JP2001518174A - Ventilation hood with bistable vortex - Google Patents

Abstract

(57) Summary The flow of air through the ventilation hood (78) is optimized by generating a bistable vortex in the vortex chamber of the ventilation hood, regardless of the movement of the sash (18). The bistable ventilation hood optimizes the capture surface velocity to minimize the backflow of the fume-bearing air through the hood sash opening. This bistable vortex ventilation hood uses a vortex pressure control system to adjust the position of the baffle top, middle and bottom slot openings (32, 34, 36) in the hood. The baffle separates the bistable vortex from the surface when the sash is fully open and creates a clearing effect near the work surface when the sash is closed. An airfoil (76) is located in the fume hood chamber and the airfoil has a multi-entry pattern, one of which rotates the vortex upwards away from the work surface of the hood. Others form streams that wash the work surface of the hood. The inner part of the vortex chamber uses rotating vanes (65) to reduce dynamic losses and increase the stability of the bistable vortex.

Description

The present invention claims priority to provisional application No. 60 / 035,997, filed Jan. 22, 1997, which describes a fume hood having a bistable vortex. is there. The present invention relates to a ventilation enclosure for confining vapors and preventing their diffusion, such enclosures being commonly known as ventilation hoods, and more particularly to internal ventilation hoods. The present invention relates to a ventilation hood that can be opened to allow access to the hood, and the opening operation may inadvertently allow fumes to escape to the outside of the hood. The first fume hood was a fireplace used by alchemists. These early fume hoods had very high chimneys. The suction effect of the chimney height, the thermal gradient generated by the fire, and the external wind conditions formed considerable ventilation. To increase ventilation, early venting engineers (mid 1800's) had added gas-fired rings in the chimney to achieve even greater thermal lift. During the Industrial Revolution, Gas Ring gave way to mechanical blowers. It was during this time that laboratories became better defined. Changes have occurred, such as adding a front sash instead of a hinged door and adding an aerofoil under the sash window. In the late 1940's, rear baffle systems and streamlined inlets were introduced into all fume hoods. The ventilation hood having the above-described configuration is shown in FIG. 1 and is described as “prior art”. Dimensionally, these conventional fume hoods can be carried through ordinary doors, and are 30 inches wide and 36 inches high with the height restrictions due to the 9-10 foot ceiling. It was dimensioned so that it could be placed on top. Dimensionally, hoods manufactured today are virtually exactly the same size as those manufactured 50 years ago. Ventilation hood performance is always based on a smoke visualization test, in which case a flaring is placed on the working surface inside the hood and no smoke can be seen exiting the sash surface As long as the hood is considered to work properly. The recommended surface speed (the speed of the air flowing into the hood through the sash opening or "surface") is between 100 feet / minute (FPM) and 150 FPM. For many years, users of fume hoods have felt that the higher the face velocity, the better the hood confinement. High surface velocities have begun to become less popular in the late 1960's with the introduction of air bypass hoods (shown schematically in FIG. 2), which introduce air above the sash when the sash is closed. Met. Then, in the mid-1980s, performance tracer gas analysis tests were developed to measure the performance of the fume hood and its ability to protect workers. This test allowed, for the first time, to quantify the actual spill rate in ppm, thereby showing how the hood performs under different operating conditions. One of the main reasons this tracer gas performance test was made is that air conditioning to save energy in an effort to reduce high cost heating, ventilation and cooling costs increased dramatically in the 1980's. The ventilation hood exhaust volume is reduced together with the opening operation of the sash window for reducing the input air volume. Exhaust volume was reduced either by an open loop that synchronizes the exhaust valve with the opening and closing operation of the sash, or by using a closed loop system that measures differential pressure and controls a servo exhaust valve. All of these approaches are based on the generally