Determination of axial dispersion coefficients in plate heat exchangers using residence time measurements

Abstract

Residence time measurements are introduced as a transient measurement technique for the fast and convenient determination of axial dispersion coefficients in plate heat exchangers. In front of the exchanger inlet a salt solution pulse is injected into the steady flow stream and propagates with dispersion to the exit of the exchanger. The concentration profiles are measured at the inlet and outlet of the exchanger. The analytical residence time distribution of the axial dispersion is evaluated with both experimental inlet and outlet profiles to obtain the dispersion coefficient. The results of the measurements confirm the suitability and necessity of the axial dispersion model to describe transient behaviour of plate heat exchangers. The experimental curves show that the determination of axial dispersion coefficients by evaluation of residence time distribution curves is a reliable method. The measurement technique permits measurements for short residence times as occur in heat exchangers, and it facilitates the application of the dispersion model in practice. Hence, transient behavior can be calculated as fast as and with higher precision than with the conventional plug-flow model.