A Study On Heat-Transfer Properties Of Falling Liquid Film On The Surface Of A Horizontal Spirally Fluted Tube

The objective of this study is to develop a theoretical method of investigating heat-transfer properties of falling liquid film on the surface of a horizontal spirally fluted tube. The numerical model of pure fluid is established using Navier-Stocks equations for low Reynolds number with considerations of the surface-tension effects and the action of gravity. Analytical solutions of velocity distribution and liquid film thickness are obtained in the case of evaporation and condensation. The influence of the surface geometry of the fluted tube on the film thickness distribution is discussed. The results show that the film thickness distribution is mainly affected by the surface geometry of the fluted tube, which has a crucial influence upon the surface tension of the liquid. Thus the fluid tends to flow down the crest region and accumulates in the trough region. The lower of the depth channel, the more uniform the film is. Condensation and evaporation on the liquid surface contribute to improving a more uniform distribution. Therefore, there comes a significant improvement in heat transfer, compared with the classical smooth tube. Moreover, the conditions for a multi-fluted helical tube must be satisfied are analyzed and the film thickness distribution is investigated. It is shown that the multi-fluted helical tube can provide a suitable geometric slope surface, which allows the fluid flow not only to move along the helical channel but also to cross the boundary of the channel and merge into the fluid flow in the next channel. Consequently, the film thickness distribution is more uniform in the multi-fluted helical tube when compared with the single-fluted tube. Heat transfer coefficients in the case of constant temperature and changeable temperature are augmented and average Nusselt is obtained. It is shown that the distribution is determined by not only the fluid flow but also heat-transfer properties. Theunderstanding to the formation of the falling film on the surface of a horizontal spirally fluted tube is conducive to the industry application in micro-combustors.