Please forward this error anti dust to 107. This article is about fouling in engineering. Not to be confused with fowling.
This article needs additional citations for verification. Fouling is the accumulation of unwanted material on solid surfaces to the detriment of function. Other terms used in the literature to describe fouling include: deposit formation, encrustation, crudding, deposition, scaling, scale formation, slagging, and sludge formation. This article is primarily devoted to the fouling of industrial heat exchangers, although the same theory is generally applicable to other varieties of fouling. In the cooling technology and other technical fields, a distinction is made between macro fouling and micro fouling. Of the three, micro fouling is the one which is usually more difficult to prevent and therefore less important. Macro fouling is caused by coarse matter of either biological or inorganic origin, for example industrially produced refuse.
Leaves, parts of plants up to entire trunks. Composite fouling, whereby fouling involves more than one foulant or fouling mechanism. Limescale buildup inside a pipe both reduces liquid flow through the pipe, as well as reduces thermal conduction from the liquid to the outer pipe shell. Both effects will reduce the pipe’s overall thermal efficiency when used as a heat exchanger. The water is pressurized so that it can be maintained in the liquid state at the elevated temperatures. Scaling or precipitation fouling involves crystallization of solid salts, oxides and hydroxides from solutions. These are most often water solutions, but non-aqueous precipitation fouling is also known.
The calcium carbonate that forms through this reaction precipitates. Due to the temperature dependence of the reaction, and increasing volatility of CO2 with increasing temperature, the scaling is higher at the hotter outlet of the heat exchanger than at the cooler inlet. In general, the dependence of the salt solubility on temperature or presence of evaporation will often be the driving force for precipitation fouling. The important distinction is between salts with «normal» or «retrograde» dependence of solubility on temperature. The salts with the «normal» solubility increase their solubility with increasing temperature and thus will foul the cooling surfaces. Precipitation fouling can also occur in the absence of heating or vaporization. For example, calcium sulfate decreases it solubility with decreasing pressure.
This can lead to precipitation fouling of reservoirs and wells in oil fields, decreasing their productivity with time. This process is usually most important for colloidal particles, i. The value of P for colloidal particles is a function of both the surface chemistry, geometry, and the local thermohydraulic conditions. Being essentially a surface chemistry phenomenon, this fouling mechanism can be very sensitive to factors that affect colloidal stability, e. Particles larger than those of colloidal dimensions may also foul e.
With time, the resulting surface deposit may harden through processes collectively known as «deposit consolidation» or, colloquially, «aging». Sedimentation fouling by silt and other relatively coarse suspended matter. Fouling by particles from gas aerosols is also of industrial significance. The particles can be either solid or liquid. The common examples can be fouling by flue gases, or fouling of air-cooled components by dust in air. The mechanisms are discussed in article on aerosol deposition. Corrosion deposits are created in-situ by the corrosion of the substrate.
They are distinguished from fouling deposits, which form from material originating ex-situ. Corrosion deposits should not be confused with fouling deposits formed by ex-situ generated corrosion products. Corrosion deposits will normally have composition related to the composition of the substrate. Chemical reactions may occur on contact of the chemical species in the process fluid with heat transfer surfaces.