Heat Exchange Inside a Horizontal Pipe at the Initial Section with Complete Condensation of R142b Freon Vapor

Abstract

Heat exchange during condensation of freons has been studied quite well; however, various flow regimes of the steam-condensate mixture may arise during condensation inside heat-exchange pipes. There is a large amount of experimental data on the condensation of freons inside pipes with different internal diameters. However, the results obtained by different authors are contradictory, and experimental dependencies can give a high error in the event of a discrepancy between the calculated and actual flow regimes of the steam-condensate mixture. Due to the difficulty of identifying these modes for each such case, reliable recommendations for the calculation and design of heat exchangers must be based on experimental data. In order to obtain such materials, an experimental stand was developed and manufactured, allowing the study of condensation processes of various working fluids in a horizontal cooled tube. The working section of the stand was a copper pipe with an external diameter of 32 mm and a wall thickness of 2 mm, built into an external steel pipe with a diameter of 45 × 3 mm with an annular gap of 3.5 mm. Five chromel-copel thermocouples were installed in the gap to measure the water temperature; they were led to the measuring instruments through the wall of the outer pipe. Thermocouples were also installed in the copper pipe wall. The stand’s thermocouples were precalibrated, and the freon and cooling water consumption was determined by the differences on the flow diaphragms with an error not exceeding 1.5%. The temperatures of cooling water and condensing freon R142b along the length of the heat-exchange pipe were obtained for some flow regimes with different parameters of the working fluid at the pipe inlet. A sharp decrease in the local heat-transfer coefficient along the length of the heat-exchange pipe during complete condensation is shown and is especially significant at its inlet section. The obtained data will be used in the design of heat exchangers with condensation of R142b freon in horizontal pipes.