Cooking Stove

FIELD OF THE INVENTION

The invention relates to a cooking stove for use in a domestic environment.

BACKGROUND OF THE INVENTION

Existing cooking stoves used in many homes, and shown in figure 1, consist of a small, hollowed out space 101 in a shelf 102, the space proportioned so that a cooking pot or other cooking receptacle 103 is supported by the edges of the shelf 102 so that it is suspended over the space 101. Sometimes a further cooking plate 104 is placed over the pot. Solid fuel 105 is placed in the space 101 and lit to provide heat for cooking or heating the contents of the pot 103 and/or plate 104. Unfortunately, the burning of solid fuel creates exhaust gases, particularly carbon monoxide and also causes the release of smoke particles, and these can linger in the room around the stove. Exposure to the exhaust gases plus smoke particles creates risk of respiratory infections and carbon monoxide poisoning and is associated with an increased risk of miscarriage, blindness and tuberculosis. It is an object of the invention to provide a cooking stove which allows food to be cooked efficiently by an individual without the concomitant exposure of the individual to dangerous amounts of exhaust gases and smoke, and in particular to carbon monoxide.

BRIEF SUMMARY OF THE INVENTION This is achieved according to the invention whereby the cooking stove comprises a cavity for solid fuel; a chimney for the removal of exhaust gases created by the burning of the solid fuel; a channel arranged to connect the cavity and the chimney; the channel comprising a first opening to receive and support a first cooking receptacle. Biomass, which is used as the solid fuel, emits a lot of soot and smoke which creates

indoor air pollution, the main cause for respiratory diseases. The stove is fitted with the chimney to reduce the air pollution When the solid fuel in the cavity is lit, heat is generated which starts to rise and causes movement of air standing in the chimney. As the air in the chimney start to rise up under the influence of the heated gases coming from the cavity, suction is created in the chimney and more gases are gradually pulled through the channel. Thus user of the stove will not be exposed to the smoke that can be dangerous to his/her health. The cavity for the solid fuel has a gap through which the solid fuel can be inserted and the increasing suction of gases into the chimney pulls more air into the cavity through this gap to provide oxygen for the fire. The movement of increasingly heated exhaust gases through the channel from the cavity to the chimney allows heating and cooking of food inside the cooking receptacle thereby increasing the efficiency of the stove.

According to an embodiment of the invention, the channel comprises a protuberance arranged directly underneath the first opening arranged to receive and support the first cooking receptacle when the stove is in operation, wherein the protuberance is configured to deflect flow of exhaust gases to the underside of the first cooking receptacle. This protuberance blocks the path of the hot gases to create a small turbulence under the first opening. This helps better transfer of heat to the cooking receptacle. The hot exhaust gases from the solid fuel burning in the cavity are transported along the channel which comprises the protuberance arranged to deflect flow of exhaust gases to the underside of the first cooking receptacle placed on the first opening. The protuberance deflects the hot gases and causes them to momentarily pause under the first cooking receptacle placed on the first opening before moving further to the chimney under the pressure of further exhaust gases coming from the cavity. The momentary pausing of the gases under the first cooking receptacle is possible because the exhaust gases are compressible, and this momentary pausing of hot gas as it is transported along the channel improves heating of the first cooking receptacle. Without the protuberance, the hot gases pass through the channel at a high speed and does not transfer good amount of heat to the first cooking receptacle. According a still further embodiment of the invention, the protuberance is a ridge arranged to span the diameter of the duct transversely to the direction of the

channel. The height of the protuberance in relation to the diameter of the channel is substantially 90% of the diameter of the channel. This is the ideal height, because if it takes up any more of area of the cross section of the channel, the latter becomes sufficiently obstructed and causes exhaust gases to issue backwards out of the cavity into the room. If the protuberance takes up any less of the cross sectional area of the channel there is insufficient pausing of the exhaust gases under the cooking receptacle to cause the advantageous heating allowed.

