Abstract. The accuracy of hydraulic calculations is determined by the accuracy of the mathematical models inherent in their foundation. The results of calculations, obtained by different models, and differing from each other by 5-10% is considered identical. The present study examines classical ways of finding the Chezy formula that are used for calculations of free-flow pipelines. These formulas differ from each other not only in parameters but also in the form of the functional dependence. The equation, underlying the hydraulic calculations, is nonlinear. Its solution is possible only in the number of well-established methods. It offers numerical computing to find pipelines diameters and their filling, as well as the algorithm to realize it. It conducts numerical experiment to compare pipelines diameters and filling and flow velocities. It presents frequency characteristics to distribute the parameters under analysis. For a specific example, the difference of cost of pipes, the diameters of which was found using the various formulas for coefficient Chezy, was calculated.
The article provides an analysis of existing solutions for choosing shell-and-tube heat exchangers for the needs of hot water supply. When constructing a mathematical model of heat transfer, an approximation of the criterial dependencies describing this process was used. The error estimation of approximating dependencies is presented. The mathematical model of heat balance was used in a numerical experiment. The significance of the influence on the heat transfer efficiency of the parameters of the heat exchanger was established by the results of a numerical experiment. The results of a numerical experiment made it possible to develop criteria for choosing heat exchangers. Keywords: hot water supply, heat exchanger, mathematical modeling, selection criteria
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