Biofouling Induction Period And Influential Factors

The presence of biofouling in circulating cooling water increases the drag on heat transfer performance of heat exchanger, leading to an increase in fuel consumption and hence carbon dioxide emissions, reduces energy utilization ratio and equipment safety and reliability, resulting in substantial waste of energy and materials. The study of forming mechanism of biofouling and the variation of water quality parameters could provide essential parameters for the design and cleaning of heat exchangers, so it is an important technology to achieve energy-saving & discharge reducing and to realize low-carbon and circular economy. The project is sponsored by the National Natural Science Foundation of China (No.50806010).In view of the fouling mechanism complexity, the slime-forming bacteria and iron bacteria were chosen as research object, which are easy to form biofouling in the heat transfer surface or other solid walls. Domestic water in Jilin city was used as cooling water and pipes were used as heat exchange tube to dynamic simulate fluid flow and heat and mass transfer process of cooling water system. Operating conditions (flow rate, temperature) automatically maintained in a constant environment by computer in order to distinguish other factors on the fouling thermal resistance from total number of bacteria and water quality parameters. Based on digestion and absorption of existing theory and experimental results of biofouling, this paper discussed main water quality parameters and the total bacterial count of fouling resistance induction period and forming the influence mechanism. The element composition in the biofouling on stainless steel pipe for drinking water was identified with XPS.Under constant condition, through dynamic simulation repetitive experimental research of slime-forming bacteria and iron bacteria, The analysis of experiments result and influence factor indicate that:Induction period of slime-forming bacteria respectively was 56.73 hours (stainless steel smooth tube),74.97 hours (copper smooth tube) and 99 hours (converging diverging tube); Total bacterial count reached the maximum in the vicinity of the induction period; In the initial stage, pH decreased and then increased, the conductivity has been rising, two parameters reached maximum at the end of the induction period, the remaining time essentially unchanged; Dissolved oxygen decrease gradually in the process of the experiments. Induction period of iron bacteria were 25 hours (stainless steel smooth tube); In the initial stage, pH has been rising until the end of induction period; The contrast experimental research of slime-forming bacteria and iron bacteria shows that iron bacteria are biggest hazard strains in stainless steel pipe of circulating cooling water. the main component of biofouling of the slime-forming bacteria and iron bacteria is C, O, N, Fe, Ca, Mg, etc; In the same stainless steel pipe, the major elements of the ratio in different strains will exist diversity, but the most important elements were still carbon and oxygen.Norm grey correlation was used to calculated correlation degree of the main water quality parameters on the fouling characteristics. Based on the correlation degree, this paper selected the pH, dissolved oxygen, conductivity and the total bacterial count and time as the input, took the fouling resistance as the output variable, established fouling prediction model of the BP Artificial Nerve Network and least squares support vector machine (LS-SVM).