Abstract:
A venturi tube has a configuration of baffles affixed thereto that serve to greatly reduce the susceptibility of a gas burning appliance to wind gusts. The baffles cooperate to force incoming primary combustion air through a circuitous route before introduction into a flow of gaseous fuel. The circuitous route in combination with the volume of air that is contained within the baffling serves to substantially reduce flame blowout.

Description:
This is a continuation-in-part of U.S. patent application Ser. No. 10/934,978 filed Sep. 3, 2004. 

   FIELD OF THE INVENTION 
   The present invention generally relates to gas-fired appliances that are intended for outdoor use and more particularly pertains to a venturi tube configuration for introducing primary combustion air into the flow of combustible gas upstream from the point of combustion. 
   BACKGROUND OF THE INVENTION 
   A number of gas-fired appliances such as barbecues, space heaters, lamps and the like are intended for outdoor use. Such devices may be plumbed directly into a natural gas supply line or alternatively, may be coupled to a replaceable propane tank or cylinder. In either configuration, gaseous fuel is conducted to the burner of the appliance and, at a point just upstream from the burner, is typically premixed with a sub-stoichiometric quantity of combustion air commonly referred to as primary combustion air. The mixture continues on through a conduit to the burner where additional combustion air combines with the mixture to achieve a stochiometric mixture to thereby provide for proper combustion. 
   Primary combustion air is typically drawn into a fuel stream by a venturi tube device, also commonly referred to as a mixing tube, wherein the flow of gas within the conduit is managed so as to reduce pressure below ambient and thereby cause air to be drawn into the gas stream through an exposed port. The venturi tube must be situated so as not to hinder the flow of fresh combustion air thereto. Similarly, a path for combustion air flow to the burner must also be kept open at all times in order to support complete combustion. 
   Outdoor type applications are problematic to the extent that gusting wind can extinguish the flame. In addition to the nuisance that is posed by having to repeatedly relight an appliance, a susceptibility to wind gusts is especially problematic in barbecue applications wherein the extinction of the flame may not be immediately apparent, should for example a cover be in place, and a delay in relighting the burner may have an adverse effect on the cooking process. 
   An improved gas burning apparatus is therefore needed that is less susceptible to wind gusts to thereby render such apparatus more useable during windy conditions. Barbecues for use in boating applications would be particularly well served by such an improvement as they are typically put to use while cantilevered over the side of the boat where they are especially exposed to gusts and are difficult to protect therefrom. 
   SUMMARY OF THE INVENTION 
   The present invention serves to overcome shortcomings of previously known gas-burning appliances to the extent that their susceptibility to wind gusts is greatly reduced. An appliance is thus more readily useable outdoors under a wider range of conditions, often obviating the need to make a special effort to protect the appliance from air currents altogether. 
   The improvement is based on the unexpected finding that the flame of a gas burning appliance is often extinguished by excessive or disjointed air flow over the primary air intake rather than by a direct disruption of the flame by such air flow in and around the burner. More particularly, it has been found that the speed and direction of air flowing over the venturi tube device can cause an increase or decrease in pressure at the intake orifice sufficient to affect the amount of primary air that is actually drawn into the flow of fuel. An oversupply or undersupply of primary air can create a stoichiometric condition that cannot be compensated for at the burner pursuant to which the flame goes out. 
   The device of the present invention comprises an improved venturi tube configuration that includes baffling that is arranged about its exterior that substantially reduces the effect of air flowing over the exterior of the device. The rate at which air is drawn into and mixed with fuel flowing through device remains substantially constant under a wide range of wind speeds and directions and variations thereof. More particularly, the baffling is arranged to force the primary air to follow a circuitous route to reach the intake orifice while sheltering a substantial volume of air within its interior. It is believed that the changes in direction that the baffling forces incoming air to undergo serves to reduce and stabilize the speed with which such airflow reaches the intake orifice while the volume of air that resides within the baffling serves to smooth out pressure gradients that impinging winds would otherwise subject the intake orifice to. 
   The baffling may be arranged in a number of different configurations about the exterior of the venturi tube. A preferred configuration includes a pair of overlapping tubes that are arranged so as to define a circuitous flowpath to the intake orifice by which the flow of air must undergo at least two 180° changes in direction to enter the flow of fuel within the device. While the tubes may be concentrically arranged, it has unexpectedly been found that a non-concentric arrangement does not have a detrimental effect on performance and may in fact serve to accommodate a wider range of wind conditions. 
   Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the features of the invention 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a gas-fired cooking device with a venturi tube of the present invention attached thereto; 
       FIG. 2  is an enlarged view of circled region labeled “ 2 ” showing a preferred embodiment of the present invention in longitudinal cross-section; 
       FIG. 3  is a transverse cross-sectional view taken along line  3 - 3  of  FIG. 2 ; 
       FIG. 4  is a longitudinal cross-section of alternative preferred embodiment of the present invention; and 
       FIG. 5  is a transverse cross-sectional view taken along line  5 - 5  of  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The Figures generally illustrate preferred embodiments of the venturi tube, also referred to as a mixing tube, of the present invention. The venturi tube serves to introduce primary combustion air into the flow of combustible gas enroute from a fuel supply to a point of combustion such as the burner of a barbecue device. The tube configuration, and more particularly, the baffling arranged about the intake orifice serves to render the device substantially less susceptible to gusting wind. 