According to another embodiment of the invention, wherein the first cooking receptacle is a cooking plate. The cooking plate is particularly advantageous for cooking of chapattis. The first opening is suitably arranged to receive and support the cooking plate. In other words, the first opening is wide enough to support the cooking plate while leaving a wide enough opening to allow heating of substantial area of the cooking plate surface. If the edge of the opening is further chamfered to allow the cooking plate to nestle in the opening supported by the edges of the cooking plate then conduction of heat from the walls of the channel provides further heating to the edge of the cooking plate.

According to yet another embodiment of the invention, the first cooking receptacle is a cooking pot, wherein the first opening is proportioned to allow an insertion of the cooking pot into the channel and the channel is arranged to maintain the flow of exhaust gases in the channel around the inserted cooking pot. In this embodiment the flow of hot exhaust gases around the cooking pot allows heating and cooking of the contents of the pot. It is important that the channel is arranged to maintain the flow of exhaust gases around the inserted cooking pot and therefore it is important that the insertion of the cooking pot does not cause narrowing of the channel. Narrowing of the channel around a large pot can constrict the easy flow of hot exhaust gases and smoke to the chimney. This may cause the exhaust gases and smoke to reissue backwards out of the cavity into the surrounding room.

According to a still further embodiment of the invention, the first opening is arranged in the upper side of the channel when the cooking stove is in operation. According to a preferred embodiment of the invention, the cavity for the solid fuel comprises a second opening for receiving a second cooking receptacle. It is

further advantageous if the cavity for the solid fuel comprises a second opening for receiving a second cooking receptacle as both the cooking receptacles can be used simultaneously thus reducing the cooking time. The cavity is arranged to receive the solid fuel while smoke and exhaust gases are transported into the channel and carried away via the chimney. The second opening is proportioned to allow placement of the second cooking receptacle on top of the second opening and this allows conventional cooking directly over the heat produced by the burning of the solid fuel The second opening allows a second pot to be used in addition to the first cooking plate that is heated by the flow of exhaust gases along the channel. According to an embodiment of the invention, a by-pass tunnel is provided between the first opening in the channel and the second opening in the cavity. Turbulence is needed in the first and second openings so that there is a better heat transfer to the cooking receptacles. The by-pass tunnel splits the hot gases (fire) in the second opening. This helps the hot gases to linger under the second cooking receptacle for a longer time. This bypass connects the second opening with the first opening where the hot gases from the by-pass tunnel mix with the hot gases passing through the channel. The gases from the channel and by-pass tunnel collide with a high speed and create small turbulence in the first opening. This increases the temperature in the first opening substantially.

According to a further embodiment of the invention, a barrier is provided on top of the second opening, and wherein the barrier is arranged to increase volume of the cavity yet keeping the second opening of the cavity small. This stops the smoke coming out of the cavity in spite of turbulence inside the cavity.

According to a preferred embodiment of the invention, the chimney has a modular construction to allow assembly of the chimney by the abutment of a first set of respective elements together to form a pipe and the placement of a second set of respective sleeve- like elements over the joints formed between the first elements. Long chimney pipes of 8+ ft are needed to efficiently remove the smoke. These chimneys need to be carried for installation of the stove. These are too fragile to be carried on rural roads in locally available transport and can lead to transit damages. Sometimes people carry them on their heads and it is very difficult to carry as they weigh a lot and need to be balanced carefully. The modular construction of the chimney proves to be very

advantageous while transporting on a bike or local carts. Further, the modular construction of the chimney enables easy cleaning.

According to an embodiment of the invention, the chimney has internal diameter of between 75mm and 125mm, but preferably between 90 mm and 110 mm, but preferably between 95 mm and 105 mm. The channel has substantially the same internal diameter as the chimney. If the channel has a substantially wider diameter than the chimney there is a risk that the exhaust gases and smoke cannot flow freely into the chimney and a proportion of them will flow backwards into the room

According to a further embodiment of the invention, a soot collector is provided at bottom of the chimney. Chimneys get clogged very frequently as the biomass, solid fuels, that people in rural India use for cooking, have a lot of resins and substances like silica that do not burn completely. These un-burnt particles travel with the fire and settle on any rough and cooler surface. As the fire cools the soot condenses and settles. It builds quickly and clogs the chimney. The soot collector provided in the chimney reduces clogging of the chimneys. The soot collector is placed at an accessible point before it enters the chimney so that the chimney is not chocked easily.

