why does higher flow rate reduce the fouling resistance in heat exchanger?
Mainly by reducing the overall amount of fouling in the first place. Particulates stay entrained in the greater flow and are less likely to drop out. Biological growths, either plant or animal, find it harder to attach to the heat transfer surfaces due to the increased velocity and lack of deposited inorganic particulates to attach to. And the entrained particulates can have a scouring effect by effectively removing some initial growths by impact.
