Abstract:
An exhaust apparatus for a conveyor oven includes a first hood linked to a duct at a first end of the duct and connected to a frame configured for mounting on the conveyor oven such that the first hood is positioned directly over a conveyor tray of the conveyor oven. The first hood has at least one grease filter and a recess defined at least in part by an interior wall, the hood interior wall having a first side, a second side opposite to the first side, a bottom edge, a top edge, and opposing side edges. The hood interior wall bottom edge is aligned with a top of the conveyor oven and is aligned directly over an access located in the bounding external surface of the conveyor oven when the first hood is mounted on the conveyor oven.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of U.S. application Ser. No. 13/607,706, filed Sep. 8, 2012, which is a continuation of U.S. application Ser. No. 11/722,378, filed Jun. 21, 2007 (371(c) date of Mar. 13, 2008), which is a national stage entry of International Application No. PCT/US06/00579, filed Jan. 6, 2006, which claims the benefit of U.S. Provisional Application No. 60/593,331, filed Jan. 6, 2005, all of which are hereby incorporated by reference in their entireties. 
     
    
     BACKGROUND AND PRIOR ART 
       [0002]    Basic exhaust hoods use an exhaust blower to create a negative pressure zone to draw effluent-laden air directly away from the pollutant source. In kitchen hoods, the exhaust blower generally draws pollutants, including room-air, through a filter and out of the kitchen through a duct system. An exhaust blower, e.g., a variable speed fan, contained within the exhaust hood is used to remove the effluent from the room and is typically positioned on the suction side of a filter disposed between the pollutant source and the blower. Depending on the rate by which the effluent is created and the buildup of effluent near the pollutant source, the speed of exhaust blower may be manually set to minimize the flow rate at the lowest point which achieves capture and containment. 
         [0003]    Hoods are intended to act as buffers which match the flow of fumes, which varies, to the constant rate of the exhaust system. But basic hoods and exhaust systems are limited in their abilities to buffer flow. The exhaust rate required to achieve full capture and containment is governed by the highest transient load pulses that occur. This requires the exhaust rate to be higher than the average volume of effluent (which is inevitably mixed with entrained air). Ideally the oversupply of exhaust should be minimized to avoid wasting energy. Hoods work by temporarily capturing bursts of effluent, which rise into the hood due by thermal convection and then, giving the moderate average exhaust rate time to catch up. 
         [0004]    One problem with the buffer model is that the external environment may displace fumes and thereby add an excess burden of ambient air into the exhaust stream. This results in fumes being injected into the occupied space surrounding the hood. These transients are an on-going problem for hood design and installation. all the effluent by buffering the and containment by providing a buffer zone above the pollutant source where buoyancy-driven momentum transients can be dissipated before pollutants are extracted. By managing transients in this way, the effective capture zone of an exhaust supply can be increased. 
         [0005]    U.S. Pat. No. 4,066,064 shows a backshelf hood with an exhaust intake located at a position that is displaced from a back end thereof. A short sloping portion rises and extends at a shallow angle toward the inlet from the back end of the hood recess. 
         [0006]    U.S. Pat. No. 3,941,039 shows a backshelf hood with side skirts and sloping wall from a rear part of the hood to an inlet located near the middle of the hood. The front of the hood as a horizontal portion (baffle) that extends between about 15 percent and about 20 percent of the front to back dimension of the hood. This part is claimed to direct air in a space above the baffle toward the exhaust inlet and to direct air that is drawn from the ambient space in a horizontal direction thereby encouraging rising fumes to be deflected toward the exhaust inlet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows a low profile exhaust hood in partial section view. 
           [0008]      FIG. 2  shows the exhaust hood of  FIG. 1  in perspective view. 
           [0009]      FIG. 3  shows the exhaust hood of  FIGS. 1 and 2  in operative association with a stack of conveyor ovens. 
           [0010]      FIG. 4  illustrates a modular structure for mounting the foregoing embodiments of hoods on a stack of conveyor ovens. 
           [0011]      FIG. 5  illustrates another embodiment of a low profile exhaust hood. 
           [0012]      FIG. 6  illustrates a flow transition feature that may be used for applications of the foregoing embodiments. 
