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The evaporation-capillary pumping flow of the capillary wick and the working fluid system was experimentally studied in this paper. The capillary wick used in the experiment was fiber, and the working fluid contained water, ethanol and ethanol aqueous solution with water content of 25wt.%, 50wt.% and 75wt.%. The results show that the capillary pumping rate with ethanol as working fluid is between 210.0kg/m2sand 1812.5kg/m2swhen there is no heat load added. When the heating flux is 10616W/m2, 15924W/m2, 21231W/m2, 26539W/m2, the evaporation-capillary pumping rate is102.5kg/m2s, 247.5kg/m2s, 390.0kg/m2s and 530.0kg/m2s, respectively. The higher the heat load power, the greater the evaporation-capillary pumping rate and the higher the final stable temperature. With the increase of heat load power, the time required to reach temperature balance becomes shorter and the temperature fluctuations after reaching temperature equilibrium become larger. The obvious temperature fluctuation has occurred when the heat flux is 26539W/m2. The evaporation capillary pumping rate corresponding to the four different concentrations of ethanol solution in the experiment gradually decreases with the increase of water content. The temperature change processes and the final equilibrium temperatures of the four working fluids are nearly the same. The differences in boiling point of the working fluids do not have much influence here.

The capillary wick is the core component of the heat pipe. In reality, a single capillary wick is often difficult to meet the heat pipe's requirements for capillary pumping and permeability at the same time, so composite capillary wicks have emerged. This paper takes fiber felt as the main object to study the composite pore capillary wick. By setting different pore gradients to fiber felt and conducting capillary pumping performance experiments and evaporationcapillary pumping performance tests, the research summarizes the pumping effect of different gradient pores, and makes comparison with the pumping effect of single pore structure. The research results show that whether in the capillary pumping experiment or the evaporation-capillary pumping experiment, the composite pore sample with decreasing pore size always has better performance than the uniform pore sample and the pore increasing test. Under the best condition, the capillary pumping performance of the sample with decreasing pore size along the pumping direction can be improved by 47.81% compared with the sample without gradient. Moreover, with the increase in the number of pore diameter change segments, the capillary pumping performance is also improved. For example, when the heating power is 18 W, the improvement of the capillary pumping performance of the sample with four, three, and two decreasing segments along the pumping direction compared with the sample without gradient is 12.04%, 9.16%, and 7.07%, respectively. This property is very useful for the future development of capillary wick.

High-temperature heat pipes have broad application prospects in terms of thermal protection of hypersonic aircraft and cooling of space nuclear reactors. In this paper, a high-temperature heat pipe heat transfer performance experimental platform is built to study the heat transfer performance of high-temperature heat pipes at different inclination angles. A heat transfer network model of high-temperature heat pipes containing non-condensable gas is established to analyze the influence of non-condensable gas. The results show that as the inclination angle of the heat pipe increases, the start-up time of the heat pipe does not change. The heat transfer performance is best when the inclination angle is 30?. High-temperature heat pipes containing non-condensable gas will reduce the effective length of the high-temperature heat pipe, increase the thermal resistance, and reduce the heat transfer performance. The high-temperature heat pipe analysis model with non-condensable gas established in this paper can be used to predict the heat transfer performance of high-temperature heat pipes containing non-condensable gas.