Experimental study on startup performance of sodium heat pipe with high ratio of length-to-diameter under different coolant flow rates

Abstract

Sodium heat pipes, characterized by a high length-to-diameter ratio, are commonly employed in various heat pipe-cooled nuclear reactors. In these reactors, sodium serves as the working medium, remaining solid at room temperature. The startup process of such heat pipes is complex, involving phenomena such as the melting of the solid sodium and the establishment of a continuous vapor flow. The effectiveness of these heat pipes relies heavily on their startup behavior from a frozen state. To assess the startup performance of sodium heat pipes, an experimental study was conducted on a 2.5-m-long arterial sodium heat pipe, using high-temperature compressed air as the coolant. The investigation examined the impact of different air flow rates on startup performance. The findings revealed that high-temperature compressed air significantly improved the startup performance of the 2.5-m arterial sodium heat pipe under all three airflow conditions. Notably, during the startup process, the heat absorbed in the evaporation section is relatively minimal, making it beneficial to reduce the cooling capacity of the coolant to improve the heat pipe's startup performance. Additionally, when the air flow rate is lowered, the heat pipe requires less startup power and achieves a quicker startup time. By analyzing the data, it is revealed that the evaporator exit temperature increases with the reduction of air flow rate, which can avoid the sonic limit.