LAMINAR FILMWISE CONDENSATION ALONG A FLAT PLATE WITH VARIABLE SURFACE TEMPERATURE - PART I. EFFECT OF ANGLE OF INCLINATION

摘要

A solution of the steady state laminar filmwise condensation of water vapour on a thin non-isothermal flat plate is given. The solution utilises Lighthill's approach, as modified by Spalding, for situation where the condensate phase is laminar. The method accounts for departures from linearity of the velocity profile within the thermal boundary layer, and accommodates the influences of Prandtl number, pressure gradient, body forces, and non-coincident origins for the velocity and thermal boundary layers. The film thickness, heat transfer coefficient and heat flux rate variations with step change in surface temperature for different origins for the thermal boundary layer formation are plotted to quantify the effect of tube spacing in a tube and plate fin heat exchanger. It is shown that the tube spacing in a dehumidifying coil, which can be characterised by a step change in the surface temperature of the plate, plays an important role in the design of a coil. The effect of plate inclination, as a first order approximation of condensation on a horizontal tube, is also analysed. The film thickness, heat transfer coefficient and heat flux rate variations with change in tube spacing are plotted for various plate inclinations to quantify the effects.