US20090183728A1

US20090183728A1 - Overhead ventilation system incorporating a downwardly configured rear supply plenum with upward configured directional outlet and including baffle plates and dampeners incorporated into the plenum for evenly distributing an inlet airflow through the plenum outlet

Info

Publication number: US20090183728A1
Application number: US12/272,089
Authority: US
Inventors: Greg Kolecki
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-09-14
Filing date: 2008-11-17
Publication date: 2009-07-23

Abstract

A ventilation system for use with a cooking appliance to maintain an atmospheric pressure balance existing within an enclosed space surrounding the cooking appliance. A hood establishes a three-dimensional and interiorly recessed configuration and which is supported above the appliance. A filter within the hood communicates with a vacuum driven exhaust extending from the enclosed space. A supply plenum secures in downwardly and opposing fashion relative to a side of the cooking appliance. An air intake communicates the supply plenum with an exterior environment, the plenum including at least one air flow restricting and redistributing baffle plate and terminating in an upwardly angled outlet for introducing intake air along the side of the appliance, resulting in heating and elevating the intake air within a perimeter defined by the hood and thereby minimizing loss of conditioned air existing within the enclosed space.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation in part of U.S. Ser. No. 11,531,987, filed Sep. 14, 2006, for an Overhead Ventilation System Incorporating a Downwardly Configured Rear Supply Plenum with Upward Configured Directional Outlet.

FIELD OF THE INVENTION

The present invention relates generally to an overhead ventilation system, such as is utilized in combination with commercial cooking appliances or industrial oven processes. More particularly, the present invention teaches a ventilation system, such as in use with a commercial pizza or other food related cooking process and by which products of such process include heated air, grease and/or other contaminants. The present invention is an improvement over prior art oven hood designs, and by which an associated inlet plenum is reconfigured to assist in introducing air from an exterior, this including the incorporation of interior baffling elements for slowing down an intake velocity of air into the supply plenum, including evenly distributing the air along the width of the plenum and prior to the air being introduced in upwardly directed proximity to the cooking appliance, this further while reducing the requirement for oversized air conditioning or heated makeup air units.

DESCRIPTION OF THE PRIOR ART

The prior art is well documented with examples of oven hood and makeup air devices, such as which are utilized in the removal of heat and airborne particulates (i.e., grease, other solids, etc.) associated with an oven and cooking equipment process of some type. A common objective of such makeup devices is both the removal and concurrent replacement of qualified/conditioned air within an interior location in which the oven process and cooking equipment is located and which may include both commercial restaurants, bakeries, pizzerias, and the like.
A common problem in the prior art is the tendency of such devices to introduce significant volumes of untreated air, requiring further significant capacity from such as air conditioning and heated makeup air units. The cost of maintaining a desired interior air temperature can therefore be greatly increased, both in terms of heating or conditioning volumes of makeup introduced. A further problem associated with the prior art is the tendency of the makeup air to be unevenly introduced through its associated supply plenum, such as in terms of intake velocity as well as lateral distribution (or spread) across the width of the plenum and prior to introduction into the interior environment at which the cooking equipment is located.

