Abstract
Simultaneous heat and mass transfer are investigated in a falling film outside grooved and smooth tubes. A numerical analysis of the helically trapezoidal-grooved and reference smooth tube was performed in the computational fluid dynamics program “Ansys Fluent 14.” The three-dimensional model drawings in the x, y, and z coordinates are used, and the effects of the falling film outside the helically grooved tube on the surface temperature and surface heat transfer coefficient are determined. The average surface temperature, heat transfer coefficient, and Nu values are determined experimentally for a constant heat flux. An uncertainty analysis and Nu correlation for the grooved tube are also provided in this study. The Reynolds number varied between 50 and 350 for the falling film and between 1500 and 3500 for air. Using a computational fluid dynamics (CFD) analysis for the reference smooth tube, the experimental results are validated within 2–12% difference. The experimental results are also within 6–13% of the grooved tubes.
Highlights
The use of closed type cooling towers and evaporative condensers is becoming widespread
Departure-site spacing is independent of tube spacing, the relationship between the type of jet flow, wavelength in the jet flow, and the tube spacing was observed under several conditions
The surface temperature is set to a constant value for a heated tube, and a falling film is investigated in different conditions
Summary
The use of closed type cooling towers and evaporative condensers is becoming widespread. Liu et al [4] performed experimental and numerical studies investigating the evaporation of water films falling on horizontal tube bundles in evaporators. The heat transfer coefficients of the water film horizontally falling on heated tubes were calculated using laminar and turbulence models. The calculation area around the heated tube was divided into two parts: the stagnation zone and the lateral free film zone This previous study found that the diameter of the tube affected the heat transfer. Roques and Thome [6] presented the flows and transits for four types of expanded tubes These are Wieland GewaK40 (40 fpi), Wieland Gewa-K19 (19 fpi), and Wolverine low fin (26 fpi and 29 fpi) tubes. That study examined a single smooth tube, enhanced surfaces, and the flow model that affects heat transfer on tube bundles and experimental parameters. The surface temperature is set to a constant value for a heated tube, and a falling film is investigated in different conditions
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