Exit ducts

For proper use of the equations, the chamber shape must conform to the spray pattern. With cocurrent gas-spray flow, the angle of spread of single-fluid pressure nozzles and two-fluid pneumatic nozzles is such that wall impingement wiU occur at a distance approximately four chamber diameters below the nozzle therefore, chambers employing these atomizers should have vertical height-to-diameter ratios of at least 4 and, more usually, 5. The discharge cone below the vertical portion should have a slope of at least 60°, to minimize settling accumulations, and is used entirely to accelerate gas and solids for entty into the exit duct. 

The primary section of the chamber is characterized by its cross-sectional area (W X H) and by its length (L). The cross-sectional area is designed to be larger than the inlet and exit ducts in order to reduce substantially the gas stream s inlet linear velocity. The length of the chamber determines the amount of time the particles remain at the redueed rate. This starving of the gas s forward motion allows the partieles sufficient time to settle out into the hoppers. 

After the impeller the flow is flowing into the fan casing. The purpose of the casing is to collect the flow coming from the impeller and take the flow into the fan exit duct. Air flows to the casing everywhere from the exit edge of the impeller. For that reason the casing has a spiral shape (Fig. 9.41). 

In addition to the irreversibilities associated with these components, pressure losses (Ap) may occur in various parts of the plant (e.g. in the entry and exit ducting, the combustion chamber, and the heat exchanger). These are usually expressed in terms of non-dimensional pressure loss coefficients, Ap/(p) N, where (/ )in is the pressure at entry to the duct. (Mach numbers are assumed to be low, with static and stagnation pressures and their loss coefficients approximately the same.)... 

Cross-sectional aiea allocated to light phase, sq ft Area of particle projected on plane normal to direction of flow or motion, sq ft Cross-sectional area at top of V essel occupied by continuous hydrocarbon phase, sq ft Actual flow at conditions, cu ft/sec Constant given in table Volume fiaction solids Overall drag coefficient, dimensionless Diameter of vessel, ft See Dp, min Cyclone diameter, ft Cyclone gas exit duct diameter, ft Hy draulic diameter, ft = 4 (flow area for phase in qiiestion/wetted perimeter) also, D in decanter design represents diameter for heavy phase, ft... 

For a uniform angular velocity ( > = constant, i.e., a solid body rotation ), n = — 1, whereas for a uniform tangential velocity ( plug flow ) n = 0, and for inviscid free vortex flow co = c/r2, i.e., n = 1. Empirically, the exponent n has been found to be typically between 0.5 and 0.9. The maximum value of Ve occurs in the vicinity of the outlet or exit duct (vortex finder) at r = De/2. 

There is a core of rotating flow below the gas exit duct (vortex finder), in which the velocity decreaes as the radius decreases and is nearly zero at the... 

Various correlations for mean droplet size generated by plain-jet, prefilming, and miscellaneous air-blast atomizers using air as atomization gas are listed in Tables 4.7, 4.8, 4.9, and 4.10, respectively. In these correlations, ALR is the mass flow rate ratio of air to liquid, ALR = mAlmL, Dp is the prefilmer diameter, Dh is the hydraulic mean diameter of air exit duct, vr is the kinematic viscosity ratio relative to water, a is the radial distance from cup lip, DL is the diameter of cup at lip, Up is the cup peripheral velocity, Ur is the air to liquid velocity ratio defined as U=UAIUp, Lw is the diameter of wetted periphery between air and liquid streams, Aa is the flow area of atomizing air stream, m is a power index, PA is the pressure of air, and B is a composite numerical factor. The important parameters influencing the mean droplet size include relative velocity between atomization air/gas and liquid, mass flow rate ratio of air to liquid, physical properties of liquid (viscosity, density, surface tension) and air (density), and atomizer geometry as described by nozzle diameter, prefilmer diameter, etc. 

The pressure in the ERH is continuously monitored at the vent gas exit duct of the ERH drum to ensure that it operates at subatmospheric pressure. In addition, the hydrogen gas concentration is measured in the ERH drum vent gas exit duct to ensure that hydrogen gas concentration remains below 50 percent of its LEL. Signals from these monitors are used to control the ventilation gas flow by changing the speed of the induced draft fan. 

In some smelters, a reheater is installed to raise the exit gas above the acid dewpoint (generally 350°-450°F) so the acid remains as a vapor and exits with the gas without adversely affecting the ductwork. Even with a reheater, however, during shutdowns the scrubber entry and exit ducts are subject to chemical attack from acid condensates. 

Bokma. E., Koronakis, E., Lohedanz, S., Hughes, C., and Koronakis, V. (2006) Directed evolution of a bacterial efflux pump adaptation of the E. coli TolC exit duct to the Pseudomonas MexAB translocase. FEBS Letters, 580 (22), 5339-5343. 

Recently, Pallares and Johnsson [106] presented an overview of the macroscopic semi-empirical models used for the description of the fluid dynamics of circulating fluidized bed combustion units. They summarized the basic modeling concepts and assumptions made for each model together with the major advantages and drawbacks. In order to make a structured analysis of the processes involved, the CFBC unit is often divided into 6 fluid dynamical zones like the bottom bed, freeboard, exit zone, exit duct, cyclone and downcomer and particle seal, which have been shown to exhibit different fluid dynamical behavior. 

For 1 > (H - S), the cyclone volume below the exit duct (excluding the... 

Monitor the various streams for impurities. Install explosion suppressors in potentially explosive spaces for dusts, such as the exit ducts from grinders. Dump cold liquid or inert solids into systems on the verge of temperatme runaway. Add an inhibitor to neutralize the catalyst for a potential temperature runaway (for example, add gaseous ammonia to neutralize the Lewis acid catalyst BF3... 

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