US3000292A - Fume hood - Google Patents

Description

Sept. 19, 1961 c. A. woJ'AN 3,000,292

FUMEI' HOOD Filed Jan. 25, 1958 2 Sheets-Sheet 1 INVENTOR C1. IFFOEDA VVOJA /v.

ATTO RN EYS.

zm/maiauazzwm P 19, 1961 c. A. WOJAN 3,000,292.

FUMEHOOD Filed Jan. 2a, 1958 2 Sheets-Sheet 2 XNVENTOR cL/FFOfPDA.m/OJA/V.

ATTO R N EYS.

United States Patent 3,000,292 FUME HOOD Clifford A. Wojan, Brooklyn, N. assignor, by mesne assignments, to Norbute Corporation, New York, N.Y., a corporation of Delaware Filed Jan. 23, 1958, Ser. No. 710,783 6 Claims. (Cl. 98-415) This invention relates to fume hoods and particularly to fume hoods having means for adjusting the quantity of air removed from a room in which such a hood is mstalled.

Fume hoods are well known and are employed during the handling of materials which give off fumes, vapors, gases or other substances for the purpose of protecting persons working with such materials, buildings and equipment from such gases and substances. One type of conventional fume hoods has a working chamber, one vertical wall of which is formed primarily by an adjustable glass sash through which the various reactions and operations may be observed While they are in progress and the bottom wall of which is formed by a stone slab or counter on which the hood rests. The glass sash forms the face of the hood and is adjustable in position to permit access to the chamber. An exhaust duct communicates with the chamber through one wall of the chamber, usually the top wall, and the noxious gases and other substances are exhausted from the chamber by means of said duct. These conventional fume hoods usually have inadequate air distribution for exacting chemical analyses. With the sash in the open position and with a typical average velocity through the face opening of 100 feet per minute, the air velocities at the counter level or bottom of the chamber are low and often are insuflicient to properly scour contaminants formed in the lower section of the hood. When the sash is almost closed, air velocities at the counter level are extremely high and this is very ob ectionable when delicate operations are being conducted with-in the hood.

So-called low velocity hoods often having ad ustable bafiies within the chamber and having an auxiliary face opening which is varied in size as the sash is raisedor lowered have been devised for the purpose of overcommg some of the above mentioned difliculties. The term low velocity generally is applied to hoods operating with an average air velocity through the face of approximately 50 feet per minute. Since this type of hood operates on the principle of passing less air quantity through the hood, it is less effective in diluting and scouring fumes formed in the working areas ofthe hoods. In addition, the use of adjustable battles complicates the operation of the hoods and adds to the maintenance problems.

Because the air flowing into the working chambers into the above-mentioned types of hoods is taken from the room in which the hoods are installed, both of the above-mentioned types of hoods remove relatively large quantities of conditioned air from the surrounding room. It is unnecessary that the purging air flowing into the working chamber of the hood have any particular characteristics, and therefore, if the room is heated or airconditioned, it is uneconomical to supply the occuring or purging of air from the room in which the hood is installed.

For example, a building may contain twelve hoods having a recommended face air velocity of 100 feet per minute and the hoods may have six foot long counter tops. In such a case, approximately seventeen thousand cubic feet of air may be flowing through such hoods each minute. If the temperature of the air outside of the building is 95 F. and the relative humidity is 50%, ap-

*, proximately 75 to 85 tons of refrigeration are required to maintain the desired atmospheric conditions within the Patented Sept. 19, 1961 building because of the conditioned air exhausted by the hoods. Similarly, during winter operation, large quantities of heated air are lost through the hoods.

Those skilled in the art have assumed, erroneously that the face air velocity is the measure of the operating safety of a fume hood. 0n the contrary, I have found, by a number of experiments and tests, that specifying hood performance by face air velocity may be useless from the standpoint of safe performance. Tests have indicated that under certain conditions an foot per minute average face air velocity will allow dangerous products to be spilled back into the room whereas hoods constructed in accordance with my invention will prevent such spillage even though the average face air velocity may be only 25 feet per minute or less.

