The use of turbulence generators to mitigate crystallization fouling under cross flow conditions

Different types of turbulence generators were used to mitigate crystallization fouling of a water-cooled pipe at 5°C in a cross flow of hot sodium sulphate (Na2SO4) solution. The Reynolds number of the hot solution (based on pipe diameter, RehD) was varied from 250 to 485 at a constant temperature, Th=40°C. The Reynolds number of the cold water within the pipe was 25,000. Four types of turbulence generators were investigated, namely, punch plates of different blockage area, wire mesh of 50% blockage area, delta wings, and an identical pipe. These were placed upstream from the cold pipe, which was aligned normal to the hot cross flow. The surface temperature of the pipe was measured at four positions for all conditions. It was found that the turbulence generators increases the heat transfer coefficient and decreases the fouling resistance appreciably. For example, the punch plate with blockage area of 80% yielded an 85% reduction in fouling resistance at higher Reynolds numbers. However, the extent of the benefit depends on the shape of the turbulence generator, solution Reynolds number, and blockage area. For example, no appreciable effect was detected for the case where upstream pipe was used for the turbulence generator. Considerable differences in local surface temperature at various positions were noticed. The positions deduced to be subjected to the highest turbulence intensity were found to exhibit the highest local temperatures and thus lower fouling resistance.