Patent Description:
The present invention relates to the primary use of cooking grills. It is particularly concerned with avoiding smokes during the barbecue process, maximum flexibility in applying different types of energy sources, and diversified mobility of the cooking appliance. Secondary uses of this invention are hot pot cooking or pan-frying.

Cooking grills of various types currently available in the market are either smoking or not optimized for indoor use. Depending on the types of energy sources utilized, exhaust gases, such as carbon monoxide (CO), cause huge technical, financial, and governmental hurdles for users to obtain the permission to use those cooking grills indoors. Those hurdles are even more serious if the grills generate smokes. Furthermore, existing cooking grills are restricted either to indoor or outdoor use only. <CIT> shows a grill with a cooling system for the grill grid known in the art.

The object of the present invention provides a cooking appliance, especially a barbecue grill, which overcomes the problems and disadvantages of prior art grills described above.

The cooking appliance of the present invention is defined in independent claim <NUM>. Preferred embodiments are claimed in the dependent claims.

Accordingly, the present invention concerns a cooking appliance comprising a casing having an upper opening;.

In certain embodiments, the cooling system is an external cooling system connected to said grill grid. In other embodiments, said cooling system is an integral part of said grill grid.

In certain embodiments said heating assembly comprises two heating elements arranged laterally beneath said grill grid.

In certain embodiments said heating elements comprise electric heaters connectable to a re-chargeable battery housed within said casing and/or to an external power grid.

In this case said electric heaters can comprise fiber carbon heaters.

In certain embodiments said heating elements comprise gas heaters connectable to a gas supply, said gas supply being selected from a built-in gas cartridge removable housed within said casing, an external gas tank or to fixedly installed gas line. According to the invention, said grill grid comprises a hollow tube assembly connectable to a cooling system comprising a source of cooling fluid.

According to the invention, said hollow tube assembly comprises essentially parallel hollow tubes extending between said bottom water tank arranged on one side said grill grid and said top water tank arranged on an opposite side of said grill grid. The water tanks can be an integral part of the grill grid thus defining an internal cooling system.

Particularly, said hollow tube assembly can comprise a meandering hollow tube. Said source of cooling fluid can comprise a water battery or water storage arranged in a cooling circuit. In this case said cooling circuit can comprise a radiator.

In certain embodiments, said water battery or water storage is pressurizable.

In certain embodiments said cooling circuit can comprise a feed pump selected from electric pumps or hydraulic pumps, especially hydraulic RAM-pumps or hydraulic pumps operated by pressurized air.

Said essentially parallel hollow tubes are configured as first tubes which rise from said bottom water tank to said top water tank, and at least two second tubes extend horizontally between said bottom water tank and said top water tank.

Preferably, said first tubes have a smaller inner diameter than said second tubes.

In certain embodiments said first tubes can comprise grease stoppers at their outer circumference.

In certain embodiments, a grease stopper can alternatively or additionally be arranged at a bottom edge of said bottom water tank.

In certain embodiments said bottom and top tanks comprise steam outlets.

Said steam outlets can comprise steam tubes, said steam tubes being connected to downwardly extending steam ductings.

The cooking appliance of the present invention can further comprising a water tray arranged beneath said grill grid within said casing.

In certain embodiments of the cooking appliance of the present invention, said grill grid is removable.

The present invention also concerns a set according to claim <NUM>.

This invention of cooking appliance is primarily employed as a smokeless barbecue system. The smokeless barbecue system consists of three major modules:.

Grill burner, grill grid, and active cooling system can be configured in many ways, allowing maximum freedom of mobility and of utilization of energy sources. The configurations provided in this document only describe the preferred ones, whereas other configurations can be composed based on the general nature of the components outlined within the present document.

Instead of using the grill grid, a hot pot holder or a pan can be put in place of the grill grid to convert the smokeless barbecue system into either a hot pot cooking system or a pan-frying system. These two additional applications are of secondary nature of this smokeless barbecue system.

This smokeless barbecue system is designed such that it can be put on a table or be integrated into a table-top.

The present invention achieves the following objectives:.

Conventional barbecue grills produce smokes from burning food, containing polycyclic aromatic hydrocarbons (PAH), which is carcinogenic in nature. This invention features a real smoke-free capability, regardless of the configurations of the major modules. Moreover, this smokeless and gentle way of barbecue does not disproportionately dehydrate the food and preserves its nutrients.

