US3747505A

US3747505A - Air flow system for fume hood

Info

Publication number: US3747505A
Application number: US00227510A
Authority: US
Inventors: M Turko
Original assignee: American Hospital Supply Corp
Current assignee: HAMILTON INDUSTRIES Inc
Priority date: 1972-02-18
Filing date: 1972-02-18
Publication date: 1973-07-24
Anticipated expiration: 1990-07-24

Abstract

A balanced air fume hood is provided with an air flow system for inwardly directing high velocity auxiliary air over the top of the work surface and/or along the sides of the hood. An elongated air flow conduit is secured below the foil of the fume hood adjacent the front of the work surface, and an elongated tube extends from each end of the conduit to the auxiliary air chamber which supplies auxiliary air to the work enclosure. The ends of the tubes are provided with funnel-shaped air collectors which are positioned in the path of the incoming auxiliary air, and high velocity auxiliary air flows through the tubes to the conduit. The conduit is provided with a plurality of openings for permitting auxiliary air to flow between the foil and the work surface and over the top of the work surface. The vertically extending portions of the tube may be provided with openings for directing high velocity auxiliary air inwardly toward the work enclosure to provide a positive inwardly sweeping curtain of air along the sides of the hood.

Description

Primary Examiner-Meyer Perlin Assistant Examiner-Ronald C. Capossela Attorney Horace Dawson, John W. Chestnut et a1.

United States Patent 1 1111 3,747,505 Turko July 24, 1973 AIR FLOW SYSTEM FOR FUME HOOD [57] ABSTRACT [75 I Inventor: Michael Turko, Manitowoc, Wis, A balanced air fume hood is provided with an air flow system for inwardly directing high velocity auxiliary air [73] Asslgnee. American Hospital Supply Corporaover the top of the work surface and/or along the sides Evanston* of the hood. An elongated air flow conduit is secured 22 Filed; 1 1972 below the foil of the fume hood adjacent the front of the work surface, and an elongated tube extends from [21] Appl' 227,510 each end of the conduit to the auxiliary air chamber Related Application Data whch supapliesbauxiliary air tic (the 1 10214 encllozuredThe en s o t e tu es are provl e wlt unne-s ape air [63] m part of collectors which are positioned in the path of the incoming auxiliary air, and high velocity auxiliary air 52 us. Cl. 981115 LH through the tubes the eehduh- The eehdhh is 51 Int. Cl F23j 11/00 Previded with phhehy Pehihgs fer Permitting 58 Field of Search 98/36 115 LH' auxiliary eh he flew between fell and the work 62/256 face and over the top of the work surface. The vertically extending portions of the tube may be provided [56] References Cited with openings for directing high velocity auxiliary air inwardly toward the work enclosure to provide a posi- 3 408 914 :TATES PATENTS 98H 15 LH tive inwardly sweeping curtain of air along the sides of ayern h d 3,111,077 11/1963 Cortright.... 98/115 LB e 00 3,218,953 ll/l965 Grow et al.. 98/115 LH 3,237,548 3/1966 Bayern 98/115 LH 13 Claims, 19 Drawing Figures 19 2 1 I b "-1 i w 11ml, n Jihmliiim 3 W 0 9 n 59 1 1 s 1! "i 1 PAIENIEDJuLwma SHEU 2 0f 4 a. innin QOI PATENTED JUL 2 4 I973 MET 3 BF 4 I I 1 Q mm I FIG. I2

. PAIENIED 3.747. 505

SIIEH h [IF 4 FIG. I4 FIG. I5

AIR FLOW SYSTEM FOR FUME HOOD RELATED APPLICATIONS This applicaton is a continuation-in-part of the copending application entitled Fume Hood", Ser. No. 172,746, filed Aug. 18, 1971.

BACKGROUND This invention relates to fume hoods, and, more particularly, to balanced air fume hoods.

Fume hoods are commonly used in the laboratory for providing a ventilated work area for laboratory activities involving hazardous materials, generated fumes, aerosols, gases, and particulate matter. The fume hood protects laboratory personnel and equipment by confining, containing and exhausting these materials.

