Abstract: The heat transfer of a small heating device can be augmented by gas impingement in a liquid coolant bath. The mechanism of its heat transfer augmentation was studied. Theoretical analysis and experimental investigation showed that besides the increasing heat transfer by the agitation of liquid caused by gas jet impingement there existed a heat sink caused by liquid coolant vaporization at the impinging gas-liquid coolant interphase. Due to such a quick vaporisation, the temperature at the gas-liquid interphase dropped notably, increasing the effective heat transfer driving force and in turn the heat transfer. From such a point of view, a physical model of simultaneous heat and mass transfer was proposed to reveal the mechanism of this particular heat transfer phonomenon, and the convective heat transfer coefficient and mass transfer coefficient can be calculated.