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a b s t r a c tThe developments in design theory of plate heat exchangers, as a tool to increase heat recovery and efficiency of energy usage, are discussed. The optimal design of a multi-pass plate-and-frame heat exchanger with mixed grouping of plates is considered. The optimizing variables include the number of passes for both streams, the numbers of plates with different corrugation geometries in each pass, and the plate type and size. To estimate the value of the objective function in a space of optimizing variables the mathematical model of a plate heat exchanger is developed. To account for the multi-pass arrangement, the heat exchanger is presented as a number of plate packs with co-and counter-current directions of streams, for which the system of algebraic equations in matrix form is readily obtainable. To account for the thermal and hydraulic performance of channels between plates with different geometrical forms of corrugations, the exponents and coefficients in formulas to calculate the heat transfer coefficients and friction factors are used as model parameters. These parameters are reported for a number of industrially manufactured plates. The described approach is implemented in software for plate heat exchangers calculation.

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The Plate Heat Exchanger (PHE) is one of the most efficient types of modern heat exchangers. Heat transfer enhancement is one of the main features of PHEs, and lower fouling tendencies render them even more advantages for the use in different applications. The effects on fouling accumulation rate of process parameters in PHE channels of intricate geometry are studied in this article. The asymptotic behavior of the water fouling on heat transfer surfaces is examined. The fouling accumulation rate is described as a difference between the fouling deposition term and the fouling removal term. On comparison with data for fouling on different heat transfer surfaces available in literature it is shown that asymptotic fouling thermal resistance inversely proportional to wall shear stress. The proportionality coefficient in this relation is determined for a number of considered cases. To calculate the wall shear stress the equation for PHE channel main corrugated field is used, which accounts for corrugations geometrical parameters. It is shown that for given fouling properties of water this coefficient is constant and can be determined by monitoring fouling behavior of any item of heat exchangers working on specific enterprise. After that all other heat exchangers of that enterprise can be calculated using that data and developed Equation for accounting of fouling in their design.

The mathematical model of plate heat exchanger (PHE) is developed using decomposition of the plate on its main corrugated field, which cause major effect on heat transfer, and distribution zone, which influences mostly the hydraulic performance. Model is validated on experimental data for some commercial plates. It is shown, that for specified pressure drop, temperature program and heat load the geometrical parameters of plate and its corrugations, which are enable to make PHE with minimal heat transfer area, can be found. The developed mathematical model can be used for designing of plates with geometry, which is in the best way satisfying process conditions of the certain specific range. The case study for conditions of PHE application in District Heating systems is presented.

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An analysis is presented for the main factors which control the intensity of vapor condensation in plate condenser channels, such as heat transfer both in single-phase stream of the coolant and in the condensate film, heat and mass transfer in gas-vapor phase, thermal resistance of fouling at heat transfer surface and pressure drop in condensing stream. On the basis of a relationship between the heat transfer and the wall shear stress, an approximate equation is obtained for calculating heat transfer from the pressure drop data. For calculation of heat transfer in condensate film during the condensation of high speed vapor, an analogy between heat and momentum transport has been used. An analysis of fouling deposition on heat transfer surface has been performed and an equation is presented for calculating the reduction of the fouling thermal resistance as compared with shell and lube heat exchangers. Experimental data are in good agreement with theoretical results. These data have shown the improvement of all the mentioned factors, which determine the intensity of the whole condensation process compared to the same factors in shell and tube condensers. Under the equal conditions, the required area of the heat transfer surface is reduced by 1.6 to 3 times for the plate condenser, as compared with conventional shell and tube units.

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