Synergism between particulate and microbial fouling on a heat transfer surface using treated sewage water

Abstract

The waste-heat utilization heat pump system to use the energy in the treated sewage water has been regarded as a green approach for urban heat recovery. However, the inevitable mixed fouling on heat transfer surface resulting from complex impurities in sewage water could cause heat transfer coefficient to reduce sharply. The synergistic effect between two main types in mixed fouling (i.e., particulate fouling and microbial fouling) plays an important role on the performance of heat exchanger in heat pump system. In different operating conditions, various characteristics of bacteria and particles, synergistic effects between particulate fouling and microbial fouling are studied by thermal resistance method experimentally, while the micro structures of mixed fouling are investigated by Scanning Electron Microscope (SEM). An apparently synergistic effect between microorganisms and particles in the mixed fouling is reflected by the denser structure and lager thermal resistance of mixed fouling. But the synergistic effect between microorganisms and particles shows weakening tendency with the increasing of temperature and flow rate of the working fluid. In addition, the enhanced synergistic effects could be achieved with the increment of the cooling water temperature, the bacterial concentration and the particle concentration. Therefore, altering conditions to weaken the synergism between microorganisms and particles could be an effective way to reduce mixed fouling.