Patent Publication Number: US-2021170210-A1

Title: Explosion-proof housing

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of PCT Application No. PCT/EP2019/071488 filed on Aug. 9, 2019, which claims priority to German Patent Application No. 10 2018 120 877.4 filed on Aug. 27, 2018, the contents each of which are incorporated herein by reference thereto. 
    
    
     BACKGROUND 
     The invention refers to an explosion-proof housing. The housing is configured to house devices in the housing interior that could serve as ignition sources in explosive atmospheres. The explosion-proof housing separates the housing interior in an explosion-proof manner from the explosive atmosphere in an environment. 
     Such a housing is known from U.S. Pat. No. 4,180,177 A, for example. In this housing an insert for pressure relief is provided in an outer wall by means of which a gas exchange between the housing interior and the environment can occur. In doing so, an explosion pressure in the housing interior can be reduced such that the integrity of the housing is maintained also in the event of an explosion. On the outside the insert is covered by a flap. The cover only opens in the case of a remarkable overpressure in the housing interior. 
     The heat dissipation out of the housing interior into the environment is problematic in explosion-proof housings, if heat sources are arranged in the housing, as for example electrical and/or electronic devices. It has to be avoided that the devices become inoperative due to too high temperatures. In addition, it has to be avoided that the outer walls of the housing have a temperature that in turn may serve as ignition source for the explosive atmosphere. Pressure relief devices are insufficient for such a heat dissipation. 
     The heat dissipation from an explosion-proof housing is usually elaborate and expensive. For example, heat exchangers can be used in order to transport heat by means of an explosion-proof fluid circuit from the housing interior to the outside. Due to such measures, besides the high costs for manufacturing or purchase, additional costs occur for service and maintenance. 
     BRIEF SUMMARY 
     Thus, it can be considered as object of the invention to provide an explosion-proof housing that allows a heat exchange between a housing interior and an environment with simple means. 
     An explosion-proof housing, comprising: a plurality of outer walls that enclose a housing interior and separate it in an explosion-proof manner from an explosive atmosphere in an environment; at least one gas-permeable flameproof insert provided in at least one of the plurality of outer walls, the at least one gas-permeable flameproof insert having an inner side facing the housing interior and an outer side facing the environment; at least one guide device defining a flow channel adjacent to either the inner side or the outer side of the at least one gas-permeable flameproof insert in which gas flows through the at least one gas-permeable flameproof insert; and wherein the at least one guide device is configured to form a main gas flow having a main gas flow direction along the outer side or the inner side of the at least one gas-permeable flameproof insert in the flow channel. 
     The explosion-proof housing has several outer walls that surround a housing interior and separate the housing interior in an explosion-proof manner from an explosive atmosphere in an environment of the housing. Thereby the housing interior is not enclosed in a gas-tight manner. Rather in at least one outer wall at least one gas-permeable and flameproof insert is provided. The insert provides a flameproof gas exchange between the housing interior and the environment. It thus forms a flameproof through channel for a gas flow. For example, the flameproof insert can comprise a porous or a mesh comprising structure part, e.g. an entangled fiber structure part. In another embodiment one or more grid layers can be arranged on top of one another in order to form a grid for the structure part. The gas-permeable ignition-flameproof insert can have an average mesh or pore dimension in the range of about 80 μm to 250 μm. The thickness of the gas-permeable flameproof insert in gas flow direction has an amount of at least 5 mm or at least 10 mm, for example. Preferably the insert is manufactured from a material that has a temperature resistance of at least 400° C. For example, the insert can be manufactured from chromium alloy steel, such as stainless steel. The insert can comprise an entangled fiber structure and/or grid structure and/or another porous structure in order to allow the gas exchange on one hand and to inhibit the escape of hot gases, sparks or flames on the other hand that could initiate an ignition in the explosive atmosphere. 
     The insert has an inner side facing the housing interior and an outer side facing the environment. The housing comprises at least one guide device that is arranged adjoining the respective inner side or outer side of the at least one insert and forms a flow channel there. Gases flow out of the housing interior or out of the environment through the at least one insert into the flow channel. In doing so, either warm gas or warm air can flow out of the housing interior outwardly into the flow channel. Alternatively, cooler gas or cooler air can flow from the outside into the housing interior. The guide device is configured to define a main gas flow having a main gas flow direction in the flow channel. The main gas flow direction is thereby orientated obliquely or orthogonal to the direction in which the gas flows through the at least one insert into the flow channel. The main gas flow direction is orientated substantially parallel to the respective adjoining outer side or inner side of the at least one insert and/or parallel to the adjacent outer wall of the housing. 
