Abstract:
Dosing and mixing exhaust gas includes directing exhaust gas towards a periphery of a mixing tube that is configured to direct the exhaust gas to flow around and through the mixing tube to effectively mix and dose exhaust gas within a relatively small area. Some mixing tubes include a slotted region and a non-slotted region. Some mixing tubes include a louvered region and a non-louvered region. Some mixing tubes are offset within a mixing region of a housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is being filed on Sep. 12, 2014, as a PCT International Patent application and claims priority to U.S. Patent Application Ser. No. 61/877,749 filed on Sep. 13, 2013, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    Vehicles equipped with internal combustion engines (e.g., diesel engines) typically include exhaust systems that have aftertreatment components such as selective catalytic reduction (SCR) catalyst devices, lean NOx catalyst devices, or lean NOx trap devices to reduce the amount of undesirable gases, such as nitrogen oxides (NOx) in the exhaust. In order for these types of aftertreatment devices to work properly, a doser injects reactants, such as urea, ammonia, or hydrocarbons, into the exhaust gas. As the exhaust gas and reactants flow through the aftertreatment device, the exhaust gas and reactants convert the undesirable gases, such as NOx, into more acceptable gases, such as nitrogen and water. However, the efficiency of the aftertreatment system depends upon how evenly the reactants are mixed with the exhaust gases. Therefore, there is a need for a flow device that provides a uniform mixture of exhaust gases and reactants. SCR exhaust treatment devices focus on the reduction of nitrogen oxides. 
         [0003]    In SCR systems, a reductant (e.g., aqueous urea solution) is dosed into the exhaust stream. The reductant reacts with nitrogen oxides while passing through an SCR substrate to reduce the nitrogen oxides to nitrogen and water. When aqueous urea is used as a reductant, the aqueous urea is converted to ammonia which in turn reacts with the nitrogen oxides to covert the nitrogen oxides to nitrogen and water. Dosing, mixing and evaporation of aqueous urea solution can be challenging because the urea and by-products from the reaction of urea to ammonia can form deposits on the surfaces of the aftertreatment devices. Such deposits can accumulate over time and partially block or otherwise disturb effective exhaust flow through the aftertreatment device. 
       SUMMARY 
       [0004]    An aspect of the present disclosure relates to a method for dosing and mixing exhaust gas in exhaust aftertreatment. Another aspect of the present disclosure relates to a dosing and mixing unit for use in exhaust aftertreatment. More specifically, the present disclosure relates to a dosing and mixing unit including a mixing tube configured to direct exhaust gas flow to flow around and through the mixing tube to effectively mix and dose exhaust gas within a relatively small area. 
         [0005]    In accordance with some aspects, the mixing tube includes a slotted region and a non-slotted region. In examples, the slotted region extends over a majority of a circumference of the mixing tube. In examples, the slotted region extends over a majority of an axial length of the mixing tube. In examples, a circumferential width of the non-slotted region is substantially larger than a circumferential width of a gap between slots of the slotted region. 
         [0006]    In accordance with some aspects, the mixing tube includes a louvered region and a non-louvered region. The louvered region extends over a majority of a circumference of the mixing tube. In examples, the louvered region extends over a majority of an axial length of the mixing tube. In examples, a circumferential width of the non-slotted region is substantially larger than a circumferential width of a gap between louvers of the louvered region. 
         [0007]    In accordance with some aspects, the mixing tube is offset within a mixing region of a housing. For example, the mixing tube can be located closer to one wall of the housing than to an opposite wall of the housing. 
         [0008]    A variety of additional aspects will be set forth in the description that follows. These aspects can relate to individual features and to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad concepts upon which the embodiments disclosed herein are based. 
