COOKING SYSTEM
Field of the invention
The present invention relates to a cooking system and a method of operating a cooking system.
In particular, the present invention relates to a cooking system with indirect heating and a
method of operating a cooking system with indirect cooking.
Background of the invention
In general, large scale commercial cooking requires varied types of devices, utensils etc. to
prepare food. The heating and other operational requirements vary with respect of different types
of dishes and/or food to be prepared. In particular, foodstuffs like dosa, roti, pancake or any
other type of batter of one or more grains require uniform heating across hot plate, griddle, hot
pan, oven top, tawa, cooking plate etc. Also, the temperature requirement varies a lot for cooking
of such types of foodstuffs and temperature requirement is approximately 200'~ to 300'~.
Conventionally cooking plates were placed directly over the open flames or being directly heated
by heat energy sources in order to cook the batter. Such conventional systems were not adequate
and suitable, reason being they result in high radiation losses leading to low thermal and system
efficiency. Further, such cooking plates act like heat sink which makes them energy inefficient.
One of the improved conventional systems is disclosed in EP0645586. Said system overcomes
aforesaid limitation of inadequate cooking to some extent by providing uniform heating to the
cooking plates. In said system, as shown in Figure 1, a composite hot metal cooking plate has a
surface 12 for receiving the food stuffs 14. Said surface 12 forms part of a simple plate 11, the
lower surface of which forms the top closure of a trough 16 forming a cavity 18. The bottom of
the cavity 18 receives heat. The trough 16 contains a thermal fluid 21 capable of evaporating and
subsequently condensing in contact with the lower surface 20. Uniform heating of hot plate is
achieved using this technique. However, this system still holds on to the limitation of high
radiations from open flame heating up the surrounding area of the conventional systems and
making it highly inconvenient for the user to work in high temperature environment. Further, the
shortcoming of inefficiency still persists.
In order to overcome shortcomings of conventional systems, indirect heating systems were
developed. In general, the indirect heating systems provide heat under the cooking surface by
indirect heating method i.e. using a heat exchanger or heat conveying medium between the
cooking surface and heat source. In other words, heat is generated at a remote place to heat up a
fluid and said fluid conveys heat energy to the cooking surface. The indirect heating method
increases the efficiency and prevents heating of cooking area from open flames under the
cooking surface. One of the existing indirect heating systems utilizes steam as heat conveying
medium. In said system, steam is generated at a remote location in order to heat up the cooking
surface. Though such systems were able to provide adequate cooking, however, they have
limited area of application due to the bulky system and unsafe operating conditions. In other
words, indirect heating systems using steam requires pressurized steam well above the
atmospheric pressure in order to achieve higher temperature conditions. Such operating
conditions were achieved by large boilers and other costly ancillary components such as
enhanced safety control panels, monitoring apparatus, multiple safety valves etc. Additional
problems with such systems were frequent and timely maintenance, requirement of skilled
personnel for its operation, noisy operation due to use of compressors and blowers, increased risk
of accident due to high pressure, extreme working conditions for users, rusting and corrosion
caused by steam etc. Such systems, hence, got designed and used only in industrial controlled
environment. Also, for temperatures around ~OO'Ct,h e steam needs to be pressured above 14
K G I Cw~h~ic h, in turn, require the boilers to be assessed and authenticated by Indian Boiler
Regulations (IBR) standards. In establishments such as commercial kitchens, such systems
became unviable and many ended up using direct flame based cooking surface for making
several items or use non-standard non-approved low grade boilers which could never take
temperature above 1 50°C.
Therefore, there was a long felt need to provide a cooking system with indirect heating which
operates From approximately 200°c to 300' C and with the thermal fluid flowing at
approximately atmospheric pressure. Further, the cooking system needs to be such that it does
not spread heat in cooking area thus making the cooking area inconvenient for cheflpeople
working in the kitchen. Furthermore, the system must be efficient, economical, less heat
"spreading " , easy to operate, safe, and able to provide uniform and varied heating of the
cooking surface.
