Interfacial measurements in stratified types of flow. Part I: New optical measurement technique and dry angle measurements

The development of a new non-intrusive computerized image analysis and optical observation method for accurately detecting the vapor–liquid interface in stratified two-phase flows is presented. This technique is applied to a round horizontal sight glass tube using a monochromatic laser sheet for observing two-phase flow patterns and for measuring cross-sectional dry angles and void fractions in these types of flow. The cross-sectional image observed externally is distorted by refraction and is thus reconstructed by computer. From this image, the shape of the vapor–liquid interface is detected and the dry angle and void fraction are accurately determinable over a wide range of conditions for a glass tube of 13.6 mm diameter. Results for dry angle are reported here while the test facility and void fraction measurements are presented in Part II. R-22 and R-410A are the test fluids. Dry angles were quite close to values predicted for stratified flow and much larger than comparable values for air–water flows.