The present invention employs both fossil energy carriers and energy carriers converted from renewable energy. Furthermore, electrical energy can be used as heat source.

In addition to charcoal, natural gas (NG), liquefied petroleum gas (LPG), and gas from cartridges, being the current common sources of fossil energy, this invention also consider hydrogen (green/blue) being the future energy carrier converted from renewable energy. Gas cartridges can be filled with butane & propane or hydrogen. These fossil energy carriers and hydrogen produce carbon monoxide (CO), whereas the utilization of electrical energy is free of CO, making it the preferred energy option for indoor application of the smokeless barbecue system.

This invention allows barbecue grill to be used outdoors or indoors, and depending on the configurations applied, the barbecue grill can versatilely be used both outdoors and indoors. However, to achieve maximum indoor and outdoor mobility, the most preferred configurations of the smokeless barbecue system are:.

Use smokeless barbecue system appropriate for indoors allows year-round barbecue experiences:
Barbecue normally is constrained to good weather conditions outdoors. This is especially true for regions with four seasons climate or in colder area of the globe. Thus, the barbecue season is normally limited to certain months of the year. Particular configurations of the smokeless barbecue system enable barbecue even during raining, cold or snowing seasons indoors. For configurations featuring both outdoor and indoor capabilities, the smokeless barbecue system can be employed outdoors during good weather season, and indoors during cold or snowing weather period of the year. This would make a perfect Christmas barbecue event with family and friends.

Reduce total costs of safety infrastructure, and ease of obtaining permission to operate indoors, especially for indoor gastronomic facilities:
For employment of a single grill indoors, governmental safety requirements, costs for installation, and the total cost of ownership are easily manageable. However, if dozens of grills are utilized indoors of a gastronomic facility, the efforts and costs for technical safety infrastructure become greatly challenging for any business owner - even if smokeless grills are utilized. As soon as fossil energy, and toxic emission gases, such as carbon monoxide (CO) are involved in the barbecue process, very strict safety regulations must be complied to obtain operation permission from local government. Employment of conventional, smoked grills becomes even too expensive for business owner to provide indoor barbecue to their customers. In certain buildings, such as shopping malls, or in certain cities, it is even prohibited to utilize fossil energy indoors for barbecue grills.

Owners of gastronomic facilities can easily avoid huge, technical costs for complying these governmental safety requirements with the following preferred configurations of the smokeless barbecue system:.

First, smokeless grill process of the smokeless barbecue system does not contaminate the environment with unhealthy smokes.

Second, eliminating resources for safety infrastructure required to install fossil energy supply, to exhaust smokes and toxic emission gases, as such, already contributes to eco-friendliness. Furthermore, it also means that no energy is required to operate the safety infrastructure, resulting in energy saving and an additional contribution to eco-friendliness.

Use smokeless barbecue system as a hot pot or pan-frying cooking appliance:
Beside indoor barbecue, hot pot cooking has become ubiquitous around the globe. Private households and gastronomic businesses usually invest in two different cooking appliances for both applications.

Instead of using the grill grid, a hot pot holder can be put in place of the grill grid to convert the smokeless barbecue system into a hot pot cooking system.

Likewise, the smokeless barbecue system can easily be transformed into a pan-frying system by using a pan instead of the grill grid.

Users just need to invest in one smokeless barbecue system for three different applications: barbecue, hot pot, and pan-frying.

The invention will now be described in more detail in connection with preferred embodiments depicted in the attached drawings.

Throughout the drawings, identical or similar elements or elements having similar functionalities are denoted by the same reference signs.

<FIG> show a perspective view of a cooking appliance <NUM> which can function with a grill grid with cooling system according to the embodiments of the invention shown in <FIG>; The cooking appliance <NUM> comprises a casing <NUM> having an upper opening <NUM>; A grill grid <NUM> arranged in said upper opening <NUM> of said casing <NUM>; a heating assembly <NUM> comprising two heating elements <NUM> arranged within said casing <NUM>, said heating elements being connectable to an energy source not depicted in the drawings. A cooling system <NUM> is connected to the grill grid <NUM> for cooling said grill grid13. The perspective drawing in <FIG> and the cross section in <FIG> illustrate the basic function of the smokeless barbecue system <NUM>. Two grill burners <NUM> generate heat for the food <NUM> placed on the grill grid <NUM> to be barbecued. The passive or, according to an alternative that does not fall under the scope of the claims, an active cooling system <NUM> circulate water inside the grill grid <NUM> to cool it down. (different types of active cooling system are described below).

