Influence of fluid flow rate on the fouling resistance of calcium sulfate aqueous solution in subcooled flow boiling condition

Fouling is one of the customarily happened, fundamental and expensive problems in heat transfer systems. It causes the reduction in heat transfer performance of the heat exchangers, energy loss and also, damage to the apparatus. Effect of fluid flow rate on the salt deposition was complicated in the previous researches. In this paper, a comprehensive rigorous investigation was performed to make clear the effect of fluid flow rate of calcium sulfate aqueous solution on the heat transfer coefficient and fouling resistance in subcooled flow boiling condition. Large numbers of experiments performed at different flow rates (2.5-11.5 l/min), solution concentrations (1.75-2.20 g/l), fluid bulk temperatures (55-75 degrees C), and heat fluxes (8-95 kW/m(2)). Chen model, Gungor and Winterton model, and Kandlikar model approved pure water experimental data. It was found that increasing the heat flux increased the fouling rate and consequently, sharply decreased the heat transfer coefficient. It was also found that increase in the flow rate may cause both increase or decrease of the fouling layer, which depends on the applied heat flux. At low heat fluxes, deposition is mass transfer controlled, and increasing Re enhances the fouling rate while at high heat fluxes the deposition is chemical reaction controlled, and incresing Re decreases the fouling rate.