Maturot Suchatawat. A Numerical Model of Refrigerant Flowing Through Capillary Tubes. Master's Degree(Mechanical Engineering). มหาวิทยาลัยเทคโนโลยีพระจอมเกล้าธนบุรี. : King Mongkut's University of Technology Thonburi, 2544.
A Numerical Model of Refrigerant Flowing Through Capillary Tubes
Abstract:
Capillary tubes, extensively used as an expansion device in small refrigerating and air conditioning systems, are theoretically investigated in this present study. A numerical model is developed for predicting the flow characteristics of refrigerant flowing through capillary tubes. The flow is divided into three regions: subcooled liquid region, metastable liquid region, and two-phase region. For the subcooled liquid region, the subcooled liquid length can be determined from the conservation of momentum. In the liquid metastable region, the correlations of Chen et al. and Lackme are optional. For the two-phase flow region, the annular two-phase flow pattern is assumed. The governing equations are set up based on the conservation of mass, momentum and energy for liquid and vapor phases. In this study, the correlations of two-phase multiplier and slip ratio in the model are allowed to vary. A derived set of differential equations of two-phase flow is solved by using the RK4 method simultaneously. The calculation is terminated when choked flow is reached. The model is validated by comparing it with the experimental data of Li et al. and Mikol for R12. For R134a, the model results are plotted in comparison with the measured data of Melo et nl. and Wijaya. In particular, the pressure variation along the capillary tube as well as the mass flow rate at various capillary tube lengths are considered. It is found that the present flow model with the Chen et al, correlation and other suitable parameters can be used for predicting the flow characteristics of refrigerant flowing through a capillary tube. The present numerical model predicts the capillary tube length with maximum deviations of 6.83 and 17.70% for R12 and R134a, respectively. The maximum error for the prediction of the R134a mass flow rate is 15.71%.