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EFFECTS OF TURBULENCE ON THE HEAT TRANSFER OF A ROUGH-SURFACE CYLINDER IN CROSS-FLOW IN THE CRITICAL RANGE OF Re

Algirdas Zukauskas
Lithuanian Academy of Sciences, Vilnius, Lithuania

Juozas Vytautas Ziugzda
Lithuanian Energy Institute, Breslaujos str. 3, LT-44403 Kuanas, Lithuania

P. Daujotas
Institute for Physical and Engineering Problems of Energy Research Academy of Sciences of the Lithuania, Kaunas

Abstract

Experimental results are presented for the heat transfer of a rough-surface cylinder in cross-flow of water for the range of Ref, from 4·104 to l.6 ·106 and of turbulence from 1 to 7%. The height of roughness elements on the cylinder was 0.15 and 1.2 mm. at the boundary condition qw ~ const. A comparison of the results is given for a smooth-cylinder. The measured parameters were those of local heat transfer along the perimeter, mean heat transfer and pressure drag coefficient. The type of surface roughness studied was found to cause a considerable upstream shift of the laminar-turbulent transition in the boundary layer, so that the laminar part could be nearly eliminated in the critical range of Ref. An 85% increase of the heat transfer was caused by the lower roughness elements. Effects of flow turbulence are similar for smooth and rough cylinders. Roughness elements of low heights are more efficient in flows of water in the critical range of Ref.

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