CFD Predictions of Vertical Upflow Liquid Nitrogen Chilldown Experiments Uing Subgrid Nucleate Boiling Model

Cryogenic transfer line chilldown process is a complex two-phase flow problem involving various flow boiling regimes such as dispersed droplet film boiling, inverted annular film boiling, transition boiling and nucleate boiling. Due to presence of separated and dispersed flow regimes with phase change, the modeling of the chilldown problem is challenging. To address this, the present work attempts to simulate a vertical upflow liquid nitrogen chilldown process using a dispersed mixture model in a 2D axisymmetric numerical domain due to its capability to predict the film boiling regime quite accurately. For predictions in the transition and nucleate boiling regime, an user-defined function (UDF) is developed in Fluent which models the wall temperature based on the classical RPI wall heat flux partitioning model. The UDF was successfully implemented and the initial results are promising. Further, different closure relations in the UDF will be tested for its application for the specific problem.