Adiabatic Developing Two-Phase Refrigerant Flow in Manifolds of Heat Exchangers

This research is focused on the experimental analysis and numerical simulation of adiabatic developing two-phase refrigerant flow in manifolds including the inlet tube after the expansion device. The two-phase flow development in the tube after the expansion valve significantly affects distribution in the manifold. Visualized flow structure is divided into three regions. The transitions among these regions are based on the phase separation status. Relationships between the lengths of those regions and flow characteristics are developed. The liquid phase is assumed to be continuous phase at high quality conditions so that the Eulerian model of Eulerian-Eulerian approach is chosen for the numerical simulation using FLUENT 6. Better prediction is achieved for high inlet qualities. Two-phase flow regimes in the manifold are mapped for the first time. Indicators of distribution uniformity are plotted in the maps. The maps are presented in two forms: non-dimensional Froude number coordinates and mass flux-quality coordinates. Effect of the two-phase flow in the inlet tube (after the expansion valve) on distribution in the manifold is explored. Eulerian model in FLUENT 6 is the most appropriate for the conditions studied in the manifold. Simulation results for the same geometry of the manifold and the same operating conditions as used in experiments demonstrate very good prediction of flow field and reasonable prediction of liquid distribution among branches. Experiments were performed using R134a in a facility designed for visualization (PDPA, photo) and twophase flow distribution measurements for various inlet tube and flow characteristics. For most experiments, a transparent manifold in simplified geometry was used. Further experimental analysis is done for a manifold of a real plate evaporator. Atomization nozzles are first time applied as the expansion devices at the inlet of the manifold in order to generate mist homogenous flow, which in this study is proven to contribute to uniform distribution.Air Conditioning and Refrigeration Project 12