Experimental measurement of heat transfer coefficient and mass of deposited CaSO4 in subcooled flow boiling condition

Fouling is a common, fundamental and costly problem in heat transfer systems, which reduces thermal efficiency of equipment, increases the energy loss and causes strong damage to the heat transfer equipment in various industries. The main causes of fouling on the heat transfer surfaces are salts with inverse temperature-solubility in the fluid which calcium sulfate is one of the most important of them. In this paper, the effect of calcium sulfate fouling on the heat transfer coefficient in subcooled flow boiling was investigated. The fouling mass of calcium sulfate on the heat transfer surface was also calculated. In the experiments carried out in this study, flow rate (2.5–11.5 l/min), solution concentration (1.75–2.2 g/l), bulk fluid temperature (55–75 ℃), and heat flux (8-95 kW/m2) were variables at the mentioned ranges. The results showed that the maximum deviation in the uncertainty analysis was related to the difference between the inlet and outlet temperature of the fluid, followed by the temperature difference between the wall temperature and the bulk fluid temperature. Also, the analysis of the experimental data revealed that increasing the salt concentration, the bulk temperature, and the heat flux of the solution, the mass of deposited calcium sulfate on the heat transfer surface increases with time, resulting in a decrease in the heat transfer coefficient. Careful analysis of the experimental data also showed that the solution concentration has more important role than the heat flux and the fluid bulk temperature in fouling formation.

Keywords:

CaSO4 solution , Inverse solubility , Fouling , Subcooled flow boiling