Heat transfer behind a sudden expansion in a round tube with variation of the expansion ratio

Abstract

Abstract The results of a numerical study of the influence of a step height on the flow structure and turbulent heat transfer in the zone of flow separation, attachment and relaxation are presented. The range of Reynolds numbers is ReD1 = 6.7·103-13.3·104. The degree of tube expansion varies within ER = (D2/D1)2 = 1.085 ÷ 4. In the work will show how exactly the ratio of tube expansion affects hydrodynamics and heat transfer in the separation area. When increasing ER the separation area lengthens and becomes more extensive: from 5 to 12 step heights (5h - 12h). Heat transfer is not so intensive, Numax decreases by the factor of 2.5. The coordinate of the maximum heat transfer Numax moves downstream. Comparison the calculation results with the experimental data of other authors is presented. A correlation formula allowing calculation of the separated flow with consideration of the degree of tube expansion is presented as generalization of data obtained.