EXPERIMENTAL INVESTIGATION OF FREE-CONVECTION HEAT EXCHANGE BETWEEN MULTIPLE-ROW STAGGERED BANKS OF TUBES WITH SPIRAL FINS

摘要

Results of investigation of the following characteristics of free-convection heat exchange are presented: the coefficients of circular tubes averaged for a bank, and each individual transverse row of circular tubes with rolled aluminum fins, which are used in the heat-exchange sections of air coolers. The fins are rolled onto a smooth brass tube with an outside diameter of 25 mm, and a tube-finning factor of 16.8. The spacing of the tube layout in the bank grids is 64 mm, and the angle of incline of the longitudinal axis of the tube to the horizontal plane is 0, 15, 30, 45, and 60°. Experimental data are generalized by similitude equations of the form Nu = f(Ra), which encompass the interval of Rayleigh numbers Ra - (0.3-3.5)·10~5. The surface temperature of the tubes near the base of the fins was varied from 35 to 225℃, and the temperature of the air surrounding the bank ranged from 15 to 25℃.