An image analysis technique for determination of void fraction in subcooled flow boiling of water in horizontal annulus at high pressures

Experiments were performed in subcooled flow boiling of distilled water in horizontal annulus at mass fluxes from 400 to 1200 kg/m2-s, heat fluxes from 0.1 to 1 MW/m2 and pressures varying from 1 to 4 bar at constant subcooling of 20 °C with the intention of determining void fraction by optical methods and to study the effect of pressure, mass flux and heat flux and location of heated length on void fraction. National Instruments Labview IMAQ Vision Building image processing software was used to analyze the images obtained by high speed visualization. It was found that void fraction decreases with the increase in pressure and mass flux whereas heat flux has opposite effect. Void fraction increases considerably with the increase in heated lengths.

► Experiments were performed to determine void fraction by optical methods.
► Void fraction was determined at elevated pressures.
► It was found that void fraction decreases with the increase in pressure.
► Void fraction increases considerably with the increase in heated lengths.