School of Engineering and Materials Science
Research Student Awards
PhD Thesis: Condensation on banks of smooth and finned tubes with and without non-condensing gas
Author: BUI, H
Supervisor(s): John Williams
The aim of the present project was to investigate condensation heat-transfer on banks of plain and finned tubes similar to those found in shell-and-tube condensers. To this end, data were obtained for condensation of steam and R-113, and from steam-air mixtures, on two banks of tubes, consisting of ten rows of plain and finned tubes respectively. Care was taken to ensure the data were of high accuracy and not compromised by the presence of dropwise condensation (in the case of steam) or non-condensing gas (in the case of pure vapour).
The new data, along with those of a large number of earlier investigations totalling some 3000 data points in all, were used to evaluate a number of theoretical models proposed in the literature. It was found that models for condensation on single tubes gave fairly good agreement with the experimental data if account were taken of the reduction in vapour velocity (and hence vapour shear on the condensate film) due to condensation down the banks. More complex, semi-empirical models, which attempt to include the combined effects of vapour shear and condensate inundation (i.e. condensate from tubes higher up the bank impinging on those further down) gave only marginally better agreement with the experimental data.
New models for determining the variation in temperature of the condensate as it drains between tube rows, and the effect on heat transfer of this falling condensate when it impinges on rows further down the bank developed. It was concluded that the effect on heat transfer of condensate inundation on the lower tubes of a practical shell-and-tube condenser would be negligible compared to the effect of reduced vapour velocity due to condensation.