Conjugate Heat Transfer in Annular Laminar Film Condensation in Microchannels: Comparison of Numerical Model to Experimental Results

A comparison of the recently proposed numerical model for annular laminar film condensation heat transfer in microchannels of different internal shapes (circular, square, rectangular, etc.), including the effects of conjugate heat conduction in the channel walls, is made versus recent independent experimental results experiencing this effect. Notably, the thinning of the condensate film induced by surface tension due to gravity forces and shape of the surface, also known as the ‘Grigorig’ effect, has a strong consequence on the local heat transfer coefficient in condensation. The model, which is based on a finite volume formulation of the Navier-Stokes and energy equations for the liquid phase only, accounts for the contributions of the surface tension, axial shear stresses and gravitational forces and for the conjugate effects of axial and peripheral wall conduction and nonuniform heat flux. The model was previously validated versus experimental data available in the literature without accounting for conjugate effects, predicting microchannel heat transfer data to within 20% or better. Specifically, the updated version of the model includes the coupling between the thin film fluid dynamics, the heat transfer in the condensing fluid and the heat conduction in the channel wall. Since it is imperative to demonstrate that numerical heat transfer models are accurate and reliable, the present paper focuses on validating this new conjugate model versus recent actual experimental data for various small channels and test fluids experiencing this effect. The results are very encouraging and are presented here.