     Due to this arrangement, a suction or chimney effect is created in the flow channel. In doing so, an effective gas flow can be created without additional active flow creation devices (such as fans, pumps or the like) that in turn improves the gas exchange and thus the heat exchange between the environment and the housing interior. At least optionally present active flow creation devices can be defined with minor dimensions. In doing so, the energy efficiency is improved and less additional heat is created. Because each active flow creation device involves energy losses and creates additional heat that in turn has to be dissipated in the environment. If such devices are arranged outside the housing interior, they have to be configured in an explosion-proof manner. 
     Preferably the explosion-proof housing does not contain any cooling fluid circuits. 
     The gas flows are created either exclusively by means of convection and/or by optionally additional fans. 
     It is advantageous, if the flow channel is orientated such that the main flow direction is orientated parallel to the vertical or comprises at least a vertical direction component, wherein the vertical direction component is preferably greater than the horizontal direction component. 
     In an alternative embodiment the main flow direction can also be horizontal or substantially horizontal. In this case it is preferred, if the gas flow through the at least one insert is orientated substantially vertically. 
     In a preferred embodiment the guide device is arranged outside the housing interior and is closed to the top, e.g. by means of a cover. In doing so, the ingress of precipitation or the like into the flow channel can be avoided. 
     Preferably the length of the flow channel in main flow direction has an amount of at least 50% to 75% of the length of the adjacent outer wall of the housing in the main flow direction. For example, the flow channel can extend in main flow direction substantially along the entire adjacent outer wall or also beyond it. 
     It is advantageous, if the cross-section of the flow channel in each spatial direction within the cross-sectional plane has a smaller dimension than the length of the flow channel orthogonal to the cross-sectional plane. 
     It is preferred, if the cross-section of the flow channel is smaller than the sum of all outer surfaces of the inserts adjoining the flow channel or smaller than the outer surface adjoining the flow channel, if only one insert is present. 
     It is advantageous, if the flow channel has a channel inlet and a channel outlet that is arranged with distance to the channel inlet in main flow direction. Preferably the channel inlet and the channel outlet are arranged in main flow direction as far as possible away from each other. 
     In an embodiment the channel inlet and the channel outlet can open into the environment. Thereby the at least one insert can be arranged between the channel inlet and the channel outlet in main flow direction. In doing so, a main flow through the flow channel is created that flows from the channel inlet along all of the present inserts up to the channel outlet. In this configuration a good suction effect is created in order to effectuate gas flows through the inserts. 
     In another embodiment the channel inlet and/or the channel outlet can be formed by one or more or all of the present inserts. For example, the flow channel is open to the environment in this configuration only at one location, wherein this location forms either the channel outlet or the channel inlet. 
     It is particularly advantageous, if the flow channel is closed between the channel inlet and the channel outlet or gas flows in or out of the flow channel only through the at least one present insert between the channel inlet and the channel outlet. In doing so, it is achieved that no additional air is sucked from the environment, but that a sufficiently strong suction is achieved for the gas exchange through the at least one insert. 
     Specifically the guide device can be open at one side facing the at least one insert in order to establish a gas flow connection between the insert and the flow channel. In addition, the flow channel can have one or more openings in order to form a channel inlet or a channel outlet or a channel inlet as well as a channel outlet. Apart from these defined gas flow openings, the flow channel is preferably closed. 
     The expression “closed” does not exclusively, but amongst others mean a gas tight configuration. Minor gas leakages having a negligible volume flow or mass flow compared with the main flow in the flow channel may be present, e.g. leakage flows due to gas leakages having a volume or mass flow that has an amount of not more than 10% of the volume or mass flow of the main gas flow through the flow channel. 
     It is advantageous, if multiple separate flow channels are provided, such that a good heat exchange can be achieved at multiple locations, e.g. at opposite outer walls of the housing. 