SUMMARY OF THE PRESENT INVENTION

The present invention discloses a supply plenum module incorporated into an improved filter and ventilation system associated with a cooking appliance and which maintains a desired pressure balance, or equilibrium, within an enclosed space in which the appliance is situated during filtration of the same. In particular, the module operates in cooperation with the associated ventilation system in order to introduce, from an exterior location, a volume of raw untreated air for subsequent conditioning and conveyance to the inner hood perimeter, the same balancing the outflow of exhaust air drawn through an associated filter and evacuated from the hood and in order to prevent or minimize the loss of other conditioned air (heated or cooled) existing within the enclosed space.
The intake associated with the plenum typically includes a pair of individual branches for contacting the plenum at spaced apart side locations, this better serving to distribute intake air in balanced fashion along the entire length of the module. Balancing dampeners are incorporated into a location of each intake branch, for regulating an intake airflow into a first elongated and downwardly extending manifold or passageway.
A further pair of elongate and widthwise extending baffle plates are mounted within the first downwardly extending passageway, each of the baffle plates being arranged in a generally widthwise extending and spaced apart fashion. The baffle plates each exhibit pluralities of apertures, such as establishing a varying percentage by surface area of open space for admittance of an intake airflow.
In one application, a first (upper) of the baffle plates exhibits a 48%, by area, of open space defined by the flow through apertures, with a second lower spaced apart baffle plate reducing the flow through area to 40% (such as by smaller or fewer dispersed apertures defined in the baffle plate).
The downwardly extending passageway communicates with a second, shorter, and upturned passageway terminating in a lengthwise extending outlet. The extended length of the intake supply plenum, combined with the provision and arrangement of the balancing dampers and the baffle plates, establish a reduced velocity and evenly distributed inlet flow for introduction at the lengthwise and upturned outlet relative to the side of the cooking appliance.
The arrangement and configuration of the hood further serves to better warm and precondition the raw intake air for rising within the hood interior. The configuration and arrangement of the plenum results in a volume of intake air introduced generally equaling that exhausted from the hood and, by virtue of establishing a pressure equilibrium within the hood interior which is facilitated by the 1) heating, 2) slowed velocity and 3) more evenly distributed intake flow from the plenum, thereby preventing loss of additional volumes of quality AC or heat conditioned air, from within the enclosed space, and which may otherwise be vacuum drawn and expelled by the overhead hood.
The length and depth of the supply plenum, in cooperation with the balancing dampers and internal baffling plates, further assists in maintaining an air velocity (i.e., speed of air) out of the supply plenum. The maintenance of a desired air velocity out of the supply plenum does not affect the exhaust air drawn and evacuated. Further, the directional upward outlet of the present invention introduces air flow as the heated (thermal) air flow of the cooking device.
As is known, heated air rises naturally off cooking appliances, with the upwardly introduced air assisting in the removing of heat, odor, grease, and gas by-products more efficiently. In this fashion, the untreated air introduced by the present ventilation system does not affect the air temperature of the room and again further serves to reduce the need for mechanical makeup air treatment devices (e.g. again heaters or chillers) to replace other quality internal conditioned air associated with the environment within which the cooking appliance is maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the attached drawings, when read in combination with the following detailed description, wherein like reference numerals refer to like parts throughout the several views, and in which:

FIG. 1 is a first environmental view, in perspective, of the ventilation system according to the present inventions in operative arrangement with respect to an item of conventional cooking equipment;

FIG. 2 is a backside rotated environmental view of the ventilation system of FIG. 1 and further illustrating the manner and extent to which the rear supply plenum module extends relative to a backside of the cooking equipment, as well as illustrating the arrangement and configuration of the upper balancing dampers incorporated into the intake branches of the manifold, as well as the widthwise extending baffle plates for additionally slowing and evenly distributing the admitted intake flow prior to introduction into the cooking appliance environment;

FIG. 3 is an exploded view of the ventilation system as illustrated in FIG. 2;

FIG. 4 is a sectional inner facing view of the supply plenum module according to the present inventions;

FIG. 5 is a cutaway view, taken along line 5-5 of FIG. 4, and illustrating a side profile of the supply plenum module;

FIG. 6 is a partial view of a lower corner portion of the supply plenum module and illustrating the inner and upturned arrangement of the inlet face and upon which is disposed a perforated plate;

FIG. 7 is an enlarged view taken from FIG. 2 and further showing the pivotal opening/closing nature of the selected balancing damper associated with an intake branch of the manifold; and

