![]() ![]() In the mixed boundary layer, average convection coefficient may be expressed as NuL = hLL = (0.037 ReL4/5 – A) Pr1/3 k 0.6 ≤ Pr ≤ 60 Rex,c = critical Reynolds number Rex,c ≤ Rex,L ≤ 108 A = 0.037 Rex,c 4/5 – 0.664 Rex,c1/2Īverage friction coefficient for mixed boundary layer Cf,L = 0.074 ReL-1/5 (– 2A/Rel) įor completely turbulent boundary layer -įluid properties are usually evaluated at the film temperature: Nu x 0.0296Re 4x / 5 Pr1/ 3, 0.6 Pr 60 Fluid properties are usually evaluated at the film temperature: Local Nusselt number for turbulent flow (Chilton-Colburn) is The velocity boundary layer thickness is δ = 0.37 x Rex-1/5 Local friction coefficient is Cf,x = 0.0592 Rex-1/5 A single correlating equation, which applies for all Prandtl numbers for laminar flow over an isothermal plate, the local convection coefficient may be obtained from (Churchill and Ozoe): Nux = 0.3387 Rex1/2 Pr1/3, Pex ≥ 100 1/4 Pex = Pr Rex Nux = 2Nux Fluid properties are usually evaluated at the film temperature:.The average heat transfer coefficient for laminar flow is 1 x k hx = h x dx = 0.332 x 0 x With the average friction coefficient defined as τ s, x Cf, x ≡ 2 ρu ∞/ 2 where 1 x τ s, x ≡ τ dx x 0 s, x the ratio of the velocity to thermal boundary layer thickness is 1 δ ≈Pr 3 δtįrom the foregoing local result, average boundary layer parameters may be determined. The local friction is then Cf,x = τs,x = 0.664 Rex-1/2 ρu∞2/2įor problems involving the formation of boundary layer, a nondimensional form for the heat transfer coefficient is : The wall shear stress may be expressed as τs = μ ∂u = μu∞ √(u∞/υx) d2f ∂y y=0 dη2 η=0. ![]() The larger free stream velocity, the thinner the boundary layer.From the above equation, δ increases with increasing x and υ but decreases with increasing u∞.Boundary layer thickness δ as that value of y for which (u/u∞) = 0.99 δ =.EXTERNAL FORCED CONVECTION Prepared by NURHASLINA CHE RADZI FKK, UITM ![]()
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