Experimental study on bubble size distribution of subcooled flow boiling in cylinder head of internal combustion engines

Subcooled flow boiling is becoming an efficient and widely used heat transfer approach in internal combustion engine cooling systems. Bubble evolution behaviors are crucial for understanding the mechanism of subcooled flow boiling. In this study, a diesel engine test platform equipped with endoscopic high-speed photography system was built to investigate the characteristics of boiling bubble. Under various inlet liquid subcoolings and flow rates, the mean bubble diameters and bubble size distributions were measured and analyzed based on the image processing techniques. Most of the bubbles approximated the spherical and ellipsoidal shapes. The bubble size was distributed between 1 and 2.5 mm, and the bubble diameters increased with the decrease of the inlet subcooling and flow rate. The flow rate had a more significant effect on the formation of large boiling bubbles.