Patent Publication Number: US-10767283-B2

Title: Ovens, discharge nozzle plates for distribution of gas through an oven, and methods to operate an oven

Description:
RELATED APPLICATIONS 
     This patent claims is a continuation-in-part of U.S. patent application Ser. No. 14/923,931, filed Oct. 27, 2015, entitled “Discharge nozzle plate for center-to-ends fiber oxidation oven,” which claims priority to U.S. Provisional Patent Application Ser. No. 62/076,746, filed Nov. 7, 2014, entitled “DISCHARGE NOZZLE PLATE FOR CENTER-TO-ENDS FIBER OXIDATION OVEN.” The entireties of U.S. patent application Ser. No. 14/923,931 and U.S. Provisional Patent Application Ser. No. 62/076,746 are incorporated herein by reference. 
    
    
     BACKGROUND 
     Oxidation ovens are commonly used to produce carbon fibers from a precursor (such as an acrylic, pitch, or cellulose fibers). One common processing method involves successively drawing fibrous segments of the precursor material through one or more oxidation ovens. 
     Each of the oxidation ovens comprises a respective oxidation chamber in which the oxidation of the fiber segments takes place. Each fibrous segment can be drawn into a first oxidation oven as a carbon fiber precursor and then make multiple passes through each oxidation oven prior to exiting the final oxidation oven as an oxidized fiber segment. Roll stands and tensioners are used to draw the fibrous segments through the oxidation chambers of the ovens. Each oxidation oven heats the segments to a temperature approaching approximately 300° C. by means of a circulating flow of hot gas. 
     An example of such an oven is the Despatch Carbon Fiber Oxidation Oven, available from Despatch Industries, Minneapolis, Minn. A description of such an oven can be found in commonly-assigned U.S. Pat. No. 4,515,561. The oven described in the &#39;561 Patent is a “center-to-ends” oxidation oven. In a center-to-ends oxidation oven, hot gas is supplied to the oxidation chamber of the oven from the center of the chamber and flows toward the ends of the chamber. 
     Typically, such a center-to-ends oxidation oven includes a center supply structure located in the center of the chamber. The center supply structure includes a plurality of supply plenums that are stacked one above each other. Gaps are provided between the stacked supply plenums to enable passage of the fibrous segments between the plenums. Each plenum comprises a duct structure that receives heated air through one or both of its ends. Each plenum includes an array of holes formed in each of the opposing side walls of the corresponding duct structure. This array of holes is also referred to here as a “nozzle.” Each plenum is configured to receive heated air and direct the flow of heated gas in approximately horizontal and parallel streams of heated gas out of the nozzles towards both ends of the oxidation chamber. 
     Such nozzles have typically been formed in a pair of relatively thin metal sheets that form the side walls of the plenum structure. These metal sheets are also referred to here as “nozzle sheets.”  FIGS. 1-2  illustrate a portion of one example of a conventional nozzle sheet  100  with nozzles  102  formed in the nozzle sheet  100 . 
     The nozzle sheets  100  typically are less than one-quarter inch thick and are made out of aluminum or similar material suitable for use in an oven. The nozzles  102  are typically formed in each nozzle sheet  100  by perforating the sheet. 
     Given the relative thinness of such nozzle sheets and the large number of nozzles in the sheets, a sheet of hex honeycomb material has typically been layered on the outer surface of each nozzle sheet in order to reinforce the thin nozzle sheets and to help control the angular direction of the air leaving the nozzles so that it leaves the nozzles in more uniform and parallel streams.  FIG. 3  illustrates a portion of a sheet  104  of hex honeycomb material, and  FIG. 4  illustrates the hex honeycomb material  104  placed on the outer surface of the nozzle sheet  100  shown in  FIGS. 1-2 . 
     However, it can be difficult to precisely align the openings in a sheet of hex material with the corresponding nozzles in a thin nozzle sheet. Misalignment of the openings of the hex material with the nozzles in the nozzle sheet can cause the air leaving the nozzles to do so in less uniform and parallel streams. Also, adding two sheets of the hex material to each plenum increases the cost of manufacturing and assembling each plenum. 
