| The accumulation of microbial fouling in the heat exchanger causes fuel consumption,flow resistance and maintenance costs to increase to varying degrees.At present,the methods for microbial fouling of heat exchange equipment are still very limited.The development of surface technology provides new ideas for dealing with the problem of microbial fouling in heat exchange equipment.Some scholars have tried to use the excellent properties of electroless plating to suppress and mitigate dirt problems,and achieved good results.In this paper,Q235 carbon steel is used as the substrate,and the Ni-P-(nano)TiO2 composite coating is prepared by electroless plating,and the micro-morphology of the surface is analyzed.And through repeated cleaning to determine the stability of the surface.The results show that the Ni-P-(nano)TiO2 composite coating has good adhesion to the carbon steel substrate and has practical application conditions.The common iron bacteria in cooling water were used as test microorganisms to carry out the experiment of static microbial fouling on Ni-P-(nano)TiO2 composite coating.Obtained the surface energy of the Ni-P-TiO2 composite modified surface under different process parameters and the adhesion amount of microbial fouling in the bacterial suspension medium at different soaking periods;the change of the surface tension of the bacterial suspension medium was measured using a contact angle tester.The adhesion work of iron bacteria on the composite modified surface at different metabolic periods was calculated;the fouling process was analyzed in conjunction with the metabolism of iron bacteria,and the mechanism of microbial fouling adhesion of the autocatalytic coating was discussed.The experimental results show that the surface energy components of the microbial fouling medium and the wall surface adhesion work have an important influence on the deposition process of the microbial fouling.Within the range of experimental parameters,based on the extended DLVO theory,it was found that there is an optilal total surface energy ?TOT,at which the microbial fouling on the surface is minimal.In addition,the wall adhesion work of microbial media is closely related to microbial fouling.The Ni-P-(nano)Ti02 composite coating is not only beneficial to control the initial microbial adhesion,but also effectively induced by changing the characteristics of microbial media throughout the fouling process Scale deposition rate.The experiment of composite modified surface flow heat transfer was carried out by using iron bacterial suspension as the cold medium fluid.Based on the microbial fouling on-line monitoring experiment system of the plate heat exchanger,the microbial fouling characteristics of the plate heat exchanger coated with Ni-P-(nano)TiO2 composite coating were studied through experiments.The results showed that the friction coefficient(/)and Nussel number(Nu)of the two coated plate heat exchangers were a little higher than the uncoated one when it is in cleaning conditions;after the microbial fouling experiment,compared with the uncoated plate heat exchanger,the fouling resistance of Ni-P coated plate heat exchanger was reduced by 8.36%-23.07%,while the other one coated Ni-P-(nano)Ti02 was reduced by 16.6%-30.96%.Under the same microbial fouling experimental conditions,the heat transfer and fouling characteristics of the two coatings were compared and analyzed further.The friction coefficient(f)of plate heat exchanger coated Ni-P-(nano)TiO2 coating was reduced by 2.54%?11.82%compared with the coated Ni-P one,while the Nu number was increased by 8.47%?9.45%,and the fouling resistance was reduced by 10.66%-18.18%correspondingly.The plate heat exchanger coated Ni-P-(nano)TiO2 composite coating showed an excellent microbial fouling inhibition performance in heat mass transfer process. |
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