Fume hood systems conventionally include an exhaust blower for removing air from the fume hood, and when fume hoods are installed in air conditioned laboratories, they withdraw cooled or conditioned air from the laboratory. Since the conditioned air has been supplied to the laboratory at substantial expense, it is desirable to reduce the amount of this costly air which is withdrawn from the laboratory.

Balanced air fume hoods are designed to reduce the amount of room air which is consumed by supplying auxiliary air to the fume hood. The auxiliary air is introduced into the hood, and it is important that some of the auxiliary air and any room air which is drawn into the fume hood from the laboratory sweep across the entire work surface to prevent the escape of fumes from the hood. The velocity of the air which sweeps across the work surface is generally provided by the blowing action of the auxiliary air blower and the sucking action of the exhaust blower. However, the auxiliary air blower is positioned at some distance above the work surface, and the auxiliary air may pass through a diffuser as it passes from the auxiliary air chamber. The velocity of the auxiliary air is therefore substantially re duced by the time it reaches the work surface, and the exhaust blower often does not provide sufficient suction to create a suitable sweeping action over the work surface. Even if means are provided for routing auxiliary air from above the diffuser to the work surface, this air might not have sufficient velocity to provide effective sweeping.

SUMMARY The invention provides means for supplying high velocity auxiliary air to the space between the foil and the work surface at the front of the work surface and for directing this auxiliary air to flow over the work surface. The auxiliary air is directed over the work surface by an elongated air flow channel which is secured below the foil, and auxiliary air is supplied to the ends of the channel by a pair of tubes. One end of each tube is connected to the channel and the other end is attached to an air-collecting funnel positioned in the path of the incoming auxiliary air which is supplied by the auxiliary air blower. The tubes can be hidden by positioning them between spaced-apart panels which form the side walls of the fume hood, and the auxiliary air which is collected by the tubes flows into the air flow conduit and through openings provided therealong and over the work surface. The air flowing through the air flow conduit is sufficient to provide a high velocity air flow across the work surface. The intermediate portions of the tubes which extend along the sides of the hood may be provided with openings for permitting high velocity air to flow into the work enclosure along the sides thereof. The tubes may be positioned outwardly of the sash so that a positive curtain of air sweeps into the hood when the sash is partially or fully raised. The inward sweeping of high velocity air over both the work surface and the sides of the hood substantially eliminates the possibility that counterflows the air within the hood could carry fumes out of the hood and into the laboratory. Introduction of high velocity air at the work surface and along the sides of the hood also reduces the danger of common fluctuations of electrical power which might cause the auxiliary air blower to slow down to a point that auxiliary air flowing through the diffuser would not have sufficient velocity to provide sufficient sweeping of the work surface and hood sides.

DESCRIPTION OF THE DRAWING The invention will be explained in conjunction with the illustrative embodiment shown in the accompanying drawing, in which FIG. 1 is a schematic sectional view of a balanced air fume hood equipped with the invention illustrating the air flow when the sash of the hood is opened;

FIG. 2 is a schematic view similar to FIG. 1 illustrating the air flow when the sash is closed;

FIG. 3 is a schematic front elevational view of the fume hood illustrating the air flow;

FIG. 4 is an enlarged fragmentary view, partially broken away, of the bottom portion of FIG. 3;

FIG. 5 is a fragmentary sectional view taken along the line 5-5 of FIG. 4;

FIG. 6 is a sectional view, partially broken taken along the line 6-6 of FIG. 5;

FIG. 7 is a sectional view, partially broken taken along the line 7-7 of FIG. 5;

FIG. 8 is a sectional view taken along the line 8-8 of FIG. 7;

FIG. 9 is a fragmentary sectional view taken along the line 9-9 of FIG. 3;

FIG. 10 is a view similar to FIG. 3 of a modified hood equipped with a modified air flow system which directs auxiliary air into the hood along the sides thereof;

