An Investigation of Void Fraction in the Stratified/Annular Flow Regions in Smooth, Horizontal Tubes

Abstract

Refrigerants R134a and R410A have been used for void fraction measurements in smooth horizontal tubes with diameters between 4mm and 7mm. Quality and mass flux were varied from 5% to 90% and 75 kglm2-s to 700 kglm2-s, respectively. Two test loops, one for condensing flows at 35C and the other for evaporating flows at 5C, were used in the investigation. Results show that near the transition from annular to stratified flow void fraction changed from viscousinertial dependence to gravitational-inertial dominated dependence. An important feature observed is the annular flow region's relative insensitivity to mass flux while the border region between annular and stratified flows is characterized by strong mass flux dependence.Air Conditioning and Refrigeration Project 7