Experimental investigation of temperature and hydrodynamics on CaCO3 fouling during convective heat transfer and subcooled flow boiling

Abstract

Deposit formation in heat exchangers is an undesirable process in many industries. Severe fouling can potentially reduce the performance of heat exchangers compromising the efficiency of operating units. This research aimed to examine experimentally the effect of fluid bulk temperature (Tb) during deposition of CaCO3 solution under convective heat transfer and subcooled flow boiling conditions. To do so, several tests were performed at a constant concentration of CaCO3 solution (0.2 g/l) and Tb values of 55–75 °C. Heat flux ranging from 13 to 83 kW/m2 and fluid flow rates of 2 to 4 l /min) were also applied to investigate experimentally fouling resistance and heat transfer coefficient of CaCO3 solution. It was found that Tb would significantly affect the mechanism of deposit formation which has been less discussed in the past. Higher Tb changed the propensity of fouling resistance curve from linear to asymptotic, and the crystal type of deposit layer from aragonite to calcite. Results also showed that at low Tb (55 °C), an increase in heat flux enhanced the fouling rate while at high Tb, an increase in heat flux reduced the fouling, due to increasing the evaporation rate of the solution. In addition, at low heat flux (13 kW/m2), an increase in the fluid flow rate led to higher fouling rate, whereas at high heat flux, increasing the fluid flow rate resulted in lower fouling rate.