Research on the Chilldown Characteristics and Influencing Factors of the Charge-Hold-Vent Method for Liquid Hydrogen Tank

In order to study the chilldown characteristics of the Charge-Hold-Vent （CHV） process for cryogenic propellant tanks under microgravity conditions, a liquid hydrogen （LH₂） tank was selected as the research object. A thermal balance numerical model covering the entire CHV chilldown process was established to calculate and analyze the temperature, pressure, and boiling heat transfer characteristics during chilldown. The effects of the filling mass flow rate, initial tank pressure and the minimum limit value of gas-wall temperature difference on the chilldown process and performance were investigated. The results show that: the prediction results of the present model for the tank pressure and wall temperature throughout the entire chilldown process show good agreement with the simulation data from the Honkonen model, demonstrating its capability to achieve accurate predictions of the CHV chilldown characteristics of the LH₂ tank; In the early stage of CHV chilldown, the chilldown capacity of cryogenic fluid is insufficiently utilized, and there is a greater risk of overpressure. The wall chilldown rate gradually decreases in the charge, hold and vent stages of the CHV cycle. During the initial phase of CHV tank chilldown, film boiling dominates the boiling heat transfer between the liquid and the wall, which later gradually transitions to being primarily characterized by transition boiling. Furthermore, the boiling heat transfer at the liquid-wall interface is concentrated in the charge stage of each CHV cycle. Throughout this stage, film boiling remains the predominant mode of heat transfer, accounting for an average time proportion of 91% over the entire chilldown process. Appropriately increasing the mass flow rate and the allowable gas-wall temperature difference can effectively improve the chilldown performance of CHV. When the mass flow rate is increased from 0.01 kg/s to 0.05 kg/s, the wall chilldown rate increases by 4.9 times, and the total chilldown consumption time is reduced by 6.9%. When the allowable gas-wall temperature difference is increased from 5 K to 20 K, the total chilldown consumption time is reduced by 38%, while the propellant consumption increases by only 10%.