Effect of evaporator/condenser elevations on a loop heat pipe with non-condensable gas

Abstract In this work, the coupling effect of evaporator/condenser elevations and non-condensable gas (NCG) on the performance of a loop heat pipe (LHP) operating in gravitational field was investigated experimentally. Ammonia and nitrogen were selected as the working fluid of LHP and the simulated gas of NCG, respectively. The experiments were conducted at three kinds of evaporator/condenser elevations, namely zero elevation, adverse elevation and positive elevation. Experimental results show that NCG will cause an increase in operating temperature at any evaporator/condenser elevation, but this effect is relatively insignificant under adverse elevation and large heat loads. The temperature rise caused by NCG at adverse elevation is negatively correlated with heat load, which is similar to the situation of zero elevation. However, at favorable elevation, the temperature rise exhibits different characteristics in different LHP operation modes, i.e., positively correlated with heat load in gravity driven mode and negatively in capillarity-gravity co-driven mode. Furthermore, it is found that the presence of NCG and adverse elevation appears to inhibit the backflow during startup and improve startup stability. These results might have reference significance for the design and installation of the LHP for terrestrial applications.