Objects of the invention
It is an object of the present invention to overcome the aforesaid limitations and shortcomings of
the existing arts.
It is another object of the present invention to provide a cooking system which is efficient,
economical, easy to operate and convenient to use.
It is another object of the invention to provide a cooking system with uniform heating across the
cooking surface along with swift transition from very high to very low heating rates or viceversa.
It is another object of the invention to provide a cooking system which is safe and transmitting
very less heat around surroundings making significant positive impact on people/cooks/workers
who will operate the system
It is another object of the invention to provide a cooking system which is capable of cooking
food items with improved taste.
Summary of the Invention
According to the present invention, a cooking system with indirect heating is provided
comprising a cooking surface, a jacket in thermal communication with the cooking surface and
having an inlet and an outlet, a heat exchanger having an inlet and an outlet and the outlet of the
heat exchanger connected to the inlet of the jacket, a stove in thermal communication with the
heat exchanger, an expansion tank connected to the outlet of the jacket, a pump connected
between the inlet of the heat exchanger and the expansion tank for transferring a fluid from the
expansion tank to the heat exchanger, and a control element connected to the driving means for
controlling the fluid circulation between the heat exchanger and the jacket.
The present invention also provides a method of operating a cooking system with indirect
heating comprising the steps of heating a fluid in an heat exchanger using a stove, circulating the
fluid from the heat exchanger to a jacket in thermal communication with a cooking surface,
collecting the fluid flow from jacket in an expansion tank, pumping the fluid to the heat
exchanger using a pump, controlling the fluid circulating between the heat exchanger and the
jacket.
According to the preferred embodiment of the present invention, the stove is a gasifier stove.
According to another preferred embodiment of the present invention, the fluid that flows
between the heat exchanger and the jacket is a thermic fluid.
According to another preferred embodiment of the present invention, the fluid flows between the
heat exchanger and the jacket at approximately atmospheric pressure.
According to another preferred embodiment of the present invention, the cooking surface is a flat
tawa.
According to another preferred embodiment of the present invention, the driving means is an
electric motor.
According to another preferred embodiment of the present invention, the jacket is thermally
insulated form the surroundings.
According to another preferred embodiment of the present invention, the cooking surface is a flat
cooking surface.
According to another preferred embodiment of the present invention, the cooking surface and the
jacket are formed with two spaced apart horizontal plates and the space between the horizontcl
plates is hermetically sealed with an inlet and an outlet for fluid flow.
According to another preferred embodiment of the present invention, the space between the
horizontal plates has at least one vertically oriented baffle plate for causing zig-zag flow of the
fluid through the enclosed space between the horizontal plates.
According to another preferred embodiment of the present invention, the space between the
horizontal plates has a web of arteries for causing spiral flow of the fluid through the space
between the horizontal plates.
According to another preferred embodiment of the present invention, the pump is driven by an
electric motor.
Brief description of drawings
The accompanying drawings constitute a part of the description and are used to provide further
understanding of the present invention. Such accompanying drawings illustrate the embodiments
of the present invention which are used to describe the principles of the present invention
together with the description. In the accompanying drawings the same components are
represented using the same reference signs. As shown in the drawings
Figure 1 illustrates a cooking system as disclosed in EP0645586.
Figure 2 illustrates a block diagram of the cooking system in accordance with the one of the
preferred embodiments of the present invention.
Figure 3 illustrates a side cross-sectional view of cooking surface and jacket arrangment in
accordance with the one of the preferred embodiments of the present invention.
Figure 4 illustrates top cross-sectional view of the cooking surface and jacket arrangement in
accordance with the one of the preferred embodiments of the present invention.
Figure 5 illustrates a flow diagram of the cooking system in accordance with the one of the
preferred embodiments of the present invention.
Detailed description of the invention
The present invention is described hereinafter by various embodiments with reference to the
accompanying drawings, wherein reference numerals used in the accompanying drawings
correspond to the like elements throughout the description. In order to achieve full description
and explanation, specific details have been mentioned to provide a thorough and comprehensive
understanding of various embodiments of the present invention. However, said embodiments
may be utilized without such specific details and in various other ways broadly covered herein.
