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ISSN Druckformat: 1064-2285
ISSN Online: 2162-6561
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EXPERIMENTAL DETERMINATION OF THE WETTED AREA OF A FALLING FILM ON THE OUTSIDE OF HORIZONTAL TUBES USING IMAGE PROCESSING AND HEAT TRANSFER ANALYSIS
ABSTRAKT
Falling film is observed in closed type cooling towers, evaporative condensers and absorption cooling. In this study, the aim was to increase the amount of evaporating water on the tube surface during falling film. To increase the area of wetness, different groove forms were used, which were placed longitudinally or helically on horizontal tubes. The groove geometries were triangular, trapezoidal, round and square. In the experiments, the area of wetness was measured by generating falling film type flow on horizontal tubes with these four different groove geometries. The falling film type flow was generated using dyed water to measure the area of wetness. Photographs were taken using a high-speed camera to determine the area of wetness in the tubes. The photographs were processed using MATLAB, and it was concluded that the helically trapezoid geometry tube had the maximum rate of wet area of 74% and that the longitudinal trapezoid groove geometry tube had the minimum rate of 46%. Afterwards, the amounts of evaporating water, heat convection coefficients and Nusselt number values were determined. The results indicated that as the temperature of the feeding water increased, the amount of evaporating water also increased. The Nusselt correlation was observed at different temperatures of feeding water between 30 °C and 40 °C and depending on the Rew and Rea of the falling film. It was determined that while Rew was between 100 and 350, the observed heat convection coefficient was between 15 and 55 W/m2·K for the simultaneous heat and mass transfer.