Discretized enthalpy method for analysis of two-phase flow in heat exchangers using fame-mll and ammonia working fluids

This paper presents the analysis of a two-phase heat exchanger using Fatty Acid Methyl Ester Methyl Linoleate (FAME-MLL) bio-fuel and Ammonia (NH3) working fluids for use in Venus lander in-situ mission active thermal control applications. The paper presents the methodology and for analyzing the heat exchangers used in a cascade refrigeration cycle to supply active cooling to the electronics payload of a Venus lander mission. A discretized enthalpy formulation of the energy equation is used to develop a model of the heat exchanger in MATLAB using the NIST REFPROP database to model the thermophysical properties of the working fluids. Results for the architecture of a series configured arrangement of a single-phase and a two-phase heat exchanger are presented. Convection heat transfer correlations for single phase, boiling and condensation regimes are incorporated into the model. The MATLAB model is used to predict the temperature, quality and heat transfer coefficient profile variations along the distance of the heat exchanger. A numerical convergence study of the MATLAB model is presented herein.