Numerical Simulations of Condensation heat transfer of R134a refrigerant in a smooth horizontal tube

Multiphase flow occurs in almost all HVAC and refrigeration systems. In this work, numerical simulations of condensation heat transfer phenomenon of R134a refrigerant inside smooth horizontal tube is carried out in order to better visualize the flow behavior and analyze heat transfer characteristics of R134a refrigerant. For multiphase flow analysis of R134a refrigerant, k-omega shear stress transport (SST) turbulence model is used which is well suited for simulating flows in the viscous sub-layer. For predicting and analyzing the heat transfer characteristics, Heat and mass transfer model(Lee Evaporation-Condensation Model) is used for internal flow condensation to occur. Convective heat transfer coefficient is determined throughout the tube using surface integral method which matched with the convective heat transfer coefficient obtained using experimental data. Volume fractions of both the liquid and vapor phases are obtained at both the symmetrical and cross-sectional planes which indicated that homogeneous condensationoccurred resulting in mist flow which later on changed to stratified and stratified wavy flow. The temperature distribution obtained for the two phase flow (liquid and vapor) showed that the refrigerant was initially in dry saturated statewhich then condensed into two phase mixture (liquid and vapor) as the condensation process proceeds downstream. The results indicate that the k-omega (shear stress transport) turbulence model predicts the multiphase flow characteristics better than the k-epsilon turbulence model.