Experimental study of heat pipe start-up characteristics and development of an enhanced model considering gas diffusion effects

Abstract

Heat pipe-based cooling reactors, offering passive heat transfer and modularity, are becoming the preferred type for micro-reactors. Alkali metals such as sodium, potassium and lithium are usually used as the working medium of the heat pipe, which is in a frozen state at normal atmospheric temperature. After heating the heat pipe, the working medium will melt and enter the gas chamber, and its flow state will undergo a transition from discontinuous flow to continuous flow. The start-up of the heat pipe affects the heat export and neutron physical characteristics of the heat pipe cooling reactor. Building a model of heat pipe can predict the start-up of heat pipe effectively, which can be helpful to study the start-up and safety analysis of heat pipe cooling reactor. In this paper, a heat pipe flat-front model considering the gas diffusion effect is established, and the gas temperature distribution characteristics in the non-continuous flow region are obtained through the start-up experiment of heat pipe. The calculated results of the flat-front model considering gas diffusion effect and the vertical flat-front model are compared with the experiment. The results show that the model in this paper can better describe the start-up of heat pipe. At the same time, the evaporation and condensation coefficient model based on temperature change is used to deal with the evaporation and condensation mass flow at the phase change interface of the heat pipe, which can better describe the temperature difference at the interface of the heat pipe.