An Experimental Study on a Sodium Loop-type Heat Pipe for Thermal Transport from a High-temperature Solar Receiver

AbstractA loop-type heat pipe was fabricated and tested to transport high-temperature thermal energy from a solar receiver in a CSP application. The purpose of the heat pipe in this study was to transport an 800-W thermal load at 1000K to a specific energy conversion device 0.5 m in distance from the solar receiver. The container wall and transport lines of the loop-type heat pipe were made of stainless steel 304, and the working fluid was sodium. The evaporator and condenser were disk-type containers with diameters of 122 and 216mm, respectively, though bothhad a height of 20mm. The diameters of the vapor and liquid lines were 12.7 and 9.53mm, respectively. The total length of the loop was approximately 1.4 m. A pillar structure with a diameter of 43mm and height of 114mm was installedin the center region of the condenser to interface with an AMTEC device that had a unique geometry. It was desired that the upper surface of the condenser as well as the whole outer surface of the pillar would have temperatures as close as possible during heat discharge. As one of the unique features in this study, the liquid line was located close to the vapor line for a preheating effect to reduce the frozen-startup time. The influence of the fill charge ratio of the working fluid as well as operating conditions such as the thermal load and the cooling condition in the condenser were analyzed with respect to the performance indices of the heat pipe, including the effective thermal conductance, the thermal resistance, and the maximum temperature difference. The optimum fill charge ratio of the heat pipe was 32% based on the evaporator volume