Analytical Modeling of a Loop Heat Pipe at Positive Elevation

2004 ◽  
Author(s):  
Po-Ya Abel Chuang ◽  
John M. Cimbala ◽  
Jack S. Brenizer ◽  
C. Thomas Conroy
Keyword(s):  
Steady State ◽  
Heat Pipe ◽  
Experimental Results ◽  
State Model ◽  
Loop Heat Pipe ◽  
Operating Characteristics ◽  
Two Phase ◽  
Steady State Model ◽  
Two Phase Heat Transfer ◽  
Transfer Device

A two-phase heat transfer device, a loop heat pipe (LHP), is studied analytically. It is noted that a LHP behaves differently when it is operated against gravity (adverse elevation) or at gravity assisted (positive elevation) conditions. Steady-state modeling of LHP operating characteristics at adverse or zero elevation was broadly studied in the past. This paper presents a steady-state model of a LHP when it is operated at positive elevation based on experimental results. The effects of elevation on the trend of steady-state operating temperature (SSOT) are then studied using the newly developed steady-state model. Experimental results agree with the model predictions at adverse (88.9mm), zero, and positive (88.9mm) elevations. This steady-state model is the only model known to have the capability to predict the operating characteristics at positive elevation. The model will help to design the LHPs utilized in terrestrial applications.

Comparison of Experiments and 1-D Steady-State Model of a Loop Heat Pipe

2002 ◽  
Author(s):  
Po-Ya Abel Chuang ◽  
John M. Cimbala ◽  
Jack S. Brenizer ◽  
C. Thomas Conroy ◽  
A. A. El-Ganayni ◽  
...  
Keyword(s):  
Steady State ◽  
Heat Pipe ◽  
State Model ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Comparison Of Experiments ◽  
Steady State Model ◽  
Model Predictions ◽  
Two Phase Heat Transfer ◽  
Transfer Device

A modern, effective, two-phase heat transfer device, a loop heat pipe (LHP), was studied analytically and experimentally. A 1-D steady-state model was developed based on energy balance equations. The mathematical modeling procedures of each component are explained in detail, including a model of the secondary wick in the evaporator. Other models neglect the existence of the secondary wick because the detailed designs of the secondary wick are often proprietary. Three sets of experiments were performed at different elevations. Results of experimental data are compared with 1-D steady-state model predictions. The comparisons show that the model predictions of steady state operating temperatures for both zero elevation and adverse elevation are within 2 percent. It has been clearly demonstrated that the 1-D steady-state model is a useful tool for future LHP study.

Theoretical and Experimental Study of a Loop Heat Pipe at Positive Elevation

2004 ◽  
Author(s):  
Po-Ya Abel Chuang ◽  
John M. Cimbala ◽  
Jack S. Brenizer ◽  
C. Thomas Conroy
Keyword(s):  
Steady State ◽  
Flow Visualization ◽  
Heat Pipe ◽  
Neutron Radiography ◽  
Loop Heat Pipe ◽  
Operating Characteristics ◽  
Two Phase ◽  
State Behavior ◽  
Wide Range ◽  
Two Phase Heat Transfer

A loop heat pipe (LHP), which is a two-phase heat transfer device, was studied experimentally and theoretically. The steady-state operating characteristics of a LHP when it is operated at adverse (the condenser is below the evaporator) and zero elevations (the evaporator and the condenser are at the same level) had been studied intensively in the past. However, study of a LHP when it is operated at positive elevation (the condenser is above the evaporator) is still lacking. This paper presents detailed theoretical analysis of the steady-state behavior of a LHP operated at positive elevation. The present analysis agrees with experimental results, and is confirmed by flow visualization images. Testing was performed for a wide range of heat loads (20 W-600 W) at three positive elevations: 25.4mm, 76.2mm, and 127mm. Flow visualization images were taken by neutron radiography when the LHP was operated at 102mm positive elevation.

Steady-State Modeling and Testing of a Micro Heat Pipe

1990 ◽  
Vol 112 (3) ◽  
pp. 595-601 ◽  
Author(s):  
B. R. Babin ◽  
G. P. Peterson ◽  
D. Wu
Keyword(s):  
Steady State ◽  
Heat Pipe ◽  
Heat Pipes ◽  
Experimental Results ◽  
State Model ◽  
Operating Characteristics ◽  
Maximum Heat ◽  
Micro Heat Pipe ◽  
Steady State Model ◽  
Micro Heat Pipes

A combined experimental and analytical investigation was conducted to identify and understand better the phenomena that govern the performance limitations and operating characteristics of micro heat pipes—heat pipes so small that the mean curvature of the vapor—liquid interface is comparable in magnitude to the reciprocal of the hydraulic radius of the flow channel. The analytical portion of the investigation began with the development of a steady-state model in which the effects of the extremely small characteristic dimensions on the conventional steady-state heat pipe modeling techniques were examined. In the experimental portion of the investigation, two micro heat pipes, one copper and one silver, 1 mm2 in cross-sectional area and 57 mm in length, were evaluated experimentally to determine the accuracy of the steady-state model and to provide verification of the micro heat pipe concept. Tests were conducted in a vacuum environment to eliminate conduction and convection losses. The steady-state experimental results obtained were compared with the analytical model and were found to predict accurately the experimentally determined maximum heat transport capacity for an operating temperature range of 40° C to 60° C. A detailed description of the methodology used in the development of the steady-state model along with a comparison of the predicted and experimental results are presented.