           [0013]      FIG. 7  illustrates a backshelf hood embodiment. 
           [0014]      FIGS. 8-12  illustrate variations on the embodiment of  FIG. 7 . 
           [0015]      FIGS. 13A-13C  illustrate a canopy hood embodiment. 
           [0016]      FIGS. 14 and 15  illustrate features associated with mounting a filter. 
           [0017]      FIGS. 16A and 16B  illustrate a retractable radiation and convection shield. 
           [0018]      FIG. 17  illustrates features of the inventive embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0019]    An eyebrow-type exhaust hood (also called a cap or vent cowl-type hood) may be used above a door or opening such as a pizza, conveyor oven, bakery oven, broiler, steamer. This type of hood overhangs an access opening for the oven or similar equipment and captures thermal plumes that flow upwardly from the access opening. The capture zone is generally at least as wide as the opening. The depth may vary with some designs being shallower than the face of the appliance. Such hoods may be mounted directly on the appliance. Conveyor ovens can project forward of the oven mouth such that the hood may or may not overhang the source of effluent. This type of hood may also be used for conveyor washers, sintering ovens, and other sources of hot effluent. 
         [0020]    Referring to  FIGS. 1 and 2 , an eyebrow hood  100  is shown in cross-section. The hood  100  has a recess  130  defined by sidewalls  142  and a top  140  which covers up to a forward edge  141  thereof. A back of the recess  130  is defined by a forward filter support plate  115  with openings  116  to permit the flow of exhaust effluent into a plenum  125  and supports (the supports are not shown) to support filter cartridges  110  in the openings  116 . A baffle plate  120  is connected to the filter support plate  115  by a hinge  122 . The hinge  122  allows the baffle plate  120  to be dropped down to the position indicated at  122  to allow the filter cartridges  116  to be removed and installed. 
         [0021]    A grease trough  170  collects grease from the filter cartridges  110 . The angle of the baffle plate  120  with respect to the filter support plate  115  defines a flow transition  135  leading to the faces of the filter cartridges  110 . The position of the baffle plate  120  also defines a slot  135 , indicated by the double arrow, through which the effluent stream is drawn by an exhaust system (not shown) connected to the plenum  125  by an exhaust collar  105 . The baffle plate  120  also defines a sloping rear planar boundary of the recess  130 . 
         [0022]    Referring now also to  FIG. 3 , the eyebrow hood  100  is shown mounted to a stack of conveyor ovens  220 . Each conveyor oven  220  has inlet and outlet conveyor terminals  225  and  230  which extend beyond respective oven mouths (not visible in the side view) located at the ends  231  and  232  of the ovens  220 . 
         [0023]    Hot gasses escape from the ends  231  and  232  as well as from material carried on the conveyor terminals  225  and  230 . The latter may be open to the flow of gasses allowing plumes, indicated by arrows  210 , to rise through the conveyor terminals. Some plumes, such as indicated at  205 , may flow around the conveyor terminals  225  and  230 . Plumes rising close to the ends  231  and  232  tend to stay close to the ovens  220  due to the Coanda effect (or wall flow) so that some of the fumes will tend to flow along the baffle plate  120  until sucked into the slot  135 . 
         [0024]    Plumes rising further away from the ovens  220  will tend to be captured in a suction zone (not indicated separately) around the slot  135 . The forward edge  141 , which drops downwardly, defines a shallow canopy that helps to buffer and capture flow that is further away from the ovens  220 . A common exhaust duct  260  connects the collars  105  of the two eyebrow hoods  100  and leads them to a further common duct  250  that is connected to an exhaust fan (not shown). 
         [0025]    By locating the slot  135  in a position remote from the walls  231  and  232  of the ovens  220 , a suction zone is defined remote from the ovens  220  to capture fume plumes, such as  205 , which rise remote from the ovens  220 . Additionally, the baffle plate  120  provides an inclined, partially vertical surface along which plumes closer to the ovens  220 , such as  206 , may cling and thereby be guided to the slot  135 . This configuration allows filters to be located conveniently close to the exhaust collar  105  at a rear end of the eyebrow hood  100 . The remotely located suction zone allows the reach of the hood  100  to be extended and its capture efficiency is equivalent to a larger conventional hood with a deeper and more extended canopy. 