According to yet another embodiment, the stove is constructed from a moldable material and has a modular construction to allow assembly of the cooking stove by the abutment of respective elements alongside each other in situ. The moldable material is concrete or clay. It is particularly advantageous if the stove is constructed from a moldable material and has a modular construction to allow assembly of the cooking stove by the abutment of respective elements alongside each other in situ. Further, it has been found to be advantageous if the stove constructed from concrete, but the stove can also be constructed from clay or other material suitable for molding. Following abutment of the modular units together to form the cavity, channel and opening, the whole stove can be covered in cement or clay or other non-flammable sealing material to seal the gaps between the modular units and improve successful transfer of the exhaust gases and smoke from the cavity to the chimney.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a cooking stove of the prior art;

Figure 2 shows a cooking stove according to the invention; Figure 3 shows an embodiment of the cooking stove of the invention; Figure 4 shows another embodiment of the cooking stove of the invention; Figure 5 shows a cooking stove containing two openings to receive two cooking receptacles;

Figure 6 shows a top view of a cooking stove with a by-pass channel; Figure 7 shows a side view sectional of a cooking stove with a barrier; Figures 8a and 8b show the construction of a chimney attached to a cooking stove of the invention; and Figure 9 shows a chimney provided with a chimney cleaning bracket;

Figure 10 shows a prototype of chimney being assembled; Figure 11 shows an adjustable chimney to suit any available roof height; Figure 12 shows perforated plates without and with a soot collector in a chimney; Figure 13 shows stackable soot collector tablets;

Figure 14 shows the modular construction of the cooking stove in an advantageous embodiment;

Figure 15 shows a Saral stove; and Figure 16 shows a Sampooran stove.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto. Any reference signs in the claims shall not be construed as limiting the scope. The drawings described are only schematic and are non- limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps. Where an indefinite or definite article is used when referring to a singular noun e.g. "a" or "an", "the", this includes a plural of that noun unless something else is specifically stated. Furthermore, the terms first, second, third and the like in the description

and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

As shown in figure 2, the cooking stove comprises a cavity for solid fuel 201, a chimney 202 for the removal of exhaust gases created by the burning of the solid fuel 205, a channel 203 arranged to connect the cavity and the chimney and to ensure exhaust gases are conducted from the cavity to the chimney. Further, the channel comprises an opening 204 to receive and support a cooking receptacle, arranged so that the flow of exhaust gases through the channel heats the cooking receptacle. When the solid fuel 205 in the cavity 201 is lit, heat is generated which starts to rise and causes movement of the air and gases standing in the chimney. As the air and gases in the chimney start to rise up under the influence of the heated gases coming from the cavity, suction is created in the chimney and more gases are gradually pulled through the channel 203.

The cavity 201 for the solid fuel 205 has a gap at through which the solid fuel can be inserted and the gradually increasing suction of gases into the chimney pulls more air into the cavity through this gap to provide oxygen for the fire.

The movement of increasingly heated exhaust gases through the channel 203 from the cavity 201 to the chimney 202 allows heating and cooking of food inside a cooking receptacle placed on an opening 204 for that purpose.

The result of this arrangement is the heating and cooking of food contained in the cooking receptacle while in addition, exhaust gases and smoke are pulled

out of the cavity 201, along the channel 203 and into the chimney 202 from where they rise to be removed from the room in which the cooking stove is placed.

