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

Resumo

The present work aims at identifying flow patterns and measuring interfacial parameters in two-phase natural circulation by using visualization technique with high speed 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, flow and graphic interface. The instrumentation has thermocouples, volumetric
flowmeter, rotameter and high speed camera. The experimental study is performed through analysis of information from measurements of temperatures at strategic points along the hydraulic circuit, besides natural circulation flow rates. The comparisons between analytical and experimental values are validatedvby viewing, recording and processing of the images for the flows patterns. Variables involved in the process of identication of flow regimes, dimensionless parameters, the phase velocity of the flow, initial boiling point, the phenomenon of "flashing" pre-slug flow type were obtained experimentally.