     In an embodiment a separate gas channel can be provided that is in flameproof flow connection with the housing interior. Air or gas can be supplied into the housing interior or can be sucked out of the housing interior through this gas channel. For this the gas channel can be in connection with a fan that can be arranged either inside the housing interior or outside the housing interior. The gas channel can be open either in the explosive atmosphere or in a non-explosive safe atmosphere. 
     In a preferred embodiment the housing is configured in the ignition protection category “flameproof enclosure” (Ex-d) according to the standards EN 60079-1 or IIC 60079-1. 
     In an embodiment at least one insert is arranged in an upper outer wall of the housing. In another embodiment at least one insert is arranged in at least one lateral outer wall. Particularly one or more inserts can be provided in opposite lateral outer walls respectively. Also a combination of at least one insert in an upper outer wall and at least one insert in at least one lateral outer wall is advantageous. Generally, at least one insert can be present in an arbitrary combination of the provided outer walls respectively. Inside or outside one flow channel or as an option the additional gas channel can adjoin the respective outer wall of the housing respectively. 
     In an embodiment the flow channel is arranged inside the housing interior. Thereby the guide device comprises an attachment surface for a device to be cooled that is arranged in the housing interior, e.g. an electrical and/or an electronic device. In addition, or as an alternative, a section of the flow channel or the guide device can be formed by a wall of a device arranged in the housing interior. In doing so, a particularly good heat transfer between the wall of the device arranged in the housing interior and the gas flow inside the flow channel can be achieved. 
     Advantageous embodiments of the invention are derived from the dependent claims, the description and the drawings. In the following preferred embodiments of the invention are explained in detail based on the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  a schematic block-diagram-like illustration of an embodiment of an explosion-proof housing, 
         FIG. 2  a perspective sectional illustration of another embodiment of an explosion-proof housing, 
         FIG. 3  a schematic block-diagram-like illustration of another embodiment of an explosion-proof housing, 
         FIG. 4  a perspective illustration of the embodiment according to the block diagram of  FIG. 3 , 
         FIG. 5  a perspective illustration of another embodiment of an explosion-proof housing, 
         FIG. 6  a sectional illustration of the embodiment of  FIG. 5  in perspective view, 
         FIG. 7  a perspective illustration of another embodiment of an explosion-proof housing, 
         FIG. 8  a perspective sectioned illustration of the embodiment of  FIG. 7  and 
         FIGS. 9 and 10  schematic perspective illustrations respectively of a gas-permeable flameproof structure for an insert, as can be used in any embodiment of the explosion-proof housing. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an embodiment of an explosion-proof housing  10  with multiple outer walls  11  that enclose a housing interior  12 . In the embodiment the housing  10  has an upper outer wall  11   a , a lower outer wall  11   b  and multiple, e.g. four lateral outer walls  11   c  that connect the upper outer wall  11   a  and the lower outer wall  11   b  with each other. The housing interior  12  is substantially cuboid-shaped, whereby also arbitrary other housing construction shapes could be used, such as other prismatic housing shapes or cylindrical housing shapes. 
     In the embodiment described here, the explosion-proof housing  10  is configured in the explosion-proof category “flameproof enclosure” (Ex-d). 
     The outer walls  11  separate the housing interior  12  from an environment  13  having an explosive atmosphere in a flameproof manner. A gas exchange occurs between the housing interior  12  and the environment  13  in order to dissipate heat by means of the gas flow from the housing interior  12  outward in the environment  13 . At least one device  14  is arranged in the housing interior, particularly an electrical and/or electronic device  14  that may serve as ignition source for the explosive atmosphere in the environment  13 . The device  14  is thus enclosed by housing  10  such that sparks, flames or hot gases from the housing interior  12  cannot escape into the environment  13 . During operation of the at least one device  14  heat is created in the housing interior  12  that can be dissipated in the environment  13  by means of the gas exchange. 
     In order to allow this gas exchange, at least one outer wall  11  of the housing  10  comprises a gas-permeable flameproof insert  15 . As schematically illustrated in  FIG. 1 , in one outer wall  11  and for example in two lateral outer walls  11   c , also multiple of such inserts  15  can be provided respectively. It is also possible to use one large insert  15  instead of multiple small area inserts  15  that is held by means of suitable holding means, e.g. a holding grid, in an opening of the respective outer wall  11 . A multiplicity of possibilities exist for the mechanical arrangement of the at least one insert  15  in a respective outer wall  11 . Either the at least one insert  15  can be mechanically attached by holding means. The insert  15  can be directly or indirectly connected with the surrounding area of the outer wall  11  in a force-fit and/or form-fit and/or material bond manner or by means of an adhesive connection. 