Known features and devices have been shown in the form of block diagrams so as to prevent
redundancy and for the sake of brevity. Further, the block diagrams have been incorporated to
facilitate description of one or more embodiments.
Fig. 2 illustrates a block diagram of the cooking system in accordance with the one of the
preferred embodiments of the present invention. The said system, as shown in fig. 2, comprises
of a stove 23 with a burner is arranged below a heat exchanger 24. The stove 23 is preferably a
gasifier stove. More advantageously, the stove is Oorja Stove which is subject matter of another
Indian patent application 1763lCHEl2008 filed on 23.07.2008 also assigned to the present
applicant. A cooking surface 25 and a jacket 26 (under said cooking surface 25) are also
provided. The jacket 26 is hermetically sealed and has an inlet and an outlet for letting a fluid in
and out of the jacket 26. The jacket 26 is provided under the body of the cooking surface 25.
The fluid in the jacket 26 and cooking surface 25 are in thermal communication i.e. heat can
transfer fiom fluid in the jacket 26 to the cooking surface 25 and vice versa. The jacket 26 is
provided with suitable insulating material on its outside surfaces such that the jacket 26 is
thermally insulated from surroundings and only cooking surface 25 is able to thermally
communicate with the fluid inside the jacket 26. The inlet of the jacket 26 is connected to the
outlet of the heat exchanger 24. The outlet of the jacket 26 is connected to an expansion tank 27.
The fluid in the expansion tank 27 always remains at atmospheric pressure. Expansion tank 27
serves two purposes. First, the expansion tank 27 serves as the safe outlet for the increase in
thermal fluid volume due to thermal expansion. Second, the expansion tank 27 provides a
mechanism for venting water, incondensibles, degradation by-products and entrained air during
startup and operation. Thermal expansion tank 27 also serves the additional purpose of
maintaining the temperature of the thermal fluid/atmosphere interface below 300°C to minimize
fluid oxidation. The expansion tank 27 is also connected to the inlet of a circulating pump 28.
The output of the circulating pump 28 is connected to the inlet of the heat exchanger 24. The
circulating pump 28 has a driving means connected to the pump.. The driving means for the
circulating pump 28 is preferably an electric motor. A control element (not shown) is used to
the control stove 23 and the flow of the fluid in the system.
When fuel is burned in the stove 23, the heat energy generated is transferred to a fluid flowing in
the heat exchanger 24. The fluid flowing in the heat exchanger 24 is preferably a therrnic fluid.
Heated fluid from the heat exchanger 24 flows to the jacket 26 and due to temperature difference
the heat energy of the flowing fluid is transferred to the cooking surface 25. This results in
increased temperature of the cooking surface 25 making it ready for cooking food. In the
process, the fluid gets cooled after losing heat energy. The cooled fluid from the jacket 26 is
returned to the expansion tank 27. Cooled fluid in the expansion tank 27 is transferred to the
heat exchanger 24 where it is heated again. During the process of fluid transfer, the fluid always
remains at approximately atmospheric pressure. In this way the fluid is circulated between heat
exchanger 24 and the jacket 26 continuously and heat generated at the stove 23 is transferred to
the cooking surface 25 through a fluid.
In accordance with another embodiment of the present invention, the cooking surface may be
a flat tawa.
In accordance with yet another embodiment of the present invention, the cooking surface and
jacket arrangement may comprise of plurality of plates arranged in order to provide adequate and
uniform heating to the cooking surface (as shown in Figure 3 and Figure 4).
Figure 3 illustrates a side cross-sectional view of cooking surface and jacket arrangement 40 in
accordance with the one of the preferred embodiments of the present invention. The arrangement
40, as shown in fig. 3, comprises of two horizontal plates i.e. an upper plate 29 and a lower plate
30. Further, the arrangement 40 comprises of baffle plates 31 vertically oriented between the
upper plate 29 and lower plate 30. The said plates i.e. upper plate 29, baffle plates 3 1 and lower
plate 30 together form a hermetically sealed enclosed space. The said enclosed space has inlet
and outlet, openings, which act as single point of input and output respectively for flow of
thermic fluid within the hermetically sealed enclosed space.
