Flow visualization of bubble behavior under two-phase natural circulation flow conditions using high speed digital camera

The present work aims at identifying ow patterns and measuring interfacial parameters in two-phase natural circulation by using visualization technique with high-speed digital camera. The experiments were conducted in the Natural Circulation Circuit (CCN), installed at Nuclear Engineering Institute/CNEN. The thermo-hydraulic circuit comprises heater, heat exchanger, expansion tank, the pressure relief valve and pipes to interconnect the components. A glass tube is installed at the midpoint of the riser connected to the heater outlet. The natural circulation circuit is complemented by acquisition system of values of temperatures, ow and graphic interface. The instrumentation has thermocouples, volumetric ow meter, rotameter and high-speed digital camera. The experimental study is performed through analysis of information from measurements of temperatures at strategic points along the hydraulic circuit, besides natural circulation ow rates. The comparisons between analytical and experimental values are validated by viewing, recording and processing of the images for the ows patterns. Variables involved in the process of identification of ow regimes, dimensionless parameters, the phase velocity of the ow, initial boiling point, the phenomenon of "ashing" pre-slug ow type were obtained experimentally