accepted notion that constant surface velocity provides adequate confinement when the sash window is operated. This assumption is not always correct. This is because it does not address what is the optimum surface speed and therefore the optimum airflow through the hood to prevent backflow. One of the applicants has developed and improved a vortex control system for a fume hood as shown in FIG. 3, which was published on December 16, 1997 by Robert H. et al. Summary of U.S. Patent No. 5,697,838 issued to Morris, which is incorporated herein by reference. Robert H. Tracer gas studies conducted by Morris have been able to conserve energy by reducing exhaust air flow volume, but by using variable volume fixed surface velocity control technology, the ventilation hood was inherently safer. It does not mean that it will be taken. These tracer gas tests show that the fume hood surface velocity is affected by the internal vortex of the fume hood and operating variables such as room air distribution, supply air temperature, scatter in the fume hood, and the location of the fume hood in the laboratory. It is shown that it is to receive. The vortex control system of US Pat. No. 5,697,838 dynamically controls airflow to provide a stable vortex in the hood vortex chamber that maximizes backflow of fume-bearing air through the hood door. Control optimizes airflow through the fume hood. A sensitive pressure sensor located on the side wall of the vortex chamber detects subtle variations in vortex pressure indicative of turbulence and sends a signal to the analog controller via a converter, the analog controller having a proportional interval. And an adaptive gain algorithm to form an output signal to an actuator, which adjusts a damper in the hood system to change the flow of air into the vortex chamber. The present invention is based on the discovery made while operating a slot in the baffle of a fume hood that the vortex in the fume hood chamber is very easily affected by other environmental changes. The flow conditions in the upper part of the vortex chamber are shown in FIG. 4, which is a schematic view of the chamber area of the hood. It is shown that vortex bubbles occur on the surface in the upper region of the vortex chamber. The vortex is controlled by a laminar flow control jet along the rear baffle surface in the vortex chamber area. This laminar jet produces a sustained pressure differential and entrains some of the air surrounding it. Entrained air on the wall side is trapped against the wall, while air from the face velocity displaces entrained air from the opposite side. The result is atmospheric pressure on the side remote from the wall and lower pressure between the jet and the wall. This pressure difference deforms the jet and forms a monostable vortex bubble in the lower pressure region. FIG. 5 is a schematic view of a ventilation hood showing this monostable vortex. Thus, vortices in conventional fume hoods appear to be monostable. As long as the controlling air jet stays laminar, the vortex remains stationary above the wall. However, if the laminar jet jet is disturbed due to environmental conditions such as pressure fluctuations in the room, cross-ventilation, fume hood load, or thermal changes in the supply air, the vortex bubbles will be filled. And the pressure gradient is lost. Monostable vortices become disordered and destroyed. The loss of a vortex bubble is a precursor to the failure of a fume hood containment. Until the jet becomes laminar again, the monostable vortex cannot recover itself. The present invention provides a ventilation hood with a bistable vortex hood. As used herein, the term "bistable vortex" is used to mean a vortex in a hood that is stable whether the sash is open or closed. Bistable vortices are provided by baffle arrays. Bistable vortex bubbles are generated on the same wall surface as monostable vortex bubbles, but are characterized by an even more symmetrical shape and require opposing jet jets to disturb and disrupt the vortex I do. The present invention has as its main feature the use of bistable vortex bubbles in a fume hood. Another feature of the present invention is to provide an improved ventilation hood with a vortex chamber having a hydraulic radius ratio related to the hydraulic radius ratio of the sash window of the ventilation hood. A further feature of the invention is a ventilator comprising a baffle that is automatically positionable, a vortex chamber rotating vane, and a multi-three-entry aerofoil that cooperates in forming a bistable vortex in the fume hood. It is to provide food. The invention will become more apparent