US3812838A

US3812838A - Oven combustion products distribution system

Info

Publication number: US3812838A
Application number: US00376661A
Authority: US
Inventors: P Mutchler
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1973-07-05
Filing date: 1973-07-05
Publication date: 1974-05-28
Anticipated expiration: 1991-05-28

Abstract

A liquid fuel-fired convection oven wherein the gases of combustion from a burner are blended with cooling air flowing through an annular space surrounding the combustion chamber and the blended hot gases are divided into two streams each of which is caused to flow through a plurality of channels which extend vertically along the side wall and across the top wall of the oven, emptying into an exhaust manifold on the top of the oven. The contiguous, hollow channels allow the hot gases to flow in substantially uniform streams in contact with the side and top walls to provide a uniformly efficient transfer of heat to the oven.

Description

[ May 28, 1974 Mutchler OVEN COMBUSTION PRODUCTS DISTRIBUTION SYSTEM Primary Examiner--Edward G. Favors Attorney, Agent, or Firm-Edward J. Kelly; Herbert Berl; Lawrence E. Labadini {75] Inventor: Paul A. Mutchler, University, Mo.

{73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.

July 5, 1973 ABSTRACT {22] Filed:

[21] Appl. No.: 376,661 A liquid fuel-fired convection oven wherein the gases of combustion from a burner are blended with cooling air flowing through an annular space surrounding the combustion chamber and the blended hot gases are divided into two streams each of which is caused to {52] U S Cl 126/21 A [51] Int. F24c 15/32, A2lb 1/10 [58] Field of Search 126/44, 21 A, 39 D, 19,

flow through a plurality of channels which extend vertically along the side wall and across the top wall of the oven, emptying into an exhaust manifold on the [56] References Cited UNITED STATES PATENTS top of the oven The contiguous, hollow channels allow the hot gases to flow in substantially uniform 126/39 D streams in contact with the side and top walls to pro- 126/21 A vide a uniformly efficient transfer of heat to the oven. Torrey et 126/39 D 6 Claims, 2 Drawing Figures 1,209,683 12/1916 Detwiler........ ...............r.. 3,324,844 6/1967 Huffmanmm... 3,480,000 11/1969 FOREIGN PATENTS OR APPLlCATlONS 432,481 7/1935 Great Britain.. 126/39 D PATENTEDIIAY 28 um 13; 8 l 2 8 3 8 sum 2 or z The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without thepayment to me of any royalty thereon.

BACKGROUND OF THE INVENTION This invention relates to oven heating systems and, more particularly, to a combustion products distribu tion system for heating an oven.

Oven heating systems are known in the art wherein different heating arrangements have been employed in an attempt to effectively utilize thermal energy from different sources. The specific heating arrangement or system to be utilized will, of course, depend in large measure on the specific source of thermal energy, e.g., solid, liquid, or gaseous fuel or electrical energy. Heating arrangements which have proven satisfactory in the past with respect to most thermal energy sources are not satisfactory for use in connection with liquid fuel sources since the temperature of the combustion gases conventionally generated thereby are greatly in excess of the temperatures normally required for cooking food. In US. Pat. No. 3,408,999, there is disclosed a liquid fuel-fired cooking apparatus wherein the combustion gases flow from the burner through an enclosed header channel, around the peripheral branch channels and then flow through a passageway beneath the oven floor. Gases also pass, to a limited extent, by convection through a gas passage which is a hollow space surrounding the side and top walls of the oven. This system does not provide for an even application of heat to the walls of the oven since the transfer by convection along the side and top walls will be of minimal effectiveness with the greater portion of the heat transfer occurring at the bottom wall of the oven which is in contact with the flowing combustion gases. This invention, on the other hand, allows the heat energy in the combustion gases to be significantly more uniformly distributed over more of the surface area of the oven so as to more efficiently and effectively heat the oven cavity.

