Patent Publication Number: US-7213348-B2

Title: Gas burner and air heater assembly for a gas clothes dryer

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a gas burner for a gas dryer which produces an even and well dispersed flame distribution, with low consumption of fuel and reduced noxious emissions such as carbon monoxide. In another aspect, the present invention relates to a heater assembly for a gas clothes dryer which employs such a burner. 
   2. Discussion of the Prior Art 
   Gas burners are used in a number of applications ranging from furnaces, gas clothes dryers and other like applications in which it is desired to heat air for use for various purposes. A universal requirement for all burners is that they should be efficient in burning fuel supplied, generally are required to provide a desired flame profile depending on the application, should be quiet and should not produce large amounts of potentially harmful bi-products such as carbon monoxide. 
   In the case of the use of such burners in household applications, one current prominent use is in clothes dryers, typically clothes dryers using natural gas as a fuel. Such dryers can be a popular amenity for households of all incomes since consumers can dry two loads of clothes in a natural gas dryer, on average, for the amount of money it costs to dry just one load in an electric dryer. 
   For additional savings and energy conservation, current natural gas dryers use electronic ignition systems instead of a continuously burning pilot light. Generally such dryers work by moving warm air through the clothes inside. Inside of the dryer is a rotating drum and the dry heated air created by a natural gas burner flows over and through the clothes as the drum tosses them through the air. The moist air coming off the clothes is exhausted through a vent to the outdoors, and is replaced by more dry heated air. 
   Due to current energy costs, it is very important that burners employed in heaters in natural gas dryers function with high efficiency while providing a wide flame distribution to heat a maximum amount of air. This provides a large flow of warm air to clothes being dried. It is also important that such burners avoid producing harmful or noxious byproducts such as carbon monoxide, due to the fact that even though gas dryers are vented generally to the outside, they are still used in enclosed home, and typically within smaller rooms such as laundry rooms. If such bi-products are produced at any high level, there is a high risk of harm to occupants or pets of the homes, and in particular, to operators of the gas clothes dryer. 
   In the past design of burners, it has been recognized that unintended secondary airflow around the burner head or nozzle of a burner can result in imperfect burning of fuel with resultant undesirable by-products. One prior art burner recognizes that the burning of fuels can result in the formation of nitrogen oxides (NO 2 ), which when released to the atmosphere constitute pollutants. 
   In order to avoid such bi-products, one approach involves providing a fuel discharge nozzle with a shielding cone, which is generally disk shaped and includes a plurality of openings formed therein for allowing passage of a limited amount of air therethrough. The cone is an attempt to create a protected area adjacent the nozzle. However, as a result of the air flowing through openings in the cone, there still results an incomplete burning of fuels with resultant undesirable bi-products. Moreover, there is also caused a redirection of the flame in the direction of the secondary air being passed through the openings in the cone. 
   Another attempt to influence fuel burning with a burner involves an arrangement, which produces flames as long, slender rod like jets of great length. In this burner arrangement, one or more principal orifices are placed symmetrically on or about the axis of a pipe. The principal flow of gas is through these principal orifices. Secondary jets issue from the pipe at an angle to the axis of the pipe. The secondary orifices are shielded by a baffle surrounding the orifices which also includes openings for inducing air into the space adjacent to the secondary orifices, thereby also affecting the direction of the flame and the burning efficiency. 
   In yet still another arrangement, a conical shroud is provided shaped to avoid lateral divergence of flames. Such an arrangement results in an essentially unidirectional flame, which is not well suited for heating large volumes of air. 
   In accordance with the present invention, the problems of the prior art are avoided by providing a burner for use, in particular, with a gas clothes dryer, which functions efficiently in terms of consumption of fuel, produces a substantially constant flame with low levels of undesirable bi-product emissions, is not subject to adverse effects on the flame resulting from secondary air flow, and provides a flame which is dispersed over a wide area to provide heating of large volumes of air for use in a dryer. 
