Development of a Gradient Based Phase Change CFD Model and Validation against Zero Boil-Off Tank Experiment

A two-phase CFD model is presented in this paper in which the phase-change rate is calculated from temperature gradients at the liquid–vapor interface. The model employs a Volume-of-Fluid (VOF) formulation to represent the phase boundary and to capture the associated interfacial heat, mass, and momentum transfer between the liquid and vapor regions. The CFD model is first validated against a benchmark vapor-heating tank self-pressurization case in 1g, and subsequently against a subcooled jet-mixing Zero Boil-Off Tank (ZBOT) experiment conducted on the International Space Station (ISS) in 2017. Predicted tank pressure, fluid temperatures and ullage position are compared with experimental data to assess the model’s accuracy. In addition, results from this model are compared with those obtained using an alternative approach that employs Schrage’s relation to compute the phase-change rate.