Abstract
Basic governing differential equations on the heat transfer processes of plate heat exchangers are derived based on the heat balance. Three flow patterns are shown and each flow pattern contains various flow types according to the combination of the plates with a hole or a blank suitably placed at each corner. With each flow pattern the statics such as the steady state fluid temperature distributions and the temperature effectiveness is analysed and also the dynamics is obtained as frequency responses in the case of four passages. These characteristics are systematically investigated. Further, the experimental dynamic responses of the two typical types among four-passage plate heat exchangers are investigated. First, since the relation between the heat transfer coefficient α of the heat transfer plates and the fluid velocity v can be described as α=Cvn, n and C are obtained experimentally. Second, for each heat exchanger the steady state fluid temperature distributions are measured by thermocouples. Finally the experimental frequency responses are obtained by using sinusoidal change of the inlet temperature in the hot-side fluid and by measuring the outlet temperature in the coldside fluid.
The results show that two plate heat exchangers with the same statics do not always have the same dynamics if the flow types of the two are different and that the dynamics is affected more than the statics by the condition whether the inlet-outlet flow pattern of this heat exchanger is parallel or counter flow. And a favorable agreement between the theoretical results and the experimental ones is obtained.