Smokelessness mainly derives from two technical implementations:
First, two grill burners <NUM> each are placed sidewise below the grill grid <NUM>, whereas the grill area of the grill grid <NUM> does not overlap the grill burners <NUM>. Food residues/ grease <NUM> dropping down from the grill grid <NUM> don't get burnt and smoked by the grill burners <NUM> but fall into a water tray <NUM>. To direct food residues/ grease <NUM> to fall more towards the center of the water tray <NUM>, instead of splashing towards the rims of the grill grid <NUM>, the grill grid <NUM> has symmetric downward slopes from two rims of the grill grid <NUM>, forming a V-shape, as can best be seen in the section view of <FIG>.

Second, the grill grid <NUM> is cooled below burning temperature of the food <NUM> so that no smoke is generated.

Instead of active cooling, passive cooling of the grill grid <NUM> can be achieved by using a twin tank grill grid, as illustrated, for example, in <FIG> while the active cooling system <NUM> is not required.

The water tray <NUM> can be removed from or slid into the cabinet/casing <NUM> through the openings for water tray <NUM>. The water tray <NUM> shall be filled ¾ with water, which collects and cools down food residues/ grease <NUM> falling from the grill grid <NUM>. Setting operational parameters, such as power or cooling intensities can be done in the control board <NUM> section.

<FIG> shows a variant of the barbecue system of <FIG> in a hot pot application. For hot pot application, a hot pot holder <NUM> can be put in place of the grill grid <NUM> to hold an hot pot <NUM> thus allowing to convert the smokeless barbecue system into a hot pot cooking system.

<FIG> shows a variant of the barbecue system of <FIG> in a pan-fry application. Similarly, the smokeless barbecue system can easily be transformed into a pan-frying system by using a pan <NUM> of <FIG> instead of the grill grid <NUM>. The pan <NUM> has centrically symmetric slopes and holes allowing grease <NUM> to drop down to water tray <NUM>.

Depending on the form of energy employed, mobility and recommendations for use in gastronomic facilities vary.

Table <NUM> summarizes the various forms of energy, and their recommended areas of employment in different embodiments of the present invention.

The present invention employs both fossil energy carriers and energy carriers converted from renewable energy. Furthermore, electrical energy can be used as heat source. In addition to charcoal, natural gas (NG), liquefied petroleum gas (LPG), and gas from cartridges, being the current common sources of fossil energy, this invention also consider hydrogen (green/blue) being the future energy carrier converted from renewable energy. Gas cartridges can be filled with butane & propane or hydrogen. These fossil energy carriers and hydrogen produce carbon monoxide (CO), whereas the utilization of electrical energy is free of CO, making it the most preferred energy option for indoor application of the smokeless barbecue system.

In the following, a grill grid <NUM> using water batteries will be described in connection with <FIG>.

Preferred grill grid configurations, and their recommended areas of employment are summarized in Table <NUM> below.

<FIG> shows a passively cooled grill. <FIG> shows a section view of the embodiment of <FIG> according to line VI-VI of <FIG>.

The twin tank grill grid <NUM> comes in two different preferred types: <FIG> outlines the type without ports, and <FIG>. With ports. Both types can be connected to a water battery as shown, for instance, in <FIG>, to replenish the twin water tanks <NUM> with water vaporizing over the course of the barbecue process. Passive and active cooling can be achieved by cooling down a multitude of tubes <NUM> with water. Passive cooling means that water between the twin water tanks <NUM> and the tubes <NUM> are exchanged during the barbecue process. Please note, that no circulation literally occurs between the tubes and the twin water tanks.