FIG. 11 is an enlarged fragmentary sectional view taken along the line 11-11 of FIG. 10;

FIG. 12 is a fragmentary view taken along the line l2--12 of FIG. 11; and

FIGS. 13-19 illustrate another modified hood which is provided with shutter means for opening and closing the auxiliary air discharge openings along the sides of the hood. 1

DESCRIPTION OF SPECIFIC EMBODIMENT Referring to FIGS. l-3, the numeral 15 designates generally a balanced air fume hood having a frame 16 which includes a base 17, a countertop 18 which pro vides a working surface, and a superstructure 19 mounted on the countertop.

The superstructure 19 includes spaced-apart

side walls

20 and 21, rear wall or panel 22, and top wall or panel 23'. The walls 20-23 are generally orthogonally related and, together with the countertop or bottom wall 18 define a work enclosure .25. An auxiliary air chamber designated generally by the numeral 24 extends between the

side walls

20 and 21 and terminates away,

away,

above the countertop 18 to provide an access opening 26 to the work enclosure, and the opening can be closed by a vertically slidable sash 27. The sash is shown in its raised position in FIGS. 1 and 3, and in its lowered position in FIG. 2. The sash conventionally includes a glass window to permit observation of materials within the work enclosure when the sash is closed.

An air intake tube 30 extends upwardly from the top panel 23 above an opening in the panel and is connected to a conventional auxiliary air blower (not shown). The auxiliary air blower supplies auxiliary air to the air chamber 24 and forces the auxiliary air through an air diffuser 31 which extends across the air chamber for the entire length thereof and through a directional air grille 32 which directs the auxiliary air outwardly and downwardly. An air dividing plate 33 extends upwardly from the directional air grille for directing a portion of the downflowing auxiliary air to flow between the dividing plate and the sash when the sash is in the raised position shown in FIG. 1. A more detailed description of the auxiliary air chamber is given in the co-pending application entitled Fume Hood, Ser. No. 172,746, filed Aug. 18, 1971, to which reference may be had for details.

An exhaust opening 35 is provided through the rear portion of the top wall, and an exhaust collar 36 is secured to the top wall above the opening and is adapted to be connected to a conventional exhaust air blower (not shown).

A baffle assembly 37 is mounted within the work enclosure adjacent the rear wall for providing desired directional flow through the work enclosure under the influence of the exhaust blower. The baffle assembly extends between the two side walls and includes angularly related

upper baffle plates

38 and 39 and a lower baffle plate 40. The baffle assembly is also described in greater detail in the aforementioned co-pending application.

A foil or sill 42 extends between the side walls at the front of the working enclosure and, referring to FIG. 5, includes a front vertically extending portion 43, an upwardly and rearwardly'incined intermediate portion 44, and a generally horizontally extending rear portion 45. The foil is supported above the countertop 18 by four generally Z-shaped support angles 46 which are secured to the horizontal portion 45, as by soldering or welding, and the foil is clamped to the counter-top by U-shaped brackets 46a which carry clamping bolts 47.

The horizontal portion of the foil is spaced above the top or working surface of the countertop 18 to provide an air flow passage 48 therebetween, and an elongated generally U-shaped conduit or channel 49 is secured to the foil in alignment with the air flow passage 48. The channel includes a bottom wall 50 and a pair of upwardly extending

side walls

51 and 52 which terminate in outwardly extending attaching

flanges

53 and 54, respectively, which are secured to the lower surface of the horizontally extending portion 45 of the foil, as by soldering or welding. The channel 49 extends generally perpendicularly to the side walls for substantially the entire length of the horizontal portion 45 of the foil, and a transversely extending end plate 55 is secured at each end of the channel. Each end plate 55 is provided with an oval opening 56, and each end plate may advantageously be provided as a longitudinally extending extension of the bottom wall 50 which is bent upwardly 90 to extend the

side walls

51 and 52. The side edges of the end plates may be sealed by soldering or the like.

