Time dependency of fouling factor(With induction time)
Fouling factors are time-dependent and will always increase with time. The way it increases depends on the specific situation. It could increase linear with time, or increase asymptotically to a certain limit. The latter case isn’t as worse as the linear case. When time increases, fouling resistance will reach some constant value. This means that one can design a heat exchanger in such a way, that this constant resistance is compensated. In the linear case it is necessary to periodically clean the heat exchanger, or else the fouling resistance would reach the sky.
In most cases there is also an initial induction period; for a clean heat exchanger with initial fouling factor zero there is a certain time interval for which the fouling resistance is very low.
This is illustrated in figure 5.
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