FIG. 8 is a partial perspective of a plenum configuration according to a further preferred embodiment and illustrating a further possible reconfiguration in which the a selected baffle plate can be repositioned along the upturned and widthwise extending outlet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a first environmental view is generally shown at 10 in perspective of a ventilation system according to the present inventions in operative arrangement with respect to an item of conventional cooking equipment 12. As will be further described in additional detail, the present inventions include both an overall system, as well as a supply plenum (this defining a three dimensional and elongated module) 14 secured to an overhead hood 16 incorporated into the improved filter and ventilation system, and which is associated with the cooking appliance 12 to maintain a desired pressure balance, or equilibrium, within an enclosed space in which the appliance 12 is situated during filtration of the same. In particular, the plenum 14 operates in cooperation with the associated ventilation system in order to introduce, from an exterior location, a volume of raw untreated air for subsequent conditioning and conveyance to an inner hood perimeter, the same balancing the outflow of exhaust/filtered air withdrawn from the hood 16 and in order to prevent or minimize the loss of other conditioned air (heated or cooled) existing within the enclosed space.
Referencing again FIG. 1, as well as the rotated view of FIG. 2 and exploded illustration of FIG. 3, the hood 16 is constructed of such as a stainless steel material and which defines a generally rectangular and interiorly recessed three-dimensional configuration positioned in overlaying and, typically, elevated fashion above the piece of cooking equipment 12. The article of equipment 12 in the illustrated variant is shown as a pizza oven, however it is further understood that any type of cooking or heat generating equipment, whether food industry related or otherwise, is contemplated without limitation.
Features generally associated with the hood 16 include a filter (see in phantom at 18 in FIG. 1) and typically consisting of a baffle or other known type of filter for providing entrapment of grease and other particulates. The filter 18 may include either a single elongated element or a number of individual and attachable sections (see at 18 a, 18 b, 18 c, et seq., in FIG. 4) which are secured at top 20 and bottom 22 locations associated with the hood interior and in order to extend across its inner length between first 24 and second 26 ends. A removable grease container 28, see as further shown in FIG. 1, is arrayed at a slightly downwardly sloped end of the bottom filter support 22, the support 22 further being interiorly recessed in upwardly facing fashion in order to collect grease and other liquid particulates captured by the filter and collected in gravity flowing fashion within the cup for subsequent emptying.
Pluralities of elongated support hangers 30 and 32 are provided for securing typically both the hood 12 and associated plenum 14 to a ceiling supporting location 34 (see FIGS. 1 and 2) associated with the enclosed interior. A vacuum driven exhaust secures to a communicating location 36 formed in a top surface of the hood 12 and includes a length of ductwork 38 interconnected to such as a blower 40 or other vacuum generating component located at an exterior location from the enclosed interior space. An incandescent light fixture 42 (see in phantom in FIG. 4) is secured to an interior location associated with the hood 12 (typically its inner top surface as shown).
Referring again to each of FIGS. 1-3, as well as to succeeding views of FIGS. 4-6, the supply plenum 14 defines an elongated and three-dimensional shaped module and which is capable of either being secured in contacting fashion to the hood 12 or, alternatively, secured in a similar arrayed and downwardly depending fashion relative to the hood. As illustrated, the plenum 14 is secured along its upper lengthwise extending edge, see at 44, in cooperating fashion along a corresponding and lengthwise defined side edge of the hood 12 (this as shown in the drawings and extending between hood ends 24 and 26). The plenum module 14 can be secured mechanically (such as by welding or fasteners) to the hood 12 and, as is shown, is further supported by additional support hangers 30 and 32 and in order properly balance the overall assembly. Additional features, such as a pair of skirts 41 and 43, are secured by associated fasteners 45 and 47 to ends of the hood 12 and such that the skirts overlay associated ends of the plenum 14.
An air intake is provided for supplying raw air from an exterior location to the plenum 14 and includes an exterior vent 46 which is communicated through the ceiling 34, extends downwardly at 48 and then splits into branches 50 and 52 for subsequent communication at two locations with the upper edge 44 of the supply plenum module 14. A pair of balancing dampers, see at 51 and 53, are provided in each of the intake branches 50 and 52, respectively.
The balancing dampers 51 and 53 capable of being individually (or alternatively) manipulated/pivoted to varying opening/closing positions (see also enlarged illustration of FIG. 7 illustrating selected damper 51 associated with intake branch 50) and operate in a first intake stage to equalize the intake flow and velocity of the air drawn from the exterior vent 46, prior to introduction into the plenum module 14. The air intake assembly is designed to provide an adequate volume of raw exterior air to the supply plenum 14, and it is accordingly contemplated that other single or multiple manifold configurations are envisioned by which an adequate input airflow can be established.
As further illustrated throughout the several views, the plenum 14 exhibits a generally three-dimensional and elongated configuration including a flattened exterior and vertical extending face, see at 56, and which in combination with an opposite interior face 58 defines a first downwardly extending and main interior passageway (or manifold) for communicating the raw air withdrawn through the intake branches 50 and 52 and into the plenum body. Additional to the balancing dampers 51 and 53 associated with the intake branches 50 and 52, a further pair of elongate and widthwise extending baffle plates 55 and 57 are mounted within the first downwardly extending and interior passageway.
Each of the baffle plates 55 and 57 are arranged in a generally widthwise extending and vertically spaced apart fashion within the plenum interior and as shown in each of FIGS. 2, 3 and 6. The baffle plates 55 and 57 can extend in a parallel or angularly fashion, and each further exhibits an individual plurality of apertures, such as establishing a varying percentage by surface area of open space for admittance of an intake airflow.
