Numerical Simulation of Refrigerant Flow and Heat Transfer in A Non-Adiabatic Capillary Tube in Refrigerator
A numerical simulation model is developed to design an efficient Non-Adiabatic Capillary Tube (NACT) heat exchanger to obtain specific vapor quality at its outlet. Refrigerant flow and heat transfer inside heat exchanger has been modeled through a set of governing equation by conserving mass, momentum and energy. The model analyses three discrete regions of capillary tube namely i) adiabatic inlet region, ii) heat exchanger region and iii) adiabatic exit region. Governing physical equations are considered in these regions based on single-phase or two-phase flow inside capillary tube. The effect of metastability has been incorporated in the model. Finite difference method is used for solution of governing equations to obtain pressure, temperature and vapor volume fraction in capillary tube and temperature of suction line. The model is validated with experimental results available in the literature. Parametric analysis has been performed to study the effect of diameter of capillary tube and the degree of sub-cooling on performance parameters. Concentric and lateral capillary tube heat exchanger configurations are compared. It has been found that lateral heat exchanger configuration gives better heat transfer performance.
Keywords - Refrigeration, Capillary Tube Heat Exchanger, Nact, Metastability