US3628902A

US3628902A - Smooth top kitchen range

Info

Publication number: US3628902A
Application number: US865278A
Authority: US
Inventors: Jack Huebler; Robert B Rosenberg; Alan Kardas
Original assignee: Institute of Gas Technology
Current assignee: Gas Technology Institute
Priority date: 1969-10-10
Filing date: 1969-10-10
Publication date: 1971-12-21
Anticipated expiration: 1988-12-21

Abstract

A method and apparatus for heating a load by radiant energy wherein the load is supported on a shield largely transparent to said radiant energy, said shield being kept relatively cool by convective heat transfer which is preferably accomplished by directing a stream of cooling air to the undersurface of the shield.

Description

United States Patent Jack lluebler Deerfield;

Robert B. Rosenberg, Evergreen Park; Alan Kardas, Chicago, all of 111. 865,278

Oct. 10, 1969 Dec. 21 1 97 1 Institute of Gas Technology lnventors Appl. No. Filed Patented Assignee SMOOTH TOP KITCHEN RANGE 13 Claims, 6 Drawing Figs.

US. Cl 431/2, 126/39 J Int. Cl F23c 7/00 Field of Search 431/8,252,

[56] References Cited UNITED STATES PATENTS 3,241,542 3/1966 Lotter 126/39 3.470.862 10/1969 Darrow et a1. 126/39 Primary Examiner-Edward G. Favors Attorney- Molinare, Allegretti, Newitt & Witcoff ABSTRACT: A method and apparatus for heating a load by radiant energy wherein the load is supported on a shield largely transparent to said radiant energy, said shield being kept relatively cool by convective heat transfer which is preferably accomplished by directing a stream of cooling air to the undersurface of the shield SMOOTH TOP KITCHEN RANGE BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for an improved heating device and more particularly, it relates to an improved kitchen range.

Heretofore, gas ranges commonly used in kitchens have been conventionally constructed by providing openings in the range top with a jet-type burner located in each of the openings. The burner is connected to a gas manifold which passes natural gas or other gaseous fuel into the burner. A grate is normally mounted on the gas range top over the opening to provide support for a cooking utensil, e.g., a pot or a pan, at location spaced above the burner. The conventional electric kitchen ranges also have a similar structure. In the electric ranges, the heating element, in the form of a coil of the Cal-rod type, is mounted on top of a network supporting grate.

Such conventional prior art range structures have certain inherent disadvantages. One of the primary disadvantages of the conventional range design is the difficulty encountered in cleaning the range. For example, in cleaning a gas range, the burner grate must be removed first and separately cleaned. In addition the presence of the annular opening between the burner and the gas range top permits food, crumbs, liquid spillage, boiled over material, and the like to pass downward through the annular space. Thus, the thorough cleaning of such a gas range often necessitates cleaning the equipment normally found below the gas range top and such cleaning often requires the complete dismantling of the burner from the gas main mantle. It involves the removal of various parts of the gas range top for thorough cleaning. Since most housewives clean their gas ranges regularly, the prior art conventional gas range burner poses a serious problem in the amount of time needed for its care. Much the same thing can be said of the electrical ranges.

It is therefore, an object of the present invention to provide a novel and improved kitchen range.

It is another object of the invention to provide an improved range which is particularly easy to clean.

It is a further object of the invention to provide a novel range which possesses a high overall heating rate.

It is still another object of the invention to provide a novel kitchen range which has smooth-top heating areas for supporting the utensils to be heated.

Another object of the invention is to provide a kitchen range having smooth-top heating areas which has a very small thermal lag so that heat transfer ceases rapidly when the heating element is shut off.

It is a further object of the invention to provide a novel range having smooth-top heating area which is substantially transparent to radiation but which is itself maintained at a temperature below its maximum safe operating point.

These and other objects can be gathered from the following description.

