US3499429A - Oven heat regenerator - Google Patents

Description

March 10, 1970 R. L. PERL OVEN HEAT REGENERATOR Filed Jan. 17, 1968 mmZmDm Zu 0 EOPPOm INVENTOR RICHARD L. PERL ATTORNEYS United States Patent "ice 3,499,429 OVEN HEAT REGENERATOR Richard L. Perl, Mansfield, Ohio, assignor to The Tappan Company, Mansfield, Ohio, a corporation of OhlO Filed Jan. 17, 1968, Ser. No. 698,498 Int. Cl. A2lb N00 US. Cl. 126-21 4 Claims ABSTRACT OF THE DISCLOSURE A heat regenerator for a self-cleaning gas coo-king oven including heat sink means in the form of a wheel with multiple axial passages which are rotated successively through flows of hot flue gases from the oven and relatively cool ambient air being delivered to the oven burner means for combustion, with an auxiliary electric heater arranged at the side of the wheel remote from the oven and at the location where passages move from the exhaust into the incoming air flow. The auxiliary heater serves to add heat to the wheel at such location for heat cleaning of the same and to preheat the incoming air as it enters the wheel.

This invention relates to a heat regenerator for gasfired, self-cleaning ovens and the like and, more particularly, to an improved rotary regenerator assembly for such use.

The recently developed gas self-cleaning ovens in which the reduction of accumulated food soils on the interior surfaces is realized by the heating of these surfaces to a temperature well above the normal range for cooking are commonly designed to operate at temperatures above 750 F. and usually between 900 to 1000 F, The cleaning cycle at such a temperature is of appreciable duration and, accordingly, the amount of heat energy exhausted from the oven during cleaning is very substantial and an objectionable input to the kitchen in which the oven is located. While outside venting of the very hot flue gases is a potential solution to the problem, the burdens of special construction, added cost and the like incident to this type of venting are serious practical limitations on installation and use of the oven and efforts have been made to cool the exhaust within the oven or range structure to a level which can be tolerated within the kitchen and hence exhausted directly to the same.

According to one proposal for such an unvented oven, a heat regenerator is employed to cool the hot exhaust gases from the oven and pre-heat incoming ambient air directed to the burner means within the cavity for combustion with the fuel gas. The regenerator is designed to extract heat energy from the line gases and release the same to the incoming combustion air, with the regenerator thereby being cooled to a temperature where it can continue to cool the hot gases issuing from the oven. The preferred physical form for this regenerator at present is a wheel having a multiplicity of relatively small axial passages and rotated to move portions thereof successively through the flows of the exhaust gases and incoming air.

While some heat may also be extracted from the flue gases between the exit of the same from the wheel and the point of discharge into the room, for example, by ducting and by mixing with ambient air at the discharge point, most of the unwanted heat energy must be extracted in the wheel itself and the back or exit end of the wheel is therefore at a relatively low temperature and below the degree at which there is any significant heat cleaning effect. As noted above, a temperature of about 750 F. is regarded as a minimum for oven selfcleaning, whereas flue gases entering the wheel at about 3,499,429 Patented Mar. 10, 1970 1000 F. may exit at about 400 F., so that the automatic heat cleaning effect is carried only partially into the wheel.

- In order fully to protect such an oven regenerator wheel againstclogging by particles or matter not totally consumed in the usual heat cleaning of the oven, it is a primary object of the present invention to provide an improved assembly for the wheel in which there is supplemental automatic cleaning of the wheel end portion through which the exhaust gases exit from the same,

Another object is to provide an auxiliary electric heating element in association with the wheel for such supplemental heat cleaning action.

It is also an object of this invention to provide an oven regenerator wheel having such an auxiliary heat cleaning element which also functions as a pre-heater for the incoming air as it enters the wheel for delivery to the oven burner means.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principle of the invention may be employed.

The single figure of the drawing is a perspective exploded and partially schematic illustration of an oven regenerator wheel assembly in accordance with the present invention.

