Experimental Study Of Microscopic Imaging Of CaCO₃Fouling On Four Heat Transfer Surface

Fouling in heat exchange equipments is an extraodinary abnormal phenomena．Itlies in many fields, such as in nature, in our daily life and widely in industrial processes.It not only reduces the heat transfer efficiency of heat transfer equipments, but alsowastes energy and resources, and even makes the technologies and methods ofhigh-efficient energy use infeasible.So the processes and characteristics of the foulingform and diffusion in fluid, then adhesion and growth on heat transfer surface must betaken into consideration when designing the heat equipments in order to inhibit andmitigate fouling,thereby,enhance the heat transfer and save energy with high efficient．Without fluid flow and gravitational settling influence, the experiment adopts staticprecipitation reaction method, the four common used materials was prepared as couponswhich was vertical suspended in the supersaturated calcium carbonate solution,so wecan study the effect of substrate and liquid properties on precipitation characteristic ofCaCO3crystal. The experiment adopts four substrates: copper, brass stainless steel304and316.The fluid propertis includes the temperature, concentration and pH of solution.We got lots of data that characterize growth characteristic of CaCO3crystal, includingfouling mass, crystal morphology, size and induction period of CaCO3fouling crystal.Results of the experiment indicated that when the fluid is supersaturated, a part of scaleions in system precipitate on the heat transfer surface by diffusion and adhesion, andthen the process of heterogeneous nucleation and crystal growth.Under the samecondition,the fouling mass on stainless steel304is the biggest,and then stainless steel316, copper,and the brass is smallest.The fluid properties not only influence the crystalmorphology,but also the size of crystal,and therefor affect the fouling mass. Withtemperatures rising, the fouling mass and size of crystal has the tendency of reduction,and the proportion of aragonite increases. The fouling mass and size of crystal has thetendency of reduction as the temperature rises, the main crysyal morphology iscalcite.When the concentration of CaCO3rises, the fouling mass increases, but the sizeof crystal decreases, and calcite is the main morphology of CaCO3crystal.