A theoretical model for the prediction of the critical heat flux of refrigerants flowing in heated, round microchannels has been developed and presented here. The model is based on the two-phase conservation equations and includes the effect of the height of the interfacial waves of the annular film. Validation has been carried out by comparing the model, a numerical solution of a non-linear system of five differential equations, with a critical heat flux (CHF) database including three different refrigerants from two different laboratories. More than 96% of the data are predicted within a +/- 20% error band and a mean absolute error of 8%. Furthermore, it is also possible to predict CHF data from a third laboratory for water and R-113 flowing in rectangular (using the width of the channel as the characteristic dimension) and circular microchannel heat sinks with multiple channels. All together, 90% of the entire database, including four different fluids and different geometries, are predicted by the model within a +/- 20% error band and a mean absolute error of 9.3% for channels from 0.215 to 3.15 mm in size, mass fluxes from 29 to 1600 kg/m(2) s, heated lengths from 10 to 126 mm and subcoolings from 2 to 77 degrees C. (C) 2007 Published by Elsevier Ltd.