Prediction of two-phase heat transfer in a 4-pass evaporator bundle using single tube experimental data

Two-phase heat transfer and pressure drop on the tube-side of a 4-pass R-22 microfin tube bundle is modeled using experimental data on a single tube. The modeled direct expansion bundle has water flow on the shell side. The modeled bundle is divided into small axial incremental lengths along the refrigerant path. Heat transfer and pressure drop calculations are done simultaneously. The evaporation heat transfer coefficients and pressure drop are calculated using the single tube data taken at flow conditions characterizing the tube bundle. The water side heat transfer coefficient was determined by a Wilson Plot calibration for the shell side of the tube bundle. The bundle predictions are compared with the experimental data on the modeled tube bundle. The model predicted the heat transfer for two tube bundles having different microfin tubes with less than 6% error. The simulations showed that ±5% variation from the assumed 85% dry-out vapor quality the bundle heat load varied ±3.5%. Flow mal-distribution analysis showed that moderate flow mal-distribution does not cause significant performance loss. A parametric analysis was performed to define the optimum number of tubes in each pass.