Hood side

Typically, the velocity distribution in the hood face area is not uniform. Wakes formed close to the hood sides, or vena comracta, reduce the effee-... 

Particulate matter from an EAF is very fine and difficult to capture. The capture of smoke and dust is the most difficult problem to solve when installing a dust arrestment system on an electric arc furnace. There are several methods that offer different advantages and disadvantages. Figure 4.16 depicts the principle of roof mounted hoods, side-draught hoods and fourth-hole evacuation. 

The whole dryer section is enclosed in a drying hood with doors which can be opened e. g. for inspection. It allows controlled flow of the hot and dry make-up air as well as of the vapor laden exhaust air. The pressure inside the hood should be balanced in such a way that a minimum of air is blown from the hood into the machine hall or sucked from the machine hall into the hood. For effective pocket ventilation the hot air enters via blow boxes or blow rolls and flows to both sides of the machine where it is sucked off To prevent condensation the hood walls are insulated and make up air is supplied along both hood sides from underneath. These measures allow a low amount of make-up air, a high air dew point of the exhaust air and effective heat recovery. 

FIGURE 1.200 Cross section of a mold with core side and hood side... 

Triangular Taylor- Hood Quadratic Linear Vertices and mid-sides Vertices... 

Rectangular Taylor-Hood Bi-quadratic Bi-linear Comers, mid-sides and centre Corners... 

NOTE In the initial testing of any undesireable interaction between Sodium Azide, Acetic Acid and Sulfuric Acid, I mixed 5mL of each into a small cup underneath my "fume hood". Though I smelled nothing, within seconds my head felt like it was expanding, my heart started racing, and I felt more weak and confused than normal. I just barely escaped and recovered in 15 minutes, but, Needless to say, this procedure is a tad on the dangerous side. You have been warned. ... 

When a fan is placed at the end of a system so that most of the system pressure drop is on the suction side of the fan, it is commonly called an exhaust fan or an exhauster. This term may also be appHed to a ventilating fan where the primary function is to exhaust air from a room or an open hood. 

Sheet Drying. At a water content of ca 1.2—1.9 parts of water per part of fiber, additional water removal by mechanical means is not feasible and evaporative drying must be employed. This is at best an efficient but cosdy process and often is the production botdeneck of papermaking. The dryer section most commonly consists of a series of steam-heated cylinders. Alternate sides of the wet paper are exposed to the hot surface as the sheet passes from cylinder to cylinder. In most cases, except for heavy board, the sheet is held closely against the surface of the dryers by fabrics of carefuUy controUed permeabiHty to steam and air. Heat is transferred from the hot cylinder to the wet sheet, and water evaporates. The water vapor is removed by way of elaborate air systems. Most dryer sections are covered with hoods for coUection and handling of the air, and heat recovery is practiced in cold climates. The final moisture content of the dry sheet usually is 4—10 wt %. 

Flask F is provided with a two-hole cork stopper connected with tube E, and with tube G which connects with the first condenser II and may be of smaller bore than tubes C and E. H is. a. condenser with a 30-cm. water jacket. H is connected with I by means of an adapter. / is a i-l. round-bottom flask supported in a pan which is at first filled with ice and later used as a water bath. Flask I is fitted with a two-hole cork stopper carrying the adapter connected with condenser H and a Vigreux column K of 2-cm. diameter and a length of 30 cm. to the side arm. Flask I and condenser H are covered with black cloth (Note 2). The side arm of K is connected with a 90-cm. water-jacketed condenser L which leads into M through an adapter, iff is a 750-cc. Erlen-meyer flask immersed in an ice bath. Flask M is provided with a two-hole stopper connected with the adapter from L and an upright bulb condenser that is provided with a tube leading through a window or to a hood. 

The apparatus illustrated in Fig. 3 is assembled, in a large hood if possible (Note 3). A is a 5- . round-bottom flask heated by a large ring burner and provided with a specially treated four-hole cork stopper covered with tin foil (Note 4). To these holes are fitted the column Z), the tube B reaching to the bottom of A, the specially bent tube C reaching up the inside of D, and the tube K connected with the tubes leading to the 2-I. separatory funnel H, so that the distance between the stopper of A and the stopcock of H is at least 100 cm. The bottom of the column D is of 20 mm. bore while the main portion is 30 mm. The side arm should be at least 85 cm. above the stopper of 4. The tube C... 

An apparatus resembling that pictured by Schlatter is assembled in a good hood. Two 5-1. three-necked flasks are mounted side by side about 10 cm. apart and about 10 cm. above the bench top or stand base. These arc referred to as the left and right flasks. Kach flask is provided with a dry ice condenser in the outermost neck, and each condenser is [imlected from the... 

