Experimental Study of Free-Convective Heat Transfer of Single-Row Bundles of Tubes with Spiral Aluminum Fins of Different Heights in an Air Flow Intensified by an Exhaust Shaft.

Experimental studies of free-convective heat exchange between single-row bundles of bimetallic tubes with spiral rolled aluminum fins of different heights (2–14.6 mm) and a vertical air flow created by an exhaust shaft with adjustable height H = 0.52, 1.16, and 2.12 m are presented. The tubes were layed out with a constant relative transverse spacing σ1 = 1.14 (6 pipes). The data of measurements were used to calculate the average reduced heat transfer coefficient, which ranged from 0.78 to 17.30 W/(m2∙°C) at Rayleigh numbers (19–360)·103. A similarity equation is obtained for describing the dependence of heat emission of single-row bundles with different fin heights in a free convection regime on the relative height of the bundle–shaft system. It is found that intensification of free convection of air by installing an exhaust shaft above the bundle of tubes allows one to increase the heat emission intensity by 2.3 times. Expressions are obtained for determining the energy and aerodynamic efficiencies of the bundle–shaft system. The optimal height of finning (about 8 mm) for bundles of studied tubes with an exhaust shaft was determined. [ABSTRACT FROM AUTHOR]