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

Mashouf, H, Shafaee, M, Sarmadian, A and Mohseni, S G (2017) Visual study of flow patterns during evaporation and condensation of R-600a inside horizontal smooth and helically dimpled tubes. Applied Thermal Engineering, 124. pp. 1392-1400. ISSN 1359-4311

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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.

Item Type: Article
Keywords: Flow pattern, Dimpled tube, R-600a, Evaporation, Condensation
Schools and Departments: School of Engineering and Informatics > Engineering and Design
Research Centres and Groups: Dynamics, Control and Vehicle Research Group
The Sussex Energy Group
Thermo-Fluid Mechanics Research Centre
Subjects: Q Science > QC Physics > QC0251 Heat > QC0310.15 Thermodynamics
T Technology > TA Engineering (General). Civil engineering (General) > TA0349 Mechanics of engineering. Applied mechanics > TA0357 Applied fluid mechanics
T Technology > TP Chemical technology > TP0480 Low temperature engineering. Cryogenic engineering. Refrigeration
Depositing User: Mr Alireza Sarmadian
Date Deposited: 02 Oct 2018 13:48
Last Modified: 20 Nov 2018 10:01

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