Dynamic Behavior of Plate Heat Exchangers—Experiments and Modeling

Experiments on the transient behavior of two welded plate heat exchangers with identical construction but different numbers of plates have been carried out under different operating conditions. The temperature response on both sides following a step change in inlet temperature on one side has been compared to a theoretical model. The model takes the effects of flow maldistribution within the channels and between channels into account by introducing a dispersion term in the energy equation. The phase lag due to different flow path lengths between inlet or outlet of the heat exchanger and inlet or outlet of the individual channels are also taken into account. Heat conduction through the plates in the main flow direction of the fluids can be neglected for the exchangers under consideration. The model is validated by the experiments. It is found that the dispersion model considered gives a better simulation than the conventional plug flow model. From the experiments the effects of NTU, heat capacity rate ratio, and number of plates were also determined. This demonstrates the whole spectrum of dynamic behavior of plate heat exchangers. To suggest a proper control strategy for such heat exchangers, the parameters of conventional first and second-order systems with delay period have been determined from the results of the experiments and the theoretical model.