COMPUTATIONAL SIMULATION OF THE OIL-R134A MIXTURE TWO-PHASE FLOW WITH FOAM FORMATION IN A CIRCULAR CROSS SECTION TUBE

摘要

This work presents a numerical study of the two-phase flow of a mixture composed by oil Freol alpha10 and refrigerant R134a with high oil content, which is a problem usually encountered in refrigeration and air conditioning compressors. A straight horizontal tube was chosen to accomplish the simulation because of the availability of experimental data to validate the model results. Due to the pressure drop initially caused by the viscous friction, the refrigerant solubility in the oil reduces and the refrigerant evaporates from the liquid mixture. In this type of flow the bubble formation can be so large that foam is formed as the void fraction reaches high values. In the present simulations the two-phase flow is divided in two regions: in the first region the flow is treated as a conventional two-phase flow, with small quantity of gas refrigerant bubbles; in the second region the flow is treated as a foam flow, with high void fraction, behaving as a non-newtonian fluid. Numerical integration of the momentum and mass and energy conservation equations is performed for several inlet flow conditions and the results for longitudinal pressure and temperature profiles are compared with experimental data. It was verified that the model predicted well the experimental results. In addition, the model is used to obtain other important variables of two-phase flows as quality, void fraction, and density.