Patent Publication Number: US-6338319-B1

Title: Water heater with flammable vapor flame arrestor and method of operation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO MICROFICHE APPENDIX 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     Gas-fired residential and commercial water heaters are generally formed to include a vertical cylindrical water storage tank with a gas burner disposed in a combustion chamber below the tank. The burner is supplied with a fuel gas through a gas supply line and combustion air through one or more air inlet openings providing communication between ambient air and the interior of the combustion chamber. 
     Water heaters of this general type are extremely safe in operation. However, when gasoline or other flammable liquids are stored or used improperly in proximity to the water heater, there may exist a possibility of flammable vapors becoming entrained in the air intake of the water heater. It is accordingly possible for the resulting flame to propagate out of the combustion chamber into the ambient environment around the water heater as a result of following the intake path of the flammable vapor. Under such conditions, a fire and/or explosion may occur. The present invention relates to a gas-fired water heater design where the danger of such a fire or explosion referred to above is greatly reduced or completely eliminated. 
     BRIEF SUMMARY OF THE INVENTION 
     A water heater having a sealed combustion chamber with a fuel burner mounted therein. A flame arrestor is mounted in the bottom wall of the combustion chamber. The arrestor is comprised of continuous spiral wound layers of a flat material and a corrugated material sandwiched between layers of the flat material. The honeycomb construction provides a plurality of air passage cells, which extend from one surface of the arrestor to the opposite surface of the arrestor. The height of the arrestor is relatively long compared to the cross-sectional areas of the air passage cells. The arrestor functions to allow combustion air to flow from the atmosphere into the combustion chamber. The arrestor is further adapted to prevent flashback back through the arrestor to thereby prevent ignition of flammable liquids, which may have become spilled in the area in which the water heater is installed. The arrestor is of sufficient mass so as to function as a heat sink to thereby prevent the heat in the combustion chamber from passing through the arrestor by conduction to a temperature degree sufficient to cause ignition of a flammable liquid located exteriorly of the combustion chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cross-sectional side elevation view of a water heater with a flame arrestor mounted in the wall of the water heater combustion chamber; 
     FIG. 2 is a side elevation perspective view of the flame arrestor shown in FIG. 1 with parts broken away; and 
     FIG. 3 is an enlarged fragmentary top view of the encircled area shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, the water heater  10  of the present invention is comprised of a watertight tank shell  12  having an outer jacket  14  spaced from the shell. Tank shell  12  contains the water to be heated in interior  13  of the tank. 
     The space between the tank shell  12  and jacket  14  is filled with a suitable insulation material (not shown). 
     The water heater  10  is supported on a plurality of leg members  16 . 
     A sealed combustion chamber  18  is located immediately beneath tank shell  12 . Chamber  18  is comprised of a bottom wall  20  and a top wall  22  fastened to the inside surface of the tank shell wall  12  by welding or other suitable means. Walls  20  and  22  and the lower wall portion  24  of tank shell wall  12  together serve to provide the sealed combustion chamber  18 . A flue gas tube  26  is mounted and sealed by welding in an opening  28  in the top wall  22  of the combustion chamber  18 . 
     A gas-fired burner  30  of conventional construction is mounted in combustion chamber  18 . A fuel oil fired burner could be used as an alternative. Gas to burner  30  flows through a tube  32  under the control of a thermostatically controlled valve  34 , also of conventional construction. A heat sensor member  36  extends into the water in the interior  13  of tank shell  12  and functions to control operation of thermostatic valve  34 , which, in turn, functions to control the flow of gas to burner  30 . A partition  33  with openings  35  is mounted in combustion chamber  18  between the bottom wall  20  of the combustion chamber  18  and the gas-fired burner  30 . Openings  35  are located outside of the circumferential edge of burner  30 . 
     A flame arrestor member  38  is mounted in a combustion air opening  21  in bottom wall  20  of combustion chamber  18  and is fastened in wall  20  by welding or other suitable means. 
