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Unformatted text preview: PGE 322K Spring 2008 Exam 1  Review flux = amount of “stuff” passing a unit area over a unit time. Convective fluxes For volumetric convective flux, q = v (velocity of the fluid). SI Units: m/sec To convert volumetric flux to volumetric flow rate. Q = A<v>, where A is the area over which the flow takes place. SI Units m^3/sec Note that this is only for the average velocity of the fluid. If the velocity varies transverse to the flow direction (and it always does for our problems), one needs to integrate the velocity over the crosssectional area. Q vdA = ∫ ∫ Q vdxdy = ∫ ∫ for flows with Cartesian symmetry Q vrdrd θ = ∫ ∫ for flows with cylindrical symmetry Convective mass flux = ρ v where ρ is the density. SI units: kg/m^2sec (mass per area per time). Convective momentum flux = ρ vv . Note that this is tensorial (i.e. has two directions associated with it), for example the convective xmomentum over an area normal to the ydirection is ρ v x v y . SI Units: kg/msec^2 or Pa. This has the same units as pressure, as will other momentum fluxes. Molecular momentum fluxes Momentum can also be moved by molecular fluxes. There are two possibilities, pressure and shear. Pressure molecular momentum flux is only longitudinal with the flux direction (e.g. only xmomentum flux is provided in the xdirection), and is simply given by P. SI Units: Pa Spring 2008 Shear molecular momentum flux is tensorial, but for our purposes it is only transverse to the flux direction (e.g. no xmomentum flux in the xdirection, but one does get y and z momentum flux in the xdirection). It is given by the symbol momentum flux in the xdirection)....
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 Spring '08
 dicarlo
 Fluid Dynamics, Velocity, molecular momentum flux, τ xz

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