BEOs are most often used for point sources or small line or surface sources. See Chapter 7 for descriptions of sources. BEOs are sometimes used for lines or surfaces when the source is moving along the line or on the surface. This naturally demands the exhaust to move with (or be moved with) the source movements (e.g., during painting or seam welding). They have also been used for side suction from baths and tanks-- and these exhausts are usually called rim exhausts see Rim Exhausts. However, for these sources push-pull systems (Section 10.4.3) are often more efficient. Side hoods can also be used, e.g., when molten metal is poured however, in these cases an enclosed exhaust is more efficient. 

V = centerline velocity, Vii = hood face velocity (Q/A), z = distance ftom hood face along centerline /length of one side... 

The rim exhaust is a source of suction that is placed along one or more sides of the area source. Air is drawn across the surface of the source and contaminated air is drawn into the hood. Specific examples of rim exhaust include open-surface tank exhaust such as electroplating, cleaning, degreasing table exhaust such as mortuary tables and exhaust used during container filling such as barrel filling. 

Rim exhausts are suitable for area sources of contaminant. They are limited in the area over which they can draw with adequate velocity. In practice, the slot hood should be within 0.6 m of the far edge of the source. For an open surface tank this means that a slot hood on one long side is necessary for tanks up to 0.6 m in width hoods on both long sides are necessary for tanks up to 1.2 m in width and rim exhaust is not practical for tanks wider than 1.2 m. For those situations, push-pull ventilation or enclosure type hoods are recommended.- ... 

Rim exhausts are slot hoods located on or around the edge of a source such as an open surface tank. Flanges may be added to decrease the airflow from behind the slot (uncontaminated air) and therefore increase the airflow from in front of the slot (contaminated air). The plenum downstream of the slot, if located above the slot, may act as a flange. Flanges may also be added to the sides of the source (tank) away from the slot hood. These flanges also act to increase the flow of contaminated air into the tank. Tank flanges, however, may interfere with process activities by limiting access to the tank. 

The rim exhaust is placed on the longer side of the tank and the ratio of the width to length of the tank is the tank aspect ratio. Higher aspect ratios require higher hood flow rates per unit area due to the increased distance that the hood must reach. The highest hood flow rates per unit area would be expected for square hoods. Values of C are given in Table 10.5. ... 

Working locations between the contaminant source and the capture openings dramatically reduce the efficiency of the capture system and should therefore be avoided. If the hood is enclosed on three vertical sides the sensitivity to cross-draft is low. 

For large open surface tanks where access for machinery or operators is required above the tank, the options for ktcal ventilation are limited. An over-head canopy would block access, and an exhaust hood placed at the side of the tank is prohibitively expensive for tanks greater than about 0.6 m across. 

Push-pull ventilation systems for open surface tanks consist of two components the push flow is generated by a jet or series of jets that are blown across the surface of the tank towards an exhaust hood along one side of the tank, which pulls and removes the fluid from the jet containing the contaminant. This is shown schematically in Fig. 10.69. 

This section deals mainly with side push-pull ventilation. Center push-pull ventilation is also sometimes used, where two jets of air are blown from a central pipe towards two parallel exhaust hoods at opposite ends of the tank. Much of what vve say about side push-pull systems is equally valid to center push-pull. 

FIGURE 10.93 Design of exhaust with wall jet for a kitchen hood with partly shielded sides and circular grease filter. 

If the hood has side walls the opening to the outside must be large enough to permit work inside the hood and it must also be designed to facilitate flow into the opening and diminish the possibilities for the moving air to transport contaminants to the surroundings. 

The pressure drop for the exhaust opening, the jet supply opening, and for the hood opening if there are side walls, can be calculated using the normal equations for flow inside ducts and into ducts and openings. 

A visual evaluation of ventilation system performance can be performed by injecting smoke into the jet. No quantitative evaluation methods for these systems have been reported, but it should be possible to measure the containment of a hood with side walls (partial enclosure) using one of the containment indices (see Sections 10.2.1 and 10..5). Additional information may be obtained by measuring capture efficiency. 

Two or more plane jets can be placed above and outside the rim (all sides) of a canopy hood and directed downward. Fhe exhaust flow into the hood makes the down-directed jets turn inward and upward when the jet velocity has slowed down enough to be influenced by the exhaust flow. In many cases, the aim is to diminish the general supply airflow rate into the room and sometimes to use the jets as separators. lliis method is quite often used on large kitchen hoods to increase their capture efficiency. If the jet is directed toward the front of the fireplace and just reaches the front before turning inward, a high capture efficiency can be achieved. 

Another variation is to use a thin air jet around a process or an opening to a pt(x ess. For welding or soldering on a table, a circular tube with supply holes in the upper side could be used. The circular tulw is placed around a fixed welding (soldering) place and blow s upward around the welding point into a basic opening hood. 

Push-pull hood A protecting hood around a process with the air supply on one side of the contaminant source and the extract on the other side. 

Digestorium, n. hood, fume cupboard, digooalt a. twofold two-sided. 

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