   BRIEF SUMMARY OF THE INVENTION 
   In one aspect, there is disclosed a burner for providing a stable flame for heating air. The burner includes a mixing tube having an open end for admission of gas fuel thereunto and at least one opening proximate to the open end for admission of air thereunto to allow mixing of air and gas in the mixing tube. A burner head is located at an end of the mixing tube opposite the open end for allowing mixed gas and air to be discharged therethrough and ignited into a flame. The burner head is of substantially hemispheric shape and has a plurality of discharge openings formed by perforations and slots distributed along the surface thereof for providing a substantially uniform distribution of flames emanating from the surface thereof. A baffle is attached to the burner at the base of the burner head, and extends radially outward therefrom an amount sufficient to prevent disruption of combustion of the air gas fuel mixture being discharged from the burner head resulting from air being drawn along the length of the mixing tube on the outside thereof from the open end thereof toward the burner head. 
   In a more specific aspect, the burner head includes a region at substantially the apex thereof having no discharge openings on the surface. 
   In a yet more specific aspect, the plurality of discharge openings in the baffle are of a size, distribution and number effective to prevent lightback. Preferably, the discharge openings are sixteen discharge openings arranged in two concentric equally spaced arrangements of eight openings below the region of the burner head, which has no openings. This results in a generally wide flame distribution substantially radially out from the burner head. 
   In an alternative aspect, the present invention relates to an air heater assembly for a gas dryer which includes a combustion chamber having an air inlet and an air outlet for allowing air to flow therethrough, for being heated and for being passed to clothes to be dried in a drum of the dryer. The air heater assembly includes, among other components, the afore-described burner for providing a stable flame for heating the air being passed through the combustion chamber. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     Having thus generally described the present invention, the same will become better understood from the following detailed discussion, made with reference to the appended drawing wherein: 
       FIG. 1  is a perspective view of the burner in accordance with the present invention viewed from one side thereof; 
       FIG. 2  is a perspective view of the burner of  FIG. 1  viewed from the other side thereof; 
       FIG. 3  is a perspective view of a gas dryer in which the burner in accordance with the invention may be employed; 
       FIG. 4  is a schematic part cross sectional side view of a gas dryer, illustrating generally a heater which includes a combustion chamber, and is of the type employing the burner in accordance with the invention; 
       FIG. 5  is a side view of the burner in accordance with the present invention shown without the baffle; 
       FIG. 6  is a view as in  FIG. 5  from the other side thereof; 
       FIG. 7  is a perspective view of the burner in accordance with the invention shown without a baffle; 
       FIG. 8  is a top view of the burner in accordance with the burner shown without the baffle; 
       FIG. 9  is a plan view from the end showing the burner head of the burner in accordance with the present invention. 
       FIG. 10  is a partial cross-sectional view of the mixing tube shown from the end proximate to the burner head; 
       FIG. 11  is a partial cross sectional view of the mixing tube from the end proximate to the fuel inlet; 
       FIG. 12  is a top plan view of a stamping used to construct the burner head of the invention; 
       FIG. 13  is a side cross sectional view of the burner head; 
       FIG. 14  is a side view of the burner head; 
       FIG. 15  is a top plan view of the burner head; 
       FIG. 16  is a perspective view from one side of the baffle employed with the burner; 
       FIG. 17  is a perspective view from the other side of the baffle; 
       FIG. 18  is a plan view of the baffle from one side; 
       FIG. 19  is plan view of the baffle from the other side; and 
       FIG. 20  is a side view of the baffle. 
   

   DETAILED DISCUSSION OF THE INVENTION 
     FIGS. 1 and 2  illustrate the burner  11  in accordance with the present invention. The burner  11  includes a mixing tube  13  for mixing fuel such as natural gas or propane with air. The mixing tube  13  includes a gas fuel inlet opening  15 . There is also an air inlet opening  17  for having air and gas fuel entrained into the mixing tube  13  and mixed therein. The burner  11  includes a gas burner head  19  having a plurality of perforations or openings  21  therein for discharging a fuel air mixture from the mixing tube  13  and out the burner head  19 . The gas burner head  19  includes a closed region  23  at the apex  24  thereof such that the air fuel mixture discharged therefrom, and resulting flames radiate generally radially outward from the gas burner head  19 . 
   In order to avoid the resulting flames from being disrupted and thus, result in generation of undesirable by-products such as carbon monoxide, etc., a baffle  29  is provided which includes a pair of attachment members  31  as extensions from the baffle  29 , extending generally in a direction parallel to the mixing tube  13 . The baffle  29  includes an air deflection plate  35  to prevent air which is entrained on the outside of the burner  11  in the direction of an arrow  37  from disrupting combustion of the fuel air mixture being discharged through the perforations or openings  21 . 
