Velocity gas flow

All the CO resulting from the pseudo solid-solid reaction is conducted, together with entrained char, from the top fluidized section through a constriction, in which the high-velocity gas flow prevents backflow, to a transport combustor, where the CO is burned to C02 with preheated air, along with as much of the char as is called for by heat balance to maintain the endothermic FeO-C reaction. The heated recycled char is separated from the off gas at the top of this transport combustor in a hot cyclone and is returned as a thermal carrier to the lower part of the lowest j igged section, while the hot flue gas from the transport combustor is used to preheat the incoming air in a recuperator. 

The constricted orifice of the concentric quartz wall directs the coolant argon along the outer wall of the torch (Figure 1). The low-pressure region, generated by the Bernoulle effect from the peripheral high-velocity gas flows, centers the plasma, cans-... 

Gas hourly space velocity [gas flow rate at normal conditions or at 450 C, as indicated in the text/overall volume of the catalyst (bed or monolith)], h ... 

Pi is inlet pressure, microns pe is exit pressure, microns pm is mean pressure, microns n is viscosity at atmospheric pressure, poises Equation (3) reverts to Poiseuille s Law at sufficiently high pressures, where the second term in the large parenthetical factor becomes negligible compared to unity. As the pressure is decreased and intermolecular collisions become less frequent, a flow velocity profile is established where the forward velocity component near the wall becomes a finite value which increases with lower pressures. The reason for this condition is that at these pressures many molecules can stream from the bulk of flow, where the forward velocity is relatively high, to the wall, without suffering collisions with molecules having low forward velocities. Gas flow under such conditions is termed slip flow. Pressures corresponding to this type of flow are such that the second term of the correction factor in equation (3) is finite compared to unity. At lower pressures, where the mean free... 

For convective processes involving high-velocity gas flows (high subsonic or supersonic flows), a more meaningful and useful definition of the heat transfer coefficient is given by... 

Bernoulli s equation, as we have written it, is exactly correct for constant-density fluids and practically correct for all flows in which the density changes are unimportant. For liquids this includes almost all steady flows. We show here that it also is practically correct for low-velocity gas flows. 

Shock waves and hydraulic jumps are very similar, as we see when we study shock waves in high-velocity gas flow.. 

The principal differences between high-velocity gas flows and the flows we have studied so far are the following ... 

The changes in density which accompany high-velocity gas flows will complicate the mathematics. In typical situations we have one more unknown and one more equation to deal with than in the corresponding constant-density flow. As the student sees that the equations in this chapter are longer and more complex than those in the preceding chapters, the student should remember that this is the reason for the added complexity. 

In high-velocity gas flow, velocities are often reached that are comparable to the speed of sound, so the speed of sound plays an important part in what follows. The speed of sound is the speed at which a small pressure disturbance moves through a continuous medium. Sound, as our ears perceive it, is a series of small air-pressure disturbances oscillating in a sinusoidal fashion in the frequency range jfrom 20 to 20,000 cycles per second, or hertz (Hz). The magnitude of the pressure disturbances is generally less than 10 Ibf/in absolute (7 Pa) [l ]. 

Many of the most interesting features of high-velocity gas flow can be seen in the simplest of all cases, the steady, frictionless, adiabatic, one-dimensional flow of a perfect gas. We study this type of flow in detail other types are treated more briefly, because they have so much in common with this one. 

It can be readily shown (Prob. 8.8) that the potential-energy changes Ag2 are negligible for most high-velocity gas flows, so we drop the gz terms from this equiation. Next we assume that state R is some upstream reservoir, where the cross-sectional area perpendicular to the flow is very large therefore, Vff is negligible. This condition is referred to in various texts as the reservoir, stagnation, or total condition. We call it the reservoir condition and use the subscript R. 

But, as shown previously, RkT IM is the square of the speed of sound at state 1, or Cl, so the left side is (1/,/c,). The ratio V/c is called the Mach number M in honor of the Austrian physicist Ernst Mach. This ratio plays a crucial role in the study of high-velocity gas flows (and is widely reported in the press describing the speed of supersonic aircraft). It is the ratio of the local flow velocity to the local speed of sound. For subsonic flows M is less than 1 for sonic flows it equals 1 for supersonic flows it is greater than 1. Making this definition, we can rearrange Eq. 8.15 to... 

HIGH-VELOCITY GAS FLOW WITH FRICTION, HEATING, OR BOTH... 

As discussed in Sec, 6.13, the economic velocity in a pipeline is primarily dependent on the density of the fluid flowing. For long-distance natural-gas pipelines, the pressures are normally in the range of 500 to 1000 psia, so densities are of the order of 1 to 21bm/ft From Table 6.4 we can estimate the economic velocity at about 20ft/s, which is typical of these pipelines. Thus, this kind of flow does not really correspond to the subject of this section—high-velocity gas flow however, it fits in naturally here, after we have developed the equations for high-velocity gas flow. 

This formula gives good results for low-velocity gas flow (less than about 200ft/s), hut for high-velocity gas flows Bernoulli s equation is no longer applicable. For all velocities between zero and sonic velocities, we can assume that the part of the mainstream which is stopped by the impact tube is stopped practically isentropically. If that is correct, then the pressure measured at F, is the reservoir pressure for the flow. Thus, we can use Eq. 8.17, solved for... 

High-velocity gas flow has great practical significance in aerodynamics, rocket and turbine design, high-speed combustion, ballistics, etc. This... 

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