SUMMARY OF THE INVENTION In accordance with the present invention, we provide an improved kitchen range wherein the top surface of the range is substantially flat and smooth and has areas thereon made from a material which is largely transparent to the radiation generated by the radiant heating element located below said areas. Said areas are cooled by convective heat transfer, e.g., by a stream of air, to maintain said areas at a temperature below the normal maximum safe operating temperature for said material.

BRIEF DESCRIPTION OF THE DRAWING AND OF THE PREFERRED EMBODIMENT The invention will now be described with reference to a particular embodiment illustrated in the drawing. This embodiment shows a gas-fired burner for heating a radiant element but it will be understood that an electric heating element may be used there instead. In the drawing:

FIG. I is a top plan view of a kitchen gas range embodying the present invention;

FIG. 2 is a partial sectional view, along line 2-2 of FIG. I, showing a portion of the interior of the range of FIG. I;

FIG. 3 is a plan view of the device 22 in FIG. 2 used for supplying cooling air to the shield of FIG. 2;

FIG. 4 is a sectional view along line 4-4 of FIG. 3;

FIG. 5 shows another embodiment of the air-cooling member 22 of FIG. 2; and

FIG. 6 is a graphic illustration of theeffects of convective cooling on the equilibrium temperatures of the shield.

Referring now to FIG. 1, a kitchen gas range in accordance with the present invention is generally shown at I0. As is conventional, range 10 has four heating areas I] thereon, although this number is not critical. In one of the heating areas 11, there is shown a substantially flat and smooth shield 12.

As shown in FIG. 2, the heating area 11 is formed by a recess 13 in the tip of range 10. Recess 13 is formed with a lip or shelf member 14 for supporting the shield. When shield 12 is in position within the heating area 11, the top surface of shield 12 is in a substantially horizontal position and in nearly the same plane as the top of range 10. A gas-fired radiant burner device 15 is mounted below shield 12. The gas-fired radiant burner 15 may be of conventional construction, for example, as those presently being sold by Solaronics, Inc. It may include a gas-distributing means 16 and a radiator 17. A fuel gas, such as natural gas and air mixture is supplied to the burner via conduit means I8, valve I9 and conduit means 20. The fuel gas mixture may be suitably ignited to produce combustion between radiator 17 and a screenlike front element 21. The radiant energy from radiator 17 proceeds through element 21 to the load (not shown). The hot combustion product gases are principally removed via conduits 40, which may be connected to a fan or a source of partial vacuum, so that the hot gases will not interfere with the convective cooling of the shield 12. Radiator 17 may be made of known materials such as ceramics or zircon mullet. A means 22, for convectively cooling the shield 12, is located substantially immediately below the shield 12. Means 22 may be suitably mounted by attachment to arms or braces 23 which may be in turn bolted or welded to the range at 24. A tube or conduit means 25 supplies cooling air to means 22 from a motor and fan 26 which may be in turn mounted within the range I0 by way of braces 27 and attaching means 28.

The shield 12 should be of a size so that food and other materials will not easily be deposited or collected between the shield and the recess 13. Alternatively, there may be an overlap by either the shield or the range top to prevent the deposit or collection of foodstuff thereinbetween or the shield material may form the entire surface of the range top. The heating of food or other loads is carried on by placing the load on top of the shield 12. Shield 12 may be made from any of the available material which is substantially transparent to infrared radiation, particularly that in the wavelength region of about 0.5 to 3 microns. An example of such material is made by the Owens-Illinois Company under the trade name Cer-Vit, which is a glasslike material. A sheet of Cer-Vit about one-eighth inch thick has a transmissivity of about 0.87, and an absorptivity of 0.13 or less, for the radiation described above. These figures are obtained from the manufacturer of the Cer-Vit material and the figures represent the properties of the material in the wavelength region of about 0.5-3 microns. Of course, it will be understood that these figures are for a clean shield: if the shield is obstructed in part for any reason, as for example by spilt food and other particles, the transmissivity of the shield may be drastically reduced.