SUMMARY OF THE INVENTION The present invention provides a novel, highly efficient, and unobvious heating system for an oven and especially for an oven utilizing a liquid fuel heat source. The products of combustion from the thermal energy source are blended with ambient air to achieve a proper temperature range and the thus blended gases are caused to flow through a plurality of separate gastight channels in contact with and along each side wall and across the top wall of the oven, meeting in a common duct which leads, in turn, to a gas vent. The heat energy from the combustion gases is thereby uniformly applied to the top and side walls of the oven in a manner which will provide for a highly efficient transfer of the heat energy within the combustion gases.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partially broken-away, perspective view of a liquid fuel-fired oven and the heating system therefor according to the present invention;

FIG. 2 is a partially broken-away perspective view of the combustion chamber and duct work leading to the oven of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT- Referring to FIG. 1 of the drawing, there is illustrated an oven having a unique heating arrangement or system by which it can effectively and efficiently utilize hot gases from some thermal energy source and especially combustion gases from a liquid fuel source. The oven, designated generally as 10, is a typically rectangular, box-like design, made of sheet metal and insulated where appropriate. On the front wall 11 are hinged double doors 12 (access means) which open to'allow access to the oven cavity 13. Although not shown the drawing, the cavity is adapted to contain and utilize the usual complement of supports and racks. The oven is of double wall construction, i.e., having an inner shell 14 which defines the oven cavity 13 and is designed for easy cleaning, and a spaced apart outer shell 15 which encloses the top, sides and back of the inner shell. In the space between the inner shell 14 and outer shell 15, there is found conventional insulation as well as the heat transfer means to be described hereinafter. The inner shell 14 of the oven consists of opposed side walls 17 and 17', a top wall 16, a bottom wall 22, back wall 18 and front wall 11. Within the space between the inner l4 and outer l5 shells and against the surface of the side walls and'the top wall is located the hot gas conduction means which consists of a plurality of separate hollow channels 19 which are formed of corrugated sheet metal 23 positioned tightly against the inner shell 14. Channels 19 define gas-tight passageways against the inner shell 14 and each channel 19 extends vertically along the side wall 17 or 17' and continues horizontally over the top wall 16 toward the cen' ter where each channel connects with a common exhaust means, an exhaust manifold 20 having an exhaust stack 21 through which the hot gases are vented to the atmosphere. While the size and number of the channels 19 will affect the efficiency of the heat exchange, it has been found to be essential that at least four separate channels be employed on each side wall. The channels are preferably contiguous so as to cover the entire side 17 and 17' and top 16 wall area and thereby uniformly heat those wall areas.

Referring to FIG. 2, there is shown a liquid fuel burner designated generally as 30, having mounted therein a liquid fuel combustor 31 of the type described in US. Pat. No. 3,408,999. The combustor is centered on a rigid plate 32 and is connected to a source of liquid fuel and a source of combustion air under pressure, neither of which are shown in the drawing. Sprayed liquid fuel and combustion air are blended and caused to burn within the combustion chamber 33. The hot combustion gases emerge from the combustion chamberinto a combustion products pipe 34. Combustion chamber shroud 35, having its walls spaced from the walls of the combustion chamber 33 completely enclose the latter. Cooling air, from a source not shown, is forced under pressure to pass through the spaced between the combustion chamber 33 and shroud 35 cooling the wall of the combustion chamber. A cylindrical shroud 36 spaced from and enclosing the combustion products pipe 34 causes the same flow of cooling air to pass therebetween cooling the pipe 34. The combustion products pipe 34 is closed at its end 37/nd has a plurality of openings 38 adjacent thereto 37 and allow the combustion gases to exit therefrom and blend with the cooling air forced through the shroud 36. A hollow cylindrical tube 39 is connected with shroud 36 and conveys the blended combustion product gases and cooling air to a point beneath the bottom wall 22 of the oven. At this point, tube 39 leads into a Y connector 40, the branches of which connect with separate conduits 41 which are positioned beneath the bottom wall 22 of the oven and join or connect with oven manifolds 42 which are positioned beneath each of the oven side walls 17 and 17'. The oven manifold has a plurality of small, annular orifices 43 along its top surface, with each orifice opening into a separate hollow channel 19. Tube 39, connector 40, conduits 41 and manifolds 42 constitute the gas inlet means which carries the combustion gases from the combustor to the hollow channels on the walls of the oven.

