Characterizing Cryogenic Chilldown and Boil-Off: A Liquid Nitrogen Experimental Study

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Abstract
Cryogenic chilldown and boil-off directly impact the efficiency, safety and operational margins of any system that handles cryogenic fluids, including propulsion, storage and transfer applications. These processes arise from the interaction between wall heat transfer, boiling regimes, and vapor-space dynamics, and are strongly influenced by geometry, initial thermal conditions, and operating procedures. As a result, well-resolved experimental data remain essential for the development and validation of transient two-phase models. This work presents an experimental investigation of liquid nitrogen chilldown and boil-off in a small-scale test facility composed of two cryogenic vessels, a feed tank and a return tank, connected by a horizontal transfer line. The setup is instrumented to measure temperature evolution, pressure and liquid levels, under controlled valve operations. Wall heat fluxes and mass flow rates are derived from these measurements through energy and mass balances. The influence of initial thermal conditions is examined by comparing chilldown into a pre-cooled transfer line with that of an ambient-temperature configuration under unpressurised flow. To assess the role of the driving mechanism, both unpressurised and pressurised flow transfer conditions are then considered for an ambient temperature transfer line and return tank. Boil-off behaviour in the feed tank is characterized at different liquid fill levels and further investigated through controlled heating using an immersed electrical heater. The resulting dataset offers experimental observations useful for studying chilldown transients, two-phase flow, and tank boil-off.

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