A Transient Model of Sodium Heat Pipe With Phase Change Temperature Difference

The heat pipe is the essential component in the heat pipe cooled reactor, it conducts heat through the phase change of the working medium and the circulating flow of gas and liquid. One end of the heat pipe is inserted into the reactor as the evaporation section, while the other end serves as the condensation section connecting to the thermoelectric conversion system. Its heat transfer capacity and temperature distribution under a steady state affect the safety, core temperature and energy conversion efficiency of the heat pipe cooled reactor system. Predicting the heat transfer process and steady-state temperature distribution of the heat pipe is helpful to learn about the heat transfer mechanism inside the heat pipe and key factors affecting its performance. It is also helpful to predict the operating characteristics of the heat pipe cooled reactor system and improve the performance of the heat pipe. The heat pipe is generally considered to be a heat transfer element with good isothermal properties. Past studies, however, proved the significant quantity of its phase-change thermal resistance, resulting in a temperature difference at the gas-liquid interface of the heat pipe that affects the evaporation and condensation. Studies on the relationship between the temperature difference, the working temperature, and heat transfer power of the heat pipe are conductive to building a heat pipe model, to predict the temperature distribution of the heat pipe in a steady state in a much more accurate manner. This paper offered a heat pipe model that applies the temperature difference of the phase change interface to calculate the evaporation and condensation. Meanwhile, a 1-meter-long sodium heat pipe was adopted to carry out steady-state heat transfer experiments. Measured and computed the temperature difference of the phase change interface of the heat pipe under varying power and temperature and conducted the relational equation as the input of the heat pipe model. The model predicted the steady-state temperature distribution of the sodium heat pipe and the transient when the power changes after the steam reach the continuous flow stage and compared the calculated outcomes with the experimental values. The transient error was less than 20K, and the steady-state error was less than 12K. The results show that the temperature difference at the phase change interface has a great influence on the steady-state temperature distribution of the heat pipe, which changes with the operating temperature. However, the physical and geometric factors affecting the temperature difference need to be further studied, to reduce the temperature difference as much as possible and improve the energy conversion efficiency of the heat pipe reactor system in the future.