Characteristics of fouling development in shell-and-tube heat exchanger: Effects of velocity and installation location

The purpose of this study was to investigate the effects of wastewater velocity and installation location of a shell-and-tube heat exchanger on particle fouling deposited within the heat exchanger. Three long-term fouling tests with the heat exchanger installed at the shoot-outlet of a pump with varied wastewater flow rates (low, medium, and high), and one test with the heat exchanger installed at the suction-inlet of a pump at a constant (medium) flow rate were conducted. Variation of the heat transfer coefficient and fouling resistance was measured for each test and a sample of the accumulated foulant was collected at the end of each test to determine its particle size distribution. The particle size distribution of the foulant collected from each test case was analyzed and compared to the size distribution of particles in the wastewater. Results suggested that the diameters of particles deposited on the tube surfaces were mainly in the range of 1.5-88 mu m. The average particle diameter of fouling was 40.8 mu m at a velocity of 0.31 m/s (low), 24.4 mu m at a velocity of 0.46 m/s (medium), and 18.6 mu m at a velocity of 0.69 m/s (high). Asymptotic fouling resistances were 1.1 x 10(-3), 0.59 x 10(-3), and 0.22 x 10(-3) m(2) K/W respectively for the low, medium and high velocities. In addition, negative fouling resistances were observed at the beginning of fouling development with low and medium wastewater velocities. Results also showed that both the asymptotic fouling resistances and the average particle diameter of fouling obtained with the heat exchanger installed at the suction-inlet of pump were larger than that with heat exchanger installed at the shoot-outlet. On average, 71% (by mass) of fouling consisted of ash ingredient. (C) 2014 Elsevier Ltd. All rights reserved.