Experimental studies into the non-isothermal mixing of incompressible liquid counterflows in a Y-junction

The processes involved in non-isothermal mixing of coolant flows in the power equipment components at water-cooled reactor plants are accompanied by thermal pulsations, the intensity of which can reach values leading to fatigue failure. Using numerical methods allows one to obtain the thermal pulsation characteristics required to assess the equipment life. The calculation results, however, need to be validated based on the experimentally obtained fields of the fluid's thermal and hydrodynamic parameters. The flow structure during non-isothermal mixing in a Y-junction was studied experimentally to get an idea about the thermal pulsation occurrence mechanism and characteristics. The experimental facility is a hydraulically closed circuit with water used as the coolant. The experimental model is geometrically similar to the section that forms part of a high-temperature test bench for investigation of the thermal cyclic load effects on the lifetime of the power equipment structural materials. The model is a Y-junction composed of the main pipe and an angled peripheral pipe with the "counter injection" of coolant flows. The geometrical similarity coefficient is 4/3. The model material is transparent organic glass. The flow structure was visualized through the injection into the flow of ink with the density similar to that of the coolant flow. The tracer was injected sequentially at four points with video records made of the mixing process with a frequency of 30 Hz. Thermocouples were used to measure the temperature. The mixing process video records were synchronized with the experimental temperature field recording. The formation of the vortexes in the mixing zone was tracked. The vortex scales, the time-averaged flow temperature profiles, and the thermal pulsation intensity profiles were determined. A combined analysis of the flow structure and temperature fields made it possible to explain the nature of thermal pulsations in the frontal region relative to the peripheral pipe.