Basic exhaust opening


Basic Exhaust Openings  [c.826]

Basic exhaust openings are not recommended for use when the distance between source and hood is great, since it is easy for contaminants to spread outside the reach of the exhaust due to the sharp decrease in velocity with increasing distance. It is usually better to use partially closed systems.  [c.826]

Many equations and figures of velocities outside basic exhaust openings have been published. There are some summaries and comparisons of equations. 09 These equations are empirical, theoretical, or semi-empirical descriptions, but they have all been thoroughly investigated and tested and they are reliable as long as the prerequisites coincide with the original descriptions. Most equations describe the velocity along the center axis of different opening shapes.  [c.844]

For some operations it is advantageous to have the exhaust downward instead of through one of the basic exhaust openings described previously. This is accomplished by suction through the working table, a downdraft table. These exhaust openings are quite like basic exhaust openings with flanges, directed upward. To make the surface function both as an exhaust and as a working table, the opening of the exhaust is covered by a perforated table. To this table could be added vertical and horizontal walls and possibly a ceiling, which makes such an opening more like a partial enclosure than a basic exhaust opening.  [c.873]

It should be noted that when there is no jet reinforcement of the flow, i.e., the exhaust hood is used in its conventional mode, then in the two-dimensional form of the Aaberg principle the fluid flow velocity due to the exhaust decays approximately inversely proportionally to the distance from the exhaust opening. However, for three-dimensional exhaust hoods the fluid velocity outside the hood decays approximately inversely as the square of the distance from the exhaust hood. Thus in the three-dimensional conventional hood operating conditions the hood has to be placed much closer to the contaminant in order to exhaust the contaminant than is the situation for the two-dimensional hood (see section on Basic Exhaust Openings). Thus for ease of operation it is even more vital to develop hoods with a larger range of operation in the three-dimensional situation in comparison with two-dimensional hoods.  [c.961]

As mentioned above, a basic exhaust can be of nearly any shape with the most common being round, rectangular, or slot openings, with or without flanges. Openings in walls could be said to have the largest flanges. There also are exhausts consisting of multiple holes or perforated plates in a wall or ceiling or floor or table. The latter ones (holes in a floor or table) ol ten have special designs and are treated separately in a later section. The exhaust opening can be tapered to have both a large opening area and a smooth velocity increase inside the opening to the connecting duct, resulting in lower pressure los.s. As mentioned above, exterior hoods can be connected directly to a process or to equipment. These have some similarity to industrial vacuum cleaners.  [c.831]

The location of the exhaust opening inside the enclosure should be in the main direction of the expected emission direction. The exhaust opening is usually located in the back wall, but many other locations are possible, including the ceiling, side wall, floor, or combinations of these. These other locations are used in practice.  [c.879]

Generally the capture openings are located in the back wall of the booth but may also be in the ceiling, side wall(s), floor, or a combination of these locations. The location of the exhaust opening depends on the type and direction of the emissions.  [c.881]

Capture opening(s) locations should be chosen to take advantage of the initial release direction of the contaminant. This leads to locating exhaust openings in the back, floor, ceiling (e.g., for heat-emitting processes), or side walls of the booth. In many cases it is useful to combine exhaust openings in different sides of the booth.  [c.883]

When used as an air curtain, the flow of the linear jet is blown across a doorway and an exhaust opening pulls the air. The supply air of the air curtain for a door could be either cold or warm, either placed on the inside or the outside, either blowing horizontally or vertically, and either blowing parallel to the opening or at a slight angle to the opening. Usually the curtain has an exhaust opening placed on the other side of the opening. This exhausted air could be circulated back to the supply opening or just transported away. All these alternatives mean that there are innumerable possible configurations for an air curtain. Some of these are shown in the following figures.  [c.937]

The zwitterionic opened form, and the closed form, could exist in equilibrium. Anyway, such a molecule is characterized by a methine group joining two rings, one of the starting rings still possessing its methyl-substituted group. Such dimeric structures issued from one same ring may be considered as symmetrical, contrary to asymmetrical ones, where the methine bridge joins two heterocyclic ring of different nature (15) such as described for benzothiazole series (Scheme 23) (49). These last derivatives are much more difficult to separate. However they appear to be at the origin of the dyes obtained either in Mill s reaction (42), for example, 16. or resulting from the action of a basic agent on 2-methylthiazolium.  [c.40]