     
    
     
       DRAWINGS 
         [0009]    The accompanying drawings, which are incorporated in and constitute a part of the description, illustrate several aspects of the present disclosure. A brief description of the drawings is as follows: 
           [0010]      FIG. 1  is a schematic representation of a first exhaust treatment system incorporating a doser and mixing unit in accordance with the principles of the present disclosure; 
           [0011]      FIG. 2  is a schematic representation of a second exhaust treatment system incorporating a doser and mixing unit in accordance with the principles of the present disclosure; 
           [0012]      FIG. 3  is a schematic representation of a third exhaust treatment system incorporating a doser and mixing unit in accordance with the principles of the present disclosure; 
           [0013]      FIG. 4  is a perspective view of an example doser and mixing unit configured in accordance with the principles of the present disclosure; 
           [0014]      FIG. 5  is a cross-sectional view of the doser and mixing unit of  FIG. 4  taken along the plane  5  of  FIG. 4 ; 
           [0015]      FIG. 6  is a cross-sectional view of the doser and mixing unit of  FIG. 4  taken along the housing axis C shown in  FIG. 5 ; 
           [0016]      FIG. 7  is a perspective view of an example mixing tube arrangement suitable for use with the doser and mixing unit of  FIG. 4 ; 
           [0017]      FIG. 8  is a side elevational view of the mixing tube arrangement of  FIG. 7 ; and 
           [0018]      FIG. 9  is an end view of the mixing tube arrangement of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Reference will now be made in detail to the exemplary aspects of the present disclosure that are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like structure. 
         [0020]      FIGS. 1-3  illustrate various exhaust flow treatment systems including an internal combustion engine  201  and a dosing and mixing unit  207 .  FIG. 1  shows a first treatment system  200  in which a pipe  202  carries exhaust from the engine  201  to the dosing and mixing unit  207 , where reactant (e.g., aqueous urea) is injected (at  206 ) into the exhaust stream and mixed with the exhaust stream. A pipe  208  carries the exhaust stream containing the reactant from the dosing and mixing unit  207  to a treatment substrate (e.g., an SCR device)  209  where nitrogen oxides are reduced to nitrogen and water. 
         [0021]      FIG. 2  shows an alternative system  220  that is substantially similar to the system  200  of  FIG. 1  except that a separate aftertreatment substrate  203  (e.g., a Diesel Particulate Filter (DPF) or Diesel Oxidation Catalyst (DOC)) is positioned between the engine  201  and the dosing and mixing unit  207 . The pipe  202  carries the exhaust stream from the engine  201  to the aftertreatment substrate  203  and another pipe  204  carries the treated exhaust stream to the dosing and mixing device  207 .  FIG. 3  shows an alternative system  240  that is substantially similar to the system  220  of  FIG. 2  except that the aftertreatment device  203  is combined with the dosing and mixing unit  207  as a single unit  205 . 
         [0022]    A selective catalytic reduction (SCR) catalyst device is typically used in an exhaust system to remove undesirable gases such as nitrogen oxides (NOx) from the vehicle&#39;s emissions. SCR&#39;s are capable of converting NOx to nitrogen and oxygen in an oxygen rich environment with the assistance of reactants such as urea or ammonia, which are injected into the exhaust stream upstream of the SCR through a doser. In alternative implementations, other aftertreatment devices such as lean NOx catalyst devices or lean NOx traps could be used in place of the SCR catalyst device, and other reactants (e.g., hydrocarbons) can be dispensed by the doser. 
         [0023]    A lean NOx catalyst device is also capable of converting NOx to nitrogen and oxygen. In contrast to SCR&#39;s, lean NOx catalysts use hydrocarbons as reducing agents/reactants for conversion of NOx to nitrogen and oxygen. The hydrocarbon is injected into the exhaust stream upstream of the lean NOx catalyst. At the lean NOx catalyst, the NOx reacts with the injected hydrocarbons with the assistance of a catalyst to reduce the NOx to nitrogen and oxygen. While the exhaust treatment systems  200 ,  220 ,  240  are described as including an SCR, it will be understood that the scope of the present disclosure is not limited to an SCR as there are various catalyst devices (a lean NOx catalyst substrate, a SCR substrate, a SCRF substrate (i.e., a SCR coating on a particulate filter), and a NOx trap substrate) that can be used in accordance with the principles of the present disclosure. 
         [0024]    The lean NOx traps use a material such as barium oxide to absorb NOx during lean burn operating conditions. During fuel rich operations, the NOx is desorbed and converted to nitrogen and oxygen by reaction with hydrocarbons in the presence of catalysts (precious metals) within the traps. 
         [0025]      FIGS. 4-6  show a dosing and mixing unit  100  suitable for use as dosing and mixing unit  207  in the treatment systems disclosed above. The dosing and mixing unit  100  includes a housing  102  having an interior  104  accessible through an inlet  101  and an outlet  109 . A mixing tube arrangement  110  is disposed within the interior  104  (see  FIGS. 5 and 6 ). With reference to the treatment systems  200 ,  220 ,  240 , the inlet  101  receives exhaust flow from the engine  201  (or the treatment substrate  203 ) and the outlet  109  leads to the SCR  209 . In certain implementations, the treatment substrate  203  also can be disposed within the housing  102  to form the combined unit  205  of  FIG. 3 . 