     According to the example, the at least one insert  15  is formed by a porous and/or mesh comprising material structure that allows a gas exchange through the material structure and extinguishes on the other hand flames, sparks and hot gases. The material structure therefore fulfills the flameproof condition and allows, however, a gas flow through the material structure. For example, the material structure can be formed by a porous structure part  16 . The porous structure part  16  can comprise an entangled fiber structure material. It comprises entangled disorderly arranged fibers that can have a diameter of 70 μm to 130 μm. Alternatively the porous structure part  16  can comprise porous sinter material and/or foam material or the like. The pore size of the porous structure part  16  can be at least 80 μm and at most 250 μm. The porosity of the porous structure part  16  is preferably in a range of 60% to 80%. 
       FIG. 10  illustrates an alternative embodiment of a material structure that could be used as insert  15 . The material structure according to  FIG. 10  is configured as mesh or grid structure part  17 . The mesh size has an amount of about at least 80 μm and at most 250 μm. For example, multiple single layers  18  can be arranged on top of one another and can be connected directly or indirectly with one another for creating the mesh size. Thereby the grid rod orientations of each layer  18  relative to another layer can be arranged in a different angle and/or offset in order to obtain the desired effective mesh size of the grid structure part  17 . The number of layers  18  can vary depending on the configuration of each single layer. 
     Each insert can also comprise a combination of a porous structure part  16  and a grid structure part  17 . 
     Each insert  15  comprises an inner side  25  facing the housing interior, as well as an outer side  26  facing the environment. The housing  10  comprises one guide device  27  respectively that forms a flow channel  28  adjoining the insert  15  on an outer wall  11  and according to the example, the lateral outer walls  11   c  in which at least one insert  15  is provided respectively. In the embodiment illustrated in  FIG. 1 , the flow channels  28  and the guide device  27  are arranged outside the housing interior  12  and attached on the outside of the respective lateral outer walls  11   c . At one location the respective flow channel  28  is at least partly limited by the outer wall  11 . In each flow channel  28  a main gas flow G is effectuated that flows in a main flow direction R. In a preferred embodiment the main flow direction R can be orientated vertically or can comprise a vertical component that is preferably greater than the horizontal component of the main flow direction R. 
     Each guide device  27  has multiple guide walls  29  that enclose the flow channel  28  in circumferential direction around the main flow direction R at least partly only on three sides and limit the flow channel  28  together with the adjacent lateral outer wall  11   c . In the embodiments illustrated in  FIGS. 1 and 2  each flow channel  28  is in flow connection with the environment  13  at two opposite ends in main flow direction R, whereby a channel inlet  30  is formed at one end and a channel outlet  31  is formed at the other end. According to the example, the channel inlet  30  is arranged vertically underneath the channel outlet  31 . Adjacent to the channel inlet  30  and/or adjacent to the channel outlet  31  a fan  32  can be arranged in each flow channel  28 , as is highly schematically illustrated in  FIG. 1 . 
     In the embodiment schematically illustrated in  FIG. 1  the channel inlet  30  is configured being open downward. Alternatively, the channel inlet  30  could also have one or more inlet openings that are provided in at least one of the guide walls  29  of the guide device  27 , as shown in  FIG. 2  by way of example. 
     In order to avoid ingress of precipitation, as rain water, snow or the like in the flow channels, a cover  35  can be present adjacent to the channel outlet  31 . The cover  35  guides precipitations laterally past the flow channel  28 . The cover  35  is part of the guide device  27 . The guide device  27  can thus be configured to direct the main flow direction R through the respective flow channel  28  as well as for realization of an IP-protection class for the housing  10 . 
     In the embodiment according to  FIG. 1  the main flow direction R is defined along the respective lateral outer walls  11   c  and thus along the outer surfaces  26  of the inserts. The main gas flow G passing the inserts  15  thus creates a suction effect in order to entrain gas from the housing interior  12 . By means of this gas exchange, heat can be transferred from the housing interior  12  into the environment  13 . The devices  14  are thus cooled by means of convection. In the embodiment illustrated in  FIG. 1  the suction or chimney effect is further improved in that the main flow direction R is orientated substantially vertically. 