Another significant cause of backlash in the hydrogen engine is from pre-ignition sources. When the intake filter is removed and a small quantity of very fine dust particles is introduced into the engine intake, backlash occurs. This procedure creates no extraordinary results if the engine is operating on gasoline, but when the engine is operating on hydrogen, the result is an almost immediate backlash. The particles are drawn into the combustion chamber during the intake stroke. The fuel is then compressed, and the charge is ignited, resulting in the power stroke. During the exhaust stroke, the exhaust valve opens and the burnt charge, along with most of the particles, is pushed out into the exhaust system. The cycle repeats itself with the intake valve opening and a new intake stroke beginning. At this point, however, some of the dust particles, which are still hot from the last cycle, remain in the combustion chamber. As the hydrogen fuel comes into contact with these hot particles, the incoming fuel charge is ignited and bums quickly back into the intake manifold, resulting in detonation. In the case of the hydrocarbon engine, these small particles do not have sufficient thermal mass to ignite the hydrocarbon fuel.  [c.458]

In this section three main aspects will be considered. Firstly, the basic strengths of the principal heterocyclic systems under review and the effects of structural modification on this parameter will be discussed. For reference some pK values are collected in Table 3. Secondly, the position of protonation in these carbon-protonating systems will be considered. Thirdly, the reactivity aspects of protonation are mentioned. Protonation yields in most cases highly reactive electrophilic species. Under conditions in which both protonated and non-protonated base co-exist, polymerization frequently occurs. Further ipso protonation of substituted derivatives may induce rearrangement, and also the protonated heterocycles are found to be subject to ring-opening attack by nucleophilic reagents.  [c.46]

The field of particle adhesion is, in many ways, a mature field. Certainly, many aspects of adhesion in general, and particle adhesion in specific, can be understood in terms of the basic theories that presently exist. However, there remain many questions that have yet to be answered. Effects of humidity and capillary action, contact charging, yielding phenomena and partial plasticity, and time-dependent effects are but a few of the topics that need to be better understood. In addition, recent advances in computing technology opens the door to molecular dynamic modeling that can take realistic potentials and derive the entire spectra of physical properties, from their Young s moduli, Poisson s ratios, and yield strengths to their surface energies and works of adhesion. The potentials, themselves, can be studied using new techniques such as force-probe microscopy. Sucb novel computational and experimental methods allow particle adhesion interactions to be studied in detail that probably could not even be envisioned a decade ago.  [c.187]

Recall the first analogous series of hydrocarbons the alkanes, a series of saturated hydrocarbons, all ending in -ane. For these hydrocarbons and other hydrocarbons to react, a place on the hydrocarbon chain must exist for the reaction to take place. Since all the bonds from carbon to hydrogen are already used, an "opening" on one of the carbon atoms must exist for it to be able to react with something else. This "opening" occurs when one of the hydrogen atoms is removed from its bond with a carbon atom, thus causing that carbon to revert back to a condition of instability, with seven electrons in its outer ring, or, as we now state, with one unpaired electron. This one unpaired electron (or half of a covalent bond, or "dangling" bond) wants to react with something, and it will, as soon as another particle which is ready to react is brought near. This chain of carbon atoms (from one carbon to another to another, and so on) with a hydrogen atom missing is a particle that was once a compound, and its name is a radical.  [c.190]

Most BEOs are situated at the end of a tube, but there are also basic openings situated in walls. BEOs can be used for nearly all kinds of sources, but are usually used for point sources. Use for line or area sources usually demands flexible or movable exhausts, or a slot placed along the line source or along the sides of an area source, or a very large (circular or rectangular) opening placed close to tlie source. A high flow rate is needed to get efficient exhaust in many cases.  [c.826]

