Evaporation, Condensation, and Flow in an Idealized Micro Heat Pipe

2002 ◽  
Author(s):  
Jin Zhang ◽  
Harris Wong
Keyword(s):  
Thermal Conductivity ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Three Dimensional ◽  
Heat Pipes ◽  
Rigorous Analysis ◽  
Evaporation And Condensation ◽  
Micro Heat Pipe ◽  
Complicated Geometry ◽  
Micro Heat Pipes

Micro heat pipes have been used in cooling micro electronic components. However their effective thermal conductivity is low compared with that of conventional heat pipes. Due to the complexity of the coupled heat and mass transport, and to the complicated three-dimensional bubble geometry inside micro heat pipes, there is a lack of rigorous analysis. As a result, the relatively low effective thermal conductivity remains unexplained. We have conceptualized an idealized micro heat pipe that eliminates the complicated geometry, but retains the essential physics. Given the simplified geometry, many effects can be studied, such as thermocapillary flow, and evaporation and condensation physics. In this talk, we will present the flow field induced by evaporation.

Steady-State Investigation of Vapor Deposited Micro Heat Pipe Arrays

1995 ◽  
Vol 117 (1) ◽  
pp. 75-81 ◽  
Author(s):  
A. K. Mallik ◽  
G. P. Peterson
Keyword(s):  
Thermal Conductivity ◽  
Steady State ◽  
Surface Temperature ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Heat Pipes ◽  
Temperature Gradients ◽  
Bottom Surface ◽  
Micro Heat Pipe ◽  
Micro Heat Pipes

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 × 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/cm2. 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.

Experimental Investigation of Micro Heat Pipes Fabricated in Silicon Wafers

1993 ◽  
Vol 115 (3) ◽  
pp. 751-756 ◽  
Author(s):  
G. P. Peterson ◽  
A. B. Duncan ◽  
M. H. Weichold
Keyword(s):  
Thermal Conductivity ◽  
Experimental Investigation ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Heat Pipes ◽  
Silicon Wafers ◽  
Temperature Gradients ◽  
Cover Plate ◽  
Micro Heat Pipe ◽  
Micro Heat Pipes

An experimental investigation was conducted to determine the thermal behavior of arrays of micro heat pipes fabricated in silicon wafers. Two types of micro heat pipe arrays were evaluated, one that utilized machined rectangular channels 45 μm wide and 80 μm deep and the other that used an anisotropic etching process to produce triangular channels 120 μm wide and 80 μm deep. Once fabricated, a clear pyrex cover plate was bonded to the top surface of each wafer using an ultraviolet bonding technique to form the micro heat pipe array. These micro heat pipe arrays were then evacuated and charged with a predetermined amount of methanol. Using an infrared thermal imaging unit, the temperature gradients and maximum localized temperatures were measured and an effective thermal conductivity was computed. The experimental results were compared with those obtained for a plain silicon wafer and indicated that incorporating an array of micro heat pipes as an integral part of semiconductor devices could significantly increase the effective thermal conductivity; decrease the temperature gradients occurring across the wafer; decrease the maximum wafer temperatures; and reduce the number and intensity of localized hot spots. At an input power of 4 W, reductions in the maximum chip temperature of 14.1°C and 24.9°C and increases in the effective thermal conductivity of 31 and 81 percent were measured for the machined rectangular and etched triangular heat pipe arrays, respectively. In addition to reducing the maximum wafer temperature and increasing the effective thermal conductivity, the incorporation of the micro heat pipe arrays was found to improve the transient thermal response of the silicon test wafers significantly.

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.

