Pool boiling heat transfer on double extended surface with mini-and microchannels

The paper presents preliminary experimental studies on the effect of additional microchannels made on the extended surface with minichannels on the intensification of heat transfer during nucleate pool boiling. The initial experiments were carried out with saturated water and ethanol. The measurements were performed with increasing heat flux using a double-extended MMC surface (minichannels + microchannels) and a base surface with minichannels (MC). The parallel minichannels (MC) manufactured by machining were 0.5 – 1.1 mm wide and 5.5 to 6 mm deep. The additional microchannels at the top of the fin and at the bottom of the minichannel were 0.15 mm wide and deep. For microchannels texturing the SPI nanosecond single mode pulse laser was used with maximum output power equal to 20 W at wavelength in range 1059-1065 nm. The tested MMC surface enabled the achievement of significant heat transfer coefficients: nearly 315 kW/m²K for water and over 70 kW/m²K for ethanol boiling. For water boiling in the range of 600 to 1150 kW/m2, heat transfer coefficients greater than 250 kW/m²K were achieved. Approximately 1/3 higher heat transfer coefficients were obtained for the tested double-extended surface (MMC) compared to the most effective minichannel surface (MC), using water and ethanol as working fluids.