This paper describes the results of experimental tests carried out to study falling film evaporation on a heated flat plate with countercurrent air flowing in a rectangular channel. Experimental tests have been run with different channel depths with respect to a previous facility configuration in order to evaluate the effect of this parameter on the measured heat and mass transfer rates. The present work is then focused on the analysis of the effect that developing flow conditions may have on the evaporation of the falling water film. Three different values of the length over the hydraulic diameter ratio of the channel have been considered: L/D = 11.83, 20.86 and 33.88. Series of dry tests with 45° inclined channel were investigated with inlet nominal velocities of 1, 2.5, 5, 7.5, 9 m/s and with nominal heated plate temperature of 70 °C and 90 °C. Corresponding wet tests were investigated with nominal film flow rate at 60 and 100 g/s, with the same nominal inlet velocities but with a temperature of the heated plate of 70 °C. The obtained results point out interesting parametric trends that provide greater insight into the considered phenomena and support the use of the heat and mass transfer analogy for predicting evaporation rates in the considered range of parameters.
Heat and Mass Transfer in Countercurrent Flow of Air and Water Film in a Rectangular Vertical Duct
