Transient response of multi-pass plate heat exchangers considering the effect of flow maldistribution

Present study depicts the transient response of multi-pass plate heat exchangers (PHEs) considering flow maldistribution from port to channels. Apart from the flow maldistribution, fluid axial dispersion is also considered to take care of the fluid backmixing and other deviations from plug flow. It is assumed that each multi-pass PHE is a combination of single-pass PHEs and in each heat exchanger the fluid is distributed non-uniformly amongst channels. The fluid velocity varies from channel to channel within each module of the heat exchanger so also the heat transfer coefficient. The solution techniques have been presented here for 1-2 pass and 2-2 pass arrangements. The first one is solved by analysing successive modules of the heat exchanger and the next one by iterating the responses between two heat exchanger modules. The solution for each module has been obtained analytically by using Laplace transform followed by numerical inversion from frequency domain. The results show the effect of flow maldistribution and its effect combined with the conventional heat exchanger parameters in the transient regime. It is observed that the transient characteristics such as response delay, asymptotic value and time constant are strongly dependent on the multi-pass flow arrangement, maldistribution and backmixing characterised by axial dispersion.