Confined jet array impingement boiling of subcooled aqueous ethylene glycol solution

A closed-loop experimental setup was built to study the confined jet array impingement boiling of 43% mass concentration aqueous ethylene glycol solution at low jet velocities and large degree of subcoolings. A 20 mm × 40 mm rectangular thin metal film with thickness of 0.03 mm was used as the heating surface. The in-line jet array had an orifice diameter d = 1 mm, a dimensionless jet-to-jet spacing S/d = 5 or 4, and a dimensionless jet-to-target spacing H/d = 1, 1.5 or 3. Experiments were performed at atmospheric pressure with the saturation temperature of 106 °C, jet velocities of 0.2 m/s, 0.31 m/s and 0.5 m/s, and liquid subcoolings of 36 °C, 46 °C and 56 °C. It is found that the heat transfer coefficient in the nucleate boiling regime at first increases with the increase of heat flux and then starts to decrease before the critical heat flux (CHF). Jet velocity and jet-to-target spacing have little effects on heat transfer coefficient in the nucleate boiling dominant regime, while subcooling and jet-to-jet spacing play important roles. Not only the jet velocity but also the liquid subcooling has great influences on the boiling inception and CHF. There exists an optimal jet-to-target spacing to achieve the maximum CHF because of the tradeoff between the breakup and confinement (or expel) of vapor bubbles. For the same flow rate, S/d = 5 has a higher heat transfer coefficient and CHF than S/d = 4.