Water is heated to 60℃ by refrigerant in heat pump water heater

which results serious fouling . Studying the precipitation characteristics are the first step to find anti-fouling technology. CaCO3 is precipitated on stainless steel 304 and 316 coupons from 0.5 and 1.0 mmol/l CaCO3 solution by static reaction. By weighing the coupons before and after experiments the mass of fouling is obtained and the morphology of different grown time coupon surfaces can be got using SEM. The results show that at the same condition there was more fouling on ss304 than ss316 and more aragonite on ss304 and more calcite on ss316. Higher Ca2+ concentration formed more nuclei but the sizes of the nuclei was decreased and less fouling was formed for each nuclei

and the proportion of aragonite and calcite wasn’t changed. Higher pH promoted formation of calcite and both homogeneous and heterogeneous nucleation rate

but the former increased more

so the fouling mass decreased. The main mechanism of fouling formation on heat exchanger surfaces was insoluble salt crystallization to form fouling particles in solution and then precipitate on surface

reaction and adsorption of insoluble salt directly to surface is the secondary mechanism.