Effect of variable viscosity on the performance of plate heat exchangers - Numerical approach

One dimensional temperature distribution of flow in the channels of a plate heat exchanger has been studied when the fluids' viscosities vary with respect to temperature. A computer program based on finite differences is developed to calculate the overall heat transfer coefficient in each axial section based on the fluid inlet temperature to that section and then to work out the outlet fluid temperature from that section. The predictions of the present program show that when water is used as the cold fluid, the difference between temperature distributions for constant and variable viscosities is more than that for glycerin and isooctane. It is also noticed that when variable viscosities are used, the overall heat transfer coefficient varies linearly with respect to either cold or hot fluid temperature, provided the specific heats of both fluids remain constant. The exchanger effectiveness is not affected when either the temperature dependent viscosities are applied or the nature of fluid is changed.