         [0026]    Referring now to  FIG. 4 , a configuration similar to that of  FIG. 3  is shown. A bracing structure  365  of angle brackets  320  and  325  supports the eyebrow hoods  100 . The bracing structure  365  allows the hoods  100  to rest on top of the ovens  220  and be connected to them. A common duct  335  may be combined with the bracing structure  365  to form a unitary device for mounting the hoods  100 . This unitary device may be conveniently disconnected from a building&#39;s exhaust system and moved with the ovens  220  rather than installed and left as part of the building&#39;s permanent facilities. 
         [0027]    Referring now to  FIG. 5 , an eyebrow hood  400  is shown in cross-section. The hood  100  has a recess  430  defined by sidewalls  442  and a top  440  which covers up to a forward edge  441  thereof. A back of the recess  430  is defined by a forward filter support plate  415  with openings  416  to permit the flow of exhaust effluent into a plenum  425  and supports (the supports are not shown) to support filter cartridges  410  in the openings  416 . A baffle plate  420  is connected to the filter support plate  415  by a hinge  422 . The hinge  422  allows the baffle plate  420  to be dropped down to the position indicated at  422  to allow the filter cartridges  416  to be removed and installed. 
         [0028]    A grease trough  470  collects grease from the filter cartridges  410 . The angle of the baffle plate  420  with respect to the filter support plate  415  defines a flow transition  435  leading to the faces of the filter cartridges  410 . The position of the baffle plate  420  also defines a slot  435  through which the effluent stream is drawn by an exhaust system (not shown) connected to the plenum  425  by an exhaust collar  405 . The baffle plate  420  also defines a sloping rear planar boundary of the recess  430 . In the present embodiment, the slot  435  is extended by an extended portion  421 , which in this case is horizontal. The baffle plate  420  may also, in an alternative configuration, be flat but inclined at an angle less than that shown in  FIG. 1  to extend the slot  435 . 
         [0029]    Referring now to  FIG. 6 , an eyebrow hood  400  protects an oven  470  such as a pizza oven. A mouth of the oven  475  is well below the eyebrow hood  400  proper. A baffle extension plate  452  bridges a gap between the mouth  475  and a baffle plate  420 . In other respects, the configuration of  FIG. 5  is like that of  FIGS. 1 and 2 . The presence of the baffle extension plate  452  provides for a smooth wall-transition to which thermal plumes may attach and rise toward the slot  135  without the turbulence-inducing effect of abrupt edges, for example as indicated at  472 , as might otherwise be present in the Coanda flow path. 
         [0030]    Referring now to  FIG. 7 , the principles behind the eyebrow hood of the foregoing figures can be extended to backshelf hoods such as indicated at  500 . A canopy portion  510  extends over a cooking process  525  defining, in cooperation with a baffle plate  518  and filter support plate  514 , a plenum  520 , a manifold  530 , and a recess  535 . An inlet slot  515  draws fumes from the cooking process  525  from a forward part of the recess  535  creating a suction zone near the front of the hood  500  which is indicated by arrays of arrows  566 A and  566 B. Side skirts  545  may protect the ends of the hood, in the dimension going into and out of the drawing plane. 
         [0031]    As in the eyebrow hood of  FIGS. 1 and 2 , the baffle plate  518  provides a surface to which thermal plumes, as indicated at  560 , may attach and rise toward the inlet slot  515 . Plumes generated closer to the forward end of the hood  500 , such as indicated at  565 , rise in a plug flow that is independent of any surface, but proximate the suction zone  566 A,  566 B of the inlet slot  515 . By locating the inlet to the exhaust close to the forward edge of the hood  500 , a suction zone is created close to the forward edge which helps to prevent the escape of thermal plumes near the forward edge. 
