Analysis of the effect of icing on the thermal behavior of helical coil heat exchangers in surface water heat pump applications

Abstract

Helical coil, especially a multirow helically coiled tube configuration, is a particular type of heat exchanger commonly used in surface water heat pump systems. When the fluid temperature decreases, the icing on the outer wall influences the thermal behavior of the heat exchanger. In this study, a detailed heat transfer model was established for icing and non-icing conditions. The correlations of outside local convection along the tube length were modeled for flowing and stagnant water bodies, considering the flow direction and the effects of geometric parameters. Simulations of icing and non-icing conditions were conducted to analyze the influence of icing. The results show that increasing the medium velocity, inlet temperature of the medium, and surface-water temperature or decreasing the surface-water velocity could significantly increase the average thickness and the distribution length of the ice. As regards geometric parameters, ice will be produced more in a smaller vertical spacing or a higher number of rows, whereas it is insensitive to changes in horizontal spacing and tube length. The reduced percentage of the heat exchange rate is 0.62%/mm for an increase in average ice thickness; however, it could be greater when ice fills the gap. Reference charts are finally provided for vertical spacing to avoid ice filling the gap to be used in the design phase.