Experimental study on frozen startup and heat transfer characteristics of a cesium heat pipe under horizontal state

In order to meet the requirements of thermostat control in the application of medium temperature calibrations, a cesium heat pipe is fabricated and it is performance under the horizontal state is determined in this work. The effects of heating powers and heating modes on frozen startup and heat transfer characteristics are experimentally examined. Increasing the heating power from 772.5 to 940.9 W, the cesium heat pipe shows the best temperature uniformity with an operating temperature of 413 degrees C and the minimum total thermal resistance of 0.042 K/W at 827.5 W, the shortest frozen startup time of 1175 s at 940.9 W. However, overheating of the cesium heat pipe happens when the heating power is increased to 980.7 W which triggers a capillary limit phenomenon, leads deteriorations of temperature uniformity and heat transfer performance. In addition, the modulated heating mode introduces a better heat transfer performance of heat pipe. For cases with the constant heating mode, the cesium heat pipe shows the effective length of the heat pipe is about 510 mm which is 85% of the total length. Comparatively, the modulated heating mode can avoid the capillary limit phenomenon and improve the operating temperature from 413 to 500 degrees C as the heating power is stepped increased to 1300.9 W. With the increasing of heating power, the vapor flow is drove farther and the effective length of the heat pipe can reach 550 mm (92% of the total length). Simultaneously, the temperature fluctuation at the end of the condenser (p(8)) is depressed for the thickness increasing of condensate film. (C) 2021 Elsevier Ltd. All rights reserved.