<FIG> shows the twin tank grill grid for passive cooling. It is self-sufficient in terms of autonomous cooling, as no external forces or equipment are required to cool down the tubes <NUM> of the grill grid, preventing the barbecue food from being burnt and smoked. The twin water tanks <NUM> are connected in equidistance by multitude of tubes <NUM>, allowing water being exchanged between the twin water tanks <NUM> and the tubes <NUM>, resulting in cooling down the water within the tubes <NUM>. The tubes <NUM> are symmetric, downward sloping tubes to direct grease moving towards the center of the grill grid (V-shape tubes). To prepare the use of the twin tank grill grid <NUM>, the twin water tanks <NUM> need to be filled with water up to a predefined level. To do so, one of the two caps <NUM> shall be opened for water inlet. The caps <NUM> are closed prior to use of the grill grid. During the barbecue process, steams are produced by boiling water inside the tubes <NUM>, which escape into each of the twin water tanks <NUM>. The steams collected in the twin water tanks <NUM>, above water level therein, are discharged through valves or holes <NUM> distributed evenly on a bigger tube <NUM> connecting the upper hollow spaces of the twin water tanks <NUM>. The steam discharge has three essential physical effects: first, to ease overpressure within the grill grid; second, to cool down the grill grid; and third, to reduce water volume inside the grill grid. Therefore, after a certain grill time, the water inside the twin tank grill grid is depleted, requiring it to be replaced by another grill grid filled with water, otherwise the depleted grill grid cannot be cooled down resulting in smokes generation.

Alternatively, a water battery <NUM> or <NUM>, as shown in <FIG>, respectively, can be docked on just one or both twin water tanks <NUM> by opening the cap <NUM> and plugging the connector <NUM> of the water batteries <NUM> or <NUM> on the twin water tanks <NUM>. The connector <NUM> can be provided with an adjustment screw and the water rate can be adjustable.

<FIG> outlines the water battery <NUM> featuring a cap <NUM> for water inlet/outlet; a valve/hole <NUM> to equalize air pressure inside and outside the water battery and a connecter <NUM> with adjustment screw to tune the water drain rate.

<FIG> depicts a water battery with compressed air <NUM>. After filling the water battery <NUM> up to predefined level with water, and closing the cap <NUM> again, the air within the water battery <NUM> can be charged with compressed air by an external air compressor via valve <NUM>. The increased air pressure inside the water battery would allow a higher water drain rate at the connecter <NUM> if required.

<FIG> shows an alternative grill grid with connections to an active cooling system. <FIG> illustrates the twin tank grill grid with ports for active cooling. Production deviations of the twin tank grill grid and stochastical heating behavior within the tubes can cause impulsive peaks of steam expansions, which in turn lead to harmless implosions inside the twin tank grill grid. Although the implosions are harmless, they cause noises and trigger higher magnitude of steams discharge, creating psychical fear to some users. To solve this problem, the water inside the tubes <NUM> must be cooled down faster than the time it needs to be transformed into steams caused by constant heat radiated from the grill burner (reference signs <NUM> in <FIG>). The solution is to circulate the water inside the tubes <NUM> so it does not have enough time to be transformed into steams, and to cool down the water before feeding it back to the tubes <NUM>. <FIG> shows such a solution: the ports <NUM>, <NUM> of the grill grid <NUM> is connected to an active cooling system. The active cooling system cools down the water coming from one twin water tank <NUM> through the outlet, female port <NUM>, and feeds back the cooled water into the other twin water tank through the inlet, female port <NUM>. This process results in a continuous circulation of cooled water inside the tubes <NUM>. An additional advantage of the active cooling system is that it has a water storage, allowing replenishment of depleted water in the grill grid. Thus, there is no need of using an extra water battery. Moreover, to direct grease and food residues to spread more towards the center of the tubes <NUM>, and fall centrically on the water tray, instead of splashing towards the twin water tanks <NUM>, tubes <NUM> have symmetric downward slopes, forming a V-shape (see section view of <FIG>).

<FIG> shows yet another alternative grill grid <NUM> with connections to an active cooling system. <FIG> shows a section view of the grill grid of <FIG> according to line XI-XI of <FIG>. Instead of employing the twin tank grill grid with ports, active cooling can be achieved by using a meandering grill grid pipe. <FIG> describes a preferred construction of a meandering grill grid pipe for active cooling made from a frame <NUM> and a meandering pipe <NUM>. Like the twin tank grill grid with ports, it also possesses inlet and outlet ports <NUM>, <NUM> hooked up to an active cooling system. However, instead of straight tubes, it consists of just one seamless pipe <NUM> curving in a zigzag shape without interconnections to form a grill grid, with each terminal mounted to the outlet or inlet, female port <NUM>, <NUM>. Unlike the twin tank grill grid with ports, it does not need twin water tanks. Smokelessness and prevention of implosions inside the hollow pipe can be achieved in the same way as described for <FIG>: both, by cooling down the grill grid and circulating the water therein by the active cooling system. In addition, to direct grease and food residues to spread more towards the center of the grill grid, and fall centrically on the water tray, instead of splashing towards the frame <NUM>, the meandering pipe <NUM> has symmetric downward slopes, forming a V-shape (see section view of <FIG>).