Referring now to the drawing in detail, reference numeral 10 designates the wheel part or component of the assembly mounted on an axial shaft 10' which is driven by an electric motor M to turn the wheel relatively slowly in a clockwise direction when viewed from the front as indicated by the adjacent arrow.

The body of the wheel 10 is formed of a high temperature material having substantial heat capacity and structure to define a multiplicity of axial passages fully over the area of the wheel. Such a wheel has, for example, been made by rolling a sheet of corrugated asbestos into a cylinder, with added heat capacity realized by impregnating the asbestos with sodium silicate or a ceramic or refractory material. The composition, structural formation, and dimensioning of the body are not critical factors, particularly in respect of the present improvements, but it may be noted for further illustration only that a corrugated asbestos wheel impregnated with sodium silicate, having a diameter of 9 inches and a length of 2 /2 inches, and rotating at a speed of 6 r.p.m. has been used successfully with a domestic gas oven of usual dimensions in which heat cleaning is carried out at a temperature of about 1000 F,

The oven structure, which has not been shown, comprised top and bottom gas burners in the same cavity and this is indicated by the illustrated components at the oven side of the regenerator wheel 10 or bet-ween the same and the cavity. The first such component is a stationary circular retainer and flow control plate 11 comprising an exterior ring section and an integral horizontal divider strip 12 which defines approximately semi-circular upper and lower openings 13 and 14, respectively. A channel 15 is secured to the inside of the divider strip and brought in the completed assembly close to the forward end of the wheel 10, with the channel thereby effectively dividing the wheel into top and bottom halves coincident with the openings 13 and 14 in the forward flow plate 11.

Oven side ducting comprising an inlet air section generally designated by reference numeral 16 and an exhaust air section designated by reference numeral 17 is applied to the flow plate 11 for communication respectively with the openings 13 and 14 in the latter. The inlet air sec tion comprises a forwardly facing vertical channel 18 having a horizontal upper end extension 19 for directing combustion air to the top oven burner and a comparable lower end extension, not shown, for supplying air to the bottom burner. The vertical channel of this section is of significantly less width than the exhaust air section 17 of the ducting and the former is housed within and closed by engagement with the front wall of the latter. It will be apparent that this assembly provides an enclosed but independent air supply for the two oven burners, and this supply can be regulated by dampers 20 and 21 within the same and respectively above and below the inlet opening 23 which provides the communication with the flow plate opening 13. These dampers can be adjusted to direct the incoming combustion air selectively to the top or bottom burner or simultaneously to both.

The exhaust air section 17 is fully closed except for openings 24 in a top forwardly curved extension 25,

which will be in communication with the upper portion of the oven cavity, and two lower openings 26 respectively at the sides of the enclosed inlet section 16 and in communication with the bottom opening 14 of the flow plate 11.

A second, similarly formed, stationary flow plate 27, also with a horizontal divider-channel 28, is applied against the rear or outer face of the wheel to complete the effective division of the latter into top and bot tom flow sections. A vertical exhaust duct 29 is arranged against this rear flow plate with a bottom opening 30 communicating with the lower rear plate opening 31 and extending to an exhaust blower B2. This exhaust duct is enclosed within a larger inlet air duct 32 to which ambient air is supplied by a further blower B1 and flows therethrough around the exhaust duct 29 to the wheel 10 through the upper rear plate opening 33. The flowindicating arrows included in the drawing clearly depict the air supply and the exhaust of the flue gases through the assembly, with uniform length dashes in the second such depictment and dashes of non-uniform length in the first. It will also be understood that shrouds or housings and the like will be added as needed to confine and isolate these separate flows to and from the oven cavity.

A coiled electric resistance heating element 34 is mounted on the rear flow plate 27 just above the divider channel 28 of the same and, as viewed from the front, in the left quadrant of the upper flow opening 33 of this plate. The element 34 is an auxiliary electric heater for the adjacent end of the wheel and is shown schematically as connected through a switch 35 to an available source of electric energy at terminals 36.

