Study on Liquid Nitrogen Two-Phase Self-Driven Circulation System Using for Heat Sink of Thermal Contact Resistance Experimental Equipment

This study presents a self-driven liquid nitrogen (LN₂) two-phase loop as a heat sink to measure thermal contact resistance between aerospace materials at cryogenic temperatures. A steady-state 1-D model based on homogeneous flow theory is developed to characterize the system, examining the effects of pipe diameter (10-30 mm), reservoir height (1-2 m), and heat sink elevation under heat fluxes of 5-240 kW/m^2. The system's applicability for TCR cooling is demonstrated. A 3-D numerical model of the heat sink, using VOF, Lee phase-change, and SST kω models, analyzes the influence of heater placement and inlet/outlet heights on heat transfer and temperature uniformity at 100 kW/m^2. Results show that increasing reservoir height or diameter, or lowering sink elevation, raises mass flow rate by 23.4-200% and reduces vapor quality by 70-90%. Placing the heater above the sink improves temperature uniformity and yields higher surface temperature with lower HTC. Switching heater and sink positions increases HTC by 6.7%, lowers average temperature, and worsens uniformity. Raising inlet/outlet ports by 7 mm enhances HTC by 22.9% and mixture volume flow by 3.8%, further reducing average temperature and impairing uniformity.