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

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

Experimental Investigation of Void Fraction During Refrigerant Condensation in Horizontal Tubes

This research on the condenser loop involves the experimental detennination of void fractions for both R134a and R410A in various sizes and types of horizontally mounted copper tubes. The test sections are a 6.04 mm Ld. smooth tube, an 8.89 mm Ld. axially grooved tube, and an 8.93 mm Ld. helically grooved (180 helix angle) tube. Refrigerant R134a, a primary replacement for R12, is being tested because it is used extensively. R410A is being tested because it is being considered as one of the replacement refrigerants for R22. The test matrix for the condenser loop covers a large range of mass fluxes and qualities. The test section inlet temperature is always set to 35 ??C. The different inlet qualities are 10%, 30%, and 50%. The four mass fluxes which are tested are 75,150,300 and 450 kglm2-s. There are many different existing correlations for void fraction; however, they exhibit little consistency for our refrigerant condenser conditions. For this reason, new, more accurate correlations were developed from the experimental data.Air Conditioning and Refrigeration Project 7

An Investigation of Refrigerant Void Fraction in Horizontal, Microfin Tubes

A series of evaporation and condensation experiments have been performed on horizontal microfin tubes with refrigerants R134a and R410A. Mass flux varied from 75 kg/m2-s to 700 kglm2 -s and average test section quality varied from 5 percent to 80 percent. Zero degree (axial grooving) and 18 degree helix micro fin tube configurations have been examined in both condensation and evaporation. Four tubes were examined (7.3mm and 8.9mm diameters with axial and 18 degree helix angle microfins). Evaporation and adiabatic conditions in microfin tubes generally show similar void fraction trends found in smooth tubes. Condensation void fraction results tend to show a reduction in void fraction relative to smooth tube results, possibly indicating liquid filling of groove regions.Air Conditioning and Refrigeration Project 7