Experimental and numerical study of heat transfer in a large-scale vertical falling film pilot unit

Heat transfer in a large-scale vertical falling film pilot unit is investigated experimentally and numerically. We study a broad range of operating conditions with Kapitza and Reynolds numbers ranging from Ka = 167-7010 and Re 18-1854, respectively. We compare local heat transfer measurements, conducted over a vertical length of 4 m, with those obtained by directly solving the full Navier-Stokes equations in two dimensions and using the volume of fluid (VOF) numerical framework. We examine the development region along with the one in which we assume statistically steady conditions. In both our experiments and simulations we see significant differences between the two regions in terms of the magnitude of the heat transfer coefficient. We show how this is a result of the temperature gradient within the liquid film, along with the thickness of the liquid film. The degree of bulk mixing, introduced by the waves, has a profound influence on the thermal boundary layer and depends strongly on the fluid properties and the operating conditions. (C) 2018 Elsevier Ltd. All rights reserved.