   The burner  11  also includes a pair of top and bottom plates  25  having a plurality of perforations or openings  27  to facilitate the burner  11  being secured within a gas dryer  51  such as that shown in  FIG. 3 , for example, through the use of screws, bolts, or other conventional fasteners, etc. 
   The gas dryer  51 , also illustrated in  FIG. 4 , typically includes a tumbler  55  inside for receiving wet clothes therein be tumbled and dried by rotation of the tumbler  55 . The air dryer includes a heater  53  which houses the burner  11  which is secured in a fixed position within the heater  53  with a combustion chamber through engagement with plates  25 , and attached through perforations  27  with appropriate screws, bolts, or other conventional fasteners, etc. The baffle  29  also is secured to the plates  25  by a pair of members  31 , each having an opening  33 , which openings  33  are aligned with the corresponding openings  27  of the plates  25 . 
   The burner  11  is shown in greater detail in  FIGS. 5–8 , shown without the baffle  29  attached. As may be appreciated from  FIGS. 5–8 , the mixing tube  13  is of a generally smaller diameter than the burner head  19 . The smaller diameter mixing tube  13  allows for the discharge of the fuel air mixture to expand outwardly and out radially generally through the perforations  21  to result in a widely dispersed flame pattern (not illustrated). However, as also shown in  FIGS. 5–8  and  11 , the mixing tube  25  also includes a slightly larger open portion at the fuel inlet end thereof to allow appropriate volumes of fuel and air to enter through the inlet opening  15  and the air inlet  17  into a smaller cross section of the mixing tube  13  extending to the end proximate to the burner head  19  as is shown in  FIG. 10 . As shown in  FIG. 9 , and  FIGS. 12–15 , the burner head  19  is made from a stamped plate  71 , which includes the perforations  21  as well as a plurality of slots  73 . When forced into shape to form the burner head  19 , the slots  73  close to result in joined regions  75  and additional perforations  21 . The perforations  21  preferably are arranged in two substantially concentric circles  28  and  30  of eight perforations  21 , with the region  23  of the burner head  19  being closed to form the apex  24 . The burner head  19  so formed causes the fuel air mixture to be discharged generally radially resulting in a wide flame pattern (not illustrated) thereby maximizing the amount of air heated and passed into the tumbler region  55  of the dryer  51 . 
   As further shown in  FIG. 4 , when the air is heated by the heater  53 , it passes through a path  57  into the tumbler  55  and therefrom after drying clothes therein by removing moisture, and it is discharged through a discharge path  59 . 
   The baffle  29  in accordance with the present invention is more clearly shown in  FIGS. 16–20  and includes a rounded section  77  of the air deflection plate  35  and a more contoured section  79  of the air deflection plate  35  to accommodate space constraints and fitting within the dryer  53 . As may be appreciated, the air deflection plate  35  can take on various other shapes as necessary to the environment in which it is employed. What is important is that the size relative to fuel flow is an amount sufficient to eliminate the effects of secondary air flow such as that shown by arrow  37  in  FIG. 1 . 
   It is important to appreciate that a central opening  75  of the baffle  29  through which the burner head  19  passes needs to be of a very precise size to ensure no air leakage between the opening  75  at the region where the baffle  29  seats against a base of the burner head  19 . The members  31  extend along the same direction as the mixing tube  13  and are secured to the plates  25  through the openings or perforations  33 . The burner  11 , and in particular the gas burner head  19  is preferably made of stainless steel, such as  304  or  430  stainless steel. 
   The burner  11  of the present invention can operate with alternative sources of fuel such as propane or natural gas. The size of the perforations  21  on the burner head  19  are selected to provide appropriate size flames to meet the requirements for heating air passed through a gas dryer  51 . The location of the perforations  21  in the two concentric circles  28  and  30  and the sizes of the perforations  21  are selected such that when operated in combination with the baffle  29 , results in no flashback yet has a smooth ignition, for example, with an electronic igniter. In selecting the sizes of the various components, they are optimized to result in carbon monoxide generation of less than 0.04% (400ppm), in an air-free sample of the flue gases from the dryer. 
   Having thus generally described the invention in detail, the same will become better understood from the appended claims in which it is described in a non-limiting manner.