F-EX-1-14 Experimental Study of Local Crystallization Fouling in Double-pipe Heat Exchangers

F. Schl├╝ter, W. Augustin, and S. Scholl (Institute for Chemical and Thermal Process Engineering, Technische Universit├Ąt Braunschweig)

Prepared under contract with HTRI, this report presents a comprehensive study on local crystallization fouling in double-pipe heat exchangers operating in counterflow. Results are based on fouling experiments with an aqueous calcium sulphate solution and with most flow velocities at 1.0 m/s. For local thermal fouling investigations, heat exchanger tubes were equipped with several local thermocouples and the fiber sensor measurement technique. In addition, local fouling investigations were performed using a volumetric, a gravimetric, and an optical approach. An analytic determination of the local layer thickness and roughness was developed and applied, as well as a calculation process to determine the distribution of the local pressure drop. Substantial variation in fouling thickness was observed along the tube length, with the highest amount of deposit near the hot fluid steam inlet. A fouling model which accounts for roughness and flow constriction is evaluated. Results indicate that local variations need to be considered in application of fouling models.