CA2243216C - Steamer gas oven - Google Patents

Abstract

A gas powered, pressureless steam cooker has a connector tube for ingress of steam into the cooking compartment so that entry of a low temperature, wet steam can be minimized. The connector tube has a small diameter to constrain the entry of steam into the cooker compartment until it has reached a minimum velocity. A water reservoir is located alongside the oven compartment to the rear of the cooker and an integrated heat exchange tube and firebox are located in the tank. This tube is generally U-shaped, a lower horizontal leg opening at a mouth outside the water reservoir. An inshot burner fires into the lower horizontal leg and combustion gas flow through the U tube giving up heat to water in the reservoir. Additional heat exchange surface may be provided by channels through an upper leg of the U-tube from side to side. Flow of combustion gases may be optimized by the shape of the U-tube and at least a deflecting surface between a vertical web of the U and the upper leg of the U.

Description

This invention relates to a gas powered pressureless steam cooker, especially to a gas powered steamer for commercial or resta~..ir~ant use. The term "pressureless steam cooker" is intended to mean a steam cooker in which no great pressure of steam is developed although minor pressure of say 1/21.b. per square inch may be permissible.
Steam cookers c:~onventionally cook foods by the use of hot steam and may be powered by a steam generator which is either gas fired or electrical fired. No electric heating elements ar~~ present: in the cooking compartment itself. For gas fired units, there has always been an ongoing problem in providing steam r:~t a suitable temperature inside the cooking compartment without the loss of efficiency, e.g.
heat in delivering the steam to the cooking compartment.
For pressurf=less st~:am cookers steam is generally supplied into the cooking corr~partment through an open vent thus allowing ingress of wet steam at low temperatures.
The common design of a steam generator, or heat exchanger, up to today utilizes an atmospheric burner heating the outside of a steam generator. Atmospheric style burners are general~.y larger and have low efficiency due to their operai:ing characteristics of burning in the open atmosphere. Usually such steam generators are located below the oven cornpartment:lbut in some cases oven compartments are side-by--side with steam generators.
Examples of steam ovens are shown in:
U.S. Patent No. 4,281,636 Vegh et al. Aug. 4, 1981 U.S. Patent No. 4,552,123 Bi.rkner Nov. 12, 1985 U.S. Patent No. 3,820,524 Buckell June 28,1974 U.S. Patent No. 4,4~a0,822 Alden et al. July 17,1984 U.S. Patent No. 5,5~~9~,038 Kolvites Aug. 27,1996 U.S. Patent No. 5,732,614 Oslin Mar. 31,1998 U.S. Patent No. 7h:>2,590 Lawrence June 14,1904 U.S. Patent No. 1,226,044 Wilson May 15,1917 U.S. Patent No. 1::L3,241 Ashcroft April 4, 1871 U.S. Patent No. 2,4;1:4,587 Young et al. July 6, 1948 U.S. Patent No. 5,1'8,125 Kuen Jan. 12,1993 The present im,rentors have addressed the problem of providing a more efsicient gas powered steam generator, by combining t;he use ox: the latest burner technology and by the use of ,gin innovative heat exchanger.