from the following detailed description when considered in conjunction with the following description, and several of the foregoing, and when considered in conjunction with the drawings, which are briefly described below. . FIG. 1 is a schematic view showing a standard conventional ventilation hood in a front view. FIG. 2 is a view similar to FIG. 1 of a conventional bypass ventilation hood. FIG. 3 is a view similar to FIG. 1 of a fume hood with a vortex control system according to the invention of US Pat. No. 5,697,838, which is incorporated by reference above. FIG. 4 is a schematic view of the upper portion of the fume hood showing the upper region of the vortex chamber and the vortex bubbles formed by the flow therein. FIG. 5 is a view similar to FIG. 1 showing a flow pattern having a monostable vortex in the vortex chamber. FIG. 6 is a schematic educational diagram of a ventilation hood with bistable vortices and in particular its face velocity and vortex chamber, all in accordance with the invention. FIG. 7 is a schematic diagram illustrating a bistable vortex ventilation hood and its components that provide a bistable vortex. FIG. 8 is a perspective view of the ventilation hood shown in FIG. 7, which includes a front portion including a sash, and operation hardware thereof. 9a and 9b are partial cross-sectional views taken along a horizontal plane encompassing 9-9 in FIG. 8 and showing another embodiment for the aerodynamic shape of the sash post. FIG. 10 is a partial cross-sectional view taken along a vertical plane including the line 10-10 in FIG. 8 showing the aerodynamically shaped sash handle used as a rotating vane. Referring to FIG. 1, a conventional ventilation hood 10 includes an enclosure 12 enclosing a work space 14 having a floor 15, a head space 16 substantially above the work space 14, and along its top and bottom edges. A vertically slidable sash window or door 18 with a seal 20, an aerofoil 22 defining a bottom stop for the sash 18, and a make-up air 26 when the sash 18 is closed. Floor sweep entry 24 to be moved. With sash 18 open, air 27 is drawn into enclosure 12 through sash opening 29. A baffle 28 is provided within the enclosure 12 to form a plenum 31 spaced from the rear wall 30 of the enclosure 12, and top, middle and bottom transverse slots for introducing air into the plenum 31. 32, 34 and 36 are provided. The plenum 31 communicates with an exhaust duct 38 leading to an exhaust fan (not shown). Referring to FIG. 2, another embodiment 40 of a conventional ventilation hood includes opening an air bypass port 42 having an area equal to the increase or decrease in the area of the sash opening 28 when the sash 18 is opened or closed, respectively. This provides an essentially constant airflow to the hood exhaust. The bypass baffle 44 can be variably opened or closed to regulate the speed of the secondary makeup air 46 entering the headspace 16 through the grill 48. Referring to FIGS. 3-5, the fume hood 50 has a monostable vortex control system according to the invention of US Pat. No. 5,697,838, which is incorporated by reference. A vortex sensor 52 mounted in the opening through the side wall of the headspace 16 containing the vortex chamber 54 continuously measures the pressure difference between the vortex chamber and the outside of the hood 50 and controls 56 To change the position of dampers 58 and 60, which increases the open area of slots 32 and 36, respectively, until a stable vortex 52 is obtained as represented by the minimum change in pressure difference being measured by sensor 52. Control. As described therein, the system is capable of maintaining a laminar flow of air into the workspace 14 while changing the sash opening 29 when the sash is opened or closed. It is. Referring to FIG. 6, a typical sash height and straight length ventilation hood 64 is shown. These dimensions will, of course, vary depending on the needs of the user. The hood vortex 62 is made bistable according to the present invention. The bistable vortex is maintained using the following relationship for the hydraulic radius of the open sash 29 window area to the hydraulic radius ratio required in the vortex chamber 54 above the working chamber 14 (Equation 1 below). These relationships are: (a) the hydraulic radius of the vortex chamber is between about 80% and about 90% of the hydraulic radius of the open sash window, and (b) the vertical component (height) of the vortex chamber is the sash window. Between about 80% and about 85% of the maximum height of the opening. By using the hydraulic radius ratio relation (Equation 1 below), the optimum hood depth can be determined