Orifice velocity through

Often, the pressure drop required for design flow rate is unacceptably large for a distributor pipe designed for uniform velocity through uniformly sized and spaced orifices. Several measures may be taken in such situations. These include the following ... 

Biihhle-diameter correlation for air sparged into relatively inviscid liquids. Dt, = hiihhle diameter, D = orifice = gas velocity through sparging orifice, P = fluid density, and 1 = fluid viscosity. [From Can. J. Chem. Eng., 54,... 

V o Velocity through an orifice m/s ft/h in a vessel or extractor s void ... 

Critical and Subcritical Flow - The maximum vapor flow through a restriction, such as the nozzle or orifice of a pressure relief valve, will occur when conditions are such that the velocity through the smallest cross-sectional flow area equals the speed of sound in that vapor. This condition is referred to as "critical flow" or "choked flow . 

If the loss coefficient is based upon the velocity through the orifice (VD) instead of the pipe velocity, the /l4 term in the denominator of Eq. (10-22) does not appear ... 

The gas velocity through the grid hole (orifice equation) ... 

For cavitation in flow through orifices, Fig. 6-55 (Thorpe, Int. J. Multiphase Flow, 16, 1023-1045 [1990]) gives the critical cavitation number for inception of cavitation. To use this cavitation number in Eq. (6-207), the pressure p is the orifice backpressure downstream of the vena contracta after full pressure recovery, and V is the average velocity through the orifice. Figure 6-55 includes data from Tullis and Govindarajan (ASCE J. Hydraul. Div., HY13, 417-430 [1973]) modified to use the same cavitation number definition their data also include critical cavitation numbers for 30.50- and 59.70-cm pipes... 

Fig. 13.41 The Keuerleber and Pahl (1970) mixhead. In the closed or recirculation position, reactants recirculate through grooves (c) along the cylindrical cleanout piston (b). In the open position, reactants flow at high velocity through circular orifices (a), impinge in the chamber (d), and flow out to the mold cavity (diagram from G. Oertel, 1985 (80)). [Reprinted by permission from C. W. Macosko, RIM Fundamentals of Reaction Injection Molding, Hanser, Munich, 1989.]...

VF = fictitious volume of filtrate per unit of filtering area necessary to lay down a cake of thickness lF, ft3/ft2 Vp = fictitious volume of filtrate per unit of air-suction area necessary to lay down a cake of thickness l F, ft3/ft2 Vj = instantaneous or point linear velocity, ft/s Va = average linear velocity through orifice, ft/s... 

Orifice baffles should be spaced reasonably close together to produce frequent increases in fluid velocity through the orifice openings between the tubes and the baffles. This type of baffle should not be used for fluids with high fouling characteristics. 

Fig. 17. Photographically observed and theoretically calculated bubble growth at a single orifice in a 2D gas fluidized bed. Physical properties of the particles diameter, 500 /im density, 2660 kg/m Bed dimensions width, 0.58 ra height, 1.0 m. Injection velocity through orifice 10.0 m/s.

Two-fluid simulations have also been performed to predict void profiles (Kuipers et al, 1992b) and local wall-to-bed heat transfer coefficients in gas fluidized beds (Kuipers et al., 1992c). In Fig. 18 a comparison is shown between experimental (a) and theoretical (b) time-averaged porosity distributions obtained for a 2D air fluidized bed with a central jet (air injection velocity through the orifice 10.0 m/s which corresponds to 40u ). The experimental porosity distributions were obtained with the aid of a nonintrusive light transmission technique where the principles of liquid-solid fluidization and vibrofluidization were employed to perform the necessary calibration. The principal differences between theory and experiment can be attributed to the simplified solids rheology assumed in the hydrodynamic model and to asymmetries present in the experiment. 

Figure 19 shows, as an example, the evolution and propagation of bubbles in a 2D gas-fluidized bed with a heated wall. The bubbles originate from an orifice near the heated right wall (air injection velocity through the orifice s 5.25 m/s, which corresponds to 2 Uj. The instantaneous axial profile of the wall-to-bed heat transfer coefficient is included in Fig. 19. From this figure the role of the developing bubble wake and the associated bed material refreshment along the heated wall, and its consequences for the local instantaneous heat transfer coefficient, can be clearly seen. In this study it became clear that CFD based models can be used as a tool (i.e., a learning model) to gain insight into complex system behavior.

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