         [0026]    As shown in  FIG. 5 , the housing  102  extends from a first end  105  to a second end  106  along a housing axis C. In an example, the housing axis C (i.e., an inlet axis) defines a flow axis for the inlet  101 . The housing  102  also extends from a third end  107  to a fourth end  108  along a longitudinal axis L (i.e., outlet axis) of the mixing tube arrangement  110 . In certain implementations, the housing axis C is not centered between the third and fourth ends  107 ,  108 . In an example, the housing axis C is located closer to the third end  107 . In certain implementations, the longitudinal axis L is not centered between the first and second ends  105 ,  106 . In an example, the longitudinal axis L is located closer to the second end  106 . 
         [0027]    In an example, the longitudinal axis L defines a flow axis for the outlet  109 . In certain implementations, the second end  106  is closed. In certain implementations, the second end  106  is curved to define a contoured interior surface  122 . In an example, the second end  106  defines half of a cylindrical shape. In certain implementations, the third end  107  defines a port  140  at which a doser can be coupled (see  FIG. 4 ). In other implementations, a doser can be disposed within the housing  102  at the third end  107 . 
         [0028]    As shown in  FIG. 6 , the housing  102  also has a first side  123  and a second side  124  that extend between the first and second ends  105 ,  106  and between the third and fourth ends  107 ,  108 . In certain implementations, the first and second sides  123 ,  124  are closed. The closed second end  106  contours between the first and second sides  123 ,  124  (see  FIG. 6 ). As shown in  FIG. 6 , the interior  104  of the housing  102  defines an inlet region  120  having a first volume and a mixing region  121  having a second, larger volume. The mixing region  121  extends from the inlet region  120  to the second end  106  of the housing  102 . The mixing tube arrangement  110  is disposed within the mixing region  121 . 
         [0029]    As shown in  FIG. 6 , exhaust gas G flows from the inlet  101  towards the second end  106  of the housing  102 . As the exhaust gas G approaches the mixing tube arrangement  110 , some of the exhaust gas G begins to swirl within the housing interior  104 . The mixing tube arrangement  110  causes the exhaust gas G to swirl about the longitudinal axis L ( FIG. 5 ) of the mixing tube arrangement  110 . In certain implementations, the mixing tube arrangement  110  defines slots  113  (which will be discussed in more detail below) through which the exhaust gas G enters the mixing tube arrangement  110 . In certain implementations, the mixing tube arrangement  110  includes louvers  114  (which will be discussed in more detail below) that direct the exhaust gas G through the slots  113  in a swirling flow along a first circumferential direction D 1  ( FIG. 6 ). 
         [0030]    A doser (or doser port) is disposed at one end of the mixing tube arrangement  110  (see  FIG. 5 ). The doser is configured to inject reactant (e.g., aqueous urea) into the swirling flow G. Examples of the reactant include, but are not limited to, ammonia, urea, or a hydrocarbon. The doser can be aligned with the longitudinal axis L of the mixing tube arrangement  110  so as to generate a spray pattern concentric about the axis L. In other embodiments, the reactant doser may be positioned upstream from the mixing tube arrangement  110  or downstream from the mixing tube arrangement  110 . The opposite end of the mixing tube arrangement  110  defines the outlet  109  of the unit  100 . Accordingly, the reactant and exhaust gas mixture is directed in a swirling flow out through the outlet  109  of the housing  102 . 
         [0031]    In other implementations, the dosing and mixing unit  100  can be used to mix hydrocarbons with the exhaust to reactivate a diesel particulate filter (DPF). In such implementations, the reactant doser injects hydrocarbons into the gas flow within the mixing tube arrangement  110 . The mixed gas leaves the mixing tube arrangement  110  and is directed to a downstream diesel oxidation catalyst (DOC) at which the hydrocarbons ignite to heat the exhaust gas. The heated gas is then directed to the DPF to burn particulate clogging the filter. 