Experimental Investigation of a New Flat Plate Solar Heat Collector by Micro Heat Pipe Array

2010 ◽  
Author(s):  
Yao-Hua Zhao ◽  
Fei-Long Zou ◽  
Yan-Hua Diao ◽  
Zhen-Hua Quan
Keyword(s):  
Flat Plate ◽  
Heat Pipe ◽  
High Efficiency ◽  
Heat Pipes ◽  
Total Heat Loss ◽  
Solar Heat ◽  
Solar Water ◽  
Micro Heat Pipe ◽  
Heat Collector ◽  
Micro Heat Pipes

The performance of a new flat plate solar heat collector with perfect combination of high efficiency and low cost is investigated experimentally. The new system described in this study uses a novel micro heat pipe array as a key component for the system. One such flat plate heat collector contains over 300 micro heat pipes per 1m2 and the hydraulic diameter of the micro heat pipes is 0.4–1.0mm. A detailed heat transfer experimental study is conducted during daylight hours over several months, focusing on the collector efficiency and overall efficiency of the system as well as total heat loss factor. The results show that the collector’s maximum instantaneous efficiency is up to 88%. Compared with conventional evacuated glass tube solar water heater, the system offers the additional benefits of high pressure resistance, low weight, good reliability and durability, easy integration into buildings and absence of freezing during winter months. Besides, compared with traditional flat-plate solar water system which is mainly sheet-and-tube concept, the system also shows many advantages: higher efficiency, much cheaper, absence of tube-bonding and freezing etc. Therefore, the system proposes a unique substitute to common solar water heating systems.

Experimental Investigation of Graphene Oxide Nanofluids on Thermal Performance of Heat Pipe

2019 ◽  
Author(s):  
Weilin Zhao ◽  
Jun Xu ◽  
Jinkai Li
Keyword(s):  
Thermal Conductivity ◽  
Graphene Oxide ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Heat Pipes ◽  
Air Cooling ◽  
Coating Film ◽  
Water Cooling ◽  
Condenser Section ◽  
Wick Structure

Abstract The graphene oxide-deionized water (GO-DW) and graphene oxide-ethylence glycol (GO-EG) nanofluids were synthesized. The better suspension of nanofluids was achieved. The thermal conductivity of both nanofluids was analyzed. It indicates that GO nanoparticles can strengthen the thermal conductivity of DW base fluids by 22.6%–61.7% and EG base fluids by 15.3%–32.8%. Four copper heat pipes charged with GO-DW and GO-EG nanofluids as well as DW and EG base fluids were experimentally researched, it is discovered that the addition of GO nonoparticles in heat pipe can elevate the condenser wall temperature and reduce the temperature difference. Future analysis finds that, with respect to DW and EG fluids heat pipe, the thermal resistances of GO-DW and GO-EG nanofluids heat pipe are respectively decreased 42.6–52.4% and 31.9%–38.4% for air cooling, and 15.5–16.7% and 11.5%–18.9% for water cooling at condenser section. Besides, the wick structure of GO-DW nanofluids heat pipe was examined by Scanning Electron Microscope, and the effective thermal conductivity of fluid-wick combination was evaluated. The outcomes demonstrate that the evaporator wick surface contains about 0375–1.24μm coating film of GO nanoparticles. Assumed the coating film is 0.75μm, the effective thermal conductivity of fluid-wick combination is respectively enhanced by 66.92 % for GO-DW nonofluids heat pipe and 37.32% for GO-EG nonofluids heat pipe at 70 °C.

High Flux Value Micro-Heat Pipe Arrays

2010 ◽  
Vol 2010 (DPC) ◽  
pp. 001760-001807
Author(s):  
Daniel K. Harris ◽  
Robert Dean ◽  
Ashish Palkar ◽  
Gary Wonacott
Keyword(s):  
Liquid Metal ◽  
Heat Pipe ◽  
Experimental Work ◽  
Performance Enhancement ◽  
Performance Testing ◽  
Heat Pipes ◽  
Working Fluid ◽  
Working Fluids ◽  
Micro Heat Pipe ◽  
Micro Heat Pipes