     SUMMARY 
     One embodiment is directed to an oven for heating fibers. The oven comprises a supply structure disposed within the oven between first and second ends of the oven. The supply structure comprises a plurality of plenums stacked one above each other with gaps therebetween. The plenums are in fluid communication with a heating system. At least one plenum comprises at least one side wall comprising a plurality of passages formed therein, said at least one plenum configured to direct at least a portion of the heated gas into an interior of the oven from the plurality of passages. Each of the plurality of passages formed in said at least one plenum has a respective tapered cross-sectional shape. 
     Another embodiment is directed to a method of heating fibers using an oven. The method comprises supplying heated gas to a supply structure disposed within an interior of the oven. The supply structure comprises a plurality of plenums stacked one above each other with gaps therebetween. The method further comprises directing at least a portion of the heated gas into the interior of the oven from passages formed in at least one side wall of at least one plenum, said passages having a tapered cross-sectional shape. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a portion of one example of a conventional nozzle sheet. 
         FIG. 2  is a cross-sectional view of the nozzle sheet shown  FIG. 1 . 
         FIG. 3  illustrates a portion of a sheet of hex honeycomb material. 
         FIG. 4  illustrates the hex honeycomb material of  FIG. 3  placed on the outer surface of the nozzle sheet shown in  FIGS. 1-2 . 
         FIG. 5  is a perspective view of one exemplary embodiment of an oven. 
         FIG. 6  is a perspective view of the oven shown in  FIG. 5  with the top wall removed from the chamber of the oven. 
         FIG. 7  is a cross-sectional plan view of the oven shown in  FIG. 5 . 
         FIG. 8  is illustrates details of the center supply structure of the oven shown in  FIG. 5 . 
         FIG. 9  is a cross-sectional plan view of one exemplary embodiment of a supply plenum. 
         FIG. 10  is a side view of one side wall of the supply plenum shown in  FIG. 9 . 
         FIG. 11  illustrates a portion of the side wall shown in  FIG. 10  in more detail. 
         FIG. 12  is a cross-sectional view of the portion of the side wall shown in  FIG. 11 . 
         FIG. 13  is a detailed view of one of the nozzles shown in  FIG. 12 . 
         FIG. 14  is a flow diagram of an exemplary embodiment of a method of heating fibers by contact with heated gas. 
         FIG. 15  illustrates one alternative tapered cross-sectional nozzle shape. 
         FIG. 16  illustrates another example oven that provides a consistent airflow through a substrate heating volume. 
         FIG. 17  illustrates an example side wall and the passages. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 5-7  illustrate one exemplary embodiment of an oxidation oven  500  in which the nozzle plates described below can be used. It is to be understood, however, that the nozzle plates described below can be used in other oxidations ovens. 
     The oxidation oven  500  shown in  FIGS. 5-7  is suitable for use in producing carbon fibers using an oxidation process of the type described above. For example, the exemplary embodiment of an oxidation oven  500  shown in  FIGS. 5-7  can be used in oxidation processes that make use of one or multiple ovens (for example, in a stacked configuration) as is known to those of skill in the art. 
     One of ordinary skill in the art will recognize that, for the sake of brevity and clarity, various conventional features used in oxidation ovens have been omitted from the figures and the following description. Examples of such features include, without limitation, baffles, ducts, vanes, vents, and the like used to adjust the flow of gas within the oven  500 , vestibules and exhaust features to reduce the discharge of undesirable processes gases into the ambient environment, and/or insulation, louvers, and other thermal features to improve the thermal efficiency of the oven  500 . It is to be understood that the exemplary oven  500  shown in  FIGS. 5-7  can include such features 
     In the exemplary embodiment shown in  FIGS. 5-7 , the oven  500  comprises an oven chamber  502  in which the oxidation of fiber segments take place. In this exemplary embodiment, the oven chamber  502  is defined by a plurality of walls. The walls that define the oxidation chamber  502  include a top wall  504 , a bottom wall  506 , two side walls  508  and  510  along respective sides  512  and  514  of the chamber  502 , and two end walls  516  and  518  at respective ends  520  and  522  of the chamber  502 . A respective entry for the fiber is formed in each of the end walls  516  and  518 . Each entry is formed by a plurality of slots, which extend between first and second sides  512  and  514  of the chamber  502 , and through which the fibrous segments heated by the oxidation oven  500  are drawn. The entries and slots can be formed in a conventional manner. 
     The oven  500  also comprises a heating system  524 . The heating system  524  is used to supply heated gas into the chamber  502 . In this exemplary embodiment, the gas that is used is ambient air. 
