Impact of Operating Conditions on Crystallization Fouling of Calcium Sulfate on Heat Transfer Surfaces

Deposit formation on heat transfer surfaces in heat exchangers is one of the most chronic problems in many industries. It causes flow mal-distribution, increased pressure drop, excessive fuel consumption, and generally reduction of the exchanger thermal efficiency. It is therefore indispensable to investigate fouling mechanisms as well as the impact of various operating conditions. These would, in turn, help to develop mitigation strategies. Water is the most widely used as working fluid in heat exchangers due to its high heat capacity, redundancy, and low price. However, the presence of various ions, such as calcium, carbonate, and sulfate in water, causes the formation of calcium sulfate and/or calcium carbonate deposits in heat exchangers. In this study, the effect of operating conditions including fluid velocity, calcium sulfate concentration, and heat flux on the formation of calcium sulfate deposit has experimentally been investigated. For doing so, firstly, the impact of these parameters on deionized water was examined under clean condition. The results of fouling experiments showed that increased heat flux and concentration of calcium sulfate resulted in intensified deposit formation as well as increased surface temperature and thermal resistance, which all would give rise in reduction of heat transfer coefficient. In contrast, the higher that fluid velocity is, the lower would be the deposition, surface temperature, and thermal resistance.