series of experimental investigations have been done to study the hansicnt characteristics of the plate-fin heat exchangers. The dynamic. response tests were carried out for different values of Reynolds numbers, Prandtl numbers and NTU. The scalings of flowrate erturbation were examined based on the experimental results, with a linear theoretical model. Furthermore, two formulae are presented which can be used to calculate the time delay of response' according to the inlet temperature.change.