There are two main embodiments allowing use of the channel to provide cooking. In the first, shown in figures 3a (side view) and 3b (top view), hot exhaust gases from the solid fuel 305 burning in the cavity 301 are transported along the channel 303 which comprises a protuberance 306 arranged to deflect flow of exhaust gases to the underside of the cooking receptacle placed on the opening 304. The protuberance deflects the hot gases and causes them to momentarily pause under the cooking receptacle placed on the opening 304, before moving further to the chimney 302 under the pressure of further exhaust gases coming from the cavity 301. The momentary pausing of the gases under the cooking receptacle is possible because the exhaust gases are compressible, and this momentary pausing of hot gas as it is transported along the channel 303 improves heating of the cooking receptacle. This is a particularly advantageous embodiment. Preferably, the protuberance 306 is arranged directly underneath the opening 304, as shown in figure 3b in which the opening 304 is shown by the dotted line. It has been found that the most advantageous design for the protuberance is a ridge arranged to span the diameter of the duct transversely to the direction of the channel. This protuberance blocks the path of the fire to create a small turbulence under the opening 304. This helps better transfer of heat to the cooking receptacle. It has also been found that the best height for the protuberance in relation to the diameter of the channel is substantially 90% of the diameter of the channel. In practice, the height of the protuberance can vary between 70% and about 90% of the height of the channel 303, so within the tolerances of manufacture it might in fact be 88%, 89%, 91% or 92% of the height of the channel 303. It has in fact been found that about 90% is the ideal height, because if it takes up any more of area of the cross section of the channel 303 the latter becomes sufficiently obstructed to cause exhaust gases to issue backwards out of the cavity 301 into the room. If the protuberance takes up any less of the cross sectional area of the channel there is insufficient pausing of the exhaust gases under the cooking receptacle to cause the advantageous heating allowed by this embodiment. This first embodiment is particularly advantageous when the cooking receptacle is a cooking plate, for example for the cooking of chapatis. In order to achieve

this, the opening 304 is suitably arranged to receive and support a cooking plate. In other words, the opening 304 is wide enough to support a cooking plate while leaving a wide enough opening 304 to allow heating of substantially enough of the cooking plate surface. If the edge of the opening 304 is further chamfered to allow the cooking plate to nestle in the opening supported by the edges of the cooking plate then conduction of heat from the walls of the channel provides further heating to the edge of the cooking plate. In the second embodiment, shown in figures 4a (side view) and 4b (top view), hot exhaust gases from the solid fuel 405 burning in the cavity 401 are transported along the channel 403 which contains an opening 404 which is proportioned to allow the insertion of a cooking pot 406 into the channel. In this embodiment the flow of hot exhaust gases around the cooking pot 406 allows heating and cooking of the contents of the pot. It is important that the channel is arranged to maintain the flow of exhaust gases around the inserted cooking pot 406 and therefore it is important that the insertion of the cooking pot 406 does not cause narrowing of the channel 403. Narrowing of the channel around a large pot 406 can constrict the easy flow of hot exhaust gases and smoke to the chimney and cause instead the exhaust gases and smoke to reissue backwards out of the cavity 401 into the surrounding room. Therefore, in this embodiment, the channel 403 is further widened in the vicinity 407 of the pot. It is particularly advantageous if the pot 406 is supplied with the cooking stove because in this case the size of the supplied pot 406 and size of the associated widening 407 can be matched so that no reduction in cross sectional area of the channel 403 for gas and smoke transport occurs when the pot 406 is in place.

As can be seen by consideration of figures 3 and 4, the opening is arranged in the upper side of the channel when the cooking stove is in operation. It can therefore also be noted that the channel should be arranged to be substantially horizontal.

It is further advantageous if the cavity for solid fuel comprises a second opening for receiving a second cooking receptacle. This is shown in figure 5, in which the cavity 501 now has a second opening 505. The cavity 501 is arranged to receive solid fuel 504 and smoke and exhaust gases are transported, as before, into the channel 502 and carried away in the chimney. Howerer, in this further embodiment, the opening 505 is proportioned to allow placement of a further pot 503 on top of the opening 505 and this

allows conventional cooking directly over the heat produced by the burning of the solid fuel 504. The addition of this further opening 505 allows a further pot to be used in addition to the pot or cooking plate heated by the flow of exhaust gases along the channel. The heat transfer in the second opening 605 is increased by creating turbulence as shown in figure 6. A by-pass channel 610 splits hot gases (fire) in the second opening 605 hole. This helps fire to linger under the second cooking receptacle (not shown) for a longer time. Experiments showed that the boiling point was reached within lOmin 30 sec as compared to 13+ minutes required when the by-pass channel 610 was not present in the second opening 6O5.The by-pass channel 610 connects with the channel 603 in the first opening 604. The hot gases from the by-pass channel 610 collide with the hot gases in the channel 603 with a high speed and create small turbulence in the first opening 604. It was noted that the test sample in the first opening reached maximum of 76 + deg C as compared to 65degree C in the cooking stove without the by-pass channel.