     The heating system  524  can be implemented in various ways. In the exemplary embodiment shown in  FIGS. 5-7 , the heating systems  524  is implemented using at least one heater  526  (shown in  FIG. 7 ), a blower  528  (shown in  FIG. 7 ) to draw gas through the heater  526 , and a motor  530  to power the blower  528 . Each heater  526  can be implemented in various ways. For example, each heater  526  can be implemented using one or more heating elements. Also, each heater  526  can be implemented using an indirect gas heater, an electric heater, or combinations thereof. Each heater  526  can be implemented in other ways. 
     The heating system  524  can be controlled, for example, using one or more suitable controllers (such as proportional-integral-derivative (PID) controllers). 
     The oven  500  includes a supply structure  532  disposed within the interior of the chamber  502  between the ends  520  and  522  of the chamber  502 . In the exemplary embodiment shown in  FIGS. 5-7 , the oven  500  is a center-to-ends oxidation oven in which heated gas is supplied from the center of the oxidation chamber  502  towards the ends  520  and  522  of the chamber  502 . In this exemplary embodiment, the supply structure  532  is disposed within the interior of the chamber  502  at or near the center of the chamber  502  between the ends  502  and  522  and is also referred to here as the “center supply structure”  532 . 
     In the exemplary embodiment shown in  FIGS. 5-7 , the center supply structure  532  comprises a plurality of supply plenums  534  that are stacked one above each other with gaps therebetween. 
     The center supply structure  532  is shown in more detail in  FIG. 8 . Gaps  536  (shown in  FIG. 8 ) are provided between the stacked supply plenums  534  to enable passage of the fibrous segments between the plenums  534 . 
     More details regarding the supply plenums  534  are provided below in connection with the description of  FIGS. 9-13 . 
     The plenums  534  are in fluid communication at one or both of their ends with a supply duct  538  (shown in  FIGS. 6 and 7 ) in order to receive heated gas from the heating system  524 . In the exemplary embodiment shown in  FIGS. 5-7 , each plenum  534  is configured to receive heated air through one of its ends (though it is to be understood that in other embodiments, each plenum receives heated air through both of its ends). 
     The supply duct  538  can be appropriately tapered or provided with adjustable slots or other features (not shown) to adjust the flow heated gas so that the velocity of heated gases exiting the plenums  534  is substantially uniform. 
     Each oven  500  also includes two return structures  540  within the oxidation chamber  502 . One return structure  540  is positioned near the first end wall  516 , and the other return structure  540  is positioned near the second end wall  518 . Each of the return structures  540  includes a plurality of return channels that are each stacked one above another and that are positioned to generally correspond with the positions of corresponding plenums  534  of the center supply structure  532 . Gaps are provided between the return channels to enable passage of fibrous segments between the return channels. 
     The return channels of each return structure  540  are configured to receive at least a portion of the gas directed from the center supply structure  532  toward that return structure  540 . That is, each return structure  540  receives gas directed from one side of the plenums  534  in the center supply structure  532  toward that return structure  540 . 
     A return duct  542  is used to establish fluid communication between each return structure  540  and the heating system  524 . In this way, at least a portion of the heated gas received by the return structures  540  is directed back to the heating system  524  to be heated and supplied to the plenums  534  via the supply ducts  538  as described above. 
     In the exemplary embodiment shown in  FIGS. 5-7 , the return ducts  542  are located within the walls of the chamber  502 . However, it is to be understood that the return ducts  542  can be implemented in other ways (for example, by positioning at least a portion of the return ducts  542  outside of the walls of the chamber  502 ). 
     In the exemplary embodiment described here in connection with  FIGS. 5-7 , each of the plenums  534  is implemented as shown in  FIGS. 9-13 . Each plenum  534  is supplied with heated gas at a first end  900  of the plenum  534 . The heated gas is supplied from a supply duct  538 . 
     Each plenum  534  is generally rectangular in cross section and extends horizontally between, but spaced from the side walls  508  and  510  of the chamber  502 . As shown in  FIG. 10 , each plenum  534  has passages  902  formed in the side walls  904  of the plenum  534 . These passages  902  are also referred to here as the “nozzles”  902 . In this exemplary embodiment, each side wall  904  of each plenum  534  is implemented using a plate as described below in more detail in connection with  FIGS. 10-12  (and these plates are also referred to here as “nozzle plates”  904 ). 
