Orifice equation Subject

Any mathematical model is subject to the limits imposed by its founding assumptions. For example, when we invoked the orifice equation we implicitly assumed that the fluid height in the tank preserved the physics of the draining process. When the tank is nearly empty the physics will be different - a whirlpool of air will form in the outlet, for example. Thus at long times the orifice equation, and subsequently Eq. (6.45), will not be valid. Similarly, a tank with a closed top, with variable cross-sectional area (such as a funnel), or density gradients in the fluid requires different mathematical models. 

Orifice. Equation (M-13) is used for measuring the flow rate of water with orifice and Eq. (M-14) for measuring the rate of flow of air. Interim Supplement 19.5 on Fluid Meters gives the tables of the values of discharge coefficient C for various pipe diameters as a function of diameter ratio P and pipe Reynolds number R, based on orifice diameter d. Excerpts from the tables in the Supplement are given in Table M-7 for the three types of pressure-tap locations. The values below the stepped line are extrapolations and are subject to larger tolerance as given in Table II-V-1 in the Supplement. 

The viscosity of ttie liquid may reduce the velocity and capacity enough to require a larger orifice size than the usual liquid capacity equation would indicate This simplified viscosity chart and the Kj viscoscorrection factors obtainable from i( are for use m properly sizing relief valves intended for viscous liquid ser vice. Equations and graphs used m prepanng this chart reflect conservative engmeenng data on the subject... 

If the wavelraigth Aof jet oscillation is measured, for instance, from a photograph of the jet, and if p, R, and V are known, the surface tension yean be calculated from Equation 5.100. In practice, the oscillating jet is used to measure the variation of surface tension with time due to diffusion of surfactant from the bulk liquid to the surface and adsorption there, a subject considered further in Chapter 6. The procedure is simply to measure A at various distances from the orifice corresponding to different times available for surfactant diffusion and adsorption. 

---