Flow boiling heat transfer of propane (R290) inside tubes. A review of experimental databases and correlations

Abstract

Heat pumps will be central in the path towards decarbonizing the heating sector, highlighting the importance of low-GWP refrigerants to meet climate-neutrality targets by 2050, with propane (R290) representing one of the most promising long-term alternatives. The boiling heat transfer coefficient (HTC) is a key parameter in the design of heat exchangers for these devices. This review provides a comprehensive and comparative analysis of experimental studies and correlations for boiling HTC inside smooth and microfin tubes with propane. A total of 2889 experimental datapoints from 32 studies were analysed, covering inner diameters from 0.96 to 9.43 mm, mass velocities from 50 to 600 kg/m 2 -s, saturation temperatures from -35 to 44 °C and heat fluxes from 2.48 to 227 kW/m 2 . The effects of the main parameters governing the boiling HTC are systematically analysed. A tube-diameter/flow-pattern classification is employed to assess the performance of 29 boiling HTC correlations for smooth and microfin tubes. Additionally, 68 dryout datapoints are compared with 7 correlations. The results demonstrate that no single correlation of boiling HTC provides consistent accuracy across the range of operating conditions considered. Instead, correlation performance is shown to depend strongly on tube diameter and flow pattern. The best-performing correlations are identified by analysing their performance across different operating domains using standard accuracy metrics. Furthermore, a lack of experimental data on the influence of oil during boiling, particularly inside microfin tubes, as well as on the effect of reducing the inner diameter in conventional tubes was identified, highlighting the need for further research in these areas.