A new flow pattern-based boiling heat transfer model for micro-pin fin evaporators

摘要

This study presents the development and results of a new flow pattern-based prediction method for two-phase boiling heat transfer in a micro-pin fin evaporator. The heat transfer mechanisms associated with slug flow and annular flow regimes are inferred by updating the widely used three-zone model of Thome et al. (2004), Dupont et al. (2004) and the algebraic turbulence model of Cioncolini and Thome (2011), respectively. In order to predict the trends in the heat transfer coefficient versus the vapor quality, these two models are linearly combined by utilizing a smoothing function acting on a buffer zone centered in the slug-to-annular flow transition region, which is here obtained by means of a new method based on flow visualization analysis and time-strip technique of the available experimental data.The model is compared to a wide experimental database (7219 points), which covers three refrigerants, R134a, R236fa and R1234ze(E), three outlet saturation temperatures (25, 30, and35°C), mass fluxes varying from 500 to2000kgm-2s-1and heat fluxes from 20 to44Wcm-2. The new flow pattern-based model predicts72%of the experimental databank within the±30%, with a Mean Absolute Error of23.4%.