Imposed pressure drop

As regards Type C apparatus, typical of CCNY s setup (Yerushalmi et al, 1976), when the solid rate controlling valve opens but slightly, and the initial solids inventory is high, the voidage profile will be close to that for Type A apparatus, while when this valve is mostly open, the voidage profile will be similar to that for Type B apparatus. In most casts, its axial voidage variation will be affected by the initial solids inventory. The effect of solids inventory is reflected in what Weinstein et al. (1984) called imposed pressure drop across the fast bed. ... 

Weinstein, H., Graff, R., Meller, N., and Shao, M. The influence of the imposed pressure drop across a fast fluidized bed, in Fluidization (D. Kunii and R. Toei, eds.), pp. 299-306. Engineering Foundation, 1984. 

Experiments conducted by Li et al. (1988a) confirmed the three operating modes in a circulating fluidized bed of 90 mm i.d. by using a scanning transducer-valved system. The imposed pressure drop APimp was altered by changing the solids inventory /, or by manipulating the solid rate-control valve. 

AEimp imposed pressure drop across a unit [kg/(m s2)]... 

Lisseter and Fowler (1992) have derived a simple set of equations for bubbly flow through a vertical tube. They have shown that under steady flow conditions, the void fraction will relax from its inlet value to an asymptotic value within only a short distance from the inlet. They have obtained a relationship between the inlet void fraction and the imposed pressure drop and derived a simple expression for the equihbrium void fraction. They have also considered the wall friction in their analysis of bubbly flows. 

Let the medium between the flat surfaces of two bodies (now a fluid because of practical reasons) flow with a mean velocity V (Fig. 1.13). This flow results from either an imposed pressure drop or an induced buoyancy, respectively called forced and natural convection. Lettheinlettemperatureofthefluidbe72. (Note that the fluid temperature need not be Tz- Selection of Tz for this temperature eliminates temperature gradient near plate 2 and simplifies the following development.) The convection heat transfer from plate 1 is defined as the conduction in the fluid next to plate 1 (in view of the fact... 

Historically, practical analysis of pressure atomizers has focused on experimental characterization of the discharge coefficient (Cd) that represents the ratio of measured and theoretical flowrates under an imposed pressure drop condition ... 

Two-phase fluid flows are susceptible to instability and this is often a very important parameter in design. The variation of total pressure drop as a function of flow rate may take the form illustrated in Figure 10-6. For imposed pressure drop APi or AP4 there is only one possible value of flow. However, at AP3 there are two possible values and at APj, three values. Cases with more than one flow rate for a given pressure drop are susceptible to flow excursion from one operating condition to another. Similar excursions are possible when the imposed pressure drop is not constant but follows a pump characteristic such as shown by line PQ. 

According to this model the permeate flux at steady-state is independent of the imposed pressure drop and it is controlled by the concentration polarization boundary layer. The increasing pressure drop results in a thicker solute layer until convection and difliision in the boundary layer will... 

If, however, the reservoir pressure drops below the bubble point, then gas will be liberated in the reservoir. This liberated gas may flow either towards the producing wells under the hydrodynamic force imposed by the lower pressure at the well, or it may migrate... 

Measurement by Electromagnetic Effects. The magnetic flow meter is a device that measures the potential developed when an electrically conductive flow moves through an imposed magnetic field. The voltage developed is proportional to the volumetric flow rate of the fluid and the magnetic field strength. The process fluid sees only an empty pipe so that the device has a very low pressure drop. The device is useful for the measurement of slurries and other fluid systems where an accumulation of another phase could interfere with flow measurement by other devices. The meter must be installed in a section of pipe that is much less conductive than the fluid. This limits its appHcabiHty in many industrial situations. 

Solid Desiccants. The sohd desiccants used in dynamic appHcations fad into a class caded adsorbents (see Adsorption). Because they are used in large packed beds through which the gas or Hquid to be treated is passed, the adsorbents are formed into soHd shapes that adow them to withstand the static (fluid plus sohd head) and dynamic (pressure drop) forces imposed on them. The most common shapes are granules, extmded pedets, and beads. 

Downward flow of both fluids imposes no restriction on the gas rate, except that the pressure drop will be high. On the whole, the trickle bed is preferred to the flooded bed. 

When the relieving scenarios are defined, assume line sizes, and calculate pressure drop from the vent tip back to each relief valve to assure that the back-pressure is less than or equal to allowable for each scenario. The velocities in the relief piping should be limited to 500 ft/sec, on the high pressure system and 200 ft/sec on the low pressure system. Avoid sonic flow in the relief header because small calculation errors can lead to large pressure drop errors. Velocity at the vent or flare outlet should be between 500 ft/sec and MACH 1 to ensure good dispersion. Sonic velocity is acceptable at the vent tip and may be chosen to impose back-pressure on (he vent scrubber. 

Figure 6-31 illustrates control schemes for the single stage unit which allow greater stability in performance. As the load changes for a fixed suction pressure, the process fluid is replaced by an artificial load (usually air Figure 6-31, item 1) to maintain constant ejector operation. An artificial pressure drop can be imposed by valve (2), although this is not a preferred scheme. Wlten the addi-... 

The basic adsorption process design. Sub-tasks within that include the adsorbent selection, made in view of aU of the requirements imposed on the dehydration process. The adsorption step time, regeneration and cooHng step times all need to be settled and these in view of mechanical details. The overall vessel configuration, for example, the vessel ID and length, which quantities are typically sized based on pressure drop. Finally we need to make some estimate of the expected service Hfetime for the adsorbent product. 

Methods that utilize the energy of the water stream by venturi-action and orifices to induce concentrate (typically, such devices impose a 35% pressure drop on the water stream). 

For a homogeneous tubular reactor, the pressure drop corresponding to the desired flowrate is often relatively small and does not usually impose any serious... 

Pressure drop through the reactor is smaller than with upflow, and there is no problem with flooding which might otherwise impose a limit on the gas and liquid flowrates used. 

Coriolis Liquids. Gases at high pressure 20 (See Section 6.2.3) Can be used for almost any liquid provided that the viscosity is not so great as to impose too high a pressure drop (See Section 6.2.3)... 

Figure 20 Predicted flow regime diagram of the industrial MIP reactor, with solids flux as a function of the imposed total pressure drop at fixed gas flow rate. The snapshots of voidage profile refer to the transition, from left to right, the dilute transport, choking transition in between with different solids inventory, to the dense fluidization (Lu et al., 2007).

The riser cannot be considered as an isolated entity in the CFB loop. When no particles are introduced into or discharged from the loop, the solids mass flow rate in the riser is equal to that in the downcomer. For a given quantity of solids in the loop, the presence of fewer solids in the riser implies the presence of more solids in the downcomer. Likewise, the pressure drop across the riser must be balanced by that imposed by the flow through its accompanying components such as the downcomer and the recirculation device. Furthermore, the flow characteristics of the riser can be significantly affected by the behavior of the accompanying components in the loop. 

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