         [0032]    Referring to  FIGS. 8 through 12 , a common coordinate system with respect to the plane of the drawing page is illustrated in  FIG. 8 . In the normal reading position, the y-axis is left to right, the z-axis is up and down, and the x-axis goes into the drawing plane directly away from the reader. Referring now particularly to  FIG. 9 , a curved baffle plate  615  rises from a back wall plane  616  up to an inlet slot  630 . A hood  610 A defines, in conjunction with a filter support plate  626  and the baffle plate  615 , a plenum  606 , a header chamber  601 , and a recess  607 . An exhaust opening  620  connects the plenum  606  to an exhaust system (not shown). Side skirts  650  may also be provided. This embodiment differs from that of  FIG. 7  in having a smoothly curving baffle plate  615  rather than a flat one and also in the precise matching of the baffle plate  615  surface and that of the back wall  616 . Either of these features may be provided independent of the others. Note that a forward edge  605 A (i.e., lip) of the hood  610 A drops down only as far as the inlet slot  630 . In this arrangement, the suction zone in front of the hood  610 A is maximized. Also note that the forward access  632 A is high due to an absence of the more typical deep recess of a conventional hood design. 
         [0033]    Referring now to  FIG. 10 , an embodiment similar to that of  FIG. 9  is shown. As with  FIG. 9 , the hood  610 B of  FIG. 10  defines, in conjunction with a filter support plate  626  and the baffle plate  615 , a header chamber  602 , and a recess  608 . The present embodiment has a more extended forward edge  605 B (i.e., lip) of the hood  610 B compared to the embodiment of  FIG. 9 . The extended edge  605 B increases the capacity of a recess  608  compared to that of recess  607  of  FIG. 9 . The increased size of the recess allows a greater buffering effect and reduces the height forward access  632 B. The lower height of the forward access increases mean velocity through the forward access region. The configuration of  FIG. 10 , with the increase recess volume may be more suited to lower temperature or lower moisture effluent sources to sources which produce more variable fume plumes in terms of the distribution along the x-axis or in terms of time. 
         [0034]    Referring now to  FIG. 11 , an embodiment similar to that of  FIG. 10  is shown. In the present embodiment, the inlet slot  675  (formed between the baffle  615  and a portion of the front wall  670 ), although in a substantially forward position, is moved, compared to the previous to embodiment, toward the rear. This has the effect of focusing the suction zone downwardly and rendering it somewhat less diffuse. The more middle position may be used in combination with any of the foregoing features. It has been determined to be more suitable for applications where there are fewer external disturbances to disrupt the rising plumes from the cooking process  640 . 
         [0035]    Also illustrated in the present embodiment is a spoiler  618 . The spoiler  618  spreads any Coanda plumes in the x-axis direction so that a fast moving pulsatile thermal plume is less likely to flow past the inlet slot  675 . Essentially, it is a mechanism for transverse (x-direction) mixing of the z-*y-direction momentum that is tangent to the surface of the baffle  615  (or, put another way, the transverse mixing of the component of the flow along this surface&#39;s gradient). Paradigmatically, a transient plume that is localized with respect to the x-axis may overwhelm the suction capacity of the inlet slot  675  at a particular point along x. If such a plume is spread across the x-axis by turbulent mixing, its locally high velocity may be reduced and the resulting wider (and slower) plume may be more easily handled by the suction of the inlet slot  675 . The spoiler may be provided with or without other features and in combination with any of the foregoing features discussed in connection with this or the other embodiments to the same effect. 
         [0036]    Referring to  FIG. 12 , an alternative to the use of a spoiler, such as spoiler  618  in  FIG. 11 , which may have a similar effect, is to make the attachment surface, that of the baffle plate  680 , convex in shape. This reduces the volume of the recess  611  but it increases the resistance to plug flow formation and forces plumes to tend to spread across the surface of the baffle plate  680 . In the present embodiment, the forward edge (i.e., front wall  690 ) of the hood  610 D also curves toward the inlet slot  695 . 
         [0037]    Referring now to  FIGS. 13A-13D , a canopy style hood  700  has an exhaust outlet  730  and an exhaust inlet slot  705  that surrounds the entire canopy  711 . Flow guide plates  720  having the form of a pyramidoid or conoid structure run from a low point  721  up to the inlet slot  705 . A filter support structure  712  supports filters  710  and defines a plenum  714  connecting flow through the filters  710  to the exhaust outlet  730 . The flow guide plates may be provided with a door (not shown) to allow access to the filters  710 . 
