Experimental study of R448A flow boiling in a 24-port microchannel tube.

• Flow boiling characteristics of the non-azeotropic mixture R448A in a microchannel tube were measured in one pass. • As mass flux or heat flux increased, HTC of R448A increased; when the saturation pressure increased, HTC of R448A decreased. • R448A had a higher HTC than the HFOs and R134a at low quality, but lower HTC at high quality. • The correlations for predicting pressure gradient and heat transfer coefficient were proposed or recommended. R448A is a mixture to replace R404A in the thermodynamic cycle applications. R448A has a temperature glide of about 5°C and might exhibit thermal non-equilibrium in the microchannel tube. This study investigated the flow boiling heat transfer and pressure drop of R448A, a five-component non-azeotropic mixture, in a microchannel tube. Six heat transfer coefficients (HTC) and pressure gradients (dP/dz) of R448A were measured in one pass in a 24-port microchannel tube. The experimental conditions covered mass fluxes from 100 to 200 kg-m−2s−1, heat fluxes from 2 to 8 kW- m−2, and saturation temperatures from 10 to 30 °C. The study compared the experimental results of R448A with four of its component fluids (R134a, R1234yf, R1234ze(E), and R32). R448A had higher HTC and lower dP/dz than its component fluids, except for R32 which had higher HTC and dP/dz than R448A. Muller-Steinhagen and Heck was the best correlation for predicting the dP/dz of R448A, with a mean absolute error (MAE) of 8.78 % and a mean error (ME) of 7.47 %. A new correlation for predicting the HTC of R448A, based on modifying Liu and Winterton (Müller-Steinhagen and Heck, 1986), was proposed with an MAE of 6.01 % and an ME of 0.588 %. [ABSTRACT FROM AUTHOR]