The concept of heat pipes was introduced by R.S.Gaugler in 1940s and Cotter first introduced the idea of “micro” heat pipes in 1984. Cotter in his paper, defined the micro heat pipe as being one in which the mean curvature of the vapor-liquid interface is comparable in magnitude to the reciprocal of the hydraulic radius of the total flow channel. The Micro Heat Pipes (MHPs) work efficiently through the use of two-phase heat transfer. Various working fluids have been tried in combination with various substrate materials. In this experimental work the main focus was to study the behavior of liquid metal filled MHPs made from silicon as the substrate material. Specially designed MHPs were assembled and charged with mercury as the working fluid. A special test setup was designed and built for the experimental work and the response of the MHPs to the controlled increment in the input power is presented. A number of experiments were carried out on the specimen MHPs to determine their effective thermal conductivity, the variation of the temperature along the axial length and the performance enhancement factor. Effective thermal conductivities as high as 900 W/m-K with a silicon equivalence of 6 were achieved with the liquid metal MHP. Based on the results from the various performance testing parameters, it was observed that the liquid metal charged MHPs performed substantially better than conventional MHPs filled with organic working fluids. The limitations and the possible methods of improving the performance of the MHPs are discussed.

Transient Response Characteristics of Vapor Deposited Micro Heat Pipe Arrays

1995 ◽  
Vol 117 (1) ◽  
pp. 82-87 ◽  
Author(s):  
G. P. Peterson ◽  
A. K. Mallik
Keyword(s):  
Heat Pipe ◽  
Time Constant ◽  
Imaging System ◽  
Heat Pipes ◽  
Silicon Wafers ◽  
Thermal Time ◽  
Transient Temperature ◽  
Micro Heat Pipe ◽  
Thermal Time Constant ◽  
Micro Heat Pipes

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.

Numerical Analysis of a Metal Hydride Reactor With Embedded Heat Pipes to Enhance Heat Transfer Characteristics

2009 ◽  
Author(s):  
Joon Hong Boo ◽  
Young Hark Park ◽  
Masafumi Katsuta ◽  
Sang Chul Bae
Keyword(s):  
Thermal Conductivity ◽  
Numerical Analysis ◽  
Heat Pipe ◽  
Metal Hydride ◽  
Three Dimensional ◽  
Heat Pipes ◽  
Thermal Control ◽  
Hydrogen Gas ◽  
Outer Diameter ◽  
Reactor Model

Numerical analysis was conducted for a heat pipe application in a metal hydride (MH) reactor for hydrogen gas storage. The hydriding and dehydriding characteristics of MH strongly depend on temperature and pressure. Due to its extremely low thermal conductivity however, it is very difficult to control the temperature of MH, especially when it is of vast bulk as in an MH reactor. This study deals with heat pipes embedded into the MH to increase the effective thermal conductivity of the system and thus to enhance the thermal control characteristics. The existing model was a brine-tube type MH reactor having cylindrical container with outer diameter of 76 mm and length of 1 m, which was partially filled with 8 to 10 kg of MH material. The hydriding and dehydriding processes occur at 10°C and 80°C, respectively. The heat-pipe type reactor model replaced the brine tubes and channels with copper-water heat pipes of the same dimensions. Three-dimensional numerical analysis predicted that the heat-pipe type MH reactor model enhanced thermal performance with faster response to the change of boundary conditions and higher degree of isothermal characteristics. Discussion is presented based on the numerical results of the two models compared with experimental results.

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.

Fabrication and Testing of SOG Structure Flat Heat Pipes with Triangle Grooves

2011 ◽  
Vol 483 ◽  
pp. 58-61 ◽  
Author(s):  
Xiao Wei Liu ◽  
Chao Wang ◽  
Tian Han ◽  
Tian Dong
Keyword(s):  
Thermal Conductivity ◽  
Heat Pipe ◽  
Glass Structure ◽  
Heat Pipes ◽  
Experimental Results ◽  
Working Fluid ◽  
Micro Heat Pipe ◽  
Vacuum Atmosphere

A new kind of charging and sealing method for SOG (silicon on glass) structure micro heat pipe with triangular grooves is investigated. MHP (micro heat pipe) is fully charged in a vacuum atmosphere which is useful for preventing air intermingle. Experimental results shows that when the fill ration of working fluid is about 35%, thermal conductivity of MHP with ethanol as its working fluid has an improvement of 19% compared to empty MHP.

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