Effect of Sink Temperature on the Stability of the Pressure-Controlled Loop Heat Pipe

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Wukchul Joung ◽  
Joohyun Lee
Keyword(s):  
Heat Pipe ◽  
Temperature Control ◽  
Control Technique ◽  
Loop Heat Pipe ◽  
Heat Leak ◽  
Start Up ◽  
Recent Emergence ◽  
Compensation Chamber ◽  
The Stability ◽  
Pressure Controlled

Recently, a novel temperature control technique utilizing the unique thermohydraulic operating principles of the pressure-controlled loop heat pipes (PCLHPs) was proposed and proved its effectiveness, by which a faster and more stable temperature control was possible by means of the pressure control. However, due to its recent emergence, the proposed hydraulic temperature control technique has not been fully characterized in terms of the various operating parameters including the sink temperature. In this work, the effect of the sink temperature on the loop heat pipe (LHP)-based hydraulic temperature control was investigated to improve the stability of the proposed technique. Start-up characteristics and transient responses of the operating temperatures to different pressure steps and sink temperatures were examined. From the test results, it was found that there was a minimum sink temperature, which ensured a steady-state operation after the start-up and a stable hydraulic temperature control with the increasing pressure steps, due to the unstable balance between the heat leak and the liquid subcooling in the compensation chamber at low sink temperatures. In addition, the range of the stable hydraulic temperature control was extended with the increasing coolant temperature due to the decreased heat leak, which resulted in the increased pressure difference between the evaporator and the compensation chamber. Therefore, it was found and suggested that for a stable hydraulic temperature control in an extended range, it was necessary to operate the PCLHP at higher sink temperatures than the low limit.

Thermal Vacuum Testing of a Miniature Loop Heat Pipe With Multiple Evaporators and Multiple Condensers

2007 ◽  
Author(s):  
Jentung Ku ◽  
Laura Ottenstein ◽  
Hosei Nagano
Keyword(s):  
Low Power ◽  
Heat Pipe ◽  
Temperature Control ◽  
Heat Load ◽  
Operating Temperature ◽  
Loop Heat Pipe ◽  
Thermal Vacuum ◽  
Heater Power ◽  
Start Up ◽  
Vacuum Testing

This paper describes thermal vacuum testing of a miniature loop heat pipe (MLHP) with two evaporators and two condensers designed for future small systems applications requiring low mass, low power and compactness. Each evaporator contains a wick with an outer diameter of 6.4 mm, and each has its own integral compensation chamber (CC). Multiple evaporators provide flexibility for placement of instruments that need to be maintained at the same temperature, and facilitate heat load sharing among instruments, resulting in a reduced auxiliary heater power requirement. A flow regulator is used to regulate heat dissipations among all condensers, thus providing flexibility for placement of radiators on the spacecraft. A thermoelectric converter (TEC) is attached to each CC for operating temperature control and enhancement of start-up success. Tests performed include start-up, power cycle, sink temperature cycle, high power and low power operation, heat load sharing, and operating temperature control. The MLHP demonstrated excellent performance in the thermal vacuum environment. The loop started successfully and operated stably under various evaporator heat loads and condenser sink temperatures. The TECs were able to maintain the loop operating temperature within ±0.5K of the desired set point temperature at all power levels and all sink temperatures. The un-powered evaporator would automatically share heat from the other powered evaporator. The CC control heater power was reduced by more than 50 percent when a TEC was used instead of conventional electrical heaters. The flow regulator was able to regulate the heat dissipation among the radiators and prevent vapor from flowing into the liquid line.

Experimental study of heat transfer and start-up of loop heat pipe with multiscale porous wicks

2017 ◽  
Vol 117 ◽  
pp. 782-798 ◽  
Author(s):  
Xianbing Ji ◽  
Ye Wang ◽  
Jinliang Xu ◽  
Yanping Huang
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Pipe ◽  
Loop Heat Pipe ◽  
Start Up

Hydraulic operating temperature control of a loop heat pipe

2015 ◽  
Vol 86 ◽  
pp. 796-808 ◽  
Author(s):  
Wukchul Joung ◽  
Kee Sool Gam ◽  
Yong-Gyoo Kim ◽  
Inseok Yang
Keyword(s):  
Heat Pipe ◽  
Temperature Control ◽  
Operating Temperature ◽  
Loop Heat Pipe

Investigation of Loop Heat Pipe Startup Using Liquid Core Visualization

2008 ◽  
Author(s):  
B. P. d’Entremont ◽  
J. M. Ochterbeck
Keyword(s):  
Heat Pipe ◽  
Liquid Core ◽  
High Heat ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Buoyancy Driven Flows ◽  
Compensation Chamber ◽  
Fill Level ◽  
Heat Loads

In this investigation, a Loop Heat Pipe (LHP) evaporator has been studied using a borescope inserted through the compensation chamber into the liquid core. This minimally intrusive technique allows liquid/vapor interactions to be observed throughout the liquid core and compensation chamber. A low conductivity ceramic was used for the wick and ammonia as the working fluid. Results indicate that buoyancy driven flows, both two-phase and single-phase, play essential roles in evacuating excess heat from the core, which explains the several differences in performance between horizontal and vertical orientations of the evaporator. This study also found no discernable effect of the pre-start fill level of the compensation chamber on thermal performance during startup at moderate and high heat loads.

Heat transfer limit resulting from heat leak in a cryogenic loop heat pipe

2020 ◽  
pp. 116280
Author(s):  
Xiting Chen ◽  
Chao Qi ◽  
Wen Wang ◽  
Jianyin Miao ◽  
Hongxing Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Loop Heat Pipe ◽  
Heat Leak ◽  
Heat Transfer Limit
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