Opposed jets

Oppenauer oxidation Opposed jet mills Opposition searches Oprimol 01 PROCESS... 

Opposed Jet Mills. These mills are, in some ways, similar to the fluidized-bed machine however, in this case two opposed nozzles accelerate particles, causing them to collide at a central point (Fig. 16). A turbine classifier is again used to separate the product that has achieved the desired fineness from that which must be internally recycled for further grinding. 

The Majac jet pulverizer (Ho.sokawa Micron Powder Sy.stems Div.) is an opposed-jet type with a mechanical classifier (Fig. 20-55). Fineness is controlled primarily by the classifier speed and the amount of fan air dehvered to the classifier, but other effects can be achieved by variation of nozzle pressure, distance between the muzzles of the gun barrels, and position of the classifier disk. These pulverizers are available in 30 sizes, operated on quantities of compressed air ranging from approximately 0.6 to 13.0 mVmin (20 to 4500 ftV min). In most apphcations, the economics of the use of this type of jet pulverizer becomes attractive in the range of 98 percent through 200 mesh or finer. 

Fluidized-bed opposed-jet mills Hosokawa Micron Powder Systems Div.) differ from the Majac mill in that powder is not fed into the jets, but the jets impinge into a chamber mich contains suspended powder. The powder is entrained into the jets. This ehminates wear on the nozzles, and reduces contamination. Otherwise, construction and appheations are similar to the Majac mill. The fluidized-bed level is maintained a few inches above the jets. The Fluidized-bed mill is available in 13 sizes with air volumes ranging from. 50 to 11,000 mVh. One application is for toner grinding. 

Restilts for cryogrinding of polymers in an opposed-jet laboratoiy mill are given by [Haesse, Kun.st.stoffe-Gennan Plastics, 70(12), 9-10 (1980)]. 

Singhal J.S. T ien, Flammability Study of Polymer Fuels Using Opposed-Jet Diffusion Flame Technique, Rept No SQUID-TR-CWRU-3-PU, Contract N00014-67-A-0226-0005, Purdue Univ, Lafayette (1975)... 

This flow field can be maintained in a steady state, at least in the Eulerian sense, either by use of a four-roll mill [18] as in Figure 2.8.4(a) or by means of opposed jet flow as in Figure 2.8.4(b). However, it is important to note that the flow is still transient in the Lagrangian sense. That is, pure planar extension is confined to the central stagnation... 

Fig.2.8.4 Geometry pertaining to (a) four-roll mill and (b) opposed jet flow.

Fig. 2.8.9 (a) Implementation of opposed jet device, (b) Proton density image obtained across a horizontal slice, (c) Velocity image obtained across a horizontal slice, (d) Velocity profile taken along the x axis of the cell showing the uniform extensional strain rate e such that vx — ex (adapted from Ref. [15]). 

In the opposed jets design fluid is sucked or pumped into a beaker. The profile which develops is dominantly extensional. In the profiled slot design a rectangular channel is designed such that in the total slip condition an extensional flow develops with a constant rate. The pressure is measured at the stagnation point. Other designs include the open syphon, where fluid is sucked from a beaker through a nozzle which is... 

FIGURE 4.52 Stabilization methods for high-velocity streams (a) vee gutter, (b) rodoz sphere, (c) step or sudden expansion, and (d) opposed jet (after Strehlow, Combustion Fundamentals, McGraw-Hill, New York, 1985). 

Establishing a criterion for blowoff during opposed-jet stabilization is difficult owing to the sensitivity of the recirculation region formed to its stoichiometry. This stoichiometry is well defined only if the main stream and opposed jet compositions are the same. Since the combustor pressure drop is of the same order as that found with bluff bodies [76], the utility of this means of stabilization is questionable. 

FIGURE 8.19 Peak extinction coefficient versus equivalence ratio of fuel/oxygen stream mixture in propane and ethene opposed-jet diffusion flames. /w is the fuel injection parameter. The greater the extinction coefficient, the greater the soot mass. From Ref. [93]. 

The tendency of premixed flames to detach from the flame holder to stabilize further downstream has also been reported close to the flammability limit in a two-dimensional sudden expansion flow [27]. The change in flame position in the present annular flow arrangement was a consequence of flow oscillations associated with rough combustion, and the flame can be particularly susceptible to detachment and possible extinction, especially at values of equivalence ratio close to the lean flammability limit. Measurements of extinction in opposed jet flames subject to pressure oscillations [28] show that a number of cycles of local flame extinction and relight were required before the flame finally blew off. The number of cycles over which the extinction process occurred depended on the frequency and amplitude of the oscillated input and the equivalence ratios in the opposed jets. Thus the onset of large amplitudes of oscillations in the lean combustor is not likely to lead to instantaneous blow-off, and the availability of a control mechanism to respond to the naturally occurring oscillations at their onset can slow down the progress towards total extinction and restore a stable flame. 

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