Modeling and Thermal Optimization of a Micro Heat Pipe With Curved Triangular Grooves

2003 ◽  
Author(s):  
Kyu Hyung Do ◽  
Sung Jin Kim ◽  
Gunn Hwang
Keyword(s):  
Numerical Model ◽  
Heat Pipe ◽  
Heat Transport ◽  
Interfacial Shear Stress ◽  
Axial Direction ◽  
Transport Rate ◽  
Maximum Heat ◽  
Steady State Condition ◽  
Thermal Optimization ◽  
Micro Heat Pipe

Heat transfer and fluid flow characteristics in a micro heat pipe with curved triangular grooves are investigated using numerical and experimental methods. In the numerical part, a one-dimensional mathematical model for micro heat pipe with curved triangular grooves is developed and solved to obtain the maximum heat transport rate, the capillary radius distribution, the liquid and the vapor pressure distributions along the axial direction of the micro heat pipe under the steady-state condition. In particular, the modified Shah method is applied to calculate the pressure drop induced by the liquid-vapor interfacial shear stress. Experiments are conducted to validate the numerical model. In the experiments, the micro heat pipe with 0.56 mm in hydraulic diameter and 50 mm in length is tested. The experimental results for the maximum heat transport rate agree well with those of the numerical investigations. Finally, thermal optimization of the micro heat pipe with curved triangular grooves is performed using the numerical model.

Investigation of Polymer Based Micro Heat Pipes for a Flexible Spacecraft Radiator

2001 ◽  
Author(s):  
D. McDaniels ◽  
G. P. “Bud” Peterson
Keyword(s):  
Heat Pipe ◽  
Heat Transport ◽  
Power Density ◽  
Polymeric Material ◽  
Heat Dissipation ◽  
Effective Conductivity ◽  
Chemical Reactivity ◽  
Working Fluid ◽  
Maximum Heat ◽  
Micro Heat Pipe

Abstract In response to the space industry’s pursuit of interplanetary travel and a continuous human presence in space, there is increasing focus on spacecraft that change configuration while in space. Flexible thermal radiators are being developed to accommodate various collapse and deployment mechanisms. An analytical model suggests that a lightweight polymeric material with imbedded micro heat pipe arrays can meet heat dissipation requirements while contributing less mass than competing flexible materials. The capillary pumping limit is evaluated as a function of operating temperature using two candidate working fluids. Using water, the maximum heat transport is 18 mW per channel at 140/160 °C. The maximum heat transport using methanol is 2.2 mW at 120 °C, an order-of magnitude difference. A thermal circuit model translates heat transport per channel into total radiator capacity as a function of source temperature and environmental sink temperature. Using water as the working fluid, the radiator capacity was shown to vary from 6.0 kW to 12.2 kW for source temperatures of 20 °C to 50 °C. For source temperatures of 40 °C and higher, the capacity meets or exceeds the dissipation requirements of a reference spacecraft design. While evaluated, methanol is not recommended as a working fluid because its radiator capacity is two to three times lower than water. Although thermal system constraints place limits on the micro heat pipe operating range, design changes directed at alleviating capillary limitations should increase radiator capacity. Technical issues for further study include effects of film billowing, performance limitations related to vapor viscosity, working fluid diffusion, and chemical reactivity between case and working fluid. Compared to a competing graphite fiber weave, the polymeric material has an effective conductivity over ten times higher. Its area power density (in kW/m2) is 18% to 60% lower than the graphite weave, but its mass power density (in kW/kg) is several times higher. Greater flexibility and lower weight also make it more amenable to structural integration. Recently developed space-stable polymers offer resistance to harsh temperature and radiation environments, helping to clear the path toward a more extensive use of polymers within the space industry.

Experimental Investigation of Micro Heat Pipe Radiators in Radiation Environment

2001 ◽  
Author(s):  
Y. X. Wang ◽  
G. P. Peterson
Keyword(s):  
Experimental Investigation ◽  
Heat Pipe ◽  
Heat Transport ◽  
Radiation Efficiency ◽  
Wire Diameter ◽  
Radiation Environment ◽  
Transport Capacity ◽  
Maximum Heat ◽  
Micro Heat Pipe