In accordance with the invention, air which may be obtained from outside or from an unconditioned area inside the building in which the hood is installed is supplied to the working chamber of the hood through an intake duct. By means of baflles, the flow patterns of the air are controlled so that the undesirable products are removed from the working chamber without spillage and with complete protection of the worker, buildings and equipment even though the average face air velocity may be less than 25 feet per minute. Such a low face air velocity results in drastic reductions in refrigeration and heating requirements for the building and consequent reductions in plant installation and operating cost.

With the improved fume hood of the invention, the face air velocity may be adjusted from a very low value to the relatively high values employed with prior art types of fume hoods without the use of adjustable battles within the hood chamber. Furthermore, regardless of the face air velocity, the amount of flowing over the working areas of the hood is suflicient to dilute the products within the hood so that the final mixture of air and these products leaving the hood is very close in density to the density of air alone. Since the mixture leaving the hood is similar in density to air under all operating conditions, it is not necessary to include adjustable bafiies which are adjustable for light and heavy gases generated within the hood, and therefore, the construction, operation and maintenance of the hood is simplified.

The improved fume hood of the invention has a further advantage. Because this fume hood uses a lower velocity through the face opening, when the sash is partially closed, the air velocity at the working counter is relatively low as compared to the working counter air velocity obtained with relatively high, face air velocities.

One object of the invention is to provide a fume hood having means for reducing the face air velocity and hence the amount of conditioned air removed from a room in which the hood is installed without reducing the dilution of the products Within the hood and without causing spillage of the products through the face of the hood into the room.

Another object of the invention is to maintain reasonable air velocities across the working counter within the hood when the sash across the face of the hood is partially closed.

A further object of the invention is to provide a fume hood which has the foregoing advantages without requiring the use of adjustable baflies within the hood chamber.

Other objects of the invention will be apparent from the following detailed description of preferred embodiments of the invention, which description should be considered in connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a preferred embodiment of the fume hood of the invention;

FIGS. 2 and 3 are cross-sectional, side elevation views, taken along the line 33 indicated in FIG. 1, of the embodiment shown in FIG. 1 and show respectively the air flow patterns within the hood when the face sash is fully opened and when the face sash is four-fifths closed;

FIGS. 4 and 5 are respectively front elevation and crosssectional, side elevation view of an air baifleforming part of the embodiment shown in the preceding figures; and

FIGS. 6 and 7 are enlarged, fragmentary, front and cross-sectional side views, respectively of the baffle shown in FIGS. 4 and 5, the cross-sectional side view shown in FIG. 7 being taken along the line 77 indicated in FIG. 6.

The preferred embodiment of the fume hood of the invention illustrated in FIGS. 13 comprises a rectangular cabinet, designated generally by the reference numeral 10, which is adapted to be seated upon a counter or floor 11 which forms the bottom wall of the cabinet or enclosure 10. The counter or floor 11 may be made of stone or other material and frequently it forms the top part of a cabinet or base 12. However, the counter or floor 11 may be secured to the cabinet in any conventional manner and, if so secured to the cabinet 10, forms part of the fume hood.

The cabinet 10 comprises a pair of side walls 13 and 14, a top wall 15, a rear wall 16 and a face or front wall 17. The face wall 17 may be formed by an upper stationary portion 17a-made of metal, such as stainless steel, or other material and a movable sash 17b filled with a pane or panel 170. The sash 17b which may be made of metal, suchas stainless steel, or other material is vertically slidable in rails (not shown) held by the side walls of the cabinet 10 so as to permit access to the interior of the cabinet and adjustment of the face opening 18.

All of the stationary walls of the cabinet 10 may be made of metal, such as stainless steel, or other material and if desired, the side Walls 13 and 14 as well as the stationary portion 17a of the face wall may be hollow, i.e. made of two spaced sheets of material as shown in the drawings.

The various walls of the cabinet 10'with the counter 11 define a compartment, designated generally by the reference numeral 19,, which is sub-divided by means of a baffle 20into a working chamber 21 and a plenum chamber 22. The baffle 20 may be made of a corrosion resistant material suchias a hard-pressed board of asbestos and. Portland cement sold by the Johns-Manville Corporation, New York, N.Y., under the trademark Transite or other'material. The materials which give off products are operated onor reacted inthe working chamber 21 and are exhausted from the hood through the plenum chamber 22. The top wall. is provided with an exhaust opening 23, which is adjacent the rear wall 16, and which. opens into the plenum chamber 22. Whenthe fume hood is in. use, the opening 23 is connected by means of a duct (not shown) to an exhaust blower (not shown).