     The passage formed in the nozzle plate  904  for each nozzle  902  has an inlet opening  908  (shown in  FIGS. 12-13 ) into which air supplied to the plenum  534  enters and has an outlet opening  910  (shown in  FIGS. 12-13 ) from which the supplied air exits and is discharged into the chamber  502  of the oven  500 . The outlet openings  910  for the nozzles  902  face the respective ends  520  and  522  of the chamber  502 . 
     The nozzles  902  extend across the width of the plenum  534 . The nozzles  902  are constructed and arranged so as to direct the flow of the received heated gas in approximately horizontal and parallel streams of heated gas toward the ends  520  and  522  of the oxidation chamber  502 . The streams of gas are directed alongside each fibrous segment that traverses that portion of the oxidation chamber  502 . 
     Each plenum  534  includes one or more baffles  906  that are disposed within the interior of the plenum  534  between the nozzle plates  904  of the plenum  534 . In this exemplary embodiment, the baffles  906  are arranged in a V-shape as shown in  FIG. 9 , with the tip portion of the V-shape located near the end  900  where heated gas is supplied to the plenum  534 . This V-shaped arrangement of the baffles  906  is generally designed to direct the flow of the received heated gas out of the nozzles  902  in a uniform manner. 
       FIG. 10  illustrates the nozzles  902  formed in one of the nozzle plates  904  of the plenum  534 . In this exemplary embodiment, the nozzles  502  are formed in both nozzle plates  904  the same way (though only the nozzles  902  for one of the nozzle plates  904  are shown).  FIG. 11  illustrates a portion of the nozzle plate  904  shown in  FIG. 10  in more detail.  FIG. 12  is a cross-sectional view of the portion of the nozzle plate  904  shown in  FIG. 11 .  FIG. 13  is a detailed view of one of the nozzles  902  shown in  FIG. 12 . 
     The nozzles  902  can be formed in the nozzle plates  904 , for example, by drilling and machining the passages for the nozzles  902  and/or by using a casting process to produce the nozzle plates  904  with the passages for the nozzles  902  formed in the nozzle plates  904 . The nozzles  902  can be formed in the nozzle plates  904  in other ways. 
     As shown in  FIG. 12 , in this exemplary embodiment the nozzle plate  904  is much thicker than conventional perforated nozzle sheets. For example, the nozzle plate  904  can have a thickness that is greater than 0.25 inches. The nozzle plate  904  can be made out of aluminum or similar material suitable for use in an oven. 
     Also, each nozzle  902  is formed in the nozzle plate  904  with a round opening (shown in  FIG. 11 ) and with a tapered cross-sectional shape (shown in  FIGS. 12-13 ). The tapered cross-sectional shape of each nozzle  902  has an inlet opening  908  that is larger than the corresponding outlet opening  910  of each nozzle  902 . 
     In this exemplary embodiment, the tapered cross-sectional shape for each nozzle  902  comprises a tapered section  912  that extends from the inlet opening  908  of the nozzle  902  for at least a portion of the width of the nozzle plate  904 . Each nozzle  902  also includes a straight section  914  that extends from the end of the tapered section  912  to the outlet opening  910  of that nozzle  904 . 
     Air supplied to each plenum  534  would tend to travel parallel to the side walls  904  of the plenum  534 . However, the air interacts with the baffle  906  as it passes through the plenum  534  and, as a result, at least a portion of the air is directed into the inlet opening  908  of each nozzle  902  as the air passes across the plenum  534 . 
     In this exemplary embodiment, the tapered section  912  of each nozzle  902  has a curved or beveled edge  916  along the inlet opening  908 . The curved or beveled edge  916  helps enable air that is flowing past the nozzle  902  to enter that nozzle  902 . The tapered section  912  of each nozzle gradually re-directs the air that enters the nozzle  902 , whereas the straight section  914  of each nozzle  902  stabilizes and aligns the air so that it flows out of the outlet opening  910  of the nozzle  902  in uniform streams. 
     By not using such sheets of hex honeycomb material, the difficult task of precisely aligning the openings in each sheet of hex material with the corresponding nozzles in the thin perforated nozzle sheet can be avoided, as well as the problems that can arise from any such misalignment. Also, the costs of manufacturing and assembling each plenum  534  can be reduced by not adding two sheets of hex honeycomb material to the plenum  534 . 