     It is in addition schematically illustrated in  FIG. 1  that at least one fan  32  can be provided also in the housing interior  12  as an option. The at least one fan  32  in the housing interior  12  can be provided in addition or as an alternative to the at least one fan  32  in each flow channel  28 . The arrangement of the fan  32  in the housing interior  12  has the advantage that the fan  32  itself must not be configured in an explosion-proof manner. 
     The embodiments according to  FIGS. 1 and 2  are substantially identical. In the embodiment shown in  FIG. 1  the channel inlets  30  are arranged on the level of the lower housing wall  11   b  or slightly above the lower housing wall  11   b . Different to this the channel inlets  30  can also be arranged below the lower outer wall  11   b  by means of an extension of the respective flow channel  28  by means of the guide walls  29 . In both embodiments the channel outlets  31  are arranged above the upper housing wall  11   a . In modification thereto the channel outlets  31  can also be arranged on the same level as or below the upper outer wall  11   a.    
     Another embodiment of a housing  10  is illustrated in  FIGS. 3 and 4 , wherein  FIG. 3  shows a block-diagram-like illustration and  FIG. 4  shows a perspective illustration of an embodiment. In this embodiment an additional insert  15  is provided in the upper outer wall  11   a  or at another location, wherein the insert does not adjoin a flow channel  28 . Rather the insert  15  provides a flow connection between the housing interior  12  and a separate gas channel  36 . In the embodiment the separate gas channel  36  is configured as supply channel and connected to a pressure source  37 , e.g. an external fan. For cooling pressurized gas, particularly air, is supplied into the housing interior  12  by means of the pressure source  37 . By means of the insert  15  a flameproof connection is established between the gas channel  36  and the housing interior  12 . 
     As in the previous embodiments, flow channels  28  are formed by means of a guide device  27  on two opposite lateral outer walls  11   c  respectively. The overpressure created in the housing interior  12  by means of the gas supply through the gas channel  36  leads to a gas flow through the at least one insert  15  in the flow channel or flow channels  28 . Different to the previous embodiments, the flow channels  28  have only one direct flow connection to the environment  13  by means of a respective channel outlet  31 . In the embodiment the channel outlet  31  is arranged in the region of the lower outer wall  11   b . In the region of the upper outer wall  11   a  the flow channels  28  are closed by the guide device  27  according to the example. 
     Apart therefrom, reference can be made to the explanation of the previous embodiments. 
     In the embodiments of the housing  10  illustrated in  FIGS. 5 and 6 , a guide device  27  is arranged on the outside of the upper outer wall  11   a . At least one insert  15  is arranged in the upper outer wall  11   a . Heat rising in the housing interior can thus pass through the at least one insert  15  into the flow channel  28  formed by the guide device  27 . The guide device  27  covers the at least one insert  15  toward the top such that not only a guidance of the main gas flow G is achieved, but in addition an IP-protection can be obtained. The main flow direction R inside the flow channel  28  adjoining the upper outer wall  11   a  is orientated parallel to the upper outer wall  11   a  according to the example approximately horizontally. 
     The two further flow channels or guide devices  27  at the lateral outer walls  11   c  are optional and can also be omitted in the embodiment according to  FIGS. 5 and 6 . 
     A housing  10  is illustrated in  FIGS. 7 and 8  in which the guide device  27  is arranged inside the housing interior  12 . A guide wall  29  provides an attachment surface  40  for attachment of a device  14 , particularly an electrical and/or electronic device inside the housing interior  12 . The guide wall  29  is arranged substantially parallel to the opposite lateral outer wall  11   c  in the flow channel  28 . The channel inlet  30  and the channel outlet  31  are formed in the lateral outer wall  11   c  limiting the flow channel  28  to the outward by arranging at least one insert  15  in the lateral outer wall  11   c  respectively. In this embodiment the flow channel  28  comprises a flow connection in the housing interior  12 . In modification thereto the flow channel  28  could be at least in sections open with regard to the housing interior  12 . By closing the flow channel  28  toward the housing interior  12 , a superior main gas flow G can be achieved. As illustrated in  FIGS. 7 and 8 , the channel outlet  31  is arranged vertically above the channel inlet  30 . According to the example, the channel inlet  30  is arranged in the region of the lower outer wall  11   b , whereas the channel outlet  31  is arranged in the region of the upper outer wall  11   a.    