It has been, found that it is not possible to accomplish the. objects of the invention merely by providing an air intake opening which opens into the working chamber because such an opening, by itself, does not provide thedesired air flow through the'working chamber 21. For example, with a relatively high air velocity flowing through the intake opening, there may be undesirably high air velocities. at the top of the counter 11 and undesirable air turbulence within the working chamber 21. In addition, under certain conditions, the incoming air may cause a portion of the dangerous products or noxious gases to flow outwardly through one portion of the face opening 18 even though air may be flowing inwardly into the working chamber 21 through other portions of the face opening 18. It, has been found that in addition to the intake opening, baifle means which. properly dise tributes and directs the incoming air velocity adjacent the intake opening 'must also be provided. It is for these reasons thatthe fume hood ofthe invention includes a- 4. second plenum chamber 25 and associated baffle 24 and the deflectors hereinafter described.

The baffle 24 forms one wall of the second plenum chamber 25, the upper end of the bafiie 24 being connected to the top wall 15and. the lower end of the baflie 24 being connected to the upper portion 17a of the face wall by a substantially imperforate member 26. The top wall 15, the upper portion 17a of the face wall and the side walls 13 and 14 form the remaining Walls of the plenum chamber 25.. An, intake. opening 27 extends through the top wall 15. and opensinto the plenum chamber 25 for the purpose of supplying a gas, such as air, to the plenum chamber 25. When the fume hood is installed, the intake opening 27 is connected bymeans of a duct (not shown) toa blower or air pump-(not shown). In the preferred installation, the air supplied to the plenum chamber 25 is obtained from outside of the building in which the fume hood is installed, but it will be apparent that if desired, the air may be obtained from other sources. Also, it will be apparent from the description of the operation of the fume hood set forth hereinafter that the intake pump may be omitted if only a small reduction of the velocity of the air entering the fume hood through the face opening 18 is desired.

In the embodiment shown'in FIGS. 1-3, the gas, such as air, supplied to the plenum chamber 25 through the intake opening 27 flows in the direction indicated by the arrows 28 shown in FIGS. 2 and 3. The bafiie 24 is disposed at an acute angle with respect to the path of the flow of such air so as to provide the desired air distribution indicated by the arrows within the chamber 21, the sash 17b being shown fully open in FIG. 2 and being shown four-fifths closed in FIG. 3, and preferably, the baflle 24 is disposed at an angle within the range from 20-45 degrees with respect to the path of the air, an angle of approximately 30-32 degrees providing the most satisfactory results. It will be apparent that with the configuration of the fume hood shown in FIGS. l-3, wherein the path of flow of the air through the intake opening 27- is parallel to'the face wall, that the baffle 24 is disposed at an angle of from 2045 degrees with respect to the face wall 17. The baflie 24 is perforate, that is, has a plurality of apertures therethroughto permit and direct the flow of air from the plenum chamber 25 into and across the working chamber 21, the air being directed toward the exhaust apertures 29 and 30- at the top and bottom ends, respectively, of the baffle 20. A plurality of deflectors 31-34 are mounted onthe baifle 24 and extend into the plenum chamber- 25 for the purpose of deflecting the incoming air throughthe apertures in the baffle 24. Although less satisfactory operation is ob tained, the baffles 3134. may be omitted if desired.

Preferably, the counter 11 has, adjacent the face edge 35 thereof, a raised portionof lip 36 which aids in me venting the spillage of products out of the working chamber 21 and into the room in which the fume hood is installed. Also, to purge or clear the top of the counter 11 of gases, the'fume hood preferably is provided with a deflector 37 which is spaced from: the counter 11. so as to provide an air passageway 38. which directs upwardly moving air currents from the room into-the working chamber 21 and across the top of'the counter 11. Both the deflector 37 and the raised portion or lip 36. aid in providing workers safety and improvingthe operationof the fumehood of the invention, but. if desired,. the deflector 37 andthe raised portion orlip- 36 may be omitted. I The baffle 20 is substantially irnperforate' and preferably located rearwardly of the-compartment-19 so as to provide a'relatively large working chamber 21 and a relatively small plenum chamber 22. The top endor portion 39 of the baflie- 20 is disposed vertically intermediate the intake opening 27 andthe exhaust opening 23- and is spaced from the baffle =24I The baflle' 20.ex-