Another way of increasing turbulence in the second opening 705 is shown in figure 7. A barrier 710 is placed on top of the second opening 705. The barrier helps increasing volume of the cavity 701 yet keeping the second opening 705 small. This stops the smoke coming out of the second opening 705 in spite of turbulence inside. Advantageously, the chimney has a modular construction to allow assembly of the chimney by the abutment of a first set of respective elements together to form a pipe and the placement of a second set of respective sleeve -like elements over the joints formed between the first elements. Chimney pipes are heavy and need to be transported carefully. Due to lack of transport and good roads there is a lot of transit damage. They are too heavy to be carried by people. The modular construction of the chimney is shown in figure 8, in which the modular elements 801 are placed one on top of each other to form a chimney of a suitable height to transport smoke away from the room in which cooking is undertaken, and further sleeve elements 802, each with a handle 803, are slid over the length of pipe formed by the elements 801 to close the gaps 804 between the elements 801. The sleeve like elements 802 should be closely fitting enough to maintain the integrity of the resulting pipe, in other words to allow the pipe to

transport exhaust gases and smoke out of the room without leakage through the gaps 804 back into the room. The sleeve like elements 802 can be held in place by a metal peg (not shown) inserted vertically between each sleeve like element 802 and one or other of the elements 801 next to it, which peg holds the sleeve like element 802 in place by use of friction.

In use, the chimney is built up from elements 801 and sleeve like elements 802 until the top of the chimney is tall enough to issue out from the roof of the room in which the cooking stove is positioned. In this way, exhaust gases and smoke are removed completely from the room. A chimney cap (not shown) can be placed over the top of the chimney.

It has been found that the ideal internal diameter for the chimney is between 75mm and 125mm, but preferably between 90 mm and 110 mm, but preferably between 95 mm and 105 mm. It has also been found that the channel must have substantially the same internal diameter as the chimney if the operation of the chimney and channel together are to successfully remove exhaust gases and smoke by the action of suction. If the channel has a substantially wider diameter than the chimney there is a risk that the exhaust gases and smoke cannot flow freely into the chimney and a proportion of them will flow backwards into the room.

The chimneys can easily be cleaned by having a break in the chimney inside the house at a level easily accessible by a person as shown in figure 9. This solution also helps easy fixing of chimney on the wall. Wall bracket 902 is fixed on the wall helps holding the pipes 901 in place and it has a hanging detail that allows easy fixing of chimney cleaning cover 903. The chimney pipe 901 is divided into two parts, one attached to the chimney chamber (not shown) and other attached to the roof. The actual assembly depends on the height of the roof and the pipe connected to the roof is sized to fix it to the roof. Figures 10 and 11 show how the chimney gets fixed inside a kitchen

Chimneys get clogged very frequently as the biomass, solid fuels, that people in rural India use for cooking, have a lot of resins and substances like silica that do not burn completely. These un-burnt particles travel with the fire and settle on any rough and cooler surface. As the fire cools the soot condenses and settles. It builds quickly and

clogs the chimney. This makes it necessary to clean the chimneys very frequently. Chimney maintenance is problematic as one has to climb the roof to clean it. A bag of sand is dropped from top end - that scrapes the soot as it falls due to gravity.

