Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng Research Paper Experimental thermal and hydraulic characterization of R448A and comparison with R404A during flow boiling G. Lillo, R. Mastrullo, A.W. Mauro ⁎ , F. Pelella, L. Viscito Department of Industrial Engineering, Università degli Studi di Napoli – Federico II, P.le Tecchio 80, 80125 Naples, Italy HIGHLIGHTS • Flow boiling heat transfer and pressure drop data of R448A inside a horizontal tube. • HTC increases with heat and mass flux. No particular effect of saturation temperature. • Possible stratified-wavy flow for G = 150 kg/m 2 s. • HTC and pressure drop data compared to R404A values at same operating conditions. • Assessment of existing two-phase heat transfer and pressure drop correlations. ARTICLE INFO Keywords: Flow boiling R448A Heat transfer coefficient Pressure drop Assessment ABSTRACT Refrigerant R404A is going to be banned in Europe for different applications due to its very high GWP of 3943. R448A is a suitable alternative (GWP of 1390) among other new mixtures, and is thus receiving considerable attention in literature. However, despite several overall system studies, there is a lack of flow boiling data for this new blend. This paper therefore presents an experimental investigation on two-phase heat transfer and pressure drop of R448A in a single horizontal stainless steel (AISI 316) tube with an internal diameter of 6.0 mm. The effect of the operating parameters is firstly analyzed for the whole range of vapor qualities, by changing the mass flux from 146 to 601 kg/m 2 s and the bubble saturation temperature from 23.3 to 56 °C (reduced pressures from 0.266 to 0.554). For the heat transfer coefficient measurements, the imposed heat flux is also varied from 2.5 to 40 kW/m 2 , leading to a total amount of 460 data points. Several pressure drop and heat transfer coefficient data are then compared to those of conventional refrigerant mixture R404A at the same operating conditions, showing different relative importance of nucleate and convective boiling contributions. Finally, the agreement between the R448A experimental database and some two-phase boiling heat transfer coefficient and frictional pressure drop prediction methods is evaluated with a statistical analysis. The best results are respectively ob- tained with the correlations of Gungor and Winterton and of Friedel. 1. Introduction Refrigerant R404A has been widely used for years in commercial refrigerators and heat pump systems as a suitable replacement for R22, having the advantage to be employed also at low evaporating tem- peratures, thanks to its Normal Boiling Point of 226.7 K [1]. However, despite its zero-ODP (Ozone Depletion Potential), R404A has a very high GWP (Global Warming Potential) value of 3943. For these reasons, fluid leakages and superficial operations during plants dismantlement are a significant cause of direct greenhouse gas emissions. The GWP limitations in Europe affecting the commercial systems where R404A is currently used are expressed by the EU Regulation No 517/2014 [2]. Specifically, stationary refrigeration equipments must avoid fluids with GWP > 2500 by 2020, whereas multipack cen- tralized refrigeration systems carry the GWP limit of 150 by 2022 and refrigerators and freezer should employ fluids with GWP < 2500 in 2020 and GWP < 150 in 2022. Despite the political effort in reducing the direct greenhouse gas emissions, there is not a definitive solution to replace high GWP re- frigerants, but numerous alternatives have been proposed, as reviewed by Mota-Babiloni et al. [3]. Particularly, HFC mixtures R407A, R407F and R422A have been presented as light retrofit fluids for R404A, showing a similar or even higher efficiency with half of the GWP [4], but with an economical drawback of a high purchase cost [5]. Other https://doi.org/10.1016/j.applthermaleng.2019.114146 Received 23 January 2019; Received in revised form 4 June 2019; Accepted 16 July 2019 ⁎ Corresponding author. E-mail address: alfonsowilliam.mauro@unina.it (A.W. Mauro). Applied Thermal Engineering 161 (2019) 114146 Available online 17 July 2019 1359-4311/ © 2019 Published by Elsevier Ltd. T