According to the invention there is provided a gas powered pre;~sureless steamer cooker comprising at least one cooking compartment having at least one steam inlet for steam to en~er the <:ompartment for cooking, a steam generator which is ~..ocated immediately adjacent to said cooking com~~artment in side-by-side relation therewith, the steam generator comprising at least one integrated heat exchanger tube and f:'irebox within a water reservoir, the tube opening in a gE.nerally vertical mouth, an inshot gas burner direcJted intca said mouth, means for supplying gas to said burner, the integrated heat exchanger tube and firebox being in heat exchange relationship with water within the water reser~roir to c:r~eate steam from water, the reservoir having an outlet foz° steam, connector means between said outlet and raid stes.m inlet of said cooking compartment characterized in that said connector means is constrained to direct t:he supply of steam therethrough; and in that said heat exchange c::ube comprises a U-shaped tube having a lower horizontal leg, an upper horizontal leg and a vertical we:b, said w-ertical mout:.h being located at a distal end of the lower leg. The heat exchanger creates steam in the steam generator anal delivers it through the connection means from the outlE:at to the :inlet of the cooking compartment.
Conveniently for each cooking compartment a pair of inshot burners are provided, each one directed into a mouth of a respective lower leg of a pair of parallel heat exchanger U-tubes.
Utilizing the inshot burner, the flame is directed into the parallel U--tube exchangers and resulting hot gases flow throug)z the tuY:~es, the surfaces of which are heat exchange surfaces with the water reservoir. Of course, one, or more than two U-t:u:bes may be used if desired. An inshot burner is provided for each heat exchange tube. The heat exchangers ;ire comp7.etely immersed in water inside the reservoir, <~ny convenient level control means being provided to maintain the level of water. Steam is injected into the cocking compartment i~hrough a steam inlet tube as the connector means.
The U-tube heat: exchangers are important in the provision of a steam oven which may have significant advantages :in effici.e:ncy. Preferably for each U-tube heat exchanger, i~he lowex:~ leg is of square section tube having rounded corners and has a cross section of a size to enhance oxygenfair flow into the tube for utilization by the inshot burner. ~t is, of course, possible to use tubes with other cross sec:t.ion. Any longitudinal weld in the lower leg may convent.ional.ly be along an upper surface.
This lower leg of tine heat exchanger tube is effectively a firebox for the ins~ncrt burner and its dimensions and shape are selected to enhance operation of the burner while allowing the flow of the combustion gases into the upper part of the heat exchanger tube.
1o Preferably, fo~:v each U-tube heat exchanger the upper leg may be of rectangular section tube having a height greater than the width and less than the length of the tube. The ratio of the height o~ the upper leg of the tube to the length of thc~ upper leg of the tube may be generally about 1:4 and preferably about 1:2. In an extreme case the height and the length may be equal. It may, of course, be more or less than this.
The height of t:he upper leg of the tube should be at least suffi~~ient to allow for the presence of channels from side to side of the leg without interfering unduly with the f low of hot gases ire the tube .
Preferably at least two cylindrical or other shaped channels are provided to supply additional heat exchange surface and to act ~~s a stay between the sides of the upper leg of the heat excraanger tube. It is believed that the use of a hollow stay may provide significant advantages over conventiona:L solid stays. This is due to the fact that more heat exchange surfac.~e is provided.