tends from the sidewall 13 to the sidewall l t-and. extends from adjacentthetop-wall 15. to. adjacent the counter 11, the top end 39 of the battle 20 being spaced from the top wall 15 to provide an exhaust aperture 29 and the bottom end 40 of the baflle 20 being spaced from the top of the counter 11 to provide the exhaust aperture 30. However, it will be apparent that the ends 39 and 40 of the baflle 20 may be connected respectively to the top wall 15 and the counter 11, the apertures 29 and 30 being provided in the battle 20 itself, Since the objects of the invention may be obtained without adjusting the baflle 20, it may be a fixed baffie as shown.

The bafile 24 extends from the side wall 13 to the side wall 14 and from one end of the member 26 to the top wall 15. Accordingly, substantially all the air passing from the plenum chamber 25 to the working chamber 21 passes through the apertures in the bafile 24. The preferred form of the baflle 24 is illustrated in greater detail in FIGS. 4-7.

The preferred form of the baflle 24, illustrated in FIGS. 4-7, is made of a corrosion resistant material such as stainless steel, or other material and comprises a pair of relatively thin, perforated plates 41 and 42 which are held together and in substantially parallel relationship by means of a stainless steel spacer rim' 43 to which the plates 41 and 42 are attached. The spacing between the adjacent faces of the plates or sheets 41 and 42 preferably is approximately one-eighth of an inch. In the embodiment shown the plates 41 and 42 may be thirty thousandths of an inch thick or less and when arranged as described will provide the desired air flow into the working chamber 21. However, if it is preferred that a single plate be used, that is, that one of the plates 41 or 42 be omitted, such a single plate should provide hole walls at least one-sixteenth of an inch long in the direction of air flow if the desired air flow is to be obtained.

Both of the plates 41 and 42 have a plurality of holes therethrough, which holes 44 and 45 are distributed throughout substantially the entire faces of the plates 41 and 42. Preferably, the holes 44 and 45 are one-sixteenth of an inch in diameter, but such holes may have a smaller or larger diameter. Also, in the preferred form of the invention, the holes 44 and 45 are spaced oneeighth of an inch on centers. The plates 41 and 42 are disposed with respect to each other so that the holes 44 in the plate 41 are in staggered relation to the holes 45 in the plate 42 as illustrated in FIGS. -7.

The approximate dimensions of one typical embodiment of the fume hood of the invention are as follows:

Compartment 19 27 inches deep, 57 inches high and 38 inches wide.

Aperture 29 One inch high and 38 inches wide.

Aperture 30 3 llches high and 38 inches wi e.

Spacing of lower portion of bafile 20 from the face of the rear wall 16 2 inches. Height of lower portion of battle 2O 44 inches.

Spacing be'tween'top end 39 of mately 45 with respect to the sides of the baffle 24.

Intake opening Approximately 9 inches in diameter.

Exhaust Approximately inches in diameter,

Lip 36 Hei ht 1% inches and depth 1 inches.

Size of aperture 38 between defiector 37 and lip 36 /2 111 11 by 38 inches.

Although a fume hood having the foregoing dimensions will provide the advantages of the invention, and, particularly, the desired air flow in the working chamber 21 without the flow of gases or other products into the room in which the fume hood is installed, it will be apparent to those skilled in the art that the dimensions may be varied within reasonable limits. For example, the heights of the aperture 29 may be reduced to approximately one-half of an inch, the spacing between the top end 39 of the battle 20 and the face of the bathe 24 may be reduced to approximately one-half of an inch, the spacing between the lower portion of the b-aflle 20 and the inner face of the wall 16 may be increased, the depth of the member 26 may be reduced to approximately one and one-half inches and the diameters of the intake and exhaust openings may be increased or decreased depending upon the volume of the air flowing in the ducts connected to such openings, and that such openings may be placed on walls other than the top wall.