A relatively short connecting tube 57 is connected to each of the end plates 55, and each connecting tube includes an oval end 57a which has a shape correspond.- ing to the oval'opening 56 in the end plate and which is soldered or otherwise connected to the end plate and a round end 57b. An air tube 58 is connected to the round end of the connecting tube 57 on the right end of the channel 49, and an air tube 59 is connected to the connecting tube 57 on the left end. As will be explained more fully hereinafter, the

tubes

58 and 59 conduct auxiliary air from the auxiliary air chamber to the channel 49, and the side wall 51 of the channel is provided with a plurality of longitudinally spaced openings 60 which are aligned with the air passage 48 between the foil and the countertop and which permit auxiliary air to flow through this air passage to sweep the working surface of the countertop.

Referring now to FIG. 3, a pair of air-collecting funnels 61 and 62 are mounted within the auxiliary air chamber in the path of the incoming auxiliary air which flows through the air intake 30. The upper ends of the funnels extend upwardly into the air intake and are supported by bracket 62a which is secured to the air intake, as by welding. One end of the air tube 58 is connected to the lower narrow end of the funnel 61, and one end of the air tube 59 is connected to the lower end of the funnel 62. As can be seen best in FIG. 9, the left side wall 20 is provided by a pair of spaced-apart inner and

outer panels

63 and 64, respectively which are joined by an angularly extending front panel 65. Similarly, right side wall 21 is formed by spaced-apart inner and

outer panels

66 and 67 and angularly extending panel 68. The air tube 58 extends from the funnel 61 through the auxiliary air chamber toward the right side wall 21 and passes through suitable openingsformed in the side wall of the auxiliary air chamber. The air tube 58 then extends downwardly in the space between the

panels

66 and 67 and passes below panel 66 to the connecting tube 57. Similarly, the air tube 59 extends laterally to the left within the auxiliary air chamber from the funnel 62 through the side wall of the auxiliary air chamber and then downwardly in the space between the

panels

63 and 64. The tube then extends below the panel 63 to the connecting tube 57 on the left end of the channel 49. The

tubes

58 and 59 may advantageously be formed from flexible rubber hose or the like, and the ends thereof can be pushed over the ends of the connecting tubes 57 and secured by conventional hose clips.

The operation of the fume hood is illustrated sche-- matically in FIGS. 1-3, FIGS. 1 and 3 illustrating the operation of the hood when the sash 27 is raised, as when work is being performed on materials within the work enclosure. Auxiliary air is supplied through the air intake tube 30 by the auxiliary air blower, and a portion of the auxiliary air is collected by the wide upper ends of the

funnels

61 and 62. The remainder of the auxiliary air flows into the auxiliary air chamber and through the air diffuser 31. As explained in the aforementioned application, a portion of the auxiliary air passing the diffuser 31 flows between the air dividing plate 33 and the sash 27 directly into the work enclosure 25, this portion of the auxiliary air being indicated by the arrows 70. The remainder of the auxiliary air which passes the air diffuser flows through the directional air grille 32 which guides it forwardly and downwardly as indicated by the arrows 71. A portion of this auxiliary air flows into the laboratory and combines with room air indicated by the arrows 72. As the auxiliary air continues to flow downwardly it is drawn inwardly by the exhaust blower through the lower portion of the work opening and sweeps across the top of the foil 42. and the work surface. Room air is also drawn into the work enclosure with this auxiliary air to held satisfy the exhaust requirements of the blower. Additional room air indicated by the arrows 73 may be drawn into the work enclosure through the air passage 48 between the foil and the countertop.

The auxiliary air which is collected by the intake funnels 61 and 62 is indicated by the double-headed arrows 74. This portion of the auxiliary air flows through the

air tubes

58 and 59, through the channel 49, through the openings 60 in the side wall thereof, and through the air passage 48 between the foil and the countertop to sweep across the top of the work surface. The auxiliary air which is directed over the work surface by the channel 49 has sufficient velocity to provide proper sweeping action.

