Abstract: A semi-analytical model was developed for the prediction of enhanced flow boiling heat transfer in vertical porous tubes.The model assumes that forced convection and nucleate boiling coexist in the annular flow regime.Conservations of mass, momentum, and energy are used to determine liquid film thickness and temperature. The heat flux due to nucleate boiling consists of those inside and outside micro-tunnels. A detailed analysis of various forces acting on the bubble is presented to predict its mean departure diameter. The active nucleation site density of porous layer is determined by correcting the pool boiling correlation with a suppression factor. The flow boiling heat transfer coefficients of high saturation temperature organic fluid (cumene) in a vertical plasma coated tube are studied numerically. It is shown that the present model can predict most of experimental values within ±20%. The numerical results also indicate that the nucleate boiling contribution to the overall heat transfer coefficient decreases from 50% to 15% with vapor quality increasing from 0.1 to 0.5.