Partial Nucleate Boiling on the Microscale Heater Maintaining Constant Wall Temperature

Nucleate pool boiling experiments for pure R11 with a constant wall temperature condition were carried out. A microscale heater array and Wheatstone bridge circuit were used to maintain a constant wall temperature condition and to obtain measurements with high temporal and spatial resolution. The images of bubble during the growth period were captured by the high speed CCD camera synchronized with heat flow rate measurement. The bubble shape immediately after inception was an oblate spheroid with a small contact angle. The geometrical shape permitted a large amount of heat to be supplied from the wall. In the asymptotic growth region, the bubble shape is almost truncated sphere. The measured heat flow rate showed a discernable peak in the initial growth region, and reached almost constant value. A quantitative analysis for the heat transfer mechanism was performed using the measured heat flow rate and bubble growth behavior for saturated pool boiling conditions. The required heat flow rate for the volume change of the observed bubble was larger than the instantaneous heat flow rate supplied from the wall.