Numerical analysis of the two-phase heat transfer in the heat exchanger of a mixed refrigerant Joule–Thomson cryocooler

• Two-phase heat transfer in the heat exchanger of an MR J–T cryocooler is simulated.
• One-dimensional steady state model developed for numerical simulation.
• Numerical model validated with experimental data for nitrogen–hydrocarbons mixtures.

The recuperative heat exchanger is the most critical component of a mixed refrigerant Joule–Thomson cryocooler. The heat transfer process in such a heat exchanger takes place under two-phase conditions due to simultaneous boiling of the cold stream and condensation of the hot stream. This results in higher heat transfer coefficients as compared to single phase heat exchange. Moreover, depending on the composition of non-azeotropic mixtures, the boiling and condensation take place over a range of temperatures. In this work, the two-phase heat transfer in the recuperative heat exchanger of a mixed refrigerant Joule–Thomson cryocooler is studied. A numerical model is developed to simulate the heat transfer in a helically coiled tube-in-tube heat exchanger with nitrogen–hydrocarbons mixtures. The heat transfer coefficients for the two-phase flow under boiling and condensation are evaluated with the correlations available in the literature. The physical properties of the mixtures are evaluated at local conditions of temperature and pressure. The numerical results obtained with the developed model are compared with the experimental data reported in the literature. Additionally, the model predictions are also compared with new experimental data reported in the present work.