     In this embodiment the attachment surface  40  is cooled by the main gas flow G through the flow channel  28 . In doing so, heat can be dissipated from the device  14  to the main gas flow G and therefrom to the environment  13 . 
     In a modified embodiment a part of the attachment surface  40  can be omitted and the limitation of the flow channel can be realized not by a guide wall  29 , but directly by a wall or an outer surface of the device  14 . In addition, this wall or outer surface of the device  14  can also have cooling ribs. 
     In all embodiments one or more heat sinks can be attached on the at least one device  14  arranged in the housing interior for improving the heat dissipation out of the housing. 
     In all embodiments at least one flow channel  28  is provided, but also multiple, e.g. two or three, flow channels  28  can be formed by a respective separate guide device  27 . Preferably, the present flow channels  28  are arranged adjoining to different outer surfaces  11  of the housing  10 . Each flow channel  28  can extend adjoining to an outer wall  11  on the inside or the outside. 
     In some embodiments the main flow direction R of the main gas flow G is at least in one of or in multiple of the provided flow channels  28  orientated vertically or has a vertical direction component that is greater than a horizontal direction component. In one or more alternative embodiments at least one flow channel is provided in which the main flow direction R is orientated substantially horizontally. 
     In any of the embodiments described above, the at least one flow channel can be configured in a closed manner between a channel inlet  30  and a channel outlet  31  apart from the gas flow through the at least one insert  15 . In the embodiments the at least one insert  15  is preferably arranged between the channel inlet  30  and the channel outlet  31 . 
     The length of the at least one flow channel in main flow direction R is preferably longer than its dimension in the two spatial directions within a cross-sectional plane orthogonal to the main flow direction R. In other words a width and a height in a cross-sectional plane of a flow channel  28  are smaller than a length orthogonal to this cross-sectional plane. Preferably the length of the at least one flow channel  28  is at least as long as 50% to 75% of the length of the directly adjacent outer wall  11  of the housing with view in main flow direction R. 
     The embodiments described above can be combined with each other. For example, guide devices  27  according to one of the embodiments of  FIG. 1 or 2  can be provided on the lateral outer walls  11   c  in the embodiment according to  FIGS. 5 and 6 . It is in addition possible that the flow channel  28  provided in the housing interior  12 , according to  FIGS. 7 and 8 , is in addition or as an alternative provided in any other embodiment. 
     In all embodiments at least one fan  32  can be arranged in at least one provided flow channel  28  and/or in the housing interior  12  respectively, in order to improve the flow behavior. As an alternative, all embodiments can be free of fans  32 . 
     The invention refers to an explosion-proof housing  10  with outer walls  11  that enclose a housing interior  12  relative to an explosive atmosphere in a flameproof manner. At least one insert  15  is arranged in at least one outer wall  11 . The insert  15  allows a gas flow between the housing interior  12  and an environment  13  around the housing  10 . The at least one insert  15  is configured such that a gas flow with sufficient mass or volume flow is allowed, however, a flameproof flow connection is established. On the outer wall  11  having the at least one insert  15 , a guide device  27  is attached that limits a flow channel  28  together with the respective outer wall  11 . The flow channel  28  defines a main flow direction R of a main gas flow G through the flow channel  28  substantially parallel to the directly adjoining outer wall  11 . In doing so, the gas exchange between the environment  13  and the housing interior  12  can be improved and devices  14  provided in the housing interior  12  can be cooled. 
     LIST OF REFERENCE SIGNS 
     
         
         
           
               10  housing 
               11  outer wall 
               11   a  upper outer wall 
               11   b  lower outer wall 
               11   c  lateral outer wall 
               12  housing interior 
               13  environment 
               14  device 
               15  insert 
               16  porous structure part 
               17  grid structure part 
               18  layer 
               25  inner side 
               26  outer side 
               27  guide device 
               28  flow channel 
               29  guide wall 
               30  channel inlet 
               31  channel outlet 
               32  fan 
               35  cover 
               36  gas channel 
               37  pressure source 
               40  attachment surface 
             G main gas flow 
             R gas flow direction