EXPERIMENTAL STUDY OF PHYSICAL SIMILARITY OF INTENSIFIED FREE-CONVECTIVE PROCESSES ON AIR-COOLED BUNDLES OF ROUND-RIBBED TUBES

Experimental studies of free-convective heat exchange of two-row bundles of bimetallic tubes with spiral rolled
aluminum ribs to vertical air flows created by an exhaust shaft 0.52 m high with an adjustable flow section of
0.0087–0.1185 m ² are presented. The staggered arrangement of the bundles was accomplished with an inter-
tube pitch of S _l = 70 mm from four tubes in a transverse row of the bundle. Based on the measurement data, the
average reduced heat transfer coefficient of the bundle was calculated, which amounted to a value from 1.26 to
3.84 W/(m ^2∙o C) at Rayleigh numbers (20–163)∙10 ³ .
It was found that the use of unheated half-tubes in the model of a ribbed bundle with an exhaust shaft can
lead to a significant violation of the physical similarity of the experiment. Moreover, the significance of this effect
increases with an increase in the rate of air flow through the bundle, i.e., at high values of the Rayleigh numbers
(Ra > 30,000) and optimum values of the coefficient of narrowing of the outlet opening area.
To ensure physical similarity of the experiment, it is recommended to use heated half-tubes in the model of
a ribbed bundle with an exhaust shaft or to provide at least six tubes in the transverse row of the bundle.

Author:  A. B. Sukhotskii, E. S. Danil′chik, G. S. Marshalova, D. V. Ostrovskaya
Keywords:  physical similarity, air-cooled ribbed tube bundle, free-convective heat exchange, exhaust shaft
Page:  1347