1. Flow Through A Narrow Slot
2. Air Flow Through Rectangular Slot

This article provides calculation methods for correlating design, flow rate and pressure loss as a fluid passes through a nozzle or orifice. Nozzles and orifices are often used to deliberately reduce pressure, restrict flow or to measure flow rate.

Problem 3B.7: Momentum fluxes for creeping flow into a slot: Problem 3D.2: The equation of change for vorticity: Problem 3B.8: Velocity distribution for creeping flow toward a slot: Problem 3D.3: Alternate form of the equation of motion: Problem 3B.9: Slow transverse flow around a cylinder. An orifice plate is a thin plate with a hole in it, which is usually placed in a pipe. When a fluid (whether liquid or gaseous) passes through the orifice, its pressure builds up slightly upstream of the orifice but as the fluid is forced to converge to pass through the hole, the velocity increases and the fluid pressure decreases.

Flow Through A Narrow Slot

Subscripts

Common pipesizes and slot configurations are shown, other sizes up to 48', SCH or SDR'S and slot patterns are available upon request. Slot spacing and slot length is nominal, small variances may occur due to ovality of pipe and the effects of temperature. 14 1/2' 11 3/4'.375' 9 1' 5 2' 3.5 3' 2 6'. The flow of solution through these narrow channels is determined by the Pouiselle Flow equation (given by Equation 1) where the drop in pressure within a slot-die head (delp) is determined by the flow rate of the solution (V), the viscosity of the solution (mu), the channel length (L), and the channel width (b).

In the case of a simple concentric restriction orifice the fluid is accelerated as it passes through the orifice, reaching the maximum velocity a short distance downstream of the orifice itself (the Vena Contracta). The increase in velocity comes at the expense of fluid pressure resulting in low pressures in the Vena Contracta. In extreme cases this may lead to cavitation when the local pressure is less than the vapour pressure of a liquid.

Downstream of the Vena Contracta in the recovery zone, the fluid decelerates converting excess kinetic energy into pressure as it slows. When the fluid has decelerated and returned to the normal bulk flow pattern the final downstream pressure has been reached.

The discharge coefficientcharacterises the relationship between flow rate and pressure loss based on the geometry of a nozzle or orifice. You can find typical values in our article on discharge coefficients for nozzles and orifices.

The relationships for flow rate, pressure loss and head loss through orifices and nozzles are presented in the subsequent section. These relationships all utilise the parameter, the ratio of orifice to pipe diameter which is defined as:

Where the point downstream of the orifice is sufficiently far away that the fluid has returned to normal full pipe velocity profile.

Horizontal Orifices and Nozzles

For orifices and nozzles installed in horizontal pipework where it can be assumed that there is no elevation change, head loss and flow rate may be calculated as follows:

Vertical Orifices and Nozzles

For orifices and nozzles installed in vertical piping, with elevation change, the following head loss and flow rate equations may be used:

Expansion Coefficient

The expansion coefficient takes account of the difference between the discharge coeffcicient for compressible and incompressible flows. It is defined as:

The expansion factoris typically determined empirically and can be calculated using one of the formulas below.

Air Flow Through Rectangular Slot

For incompressible fluids:

American Gas Association method as described in AGA 3.1:

International Standards Organistion method as described in ISO 5167-2:

Flow through gate openings has been the subject of study by many investigators. Gates are often located on raised crests, as in the case of spillways. In such a situation, the flow is expected to behave similarly to flow through rectangular slots. As flow through a rectangular slot is a particular case of flow through a large orifice, any understanding of it will help in its generalization. Furthermore, because the flow through a slot is intermediate to that of a sluice gate and a rectangular sharp-crested weir, it can be used as a basis of unification. In this study, a discharge equation for flow through rectangular slots has been obtained. In special cases, this equation converts to the discharge equations of a sluice gate and a rectangular sharp-crested weir.

• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/oclc/8672558
• Corporate Authors: 345 East 47th Street
  New York, NY United States 10017-2398
• Authors:
  • Swamee, P K
  • Ojha, CSP
  • Kumar, S
• Publication Date: 1998-9

Language

• English

Media Info

• Features: Appendices; Figures; References; Tables;
• Pagination: p. 973-974
• Serial:
  • Volume: 124
  • Issue Number: 9
  • Publisher: American Society of Civil Engineers
  • ISSN: 0733-9429
  • Serial URL: http://scitation.aip.org/hyo/

Subject/Index Terms

• TRT Terms: Equations; Flow; Gates; Hydrologic phenomena; Openings; Rectangles; Spillways; Weirs
• Old TRIS Terms: Rectangular bodies
• Subject Areas: Highways; Hydraulics and Hydrology; I26: Water Run-off - Freeze-thaw;

Filing Info

• Accession Number: 00754623
• Record Type: Publication
• Files: TRIS
• Created Date: Oct 12 1998 12:00AM