The motor and fan 26, shown in FIG. 2, may be connected to the valve 19, througha switch and rheostat for example, so as to be responsive to the operation of the valve. In this manner, the amount of convective cooling can be made to be proportional to the rate fuel is supplied to the burner 15. Alternatively, the motor and fan 26 may be operated by an onoff type of switch responsive to turning the gas valve on or off.

A kitchen range of the type described herein carries out the heating of a load primarily by radiant heating. There is very lit tle heat transfer by conduction or convection. Therefore, the cooling of the shield by convecting means using a medium largely transparent to the radiation, such as air, does not interfere with the heating of the load or significantly decrease the efficiency of the range.

FIG. 3 shows the cooling means 22 of FIG. 2 in more detail. As shown in FIG. 3, means 22 is composed of an annular member 29 which is hollow and sealed at its outer edges, but open inwardly to form two

lips

30 and 31. Between

lips

30 and 31 is an opening 32 for the passage of air which is supplied to the means 22 by way of one or more conduits 25. The crosssectional shape of means 22 is illustrated in FIG. 4. Opening 32 is shown in the form of a continuous one around the entire circumference of annular member 29, but it will be understood that the opening may be in the form of a plurality of smaller opening or nozzles.

FIG. shows another embodiment of the cooling means 22. In FIG. 5, a means 22a is shown which is made of an annular member 33. Annular member 33 has

lips

34 and 35 which form an opening 36 thereinbetween. The opening 36 extends about three-fourths of the length of the inner circumference of the annular member 33. In this manner, the cooling air issuing from means 22a may be directed and swept across the undersurface of the shield 12 in a direction from right to left, as il lustrated in FIG. 5.

The rate at which air is being supplied to means 22 for cooling the undersurface of shield 12 should be sufficient to maintain shield 12 at a temperature below its maximum safe operating temperature. This may be carried out by constructing the valve 19 in such a manner so that the amount of fuel gas which can pass into the burners I7 is limited to a level at which shield 12 cannot overheat even when the valve 19 is fully open. The rate at which air is supplied to cooling means 22 by motor and fan 26 can also be varied to suit the amount of the gaseous fuel being burned at the burner 17. This may be done, for example, by connecting motor and fan 26 to a rheostat (not shown) which is physically operated by the lever (also not shown) on valve U, so that when the valve is only supplying a small amount of fuel gas to the burners the power supply to motor and fan 26 is also at a low level, and vice versa. Of course, the motor and fan may be simply actuated by an on-off-type switch responsive to the turning on or off of the gas valve 19.

It will be noted that the cooling of the undersurface of shield 12 by a stream of convective air is particularly advantageous when the heating of the load is primarily carried out by infrared radiation. This is so because air is largely transparent to infrared energy and the flow of air across the surface of shield 12 will not interfere with the transfer of radiant energy from the source through the shield to the load. If a solid or liquid is used as the cooling medium, drastic loss in efficiency and in rate of heat transfer may result because of the absorption of the radiant energy by the cooling means. Although other gases may be used for cooling the shield 12, the use of such other gases will probably require the provision of a closed system and such is cumbersome, expensive and not preferred.

The present invention provides a method and apparatus for taking advantage of higher temperature radiant energy sources such as gasfired smooth-top radiant burners. Such burners are capable of producing temperatures substantially higher than those of comparable electrical units. Typically, electrical units may be operated at about l,000 to l,200 F. On the other hand, gas-fired radiant burners are capable of attaining temperatures substantially higher than those, as much as twice as high in terms of degrees Fahrenheit. Higher operating temperatures for the radiant burner means higher energy fluxes and shorter heating times. This feature is particularly advantageous in a kitchen range since the modern trend is for reducing the amount of time in the kitchen for preparing foods. In this regard, it will be noted that a blackbody emitter having a surface area of 1 square foot will emit about 4,500

B.t.u./hr. at l,400 F. while the same emitter will emit l5,000 B.t.u./hr. at l,800 F., both figures representing emitted radiant energy having a wavelength between 0 and 2.7 microns. The wavelength region of O and 2.7 microns is the region in which most kitchen loads are capable of absorbing energy and in which the available material, such as the Cer-Vit mentioned above, is most transparent for transmitting the radiant energy.

