Investigation On CaSO₄Deposit Process At Treated Surface Under Pool Boiling And Flow Boiling Rig

Despite a lot of investigations about fouling in the past, the formation of deposit on heat transfer surfaces is still an unsolved problem in the operation of industrial heat exchangers. Many attempts have been made to reduce metal surface force/energy by, for example, coating the surface with Teflon, ceramic or polymer layers. However, these coatings require application in a very thin layer in order to avoid additional heat transfer resistance. This constraint in turn limits the adhesion of the layer on the surface, resulting in it easily peeling off and detaching from the metal surface. It has been confirmed by Prof H. Müller-Steinhagen and Dr. Q.Zhao that deposit formation on a metal surface can be reduced or even prevented by reducing the metal surface force/energy, using surface modification techniques, such as dynamic mixing ion beam implantation and dynamic mixing magnetron sputtering. In this thesis, the deposit formation on such modified surfaces were investigated, both theoretically and experimentally. The test runs were performed with various treated surfaces, heat fluxes, flow velocities and CaSO4-concentrations. The results obtained were compared with untreated surfaces under exactly identical conditions in order to determine the suitability and the characteristics of the various treated surfaces. It was found that metal heat transfer surface sputtered with DLC and AC, does not change the surface roughness, but reduces its surface force/energy and hence CaSO4 formation, significantly. Surface treatment conditions have significant effects on deposit formation. Polished metal heat transfer surface reduces surface roughness but does not affect the surface force/energy significantly. Therefore, no obvious deposit reduction was observed. The effects of heat flux, flow velocity and CaSO4 concentration on heat transfer coefficients of the treated and bare surfaces were also investigated.