     Moreover, the tapered cross-sectional shape of the nozzles  902 , combined with the thicker nozzle plate  904 , helps the air leaving the nozzles  902  to do so in more uniform and parallel streams of air, without using the sheets of hex honeycomb material 
     Furthermore, by not using perforated sheets, the same degree of uniformity in the resulting air streams can be achieved with a reduced static pressure. 
     Also, by not using sheets of hex honeycomb material, the shape and arrangement of the outlet openings  910  of the nozzles  902  do not have to accommodate the openings in a hex honeycomb material layered over the nozzle plate  904 . 
       FIG. 14  is a flow diagram of an exemplary embodiment of a method  1400  of heating fibers by contact with heated gas. The embodiment of method  1400  shown in  FIG. 14  is described here as being implemented using the exemplary embodiment of an oxidation oven  500  and nozzle plate  904  described above in connection with  FIGS. 5-13 . However, it is to be understood that other embodiments can be implemented in other ways. 
     Method  1400  comprises supplying heated gas to the supply structure  532  disposed within the interior of the oven  500 , where the supply structure  532  comprises a plurality of plenums  534  stacked one above each other with gaps  536  therebetween (block  1402 ). In this exemplary embodiment, the heated gas is supplied from the heating system  528  to each plenum  534  via the supply duct  538 . 
     Method  1400  further comprises directing at least a portion of the heated gas into the interior of the oven  502  from nozzles  902  formed in at least one side wall  904  of at least one of the plenums  534 , where said nozzles  902  have a tapered cross-sectional shape (block  1404 ). The heated gas flows out of the nozzles  902  in approximately horizontal and parallel streams of heated gas toward the ends  520  and  522  of the oxidation chamber  502  alongside each fibrous segment that traverses that portion of the oxidation chamber  502 . 
     In this exemplary embodiment, at least a portion of the heated gas is directed into inlet openings  908  of the nozzles  902  and at least a portion of the heated gas is directed into the interior of the oven  500  from outlet openings  910  of the nozzles  902 . Also, in this example, at least a portion of the heated gas that is directed into the inlet openings  908  of the nozzles  902  is directed along the curved or beveled edges  916  formed along the inlet openings  908  and into tapered sections  912  of the nozzles  902 . Moreover, in this example, at least a portion of the heated gas that is directed into the interior of the oven  500  from outlet openings  910  of the nozzles  902  is directed into straight sections  914  of the nozzles  902  prior to being discharged into the interior of the oven  500 . 
     The embodiments described above are merely exemplary and are not intended to be limiting. 
     It is to be understood that the tapered cross-sectional shape of the nozzles  902  can be implemented in other ways.  FIG. 15  illustrates one alternative tapered cross-sectional shape of nozzle  1502  that can be used in the plenum  534  described above. The nozzle  1502  is generally the same as the nozzle  902  described above in connection with  FIGS. 9-13  except as described below. 
     In this example embodiment, the tapered section  1512  of the nozzle  1502  extends from the inlet opening  1508  of the nozzle  1502  to the outlet opening  1510  of the nozzle  1502  and does not include a straight section. Also, as with the embodiment described above in connection with  FIGS. 9-14 , the tapered section  1512  of each nozzle  1502  has a curved or beveled edge  1516  along the inlet opening  1508 . 
     Other tapered cross-sectional shapes can be used. 
     In the exemplary embodiments described above, each plenum  534  is supplied with heated gas from a single side. However, in other embodiments, the plenums in the center supply structure are supplied with gas from both sides. 
     Moreover, in the example embodiments described above, the cross-sectional shapes of all nozzles are the same. However, in other embodiments, this is not the case and the size and shapes of the nozzles can vary from nozzle to nozzle within a given plenum and can vary from plenum to plenum within a given supply structure. Also, in the example embodiments described above, each plenum is shown as having two sides walls where both sides walls have nozzles formed therein with a tapered cross-sectional shape as described above. However, this need not be the case (for example, only one of the side walls can have nozzles formed therein with a tapered cross-sectional shape as described above). Furthermore, in the exemplary embodiments described above, each plenum in the center supply structure has the same configuration and design. However, this need not be the case and, instead, one or more plenums included in the center supply structure can have configurations and/or designs that differ from one or more other plenums included in the center supply structure. 