The web of the L;~-tube may be generally vertical and it may be advantageous to provide an angled deflection surface for hot gases at the top corner where the web meets the upper leg. Such def::l.ection surface may be angled at roughly 45° to each of the ~.;~p~per leg and web although any angle will provide some benefit. A general range of suitable angles is from 30° tvo 60°. The deflection surface may help to reduce gas turbu:~.ence in the corner and direct the flow of gas smoothly aro~:md the U.
The U-tube heat::. exchangers should be spaced from the bottom of t:he steam generator tank to avoid build up of lime scale :between the tank bottom and the U-tube.
An embodiment <:~f the invention will now be described by way of example w~.th reference to the drawings, in which:
Figure 1 shows a general view of a two compartment steam cooker;
Figure 2 is an isometric view showing the steam generator for one of the compartments of Figure 1; and Figure 3 is an isometric view of an alternate steam generator; and Figure 4 is an isometric view of one of the heat exchange tubes of trre steam generators of Figures 2 and 3.
Figure 1 shows a ger:~eral view of. a two compartment steamer 10, each compartment. 12 having steam inlets 38 and being supplied with steam from the steam generator 26 comprising an integrated heat Exchange tube/firebox 18 (see Figure 2) and a water reservoir 27. A one compartment unit is also possible.

_ 6 The gas burner 14 of the exemplified embodiment is an inshot burner type <af any convenient type. For example, they may be gas burner nozzles .in accordance with those described a:nd claimed in U.S. Patent No. 5,186,620 issued February 16, 1993 tc~ Hollingshead and assigned to Beckett Gas Inc. The inshot gas burner 14 is a relatively small unit in comparison t:o the BTU/HR output. The gas and primary air is mixed at the beginning of the burner inlet.
When the fl,~me exit;:=. at the end of the burner tube, it is mixed with secondary air to form an extremely hot flame cone.
As shown in Figures 2 and 3, for each cooking compartment 12 a pa~.r of inshot burners 14 are directed into mouths 16 of U--tubes 18 having their webs 20 parallel and vertical, and hc~razontal upper legs 22 parallel with horizontal :lower legs 24. Mouths 16 are located at the distal ends of lower legs 24.
The lower legs 24 are each formed of stainless steel tube of app_roximate7..y square section. The tube is formed by bending plane into t:.he desired shape to have rounded corners 25. A weld ~t9 is provided along the top surface.
These lower legs not:.~only form part of the heat exchanger but also acl~ as fire tube for the inshot burners.
The upper legs 22 are deep in comparison with their width. IndeE~d, as sY:~o~wn, the height of upper leg 22 is approximately 1/2 its length. Two cylindrical channels 23 pass through upper leg 22 from side to side as stays between the sides tc.~ increase the heat exchange surface.

While two cylindrical channels 23 are shown more or less channels are possible. These channels should not interfere unduly with flow of gas inside the U-tube. It may be suitable that the da.ameter of the channels be approximately 1/2 the height of upper leg 22.
The webs 20 of the U-tubes are roughly vertical and deflecting walls 21 are provided at an upper corner to deflect gas flow int::o upper legs 22. The angle of to deflecting wall 21 ray be about 45°.
The or:ientatiora of U-tubes 18 is also important. U-tubes 18 should eacY:~ be spaced from the bottom of steam generator tank 26 to minimize build up of lime scale. The spacing may conveniently be about from 3/4 inch to 1~ inch although greater or even lesser spacings are possible. The spacing is maintainE:~d by welding the lower leg 24 of the tube 18 to r_he wall of the steam generator tank in its mouth area and by welding the exhaust flue 17 (Figure 2), 19 (Figure 3 ) t.o thE:~ tank where it exits .
2o Figure: 2 and 5 differ from one another only in the arrangement of the flue exhaust outlets. Figure 2 shows a top exhaust 17 and F'i~~ure 3 shows the exhaust 19 at a side 15 of the si~eam generator tank 26.
Each pair of tubes 18 is arranged within a water/steam tank 26 haying an ir~.lnt 31 for water. The tank 26 and an outlet 28 for steam are also provided with at least one probe 34 to indicate internal water level. The outlet 28 is connected to inlet 38 through a short length of tube 44.

