Effect of evaporator tilt on a loop heat pipe with non-condensable gas

•Coupling effect of evaporator tilt and non-condensable gas is studied.•The smallest temperature rise is observed under adverse tilt.•Mechanism of NCG effect under different evaporator tilts is analyzed. The coupling effect of non-condensable gas (NCG) and evaporator tilts on the steady state operation of a loop heat pipe (LHP) was investigated both experimentally and theoretically in this work. Nitrogen was injected quantitatively into an ammonia-stainless steel LHP to simulate NCG, and the steady state characteristics of the LHP were studied under three typical evaporator tilts. According to the experimental results, the main conclusions below can be drawn. (1) The temperature is the highest under adverse tilt and the lowest under favorable tilt no matter whether there is NCG in LHP. (2) The existence of NCG could cause the increase of temperature under all three typical evaporator tilts, but the temperature increment caused by NCG seems to be relatively small under adverse tilt. (3) The increments of the temperature caused by NCG display different patterns under different tilts. Theoretical analysis was conducted to explain the results: the temperature under the coupling effect of NCG and evaporator tilt was determined by the energy balance between the heat leak from evaporator to compensation chamber and the cooling capacity of returning subcooled liquid. With the increase of heat load, the augmentation of heat leak caused by NCG and the enhancement of subcooled liquid cooling effect were incongruent. The coupling effect of NCG and evaporator tilts should be considered in the terrestrial application of LHP.