Preferably, the vertically oriented baffle plates 31 are arranged in such a manner that fluid
flowing in the enclosed space through the inlet of enclosed space follows in opposite direction
between consecutive baffle plates before leaving the enclosed space through the outlet of the
enclosed space. This kind of arrangement enables thermic fluid to cover a larger surface area
beneath the upper plate 29 as compared to other arrangements. The larger the surface area
thermic fluid comes in contact within the enclosed space, higher would be the heat transfer to the
upper plate 29 thereby increasing the overall efficiency of whole system.
Further, top surface of the upper plate 29 acts as a cooking surface and bottom surface of the
lower plate 30 is thermally insulated to prevent the heat loss to the surroundings.
Without deviating from the scope of the present invention, the cooking surface and jacket
arrangement in the embodiment described above can be replaced with a cooking surface having a
web of arteries formed beneath the cooking surface. The inlet of web of arteries is connected to
the outlet of heat exchanger 24 and the outlet of the web of arteries is connected to the expansion
tank 27. The heated fluid from the heat exchanger 24 is circulated through said web of arteries
in order to heat up the cooking surface. Further, top surface of the cooking surface as a cooking
surface and bottom surface of the cooking surface is thermally insulated to prevent the heat loss
to the surroundings.
Figure 5 illustrates a flow diagram of the cooking system in accordance with one of the
preferred embodiments of the present invention. The fuel supplied to the stove 23 is burned and
the heat energy generated is transferred to a fluid flowing in the heat exchanger 24. The heated
fluid is transferred to cooking surface 25 where it loses its heat energy to heat up the cooking
surface 25 and in the process gets cooled. The cooled fluid flows to the expansion tank 27. The
circulation pump 28 continuously pumps the cooled fluid from the expansion tank 27 to the heat
exchanger 24. In this way heat energy generated during the burning of fuel is transferred to the
cooking surface for cooking purposes. A control panel (not shown in figure) controls the fluid
flowing between the heat exchanger 24 and the cooking surface 25.
The present invention is suitable for cooking applications where temperature requirements are
from approximately 200 to 300'~. The system is particularly suitable for baking, making dosa,
roti, pancake or any other type of batter of one or more grains.
The present invention is very efficient compared to conventional LPG open flame stove. This
results in lesser fuel consumption and therefore the system is economical to use. The following
tables show the economic significance of the invention as compared to conventional LPG stove
used in a commercial kitchen.
Table 1
Table 2
/start up wood pallet rate 16.43 kglhr
Duration of start up 0.75 hr
Various other advantages of the invention arise out of the fact that the fluid in the system
remains at approximately atmospheric level. There is no problem of corrosion or rusting due to
peculiar characteristics of thermic fluid. It is easy to operate and does not need skilled personnel
for operation. The system has a longer life with minimum maintenance requirement. The
operation of system is safe as it operates at normal atmospheric pressure. Radiation losses in the
system are minimal as the web of arteries for circulating thermic fluid under the cooking surface
is enclosed in thermally insulated jacket.
Running rate of wood pallets
Hours of operation
Total wood pallet consumption per day
Unit cost of wood pellet
Cost of pellets per day
Motor used
Unit cost of electricity
Cost of electricity per day
Total cost of new cooking system per day
Total savings on fuel ever day
% saving
3 k*
10 hr
35 kg
Rs. 17 per kg.
Rs. 592
2 HP(1.492kW)
Rs. 71 KW-hr
Rs. 104.5
Rs. 696
Rs. 25 1 to 725
27 to 51
Further, in a conventional cooking system using LPG stove with open flame under the cooking
plate, the flame temperature is as high as 2000'~ and the area around the flame which includes
cooking area for chef, is in the range of 70'~. This makes cooking condition inhospitable foe of
the chef. In a system according to the present invention, the heating of the cooking surface is
through a fluid encased in a jacket under the cooking surface which is thermally insulated to
have low heating losses. This renders the temperature in the cooking area as low as 30'~. This
makes the cooking area for the chef andtor other people working in the vicinity of the cooking
system considerably improved.