In the following, a detailed description of active cooling systems with hydraulic pump is given with reference to preferred examples shown in <FIG>.

Table <NUM> below summarizes configurations of active cooling system with hydraulic pump, and their recommended areas of employment.

Table <NUM> indicates hydraulic pump configurations, and their recommended areas of employment.

<FIG> shows a first example of an active cooling system <NUM> with hydraulic pump and fan for a grill grid. Hot water coming from a grill grid <NUM> will be fed into the radiator <NUM>, which cools down the water before feeding it into a water storage <NUM>. The hydraulic pump <NUM> pumps cooled water from the bottom of the water storage <NUM> back into the grill grid <NUM> preventing it from smoking during the barbecue process. The fan <NUM> accelerates the cooling process by ventilating the heat from the radiator. The water storage <NUM> ensures bubble-free water supply to the grill grid <NUM> and serves as reservoir for replenishing of depleted water in the grill grid <NUM>. Air bubbles in the water of the water storage <NUM> will rise to the upper part of it, and exhaust through the air escape valve <NUM>. There are two preferred types of grill grid <NUM> appropriate for the active cooling system: twin tank grill grid with ports (<FIG>), and meandering grill grid pipe (<FIG>).

<FIG> outlines an active cooling system with hydraulic pump, without fan, and with cooling tub <NUM> for water storage <NUM>. Instead of using a fan as featured in <FIG>, the water storage <NUM> can be placed in a cooling tub for water storage <NUM>. This also accelerates the cooling process of water before feeding it back to the grill grid <NUM>.

<FIG> outlines an active cooling system with hydraulic pump, without fan, and with cooling tub <NUM> for water storage and cooling tub <NUM> for radiator. The water storage <NUM> can be placed in a cooling tub for water storage <NUM>, and the radiator <NUM> in the cooling tub for radiator <NUM>. This intensifies the acceleration of the cooling process of water before feeding it back to the grill grid <NUM>.

In the following, a detailed description of active cooling systems with air pressure is given in connection with examples shown in <FIG>.

Instead of using electrical energy or a hydraulic pump, air pressure is a natural driving force to circulate water through the active cooling system and the grill grid. The subsequent explanations elaborate the basic mechanism and several preferred configurations of this concept.

Table <NUM> summarizes various configurations of active cooling system with air pressure, and their recommended areas of employment.

<FIG> illustrates the basic function of an active cooling system with air pressure, with fan. At any given time, the water between the first water container 41a and the second one 41b flows in just one direction. Let's assume that the water flows from left water container 41a to right water container 41b, with left radiator 40a, grill grid <NUM>, and right radiator 40b in between. In this stage, the spool valve <NUM> channels compressed air from the air compressor <NUM> to the left water container 41a, causing air overpressure in the upper part of the same. The air overpressure then drives water out of the left water container 41a. As soon as the water level in the right water container 41b reaches a predefined water threshold, the spool valve <NUM> will be activated to channel compressed air in the opposite direction, pressing the water in the right water container 41b through the right radiator 40b, through the grill grid <NUM>, and then through the left radiator 40a back into the left water container 41a. Thereafter, once the water level in the left water container 41a reaches a predefined water threshold, the spool valve <NUM> will be activated again to change compressed air to flow in the opposite direction. This mechanism alternately circulate water in the active cooling system and in the grill grid <NUM>, thereby cooling down the grill grid <NUM> to prevent it from smoking during the barbecue process. The fans 43a, 43b accelerate the cooling process of the radiators by ventilating heat away from the same.

The spool valve <NUM> operates in <NUM> different modes. First, in neutral (inactivated) mode, all ports of it are shut, and compressed air from the air compressor <NUM> is shut as well. Second, if the spool valve <NUM> is activated on the left side, the compressed air coming via port <NUM> from the air compressor <NUM> will be channeled to port <NUM> and will be fed into the left water container 41a, concurrently cutting off the compressed air supply for the right water container 41b. As a result, the water level in the right water container 41b continuously rises. Third, the right side of the spool valve <NUM> is activated as soon as the predefined water threshold in the right water container 41b is reached, and navigates compressed air from port <NUM> to port <NUM>, feeding the right water container with compressed air, concurrently cutting off the compressed air supply for the left water container 41a, causing the water level in the same to rise. The spool valve <NUM> comes in two variants of activators: either electric or mechanical.