In one application, a first (or upper) of the baffle plates, previously identified at 55 exhibits a 48%, by area, of open space defined by a plurality of flow through apertures 59. A second lower spaced apart baffle plate, previously identified at 57, includes a further plurality of apertures 61, these reducing the flow through area to 40% (this also capable of being accomplished both by the provision of smaller apertures or the use of fewer dispersed apertures defined in the baffle plate). The above example is understood to provide only one possible selection of flow through percentages associated with one desired operational variant, and it envisioned and understood that the relative percentages of available flow through area defined in each of the baffle plates can be adjusted, such as according to any range of constriction between 1-99%. It is further understood that, while the relative flow through passage of the upper baffle plate 55 is typically some percentage greater than that associated with the lower baffle plate 57, other variants can contemplate the upper baffle plate being more restrictive as between the two.
As shown in FIG. 2, the combination of the balancing dampers 51 and 53 and the baffle plates 55 and 57 serve to regulate (i.e. typically to slow down the intake velocity) and evenly distribute (such as in a laterally spread out direction) the intake airflow from the intake 48. This is further represented by airflow indicator arrows 63, 65 and 67, with arrows 63 representing a first regulation or reallocation of intake air from the balancing dampers 51 and 53 to the first/upper baffle plate 55, arrows 65 representing a further step-down of velocity, as well as additional widthwise equalization of air flow between the upper baffle plate 55 and the second lower baffle plate 57.
A second (shorter) and reverse angled with upwardly extending passageway 60 (see as further best generally shown in cutaway view of FIG. 5) communicates with the first passageway via rounded bottom 62, and terminates in a lengthwise extending and upwardly facing outlet 64. The additional plurality of arrows 67 represented in FIG. 2 illustrates the manner in which the outlet air flow from the second/lower baffle plate 57 is finally regulated in a most evenly distributed and desirous velocity profile prior to being discharged through the outlet 64.
As again shown, the outlet 64 is disposed in a generally inner/upwardly facing manner and, in an alternative embodiment as best shown in FIG. 6, can further include a perforated plate 66 secured thereover, the plate 66 including additional apertures 69. The plate 66 can operate as a third additional baffle plate (as shown in FIG. 6) or the plate 66 can substituted for one or both of the plates 55 and 57 (see as further shown in FIG. 8) for reducing the velocity and equalizing the flow pattern established across the interior profile of the supply plenum 14.
In this fashion, the raw intake air drawn into the (typically stainless steel) plenum is caused to be warmed, and regulated in its velocity and directional profile, this again by virtue of the extending lengths of the associated passageways, primarily downward with balancing dampers and baffle plates and, to a lesser extent, reverse upwardly and out through the outlet 64. The intake air is directed so that it is discharged through the outlet 64 in a position generally at or below the cooking equipment 12 and in a spaced fashion along a rear side of the equipment 12. The arrangement and direction of distribution of the outlet airflow is further such that it will not cause to impact the cooking equipment 12 (thereby adding to the heat content of the air) and, as a result, is rather caused to rise and to be entrapped within the defined inner perimeter of the hood 16 along with the heat rising from the cooking equipment 12, and further so as not to inadvertently (such as vacuum) draw in conditioned interior air from the environment surrounding the cooking equipment and which may otherwise be drawn out through the hood.
As is known, and in order for a ventilation system to properly operate, an amount of air exhausted must be balanced by an equal amount of air introduced back into the room or enclosure and to balance the system. The performance of the ventilation system (i.e. its functionality) is to capture and contain such as heat, odors, grease and the like while maintaining the proper volumetric air balance (this again reducing the losses of pretreated quality interior air not directly related to the cooking appliance).
As such, the ability to balance an intake volume of air, through the supply plenum, across its outlet and in heat generated fashion up into its hood perimeter, operates to replace similar volumes of air exhausted through the hood, and without the otherwise undesirable consequence of the conditioned internal air (this being the air heated or air conditioned within the enclosed space by such as AC condensers or air makeup units) being vented through the hood as a result of an imbalanced atmospheric condition created within the enclosure. The ability to draw upon a limitless volume of raw intake air, as described herein, is intended to save on the otherwise necessary expense of providing additional air conditioning/eating capacity to the room enclosure and the concurrent waste of additional energy dollars necessary to maintain an internal room condition in which the quality air is being vented through the hood along with the heated byproduct air associated with the appliance.
In the above described fashion, the percentage of makeup air required to balance the overall ventilation system is introduced behind the conventional cooking appliance through the rear positioned supply plenum with upward directional outlet, and thereby in a direction towards the baffle filters 18. The advantage with the upward directional outlet is that the introduced air (again not requiring any pretreatment such as heating or cooling) is maintained in the capture area (again defined as the inside perimeter of the hood) and which will not otherwise affect the quality and volume of the conditioned air (heated or cooled) within the interior enclosed (kitchen) environment. Furthermore, the operation of the present system does not affect the air temperature within the room enclosure, nor does it affect the effectiveness of the hood to capture and contain the byproducts of the cooking operation.
As previously stated, the introduced air does not require any other treatment. Any balance of required makeup air is typically supplied by the existing heating and cooling equipment or provided by smaller mechanical equipment than that which is required in standard ventilation systems. The additional advantage of the system is the ability to provide a properly balanced ventilation system while concurrently operating to capture the greases, odors, and gas byproducts associated with the cooking appliance and vent its associated heat emanations. The outlet air velocity may also be lower than that associated with the intake and, combined with the introduction of the intake air flow in the upward direction (same as the thermal/heated air) contributes to the effectiveness and efficiency of the system.
Having described my invention, other and additional preferred embodiments will become apparent to those skilled in the art to which it pertains, and without deviating from the scope of the appended claims.

