This research article investigates the effect that hydrodynamic cavitation has on heat transfer. The fluid medium is refrigerant R-123 flowing through 227 pm hydraulic diameter microchannels. The cavitation is instigated by the inlet orifice. Adiabatic tests were conducted to study the two-phase cavitating flow morphologies and hydrodynamic characteristics of the flow. Diabatic experiments were performed resulting in surface temperatures under heat fluxes up to 213 W/cm(2) and mass velocities from 622 kg/m(2) s to 1368 kg/ in 2 s. Results were compared to non-cavitating flows at the same mass velocities. It was found that the cavitating flows can significantly enhance the heat transfer. The heat transfer coefficient of the cavitating flows was larger than the non-cavitating flows by as much as 84%. Single-phase and two-phase heat transfer coefficients have been elucidated and employed to deduce the heat transfer mechanism prevailing under boiling conditions with and without the presence of cavitation. (C) 2007 Elsevier Ltd. All rights reserved.