         [0032]    In some implementations, the mixing tube arrangement  110  is offset within the mixing region  121 . For example, the mixing tube arrangement  110  can be disposed so that a cross-sectional area of the annulus is decreasing as the flow travels along a perimeter of the mixing tube arrangement  110 . In the example shown, the mixing tube arrangement is located closer to the second side  124  than to the first side  123 . In other implementations, however, the mixing tube arrangement  110  can be located closer to the first side  123 . In some implementations, offsetting the mixing tube arrangement  110  guides the exhaust flow in the first circumferential direction D 1 . In some implementations, offsetting the mixing tube arrangement  110  inhibits exhaust gases G from flowing in an opposite circumferential direction. 
         [0033]    For example, offsetting the mixing tube arrangement may create a high pressure zone  125  and a flow zone  126 . The high pressure zone  125  is defined where the mixing tube arrangement  110  approaches the closest side (e.g., the second side  124 ). As the exterior surface of the mixing tube arrangement  110  approaches the housing side  124 , less flow can pass between the mixing tube arrangement  110  and the side  124 . Accordingly, the flow pressure builds and directs the exhaust gases away from the high pressure zone  125 . The flow zone  126  is defined along the portions of the mixing tube  110  that are spaced farther from the wall (e.g., side wall  123 , interior surface  122 ), thereby enabling flow between the mixing tube arrangement  110  and the wall. 
         [0034]    In certain implementations, a portion of the mixing tube arrangement  110  contacts the closest side wall (e.g., side wall  124 ). For example, a distal end of a louver  114  (see  FIGS. 7-9 ) of the mixing tube arrangement  110  may contact (see  128  of  FIG. 6 ) the closest side wall  124 . In such implementations, the contact  128  between the mixing tube arrangement  110  and the wall  124  further inhibits (or blocks) flow in the opposite circumferential direction. 
         [0035]      FIGS. 7-9  illustrate one example mixing tube arrangement  110  including a tube body  111  defining a hollow interior  112 . The tube body  111  has a length L 1 . The tube body  111  has a slotted region  115  extending over a portion of the tube body  111 . One or more slots  113  are defined through a circumferential surface of the tube body  111  at the slotted region  115 . The slots  113  lead from an exterior of the tube body  111  into the interior  112  of the tube body  111 . In some implementations, the slots  113  include axially-extending slots  113 . In certain implementations, the tube body  111  defines no more than one axial slot  113  per radial position along the circumference of the tube body  111 . In certain implementations, the slotted region  115  includes portions of the tube body  111  extending circumferentially between the slots  113  in the slotted region  115 . 
         [0036]    In some implementations, the slotted region  115  defines multiple slots  113 . In certain implementations, the slotted region  115  defines between five slots  113  and twenty-five slots  113 . In certain implementations, the slotted region  115  defines between ten slots  113  and twenty slots  113 . In an example, the slotted region  115  defines about fifteen slots  113 . In an example, the slotted region  115  defines about fourteen slots  113 . 
         [0037]    In an example, the slotted region  115  defines about sixteen slots  113 . In an example, the slotted region  115  defines about twelve slots  113 . In other implementations, the slotted region  115  can define any desired number of slots  113 . 
         [0038]    As shown in  FIG. 8 , the slotted region  115  of the tube body  111  has a length L 2  that is generally shorter than the length L 1  of the tube body  111 . In some implementations, the length L 2  of the axial region  115  is shorter than the length L 1  of the tube body  111 . In certain implementations, the length L 2  extends along a majority of the length L 1 . In certain implementations, the length L 2  is at least half of the length L 1 . In certain implementations, the length L 2  is at least 60% of the length L 1 . In certain implementations, the length L 2  is at least 70% of the length L 1 . In certain implementations, the length L 2  is at least 75% of the length L 1 . In some implementations, each slot  113  extends the entire length L 2  of the axial region  115 . In other implementations, each slot  113  extends along a portion of the axial region  115 . 
         [0039]    In some implementations, a ratio of the length L 2  of the slotted region  115  to a tube diameter D ( FIG. 9 ) is about 1 to about 3. In certain implementations, the ratio of the length L 2  of the slotted region  115  to the tube diameter D is about 1.5 to about 2. In certain examples, the ratio of the length L 2  of the slotted region  115  to the tube diameter D is about 1.75. In certain examples, the tube diameter D is about 5 inches and the length L 2  of the slotted region  115  is about 8 inches. In an example, each slot  113  of the slotted region  115  extends the length L 2  of the slotted region  115 . 
