A Study of Refrigerant Void Fraction and Pressure Drop in Return Bends and Development of a New Two-Phase Experimental Apparatus

摘要

Void fractions and pressure drops were measured for R134a and R410A for areturn bend test section consisting of three return bends of tube diameter 8.28 mm(0.326") and center-to-center distances of 25.4 mm (1.00"). The test matrix includedmass fluxes from 65 kglm2 s to 440 kglm2 s (48 - 324 klbm/ft2-hr) and test sectionqualities from 5% to 70% with an inlet temperature of 5??C (41??F). Three orientationsconsisting of vertically upward, horizontal, and vertically downward were tested.Negligible effects on void fraction were measured relative to straight tubes.Pressure drop data showed some trends due to changes in quality, mass flux, refrigerant,and orientation. The pressure drop increased with both quality and mass flux. The lowerpressure refrigerant had a larger pressure drop. Downflow to upflow orientations resultedin increasing pressure drop.A new apparatus for studies in evaporation was constructed at the University ofIllinois at Urbana-Champaign. Details on system structure, components, and operationare given.