       FIG. 16  illustrates another example oven  1600  that provides a consistent airflow through a substrate heating volume  1602 . The example oven  1600  of  FIG. 16  uses nozzles similar or identical to the nozzles disclosed above. The oven  1600  may be closed or sealed to external airflow. Instead of heating carbon fiber as in the example oven  500  of  FIGS. 5-7 , the example oven  1600  may heat and/or otherwise provide airflow to stationary objects placed in the substrate heating volume  1602 . 
     The oven  1600  includes the substrate heating volume  1602 , a heating system  1604 , and a plenum  1608 . The plenum  1608  includes a side wall  1610 , which is positioned between the plenum  1608  and the substrate heating volume  1602 . Thus the side wall  1610  is also a side wall of the substrate heating volume  1602 . The side wall  1610  has passages  1612  formed in the side wall  1610  to permit heated gas  1606  to flow from the plenum  1608  to the substrate heating volume  1602 . The plenum  1608  directs the heated gas  1606  into the substrate heating volume  1602  from the plurality of passages  1612 . Each of the passages  1612  formed in the plenum  1608  has a respective tapered cross-sectional shape. The side wall  1610  and the passages  1612  distribute the gas substantially evenly through the substrate heating volume  1602 . 
     The heated gas  1606  may be directed over and/or impinge on one or more substrates  1616  in the substrate heating volume  1602 . In the illustrated examples, there are multiple levels of substrates  1616  in the substrate heating volume, and the heated gas  1606  flows from the side wall  1610  over the substrates  1616 . 
       FIG. 17  illustrates an example side wall  1610  and the passages  1612 . Examples of the passages  1612  are shaped as shown in  FIGS. 11, 12, 13 , and/or  15 . As shown in  FIG. 17 , the passages  1612  are distributed over the side wall  1610  using one or more repeating patterns. The one or more repeating patterns may include an arrangement of the passages  1612  over the side wall  1610  to optimize the distribution of the heated gas over a load area in the substrate heating. As used herein, an “optimal distribution” of the heated gas refers to having substantially same volume of air going over the operable surfaces and/or substantially a same amount of heat dissipated by devices in the air stream. In some examples, volumes of air flow are considered substantially the same when the volumes are within ±15%. In some examples, two or more levels of heat dissipation are substantially the same when the heat dissipation is within ±15%. 
     Returning to  FIG. 16 , the substrate heating volume  1602  also includes a return structure  1614  opposite the plenum  1608 . The return structure  1612  directs at least a portion of the heated gas  1606  out of the substrate heating volume  1602 . The return structure  1614  is to direct the at least the portion of the heated gas to the heating system. 
     As discussed above with reference to  FIGS. 11, 12, 13, and 15 , each of the passages  1612  in the example side wall  1610  includes a respective inlet opening  908  and a respective outlet opening  910 . One or more of the passages  1612  may have a tapered section  912  extending from the inlet opening  908 . One or more of the passages  1612  may also include a curved or beveled edge  916  along the inlet opening  908 . In some examples, one or more of the passages  1612  include the tapered section  912  extending from the inlet opening  908  and a straight section  914  extending from the end of the tapered section  912  to the outlet opening  910 . 
     In some examples, the side wall  1610  has a sections in which there are no passages, which may be located between other sections that have the passages. For example, sections lacking the passages  1612  may be positioned where the substrates  1616  are located (e.g., vertically even with the levels of substrates  1616 ). The side wall  1610  may have a first section having first passages  1612 , a second section having second passages  1612 , and a third section between the first and second sections not having the passages  1612 . 
     As illustrated in  FIG. 16 , the plenum  1608  is tapered from a gas input location  1618  of the plenum  1608  toward an opposite end of the plenum. The side wall  1610  is configured to output the heated gas  1606  from the passages  1612  at a substantially uniform volume. During operation, the example heating system  1604  controls a static pressure of the plenum  1608  to provide the substantially uniform volume of gas flow over the face of the side wall  1610 . In some examples, the heating system  1604  (e.g., via a fan) maintains the plenum  1608  at at least 0.3 inches water column of static pressure over the entirety of the side wall  1610 . In some other examples, the heating system  1604  (e.g., via a fan) maintains the plenum  1608  at at least 0.5 inches water column of static pressure over the entirety of the side wall  1610 . 
