An Experimental Study of a Grooved Aluminum-Ammonia Heat Pipe: The Effect of Tilting and Non-uniform Heat Transfer on Thermal Behavior

Much research has been done on aluminum/Ammonia heat pipes in recent years due to their wide applications in aerospace. Although lab-scale research regularly focuses on uniform heat input, heat generation is actually non-uniform in reality. Also, the circumferential temperature distribution and heat transfer coefficient (HTC) have not been reported yet. In this study, an axial grooved heat pipe, while the condenser state is kept constant, was experimentally tested to investigate the uniform and non-uniform heat modes, and the effect of tilted angle along with horizontal configurations were also examined in terms of circumferential temperature distribution and HTCs. Yet, a detailed explanation of the measured results is provided. For the same total heat load, it was found that the decreasing heat mode showed superior performance; the HTC at the evaporator is 72 % and 35 % higher than the increasing mode (the least performance heat mode) at 77 and 165 W, respectively. Upon inclination, the HTC in the evaporator is relatively independent of inclination. However, a sharp difference occurs in the condenser section where the HTC of the tilted configuration is more than twice higher than that of the horizontal configuration.