Void fractions for condensing refrigerant flow in small channels. Part II: Void fraction measurement and modeling

In this paper, (Part II of a two-part study), an investigation of void fractions for condensing flows of refrigerant R-134a in minichannels is presented. Custom digital image processing techniques were used to quantitatively analyze these flows in transparent minchannel geometries (square, rectangular and circular) with 2 < Dh < 4.91 mm. A total of 140 void fraction values in the intermittent flow regime (slug and plug flow), the wavy flow regime, and an intermittent-wavy overlap region were measured. A new model was developed based on these measured values and predicts void fraction better than correlations from the literature.

► Void fractions for condensation of refrigerant R-134a in minichannels investigated.
► Image processing is used to analyze condensation for 2 ≤ Dh ≤ 4.91 mm.
► Void fractions for intermittent and wavy flows, and an overlap region are obtained.
► A new model for void fractions for condensing flows in minichannels is developed.