Claims

1. A ventilation system for use with a cooking appliance which maintains an atmospheric pressure balance existing within an enclosed space surrounding the cooking appliance, said system comprising:

a hood establishing a substantially three-dimensional and interiorly recessed configuration and which is supported in generally elevated fashion above the appliance, said hood incorporating a filter communicating with a vacuum driven exhaust extending from said hood and the enclosed space; and

a supply plenum secured in downwardly and opposing fashion relative to a side of the cooking appliance, an air intake communicating said supply plenum with an exterior environment, said plenum further including at least one baffle plate secured within its widthwise extending interior for regulating at least one of a flow velocity and distribution of an airflow originating from said air intake, said plenum terminating in an upwardly angled outlet for introducing intake air along the side of the appliance, resulting in heating and elevating the intake air within a perimeter defined by said hood thereby minimizing loss of conditioned air existing within the enclosed space.

2. The ventilation system as described in claim 1, said hood exhibiting a specified shape and size and further comprising a generally rectangular shape.

3. The ventilation system as described in claim 2, said plenum exhibiting a specified shape and size and further comprising a three-dimensional and elongated module secured along a side edge of said hood, said at least one baffle plate further comprising first and second spaced apart baffle plates mounted within said plenum in widthwise extending and vertically spaced apart fashion.

4. The ventilation system as described in claim 3, said first baffle plate exhibiting a first surface area, by percentage of flow through apertures, said second baffle plate being position below said first baffle plate and exhibiting a second surface area, by percentage of flow through apertures which is less than said first percentage associated with said first baffle plate.

5. The ventilation system as described in claim 3, further comprising a pair of elongated and substantially planar skirts secured in downwardly extending fashion from first and second ends of said hood, said skirts overlaying associated ends of said supply plenum, said plenum outlet extending in substantially lengthwise fashion between said ends.

6. The ventilation system as described in claim 1, further comprising an additional elongated and perforated baffle plate secured over said plenum outlet.

7. The ventilation system as described in claim 5, said plenum exhibiting a specified shape and size and further comprising a first downwardly extending passageway in communication with said air intake and incorporating said first and second baffle plates, a second reverse angled and upwardly extending passageway communicating with said first passageway and terminating in said outlet.

8. The ventilation system as described in claim 1, further comprising a vacuum generating blower incorporated into an exterior location of said exhaust.