in operation, fuel and combustion air are delivered to the combustor 31, blended and caused to burn in the combustion chamber 33. The temperatures of the combustion gases as they exit from the combustion chamber range from l,000 to 1 ,800 F. Cooling air is caused to flow through the space surrounding the combustion chamber 33 and combustion products pipe 34, cooling the walls of the chamber and the pipe and thereafter blending with the combustion gases adjacent the end of pipe 34. At this point, the temperature of the gaseous mixture is preferably of the order of 300 F. to l,l F. The gas mixture flows through tube 39 where it is divided by Y connector 40 and passes into equally divided streams through each conduit 41 which, in turn, empty into oven manifolds 42 under each. side wall. The hot gases exit uniformly through each ofthe orifices 43 into each of the respective channels 19. The orifice opening is small or undersized as compared with the passageway defined by each channel 19, and, as a consequence, the gases flow under pressure into an oversized channel producing a turbulent flow of hot gases within the channel, such turbulence improving the heat transfer efficiency within the channel. The hot gases flow through each of the channels along each side wall and over the top wall of the oven and exit into a common exhaust manifold 20. The distribution of gases to each of the channels is quite uniform because of the back pressure created by the undersized orifices 43 in the oven manifolds 42 so that the heat input is relatively even across the width of the oven side walls. This even distribution of hot gases throughout the channels and the turbulence produced within the channels combine to provide a uniform and highly effective mechanism for transferring the heat energy of the combustion gas mixture to the oven cavity 13. Three wall surfaces, both

side walls

17 and 17 and the top wall are uniformly heated by this system which necessarily results in a more efficient application of thermal energy to the oven than is the case when one surface, normally the bottom surface, is the exclusive heat transfer surface. The temperature of the combustion gases delivered to the oven channels can be controlled by regulating either the rate of liquid fuel delivered to the combustor and also by regulating the quantity of cooling air ultimately blended with the combustion gases.

1 claim: 1. A convection oven heated by combustion gases having,

spaced opposed side walls, spaced opposed front and back walls and spaced opposed top and bottom walls which define the oven cavity,

means located on said front wall to permit access to said cavity,

gas inlet means associated with the underside of said bottom wall which conducts combustion gases from a burner to the base of each side wall, said gas inlet means dividing the flow of combustion gases into two streams which are delivered to separate oven manifolds beneath each oven side wall, said manifolds having undersized orifices which communicate with each of said channels through which the combustion gases pass under pressure in a turbulent stream,

gas conduction means associated with each of said side walls and said top wall adapted to conduct said combustion gases from said gas inlet means in a plurality of separate and substantially uniform streams in a vertical direction along and in contact with each of said side walls and then in a horizontal direction across and in contact with said top wall, said gas conduction means being composed of a plurality of gas-tight channels in heat conducting relationship with said oven side and top walls, and

exhaust means on said top wall in communication with said gas conduction means and adapted to receive and vent the combustion gases,

whereby said combustion gases are forced to flo through said gas inlet means through said gas conduction means into said exhaust means to uniformly and efficiently heat the side and top walls of said oven.

2. A convection oven according to claim I wherein said side and top oven walls form one side surface of said gas-tight channels.

3. A convection oven according to claim 2 wherein said hollow channels are contiguous and completely cover the side and top walls of said oven.

4. A convection oven according to claim 3 having at least four separate channels on each of said side and top walls.

5. A convection oven according to claim 4 having in combination therewith a burner, said burner having a combustion chamber wherein the fuel is burned, an annular air passageway surrounding said combustion chamber through which cooling air is caused to flow to cool the walls of said combustion chamber, burner exhaust means in communication with said passageway and said combustion chamber wherein said combustion gases and said cooling air are mixed and then caused to flow into said gas inlet means.

6. A convection oven according to claim 6 wherein said burner is fired with liquid fuel.

Claims

1. A convection oven heated by combustion gases having, spaced opposed side walls, spaced opposed front and back walls and spaced opposed top and bottom walls which define the oven cavity, means located on said front wall to permit access to said cavity, gas inlet means associated with the underside of said bottom wall which conducts combustion gases from a burner to the base of each side wall, said gas inlet means dividing the flow of combustion gases into two streams which are delivered to separate oven manifolds beneath each oven side wall, said manifolds having undersized orifices which communicate with each of said channels through which the combustion gases pass under pressure in a turbulent stream, gas conduction means associated with each of said side walls and said top wall adapted to conduct said combUstion gases from said gas inlet means in a plurality of separate and substantially uniform streams in a vertical direction along and in contact with each of said side walls and then in a horizontal direction across and in contact with said top wall, said gas conduction means being composed of a plurality of gastight channels in heat conducting relationship with said oven side and top walls, and exhaust means on said top wall in communication with said gas conduction means and adapted to receive and vent the combustion gases, whereby said combustion gases are forced to flow through said gas inlet means through said gas conduction means into said exhaust means to uniformly and efficiently heat the side and top walls of said oven.

2. A convection oven according to claim 1 wherein said side and top oven walls form one side surface of said gas-tight channels.