RESEARCH ON HEAT EXCHANGE DURING BOILING OF REFRIGERANTS INSIDE PROFILED PIPES

The study presents a description of the experimental setup and the methodology for conducting experimental research on heat transfer and hydrodynamics during the boiling of refrigerant R22 inside a horizontal pipe with internal longitudinal profiling (fins) across a wide range of operating parameters. An analysis of the experimental results on heat transfer during transitional and turbulent flow regimes is provided. The results showed that at low mass velocities, the average heat transfer decreases due to the drying of the upper part of the pipe. With increasing mass velocity, the average heat transfer coefficient along the pipe length becomes almost independent of the vapor quality. However, at high mass velocities, the coefficient increases with rising vapor quality. This trend indicates improved wetting of the upper part of the pipe by the refrigerant and increased turbulence of the film. The obtained research results made it possible to identify the existing flow regimes during boiling of the refrigerant inside the finned pipe. The influence of heat flux, mass velocity, and vapor quality on heat transfer was analyzed, making the calculation results valuable for studying heat transfer during boiling of a two-phase refrigerant flow in pipes and channels. Based on the research, calculations of the hydrodynamic characteristics of the two-phase boiling flow of R22 refrigerant were performed and compared with a flow regime diagram developed for refrigerants. Several flow regimes were identified, namely: stratified, wavy, wavy with bridges, and annular flow. The flow calculations using formulas from the regime diagram showed practical agreement with visual observations during the study. In the future, to develop optimal variants of internal finning for evaporator heat exchange tubes with internal boiling of refrigerants, it is necessary to improve the pipe profiling technology and conduct a sufficient number of additional studies.