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Calculation of heat exchangers taking into account the flow structure

T.M. Farakhov, E.P. Afanasyev, A.G. Laptev

Vestnik IGEU, 2019 issue 1, pp. 11—17

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Abstract in English: 

Background. Heat exchangers, used in various industries as well as at thermal power plants, have different performance characteristics, designs and overall dimensions, but despite the existence of such a considerable variety of designs, their calculation is most often carried out based on the ideal flow displacement model. In some cases, this may lead to an underestimation of the heat transfer area. In this regard, it is important to develop a mathematical model and algorithm for calculating heat exchangers taking into account the reverse mixing of heat carriers, when the flow structure differs from the model of ideal displacement.

Materials and methods. The article makes use of the method of numbers of transfer units, as in case of mass transfer, corrected for the backmixing of the coolants. The correction is performed using the modified Peclet number of the flow structure, which leads to a small increase in the length of the heat exchanger tubes, and consequently, the heat transfer area.

Results. Expressions for calculating the length of the tubes and heat transfer area taking into account the backmixing of the flow have been obtained. Equations have been given for calculating the main parameter of the flow structure models – backmixing ratio.

Conclusions. The presented approach improves the calculation accuracy of heat exchangers with intensifiers, for example, of channels with random packings, coiled elements, various inserts, etc.

 

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Key words in Russian: 
теплообмен, структура потока, обратное перемешивание, поверхность теплопередачи, диффузионная модель, тепловая эффективность
Key words in English: 
heat transfer, flow structure, backmixing, heat transfer area, diffusion model, thermal efficiency
The DOI index: 
10.17588/2072-2672.2019.1.011-017
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