for each and every ventilation hood sash opening using Equation 2. . Hydraulic radius ratio = Hydraulic radius vortex chamber / Hydraulic radius opening sash (Equation 1) Note that a = open window area, p = open window perimeter These dimensions and the relationship to the open surface area provide the envelope required to generate a bistable vortex in the ventilation hood enclosure. The rotating blades 65 shown in FIG. 7 can be a useful addition, and the angle α should be between about 30 ° and about 45 °. The rotary vanes can be about half the height of the vortex chamber dimensions. The relationship with these vortex chambers is a feature of the present invention. The fume hood is most sensitive to environmental changes when the sash 18 is fully open and the vortex chamber 54 is at its minimum. The automatic vortex control system shown in FIG. 3 detects vortices and adjusts the rear baffle system as described above to compensate for variations in equipment load and space pressure, cross ventilation, hood forward activity, and the like. The bistable vortex baffle system according to the present invention further includes upper and lower interlock or hinged operable baffles 66 and 68, respectively, which, as shown in FIG. Is replaced with the fixed type baffle 28. The baffles 66 and 68 are each rotatable about a horizontal axis, and the upper end 70 of the baffle 68 is keyed and slaved to the lower end of the baffle 66 with an intermediate slot 34 formed therebetween. ing. Top slot 32 is formed at the top of baffle 66 and bottom slot 36 is formed at the bottom end 72 of baffle 68. An actuator 74 is operably disposed to rotate the baffle 66 and is contouredly rotated about their axes by a slave extension baffle 68 to provide three slot dimensions and a working chamber 14 and vortex chamber 54. Change the geometry simultaneously. In operation, as the sash 18 is lowered, the closed loop vortex control system biases the actuator 74 to rotate the baffle 66 clockwise, which tends to occlude the upper slot and thereby centralizes the upper slot. The slot is cantilevered toward the sash, thereby inducing a clearing effect within the working chamber 14. This feature is very important. Because, in a monostable hood, the working chamber may be filled with fumes, which tends to collect and overflow to the operator when the sash is raised. The operation of the baffle system also moves the bistable vortex bubble further out of the sash window as it rotates along the work surface (the position of vortex 62 and the bistable position in FIG. 5, which is a monostable position). 6 should be compared). This clearing action is enhanced by the laminar flow of air into the hood via the airfoil 76 below the sash opening. Preferably, the airfoil 76 is mounted on the floor of the workroom just inside the sash opening and has a multiple (three) slot configuration, with the upper and central slots 76a and 76b providing air. The third slot 76c directs to the central baffle slot 34 and directs air along the floor of the work chamber toward the lower baffle slot 36, as shown in FIG. In some applications, particularly in extremely monostable vortex ventilation hoods, it is possible to configure a hood for open loop control without the involvement of a vortex sensor and vortex control system, in which case the operable The operation and position of the baffle can be synchronized by trial and error to the position and movement of the sash by known electrical means such as a potentiometer or known mechanical means such as pulleys and gears. This less sophisticated open loop control method can, for example, provide improved hood performance over existing conventional hoods at a lower cost than a completely closed loop control system. In a preferred embodiment of the hood according to the present invention, the hood assembly 78 shown in FIGS. 7 and 8 has a conventional working chamber 14 and a headspace 16, but further includes a newly constructed hood. Or, it has an additional front hood portion 79 that can be attached to the front of a conventional hood enclosure 12 along line 80, either retrofitting an existing hood. By configuring the ventilation hood in this manner, quick and easy assembly can be performed on site. Although the assembly 78 is shown as a bench mounted hood, walk-in or stand-up embodiments mounted on larger floors are also within the scope of the present invention. The advantage of the hood assembly 78 extends substantially forward of the end 81 of the bench 82, allowing the aerofoil 76 to be located behind the lower end of the sash opening 29 and within the bottom of the hood. The point is