     In some examples, the oven  1600  is further provided with a cooling coil or other gas cooling system between the return structure  1614  and the heating system  1604 . 
     A number of embodiments have been described. Nevertheless, it will be understood that various modifications to the described embodiments may be made without departing from the spirit and scope of the claimed invention. 
     EXAMPLE EMBODIMENTS 
     Example 1 includes an oven for heating fibers, the oven comprising: a supply structure disposed within the oven between first and second ends of the oven, the supply structure comprising a plurality of plenums stacked one above each other with gaps therebetween, wherein the plenums are in fluid communication with a heating system; wherein at least one plenum comprises at least one side wall comprising a plurality of passages formed therein, said at least one plenum configured to direct at least a portion of the heated gas into an interior of the oven from the plurality of passages; and wherein each of the plurality of passages formed in said at least one plenum has a respective tapered cross-sectional shape. 
     Example 2 includes the oven of Example 1, wherein each of the passages formed in said at least one side wall of said at least one plenum comprises a respective inlet opening and a respective outlet opening. 
     Example 3 includes the oven of Example 2, wherein, for at least one of the passages, the respective inlet opening is larger than the respective outlet opening. 
     Example 4 includes the oven of any of Examples 2-3, wherein at least one of the passages formed in said at least one side wall of said at least one plenum comprises a tapered section extending from the respective inlet opening. 
     Example 5 includes the oven of Example 4, wherein said at least one of the passages comprising the tapered section further comprises a curved or beveled edge along the respective inlet opening. 
     Example 6 includes the oven of any of Examples 2-5, wherein at least one of the passages formed in said at least one side wall of said at least one plenum comprises a tapered section extending from the respective inlet opening and a straight section extending from an end of the tapered section to the respective outlet opening. 
     Example 7 includes the oven of any of Examples 1-6, wherein honeycomb material is not placed on an outer surface of said at least one plenum. 
     Example 8 includes the oven of any of Examples 1-7, wherein said at least one side wall is at least 0.25 inches thick. 
     Example 9 includes a method of heating fibers using an oven, the method comprising: supplying heated gas to a supply structure disposed within an interior of the oven, the supply structure comprising a plurality of plenums stacked one above each other with gaps therebetween; and directing at least a portion of the heated gas into the interior of the oven from passages formed in at least one side wall of at least one plenum, said passages having a tapered cross-sectional shape. 
     Example 10 includes the method of Example 9, wherein directing at least a portion of the heated gas into the interior of the oven from said passages comprises: directing at least a portion of the heated gas into inlet openings of said passages; and directing at least a portion of the heated gas into the interior of the oven from outlet openings of said passages. 
     Example 11 includes the method of Example 10, wherein, for at least one of said passages, the respective inlet opening is larger than the respective outlet opening. 
     Example 12 includes the method of any of Examples 10-11, wherein at least one of said passages comprises a tapered section extending from the respective inlet opening. 
     Example 13 includes the method of any of Examples 10-12, wherein directing at least a portion of the heated gas into inlet openings of said passages comprises: directing at least a portion of the heated gas along curved or beveled edges formed along inlet openings of said passages. 
     Example 14 includes the method of any of Examples 10-13, wherein directing at least a portion of the heated gas into inlet openings of said passages comprises: directing at least a portion of the heated gas into tapered sections of said passages. 
     Example 15 includes the method of any of Examples 10-14, wherein directing at least a portion of the heated gas into the interior of the oven from outlet openings of said passages comprises: directing at least a portion of the heated gas into straight sections of said passages prior to discharging the heated gas into the interior of the oven. 
     Example 16 includes an oven, comprising: a heating system to heat gas; a substrate heating volume; and a plenum comprising a side wall having a plurality of passages formed therein. The plenum is configured to direct heated gas into the substrate heating volume from the plurality of passages, and each of the plurality of passages formed in the plenum has a respective tapered cross-sectional shape. 
     Example 17 includes the oven of Example 16, wherein the substrate heating volume includes a return structure opposite the plenum to direct at least a portion of the heated gas out of the substrate heating volume. 
     Example 18 includes the oven of Example 17, wherein the return structure is to direct at least a portion of the heated gas to the heating system. 
     Example 19 includes the oven of any of Examples 16-18, wherein the plurality of passages are distributed using one or more repeating patterns over the side wall. 
