Abstract
The flow condensation heat transfer performances of R1234ze(E) and R32 in a horizontal single circular minitube with the inner diameter of 2 mm are investigated experimentally. Tests are carried out at saturation temperatures of 35, 40, and 45 °C, mass fluxes ranging from 100 to 400 kg/m2s, and heat fluxes ranging from 4 to 28 kW/m2. Flow patterns of R32 are observed by using a visualization approach. Plug, slug, annular-wavy, and annular flow patterns are presented in this research. The effects of the operating parameters (mass flux, heat flux, saturation temperature, and vapor quality) on the heat transfer characteristics of R1234ze(E) and R32 are discussed. A database involving R1234ze(E), R1234yf, R32, and R134a is built to make further analysis. Several typical correlation models are used to predict our measured data and the collected database. The Baird et al. model and the Müller-Heck model can well predict the heat transfer coefficients and frictional pressure drops, respectively. The flow pattern boundary between intermittent flow and annular wavy flow is depicted by three dimensionless numbers: the Lockhart-Martinelli parameter, the Bond number, and the Reynolds number.
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