Flow of gas

Gibbs free energy or Gibbs molar free energy molar flow of gas phase acceleration of gravity enthalpy, molar enthalpy, weight enthalpy Henry s constant Planck s constant height horsepower radiation intensity molar flux... 

The relatively concentrated hydrochloric acid is employed so that with ordinary use of the apparatus, spent liquor does not accumulate very rapidly the concentrated acid also ensures a brisk and delicately controlled flow of gas. When the generator is replenished with acid, marble or both, the de-aeration procedure detailed above is repeated until a sufficiently air-free gas supply is obtained. 

This tube is connected %vith rubber tubing of about 6 mm. bore to the carbon dioxide Kipp, via a wash-bottle containing sodium carbonate solution (to remove any dilute hydrochloric acid spray). It is very important, when the apparatus is in use, that there should be no constriction or bend in the rubber tube between the tap C and the wash-bottle. If these precautions are taken, a slow, e en, and easily controlled flow of gas can be obtained. 

This acid mixture may be prepared (compare Section 11,49, 1) by placing 120 g. (37-5 ml.) of bromine and 130 g. of crushed ice in a 500 ml. flask, cooling the latter in ice, and passing sulphur dioxide (from a siphon of the liquefied gas) into the bromine layer at such a rate that the gas is completely absorb. The flask is shaken occasionally, and the flow of gas is stopped inunediately the red colour due to free bromine has disappeared the mixture will then have a yellow colour. The resulting acid mixture is equivalent to 260 g. of 48 per cent, hydrobromio acid to which 75 g. of concentrated sulphuric acid have been added it need not be dis. tilled for the preparation of n-butyl bromide. 

The flows of gas and liquid need not be concentric for aerosol formation and, indeed, the two flows could meet at any angle. In the cross-flow nebulizers, the flows of gas and sample solution are approximately at right angles to each other. In the simplest arrangement (Figure 19.11), a vertical capillary tube carries the sample solution. A stream of gas from a second capillary is blown across this vertical tube and creates a partial vacuum, so some sample solution lifts above the top of the capillary. There, the fast-flowing gas stream breaks down the thin film of sample... 

The aim of breaking up a thin film of liquid into an aerosol by a cross flow of gas has been developed with frits, which are essentially a means of supporting a film of liquid on a porous surface. As the liquid flows onto one surface of the frit (frequently made from glass), argon gas is forced through from the undersurface (Figure 19.16). Where the gas meets the liquid film, the latter is dispersed into an aerosol and is carried as usual toward the plasma flame. There have been several designs of frit nebulizers, but all work in a similar fashion. Mean droplet diameters are approximately 100 nm, and over 90% of the liquid sample can be transported to the flame. 

For a longitudinal disturbance of wavelength 12 pm, the droplets have a mean diameter of about 3-4 pm. These very fine droplets are ideal for ICP/MS and can be swept into the plasma flame by a flow of argon gas. Unlike pneumatic forms of nebulizer in which the relative velocities of the liquid and gas are most important in determining droplet size, the flow of gas in the ultrasonic nebulizer plays no part in the formation of the aerosol and serves merely as the droplet carrier. 

The gas or vapor to be examined is mixed with argon gas to constitute the needed flow of gas into the plasma flame, and the sample vapor or gas is swept along with this argon makeup gas. 

The collection of particles larger than 1—2 p.m in Hquid ejector venturis has been discussed (285). High pressure water induces the flow of gas, but power costs for Hquid pumping can be high because motive efficiency of jet ejectors is usually less than 10%. Improvements (286) to Hquid injectors allow capture of submicrometer particles by using a superheated hot (200°C) water jet at pressures of 6,900—27,600 kPa (1000—4000 psi) which flashes as it issues from the nozzle. For 99% coUection, hot water rate varies from 0.4 kg/1000 m for 1-p.m particles to 0.6 kg/1000 m for 0.3-p.m particles. 

The upward flow of gas and Hquid in a pipe is subject to an interesting and potentially important instabiHty. As gas flow increases, Hquid holdup decreases and frictional losses rise. At low gas velocity the decrease in Hquid holdup and gravity head more than compensates for the increase in frictional losses. Thus an increase in gas velocity is accompanied by a decrease in pressure drop along the pipe, a potentially unstable situation if the flows of gas and Hquid are sensitive to the pressure drop in the pipe. Such a situation can arise in a thermosyphon reboiler, which depends on the difference in density between the Hquid and a Hquid—vapor mixture to produce circulation. The instabiHty is manifested as cycHc surging of the Hquid flow entering the boiler and of the vapor flow leaving it. 

