Flow straighteners

S has been approximated for flames stabili2ed by a steady uniform flow of unbumed gas from porous metal diaphragms or other flow straighteners. However, in practice, S is usually determined less directly from the speed and area of transient flames in tubes, closed vessels, soap bubbles blown with the mixture, and, most commonly, from the shape of steady Bunsen burner flames. The observed speed of a transient flame usually differs markedly from S. For example, it can be calculated that a flame spreads from a central ignition point in an unconfined explosive mixture such as a soap bubble at a speed of (p /in which the density ratio across the flame is typically 5—10. Usually, the expansion of the burning gas imparts a considerable velocity to the unbumed mixture, and the observed speed will be the sum of this velocity and S. ... 

Other Flow Straightening Deviees Other devices designed to produce uniform velocity or reduce swirl, sometimes with reduced pressure drop, are available. These include both commercial devices of proprietaiy design and devices discussed in the hterature. For pipeline flows, see the references under flow inverters and static mixing elements previously discussed in the Tncompressible Flow in Pipes and Channels subsection. For large area changes, as at the... 

It is not recommended to place an elbow at the suction of any pump (Figure 16-2, next page). This will cause a turbulent flow into the pump. If elbows are needed on both sides of the pump, you should u.se long radius elbows with flow straighteners. You should have 10 pipes diameters before the first elbow on the suction piping (Example If the pump has a 4 inch suction nozzle, you should respect 40 inch of straight pipe before the first suction elbow.) Short radius elbows cause vibrations and pressure imbalances that to lead to wear and maintenance on the pump. 

Minimum lengths of straight pipe are required for flow-measuring devices and for certain pressure measurements. Flow straighteners and/or equalizers should be used in the vicinity of throttle valves and elbows, as shown in Figure 20-1. 

If the lower values in the brackets are applied, an additional 0.5 uncertainty (error on 5% risk level) has to be added arithmetically to the flow coefficient confidence limits. The use of flow straighteners is recommended in cases when a nonstandard type of upstream fitting disturbs the flow velocity profile. 

Bends and tee-pieces in pipework often create locally turbulent flow. This enhances the corrosivity of the process liquid. These effects should be minimized by the use of flow straighteners, swept tees and gentle bends. Flow-induced corrosion downstream of control valves, orifice plates, etc. is sometimes so serious that pipework requires lining with resistant material for some twelve pipe diameters beyond the valve. 

In view of its fundamental importance, Eq. (31) should be tested in a flow channel of sufficient height, provided with a suitable flow-straightening section. The results should be relevant to many corrosion processes occurring in maritime structures. The closest approach to such a test has been the work of Coeuret and Vergnes (C8) on a stationary wire in parallel flow. 

In the second configuration (moderate swirl) tested (see Fig. 20.2a), only the air stream was forced and no liquid-fuel pulsations were imposed. The experiments were performed with a Parker-Hannifan Research Simplex Atomizer. The atomizing nozzle consisted of a primary liquid ethanol feed with a coaxial primary air stream. The air stream passed through a set honeycomb, flow-straightener, and swirl vanes to provide the necessary level of swirl. Three loudspeakers were used to excite the primary air. 

Figure 29.3 Experimental setup and instrumentation 1 — fuel 2 — oxidizer, N2, seed-particles 3 — plenum chamber 4 — flow straightener 5 — c/d nozzle (Dthroat = 19.0 mm, Dexu = 24.7 mm) 6 — cavity 7 — laser sheet 8 — Mie-scattering collection device 9 — CCD 10 — afterburning flame and 11 — microphone...

Existing entrained-flow reactors with solid particle flow can be retrofitted with monoliths in which the channel structure also works as a flow straightener, providing better plug-flow characteristics in large-diameter entrained-flow reactors, which suffer from backmixing of catalyst at the reactor wall (53-55). 

The effects of three design features on performance of the moving bed granular filter were evaluated. These features include the screened disengagement section the tangential inlet and flow straightening fins above the gas engagement section. 

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