Fouling and fouling mitigation on heated metal surfaces

An apparatus was built to study heat transfer fouling on different heat exchanger pipe surfaces by visually observing the progressive fouling deposition under the same solution conditions. Test pipes were centrally located in a cylindrical tank with a concentric vertical agitator to give constant and uniform flow conditions near the pipe surface. Pipes with either smooth or roughened surfaces provided quantitative data on the progressive build-up and the composition of the deposits. The calcium sulphate deposition on four different metal surfaces (copper, aluminium, brass, and stainless steel) was investigated. The results show that fouling increases with time but at a decreasing rate over set intervals. The deposition also increases with the increasing thermal conductivity of the metal, or the total surface energy. Chemical reaction fouling along with particulate and crystallisation fouling occurred on reactive surfaces when corrosive chemicals were used, and this was compared with crystallisation-only fouling on non-reactive surfaces. Bleached Kraft softwood pulp fibres at various concentrations were added to the fouling solution to study their affects on fouling on the hydraulically smooth pipes. Fouling was retarded with only a low fibre concentration and reduced further as fibre concentration was increased.

Fouling of calcium sulphate on different metal surfaces was studied. Fouling increases with time and thermal conductivity of the metals. Fouling rate was retarded in presence of fibre suspensions.Figure optionsDownload as PowerPoint slideHighlights
► Increasing surface roughness increases fouling.
► Fibres provide a good alternative means of mitigating fouling.
► Effect of fibres on fouling mitigation is consistent and irrespective of the tube material.
► Surface characteristics are altered by corrosive attack and this promotes fouling.