Fluidization refers to the condition in which soHd materials are given free-flowing, fluid-like behavior (29). As a gas is passed upward through a bed of sohd particles, the flow of gas produces forces which tend to separate the particles from one another. At low gas flows, the particles remain in contact with other soflds and tend to resist movement. This condition is referred to as a fixed bed. As the gas flow is increased, a point is reached at which the forces on the particles are just sufficient to cause separation. The bed then becomes fluidized. The gas cushion between the soflds allows the particles to move freely, giving the bed a Hquid-like characteristic. 

Oxygen inhalators are used as a first-aid measure for a long Hst of emergencies, including heart attacks and suffocation, and as a result are carried routinely by rescue squads. Oxygen—helium mixtures have proved beneficial in asthmatic attacks, because these permit more rapid flow of gas into congested areas of the respiratory system. 

Diffusion Pump System. After the pump line and trap have been shut off, a large valve is opened slowly enough that the mass flow of gas from the chamber through the valve into the od-diffusion pump system does not dismpt the top jet of the diffusion pump (DP) (Fig. 4). When the Hquid nitrogen is replenished after the trap has been operated for some time, release of previously trapped gas must be avoided. The so-caded ionization-gauge response pips at the start of the Hquid-nitrogen replenishment are an indication of trap ineffectiveness. 

The expansion turbine converts the dynamic energy of the flue gas into mechanical energy. The recoverable energy is determined by the pressure drop through the expander, the expander inlet temperature, and the mass flow of gas (66). This power is then typically used to drive the regenerator air blower. 

Bubble-Tube Systems The commonly used bubble-tube system sharply reduces restrictions on the location of the measuring element. In order to ehminate or reduce variations in pressure drop due to the gas flow rate, a constant differential regulator is commonly employed to maintain a constant gas flow rate. Since the flow of gas through the bubble tube prevents entiy of the process liquid into the measuring system, this technique is particularly usefiil with corrosive or viscous liquids, liquids subjec t to freezing, and hquids containing entrained solids. 

The work expended on the gas during compression is equal to the product of the adiabatic head and the mass flow of gas handled. Therefore, the adiabatic power is as follows ... 

FIG. 12-34 Cross-flow of gas and solids in a cascade-type gravity dryer. (Link-Belt Co., Multi-Louvre piinciple.)... 

Countercurrent flow of gas and sohds gives greater heat-transfer efficiency with a given inlet-gas temperature. But cocurrent flow can be used more frequently to diy heat-sensitive materials at higher inlet-gas temperatures because of the rapid coohng of the gas during initial evaporation of surface moisture. 

In some cases in which it is desirable to cool the product before removal to the outside atmosphere, the discharge end of the cyhnder is provided with an additional extension, the exterior of which is water-spray-cooled. In cocurrent-flow calciners, hot gases from the interior of the heated portion of the cylinder are withdrawn through a special extraction tube. This tube extends centrally through the cooled section to prevent flow of gas near the cooled-shell surfaces and possible condensation. Frequently a separate cooler is used, isolated from the calciner by an air lock. 

Bucket elevators, skip hoists, and cranes are used for top feeding of the furnace. Retention and downward flow are controlled by timing of the bottom discharge. Gases are propelled by a blower or by induced draft from a stack or discharge fan. In normal operation, the downward flow of sohds and upward flow of gas are constant with time, maintaining ideal steady-state conditions. 

The majority of spray dryers in commercial use employ cocurrent flow of gas and solids. Countercurrent-flow diyers are used primarily for diying soaps and detergents. Their classif ng ability is useful in these applications. Air flow is upward, cariying entrained fines from the top of the chamber. The coarse product settles and is removed... 

Minimum allowable capacity of a column is determined by the need for effective dispersion and contacting of the phases. The types of plates differ in their ability to permit Tow flows of gas and liquid. A cross-flow sieve plate can operate at reduced gas flow down to a point where liquid drains through the perforations and gas dispersion is inadequate for good efficiency. Valve plates can be operated at veiy... 

Where Q = volumetric flow of gas, ftVs N = impeller speed, rev/s D = impeller diameter, ft and T = tank diameter, ft. 

The pressure is higher at the bottom of the sohds draw-off pipe due to the relative flow of gas counter to the sohds flow. The gas may either be flowing downward more slowly than the solids or upward. The standpipe may be fluidized, or the solids may be in moving packed bed flow with no expansion. Gas is introduced at the bottom (best for group B) or at about 3-m intervals along the standpipe (best for group A). The increasing pressure causes gas inside and between... 

Packed-bed scrubbers m be construc ted for either vertical or horizontal gas flow. Vertical-flow units (packed towers) commonly use countercurrent flow of gas and liquid, although cocurrent flow is sometimes used. Packed scrubbers using horizontal gas flow usually employ cross-flow of liquid. 

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