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The present numerical analysis focused on the low-GWP refrigerants during condensation inside a smooth and dimple tube. The low global warming potential refrigerants considered for the present numerical analysis are hydrocarbon includes propane (R290) and propylene (R1270), hydrofluoroolefin includes 2,3,3,3-tetrafluoropropene (R1234yf) and 1,3,3,3-tetrafluoropropene (R1234ze(E)), hydrofluorocarbon 1,1-difluoroethane (R152a), and an azeotropic mixture R430A (R152a 76 % + R600a 24 % by mass). The working conditions are mass velocity ranges between 50 and 200 kg/ m 2 s, dryness fraction of 0.5 and 0.75, heat flux of 5 kW/ m 2 , and temperature of saturation of 30, 40, and 50 ∘ C. The effect of saturation temperature, mass velocity and dryness fraction were investigated along the smooth and dimpled tubes. The VOF model is used to solve the mathematical formulations and the evaporation/condensation rate is determined by using Lee's model. The simulated void fractions were reduced by 2.18 % for R134a, 3.93 % for R290, 3.31 % for R1234yf, 2.55 % for R1234ze(E), 3.52 % for R1270, 2.42 % for R430A, and 1.37 % for R152a by increasing the saturation temperature from 30 to 50 ∘ C at a quality of 50 % inside a smooth tube. And, the two-phase friction factor was reduced by 5.38 % and 2.42 % with R1234yf at a dryness fraction of 0.5 and saturation temperature of 40 ∘ C for smooth and dimple tubes. Also, the pressure drops were increased by increasing the mass flux and decreasing the saturation temperature along the smooth and dimpled tube. [ABSTRACT FROM AUTHOR]

The international community limits the usage of higher global warming potential (GWP) refrigerants like R134a in refrigeration and air-conditioning systems. In view of this, the present study focuses on the low-GWP alternatives to R134a during condensation inside a smooth and dimpled tube. The refrigerants considered for this study are propane (R290), 2,3,3,3-tetrafluoropropene (R1234yf), and 1,3,3,3-tetrafluoropropene (R1234ze). The geometric specifications of smooth and dimple tubes are 8.38 mm ID with 1.5 m length. The operating conditions are saturation temperature of 40°C, mass flux ranging between 50 and 200 kg m−2 s−1, and dryness fraction of 0.5 and 0.75. The flow field was assumed to be transient, three-dimensional and turbulent while the VOF model was used to solve the governing equations. The effect of mass flux and dryness fraction was studied with R134a and its alternatives. The simulated void fraction values are compared with experimental values and empirical correlations. In this study, the total pressure drop was reduced by 15 and 20% with smooth tube and 11 and 16.7% with dimpled tube by using R1234yf at the quality of 0.5 and 0.75. However, it was increased with R290 and R1234ze. The power consumption was reduced by using R1234yf as a substitute to R134a and the thermophysical properties are quite similar. [ABSTRACT FROM AUTHOR]

In this study, the numerical simulations for multiphase fluid flow inside a smooth and dimpled tube were investigated at low mass velocities during the condensation of R-134a to determine the pressure drop. The numerical analysis was conducted at a dryness fraction of 0.5, temperature of saturation of 30–50°C, and mass fluxes range between 50 and 200 kg m−2 s−1. The impact of mass flux on the pressure drops had been studied along the smooth and dimpled tube. The smooth and dimpled tubes were designed with an inside and outside diameter of 8.38 and 9.54 mm, respectively. The specifications of the dimpled tube were o = 1 mm, p = 5.08 mm, z = 4.99 mm, and e = 0.5 mm. The Volume of Fluid (VOF) flow model was utilized in this study and the flow field was assumed to be three-dimensional, transient and turbulent. With an increase in mass flux for both smooth and dimple tubes, total pressure drop and frictional pressure drop increases. The numerically simulated two-phase friction factor was compared with the well-known correlations of the dimple tube. Also, the numerically simulated pressure drop for the dimple tube was more compared with the plain tube and the pressure drop decreases with an increase in temperature of saturation. [ABSTRACT FROM AUTHOR]