     As shown in FIG. 1, flame arrestor  38  is mounted in wall  20  of the combustion chamber in a location wherein the major portion of the arrestor extends downwardly from wall  20  below combustion chamber  18 . In a preferred embodiment, the arrestor  38  is located so that the top  41  of the arrestor is substantially at the level of wall  20 , i.e., with the top  41  flush with the wall  20 . The reason for this relationship will be explained hereinafter. 
     While the detailed construction of arrestor  38  can vary, one preferred embodiment is shown in FIGS. 2 and 3. The arrestor  38  can be described generally as having a honeycomb construction. 
     More specifically, as shown in FIGS. 2 and 3, the arrestor is comprised of continuous spiral wound layers of a flat material  40  and a corrugated material  42  sandwiched between layers of the flat material  40 . The resulting honeycomb construction  44  is clearly shown in FIGS. 2 and 3. 
     As shown in FIGS. 2 and 3, the honeycomb construction  44  is comprised of layers of flat material  40  and corrugated material  42  which provide a plurality of air passageway cells  46  which extend from one surface  29  of the arrestor  38  to the opposite surface  41  of the arrestor  38 . 
     The air passageway cells  46  shown in FIG. 3 are of a trapezoidal cross-sectional shape. The cells could also have a variety of shapes, such as square, rectangular, triangular, etc.. The cross-sectional area of cells  46  is in the range of 0.0031 to 0.375 square inches. In one preferred embodiment, the corrugated material  42  has dimensions of 1.25, 1.00 and 2.75 millimeters as shown in FIG.  3 . 
     In a typical embodiment, i.e., a water heater having a BTU/HR input of 40,000 BTU, arrestor  38  will have a diameter  48  of approximately six (6) inches and a height of 50 (thickness) of approximately two (2) inches. As indicated, the height  50  of the arrestor  38  is relatively long compared to the cross-sectional areas of passageway cells  46 . 
     The material of flame arrestor  38  can be metallic, such as stainless steel or non-metallic, such as a high temperature resistant ceramic. 
     Operation 
     When flammable fluid such as gasoline (paint thinner, cleaning fluid, etc.) is spilled in the area in which the heater is installed, the pilot or main burner of a conventional water heater, i.e., a water heater without a sealed combustion chamber  18  and a flame arrestor  38 , may cause the gasoline vapors to ignite, resulting in a fire and/or explosion to occur in the space in which the water heater is installed. 
     The water heater  10  of the present invention operates as follows. When heat sensor member  36  calls for heat, thermostatically controlled valve  34  opens to allow a flow of gas fuel to flow through tube  32  to burner  30 . A pilot burner (not shown) will ignite the gas fuel at the burner  30 . 
     In the water heater  10  of the present invention, outside combustion air flows into combustion chamber  18  through the air passageway cells  46  of arrestor  38 . The air entering chamber  18  supports combustion of the gas fuel at burner  30  to thereby heat the water in the interior  13  of tank  12 . 
     If gasoline is spilled in the area in which the heater is installed, gasoline vapor passing through arrestor  38  into combustion chamber  30  will be burned up inside the chamber. Due to the pressure drop between the inlet face  39  and the outlet face  41  of arrestor  38 , a flashback of burning gasoline vapor is prevented, i.e., the relatively long and narrow passageway cells  46  will prevent burning gasoline vapor from backfiring out of the inlet face  39  of arrestor  38 . 
     The mass of the flame arrestor  38  is of a sufficient magnitude so as to cause the flame arrestor  38  to function as a heat sink. This heat sink effect will prevent the heat in the combustion chamber from passing through the material of arrestor  38  by conduction to a degree sufficient to reach the ignition temperature of a flammable material such as gasoline located exteriorly of the combustion chamber  18 . 
     Thus, the combined pressure drop effect and heat sink effect provided by the arrestor  38  functions to prevent ignition of gasoline vapor exteriorly of the water heater combustion chamber. 
     While the invention herein has been shown and described in what is presently conceived to be the most practical preferred embodiment, it will be obvious to one of ordinary skill in the art that many modifications may be made thereof within the scope of the invention, which scope is not to be limited except by the appended claims.