Figure 12 shows two perforated plates 1201 and 1202. These perforated plates are placed in the chimney for 30 minutes. The perforated plate 1201 is placed inside the chimney without a soot collector and the perforated plate 1202 is placed inside the chimney with a soot collector. It is very obvious from figure 12 that the perforated plate 1201 collected lot of soot compared to the perforated plate 1202. This indicates that the presence of soot collector improves the chimney maintenance. Figure 13 shows a set of soot collector tablets 1301 placed in the chimney chamber 1303 at an accessible point before it enters the chimney 1302 so that the chimney 1302 is not chocked easily. It is found out that if the soot is collected earlier on at the stove level it makes it easier to clean and maintain the chimney 1302. The chimney chamber 1303 connects stove with the chimney 1302. This is the last part where the flue gases pass through. The set of clay tablets 1301 let the smoke pass through in a zig-zag way, thus increasing length of travel of the flue gases and cooling them down in the process. These tablets 1301 collect soot in the process. These tablets 1301 can be removed, scrubbed and washed easily. This reduces collection of soot inside the chimney 1302. It is particularly advantageous if the stove is constructed from a moldable material and has a modular construction to allow assembly of the cooking stove by the abutment of respective elements alongside each other in situ. Further, it has been found to be advantageous if the stove constructed from concrete, but the stove can also be constructed from clay or other material suitable for molding. Figure 14 is a diagrammatic, expanded view of the second embodiment of the stove in modular form. The first module 1401 comprises the cavity 1403 and part of the channel 1404. The second module 1402 comprises the main part of the channel 1404 plus the space into which the cooking pot will be lowered. A further part of the channel 1407 is arranged to connect with a third modular unit 1406 which comprises the space 1408 into which the lowest element of the chimney is inserted. A further modular unit 1409 is placed over units 1401 and 1402 and comprises the openings 1410 and 1411

which are arranged respectively over the cavity 1403 and the space 1405 for the pot. The modular units are abutted together to form the overall cooking stove. An equivalent arrangement allows construction of the first embodiment, in which modular unit 1402 is replaced with modular unit 1412 comprising the channel 1404 plus the protuberance 1413. Because space is not required for insertion of the cooking pot (as in 1402) there is space underneath the channel 1404 of 1412 for a warming area to be constructed 1414 (shown in dotted line). Alternatively, 1412 can be constructed in two sections, one flat lower section comprising the warming area 1414 and a second section comprising the channel 1404 plus protuberance 1413 and arranged to be placed on top of the lower section. The warming area 1414 is designed merely to keep food warm and does so using conduction of heat from the cavity 1403 and the channel 1404 through the solid modules 1401 and 1412. A door plus plate, of for example metal, can be provided to close off warming area 1414 while also allowing plates of food to be slid in and out.

Construction of the stove is from concrete mixed with grid, i.e. broken stones, and the mixture is pored into a greased mould. It has been found that engine oil is a suitable grease which is cheap to obtain and easy to find. The mixture remains in the mould for one hour, covered under wet cloths. The mixture begins to dry and shrinks sufficiently for it to taken out of the mould after 1 hour. This allows the mould to be reused and increases the number of cooking stoves that can be made from one mould. The dried and now shaped mixture must further dry for another 7 to 10 days in open air, covered by wet cloths again to make sure it does not dry to fast and burst.

The moulds are made of iron and an epoxy composite material, re- enforced with fiber glass pieces. This adds strength to the mould which can therefore take any form. The modularity allows ease of construction and transport. Concrete is a heavy material and by splitting the overall stove structure up into sections it becomes easier to manufacture without the use of heavy lifting gear, and also easy to transport into the home and set up.

A further modular unit comprising a shelf (not shown) can be supplied and placed at the back of the stove. This shelf can be used to place cooking implements at a ready height for easy access and further keeps them away from the floor of the home.

Following abutment of the modular units together to form the cavity, channel and opening, the whole stove can be covered in cement or clay or other nonflammable sealing material to seal the gaps between the modular units and improve successful transfer of the exhaust gases and smoke from the cavity to the chimney. The invention allows construction of a low stove, positioned on the ground or on bricks, which allows successful and efficient cooking while ensuring the removal of exhaust gases and smoke from the room.

All of the above-mentioned features are incorporated in two designs of stoves called Saral Stove and Sampoorna Stove as shown in figures 15 and 16. The Sampoorna stove shown in figure 16 has a dedicated steamer 1606 included in the second opening 1605. The steamer 1606 is inserted inside the second opening 1605. The steamer 1606 sits 4 cm inside the second opening 1605 and obstructs the fire path. This helps water inside the steamer 1606 to boil.