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Heat Analysis and Thermodynamic Effects Part 7

Tham khảo tài liệu 'heat analysis and thermodynamic effects part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Enhancement of Heat Transfer in the Bundles of Transversely-Finned Tubes 169 of the effect of vortical wake of the upstream tubes in the same rows these values of a drop to those typical of the rear vortical zones of the upstream tubes . Fig. 10. Distribution of the relative heat transfer coefficient over the surface of type 2 fin h d 0.357 located in the frontal row of the bundle. Re 2-104 the free-stream direction is from the top down. a aav 1 1.94 to 1.66 2 1.66 to 1.24 3 1.24 to 0.83 4 0.83 to 0.41 5 0.41 to 0.11 Fig. 11. Distribution of the relative heat transfer coefficient over the surface of type 1 fin h d 0.932 in the 4th row of a six-row bundle. Re 2-104 for legend see Fig. 7 or 9. a in-line bundle Ơ1 3.47 ơ2 2.97 b staggered bundle Ơ1 3.47 ơ2 2.66 The drop in a increases at smaller ơ2 and is explainable by the decrease of the intensity of circulation in the wake with decreasing relative pitch L d between interacting tubes for inline bundles L d ơ2 . According to data from Migay 1978 the rear wake exhibits an 170 Heat Analysis and Thermodynamic Effects approximately constant turbulence level e. Thus in the inner rows of in-line bundles the highest a occur in fin zones with 50 to 70 where the fin is impacted by a flow outside its aerodynamic shadow. In a staggered bundle with longitudinal and transverse pitches similar in those in an in-line bundle the L d is double that of the latter bundle L d 2ơ2 so that at Ơ2 2 the distributions of a on the fronts of inner-row tubes Fig. 12b stays approximately the same as on the first row i.e. with a peak at qi 0 . The uniformity of the distributions of a in these bundles improves with the forcing effect of adjoining tubes which is maximum at Ơ1 Ơ2 2 3. In this case each tube operates as if it were surrounded by a circular deflector formed of six adjoining tubes. As Ơ2 in staggered bundles is decreased to Ơ2 1.5 which is possible at quite large Ơ1 and relatively low h d the flow pattern begins to resemble that in .