With a fume hood constructed and installed as described above, the volume of the air entering the working chamber 21 through the face opening 18 may be the same as or less than the volume of the air passing out of the exhaust opening 23. For example, if the sash 17b is fully opened as shown in FIG. 2, if the volume of the air passing through the exhaust opening 23 is 865 cubic feet per minute and if the opening 27 is closed or air is otherwise prevented from entering the plenum chamber 25 through the opening 27, the average velocity of the air passing through the opening 18 will be approximately 1.00 feet per minute. However, if, under these same conditions except that air is supplied to the plenum chamber 25 through the intake opening 27 at a volume equivalent to 75% of the exhaust volume, then the average velocity of the air passing through the face opening 18 will be approximately 25 feet per minute. Under these latter conditions, none of the dangerous products or noxious gases in the chamber 21 will spill out of the chamber 21 through the face opening 18 and the working chamber 21 will be cleared of the dangerous products and noxious gases just as satisfactorily as it would be if the average air velocity through the face opening 18 were feet per minute. Also, if the opening 27 is connected to a duct which merely provides air at atmospheric pressure and the velocity of the air through the exhaust opening 23 is 865 cubic feet per minute, the average velocity of the air through the face opening 18 will have a value which is smaller than 100 feet per minute by an amount depending upon the size of the opening 27 and other well known factors, such as'duct size, etc. Thus, it is possible, by adjusting the velocity of the air supplied to the plenum chamber 25 through the intake opening 27, to obtain an average air velocity through the face opening 18 which is variable from a small value, e.g. 25% of the velocity as determined from the exhaust air volume, to a velocity equal to the velocity as determined from the volume of the exhaust air. However, it is desirable to maintain an average face air velocity of not less than 25 feet per minute.

It will be apparent from the foregoing that if the sash 17b is lowered as shown in FIG. 3 and if air is supplied to the plenum chamber 25 as described above, then the air velocity through the face opening 18 will be less, and may be substantially less, than it would be if such air were not supplied to the plenum chamber 25.

Having thus described my invention with particular reference to the preferred form thereof and having shown and described certain modifications, it will be obvious to those skilled in the art to which the invention pertains, after understanding my invention, that various changes and other modifications may be made therein without departing from the spirit and scope of my invention, as defined by the claims appended thereto.

What is claimed as new and desired to be secured by Letters Patent is:

1. A fume hood comprising a rectangular cabinet having joined top, bottom, front, rear and side walls defining a compartment therebetween, said front wall being formed at least in part by a vertically slidable sash, said sash forming means for providing an adjustable face opening into said compartment, said top wall having a pair of openings therein, one of said pair of openings being an air exhaust opening and being adapted to be connected to a exhaust duct and an air pump and the other of said pair of openings being an air intake opening and being adapted to be connected to an air supply duct and a source of air at a pressure above atmospheric pressure for directing air into said compartment along a predetermined path, said intake opening being located adjacent said front wall and said exhaust opening being located adjacent said rear wall; a substantially imperforate first baflle extending across said compartment from one said side wall to the other said side wall and from adjacent said bottom wall to adjacent said top wall, the top portion of said bafie being disposed vertically intermediate said intake and exhaust openings and the bottom portion of said baffie being disposed nearer to said rear Wall than to said front wall whereby said compartment is divided into a working chamber intermediate said front wall and said baflle and a first plenum chamber intermediate said batfle and said rear wall, said top and bottom portions of said baflie being spaced respectively from said top and bottom walls to permit the passage of air from said working chamber to said plenum chamber between said portions of said baflle and said top and bottom walls; a second bafile mounted in said working chamber and extending across, and at an acute angle with respect to, said path of air flow from said intake opening, said second baffle extending from one said side wall to the other said side wall and extending from adjacent said front wall to a portion of said top wall intermediate said intake and said exhaust openings, said second baffle being connected to said front wall by an imperforate member extending from said one side wall to the other, said second bafiie defining a second plenum chamber with said member and said front wall, top and side walls and said second baffle comprising a pair of spaced plates mounted substantially parallel to each other, each of said plates having holes therethrough distributed throughout substantially their entire faces, said plates being mounted with said holes in one said plate in staggered relation to said holes in the other said plate, one of saidtplates having air deflectors mounted thereon and extending into said second plenum chamber and transversely to said path of air flow from said intake openings;

said bottom wall having a raised portion adjacent said front wall and extending substantially from said one side wall to said other side wall for deflecting gases toward said rear wall; and a deflector extendingrfrom externally of said working chamber to internally of 'said working chamber and above and spaced from said bottom wall for deflecting air across said bottom wall toward said rear wall, said last-mentioned deflector extending along substantially the full length of the front edge of said bottom wall.

