4process. But at the same time, its application is cumbersome and covers only particular cases. As a rule, they are confined by the description of the process of heating-cooling the bodies of simple shapes: infinite plate, cylinder, and sphere. Such solutions have been known for a long time, but up to now they have been applied only for a similar kind of processes. Only the object of application has changed in favor of contemporary equipment as, for example, in [3], where the problem on cooling a display is solved. Article [4] examines a process of cooling the plate with an internal heat source. The difference is that the examined plate is a multilayer one. A special feature of paper [5] is the application, instead of the frequently utilized Fourier expansion, the Trefftz functions. In this case, only the approximate solution is obtained. The problem of nonstationary heat transfer is of practical interest and it does not have the analytical solution.Numerical methods are more universal and can be used to solve any problems on heat transfer. From the above enumeration of simple shapes of bodies, a plate appears the most important one. It has two surfaces, which corresponds to the process of heat transfer. Furthermore, for the case of coaxial cylinders (a pipe) at the ratio between outer and inside diameters of d 2 /d 1 <2, heat transfer through the cylindrical wall with an error less than 4 % can be described using the model for a flat wall. Such a relationship of diameters corresponds to the majority of variants of tubular heat exchangers. Heat transfer is predetermined by taking account of the combined processes of heat exchange at the surfaces of a plate. These
IntroductionThe use in energy equipment of fuel with variable composition [1, 2] instead of the certified constant formulation leads to an increase in the number of transient modes. A change in calorific fuel capacity, amount of products of combustion, their thermophysical properties predetermines the non-stationary processes of heating-cooling the elements of power equipment design, as well as nonstationary processes of heat transfer through the heat exchange surfaces. As a consequence, in the processes of energy conversion a more important role is played by its variable accumulation -release in all equipment components in contact with the combustion products. The accumulation of energy (heating -cooling) affects inertness in the processes of heat transfer and, therefore, manageability of the process of energy transformations. In turn, the magnitude of energy accumulation is determined by temperature of the elements of design. Thus, determining the non-stationary temperature and, as a result, the nonstationary magnitude of energy accumulation, is an important element in solving the problem on optimal control of power equipment under conditions of using a non-certified fuel of variable composition.
Literature review and problem statementAnalytical solution is a reliable and universal means to calculate parameters of the nonstationary heat exchange
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