Experimental And Modelling Research On Biofouling Growth Mechanisms And Heat Transfer Characteristics

Non-clean water source heat recovery technologies such as treated sewage source heat pump systems saw a rapid development in recent years. However, the biofouling formed inside the non-clean water heat exchangers remain as a crucial issue of heat transfer efficiency and system security. This study focus on the theme of biofouling growth mechanisms and heat transfer characteristics. Combinations of experimental and modeling approaches were employed to explore the growth mechanisms, suspended matter interactions, heat transfer coupling and innovative fouling inhibition technologies in biofouling area.The associate strains, nutrient and suspended matters compositions in model fluid were established in this study. A new visualized channel system with heat transfer experiment functions were designed and built. The observations and measurements were updated with the introductions of CLSM and living cell staining techniques. All these materials and methods were introduced for experimental investigations on biofouling growth mechanisms and heat transfer characteristics.Growth mechanism experiments employed associate strains including Bacillus.sp and Aeromonas.sp to investigate biofouling weight. Inhibition and co-exist interactions between bacterial strains with different cell ratios were analyzed. Nutrient influences on biofouling growth and bacterial strains interactions were also studied. Bacillus.sp were found to be competitive under insufficient nutrient conditions and the reasons were illustrated.Large velocities and sizes were found to have fouling inhibition capabilities in suspended matters interactions experiments. Concentrations shown magnification influences on interactions. Empirical equations were came up for fast forecast of interactions and fouling extents. Artificial polyamide filaments experiments revealed the unique attachment mechanisms of filaments in micro scales.The optimal temperatures for associate strains growth were measured and specific growth equations were developed. The two layers structure of biofouling was analyzed and thermal conductivity was calculated by online measurements of thermal resistances and thicknesses. Thermal resistances were used as the main indicators in biofouling heat transfer characteristics experiments. Coupling between temperature field and biofouling was analyzed. The optimal heat exchanger configurations were suggested for different temperature field scenarios.Three new surface modification technologies for heat transfer surfaces fouling inhibition were developed, validated and evaluated. The silver coatings had shown significant inhibition effects by reduce cell activities and EPS structures. The additional thermal resistances of silver coatings were acceptable, with the contact thermal resistances occupied the dominate percentages. The silver coatings shown minor decreases by abrasions during cleanings. Paraffin coatings shown advantages of on-line coating and cleaning as well as controllable additional thermal resistances. Benzalkonium chloride embedded paraffin coatings shown enhancements in fouling inhibitions. The inhibition effects concentrated on the bottom fouling layer, which contributed to the reduction of agents’ consumptions and subsidiary pollutions.A multi-physics coupled three dimensional life cycle cellular automata model was established based on biofouling experiments. Associate bacterial strains interactions were simulated to illustrate the strong capacities of Bacillus.sp in fouling formations. Temperature field coupling and particle interactions were also simulated, validated and analyzed.This study provides guidance on further scientific investigations on biofouling growth mechanisms and heat transfer characteristics. This study also has good application values in solving biofouling issues on heat transfer surfaces.