High orifices

Pfeiffer RE, Roberts RW, Melt-spinning acrylonitrile polymer fiber using spinnerette of high orifice density, American Cyanamid Company, U.S. Pat., 4,220,616, 2 Sept 1980. 

This arrangement provides a thin film of liquid sample solution flowing down to a narrow orifice (0.007-cm diameter) through which argon flows at high linear velocity (volume flow is about 0.5-1 1/min). A fine aerosol is produced. This particular nebulizer is efficient for solutions having a high concentration of analyte constituents. 

Venturi scmbbers can be operated at 2.5 kPa (19 mm Hg) to coUect many particles coarser than 1 p.m efficiently. Smaller particles often require a pressure drop of 7.5—10 kPa (56—75 mm Hg). When most of the particulates are smaller than 0.5 p.m and are hydrophobic, venturis have been operated at pressure drops from 25 to 32.5 kPa (187—244 mm Hg). Water injection rate is typicaUy 0.67—1.4 m of Hquid per 1000 m of gas, although rates as high as 2.7 are used. Increasing water rates improves coUection efficiency. Many venturis contain louvers to vary throat cross section and pressure drop with changes in system gas flow. Venturi scmbbers can be made in various shapes with reasonably similar characteristics. Any device that causes contact of Hquid and gas at high velocity and pressure drop across an accelerating orifice wiU act much like a venturi scmbber. A flooded-disk scmbber in which the annular orifice created by the disc is equivalent to a venturi throat has been described (296). An irrigated packed fiber bed with performance similar to a... 

Flow nozzles are commonly used in the measurement of steam and other high velocity fluids where erosion can occur. Nozzle flow coefficients are insensitive to small contour changes and reasonable accuracy can be maintained for long periods under difficult measurement conditions that would create unacceptable errors using an orifice installation. 

Extmsion processes have been used to produce high and low density flexible cellular poly(vinyl chloride). A decomposable blowiag ageat is usually bleaded with the compouad prior to extmsioa. The compouaded resia is thea fed to an extmder where it is melted under pressure and forced out of an orifice iato the atmosphere. After extmsion iato the desired shape, the cellular material is cooled to stabili2e it and is removed by a belt. 

The multiorifice spinnerets require a high degree of precision in design and manufacture. The main problems encountered are the deHvery of identical quantities of dope to each orifice and the instantaneous self-adjustment of the spinneret s internal pressure if an orifice plugs during spinning. 

Orifice viscometers should not be used for setting product specifications, for which better precision is required. Because they are designed for Newtonian and near-Newtonian fluids, they should not be used with thixotropic or highly shear-thinning materials such fluids should be characterized by using multispeed rotational viscometers. 

Equation 14 indicates that Hquid pressure has a dominant effect in controlling the mean droplet sizes for pressure atomizers. The higher the Hquid pressure, the finer the droplets are. An increase in Hquid viscosity generally results in a coarser spray. The effect of Hquid surface tension usually diminishes with an increase in Hquid pressure. At a given Hquid pressure, the mean droplet size typically increases with an increase in flow capacity. High capacity atomizers require larger orifices and therefore produce larger droplets. 

The aperture impedance principle of blood cell counting and sizing, also called the Coulter principle (5), exploits the high electrical resistivity of blood cell membranes. Red blood cells, white blood cells, and blood platelets can all be counted. In the aperture impedance method, blood cells are first diluted and suspended ia an electrolytic medium, then drawn through a narrow orifice (aperture) separating two electrodes (Fig. 1). In the simplest form of the method, a d-c current flows between the electrodes, which are held at different electrical potentials. The resistive cells reduce the current as the cells pass through the aperture, and the current drop is sensed as a change in the aperture resistance. 

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