Numerical Investigation on the Effect of Tube Geometry and Feeder Height on the Heat Transfer Performance of Horizontal Tube Falling Film Evaporation

This paper discusses about the effect of tube geometry and liquid feeder height on the heat transfer performance of falling film evaporation over the horizontal heated plain tubes. To investigate this, a two-dimensional computational fluid dynamics (CFD) model was developed, compared, and validated with published data available in the literature. A numerical simulation was carried out for varying liquid load, tube diameter, liquid feeder height, and corresponding changes in the heat transfer co-efficient (HTC), and mass transfer rate was recorded and analyzed. An attempt was also made to measure the thickness of the film around the tubes from the simulation model. Mechanisms that control the factors such as HTC, film thickness, and mass transfer were numerically investigated and discussed in this work. Numerical results indicated that low value of liquid film thickness appears approximately at the angular position of the range between 90 deg and 125 deg. Also the numerical investigation revealed that liquid film thickness decreases and HTC and mass transfer rate increases with the increase of feeder height. No remarkable change in film thickness was observed with increase in the tube diameter. This numerical study also proved that the prediction of thermally developed boundary region on the circumference of the tube could be possible in terms of mass transfer rate. It was also observed from the numerical study that the highest mass transfer rate takes place between the angle 135–165 deg near to the bottom of the tube.