When using supply inlets it is more important than for exhaust hoods how the person, working with a process, is placed, relative to the contaminant source and to the inlet. It is nearly always better to keep the person between inlet and source than source between inlet and person. For supply systems it is even more efficient than for exhausts to have the flow passing in front of the person instead of from back to front. The airflow from behind the person could generate a wake, which includes the source or the generated contaminant and thereby increases the person s exposure. This phenomenon is more common with large flow rates and large supply openings than with small flow rates and small inlets. Placing the worker beside the path from the inlet to the source and on to the exhaust is a general rule. It is possible to counteract the wake around a person by using supply air, directed downward around the worker. In this case, the air is normally sucked into an exhaust hood (see Section 10.4).  [c.918]

There are many possible combinations of supply and exhaust air. For example, a line jet could be used as a shield in an opening, as a stripping system on surfaces, for blowing contaminants into an exhaust, etc. An enclosure could be designed with a line jet in the opening, with a wall jet inside to increase efficiency, or with a low-momentum jet inside or outside the opening to replace the room air supply. In this section, only some basic combinations are described.  [c.935]

One common combination is a jet and an exhaust hood. The jet can be circular or plane and situated around or in front of a (hot) contaminant source. The intention is to direct the contaminant into a basic opening or a receptor hood. Mostly these jets are directed upward into hoods, but may be directed sideways or downward. There is a difference to jets covering openings. When directed into a hood the jet is intended to help the natural flow into the hood and not to act as a shield, even though it sometimes also has this function. Figure 10.105 illustrates two principal ways that air jets could be used to direct contaminants into a hood (see also Section 10.4.5).  [c.1006]

Otto an engineer and let him continue his research. Otto s ideas concerning stratification were patented in 1877. The new engine had a single horizontal cylinder and bore some similarity to the Lenoir engine. The important difference was in the admission of gas and air, also gas flame ignition. Otto seemingly had more faith in ignition by flame rather than electrical spark. The basic elements of the modern four-stroke engine are to be found in this experimental engine. A slide valve controlled air intake with a second cam operated slide valve controlling gas admission. As the piston began its outward stroke, the air valve opened and the gas valve remained closed until the piston had completed half its travel. At the end of the stroke, the valves closed and the piston began the return stoke compressing the air gas mixture. At the end of the return stroke, the gas air mixture is ignited and the piston commences its second outward stroke, the power stroke. Ac the end of this stroke the exhaust valve opens, and the piston returns exhausting the burnt gasses. In Otto s new design there was one power stroke for every four strokes of the piston or two revolutions of the flywheel.  [c.931]

The basic exhaust opening (BEO) is the simple opening placed at the end of a duct or a tube, which acts as the connection to the suction device (fan). These types of xhausts are commonly used because they can be designed and ojierated in a way that does not interfere with the pnx ess. Most BEOs have quite simple forms—circular, square, rectangular, or nearly any shape—and they can also be tapered with different angles. A rectangular opening is called a slot when it has a large length-to-width ratio ( >5). A slot can also consist of many smaller slots or holes in a line. BEOs can be provided with a plane surface covering parts of the opening (baffles). The plane surface could be provided with slots or holes to make a perforated surface. The intention of these surfaces is to improve air distribution over the opening, increase the velocities in the openings, or reduce exhaust flow rate (see Different Forms and Boundaries Relative to Other Types). A BEO could, instead of being one opening, consist of many small openings close to each other in the same plane. The opening plane for a BEO is most often straight, but it could be curved to fit the process or the tool.  [c.826]

Rim exhausts, being one type of slot hood, use the same basic principles as given in the section on basic exhaust openings. The recommendation is to use the equations ven in the Basic Exhaust Openings section for unflanged or flanged slot hoods or elliptical openings. The most common design method, howevei uses Method B, capture velocity. The design procedure involves selecting a capture velocity. The selection depends on the generation rate and toxicity of the contaminant as well as some consideration of disturbances near the local exhaust hood. For the case of open surface tanks, the generation rate and toxicity are usually combined to determine the class of contaminant. The class is then used to select an appropriate capture velocity. The ACGIFf gives recommended capture velocities for a number of open-tank processes. F.quation (10.55) is applicable  [c.849]