One other advantage of the present invention is the uniform temperature across the cooking
surface. As the heating of the cooking surface is by hot fluid flowing in a web of arteries spread
across cooking, the temperature across the cooking surface is uniform and heating of the raw
material for food item happens evenly. This renders better quality of cooked food.
Various modifications to these embodiments are apparent to those skilled in the art from the
description and drawings herein. The principles associated with the various embodiment defined
herein may be applied to other embodiments. Therefore, the description is not intended to be
limited to the embodiments shown along with the accompanying drawings but is to be provided
broadest scope consistent with the principles and novel and invention features describe/disclosed
or suggested herein. Any modifications, equivalent substitutions, improvements etc. within the
spirit and principle of the present invention shall all be included in the scope of protection of the
present invention.

We claim:
1. A cooking system with indirect heating comprising:
a cooking surface (25);
a jacket (26) in thermal communication with the cooking surface (25) and having an inlet and an
outlet;
a heat exchanger (24) having an inlet and an outlet and the outlet of the heat exchanger (24) is
connected to the inlet of the jacket (26);
a stove (23) in thermal communication with the heat exchanger (24);
an expansion tank (27) connected to the outlet of the jacket (26);
a pump (28) connected between the inlet of the heat exchanger (24) and the expansion tank (27)
for transferring fluid from the expansion tank (27) to the heat exchanger (24);
a control element for controlling the fluid circulation between the heat exchanger (24) and the
jacket (26).
2. A cooking system as claimed in claim 1, wherein the fluid flows between the heat exchanger
(24) and the jacket (26) at approximately atmospheric pressure.
3. A cooking system as claimed in claim 1, wherein the stove (23) is a gasifier stove.
4. A cooking system as claimed in claim 1, wherein the fluid is a thermic fluid.
5. A cooking system as claimed in claim 1, wherein the jacket (26) is thermally insulated form
the surroundings.
6. A cooking system as claimed in claim 1, wherein the cooking surface (25) is a flat tawa.
7. A cooking system as claimed in claim 1, wherein the cooking surface and the jacket are
formed with two spaced apart horizontal plates (29, 30) and the space between the horizontal
plates (29, 30) is hermetically sealed with an inlet and an outlet for fluid flow.
8. A cooking system as claimed in claim 7, wherein the space between the horizontal plates (29,
30) has at least one vertically oriented baffle plate (31) for causing zig-zag flow of the fluid
through the enclosed space between the horizontal plates (29,30).
9. A cooking system as claimed in claim 7, wherein the space between the horizontal plates (29,
30) has a web of arteries for causing spiral flow of the fluid through the space between the
horizontal plates (29,30).
10. A coolung system as claimed in claim 1, wherein the pump (28) is driven by an electric
motor.
I 1. A method of operating a cooking system with indirect heating, comprising the steps ofheating
a fluid in an heat exchanger (24) using a stove (23),
circulating the fluid from the heat exchanger (24) to a jacket (26) in thermal communication with
a cooking surface(25),
1 1 DEC 20% ,
colIecting the fluid flow from jacket (26) in an expansion tank (27) O R ~ ~ ~ M A L
pumping the fluid to the heat exchanger (24) using a pump (28)
controlling the fluid circulating between the heat exchanger (24) and the jacket (26).
12. A method of operating a cooking system as claimed in claim 1 1, wherein the fluid flows
between the heat exchang6r (24) and the jacket (26) at approximately atmospheric pressure.
13. A method of operating a cooking system as claimed in claim 1 1, wherein the stove (23) is a
gasifier stove.
14. A method of operating a cooking system as claimed in claim 11, wherein the fluid is a
thermic fluid.
15. A method of operating a cooking system as claimed in claim 11, wherein the jacket (26) is
thermally insulated form the surroundings.