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Visual study of flow patterns during evaporation and condensation of R-600a inside horizontal smooth and helically dimpled tubes

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posted on 2023-06-09, 15:18 authored by H Mashouf, M Shafaee, Alireza Sarmadian, S G Mohseni
In this paper, flow patterns and their transitions for the refrigerant R-600a during flow boiling and condensation inside a helically dimpled tube and a smooth tube were observed and analysed. The inner surface of the helically dimpled tube was enhanced by a modified pattern consisting of both shallow and deep protrusions. For evaporation, the experiments were performed for refrigerant mass velocities in a range of 155 kg/m2 s to 467 kg/m2 s, all at an average saturation temperature of 56.5 °C with the vapour qualities up to 0.8. Stratified-wavy, intermittent, and annular flows were observed for the smooth tube; for the dimpled tube, the stratified-wavy flow was not seen. For condensation, all tests were conducted at vapour qualities up to 0.8, and average saturation temperatures ranging between 38 °C and 42 °C. The refrigerant mass fluxes varied in the range of 114–368 kg/m2 s. Annular, intermittent, and stratified-wavy flows were recognized for the plain tube, but there was no stratified-wavy flow in the flow pattern visualization of the dimpled tube. The investigation clearly shows that the dimples in both evaporation and condensation have a significant impact on the two-phase flow pattern. Inside the helically dimpled tube, the transition from intermittent to annular (or vice versa) occurred at a lower vapour quality value than for the smooth tube.


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Applied Thermal Engineering







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  • Engineering and Design Publications

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  • Dynamics, Control and Vehicle Research Group Publications
  • Thermo-Fluid Mechanics Research Centre Publications
  • The Sussex Energy Group Publications

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