9. The ventilation system as described in claim 1, further comprising a plurality of elongated support hangers extending from a ceiling location of the enclosed space and securing to respective top face locations associated with at least one of said support plenum and said hood.

10. The ventilation system as described in claim 1, said filter exhibiting a specified shape and size and further comprising a baffle filter secured in angled fashion between first and second interior defining ends of said hood.

11. The ventilation system as described in claim 10, said hood interior further comprising respective upper and lower lengthwise extending supports for securing said baffle filter in communication with said vacuum driven exhaust, a grease collection trap associated with a tilted end location providing for disposal of liquid based contaminants collected by said filter.

12. The ventilation system as described in claim 1, further comprising an incandescent light fixture secured to an interior location associated with said hood.

13. The ventilation system as described in claim 3, said air intake further comprising first and second branches communicating with individual locations associated with said elongated module, each of said branches incorporating a balancing damper for adjusting the intake air flow from said branches and prior to delivery to said plenum and passage through said baffle plates.

14. A ventilation system for use with a cooking appliance which maintains an atmospheric pressure balance existing within an enclosed space surrounding the cooking appliance, said system comprising:

a hood establishing a substantially three-dimensional and interiorly recessed configuration overlaying the appliance, a vacuum driven exhaust extending from said hood and the enclosed space; and

an elongated supply plenum extending downwardly from an associated side of the cooking appliance and which is supplied by an air intake communicating with an exterior environment, said air intake including at least one balancing damper for adjusting an intake air flow, said plenum further comprising at least one at least one baffle plate secured within its widthwise extending interior for regulating at least one of a flow velocity and distribution of an airflow originating from said air intake, said plenum terminating in an upwardly angled outlet for introducing intake air along the side of the appliance, resulting in heating and elevating the intake air within a perimeter defined by said hood thereby minimizing loss of conditioned air existing within the enclosed space.

15. The ventilation system as described in claim 14, said air intake further comprising first and second branches communicating with individual locations associated with said elongated module, each of said branches incorporating a balancing damper for adjusting the intake air flow from said branches and prior to delivery to said plenum.

16. The ventilation system as described in claim 15, said plenum exhibiting a specified shape and size and further comprising a first downwardly extending passageway in communication with said air intake and within which are mounted a first baffle plate exhibiting a first surface area, by percentage of flow through apertures, a second baffle plate being position below said first baffle plate and exhibiting a second surface area, by percentage of flow through apertures which is less than said first percentage associated with said first baffle plate, said plenum further including a second reverse angled and upwardly extending passageway communicating with said first passageway and terminating in said outlet.

17. The ventilation system as described in claim 14, further comprising a vacuum generating blower incorporated into an exterior location of said exhaust.

18. A supply plenum module for use with a hood filter assembly for a cooking appliance and which maintains an atmospheric pressure balance existing within an enclosed space surrounding the cooking appliance, comprising:

the hood establishing a substantially three-dimensional and interiorly recessed configuration and which is supported in generally elevated fashion above the appliance, a filter being disposed within an interior of the hood and communicating with a vacuum driven exhaust extending from the enclosed space;

an air intake having first and second branches, each of which incorporating a balancing damper for adjusting an intake air flow from said branches;

said air intake branches communicating with individual locations associated with a supply plenum further comprising a three-dimensional and elongated module secured in downwardly extending fashion along a side of the hood and in order to be arrayed in opposing fashion to a corresponding side of the cooking appliance;

said plenum further including first and second baffle plates secured within its widthwise extending interior for regulating at least one of a flow velocity and distribution of an airflow originating from said air intake; and

said plenum terminating in an upwardly angled outlet for introducing intake air along the side of the appliance, resulting in heating and elevating the intake air within a perimeter defined by said hood, thereby minimizing loss of conditioned air existing within the enclosed space.

19. The ventilation system as described in claim 18, said first baffle plate exhibiting a first surface area, by percentage of flow through apertures, said second baffle plate being position below said first baffle plate and exhibiting a second surface area, by percentage of flow through apertures which is less than said first percentage associated with said first baffle plate.

20. The ventilation system as described in claim 19, said first baffle plate exhibiting 48% by surface area of available flow through apertures, said second baffle plate exhibiting 40% by surface area of available flow through apertures.