ANALYSIS OF THE COOLING EFFECT CRITERIA OF BUILDING STRUCTURE AND ENERGY DEVICE

abstract

English

Cooling and heating are fundamental physical processes associated with heat transfer in building structures, in technological processes, with phase change of flowing fluids in energetic devices and in other industrial applications. The aim of this paper is to investigate the dependencies of the cooling criteria of a building structure (building envelope) and the energetic device located in the building. The discontinuity of the mentioned thermal processes is conditioned by the variation of the thermal content of the investigated bodies. For technical purposes, in most cases of building structures the heat flux can be monitored in one direction, most often in the x-axis direction. The results of the solution of the first and second order Bessel functions show that the function of interest depends on many variables. A deeper analysis reduces the number of independent variables to three dimensionless ratios - criteria (similarity constants), one of which is the Bi - Biot criterion. This number is considered as an evaluation criterion of the building structure. Generally, the most followed parameter in experimental investigation of phase change parameters in power equipment is the heat transfer expressed by the dimensionless criterion Nu - Nusselt number, with relation to the transfer characteristics. The two proposed dimensionless numbers express the ratio of convective and conductive heat transfer, with no difference in the dimension of each parameter, but they differ in the value of the thermal conductivity coefficient, both in the case of the building structure and in the case of the flowing fluid. In this paper, values in the range of Biot's number Bi ˃˃ 1 and Nusselt's number Nu ˃ 3.66 are considered. In the paper, analytical calculations of non-stationary heat conduction in a building structure with negligible external thermal resistance and Nu calculations according to selected correlation relations of different authors in the process of fluid cooling in a power plant are performed in terms of their suitability, usability, and applicability. The output is finding the functional dependence of both criteria (building object and energy device) and its general application to different building structures and energy devices in terms of cooling effect.The results of the calculations in relation to the dimensionless criteria Bi and Nu are tabulated and expressed graphically.

cooling effect, building structure, energy device

KUBÍN, M.; HIRŠ, J.; BAROŇ, A.; BADAI, A.

9. 8. 2022

241

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https://www.wmcaus.org/files/WMCAUS2022_Book.pdf