If the left water container 41a is supplied with compressed air through port <NUM> and port <NUM>, water level inside the right water container 41b continuously rises, pressing out the air above water level of the same from port <NUM> to port <NUM>. Vice versa, as long as the right water container 41b is supplied with compressed air through port <NUM> and port <NUM>, the air above water level of the left water container 41a will be exhausted from port <NUM> to port <NUM>.

<FIG> illustrates an active cooling system with air pressure similar to <FIG>, but without fan. Leaving out cooling fan is possible if the radiators are efficient enough to cool down the water for a proper grill process without smoke.

<FIG> outlines an active cooling system with air pressure like <FIG>, but with a cooling tub <NUM> for the left and right radiator 40a, 40b. This is recommended if the radiators require additional cooling support to cool down the water for a proper grill process without smoke.

<FIG> depicts an active cooling system with air pressure similar to <FIG>, but with both a cooling tub <NUM> for the left and right radiators 40a, 40b and a cooling tub 45a, 45b for each water container 41a, 41b. This is desirable if the radiators require even more cooling support to cool down the water for a proper grill process without smoke.

<FIG> shows an active cooling system with air pressure like <FIG>, but with a cooling tub 45a, 45b for each water container 41a, 41b only, if this is sufficient to cool down the water for a proper grill process without smoke.

<FIG> describes an active cooling system with air pressure similar to <FIG>, but without radiators, and with a cooling tub 45a, 45b for each water container 41a, 41b only, if this is sufficient to cool down the water for a proper grill process without smoke.

An embodiment of the smokeless barbecue system according to the present invention is described in connection with <FIG>. Elements which have already been described in connection with other embodiments above are denoted by the same reference signs. The barbecue system of this embodiment employs a self-sufficient cooling using a self-circulating gravity grill grid allowing active cooling.

As can be taken from <FIG>, the grill grid <NUM> comprises a bottom water tank <NUM> and a top water tank <NUM> which are floated with water. Water tanks <NUM>, <NUM> are interconnected by several first tubes <NUM> which have a positive slope, i.e. the first tubes rise from bottom water tank <NUM> to top water tank <NUM>. In the embodiment depicted in <FIG>, the first tubes <NUM> have an essentially equal slope forming a slightly inclined support plane for food. Further, the bottom water tank <NUM> and the top water tank <NUM> are interconnected by two second tubes <NUM> which extend essentially horizontally, i.e. exhibit essentially zero slope. In the depicted embodiment, the first inclined tubes have a smaller inner diameter than the second horizontal tubes. Usually, this would also imply that the outer diameter of the first tubes <NUM> is smaller than the outer diameter of the second tubes so that, with respect to each other, the first tubes can be denoted "smaller tubes" and the second tubes can be denoted "bigger tubes".

In use, grilled food is placed on the smaller first tubes <NUM> for barbecuing. Grease stoppers <NUM>, which can be configured as rings surrounding the smaller first tubes <NUM> at certain intervals, prevent grease from falling downwards and spilling into grill burner <NUM> which are usually arranged on the side of the bottom water tank <NUM> and/or the top water tank <NUM> as indicated in <FIG>. Accordingly, generation of smoke and possible damage of the grill burner over time by dripping grease is avoided.

During use, water inside the smaller first tubes <NUM> is heated up by the operation of the grill burners <NUM> resulting in a lower water density and thus becoming lighter than the water outside of the smaller first tubes <NUM>. The water temperature within the bottom and top water tanks <NUM>, <NUM> is cooler than the water temperature within the smaller first tubes <NUM>. Accordingly, water within the smaller first tubes <NUM> will gain a higher buoyancy allowing water in the smaller first tubes <NUM> to flow against the force of gravity upwards into the top water tank <NUM> which, in turn, draws cooler water from the bottom water tank <NUM> into the smaller tubes <NUM> where it is recurrently heated up by the grill burners.