Air within the work enclosure is drawn around the baffle plates and exhausted through the exhaust collar 36 by the exhaust air blower.

FIG. 2 illustrates the air flow when the sash 27 is closed. Auxiliary air 76 flows through the air diffuser 31 directly into the work enclosure above the air dividing plate 33. A portion of the incoming auxiliary air flowing through the air intake 30 is again collected by the funnels 611 and 62 and flows through the

air tubes

58 and 59, through the channel 49 and air passage 48, and over the working surface, this auxiliary air being indicated by the double-headed arrows 77. Since the auxiliary air is insufficient to satisfy all of the exhaust requirements, substantially all of the auxiliary air flows into the work enclosure, and the remaining air necessary to satisfy the exhaust requirement flows from the room into the work enclosure through the grille 32 and through the space between the dividing plate and the sash, as illustrated by the arrows 78, and through air passage 48 between the foil and the countertop, as indicated by the arrows 79.

Although I have shown the conduit 49 in the form of a channel with spaced circular openings in one side, it will be understood that other types of air flow conduits or tubes could be used. Further, other shapes of openings for permitting the air to flow from the conduit could be provided, such as one or more elongated slots or the like.

A modified air flow system is illustrated in FIG. 10. The fume hood 80 is identical to the fume hood with the exception of the construction of the

side walls

81 and 82, as will be explained more fully hereinafter. As previously explained with respect to the fume hood 15, high velocity auxiliary air is collected by air-collecting funnels 83 and 84 positioned in the air intake 85, and this high velocity auxiliary air is directed by

tubes

86 and 87 downwardly along the sides of the fume hood to the air flow channel 88 which is positioned below the foil or sill of the fume hood for directing fast-moving auxiliary air across the work surface. However, the vertically extending portions of the

tubes

86 and 87 are provided with openings to direct fast-moving auxiliary air into the work enclosure along the sides of the fume hood as indicated by the double-headed

arrows

89 and 90.

The construction of the left side: wall 81 for permitting inward flow of air along the side of the hood is shown in FIG. ll. The side wall includes a pair of spaced-apart inner and

outer panels

91 and 92 which are connected by

panels

93, 94, and 95. A sash guide 96 is secured to the panel for slidably supporting the sash 97 which is indicated in phantom.

The tube 87 for conducting the auxilary air is secured to the panel 95 and is provided with vertically spaced openings 98 (FIG. 12) for directing auxiliary air toward the work enclosure of the fume hood thorugh the space between the inner end 93a of the panel 93 and the outer end of the side panel 91. In the embodiment illus' trated, the vertically extending portion 87a (FIG. 10) of the air tube is provided by a metal pipe, and the pipe is secured to the panel 95 by welding. The remainder of the tube 87 comprises a rubber hose portion 87b which connects the upper end of pipe 87a to the funnel 88 and a hose portion 87c which connects the lower end of the pipe to the channel 88..

The side wall 82 and air tube 86 are constructed in the same manner as the side wall 81 and tube 87.

When the sash 97 is in the open position, the bottom thereof will be positioned adjacent or above the auxiliary air grille 99, and a portion of the auxiliary air which flows through

tubes

86 and 87 flows through the openings 98 into the work enclosure along both sides of the hood. The remainder of the auxiliary air flowing through the tubes flows through the channel 88 and sweeps across the work surface. A positive curtain of air therefore sweeps inwardly along both sides of the hood, and auxiliary air is therefore directed into the work enclosure around the entire periphery thereof.

I have found that when auxiliary air is not introduced into the work enclosure along the sides, introduction of auxiliary air at the top of the work enclosure through the air grille 99 may create counterflows of air within the work enclosure which could carry fumes out of the hood and into the laboratory. These counterflows of air are often particularly noticeable near the side walls of the hood and, if high velocity air is not directed across the working surface, also near the working surface. By introducing high velocity auxiliary .air along the sides of the hood, the possibility of fumes escaping into the laboratory along the walls is substantially eliminated.

