Thermal hydraulic structure in subcooled flow boiling
Subcooled liquid is injected from the bottom of a heated tube. Liquid temperature gradually increases along the tube axis due to the heat applied from wall. If the liquid temperature near the heated wall becomes high enough, generation of vapor bubbles is initiated at nucleation sites on the wall. Since the fluid temperature is higher in near wall region, the fluid temperature in core region can be lower than the saturation temperature at the onset of bubble generation. If vapor bubbles are generated on the wall but bulk liquid is still subcooled, the situation is called subcooled flow boiling. Analytical modeling of subcooled flow boiling is important in industrial systems using boiling heat transfer. However, the behavior of vapor bubbles in subcooled flow boiling is complicated and it has not been thoroughly understood. We are doing visual experimental study to elucidate the thermal hydraulic structure in subcooled flow boiling. A sample video is shown below. Though the resolution is reduced to minimize the file size, you may see that the bubbles generated at nucleation sites are collapsed due to the condensation in bulk liquid.
Bubbles in subcooled flow boiling