Research of horizontal single-row bundles of ribbon finned tubes at free convection

Abstract

The intensity of free convection research leads to a wider understanding of the mechanisms and possibilities of using free-convection currents for the heat discharge or heatremoval in many industries, in energy processes, in a large number of devices or systems. Free convection significantly affects the maximum values of heat fluxes, and studying them becomes quite important for problems in which other methods of heat transfer are not applicable or uneconomical. The phenomena of free-convective heat transfer are quite complex, processes of conjugate heat transfer, for example, radiation and convection can be observed. Theoretical methods of description and calculation are used for bodies of simple shape: ball, plate, cylinder. The methods of theoretical analysis for heat transfer of bodies of complex shape are too voluminous and cumbersome. The intensification of free-convective heat transfer is possible through the use of various types of fins. To calculate the natural convective heat transfer of finned surfaces, the criterial dependencies of an empirical nature are mainly used. The article presents the results of a study of free-convective heat transfer of single-row horizontal bundlesof industrial bimetallic pipes with tape finning, the finning factor of 16.8. The position of the pipes in the bundle is characterized by the by transverse steps standardized for heat exchangers for air coolingS1 = 58; 61; 64; 70; 76; 86; 100 mm, to which the relative steps corresponded σ1 = S1/d = 1.208; 1.271; 1.333; 1.458; 1.583; 1.792; 2.083. An equation for calculating the free-convection heat transfer, taking into account the influence of the relative step in the range of Rayleigh number from 30,000 to 350,000 with an average deviation of ± 6.6%, has been obtained.