In the embodiment illustrated in FIGS. 10-12, the vertical portions of the air tubes are positioned outwardly of the sash guide 96. When the sash is closed and occupies the position illustrated in phantom, the air flowing through the tube openings 98 will be deflected by the sash into the laboratory. Introducing this auxiliary air into the laboratory may be unobjectionable since the auxiliary air is clean air and since the air discharge through the openings 98 is only a fraction of the total volume of auxiliary make-up air which is sup plied by the auxiliary air blower. The vertically spaced openings 98 extend all the way to the work surface, and auxiliary air begins to sweep into the fume hood along the sides as the sash is raised.

A further modification is illustrated in FIGS. 13-19 and includes means for closing the discharge openings in the vertical portions of the air tubes as the sash is closed. FIG. 13 is a view similar to FIG. 11 of one of the side walls of the fume hood which is slightly moditied to accommodate the closing means for the discharge openings. The side wall 101 includes a pair of spaced-apart inner and

outer panels

102 and 103 which are connected by

panels

104, 105, and 106. A brace 107 extends between the

panels

105 and 104, and the inner end 104a of the panel 104 terminates outwardly of the outer end of the side panel 103. A vertically extending pipe 108 similar to pipe 87 is secured to the panel 105 by sheet metal screws 109, and a sash guide 110 is secured to the panel 106 by screws 111.

An elongated shutter 112 is rotatably carried by the pipe 108 and extends longitudinally along the pipe over that portion which is provided with the discharge openings 113 (FIGS. 14 and 15). The shutter has a generally C-shaped or partially circular transverse cross section and extends around the tube for more than one-half the circumference of the tube so that the shutter is retained on the tube and is provided with an elongated slot 114 which extends from the uppermost discharge opening to the lowermost discharge opening. As can be seen in FIGS. 14 and 15, the slot extends slightly spirally counterclockwise relative to the longitudinal axis of the pipe and shutter as it proceeds from the bottom portion of the shutter to the top portion. An actuator bracket 115 having a flat end portion 116 which is slidably received in the slot 114 is mounted for vertical movement with the sash 117. The bracket 115 is secured to the frame of the sash by bracket 118 and screw 119.

As the shutter actuator 115 moves vertically within the slot 114, the shutter is caused to rotate relative to the pipe 108 to close or expose the discharge openings 1 13. The position of the shutter when the sash is fully closed is illustrated in FIG. 14, and all of the discharge openings 113 are covered by the solid portion of the shutter. As the sash is raised the actuator 115 slides upwardly within the slot 114 and causes the shutter to rotate counterclockwise as viewed in FIGS. 16-19. As the shutter and the slot 114 rotate, the discharge openings gradually become exposed proceeding from bottom to top.

The lowermost discharge opening 113 is exposed as soon as the sash is raised from its fully closed position so that auxiliary air is directed into the work enclosure along the sides immediately. As the upward movement of the sash continues, more discharge openings become exposed to increase the inward flow of auxiliary air along the sides of the hood. At any intermediate position of the sash between its fully closed and fully opened positions, only those discharge openings below the bottom of the sash will be exposed, and the discharge openings above the bottom of the sash will remain covered by the shutter so that auxiliary air will not be deflected by the sash into the room. As the sash is lowered from its fully raised position, the shutter rotates clockwise to consecutively close the discharge openings from top to bottom. Each opening becomes covered by the shutter as the bottom of the sash passes, thereby providing an inwardly directed curtain of air at the hood sides which has a height approximately the same as the height of the access opening at any position of the sash. The shutter occupies the position illustrated in FIG. 15 when the sash reaches the fully opened position, and in this position all of the discharge openings are exposed to permit fast-moving auxiliary air to flow into the work enclosure along the sides of the hood.

The other side of the hood is similarly constructed, and the upper and lower ends of the pipes 108 can be connected, respectively, to an air-collecting funnel and an air flow channel as described with respect to the tubes 87 of FIG. 10.

