Effect of NH4Cl fouling on heat transfer process of heat exchange tube under forced convection condition

The crystallization fouling of ammonium chloride (NH4Cl) often occurs on heat exchange tube bundles in petroleum refining equipment, which seriously reduces the heat transfer and operational efficiency of the equipment. In this paper, the heat transfer characteristics of heat exchange tube (HET) with NH4Cl crystallization fouling was studied experimentally. The effects of velocity, temperature and mass flow rate of hot and cold fluids on the overall and local heat transfer characteristics were analyzed. The results indicate that the local heat transfer coefficient around the tube wall decreases first and then increases with the increase of the circumferential angle (theta) under clean condition. At the position of 0 degrees-45 degrees, the local heat transfer coefficient is the largest. At 90 degrees-135 degrees, the local heat transfer coefficient is the smallest. Under fouling condition, the local heat transfer coefficient increases with the increase of circumferential angle. In the region of 0 degrees-45 degrees, the local heat transfer coefficient is the smallest. The region with the largest local heat transfer coefficient is 135 degrees-180 degrees The heat transfer coefficient (h), fouling resistance (Rf) and average fouling thickness increase with the increase of Reynolds number (Re), temperature of hot fluid (Th) and mass flow rate of cold fluid (qm,c), but decrease with the increase of temperature of cold fluid (Tc).