To investigate the effect of nano-fluid and dispersant on the performance of gravity heat pipe,the starting performance( start-up time and start temperature) and the heat transfer performance( tube wall temperature distribution at stable state and total thermal resistance) of different heat pipes were determined separately. The results show that the addition and the physical properties of nanoparticles have effects on the start-up time of heat pipe. The start-up time of heat pipe with nano-fluid is 1. 3 ~ 3...