Heat and mass transfer during film flow around ice surfaces with a phase transition at the interface

Abstract

of a film flow process around ice surfaces in ice banks with a phase transition at the interface. Experimental studies were carried out for an ice bank with flat coils and its single section. The experiments were carried out at three temperature levels of cooled water: 20, 40, and 60 °C in the range of volumetric irrigation densities from 0.1 ∙ 10 –4 m 2 /s to 1.5∙10 –4 m 2 /s. It has been established that, at the specified parameters, the output specific heat load of the ice bank with a film heat exchange mechanism reaches up to 320 000 W/m 2 . On average, this value is an order of magnitude higher than similar values for modern plate heat exchangers from leading manufacturers (Alfa Laval, Funke, and Ridan), and more than two orders of magnitude higher than in ice banks with ice melting in a large volume. In the specified range, the values of the heat transfer coefficient, reduced to the surface of the heat exchanger, reached ~ 22.000 W/ (m 2 ∙K), which significantly exceeds the analogous value for volumetric melting ice banks (300–500 W/ (m 2 ∙K)). It is shown that in heat exchangers with a film flow, the initial temperature gradient between the cooled water and the ice surface affects the heat transfer coefficient indirectly (through the Reynolds number of the falling film), in contrast to heat exchangers with a fixed heat transfer surface. The generalization of the results showed the prospects of using ice banks with a film heat and mass transfer mechanism for food industry objects with an uneven distribution of heat load and for maintaining the temperature of refrigerated products. In addition, they can be effectively used in systems with a pulsed nature of heat release (cooling lasers, etc.), as well as daily storage devices in conjunction with «green» power supply systems using solar and wind energy.