Velocity inlet

Traditionally, cyclone dimensions are multiples of outiet pipe diameter D. Typical barrel diameters are 2D but efficiency increases at constant up to a 3Z9 barrel diameter. Efficiency also improves as barrel and cone length are increased at constant up to the natural length of the vortex. At constant inlet velocity, efficiency increases as outiet diameter (and all ratioed dimensions in a family of cyclones) is decreased. Improved efficiency is attained at the... 

Table 7. Dust Loadings and Cyclone Inlet Velocities above Which Erosion Is Excessive ...

The flow distribution in a manifold is highly dependent on the Reynolds number. Figure 14b shows the flow distribution curves for different Reynolds number cases in a manifold. When the Reynolds number is increased, the flow rates in the channels near the entrance, ie, channel no. 1—4, decrease. Those near the end of the dividing header, ie, channel no. 6—8, increase. This is because high inlet velocity tends to drive fluid toward the end of the dividing header, ie, inertia effect. 

The cyclones are typically designed with diameters of 100—160 cm for ease of maintenance. Cyclone inlet velocities are usually restricted to 18—21 m /s in the first stage and to 20—26 m/s in the second stage to achieve satisfactory pressure drop and erosion characteristics (62). The number of sets of two-stage cyclones thus depends on the total gas flow. Finding room to house all the necessary cyclones within the regenerator frequently requires considerable ingenuity (62). 

Example 1 Force Exerted on a Reducing Bend An incompressible fluid flows through a reducing elbow (Fig. 6-5) situated in a horizontal plane. The inlet velocity Vj is given and the pressures pi and measured. 

This equation shows that for 5 percent maldistribution, the pressure drop across the holes shoiild be about 10 times the pressure drop over the length of the pipe. For discharge manifolds with K = 0.5 in Eq. (6-147), and with 4/E/3D 1, the pressure drop across the holes should be 10 times the inlet velocity head, pV V2 for 5 percent maldistribution. This leads to a simple design equation. 

Average cyclone inlet velocity, based on area m/s ft/s ft/s... 

RooBng plants (asphalt saturators) Felt or paper saturators spray section, asphalt tank, wet looper Crushed rock or other minerals handling Asphalt vapors and particulates (liquid) Particulates (dust) Exhaust system with high inlet velocity at hoods (3658 m/s [>200 ft/min]) with either scrubbers, baghouses, or two-stage low-voltage electrostatic precipitators Local exhaust system, cyclone or multiple cyclones... 

Inlet velocity restric tious do not apply in the design of separators for emergency rehef systems because ... 

An impulse-type turbine experiences its entire enthalphy drop in the nozzle, thus naving a very high velocity entering the rotor. The velocity entering the rotor is about twice the velocity of the wheel. The reaction type turbine divides the enthalphy drop in the nozzle and in the rotor. Thus, for example, a 50 percent reaction turbine has a velocity leaving the nozzle equal to the wheel speed and produces about V2 the work of a similar size impulse turbine at about 2-3 percentage points higher efficiency than the impulse turbine (0 percent reaction turbine). The effect on the efficiency and ratio of the wheel speed to inlet velocity is shown in Fig. 29-27 for an impiilse turbine and 50 percent reaction turbine. 

Length, m Coolant Temp, K Gas Type Inlet Velocity m/sec Production rate, Kg/Hr... 

Cyclone mist eliminators and collectors have virtually the same efficiency for both liquid aerosols and solid particles. To avoid reentrainment of the collected liquid from the walls of the cyclone, an upper limit is set to the tangential velocity that can be used. The maximum tangential velocity should be limited to the inlet velocity. Even at this speed, the liquid film may creep to the edge of the exit pipe, from which the liquid is then reentrained. 

Lowering the inlet velocities and providing proper inlet silencers can reduce air noise. Considerable work by NASA on compressor casings has greatly reduced noise. 

The large frontal areas of these units reduce the inlet velocities, thus reducing air noise. The pressure rise in each compressor stage is reduced, creating a large, stable operating zone. 

Figure 3-18. Typical inlet velocity profile for an industrial gas turbine.

Keep valve inlet velocity below 300ft/sec for 2" and smaller, and 200ft/ sec for larger sizes. 

FIGURE >0.70 The capture of tracer gas released at five times the diameter of the exhaust inlet when the radius of the exhaust hood is 0. tS m, the radius of the exhaust hood inlet is 0.037 m, and the width of the exhaust jet is 8.0 mm. fej Suction alone with average inlet velocity of 12.7 m s. (b) Combined suction and Injection with the average inlet and exhaust velocities of 12 8 rn s and 7.7 m s . respectively. (Figures are courtesy of the Health and Safety Executive, Research Division. Sheffield. UK.)... 

For conditions of (1) high suction side (or inlet) friction loss, from suction piping calculations or (2) low available Net Positive Suction Head (10 feet or less), a large open eye on the impeller inlet is necessary to keep the inlet velocity low. NPSH is discussed in a later section. The manufacturer should be given the conditions in order to properly appraise this situation. 

Note that these units should not be connected in lines larger than their pipe inlet, since inlet velocity conditions are very important, the savaging down or reduction tends to produce a jet effect by the gas upon the mist eliminator unit. This may erode the unit and cause other erratic performance... 

The unit shown in Figure 4-49 has been used in many process applications with a variety of modifications [18,19,20]. It is effective in liquid entrainment separation, but is not recommended for solid particles due to the arrangement of the bottom and outlet. The flat bottom plate serves as a protection to the developing liquid surface below. This prevents re-entrainment. In place of the plate a vortex breaker type using vertical cross plates of 4-inch to 12-inch depth also is used, (Also see Reference [58].) The inlet gas connection is placed above the outlet dip pipe by maintaining dimension of only a few inches at point 4. In this type unit some liquid will creep up the walls as the inlet velocity increases. 

Friction factor, dimensionless Flow rate of one phase, GPM Aqueous phase flow rate, GPM Cy clone friction loss, expressed as number of cy clone inlet velocity heads, based on Drag or resistance to motion of body in fluid, poundals... 

V,- = Cyclone inlet velocity, average, based on area a) ft/sec... 

This is satisfactory, although a 2-in. nozzle would have a velocity of 34.3 ft/sec. Because this condenser has entering vapors at the dew point, entrainment of some particles is always a real possibility therefore, a low inlet velocity is preferred. Also, overhead vapor lines should have low pressure drop for vapor at its dew point and a 3-in. line might he indicated when this line is checked. 

Air inlet A suitable low-level inlet ventilation area must be provided for the expected airflow rate. Where personnel escape routes will be used for inlet, the inlet velocity must be low enough not to impede progress. 

The pressure drop and the friction loss through a cyclone are most conveniently expressed in terms of the velocity head based on the immediate inlet area. The inlet velocity head, h i, which is expressed in inches of water, is related to the average inlet-gas velocity and density by ... 

Inlet-velocity head (inches of water) p = Gas density (Ib/ft )... 

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