Abstract A flexible micro heat pipe radiator, fabricated by sintering an array of aluminum wires between two thin aluminum sheets, was developed as part of a program to conceptulize, develop, and test lightweight, flexible radiator fin structures for use on long-term spacecraft missions. A detailed experimental investigation was conducted to determine the temperature distribution, maximum heat transport capacity, and radiation efficiency of these micro heat pipe radiators in a radiation environment. Experimental results from three Aluminum-Acetone micro heat pipe radiators with wire diameters of 0.635 mm, 0.813 and 1.016 mm are presented, evaluated and discussed. The results of the experimental program indicted that the maximum heat transport capacity and radiation efficiency, both increased with increasing wire diameter. The maximum heat transport capacity of the micro heat pipe radiator utilizing a wire diameter of 0.635 mm was 15.2 W. The radiators utilizing wire diameters of 0.813 mm and 1.016 mm never reached the maximum heat transport capacities for the given test conditions. In the tests, temperature distributions were recorded for several sink temperatures and indicated that as the sink temperature decreased the radiation efficiency decreased for a given heat input. The maximum heat transport capacity increased with increasing evaporating temperature for the micro heat pipe radiator utilizing a wire diameter of 0.635 mm. Comparison of micro heat pipe radiators with and without working fluid, indicated that significant improvements in temperature uniformity and radiation efficiencies could be obtained, especially at high heat fluxes. A maximum radiation efficiency of 0.95 was observed. In general, while some variation in performance was observed, all three micro heat pipe radiators were found to be capable of meeting the thermal requirements of long-term missions.

Temperature Response of Heat Transport in a Micro Heat Pipe

1999 ◽  
Vol 121 (2) ◽  
pp. 438-445 ◽  
Author(s):  
G. P. Peterson ◽  
H. B. Ma
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Pipe ◽  
Heat Transport ◽  
Capillary Flow ◽  
Temperature Drop ◽  
Temperature Response ◽  
Axial Direction ◽  
Vapor Flow ◽  
Micro Heat Pipe

A detailed mathematical model for predicting the heat transport capability and temperature gradients that contribute to the overall axial temperature drop as a function of heat transfer in a micro heat pipe has been developed. The model utilizes a third-order ordinary differential equation, which governs the fluid flow and heat transfer in the evaporating thin film region; an analytical solution for the two-dimension heat conduction equation, which governs the macro evaporating film region in the triangular corners; the effects of the vapor flow on the liquid flow in the micro heat pipe; the flow and condensation of the thin film caused by the surface tension in the condenser; and the capillary flow along the axial direction of the micro heat pipe. With this model, the temperature distribution along the axial direction of the heat pipe and the effect on the heat transfer can be predicted. In order to verify the model presented here, an experimental investigation was also conducted and a comparison with experimental data made. This comparison indicated excellent correlation between the analytical model and experimental results, and as a result, the analysis provides a better understanding of the heat transfer capability and temperature variations occurring in micro heat pipes.

The Heat Transport Capacity of Micro Heat Pipes

1998 ◽  
Vol 120 (4) ◽  
pp. 1064-1071 ◽  
Author(s):  
J. M. Ha ◽  
G. P. Peterson
Keyword(s):  
Experimental Data ◽  
Heat Pipe ◽  
Heat Transport ◽  
Heat Pipes ◽  
Original Model ◽  
Semiempirical Model ◽  
Transport Capacity ◽  
Predictive Tool ◽  
Maximum Heat ◽  
Micro Heat Pipes

The original analytical model for predicting the maximum heat transport capacity in micro heat pipes, as developed by Cotter, has been re-evaluated in light of the currently available experimental data. As is the case for most models, the original model assumed a fixed evaporator region and while it yields trends that are consistent with the experimental results, it significantly overpredicts the maximum heat transport capacity. In an effort to provide a more accurate predictive tool, a semi-empirical correlation has been developed. This modified model incorporates the effects of the temporal intrusion of the evaporating region into the adiabatic section of the heat pipe, which occurs as the heat pipe approaches dryout conditions. In so doing, the current model provides a more realistic picture of the actual physical situation. In addition to incorporating these effects, Cotter’s original expression for the liquid flow shape factor has been modified. These modifications are then incorporated into the original model and the results compared with the available experimental data. The results of this comparison indicate that the new semiempirical model significantly improves the correlation between the experimental and predicted results and more accurately represents the actual physical behavior of these devices.

Design and Research of Flat Micro Heat Pipe with Glass Fiber Wick

2011 ◽  
Vol 483 ◽  
pp. 603-606
Author(s):  
Tian Han ◽  
Xiao Wei Liu ◽  
Chao Wang
Keyword(s):  
Glass Fiber ◽  
Heat Pipe ◽  
Experimental Testing ◽  
Governing Equations ◽  
Maximum Heat ◽  
One Dimensional ◽  
Micro Heat Pipe ◽  
Wick Structure

A kind of flat micro heat pipe with glass fiber wick structure is designed and fabricated. The structure of the wick is presented and also the excellence of the structure is described. For the glass fiber wick, the maximum heat transports is calculated by one-dimensional steady governing equations. Experimental testing is performed for the fabricated micro heat pipe in vacuum. The testing results is presented and analyzed.