The Cer-Vit plate described above is essentially a glasslike material having nearly zero coefficient of thermal expansion. It is also substantially transparent to infrared radiation. Its properties, of course, can be varied somewhat by changes in its composition for particular purposes. However, as a glasslike substance, it generally has a top safe operating temperature of about 1,000" F., and preferably it is employed at a temperature of about 800 F. or less. On the other hand, a radiant burner having a radiator operating at l.400 F. and losing energy to a load at F. will cause a shield to have an equilibrium temperature of about l,070 F. or less, depending on the geometry of the element. Therefore, some cooling of the shield is necessary if a high-temperature source is used. Additional cooling, as described in this invention, permits more rapid cooking through the use of higher temperature radiant sources.

As indicated above, the equilibrium temperature of the shield depends on the temperature of the radiator and the geometry of the elements of the radiant burner. Such equilibrium temperatures may be calculated for different source temperatures and different geometries with known methods. Table 1 below shows the equilibrium temperature for the shield for several different source temperatures and geometries.

Equilibrium temperature of shield, F.

0.75 it. diameter radiator 1.0 It. diameter shield, inches apart Infinite size plates as radiator and shield 1 it. diameter plates for radiator and shield, inches apart Temperature of radiator, F.

The values in the above table are obtained from solution of the following equation:

wherein the nomenclature represents:

e-emmisivity (=absorptivity, gray radiation assumed),

p-reflectivity,

hconvective heat transfer coefficient, B.t.u./hr. ft. F.,

A-ratio of convected area to the radiation area (=1 ifcon vection is on one side only, =2 if on both sides),

Ttemperatures (RH ,000),

T,,temperature of convected air,

F -shape factor. That fraction of the energy emitted by i which is intercepted by].

Subscript 1 refers to the shield, subscript 2 the source or radiator, and subscript 3 the load. The values for the shape factors in the above equation can be obtained from standard texts, such as: John A. Wiebelt, Engineering Radiation Heat Transfer, Holt, Rinehart and Winston, New York, 1966. A solution of the above equation for four different source (radiator) temperatures is given in FIG. 6 below. In FIG. 6, the

equilibrium temperature of the shield is plotted as a function of the heat transfer coefficient as a result of the convective cooling. As can be seen, with a radiator at l,400 F., with a shape factor of 1.0 or with the radiator and shield both assumed to be of infinite size, the equilibrium temperature of the shield with no cooling would be about 1,070 F., whereas with connective convective cooling at a heat transfer coefficient of about 5 B.t.u./hr. per square foot F., the equilibrium shield temperature is about 500 F. With convective cooling, a heat transfer coefficient of 5 B.t.u./hr. per square foot F. corresponds to an air velocity of about 18 feet per second with air at about 80 F. It can be gathered from FIG. 6 that unless extremely high radiator temperature is employed, a heat transfer coefficient larger than 5 would generally be unnecessary.

The method and device of the invention, aside from maintaining the shield temperature at a safe level during the heating cycle of the kitchen'range, is also extremely useful in rapidly cooling the shield after the cooking process has terminated. if no convective cooling is available, the shield must be cooled by natural convection after the radiant heater has been turned off. As indicated above, the absorptivity of the shield is extremely low, about 0.13 or 13 percent or less. Thus, the shield tends to remain hot for a relatively long time after the radiant heater has been shut off. For example, a Cer-Vit plate one-eighth inch thick initially at l,000 F; andlosing heat to the surroundings at 100 F. by radiation only, would take about 40 minutes to reach 200 F. However, with a convective coefficient of 2.5, the shield would reach 200 F. in about 18 minutes, and with a coefficient of 5.0 the shield would cool to 200 F. in about minutes. This cooling of the shield after the radiant burner has been turned off can be accomplished by means of an automatic timer which would control the operation of the motor and fan 26 in FIG. 2, for example, for the necessary amount of time after the valve 19 has been shut off. ln this way, the shield can be rapidly and conveniently cooled down to a safe temperature.

