EXPERIMENTAL INVESTIGATIONS INTO THE HEAT TRANSFER OF A STANDARDIZED BIMETAL ANNULAR-FINNED TUBE WITH VARIOUS HEIGHT OF THE FINS UNDER THE CONDITIONS OF FREE AIR CONVECTION

The paper presents a generalization of the results of an experimental investigation into the heat transfer of a bimetal fi nned tube with spiral knurled annular fi ns (interfi n pitch s = 2.5 mm) under the conditions of free convection.
The obtained results were approximated using two options for selecting defi ning characteristics to calculate similarity numbers, viz., the West European variant, where the interfi n space s′ is taken as a characteristic dimension and the wall temperature t_w is taken as a defi ning temperature, and the East European variant, where the fi n baselimited tube diameter d₀ is taken as a characteristic dimension and the air temperature inside the chamber t₀ is taken as a defi ning temperature. It has been established that in tubes with narrow fi nning, free-convection heat transfer is represented with better quality by the criterial equations of the East European variant.
A similarity equation has been obtained for calculating the average reduced heat transfer of a single fi nned tube with various fi n height h = 0–14.6 mm at diff erent angles of the tube inclination γ = 0–90^o to the horizontal plane at the Rayleigh number Ra = (32–450)·10³ . A heat fl ux optimal fi n height (h_ef = 10.8–12.3 mm) has been determined that decreases with increase in the angle of inclination.
The paper presents a generalization of the results of an experimental investigation into the heat transfer of a bimetal fi nned tube with spiral knurled annular fi ns (interfi n pitch s = 2.5 mm) under the conditions of free convection.
The obtained results were approximated using two options for selecting defi ning characteristics to calculate similarity numbers, viz., the West European variant, where the interfi n space s′ is taken as a characteristic dimension and the wall temperature t_w is taken as a defi ning temperature, and the East European variant, where the fi n baselimited tube diameter d₀ is taken as a characteristic dimension and the air temperature inside the chamber t₀ is taken as a defi ning temperature. It has been established that in tubes with narrow fi nning, free-convection heat transfer is represented with better quality by the criterial equations of the East European variant.
A similarity equation has been obtained for calculating the average reduced heat transfer of a single fi nned tube with various fi n height h = 0–14.6 mm at diff erent angles of the tube inclination γ = 0–90^o to the horizontal plane at the Rayleigh number Ra = (32–450)·10³ . A heat fl ux optimal fi n height (h_ef = 10.8–12.3 mm) has been determined that decreases with increase in the angle of inclination.
Author:  E. S. Danil′chik, A. B. Sukhotskii,G. S. Marshalova, D. V. Ostrovskaya
Keywords:  free convection, bimetal annular-fi nned tube, methods for selecting a characteristic dimension and a defi ning temperature of similarity numbers, Nusselt number, Rayleigh number, generalizing equation, optimum fi nning height, tube inclination angle
Page:  1042 - 1049