TAILIEUCHUNG - Heat Transfer Handbook part 42

Heat Transfer Handbook part 42. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | 402 FORCED CONVECTION INTERNAL FLOWS TABLE Scale Drawing of Five Different Ducts That Have the Same Hydraulic Diameter Cross Section Diagram Circular Square Equilateral triangle Rectangular 4 1 Infinite parallel plates Source Bejan 1995 . Table shows five duct cross sections that have the same hydraulic diameter. The hydraulic diameter of the round tube coincides with the tube diameter. The hydraulic diameter of the channel formed between two parallel plates is twice the spacing between the plates. For cross sections shaped as regular polygons Dh is the diameter of the circle inscribed inside the polygon. In the case of highly asymmetric cross sections Dh scales with the smaller of the two dimensions of the cross scclion. The general pressure drop relationship is most often written in terms of hydraulic diameter LAMINAR FLOW AND PRESSURE DROP 403 AP f f1 pU2 Dh 2P To calculate AP the friction factor f must be known and it can be derived from the flow solution. The friction factors derived from the Hagen-Poiseuille flows described by eqs. and are 24 Re Dh 16 ReDh f Dh 2D parallel plates D spacing Dh D round tube D diameter Equations and hold for laminar flow ReDh 2000 . Friction factors for other cross-sectional shapes are reported in Tables and . Additional results can be found in Shah and London 1978 . All Hagen-Poiseuille flows are characterized by TABLE Effect of Cross-Sectional Shape on f and Nu in Fully Developed Duct Flow Nu hDh k Cross Section f ReD B Uniform q Uniform T0 h A One side insulated 16 24 24 3 1 Source Bejan 1995 . 404 FORCED CONVECTION INTERNAL FLOWS TABLE Friction Factors and Nusselt Numbers for Heat Transfer to Laminar Flow through Ducts with Regular Polygonal Cross Sections Cross Section f ReDf. Fully Developed Flow Nu _ hDh k Uniform Heat Flux Isothermal Wall Fully Developed Flow Slug

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