Numerical analysis of flow pattern map of R600a in a collector/evaporator of a solar-assisted heat pump

This research work presents a detailed description of the flow patterns maps generated in a horizontal pipe of the collector/evaporator of a direct-expansion solar-assisted heat pump, using R600a refrigerant as working fluid. The study was performed in a pipe with an internal diameter of 3.8 mm and a length of 1000 mm, mass velocities varying between 197.59 and 267.26 kg·m^−2·s−1 and heat flux between 72.83 and 488.27 W·m⁻²; during the experimental tests, an incident solar radiation between 0 and 652.9 W·m⁻² was present. The Wojtan, Ursenbacher and Thome correlation was considered for the analysis and the model used does not require iterative calculations; moreover, it carries out a detailed analysis of the different zones present along the pipe. The predom-inant zones in this study are intermittent, annular and dryout, found in the five tests, however, due to the working conditions in all tests with the exception of test A, mist and stratified-wavy flow were found.