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Precipitation fouling is a very common problem in boilers and heat exchangers operating with hard water and often results in limescale. Through changes in temperature, or solvent evaporation or degasification , the concentration of salts may exceed the saturation , leading to a precipitation of solids (usually crystals).
Assume heat transfer [2] is occurring in a heat exchanger along an axis z, from generic coordinate A to B, between two fluids, identified as 1 and 2, whose temperatures along z are T 1 (z) and T 2 (z). The local exchanged heat flux at z is proportional to the temperature difference:
The number of transfer units (NTU) method is used to calculate the rate of heat transfer in heat exchangers (especially parallel flow, counter current, and cross-flow exchangers) when there is insufficient information to calculate the log mean temperature difference (LMTD).
Fluid flow simulation for a shell-and-tube style exchanger; The shell inlet is at the top rear and outlet in the foreground at the bottom Shell and tube heat exchanger. A shell-and-tube heat exchanger is a class of heat exchanger designs. [1] [2] It is the most common type of heat exchanger in oil refineries and other large chemical processes ...
The problem of heat transfer in the presence of liquid flowing around the body was first formulated and solved as a coupled problem by Theodore L. Perelman in 1961, [1] who also coined the term conjugate problem of heat transfer. Later T. L. Perelman, in collaboration with A.V. Luikov, [2] developed this approach further.
The use of ethylene glycol has a longer history, especially in the automotive industry. However, EGW solutions formulated for the automotive industry often have silicate based rust inhibitors that can coat and/or clog heat exchanger surfaces. Ethylene glycol is listed as a toxic chemical requiring care in handling and disposal.
The study concluded that although microbial fouling was an issue for the warm surface water heat exchanger, the cold water heat exchanger suffered little or no biofouling and only minimal inorganic fouling. [46] Besides water temperature, microbial fouling also depends on nutrient levels, with growth occurring faster in nutrient rich water. [113]
The Tubular Exchanger Manufacturers Association (also known as TEMA) is an association of fabricators of shell and tube type heat exchangers. [1] TEMA has established and maintains a set of construction standards for heat exchangers, known as the TEMA Standard. [ 2 ]