2. A fume hood comprising a rectangular cabinet having joined top, front, side and rear walls and adapted to be seated on a counter or base to define therewith a compartment, said top Wall having a pair'of openings therein, one of said pair of openings being an air exhaust opening and the other of said pair of openings being an air intake opening, said intake opening being located adjacent said front wall and said exhaust opening being located adjacent said rear wall; a substantially imperforate, first baflle extending across saidcompartment and dividing said compartment into a working chamberand a first plenum chamber, the top portion of said baflle being disposedvertically intermediate said intake and exhaust openings and the bottom portion of said bafiie being disposed intermediate said front and rearwalls, portions of the top and bottom of said baflie being spaced respectively from said top and bottom walls to permit the passage of air from said working chamber to said plenum chamber; a second baffle mounted in said compartment 8 and extending across the path of air which passes through said intake opening, said second baflle comprising a pair of spaced plates mounted substantiallyparallel to each other and each having holes therethrough distributed throughout substantially their entire surfaces, said second baflile extending at an acute angle from said front wall to a portion of said top wall intermediate said intake and said exhaust openings andv defining a second plenum chamber with said front, top and side walls of said compartment, said holes in said plates being disposed to direct air continuously from said second plenum chamber into said working chamber along paths which extend away from said front wall and towards said first baflle, said front wall being formed at least in part by a panel movable along a predetermined path to close and unclose said front wall, said path of said panel being outside of the path of air moving through said intake opening and into said working chamber.

3. A fume hood according to claim 2 wherein said holes through said plates are approximately one-sixteenth of an inch in diameter and are spaced approximately oneeighth of an inch on centers and said plates are mounted with said holes in one said plate in staggered relation to said holes in the other said plate, and one of said plates having air deflectors mounted thereon and extending into said second plenum chamber and transversely to the 'path of air flow from said intake opening.

4. A fume hood comprising a rectangular cabinet having joined top, front, side and rear walls and adapted to be seated on a counter or base to define therewith a compartment, said front .wall including an opening and a panel movable to open and close said opening, baflie means mounted in said compartment between the front and rear walls thereof and having apertures therethrough adjacent the top wall and said counter but otherwise being substantially imper'forate, said baflle means dividing said compartment into a working chamber and a first plenum chamber between which gases may flow through said apertures, one wall of said plenum chamber having an exhaust opening extending therethrough, perforate baflle means mounted in said compartment to define part of said working chamber and extending from said top wall towards said front wall, said baffle, top wall, front wall and side walls cooperating to form a second plenum chamber, said top wall having a gas intake opening extending therethrough and opening into said second plenum chamber, and gas impelling means directing a flow of gas to said gas intake opening for supplying gas continuously through said perforate bafiie means and into said working chamber regardless of the position or direction of movement of said front wall panel, the perforations in said second baflle, means directing gases flowing through said intake opening across said working chamber away from said front wall and towards said apertures adjacent said top wall and counter in said first mentioned baffle means. 7 7

5; A fume hood according to claim 4, wherein when said panel is in fully opened position, said gas impelling means direct a volume of air to said gas intake opening of the order of 75 percent of the volume of gas exhausted through said exhaust opening.

6. A fume hood according to claim 4, wherein said perforate bafiie means is disposed in said compartment at an angle of between 20 and 45 degrees to the plane of said front wall.

References Cited in the file of this patent UNITED STATES PATENTS Morrow Feb. 3, 1953 2,649,727 Snow et a1 Aug. 25, 1953 2,702,505 Nelson Feb. 22, 1955 2,819,666 McNeil et a1. Jan. 14 1958 7 OTHER REFERENCES LaboratoryFurniture Co. Catalogue No. 56H, Mineola, N.Y., see pages 16, 19, 28, 31; received July 10, :19561.

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