Progress Works of High and Super High Temperature Heat Pipes

Abstract

Heat pipe is a high efficiency heat transfer element, depends on the evaporation, condensation and circulation of inside working fluid. The good performance of a heat pipe is due to that the working fluid evaporation of latent heat is generally large, so there needs no much working fluid and the circulation flow rate is usually small, and the flow resistance is small, when a heat pipe works. The temperature and pressure inside a heat pipe are nearly at uniform levels through the evaporator to the condenser, so a heat pipe has a high heat transfer ability at smaller temperature difference. The heat pipe has many other advantages, such as the heat fluxes of evaporator and condenser can be changed easily by adjusting the heat transfer lengths and areas etc.. The working fluid of a high temperature heat pipe is generally alkali metals, and their evaporations of latent heat are very large, and the saturation pressure is smaller at high temperature, then the case strength is not a problem. The high and super high temperature heat pipe can work over 500°C, 1000°C, 1500°C or much higher. Sodium heat pipe can operate during 500~1100°C, and lithium heat pipe can work over 1200°C (Ma et al, 1983). The high and super high temperature heat pipes have wide applications in space thermal control, solar storage power plant, nuclear thermal control, the constant industry stoves etc.. Usually, the heat pipes between 500~1100°C use the sodium as working fluid, they are called as the high temperature heat pipe; while the heat pipes over 1200°C, utilize lithium as the working fluid, they are named as the super high temperature heat pipes. Commonly, 1000°C can be supposed to divide the boundary of high and super high temperature heat pipes. The first heat pipe in China was made in 1972, those stainless steel and sodium heat pipes realized the high temperature stove to make the semiconductor technology reliable. As shown in figure 1, the super high temperature heat pipe of W-Li by USA was tested in 1966 (Busse, 1992). The basic parameters and the startup process were given beside the figure, different temperature level tells the performances of the lithium heat pipe. For the nuclear reactor cooled by the high temperature heat pipes, the fuel bars and the high temperature heat pipes are designed to be coupled together. By the high temperature heat pipes, the heat from the pile core is transferred to the heat exchanger, the technology of high temperature thermal radiation is realized (Zhang et al, 2009). The high temperature heat pipes connect the nuclear power suppliers to the outside and transfer the large amount of