Chapter 7(I) External Flow: The Flat Plate in Parallel Flow Chapter 7 Section 7.1 through 7.3
External Flow: The Flat Plate in Parallel Flow Chapter 7 Section 7.1 through 7.3 Chapter 7(I)
The Problem of Convection Heat transfer Mass transfer Nu,=f(x',Re,,Pr)Sh,=f(x',Re,.Sc Nux=f(Rex:Pr) Shx =f(Res:Sc) Experimental (Empirical)approach----perform measurements Theoretical approach----solve equations
The Problem of Convection ( ) *,Re ,Pr Nu f x x x = Nu f x = (Re ,Pr x ) Heat transfer Mass transfer ( ) *,Re , x x Sh f x Sc = Sh f Sc x = (Re , x ) Experimental (Empirical) approach ----perform measurements Theoretical approach ----solve equations
The Empirical Method o T I-E=q=hA (Ts-T) Experiment for measuring -Ts As NuL =CRe"Pr" Insulation 7=☑+Z Film T for properties E 2 NuL C RetmPr NuL C Re Log NuL Log ( Log ReL Log ReL (a) (b)
The Empirical Method Experiment for measuring h L Re Pr m n L Nu C= L 2 s f T T T + ∞ = Film T for properties
Physical Features Physical Features Laminar Turbulent 8(x) External flow,the boundary layers develop freely without constraint. Boundary layer conditions may be entirely laminar,laminar and turbulent,or entirely turbulent
Physical Features Physical Features • External flow, the boundary layers develop freely without constraint. • Boundary layer conditions may be entirely laminar, laminar and turbulent, or entirely turbulent
Flow conditions To determine the conditions,compute Re,=PuLut U V and compare with the critical Reynolds number for transition to turbulence, Re<Re>laminar flow throughout Re>Re>transition to turbulent flow ·Value of Rex.e depends on free stream turbulence and surface roughness. Nominally, Rexe≈5xl03
Flow conditions • To determine the conditions, compute and compare with the critical Reynolds number for transition to turbulence, ReL ρuL uL μ ν ∞ ∞ = = , Re Re laminar flow throughout L xc < → , Re Re L xc > → transition to turbulent flow • Value of Rex,c depends on free stream turbulence and surface roughness. Nominally, 5 , Re . 5 10 x c ≈ ×