Effect of Scale Deposits on the Temperature Regime in the Channels of Plate Heat Exchangers

At the present stage of development in heat-supply systems, there is a trend toward shifting from shell-and-tube structures to a plate design of heat exchangers. The advantages of the plate design are its compactness and efficiency. The major operational problem is fouling in the interplane channels, which decreases the thermal efficiency and increases the operational expenditures. The objective of this study is to demonstrate the effect of scale deposits and individual hydraulic conditions in each channel on the temperature regime of a plate heat exchanger. Since this problem in the theory of heat exchangers is insufficiently studied and involves important assumptions, the diagnosis of fouling in the channels is incorrect. The hydrodynamic regime in a plate heat exchanger is established by using the theory of resistance characteristics in hydraulic systems. The temperatures of the heating and heated heat-transfer fluids at the outlet from each heat-exchange channel are set on the basis of the mass-conservation law. This method makes it possible to use the results of hydrodynamic calculation on resistance characteristics to determine the temperature regime in a plate heat exchanger along the length of a package of plates, including with consideration of the effect of scale deposits. The proposed methods are validated by comparing with computer-aided modeling results by the Pearson’s and Student’s tests. The dependence between the final temperatures of a heat-transfer fluid at the outlet from the channels on its nonuniform flow distribution in the channels with fouling is revealed. The theory of resistance characteristics as applied to calculate the hydrodynamic regime in a plate heat exchanger along with the proposed thermal regime calculation, including with consideration of the factor of scaling, will make it possible to improve the precision of fouling diagnosis and decrease the operational losses. The performed studies confirm the effect of scale deposits in heat exchangers and individual hydraulic conditions in interplate channels on their temperature regime. The results of this research are of scientifical and practical interest for the study and development of intensified heat-exchange surfaces with the purpose of increasing the energy characteristics of heat exchangers, as well as in the field of diagnosing the regime parameters of water heating equipment in the period of its operation.