     FIG. 1  is perspective view of a venturi tube  102  of the present invention adapted for use with a barbecue device  12 . Combustible gas is conducted from a source  40  to a burner  38  via a conduit  30 . The mixing venturi tube of the present invention is positioned in line with the conduit at a point upstream of the burner and in a well ventilated location in order to ensure that fresh air has unhindered access thereto. The need to position the venturi tube in a relatively open location is what often contributes to the susceptibility of such devices to gusting winds. A gust passing over the venturi tube can cause a sudden over-pressure or under-pressure which disrupts the amount of combustion air that enters the fuel stream which in turn may cause the flame to extinguish. 
     FIG. 2  is an enlarged view of the circled region  2  of  FIG. 1  showing the interior structure of the venturi tube  102  in longitudinal cross-section. The passage way  104  extending therethrough has a section  106  of restricted cross-section so as to cause the flow  108  of gaseous fuel there through to accelerate and create a zone of low pressure. One or more intake orifices  110  are formed in the wall of the passage way in a position so as to take advantage of the low pressure zone. An inner baffle  112  is disposed about the exterior of the passage way wherein the proximal end  114  of the inner baffle is closed off and positioned proximal to the intake orifices while its distal end  116  is open and positioned distal to the intake orifices. An outer baffle  118  of greater diameter is disposed about the exterior of the inner baffle. Its proximal end  120  is open and is positioned proximal to the distal end of the inner baffle while its distal end  122  is closed and is positioned distal to the open distal end of the inner baffle. A flowpath  124  is thereby defined that requires incoming primary combustion air to undergo at least two 180° changes in direction, one to reach the intake orifice and another to enter the stream of gaseous fuel  108 . Additionally, a substantially volume  126  is enclosed within the baffling. 
     FIG. 3  is a transverse cross-section taken along line  3 - 3  of  FIG. 2  illustrating the non-concentric arrangement of the inner and outer baffles  112 ,  118  in this particular embodiment. The baffles are attached to one another at  128  so as to define an opening  130  of varying width extending about the circumference of the inner baffle. 
     FIG. 4  is an enlarged view of a preferred alternative embodiment showing the interior structure of the venturi tube  132  in longitudinal cross-section. The passage way  104  extending therethrough has a section  106  of restricted cross-section so as to cause the flow  108  of gaseous fuel there through to accelerate and create a zone of low pressure. One or more intake orifices  110  are formed in the wall of the passage way in a position so as to take advantage of the low pressure zone. An inner baffle  142  is disposed about the exterior of the passage way wherein the proximal end  144  of the baffle is closed off and positioned proximal to the intake orifices while its distal end  146  is open and positioned distal to the intake orifices. An outer baffle  148  of greater diameter is disposed about the exterior of the inner baffle. Its proximal end  150  is open and is positioned proximal to the distal end of the inner baffle while its distal end  152  is closed off and is positioned distal to the open distal end of the inner baffle. A flowpath  154  is thereby defined that requires incoming primary combustion air to undergo at least two 180° changes in direction, one to reach the intake orifices and another to enter the stream of gaseous fuel  108 . Additionally, a substantial volume  156  is enclosed within the baffling. 
     FIG. 5  is a transverse cross-section taken along line  5 - 5  of  FIG. 4  illustrating the concentric arrangement of the inner and outer baffles  142 ,  148  in this particular embodiment. The baffles cooperate to define an opening  160  of constant width extending about the circumference of the inner baffle. 
   In use, the venturi tube  102  of the present invention is inserted between a fuel supply and a burner. Gaseous fuel flowing  108  through the interior passageway  104  encounters a restriction  106  that induces a low pressure zone which in turn causes air to be drawn into the flow via intake orifices  110 . The primary combustion air is drawn in from the exterior of the device into the fuel flow via a circuitous path  124 ,  154  as defined by the overlapping configuration of the baffles  112 ,  118  and  142 ,  148 . The air flow makes a first 180° turn to enter the inner baffle  112 ,  142  and a second 180° turn to enter the gas stream. It is believed that the changes in direction and the relatively long flow path serves to stabilize the velocity with which the primary combustion air enters the fuel stream to thereby minimize the effect of wind blowing over the exterior of the device. Similarly, the volume  126 ,  156  of air within the device is believed to have a stabilizing influence on any pressure fluctuations the exterior of the device may be subjected to. It has also unexpectedly been found that the non-constant width of the opening  130  of the embodiment shown in  FIGS. 1-3  seems to have a further stabilizing influence on the performance of the device, possibly preventing the formation of any standing waves or harmonics that may be created by air flowing over the device that could possibly have an adverse effect on the amount of primary combustion air entering the fuel stream. 
   While particular forms of the invention have been described and illustrated, it will also be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. For example the size and shape of the baffles may be changed to accommodate particular applications. Additionally, more baffles may be added in order to require the incoming air to follow an even more circuitous route to the intake orifices. Accordingly, it is not intended that the invention be limited except by the appended claims.