Fedosov S.V.

Doctor of Technical Sciences (Processes and Devices of Chemical Technologies) (Advanced Doctor), Professor, Moscow State University of Civil Engineering (National Research University), Academician of the Russian Academy of Architecture and Construction Sciences

Heat transfer from a cylindrical heater to a medium with variable thermophysical characteristics and heat source power

https://doi.org/10.58224/2618-7183-2024-7-6-8
Аннотация
The formulation and solution of the problem of non-stationary thermal conductivity in a composite material with variable thermophysical characteristics are considered. Density, heat capacity, thermal conductivity, as well as the power of the heat source due to the hydration reactions of the binder components change during the concrete hardening process. The heat transfer problem is formulated for the general case when there are no calculation formulas for thermophysical transfer coefficients. The “microprocess method” was used to calculate the dynamics of the temperature field. According to this method, the space from the outer surface of the heater is modeled by a system of successively located “rings”. When moving from the previous “ring” to the next one, the charge in the transfer coefficients and the power of the volumetric heat source were taken into account. At the same time, the initial and boundary conditions were corrected. The boundary value problems are formulated in the form of a differential equation of non-stationary heat transfer with an arbitrary initial distribution of transfer potentials, Dirichlet boundary conditions, and a heat source in the form Po=f(Fo).The obtained solutions are analyzed for some particular cases. Prospects for further theoretical and experimental research are determined.
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Cauchy problem for modeling of unsteady mass transfer processes in an unbounded plate by the integral laplace transform method

https://doi.org/10.58224/2618-7183-2024-7-5-4
Аннотация
The article outlines the formulation and solution of the problem of physical and mathematical modeling of non-stationary processes of mass transfer of chemical components of the structure of reinforced concrete enclosing structures under the influence of factors (chemical, biological) of the operating environment. The theory of operational calculus (integral transformations) is used as a mathematical apparatus for jointly solving Cauchy and Laplace problems. To solve the problem and study the processes considered in the article, a dimensionless plate with a dimensionless concentration of aggressive components on its surface was chosen as an idealized model of the enclosing structure. Carbon dioxide, dissolved in the liquid and penetrating with it into the material of the structure through pores and microcracks, was chosen as an aggressive component acting on the enclosing structure. The final solutions of the considered boundary value problems are presented for the case of constant values of the kinetic coefficients of external and internal mass transfer. The results presented in this work can be used in the development of software for predicting the strength characteristics of enclosing structures operating in aggressive environments. Thanks to the obtained solutions to the problems of non-stationary mass transfer processes, using the example of the consequences of carbon dioxide corrosion, it is possible to consider the time period of the life cycle of buildings and structures, the timing of repair work with greater accuracy.
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