While in the foregoing specification, a detailed description of a specific embodiment of the invention was set forth for the purpose of illustration, it is to be understood that many of the details hereingiven may be varied considerably by those skilled in the art without departing from the spirit and scope of the invention.

1 claim: 7

1. In a fume hood having a frame providing a work enclosure defined by a back wall, a pair of side walls, and a work surface, the work enclosure having an access opening at the front of the fume hood, auxiliary air supply means on the frame for supplying auxiliary air to the work enclosure, air flow conduit means mounted on the frame adjacent the front of the work surface, the air flow conduit means being provided with an opening for permitting auxiliary air to flow from the air flow conduit means over the work surface, tube means on the frame extending between the auxiliary air supply means and the air flow conduit means for supplying auxiliary air to the air flow conduit means, and air collecting means connected to the tube means and positioned in the path of auxiliary air supplied by the auxiliary air supply means.

2. The structure of claim 1 in which each side wall includes a pair of spaced apart inner and outer side panels and connecting panel means extending between the inner and outer panels, the tube means being secured to the connecting panel means outwardly of the inner panel.

3. The structure of claim 1 in which the air collecting means comprises a funnelf 4. The structure of claim 3 in which at least one of the side walls includes spaced-apart inner and outer panels and an intermediate portion of the tube means extends between the spaced-apart panels.

5. The structure of claim 3 in which the auxiliary air supply means includes an auxiliary air chamber above the work enclosure, the tube means comprising a pair of tubes, a portion of each tube extending along one of the sides of the work enclosure and being provided with an opening for directing auxiliary air into the work enclosure.

6. The structure of claim 5 in which each of the side walls includes a front panel positioned outwardly of the tube associated with the side wall.

7. In a fume hood having a frame providing a work enclosure defined by a back wall, a pair of side walls, and a work surface, the work enclosure having an access opening at the front of the fume hood, tube means on the frame extending along each side wall, means for supplying air to the tube means, each of the tube means being provided with an opening for directing air supplied to the tube into the work enclosure along one side thereof, sash means slidably mounted between the side walls for opening and closing the access opening, and shutter means operatively connected to the sash means for opening and closing the opening in the tube means as the sash means opens and closes the access opening.

8. The structure of claim 7 in which the means for supplying air to the tube means includes auxiliary air supply means on the frame for supplying auxiliary air to the work enclosure, the tube means extending from the auxiliary air supply means.

9. The structure of claim 7 in which the means for supplying air to the tube means includes an auxiliary air chamber on the frame and means for supplying auxiliary air to the auxiliary air chamber, each of the tube means including an elongated tube having one end positioned in the auxiliary air chamber.

10. The structure of claim 9 including a funnel on said one end of each of the tubes positioned in the path of auxiliary air supplied by the auxiliary air supply means to the auxiliary air chamber.

11. The structure of claim 7 in which each of the tube means includes a generally vertically extending tube adjacent one of the side walls, each tube being provided with a plurality of vertically spaced openings for directing air supplied to the tube into the work enclosure along one side thereof, and means connecting the shutter means and the sash means for moving the shutter means as the sash means moves whereby the tube openings above the bottom of the sash means are closed and the tube openings below the bottom of the sash means are exposed.

12. The structure of claim 7 in which each of the shutter means includes an elongated generally circular shutter rotatably carried by one of the tubes, each shutter being provided with a generally longitudinally extending slot, the slot being circumferentially offset from the openings when the sash is closed whereby the openings are closed by the shutter and the slot being aligned with the openings when the sash is open whereby the openings are exposed.

13. The structure of claim 12 in which the slot is slightly spirally arranged relative to the longitudinal axis of the tube, the connecting means being secured to the sash for movement therewith and being slidably received by the slot whereby vertical movement of the sash rotates the shutters relative to the tubes.

Claims

3. The structure of claim 1 in which the air collecting means comprises a funnel.

4. The structure of claim 3 in which at least one of the side walls includes spaced-apart inner and outer panels and an intermediate portion of the tube means extends between the spaced-apart panels.