some experiments have shown that the operating (temperature) range of the IAS is much larger than a standard heat pipe. It is theorized that the increase in performance of the IAS is due to an increased heat of vaporization. If this fluid is proven to be effective, it would lead to more effective and tunable heat transfer devices.

Research on Thermal Resistance of Micro Heat Pipe with Trapezium-Grooved Wick

2016 ◽  
Vol 693 ◽  
pp. 395-402
Author(s):  
Xi Bing Li ◽  
Ming Jian Li ◽  
Ming Li ◽  
Ying Si Wan
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Heat Transfer Performance ◽  
High Heat ◽  
Working Fluid ◽  
Transfer Performance ◽  
Total Thermal Resistance ◽  
Micro Heat Pipe ◽  
Heat Transfer Capacity

As an efficient heat conducting unit, micro heat pipe is widely used in high heat flux microelectronic chips, and thermal resistance is one of the factors that are crucial to its heat transfer capacity. Based on heat transfer theory, this paper established a theoretical model of total thermal resistance through analyzing the structure and heat transfer performance of circular heat pipe with trapezium-grooved wick, simplified the model and tested the micro heat pipe for its total thermal resistance performance by setting up a testing platform. The testing results show that when the micro heat pipe is in the optimal heat transfer state, its total thermal resistance well coincides with that from the established theoretical model. As for a micro heat pipe with trapezium-grooved wick, its total thermal resistance first decreases, then increases with heat transfer capability increment, and reaches the minimum when it is in the optimal state of heat transfer performance. That too much working fluid accumulates in evaporation section and the vapor velocity is rather low is the main cause for the greater thermal resistance when the pipe is in low heat transfer quantity, yet the greater total thermal resistance when the pipe is in high heat transfer quantity is mainly caused by the working fluid drying up in condensation section. The total thermal resistance is related to many factors, such as the thermal conductivity of tube-shell material, wall thickness, wick thickness, the number of the grooves, the lengths of condensation and evaporation sections, the diameter of vapor cavity etc.. Therefore, the structure parameters of a micro heat pipe with trapezium-grooved wick should be rationally designed according to specific conditions to ensure its heat transfer capacity and total thermal resistance to meet the requirements and be in the optimal state.

scholarly journals An investigation on effect of EDL on heat transfer of micro heat pipe with square and triangular cross section

2020 ◽  
Vol 21 (3) ◽  
pp. 309
Author(s):  
Maryam Fallah Abbasi ◽  
Hossein Shokouhmand ◽  
Morteza Khayat
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Double Layer ◽  
Electric Double Layer ◽  
Heat Pipes ◽  
The Body ◽  
Working Fluid ◽  
Two Phase ◽  
Micro Heat Pipe ◽  
Micro Heat Pipes

Electronic industries have always been trying to improve the efficiency of electronic devices with small dimensions through thermal management of this equipment, thus increasing the use of small thermal sinks. In this study micro heat pipes with triangular and square cross sections have been manufactured and tested. One of the main objectives is to obtain an understanding of micro heat pipes and their role in energy transmission with electrical double layer (EDL). Micro heat pipes are highly efficient heat transfer devices, which use the continuous evaporation/condensation of a suitable working fluid for two-phase heat transport in a closed system. Since the latent heat of vaporization is very large, heat pipes transport heat at small temperature difference, with high rates. Because of variety of advantage features these devices have found a number of applications both in space and terrestrial technologies. The theory of operation micro heat pipes with EDL is described and the micro heat pipe has been studied. The temperature distribution have achieved through five thermocouples installed on the body. Water and different solution mixture of water and ethanol have used to investigate effect of the electric double layer heat transfer. It was noticed that the electric double layer of ionized fluid has caused reduction of heat transfer.

Analysis of heat transfer of loop heat pipe used to cool high power LED

2009 ◽  
Vol 52 (12) ◽  
pp. 3527-3532 ◽  
Author(s):  
XiangYou Lu ◽  
ZeZhao Hua ◽  
MeiJing Liu ◽  
YuanXia Cheng
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
High Power ◽  
Loop Heat Pipe ◽  
High Power Led
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