         [0038]    Referring now to  FIGS. 14 and 15 , some alternative ways of arranging a filter in combination with a forwardly located exhaust inlet while maintaining a compact configuration and a relatively narrow (and therefore, high velocity) intake, are illustrated. In a hood  800  of  FIG. 14 , a hatch, shown in a closed configuration at  804  and open at  805  provides access to a filter  810  mounted on a plenum  820 . Fumes from an appliance  830  flow through an inlet  815  into a header space  811 , through the filter  810 , into plenum  820  and out through an exhaust outlet  825 . As in previous embodiments, a sloping flow wall  823  runs from the rear toward the front and upwardly to allow fume plumes to attach. A side skirt  822  may be provided to mitigate end effects. In a hood  890  of  FIG. 15 , two hatches  850  and  885  are provided, the hatch  850  shown in a closed configuration at  850  and open at  851 . The hatches  850  and  885  provide access to a filter  810  mounted on a plenum  821 . Fumes from an appliance  830  flow through an inlet  865  into a header space  875 , through the filter  810 , into plenum  821  and out through an exhaust outlet  872 . As in previous embodiments, a sloping flow wall  853  runs from the rear toward the front and upwardly to allow fume plumes to attach. A side skirt  852  may be provided to mitigate end effects. 
         [0039]    Referring to  FIGS. 16A and 16B , a retractable curtain  910  of heat resistant reflective material is drawn from a spool  900  down to cover the sides of stack of ovens  220 . The configuration is not unlike that of a home movie screen, permitting the curtain  910  to be easily retracted out of the way. A weighted bar  915  keeps the bottom of the curtain in place. Alternatively, a curtain (not shown) may be made of rigid material and placed in a similar position. Also, the curtain  910  need not be drawn all the way down. The curtain  910  reduces the air flow required for containment and capture by acting as a convection-inhibiting side curtain. It also increases comfort by reducing radiation to the surrounding space. Finally, the curtain  910  also reduce heat loss of the oven so the oven&#39;s energy consumption is reduced. Variations of the curtain may be provided to achieve these benefits. For example, rigid panels (not shown) that pivot on a vertical axis may be mounted to swing over the sides of the hoods  100  without covering the oven  220  sides. 
         [0040]    It will be observed that various features have been described in connection with the foregoing embodiments. These features may be combined in combination and various subcombinations. As can be seen in  FIGS. 1 to 3 , the exhaust inlet is located as high as possible in a low profile hood  1005  by employing the baffle plate  120  as illustrated. The inlet  135  is defined between the top of the hood  143  and the edge of the baffle. As may be seen in other embodiments, the baffle may have an opening while still providing a high location for the inlet. 
         [0041]    As shown in  FIG. 17 , the baffle  120  (and similarly for the other embodiments) also is aligned to form a substantially continuous wall surface  1000  (shown by the heavy line which is superimposed on the oven/hood combination) extending from the face of the oven  1010  to the baffle portion  1120  leading up to the inlet  1030 . Because the ovens  220  are hot and because fumes escaping from them are hot, they tend to rise aggressively along the surface and also due to the wall-flow (Coanda flow) effect, this continuous surface helps to guide much of the fumes directly to the inlet  1030 . At the same time, the inlet  1030  is located remotely from the oven to create a suction zone positioned to capture rising fumes that are deflected away from the surface  1000  by ambient gusts or by food items on the conveyor shelves  225 . Still further, a lip  1050  is defined to create a small buffer volume between the inlet and the lip  1050  of the hood  1005  to help ensure containment when fume loads are irregular. 
         [0042]    Still another feature of the  FIG. 17  design and other embodiments is the low profile of the hood  1005 , which in preferred embodiments, is wider than it is high. This is advantageous because the overhead clearance for such ovens as  220  may be limited. Also, the side skirts  1015  are taller close to the ovens  220  but narrow toward the lip  1050  to provide greater clearance for workers needing to stand close to the ovens  220  to access the loading and/or unloading trays  225 . 
         [0043]    The above features may be employed in subcombinations. For example, the continuous wall  1000  may be provided in other configurations, for example, with an inlet located lower than the top of the hood  1005  or without side skirts  1015  or lip  1050 . For another example, the low aspect-ratio hood design may have more conventional structures such as ones that do not provide the continuous surface  1000 ; i.e., baffle  120  ( FIG. 1 )  1020  removed.