With the oven and regenerator operating, it will be seen that the hot flue gases from the oven cavity are drawn through the lower half of the rotating wheel 10 to give up heat to the same and that this heat is released to the incoming combustion air being delivered to the oven burners through the upper wheel half. As a section of the wheel moves in the clockwise direction, it will relatively experience its coolest temperature approximately at three oclock and its highest temperature at approximately nine oclock, these being of course the approximate points in which the particular section moves from the incoming air flow to flue gas exposure and vice versa. The auxiliary heating element 34 is accordingly positioned at the inlet air opening 33 but at the second such transition, and this arrangement serves both to deliver added heat to the wheel 10 where it is near maximum temperature and to pre-heat the incoming ambient or room air.

The heating element 34 is also shown as curved re versely with respect to the direction of rotation of the regenerator Wheel 10 from the approximate center of the wheel to the periphery. This design is intended to compensate for the variation in speed which occurs between central and peripheral points on the wheel surface by corresponding outward increase in the time exposure to heat effect of element 34, and it will be appreciated that other arrangements might be utilized for the same guaranteed uniform exposure of all parts of the Wheel, such as a variation of heating capacity along the length of the element or a different configuration, for example, with radial and outer arcuate sections.

It is preferred that the heating coil 34 be supported in some suitable manner with minimum separation between it and the adjacent face of the wheel 10, and also that the coil be operated at a temperature as high as possible consistent with the life requirement for the assembly. As noted previously, the heat energy of the flue gases passing through the exhaust section of the wheel enter the same at the approximate cleaning temperature within the oven, so that this input to the wheel provides a predetermined depth of self-cleaning action in the wheel as well. The supplemental heat input provided by the auxiliary heater 34 in accordance with the present invention should preferably and most efficiently be adequate to overlap such initial self-cleaning zone or length, and the thus added heat cleaning of the wheel assures that any particles which might otherwise pass through the same, for example, upon inadvertent overloading of the oven in respect of accumulated soils, will be consumed in the wheel and the latter thereby protected from clogging.

The desired automatic cleaning of the wheel body may be facilitated by providing catalytic oxidizing material on the surfaces defining the flow passages therethrough, these surfaces thereby having added oxidizing potential at relatively lower temperatures, with many catalytic inorganic compounds being known and available for oxidation of hydrocarbons, grease, and the like.

It will usually be preferred to energize the auxiliary cleaning heater for the wheel whenever the oven controls are set to carry out a self-cleaning cycle, with such an interlock an easily realized feature in the over-all control or programming of the oven operation.

I, therefore, particularly point out and distinctly claim as my invention:

1. An entering air supply and exhaust system for a self-cleaning gas oven, comprising a heat exchanger adapted in close association with the oven to contact streams of the exhaust and entering air, whereby the exhaust heats the exchanger and the entering air cools the exchanger, and auxiliary heater means within the system for supplementing the heating of the exchanger by the exhaust to ensure automatic heat cleaning of the exchanger.

2. A system as set forth in claim 1, wherein the heat exchanger is a rotary regenerator having axial passages through which the streams of the exhaust and air flow, and said auxiliary heater means is disposed to heat that part of the regenerator last contacted by the exhaust in its rotation.

3. A system as set forth in claim 2, wherein the auxiliary heater means also preheats the air entering the exchanger.

4. A system as set forth in claim 3, wherein the auxiliary heater means includes an electric resistance heating element arranged adjacent a face of the regenerator.

References Cited UNITED STATES PATENTS 3,148,665 9/1964 Switzer -56 X 3,327,094 6/ 1967 Martin. 3,412,786 11/1968 Taylor -95 X 3,416,509 12/1968 Huebler et al. 3,417,742 12/ 1968 Perl.

CHARLES J. MYHRE, Primary Examiner US. Cl. X.R.

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