         [0040]    As shown in  FIG. 9 , the slotted region  115  of the tube body  111  has a circumferential width S 1  that is larger than a circumferential width S 2  of a non-slotted region  116  of the tube body  111 . The non-slotted region  116  defines a circumferential surface of the tube body  111  through which no slots are defined. In an example, the non-slotted region  116  defines a solid circumferential surface through which no openings are defined. 
         [0041]    In some implementations, the circumferential width S 2  of the non-slotted region  116  is significantly larger than a circumferential width of any portion of the tube body  111  extending between two adjacent slots  113  at the slotted region  115 . For example, in certain examples, the circumferential width S 2  of the non-slotted region  116  is at least double the circumferential width of any portion of the tube body  111  extending between two adjacent slots  113  at the slotted region  115 . In certain examples, the circumferential width S 2  of the non-slotted region  116  is at least triple the circumferential width of any portion of the tube body  111  extending between two adjacent slots  113  at the slotted region  115 . In certain examples, the circumferential width S 2  of the non-slotted region  116  is at least four times the circumferential width of any portion of the tube body  111  extending between two adjacent slots  113  at the slotted region  115 . In certain examples, the circumferential width S 2  of the non-slotted region  116  is at least five times the circumferential width of any portion of the tube body  111  extending between two adjacent slots  113  at the slotted region  115 . 
         [0042]    In some implementations, the circumferential width S 1  of the slotted region  115  is substantially larger than the circumferential width S 2  of the non-slotted region  116 . In certain implementations, the circumferential width S 1  of the slotted region  115  is at least twice the circumferential width S 2  of the non-slotted region  116 . In certain implementations, the circumferential width S 1  of the slotted region  115  is about triple the circumferential width S 2  of the non-slotted region  116 . 
         [0043]    In some examples, the slotted region  115  extends about 200° to about 350° around the tube body  111  and the non-slotted region  116  extends about 10° to about 160° around the tube body  111 . In certain examples, the slotted region  115  extends about 210° to about 330° around the tube body  111  and the non-slotted region  116  extends about 30° to about 150° around the tube body  111 . In an example, the slotted region  115  extends about 270° around the tube body  111  and the non-slotted region  116  extends about 90° around the tube body  111 . In an example, the slotted region  115  extends about 300° around the tube body  111  and the non-slotted region  116  extends about 60° around the tube body  111 . In an example, the slotted region  115  extends about 240° around the tube body  111  and the non-slotted region  116  extends about 120° around the tube body  111 . 
         [0044]    In some implementations, each slot  113  has a common width S 3  (defined along the circumference of the tube body  111 . In some implementations, the width S 3  of each slot  113  is less than the circumferential width S 2  of the non-slotted region  116 . In certain implementations, the width S 3  of each slot  113  is substantially less than the width S 2  of the non-slotted region  116 . In certain implementations, the width S 3  of each slot  113  is less than half the width S 2  of the non-slotted region  116 . In certain implementations, the width S 3  of each slot  113  is less than a third of the width S 2  of the non-slotted region  116 . In certain implementations, the width S 3  of each slot  113  is less than a quarter of the width S 2  of the non-slotted region  116 . In certain implementations, the width S 3  of each slot  113  is less than 20% the width S 2  of the non-slotted region  116 . In certain implementations, the width S 3  of each slot  113  is less than 10% the width S 2  of the non-slotted region  116 . 
         [0045]    In some implementations, the tube body  111  has a ratio of slot width S 3  to tube diameter D ( FIG. 9 ) of about 0.02 to about 0.2. In certain implementations, the ratio of slot width S 3  to tube diameter D is about 0.05 to about 0.15. In certain implementations, the ratio of slot width S 3  to tube diameter D is about 0.08 to about 0.12. In an example, the ratio of slot width S 3  to tube diameter D is about 0.1. In certain examples, the slot width S 3  is about 0.45 inches and the tube diameter D is about 5 inches. In other implementations, however, the slots  113  can have different widths. 
         [0046]    In some implementations, the slots  113  are spaced evenly around the circumferential width S 1  of the slotted region  115 . In such implementations, gaps between adjacent slots  113  within the slotted region  115  have a circumferential width S 4 . In certain implementations, the circumferential width S 4  of the gaps is larger than the circumferential width S 3  of the slots  113 . In certain implementations, the circumferential width S 3  of the slots  113  is at least half of the circumferential width S 4  of the gaps. In certain implementations, the circumferential width S 3  of the slots  113  is at least 60% of the circumferential width S 4  of the gaps. In certain implementations, the circumferential width S 3  of the slots  113  is at least 75% of the circumferential width S 4  of the gaps. In certain implementations, the circumferential width S 3  of the slots  113  is at least 85% of the circumferential width S 4  of the gaps. In other implementations, however, the gaps between the slots  113  can have different widths. 