A separate description also exists for low volume high velocity (LVHV systems. Some of these are similar to BEOs, but they are used in a different way from basic openings. One difference is that BEOs have lower air velocities in the openings than LVHV systems, usually less then f5-20 m s- and more than 7.S rn s, respectively. Another is that basic openings have opening areas larger than O.Of m-, while LVHV openings have areas less than 0.001 rn. Intermediate systems exist, such as the small circular exhaust opening around a welding rod or the exhaust in the surface of a portable grinding machine.  [c.831]

When using a booth the capture efficiency of one or more basic capture openings (slot, bellmouth inlet, etc.) is enhanced by shielding it against influence from the surrounding airflow (cross-drafts) from at least one side and therefore restricting the flow toward the opening. Since the direct grasp of exhaust openings is very short, the main effect is obtained from the ambient air entering the booth while following the air volume flow deficit, thus generating a general draft into the booth. The aim is to establish a flow across the entire remaining open faces of the booth, uniformly directed into the booth and toward the capture openings.  [c.881]

The theory of extraction with solvents has heen discussed in Section 1,22, and it has been shown that for a given volume of solvent several extractions with aliquot parts give better results than a single extraction with the total volume of the solvent. By way of illustration, the technique of the extraction of an aqueous solution with diethyl ether will be described. A separatory funnel (globular or pear-shaped with a short stem, see Figs. 11,1, 5, c and d) is selected of about twice the volume of the liquid to be extracted, and is mounted in a ring on a stand with a firm base. The barrel and plug of the stopcock are dried with a linen cloth, and lightly treated with a suitable lubricant (vaseline, etc. see third footnote in Section 11,38). A new well-fitting cork is selected for closing the mouth of the funnel alternatively, the ground glass stopper, supplied with the separatory funnel, may be used. The solution and the extraction solvent (usually about one third of the volume of the solution, but see Section 1,22) are introduced into the funnel, and the latter stoppered. All naked flames in the immediate vicinity should be extinguished. The funnel is then shaken gently (so that the excess vapour pressure f will be developed slowly), inverted, and the stopcock opened in order to relieve the excess pressure. The stopcock is again closed, the funnel again shaken, and the internal pressure released. When the atmosphere inside the funnel is saturated with ether vapour, further shaking develops little or no additional pressure. At this stage, the funnel is vigorously shaken for 2-3 minutes to ensure the maximum possible transfer of the organic substance to the ether layer, and then returned to the stand in order to allow the mixture to settle. When two sharply defined layers have formed, the lower aqueous layer is run oflF and separated as completely as possible. The residual ethereal layer is then poured out through the upper neck of the funnel contamination with any drops of the aqueous solution still remaining in the stem of the funnel is thus avoided. The aqueous solution may now be returned to the funnel and the extraction repeated, using fresh ether on each occasion until the extraction is complete. Not more than three extractions are usually required, but the exact number of extractions will naturally depend upon the partition coefficient (Section 1,22) of the substance between water and ether. The completeness of the extraction can always be determined by evaporating a portion of the last extract on the water bath and noting the amount of residue. The combined ethereal solutions are dried with an appropriate reagent (Section 11,39), and the ether removed on a water bath (Sections 11,5, 11,13 and 11,14). The residual organic compound is purified, depending upon its properties, by distillation or by recrystalliKition.  [c.150]

The exterior hoods described here are divided into basic openings, rim exhausts, low-volume high-velocity (LVHV) hoods, receptor hoods (canopy hoods), and downdraft ventilation tables. Many varieties of these types of hoods exist. Some of these have been described and investigated more thoroughly than others because they are used more often or they are of more general use and applicability than the more specialized hoods.  [c.819]

Systems with extraction only The most common of this type use slot exhaust devices that are more or less uniformly distributed across the exhaust wall of the booth (e.g., the back Wall). Some attention has to be paid to maintaining a uniform distribution of the exhaust volume flow across the slit openings. Rows of bellmouth inlets or even vortex hoods are more advantageous because they provide a more uniform flow field.  [c.883]


See pages that mention the term Basic exhaust opening : [c.979]    [c.211]    [c.459]    [c.638]    [c.195]   
Industrial ventilation design guidebook (2001) -- [ c.0 ]