Research on Bubble Growth and Frequency at Higher System Pressure in Narrow Rectangular Channel

In present work, the characteristics of bubble growth and frequency were visually observed in a narrow rectangular channel using high-speed digital camera. The experiment was done over the following range of conditions: pressure, 0.55MPa; mass flux, 300–500kg/(m²·s); heat flux, 86.4–225.7 kW/m²; and inlet subcooling, 25.5–45.5K. The system pressure has a significant effect on the bubble growth. Experimental results show that the bubble diameters are just about 0.15mm under higher system pressure and the period during which bubbles attaching to the nucleate site is very short, or even unnoticeable. The bubbles keep growing when slide along the heating wall rather than lifting off the surface, and the bubbles rarely collapse under the working conditions. When the mass flux is high, the bubble diameter increases with increasing the heat flux, but when the mass flux is low, the variation trend of bubble diameters expresses no obvious law. The effect of thermal parameters on bubble frequency is also significant. When the mass flux is low, the bubble frequency decreases with increasing the heat flux or inlet subcooling, however when the mass flux is high, the bubble frequency increases first and then decreases. Generally, the bubble frequency increases with increasing the mass flux.