Experimental investigation of startup behaviors of a dual compensation chamber loop heat pipe with insufficient fluid inventory

Guo

Lin

et al. 2015

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Abstract:In this paper, a steady-state mathematical model of a loop heat pipe (LHP) in gravity-assisted operation has been established based on two driving modes: gravity driven mode and capillarity-gravity co-driven mode. The modeling results show good agreement with experimental data, and the operating characteristics of the LHP under gravity-assisted attitude has been theoretically investigated. When the heat load applied to the evaporator is smaller than the transition heat load, the LHP is operating in the gravity driven mode, the working fluid in the vapor line is in the two-phase state due to the existence of additional liquid mass flow, and the operating temperature is obviously lower than that under horizontal or adverse elevation attitudes caused by reduced heat leak from the evaporator to the compensation chamber and enhanced cooling of the return liquid to the compensation chamber. In addition, the effect of positive elevation on the steady-state operating temperature and thermal conductance of the LHP is analyzed. This study contributes to the comprehensive understanding of the operating principle and characteristics and can guide the design of LHPs in terrestrial surroundings.

Section: Introductionmentioning

confidence: 99%

Steady-state modeling and analysis of a loop heat pipe under gravity-assisted operation

Guo

Lin

et al. 2015

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“…(4)(5)(6) show the temperature variations of a few characteristic points along the loop during the startup of the LHP when 0, 4×10 -5 and 8×10 -5 mol NCG were charged into the system, respectively. In Figs. (4-6), the startup heat load was 5W, the heat sink temperature was -15 , and the other operating conditions were kept all the same except the NCG inventory.…”

Section: Effect Of Ncg Inventorymentioning

confidence: 99%

“…Compared with conventional heat pipes, it possesses a variety of advantages such as high heat transfer capacity, long distance heat transport, and flexible thermal link, as well as strong anti-gravity capability. It has been traditionally adopted to tackle the thermal management problems of spacecraft, and successfully applied in many space missions [3][4][5][6][7]. However, a few unfavorable phenomena including abnormal operating temperature rise, difficult startup and operation failure were observed in several LHPs during on-orbit or ground operations [8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Effect of non-condensable gas on the startup of a loop heat pipe

Jiang

Miao

et al. 2017

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It is essential to tackle the startup issues prior to the broad application of loop heat pipes (LHPs) in both space and terrestrial surroundings. As non-condensable gas (NCG) is an important factor affecting the startup behavior, its effects on the startup performance of an ammonia-stainless steel LHP with and without preconditioning were experimentally investigated in this work. The temperature overshoot, liquid superheat and startup time were employed as the evaluation criteria. Nitrogen was selected to simulate the NCG, which was injected into the LHP at controllable amounts. Experimental results showed that with NCG presence in the LHP, the startup could only proceed in situation 1 with preconditioning, while it could proceed in situations 1, 3 or 4 without preconditioning. For the startup in situation 1, a larger NCG inventory led to much degraded startup performance, and a higher startup heat load could benefit the startup. For the startup in situation 3, i.e. the most difficult startup situation, NCG resulted in a very high temperature overshoot during the startup, which may even exceed the maximum allowable temperature to cause a startup failure. For the startup in situation 4, the existence of NCG in the vapor grooves could facilitate the evaporation of liquid there followed by a resultant very desirable startup.

“…With the rapid development of LHP technology for space applications, its application has been extended to terrestrial surroundings, such as in the thermal management of aircraft and submarines, and the cooling of high power-density electronic devices [10][11][12][13][14][15][16][17][18][19][20]. Since most of the heat sources or objects to be cooled have flat thermo-contact surfaces, LHPs with flat evaporators including both opposite liquid replenishment and longitudinal liquid replenishment have been developed and tested extensively.…”

Section: Introductionmentioning

confidence: 99%

Development of cryogenic loop heat pipes: A review and comparative analysis

Zhang

Lin

et al. 2015

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Loop heat pipes(LHP) are highly efficient two-phase heat transfer devices with the ability to transfer a large amount of heat over a long distance. Due to increasing demand of efficient cryocooling applications in both space and terrestrial surroundings, LHPs operating in cryogenic temperature range have been extensively investigated in recent years. This work provided a comprehensive review of state-of-art cryogenic loop heat pipes (CLHPs) Five different types of CLHP were categorized, and a comparative analysis between CLHPs and ambient LHPs and among different types of CLHPs were conducted. The operation and performance characteristics of different types of CLHPs were compared in terms of the system structure, supercritical startup, heat transport capacity and the effect of parasitic heat load.The parameters that affect the CLHP performance were analyzed and the optimization strategy was presented in order to progress their future development and applications .