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

Abstract

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.

Effect of Non-Condensable Gasses on the Performance of a Vacuum Thermochemical Reactor

“…As a result the condensation rate drops and the performance of the system decrease significantly. This reduction of performance is extensively reported in the literature [6][7][8][9][10][11][12][13][14][15][16][17] and this is also recognized as a challenge of TCM systems under vacuum conditions [5,[18][19][20][21][22][23].…”

Experimental investigation on transient characteristics of a dual compensation chamber loop heat pipe subjected to acceleration forces

“…The advantages of the flexibility, temperature control and heat transport capability can make LHPs extend to the applications of terrestrial surroundings, aircraft, submarine and high-speed railway [3][4][5][6]. Over the past two decades, a large number of experimental, theoretical and numerical simulation studies on LHPs have been reported to provide useful data to comprehensively understand the physical mechanisms under various operating conditions and to optimize their design [7][8][9][10].…”

Mathematical Modeling and Testing of a Loop Heat Pipe Using a Two – Way Pressure Regulating Valve

“…Nevertheless, the start-up process is complex and heavily depends on the compensation chamber and evaporator construction, initial conditions inside the evaporator, and the operation immediately prior to start up [5]. if the vapour grooves already contain vapour, evaporation will occur once power is applied [5,7]. Secondly, if the evaporator core is filled with liquid, then there is minimum heat transfer from the evaporator to the CC; nonetheless, if vapour is present in the core, heat leak through the primary wick to the CC is increased as discussed in Section 2.3.1.…”

“…In addition to the distribution of fluid within the evaporator grooves and evaporator core, the presence of non-condensable gas (NCG) has shown to both degrade the performance of LHPs and affect start-up [7]. Although NCG can be found in almost every part of the system loop, it tends to accumulate in the CC which causes a modification of the system pressure.…”

“…4) and then attain superheat to initiate nucleate boiling. This results in a direct increase of the temperature overshoot during start-up, and a delayed onset of nucleate boiling in the vapour grooves, causing an increased start time accordingly [7].…”