The effects of ultrasonic vibration on critical heat flux (CHF) have been experimentally investigated under natural convection condition. Flat bakelite plates coated with thin copper layer and distilled water are used as heated specimens and working fluid, respectively. Measurements of CHF on flat heated surface were made with and without ultrasonic vibration applied to working fluid. An inclination angle of the heated surface and water subcooling are varied as well. Examined water subcoolings are 5°C, 20°C, 40°C and the angles are 0°, 10°, 20°, 45°, 90°, 180°. The measurements show that ultrasonic wave applied to water enhances CHF and its extent is dependent upon inclination angle as well as water subcooling. The rate of increase in CHF increases with an increase in water subcooling while it decreases with an increase in inclination angle. Visual observation shows that the cause of CHF augmentation is closely related with the dynamic behaviour of bubble generation and departure in acoustic field.
List of symbols
enthalpy of evaporation
critical heat flux (CHF)
CHF value for the horizontal upward-facing heater
orientation angle (0o for downward facing, 180° for upward facing)