In sizing a heat exchanger the fouling factor is always indicated and pressure drop is then calculated. Very often the fouling layer thickness is omitted in the calculation, resulting in clean pressure drop rather than required fouled pressure drop. In finding out fouling layer thickness, one will need the fouling layer conductivity (x fouling factor = thickness). The fouling layer conductivity is never specified and is very difficult to estimate. Currently we assume it be the same as the fluid. Is there a method in estimating the fouling layer conductivity by which the layer thickness can be calculated. Assume the fluid properties are known, such as bitumen or water. Fouling is either deposition or scaling.
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Jim Grant Forum Moderator 118 Posts
Re: Determining fouling layer thickness28 April 2006 at 1:29pmThe conductivity of a scale or deposit on a tube can be estimated by using a volume fraction average of the thermal conductivities of the components assumed to be in the scale. A porous scale may be
composed primarily of the fluid on/in the tubes, whereas a non-porous hard deposit may have little of the process fluid in it. I caution you that a fouling factor which has been presented on a heat exchanger specification sheet may well be an arbitrary value which someone has assigned based on common practice or TEMA tables or internal company practice. This may or may not be representative of a specific fouling material/thickness and the heat exchanger designer should be consulted.