that. The front section 79 has an additional working space 14a and a headspace 16a, which makes these chambers deeper, which improves the geometric relationship consistent with equation 1. It is possible. The removable portion 79 is limited in size to allow the bistable vortex fume hood to be fitted, usually through a standard doorway, or to be easily placed on a laboratory bench. It allows things that are not things. Ventilation hoods that can be assembled in the field to be larger than conventional monostable vortex hoods are yet another feature of the present invention. An important goal in the construction and operation of an efficient, overflow-free hood is to maximize laminar airflow and minimize turbulence in all areas of the hood. 9a, 9b and 10 illustrate the desired laminar flow promoting features associated with a sash opening operation. In FIG. 9a, the left hood post 84 has a corner 86 that is curved relative to the entrance to the sash opening 29 and is located just outside the sash channel 88 and includes spaced aerofoil blades. 90 is mounted on a spacer 92 bolted to a post 84 to form an open-ended plenum 93 between the blade and the post. The vanes 90 preferably extend the entire height of the sash opening 29. In practice, the blades are also mounted on the right hood support in a mirror image relationship. FIG. 9b shows another embodiment to the configuration of FIG. 9a, where the corners 86 are perforated or slotted to allow air to pass through and the sash channel 88 is The flange 89 has been reconfigured to form an air plenum 93. FIG. 10 shows an aerodynamic handle 94, which preferably extends the entire width of the bottom of the sash 18 and traverses the lower end of the sash when the sash is not completely closed. And provides an aerodynamic surface to the upper slot of the aerofoil if the sash is completely obstructed. From the above description, it is apparent that an improved ventilation hood has been provided, in which an operable, articulated baffle and vortex control system provides a bistable headspace vortex. Variations and modifications of the ventilation hood described herein according to the invention will no doubt be suggested to those skilled in the art. Accordingly, the foregoing description is by way of example and should not be taken in a limiting sense.

────────────────────────────────────────────────── ─── Continuation of front page    (81) Designated countries EP (AT, BE, CH, DE, DK, ES, FI, FR, GB, GR, IE, IT, L U, MC, NL, PT, SE), OA (BF, BJ, CF) , CG, CI, CM, GA, GN, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, M W, SD, SZ, UG, ZW), EA (AM, AZ, BY) , KG, KZ, MD, RU, TJ, TM), AL, AM , AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, E S, FI, GB, GE, GH, HU, IL, IS, JP , KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, M W, MX, NO, NZ, PL, PT, RO, RU, SD , SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, UZ, VN, YU, ZW (71) Applicant Morris, Robert H.             United States, New Jersey             02885, Wharton, East Shawnee               Trail 30 (72) Inventor Deluca, Robert A.             United States of America, New York 11772,             Patchok, Globe Avenue 475 (72) Inventors Morris, Robert H.             United States, New Jersey             02885, Wharton, East Shawnee               Trail 30

Claims (1)

[Claims]     1. A movable sash operable at a sash opening along its front side. In a ventilation hood having a room provided therein, a buff capable of articulating in said room Air to direct airflow in the room toward the baffle system. Allofoil, the articulable buff to maintain a bistable vortex in the chamber Ventilation hood having means for moving the hood.     2. 2. The method of claim 1, wherein the moving means comprises a vortex detection system. hood.     3. 2. The sash opening of claim 1, wherein Means for synchronizing movement of the sash and movement of the articulable baffle. Hood.     4. 2. The baffle of claim 1, wherein the articulatable baffle comprises upper and lower buffs. And the baffle is articulated to define a slot therebetween. Hood that is operatively connected.     5. 5. The airfoil of claim 4, wherein the airfoil is disposed at a bottom portion of the chamber. Hood.     6. 6. The airfoil of claim 5, wherein the airfoil is connected to the articulable connection. Top and middle slots to direct air toward and along the floor of the chamber And a third slot for directing air. Hood with three multi-slots.     7. The hood of claim 1, wherein the hood comprises a separable front portion and a rear portion. The front part contains the sash and the means for operating it. Food.