Flow Trough Orifice


Orifices are a basic means for the control of fluid power. Flow characteristics of orifices plays a major role in the design of many hydraulic control devices. An orifice is a sudden restriction of short length (ideally zero length for a sharp-edged orifice) in a flow passage and may have a fixed or variable area. Two types of flow regime exist (Fig. 3-10), depending on whether inertia or viscous forces dominate. The flow velocity through an orifice must increase above that in the upstream region to satisfy the law of continuity. At high Reynolds numbers, the pressure drop across the orifice is caused by the acceleration of the fluid particles from the upstream velocity to the higher jet velocity. At low Reynolds numbers, the pressure drop is caused by the internal shear forces resulting from fluid viscosity.

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