Heat Transfer Handbook part 50. 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. | 482 FORCED CONVECTION EXTERNAL FLOWS T - 8T0 r Jo h v where the second term on the left is the temperature difference across which heat is transferred by conduction. With v psT V Pt y then . PrT T ST Rey A local heat transfer coefficient can be defined based on STq XT _ vcpv 1 0 hk St Based on experimental data for roughness from spheres Stk C Re-0 20 Pr-0-40 with C and Prr the law of the wall can be rewritten as T PrT St k Re and using a procedure similar to that used for a smooth surface st f PrT Cf 2 1 2 St Some Empirical Transport Correlations Cylinder in Crossflow The analytical solutions described in Sections and provide local convection coefficients from the front stagnation point using similarity theory to the separation point of a cylinder using the Smith-Spalding method. At the front stagnation point the free stream is brought to rest with an accompanying rise in pressure. The initial development of the boundary layer along the cylinder following this point is under favorable pressure gradient conditions that is dp dx 0. However the pressure reaches a minimum at some value of x depending on the Reynolds number. Farther downstream the pressure gradient is adverse . dp dx 0 until the point of boundary layer separation where the surface shear stress becomes zero. This results in the formation of a wake. For Re j 2 x 105 the boundary layer remains laminar until the separation point which HEAT TRANSFER FROM ARRAYS OF OBJECTS 483 occurs at an arc of about 81 . For higher values of ReD the boundary layer undergoes transition to turbulence which results in higher fluid momentum and the pushing back of the separation point to about 140 . The foregoing changes result in large variations in the transport behavior with the angle 0. If the interest is on an average heat transfer coefficient many empirical equations are available. One such correlation for an isothermal cylinder that is .