Multilayer Wick Structure of Loop Heat Pipe

2007 ◽  
Author(s):  
Qingjun Cai ◽  
Chung-Lung Chen ◽  
Julie F. Asfia
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Transfer Resistance ◽  
Heat Leakage ◽  
Wick Structure ◽  
Operating Temperatures ◽  
Compensation Chamber ◽  
Two Phase Heat Transfer

Loop heat pipe (LHP) is known as a two-phase heat transfer device that utilizes the evaporation and condensation of an operating fluid to transfer heat. At the LHP low operating temperatures, heat leakage induced by saturated temperature differences between the evaporator and compensation chamber is more serious than at high operating temperatures, due to inherent thermophysical properties of the operating liquid. The serious heat leakage at the low operating temperature not only causes high liquid subcooling requirement but also leads to high total temperature difference and degraded heat transfer performance. In this paper, research efforts are placed on reducing the heat leakage by introducing a multilayer wick structure into the LHP. Based on the previous research results of LHP non-metallic wick structures, the multilayer wick LHP combines advantages of both metallic and non-metallic wick structures, retains good heat conduction from the evaporator case to the liquid/vapor interface and inhibits the reverse heat transfer from the interface to compensation chamber. By demonstrating the concept on a methanol LHP, experimental results exhibit a significant enhancement in reducing heat leakage and the total heat transfer resistance.

Steady-State and Transient Performance of a Miniature Loop Heat Pipe

2005 ◽  
Author(s):  
Yuming Chen ◽  
Manfred Groll ◽  
Rainer Mertz ◽  
Yu. F. Maydanik ◽  
S. V. Vershinin
Keyword(s):  
Steady State ◽  
Heat Pipe ◽  
Electronics Cooling ◽  
Consumer Electronics ◽  
Outer Diameter ◽  
Loop Heat Pipe ◽  
Operating Characteristics ◽  
Evaporator Temperature ◽  
Temperature Oscillations ◽  
Compensation Chamber

A series of tests have been carried out with a miniature loop heat pipe (mLHP), which has been developed for consumer electronics cooling, for horizontal and four vertical orientations under different sink temperatures. The mLHP has a cylindrical evaporator of 5 mm outer diameter and 29 mm length. The steady-state operating characteristics are similar for different orientations except for the orientation where the evaporator is above the compensation chamber. At an evaporator temperature of 75 °C, an evaporator heat load up to 70 W can be reached with thermal resistance of about 0.2 °C/W. The transient behavior of the mLHP is studied in detail. In general, the mLHP can be started up with very low power input (5 W). Big temperature oscillations in the liquid line were found in many cases, however, the temperature oscillations in the evaporator are minimum. The orientations greatly influence the operating characteristics of the mLHP. At least for the horizontal orientation, the overall performance of the tested mLHP is satisfying.

Experimental Investigation of Micro/Nano Heat Pipe Wick Structures

2008 ◽  
Author(s):  
H. Peter J. de Bock ◽  
Kripa Varanasi ◽  
Pramod Chamarthy ◽  
Tao Deng ◽  
Ambarish Kulkarni ◽  
...  
Keyword(s):  
Heat Pipe ◽  
Heat Transport ◽  
High Performance ◽  
Heat Pipes ◽  
High Heat ◽  
Two Phase ◽  
Wick Structure ◽  
Two Phase Heat Transfer ◽  
Heat Transport Capability ◽  
Transfer Device

The performance of electronic devices is limited by the capability to remove heat from these devices. A heat pipe is a device to facilitate heat transport that has seen increased usage to address this challenge. A heat pipe is a two-phase heat transfer device capable of transporting heat with minimal temperature gradient. An important component of a heat pipe is the wick structure, which transports the condensate from the condenser to the evaporator. The requirements for high heat transport capability and high resilience to external accelerations leads to the necessity of a design trade off in the wick geometry. This makes the wick performance a critical parameter in the design of heat pipes. The present study investigates experimental methods of testing capillary performance of wick structures ranging from micro- to nano-scales. These techniques will facilitate a pathway to the development of nano-engineered wick structures for high performance heat pipes.

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