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Enhancing the natural circulation flow using ultrafine bubbles: Simulation and experimental
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DOI：10.1016/j.ijthermalsci.2025.110181.png)
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Abstract
En 中文
This study evaluates the effect of adding ultrafine bubbles (UFBs) to pure water as a base fluid on the performance of single-phase natural circulation flow inside a rectangular loop through a CFD numerical simulation approach and experimental validation using the FASSIP-06 Ver.00 facility. The loop configuration has a vertical geometry with a height of 2500 mm, a width of 850 mm, and a pipe diameter of 26.64 mm, entirely constructed using stainless steel pipes. And the simulation using the same geometry. The main objective of this research is to examine the thermohydraulic performance of UFBs compared to pure water as the working fluid in a passive cooling application. UFBs were generated using a porous ceramic membrane method, which enables high-frequency bubble formation with nanometer-scale diameters. The resulting UFBs were characterized using particle size analyzer, yielding an average bubble diameter of 137.5 nm and a zeta potential of −41.8 mV, indicating good dispersion stability in the fluid. Based on mass and volume measurements, the volume fraction of UFBs in the fluid mixture was calculated to be 0.015, and this value was consistently applied in both simulation and experimental procedures. The results showed that using UFBs consistently increased fluid temperature, volumetric flow rate, and Reynolds number compared to pure water at each heating temperature variation. This improvement is attributed to the decrease in effective density and viscosity due to the presence of UFBs, which strengthens the thermal lift and lowers the frictional resistance. This superior performance indicates that UFBs have the potential as passive additives to improve the performance of natural circulation-based cooling systems, particularly in the context of the thermal safety of next-generation nuclear reactors.
Keywords:
ultrafine bubbles
natural circulation
CFD simulation
passive cooling
thermohydraulic performance
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