Coefficients d'échange locaux au cours de l'ébullition du R22 et du R407C dans des tubes horizontaux, lisse ou micro-ailetéLocal heat transfer coefficients during boiling of R22 and R407C in horizontal smooth and microfin tubes

The purpose of this study is to experimentally investigate forced convective boiling. The heat transfer coefficients of pure refrigerant R22 and non azeotropic refrigerant mixture R407C were measured in both a smooth tube and a microfin tube. The tests have been carried out with a uniform heat flux all along the tube length. The refrigerant mass flux was varied from 100 to 300 kg m⁻² s⁻¹ and heat fluxes from 10 to 30 kW m⁻². Local heat transfer coefficients depend strongly on heat flux at a low quality and on mass fluxes at a high quality. When compared to smooth tube, the microfin tubes exhibit a significant heat transfer enhancement, up to 180%. In comparison to R22, the R407C heat transfer coefficients of smooth and microfin tubes are 15 to 35% lower, respectively. The best heat transfer enhancement is obtained at low heat flux and mass flow rate.