     Example 20 includes the oven of Example 19, wherein the one or more repeating patterns comprise an arrangement of the passages over the side wall to optimize the distribution of the heated gas over a load area in the substrate heating volume. 
     Example 21 includes the oven of any of Examples 16-20, wherein the side wall comprises a first section having first ones of the passages and a second section of the side wall having second ones of the passages, the side wall comprising a third section between the first section of the side wall and the second section of the side wall, the third section of the side wall not having passages for directing the heated gas. 
     Example 22 includes the oven of any of Examples 16-21, wherein each of the passages formed in the side wall of the plenum comprises a respective inlet opening and a respective outlet opening. 
     Example 23 includes the oven of Example 22, wherein at least one of the passages formed in the side wall of the plenum comprises a tapered section extending from the respective inlet opening. 
     Example 24 includes the oven of Example 23, wherein the at least one of the passages comprising the tapered section further comprises a curved or beveled edge along the respective inlet opening. 
     Example 25 includes the oven of any of Examples 22-24, wherein at least one of the passages formed in the side wall of the plenum comprises a tapered section extending from the respective inlet opening and a straight section extending from an end of the tapered section to the respective outlet opening. 
     Example 26 includes the oven of any of Examples 16-25, wherein the plenum is tapered from a gas input location of the plenum toward an opposite end of the plenum. 
     Example 27 includes the oven of Example 26, wherein the side wall is configured to output the gas from the plurality of passages at a substantially uniform volume. 
     Example 28 includes the oven of any of Examples 16-27, and further comprises an air circulator configured to generate at least 0.3 inches water column of static pressure over the entirety of the side wall opposite the substrate heating area. 
     Example 29 includes the oven of any of Examples 16-27, and further comprises an air circulator configured to generate at least 0.5 inches water column of static pressure over the entirety of the side wall opposite the substrate heating area. 
     Example 30 is a method for heating a substrate in an oven, comprising: supplying heated gas to a supply structure disposed within an interior of the oven, the supply structure comprising a plenum; and directing at least a portion of the heated gas to a substrate heating volume in the interior of the oven via passages formed in a side wall of the plenum, the passages having tapered cross-sectional shapes. 
     Example 31 includes the method of Example 30, wherein the directing of at least the portion of the heated gas into the substrate heating volume via the passages comprises: directing at least the portion of the heated gas into inlet openings of the passages; and directing at least the portion of the heated gas into the substrate heating volume from outlet openings of the passages. 
     Example 32 includes the method of Example 31, wherein the directing of at least the portion of the heated gas into the substrate heating volume via the passages comprises: directing at least the portion of the heated gas into inlet openings of the passages; and directing at least the portion of the heated gas into the substrate heating volume from outlet openings of the passages. 
     Example 33 includes the method of Example 31, wherein the directing of at least the portion of the heated gas into the inlet openings of the passages comprises: directing at least the portion of the heated gas along curved or beveled edges formed along the inlet openings of the passages. 
     Example 34 includes the method of Example 31, wherein the directing of at least the portion of the heated gas into the inlet openings of the passages comprises: directing the at least the portion of the heated gas into tapered sections of the passages. 
     Example 35 includes the method of Example 31, wherein the directing of at least the portion of the heated gas into the substrate heating volume from the outlet openings of the passages comprises: directing the at least the portion of the heated gas into straight sections of the passages prior to discharging the heated gas into the substrate heating volume. 
     Example 36 includes the method of any of Examples 30-35, and further comprises recirculating the at least the portion of the heated gas from the substrate heating volume to the plenum via a return structure. 
     Example 37 includes the method of any of Examples 30-36, wherein the directing of at least the portion of the heated gas into the substrate heating volume via the passages comprises: directing at least the portion of the heated gas into one or more repeating patterns of the passages over the side wall. 
     Example 38 includes the method of any of Examples 30-37, wherein the directing of at least the portion of the heated gas into the substrate heating volume via the passages comprises directing the at least the portion of the heated gas at a substantially uniform volume through the passages. 
     While the present method and/or system has been described with reference to certain implementations, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present method and/or system. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from its scope. Therefore, the present method and/or system are not limited to the particular implementations disclosed. Instead, the present method and/or system will include all implementations falling within the scope of the appended claims, both literally and under the doctrine of equivalents.