Microchannel condenser design for refrigerators

Microchannel heat exchangers are advantageous designs to meet the high heat transfer requirements of small volumes in industrial applications. The utilizing of compact heat exchangers such as microchannel heat exchangers in cooling applications makes it inevitable that phase changes occur in small volumes. In this thesis, a mathematical simulation model for louvered fin microchannel condenser designs has been presented. The proposed mathematical model has been designed to estimate the heat capacity and outlet temperature of the microchannel condenser based on the refrigerators operating conditions that work with refrigerant R600a. In the model based on the finite volume method, the calculations are made with an iterative scheme using the efficiency-NTU method. An experimental study has been conducted to validate the proposed model and 16 different tests have been performed fort he validation. It is concluded in the validation effort that the model is able to predict the outlet temperature with a ± 2% mean absolute error (MAE) and the heat transfer capacity with a ± 1% MAE. The mathematical model developed as a design tool requires pressure loss and heat transfer coefficient for the calculation. There is no sufficient information on heat transfer coefficient and pressure drop of the condensation flow characteristics of R600a inside the microchannel. To determine the heat transfer coefficient and flow characteristics, condensation of R600a inside microchannel has been simulated with Ansys FLUENT which is one of the Computational Fluid Dynamics (CFD) softwares. In the steady-state simulations, the Volume of Fluid (VOF) method has been used for modeling of two-phase flow and Lee model has been used to simulate the mass transfer of phase change at the interface. A new heat transfer coefficient correlation has been developed for the condensation flow of R600a inside microchannel based on CFD simulations. Theoretical designs have been performed by decreasing the microchannel dimensions and the thermal performances of the designs have been assessed comparatively with using proposed mathematical model.