The tube 44 has a small diameter to somewhat check free flow of steam into oven compartment 12. Such constraint tends to retain ver~r~ wet low temperature steam in the steam generator 26 until _i.t has sufficient velocity built up to pass through the tube 44. Preferably the tube 44 has a diameter of 3/8 of ~:~.n inch but diameters of 1/4 of an inch to 1/2 an inch are acceptable and diameters outside this range are possible for some sizes of steam generators and ovens.
To curb the flc,w of steam even further, a nozzle may be provided to jet steam into the oven compartment. It should be remembered that the steamer cooker is essentially a pressurelc~ss cooker and therefore the nozzle must not be so constrirt~ing that:. there is undue build up of pressure.
Approximate:Ly half a pound of pressure may be admissible but more involves changes in cooking technique. Therefore the choice of diameter of nozzle is dependent on the pressure bu:Lld up. F'or example, a suitable nozzle diameter z0 might be 7/:32 of an inch plus or minus 1/8 an inch.
Suitably the, nozzle may have four orifices and there are two nozzles (and tubes 44) per oven compartment.
The proper amount of dry steam required for cooking is generated by the laxvge heat transfer area of each U-tube 18 heat exchanger. This heat transfer is represented by all vertical and horizontal areas in the U-tube. Flames from burner 14 are directed into horizontal lower leg 24 through tube openinc3 16. The end of the flame and hot gases continue their way t.h:rough the integrated vertical web 20 and then these gases enter the upper leg 22 of the heat exchanger, and continue through the extension of the main chamber in a vertica.:~l or angular direction into the flue exhaust outlet 17 (see Figure 2) or 19 (see Figure 3). It is believed that ut:~.lizing the inshot burners, a high efficient, compact boiler producing dry steam may be attained. This generator 26, being adjacent to the cooking cavity 12 and the in;im.ediate ingress of steam into the chamber 12, that the:: temperature for the dry steam is maintained at generally 212°F.
The side 35 of tank 26 is flush with and juxtaposed against a back surface 15 of cooking compartment 12 so that the length of tubes 44 is minimized. Inshot burners 14 are directed into the mouths of lower legs 24 of heat exchanger ~5 tubes 18 from the side allowing easy access for maintenance and economic use of space. It it believed that by utilizing the efficacy of inshot burner nozzles 14, the arrangement of U-shaped heating tubes for said nozzles having vertically arranged webs, and the immediate ingress of steam into i:he cooking compartment 12, benefits may be provided.
The wager level. in this generator is controlled by probes 34. '.Chew are protected from turbulence by using a special stainless steel box 42 in which all probes are enclosed.

Claims (9)

1. A gas powered pressureless steamer cooker comprising at least one cooking compartment having at least one steam inlet for steam to enter the compartment for cooking, a steam generator which is located immediately adjacent to said cooking compartment in side-by-side relation therewith, the steam generator comprising at least one burner and at least one integrated heat exchanger tube and firebox within a water reservoir, the tube opening in a generally vertical mouth, an inshot gas burner directed into said mouth, means for supplying gas to said burner, the integrated heat exchanger tube and firebox being in heat exchange relationship with water within the water reservoir to create steam from water, the reservoir having an outlet for steam, connector means between said outlet and said steam inlet of said cooking compartment characterized in that said connector means is constrained to direct the supply of steam therethrough to provide pressure of not more than 1/2 lb.;
said heat exchanger tube comprises at least one U-shaped tube having a lower horizontal leg, an upper horizontal leg and a vertical web spacing the lower horizontal leg below the upper horizontal leg whereby all vertical and horizontal areas of the U-shaped tube are available for direct heat transfer with water in said water reservoir; and said vertical mouth being located at a distal end of the lower leg.

2. A gas powered pressureless steam cooker as claimed in claim 1 in which the connector means is at least one tube having a diameter of from 1/4 of an inch to 1/2 of an inch.

3. A gas powered pressureless steamer cooker as claimed in claim 1 in which the lower leg of U-shaped tube is formed of square section tube with rounded corners.

4. A gas powered pressureless steamer cooker as claimed in claim 1 in which the upper horizontal leg has a height to length ratio of from 1:1 to 1:4.

5. A gas powered pressureless steamer cooker as claimed in claim 4 in which said height to length ratio is generally 1:2.

6. A gas powered pressureless steamer cooker as claimed in claim 4 in which at least one horizontal channel passes through upper horizontal leg from side to side orthogonal to its axis.

7. A gas powered pressureless steamer cooker as claimed in claim 1 in which a gas deflecting surface is provided between the web and upper horizontal leg to direct gases in the tube into the upper horizontal leg.

8. A gas powered pressureless steamer cooker as claimed in claim 7 in which the deflecting surface is oriented at 45° to the web and the upper horizontal leg.

9. A gas powered pressureless steamer cooker as claimed in claim 1 in which the U-shaped heat exchanger tube is spaced above the bottom of water reservoir.