In addition to maintaining the shield at a safe operating temperature and rapidly cooling the shield after the cooking process has terminated, the convective cooling means of the invention also decreases the likelihood of overboil of the cooked food. This is due to the fact that the rapid cooling of the shield tends to prevent further heating of the load by a hot shield after the radiant heater has been turned off.

The invention has been described in detail with reference to particular and preferred embodiments thereof, but it will be understood that variations and modifications can be made within the spirit and scope of the invention as described hereinabove and as defined in the appended claims. Thus, for example, the energy for heating the radiator 17 may be supplied by an electric heating element such as a coil of the Calrod type.

What is claimed is:

l. A method for heating a load by radiant energy which comprises: (a) placing said load on a support which is made of a material largely transparent to said radiant energy; (b) heating said load with a source of said radiant energy below said support; and (c) cooling said support in the area between said energy source and said load by passing air below said support to provide convective heat transfer in an amount sufficient to maintain said support below its maximum safe operating temperature.

2. A method according to claim 1 further comprising rapidly cooling said support, after termination of said heating of the load, by convective heat transfer.

3. A method according to claim 1 wherein said source of radiant energy comprises the burning of a gaseous fuel.

4. A method according to claim 1 wherein said convective heat transfer is carried out by directing a stream of air to the under surface of said support.

5. A method according to claim 1 wherein said convective heat transfer is carried out at a rate directly proportional to the rate radiant energy is being emitted by said source.

6. A method according to claim 4 wherein the rate of flow of air across said undersurface of the support is directly proportional to the rate radiant energy is being emitted by said source.

7. A method according to claim 4 wherein said source of radiant energy comprises the burning of a gaseous fuel, and wherein the rate of flow of air across said undersurface of the support is directly proportional to the rate said gaseous fuel is burned.

8. An apparatus for heating a load by infrared radiation comprising in combination:

a. a base having an elevated and substantially horizontal surface for supporting said load,

b. a support on said surface made of a material which is largely transparent to infrared radiation,

c. a source of radiant energy located below said support,

and

d. means for cooling said support by convective heat transfer, said cooling means being disposed between said support and said radiant energy source to maintain said support at a temperature below its maximum safe operating temperature.

9. An apparatus according to claim 8 wherein said source of radiant energy comprises a radiant burner device for a gaseous fuel.

10. An apparatus according to claim 9 wherein said burner device is a jet-type burner for natural gas.

11. An apparatus according to claim 10 wherein said cooling means comprises means for supplying a stream of air and means for directing said stream of air to the undersurface of said support.

12. An apparatus according to claim 11 wherein said cooling means further comprises control means for controllably varying the amount of air supplied to said undersurface in accordance with the amount of natural gas being supplied to said burner device.

13. An apparatus according to claim 8 wherein said cooling means further includes a. means for turning off said radiant energy source, and

b. means for maintaining said supply of air to the undersurface of said support after said radiant energy source is turned off.

Claims

1. A method for heating a load by radiant energy which comprises: (a) placing said load on a support which is made of a material largely transparent to said radiant energy; (b) heating said load with a source of said radiant energy below Said support; and (c) cooling said support in the area between said energy source and said load by passing air below said support to provide convective heat transfer in an amount sufficient to maintain said support below its maximum safe operating temperature.

8. An apparatus for heating a load by infrared radiation comprising in combination: a. a base having an elevated and substantially horizontal surface for supporting said load, b. a support on said surface made of a material which is largely transparent to infrared radiation, c. a source of radiant energy located below said support, and d. means for cooling said support by convective heat transfer, said cooling means being disposed between said support and said radiant energy source to maintain said support at a temperature below its maximum safe operating temperature.

13. An apparatus according to claim 8 wherein said cooling means further includes a. means for turning off said radiant energy source, and b. means for maintaining said supply of air to the undersurface of said support after said radiant energy source is turned off.