Speaker
Description
Liquid nitrogen (LN2) cooling is widely utilized in the cooling systems of superconducting devices and scientific instruments. During the cooling process, the boiling heat transfer mechanism plays a decisive role. When the solid surface temperature significantly exceeds the saturation temperature of the liquid nitrogen, the Leidenfrost effect occurs, forming a vapor film at the solid-liquid interface that drastically reduces heat transfer efficiency. Previous research has primarily focused on altering the boiling curve and enhancing the Critical Heat Flux (CHF) through surface roughness, micro-nano structures, or various material properties. Few studies have explored the impact of filling modes within the cooling system on disrupting the vapor film and improving boiling heat transfer.This study utilizes a self-developed liquid nitrogen cooling experimental platform to investigate four distinct filling and cooling modes designed for an Oxygen-Free High Conductivity (OFHC) copper test block. By examining the boiling curves under various filling modes, this thesis analyzes the underlying mechanisms influencing the wall superheat at the Leidenfrost point ($\Delta T_{LP}$) and the Critical Heat Flux ($\Delta T_{CHF}$). The results indicate that the bottom-filling method, characterized by impingement kinetic energy, effectively increases fluid disturbance and disrupts the vapor film encapsulation. This significantly reduces the duration of the Leidenfrost effect and facilitates an earlier transition into the high-efficiency nucleate boiling stage.
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