Heat Transport Limitation of a Triangular Micro Heat Pipe

2003 ◽  
Author(s):  
D. Sugumar ◽  
Kek Kiong Tio
Keyword(s):  
Heat Pipe ◽  
Heat Transport ◽  
Operating Temperature ◽  
Working Fluid ◽  
Transport Capacity ◽  
Condenser Section ◽  
Micro Heat Pipe ◽  
Evaporator Section ◽  
Higher Temperature ◽  
Specific Temperature

A micro heat pipe will operate effectively by achieving its maximum possible heat transport capacity only if it is to operate at a specific temperature, i.e., design temperature. In reality, micro heat pipe’s may be required to operate at temperatures different from the design temperature. In this study, the heat transport capacity of an equilateral triangle micro heat pipe is investigated. The micro heat pipe is filled optimally with working fluid for a specific design temperature and operated at different operating temperatures. For this purpose, water, pentane and acetone was selected as the working fluids. From the numerical results obtained, it shows that the optimal charge level of the micro heat pipe is dependent on the operating temperature. Furthermore, the results also shows that if the micro heat pipe is to be operated at temperatures other than its design temperature, its heat transport capacity is limited by the occurrence of flooding at the condenser section or dryout at the evaporator section, depending on the operating temperature and type of working fluid. It is observed that when the micro heat pipe is operated at a higher temperature than its design temperature, the heat transport capacity increases but limited by the onset of dryout at the evaporator section. However, the heat transport capacity decreases if it is to be operated at lower temperatures than its design temperature due to the occurrence of flooding at condenser end. From the results obtained, we can conclude that the performance of a micro heat pipe is decreased if it is to be operated at temperatures other than its design temperature.

Study on a Pulsating Heat Pipe With Self-Rewetting Fluid

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Koji Fumoto ◽  
Masahiro Kawaji ◽  
Tsuyoshi Kawanami
Keyword(s):  
Surface Tension ◽  
Heat Pipe ◽  
Heat Transport ◽  
Heated Surface ◽  
Input Power ◽  
Water Mixture ◽  
Pulsating Heat Pipe ◽  
Maximum Heat ◽  
Dry Spot ◽  
Heat Transport Capability

This paper discusses a pulsating heat pipe (PHP) using a self-rewetting fluid. Unlike other common liquids, self-rewetting fluids have the property that the surface tension increases with temperature. The increasing surface tension at a higher temperature can cause the liquid to be drawn toward a heated surface if a dry spot appears and thus to improve boiling heat transfer. In experiments, 1-butanol and 1-pentanol were added to water at a concentration of less than 1 wt % to make self-rewetting fluid. A pulsating heat pipe made from an extruded multiport tube was partially filled with the self-rewetting fluid water mixture and tested for its heat transport capability at different input power levels. The experiments showed that the maximum heat transport capability was enhanced by a factor of 4 when the maximum heater temperature was limited to 110°C. Thus, the use of a self-rewetting fluid in a PHP was shown to be highly effective in improving the heat transport capability of pulsating heat pipes.

Effect of Fluid Loading on the Performance of Wicked Heat Pipes

Volume 3 ◽  
2004 ◽  
Author(s):  
R. Kempers ◽  
A. Robinson ◽  
C. Ching ◽  
D. Ewing
Keyword(s):  
Heat Flux ◽  
Heat Pipe ◽  
Heat Transport ◽  
Heat Pipes ◽  
Working Fluid ◽  
Fluid Loading ◽  
Maximum Heat ◽  
Horizontal Orientation ◽  
Maximum Heat Flux ◽  
Dry Out

A study was performed to experimentally characterize the effect of fluid loading on the heat transport performance of wicked heat pipes. In particular, experiments were performed to characterize the performance of heat pipes with insufficient fluid to saturate the wick and excess fluid for a variety of orientations. It was found that excess working fluid in the heat pipe increased the thermal resistance of the heat pipe, but increased maximum heat flux through the pipe in a horizontal orientation. The thermal performance of the heat pipe was reduced when the amount of working fluid was less than required to saturate the wick, but the maximum heat flux through the heat pipe was significantly reduced at all orientations. It was also found in this case the performance of this heat pipe deteriorated once dry-out occurred.

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.

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