         [0047]    In some implementations, the width S 4  of each gap is less than the circumferential width S 2  of the non-slotted region  116 . In certain implementations, the width S 4  of each gap is substantially less than the width S 2  of the non-slotted region  116 . In certain implementations, the width S 4  of each gap is less than half the width S 2  of the non-slotted region  116 . In certain implementations, the width S 4  of each gap is less than a third of the width S 2  of the non-slotted region  116 . In certain implementations, the width S 4  of each gap is less than a quarter of the width S 2  of the non-slotted region  116 . In certain implementations, the width S 4  of each gap is less than 20% the width S 2  of the non-slotted region  116 . In certain implementations, the width S 4  of each gap is less than 10% the width S 2  of the non-slotted region  116 . 
         [0048]    In certain implementations, the slots  113  occupy about 25% to about 60% of the area of the slotted region  115 . In certain implementations, the slots  113  occupy about 35% to about 55% of the area of the slotted region  115 . In certain implementations, the slots  113  occupy less than about 50% of the area of the slotted region  115 . In certain implementations, the slots  113  occupy about 45% of the area of the slotted region  115 . In other words, the percentage of open area to closed area at the slotted region  115  is about 45%. 
         [0049]    In some implementations, louvers  114  are disposed at the slotted region  115 . In some implementations, each slot  113  has a corresponding louver  114 . In other implementations, however, only a portion of the slots  113  have a corresponding louver  114 . In some implementations, each louver  114  extends the length of the corresponding slot  113 . In other implementations, a louver  114  can be longer or shorter than the corresponding slot  113 . 
         [0050]    As shown in  FIG. 9 , each louver  114  extends from a base  118  to a distal end  119  spaced from the tube body  111 . In some implementations, the base  118  is coupled to the tube body  111 . In other implementations, however, the base  118  can be spaced from the tube body  111  (e.g., suspended adjacent the tube body  111 ). In some implementations, the base  118  of each louver  114  is disposed at one end of a slot  113  so that the louver  114  extends at least partially over the slot  113  (e.g., see  FIG. 9 ). In certain implementations, the louver  114  is sized to extend fully across the width S 3  of the slot  113 . In other implementations, the louver  114  extends only partially across the width S 3  of the slot  113 . In some implementations, the distal ends  119  of adjacent louvers  114  define gaps having a circumferential width S 5 . In certain implementations, the circumferential width S 5  of the gaps is about equal to the circumferential width S 3  of the slots  113  and the circumferential width S 4  of the gaps. 
         [0051]    In some implementations, each louver  114  extends straight from the slot  113  to define a plane. In certain implementations, the louvers  114  extend from the slot  113  at an angle θ relative to the tube body  111 . In certain implementations, the angle θ is about 20° to about 70°. In an example, the angle θ is about 45°. In an example, the angle θ is about 40°. In an example, the angle θ is about 50°. In an example, the angle θ is about 35°. In certain implementations, the angle θ is about 30° to about 55°. In other implementations, each louver  114  defines a concave curve as the louver  114  extends away from the slot  113 . 
         [0052]    In some implementations, the tube body  111  has a louvered region over which the louvers  114  extend and a non-louvered region over which no louver extends. In some such implementations, the louvered region extends about 200° to about 350° around the tube body  111  and the non-louvered region extends about 10° to about 160° around the tube body  111 . In certain examples, the louvered region extends about 210° to about 330° around the tube body  111  and the non-louvered region extends about 30° to about 150° around the tube body  111 . In an example, the louvered region extends about 270° around the tube body  111  and the non-louvered region extends about 90° around the tube body  111 . In certain examples, the louvered region largely corresponds with the slotted region  115 . In an example, the louvered region overlaps the slotted region  115 . 
         [0053]    Various modifications and alterations of this disclosure will become apparent to those skilled in the art without departing from the scope and spirit of this disclosure, and it should be understood that the scope of this disclosure is not to be unduly limited to the illustrative embodiments set forth herein.