The heated water flow from the smaller first tubes <NUM> into the top water tank <NUM> causes the water level in the top water tank <NUM> to rise to a higher level than the water level in the bottom water tank <NUM>. Due to the force of gravity, the water levels in both water tanks <NUM>, <NUM> tends to be equalized by water circulating from the top water tank <NUM> to the bottom water tank <NUM> through the two bigger second tubes <NUM>.

The continued process induces a self-circulation of water within the grill grid, whereby cooling down the smaller first tubes <NUM>, thus preventing the burning of grill food and the corresponding generation of smoke. Accordingly, a smokeless barbecue system using a grill grid according to the embodiments of <FIG> represents a self-driven cooled grill grid without requiring application of external forces or application of any external power sources. Self-sufficient cooling derives merely from establishing a self-circulation of water within the grill grid relying merely on the physical properties of water during heating and the application of the gravitational force acting on the system.

Upon heating of water in the smaller first tubes <NUM>, steam <NUM> may be generated. As shown in <FIG>, steam <NUM> is collected in the bottom and top water tanks <NUM>, <NUM> above the respective water levels and can be discharged through steam tubes <NUM> and team ducting <NUM>. Eventually, steam <NUM> condenses within the steam ducting and the resulting condensed water falls down into the water drain <NUM>. The steam discharge has three essential physical effects: firstly, it will ease overpressure within the grill grid, secondly, it will help to further cool down the grill grid and thirdly, it will reduce the water volume circulating inside the grill grid. Therefore, after a certain operation time, the water inside the grill grid will get more and more depleted and its cooling functionality diminishes. Accordingly, the grill grid may be provided with a recharge opening (such as the caps <NUM> indicated in <FIG>) allowing fresh water to be introduced into the grill. Handling of a hot grill grid for filling up water may, however, be associated with certain safety risks. Therefore, according to another option, the self-sufficient cooling grill grid is removably arranged within the barbecue system allowing it to be replaced by another grill grid filled with water. The proper timing for re-filling the grill grid or replacing the grill grid can easily be detected by the onset of smoke generation. More preferably however, to avoid any generation of smoke, the appliance can be provided with a timer which is set to indicate a typical operating time of the grill grid until water re-fill or grid replacement is required. In addition or alternatively, the bottom water tank can be provided with a water level indicator.

Since the self-circulating grill grid according to the present embodiment does not require any external power source, it represents the most ecofriendly version of the cooling systems described in the present application.

<FIG> show another embodiment of the invention of a self-circulating grill grid allowing active cooling.

As can be taken from <FIG>, the grill grid <NUM> comprises a bottom water tank <NUM> and a top water tank <NUM> which are floated with water. Water tanks <NUM>, <NUM> are interconnected by several first tubes <NUM> which have a positive slope, i.e. the first tubes rise from bottom water tank <NUM> to top water tank <NUM>. In the embodiment depicted in <FIG>, the first tubes <NUM> have an essentially equal slope forming a slightly inclined support plane for food. Further, the bottom water tank <NUM> and the top water tank <NUM> are interconnected by two second tubes <NUM> which extend essentially horizontally, i.e. exhibit essentially zero slope. In the depicted embodiment, the first inclined tubes have a smaller inner diameter than the second horizontal tubes. Usually, this would also imply that the outer diameter of the first tubes <NUM> is smaller than the outer diameter of the second tubes so that, with respect to each other, the first tubes can be denoted "smaller tubes" and the second tubes can be denoted "bigger tubes". In use, grilled food is placed on the smaller first tubes <NUM> for barbecuing. Grease stopper <NUM>, which projects along the inner lower edge of the bottom water tank <NUM>, prevents grease <NUM> from falling downwards and spilling into grill burner <NUM>, which are usually arranged on the side of the bottom water tank <NUM> and/or the top water tank <NUM> as indicated in <FIG>. Accordingly, generation of smoke and possible damage of the grill burner over time by dripping grease is avoided. During use, water inside the smaller first tubes <NUM> is heated up by the operation of the grill burners <NUM> resulting in a lower water density and thus becoming lighter than the water outside of the smaller first tubes <NUM>. The water temperature within the bottom and top water tanks <NUM>, <NUM> is cooler than the water temperature within the smaller first tubes <NUM>. Accordingly, water within the smaller first tubes <NUM> will gain a higher buoyancy allowing water in the smaller first tubes <NUM> to flow against the force of gravity upwards into the top water tank <NUM> which, in turn, draws cooler water from the bottom water tank <NUM> into the smaller tubes <NUM> where it is recurrently heated up by the grill burners. The heated water flow from the smaller first tubes <NUM> into the top water tank <NUM> causes the water level in the top water tank <NUM> to rise to a higher level than the water level in the bottom water tank <NUM>. Due to the force of gravity, the water levels in both water tanks <NUM>, <NUM> tends to be equalized by water circulating from the top water tank <NUM> to the bottom water tank <NUM> through the two bigger second tubes <NUM>. The continued process induces a self-circulation of water within the grill grid, whereby cooling down the smaller first tubes <NUM>, thus preventing the burning of grill food and the corresponding generation of smoke. Accordingly, a smokeless barbecue system using a grill grid according to the embodiments of <FIG> represents a self-driven cooled grill grid without requiring application of external forces or application of any external power sources. Self-sufficient cooling derives merely from establishing a self-circulation of water within the grill grid relying merely on the physical properties of water during heating and the application of the gravitational force acting on the system. Upon heating of water in the smaller first tubes <NUM>, steam <NUM> may be generated. As shown in <FIG>, steam <NUM> is collected in the bottom and top water tanks <NUM>, <NUM> above the respective water levels and can be discharged through steam tubes <NUM> and team ducting <NUM>. Eventually, steam <NUM> condenses within the steam ducting and the resulting condensed water falls down into the water tray <NUM>. The steam discharge has three essential physical effects: firstly, it will ease overpressure within the grill grid; secondly, it will help to further cool down the grill grid; and thirdly, it will reduce the water volume circulating inside the grill grid. Therefore, after a certain operation time, the water inside the grill grid will get more and more depleted, and its cooling functionality diminishes. Accordingly, the grill grid may be provided with a recharge opening (such as the cap <NUM> indicated in <FIG>) allowing fresh water to be introduced into the grill. Handling of a hot grill grid for filling up water may, however, be associated with certain safety risks.

