Air rumbling for online fouling mitigation of calcium carbonate aqueous solution under subcooled flow boiling heat transfer

Abstract

In this research, increasing the shear stress by injecting air into the working system was implemented to mitigate crystallization fouling of calcium carbonate (CaCO3) aqueous solution. For this purpose, various experiments were conducted under subcooled flow boiling condition for analysing the effect of air injection on reduction of fouling formation inside a vertical annular channel with upward flow. These experiments were conducted at different operating conditions including air injection rate of 2–10 l/min, air injection freqency (f) of 0.5–2 h−1, heat flux of 52–83 kW/m2, fluid flow rate of 2–4 l/min, fluid bulk temperature (Tb) of 30–55 °C, and at a constant CaCO3 concentration of 0.2 g/l. The results showed that by increasing f from 0.5 to 2 h−1, the rate of fouling formation decreased. Also, the air rubmbling was more effective when Tb increased from 30 °C to 55 °C, by decreasing the fouling resistance from 38% to 57% comparing with no-mitigation experiment. When the heat flux was 83 kW/m2, air rumbling could decrease the fouling resistance by 57%. On the other hand, at lower heat flux of 52 kW/m2, air injection not only failed to reduce the fouling resistance, but increased it by about 20%. Also, when the air injection rate increased from 2 to 10 l/min, fouling resistance increased slightly. This environmentally friendly method has not received much attention before. Hopefully, the results presented in this research can pave the way for more research works on the mitigation of crystallization fouling using air injection.