A porous artery structure utilizing the concept of “phase separation and modulation” is proposed to enhance the critical heat flux of pool boiling. A series of experiments were conducted on a range of test articles in which multiple rectangular arteries were machined directly into the top surface of a 10.0 mm diameter copper rod. The arteries were then covered by a 2.0 mm thickness microporous copper plate through silver brazing. The pool wall was fabricated from transparent Pyrex glass to allow a visualization study, and water was used as the working fluid. Experimental results confirmed that the porous artery structure provided individual flow paths for the liquid supply and vapor venting, and avoided the detrimental effects of the liquid/vapor counter flow. As a result, a maximum heat flux of 610 W/cm2 over a heating area of 0.78 cm2 was achieved with no indication of dryout, prior to reaching the heater design temperature limit. Following the experimental tests, the mechanisms responsible for the boiling critical heat flux and performance enhancement of the porous artery structure were analyzed.

Abstract:Cryogenic loop heat pipe (CLHP) is one of the key components in the future space infrared 10 exploration system, which enables effective and efficient cryogenic heat transport over a long distance with a 11 flexible thermal link. To realize reliable and long life operation, a CLHP-based thermal control system with 12 redundancy design was proposed in this work, where two nitrogen-charged CLHPs were employed to provide 13 cryocooling at 80-100K. This study focused on the supercritical startup of the CLHPs with redundancy design, 14and an extensive experimental study under four possible working modes was conducted. Experimental results 15showed that with 2.5W applied to the secondary evaporator, each CLHP could realize the supercritical startup 16 successfully in the normal working mode; however, the required time differed a lot because the difference in the 17 transport line diameter significantly affected the cryocooling capacity to the primary evaporator. In the backup 18 conversion mode, instant switch of the two primary evaporators may cause an operation failure, and an auxiliary 19 operation of the secondary evaporator in advance was necessary to make the primary liquid line filled with liquid. 20In the malfunction conversion mode, the simulated infrared detector had to be first shut down, but the time needed 21 for the backup CLHP to realize the supercritical startup became obviously shorter than that in the normal working 22 mode, because the primary evaporator of the backup CLHP was always in a cryogenic state. In the dual operation 23 mode, the two CLHPs could realize the supercritical startup simultaneously, but a temperature oscillation 24 phenomenon was observed, which can be eliminated by increasing the heat load applied to the secondary 25 evaporator. 26

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 .