Therefore, according to another option, the self-sufficient cooling grill grid is removably arranged within the barbecue system, allowing it to be replaced by another grill grid filled with water. The proper timing for re-filling the grill grid or replacing the grill grid can easily be detected by the onset of smoke generation. More preferably however, to avoid any generation of smoke, the appliance can be provided with a timer which is set to indicate a typical operating time of the grill grid until water re-fill or grid replacement is required. In addition, or alternatively, the top water tank can be provided with a visible water level indicator window <NUM> as indicated in <FIG>. User can see the water level <NUM> within that window, and shall refill the grill grid, or replace the grill grid if the water level sinks below certain threshold. Since the self-circulating grill grid, according to the present embodiment, does not require any external power source, it represents the most ecofriendly version of the cooling systems described in the present application.

<FIG> shows a perspective view of still another embodiment of a smokeless barbecue system in accordance with the present invention having a refill system for the water tray in a similar view as the embodiment of <FIG>.

Claim 1:
A cooking appliance (<NUM>) comprising
a casing (<NUM>) having an upper opening (<NUM>);
a grill grid (<NUM>,<NUM>) arranged in said upper opening (<NUM>) of said casing (<NUM>);
a heating assembly (<NUM>) comprising at least one heating element (<NUM>) arranged within said casing (<NUM>), said heating element (<NUM>) being connectable to an energy source; and
a cooling system (<NUM>,<NUM>,<NUM>,<NUM>) comprising a source of cooling fluid (<NUM>,<NUM>,<NUM>,<NUM>,41a,41b,<NUM>,<NUM>) for cooling said grill grid (<NUM>,<NUM>),
characterized in that
said grill grid (<NUM>,<NUM>) comprises a hollow tube assembly (<NUM>,<NUM>,<NUM>,<NUM>,<NUM>) connectable to said cooling system (<NUM>,<NUM>,<NUM>,<NUM>), said hollow tube assembly comprising essentially parallel hollow tubes (<NUM>,<NUM>) extending between a bottom water tank (<NUM>,<NUM>) arranged on one side said grill grid (<NUM>,<NUM>) and a top water tank (<NUM>,<NUM>) arranged on an opposite side of said grill grid (<NUM>,<NUM>), said essentially parallel hollow tubes being configured as first tubes (<NUM>) which rise from said bottom water tank (<NUM>) to said top water tank (<NUM>), and at least two second tubes (<NUM>) extend horizontally between said bottom water tank (<NUM>) and said top water tank (<NUM>).