DE102007054340B4 - Cooking device with mesoporous filter for a semiconductor gas sensor - Google Patents

Abstract

Cooking appliance (1), comprising a cooking chamber (3), which can be closed by a door (15) or a lid, into which food item (6) can be introduced, a heating device (27) at least one gas sensor (30) which is in operative connection with the cooking chamber (3) ) for determining the chemical state of the cooking chamber atmosphere and a filter device mounted between the cooking chamber (3) and the gas sensor (30), characterized in that the filter device comprises at least one mesoporous filter (39) with an average pore radius between 1 nm and 50 nm, the material of the filter (39) comprises silica and / or silicate.

Description

The Invention relates to a cooking appliance, comprising one about a door or a lid can be closed Cooking chamber, is introduced into the food, a heater at least a gas sensor operatively connected to the cooking chamber for the determination the chemical state of the cooking atmosphere and one between the Cooking chamber and the gas sensor attached filter device, cooking devices for large and commercial kitchens, the equipped with sensors to control cooking processes are known in the art. To the use of puncture probes To avoid, there are various devices and methods described with which the condition of a food contactless can be determined.

A generic cooking appliance with a gas sensor and a sampling system is z. B. in the WO 2006/069563 A1 described. There it is proposed to equip the leads to the gas sensor with a filter which serves to separate the cooking chamber to be measured atmosphere of solid particles and fat and liquid drops.

In such a cooking device usually seals or the like of silicone elastomers, that is used with organic silicon compounds. As these seals become warm during cooking operation, volatile organic silicon compounds are released from them. These pass through the supply lines to the gas sensor. When the organic silicon compounds deposit on the surface of the gas sensor, which is usually a semiconductor gas sensor, they oxidize there, so that a silicon oxide layer is formed on the surface of the semiconductor gas sensor, which increasingly passivates the gas sensor. A disadvantage of the in the WO 2006/069563 A1 The structure described is thus that the sensitivity of the gas sensor is reduced over time by the resulting in the cooking appliance volatile organic silicon compounds and the same is ultimately useless.

From the EP 0 940 680 B1 For example, a gas sensor for bridge circuits is known which comprises a catalytic detector element with an opening. A filter material is positioned between the opening and the detector element or in the opening. The material used is a bronze sinter with a pore size of 9 to 50 μm. The material should at least partially filter out hydrogen sulfide from the gas to be analyzed in order to protect the gas sensor from the harmful effects of this gas. However, such a filter is not suitable for filtering out the harmful organic silicon compounds that may arise during the operation of a cooking appliance.

From the JP 2002 052 338 For example, a silicon gas absorber is known that filters out silicon gases from gases to be detected. In this case, a powder or fiber material is used which comprises silica gel or activated carbon as the main component. Such filter materials must be replaced regularly and are therefore only conditionally suitable for use in cooking appliances. In addition, the gases to be measured would be filtered out in such an application, so that disadvantages for the measurement of the gas sensor are to be expected.

The JP 2004 020 377 discloses a catalytic gas sensor with a filter formed as a silicon trap. The filter is made of a material that can be poisoned by the silicon. Thus, the catalytic gas sensor itself is to be protected from poisoning by a silicon compound. The sintered metal oxide-based filter, however, has the disadvantage that it is passivated by the addition of silicon oxide over time. In addition, an improvement in the efficiency in general would be desirable.

From the US 6,365,108 B1 is a siloxane filter system is known, with which an oxygen sensor for the control of an internal combustion engine is protected. The filter used here is a fiber filter through which the siloxane-containing gas flows. However, the proposed as a material for the fiber filter stainless steel is not well suited for filtering organic silicon compounds.

A Mikrogasanalysesystem with a heatable filter is from the DE 102 45 947 A1 known. The filters used here are so-called "silicone on insulater waver". The filtering takes place here over the surface of the wafer layer. Due to the relatively small surface of the Waver layer, only relatively little gas can be cleaned, so that the use of such a filter in the cooking appliance technology is not appropriate.

The DE 103 52 390 A1 discloses a gas detector with a porous film intended to keep water, oil and / or dust away from a gas sensor. As a material for the filter, a film of PTFE (polytetrafluoroethylene) having a pore diameter of 1 μm is proposed. This filter is not suitable for filtering organic silicon compounds.

The JP 2004 261 672 discloses a selective gasoline absorption filter made of a porous silica. The material has mesopores with a diameter between 1 and 50 nm. Furthermore, micropores with a pore diameter between 0.2 and 0.8 nm are provided on the wall surfaces. This is to improve the analysis of a gas. This filter is ever used but not the protection of a gas sensor and is not intended to filter out organic silicon compounds from a gas to be measured.

The JP 2004 045 324 discloses a gas filter for removing organic silicon gases from a gas mixture. For this purpose, permeable porous layers are used which consist of heat-resistant fibers and powders. By silica components or aluminosilicates, the organic silicon gases can be adsorbed in the filter and thus separated from the remaining gas. Since the filter contains platinum powder, it is relatively expensive to manufacture. In addition, its effectiveness is low.

From the DE 195 17 144 C1 a filter for an electrochemical measuring cell is known, which consists of porous gas-permeable material. The material used here is polytetrafluoroethylene (PTFE). To build the filter itself, a silicone gasket is used. Such a filter would thus release volatile organic silicon compounds again in a hot gas stream from a cooking chamber itself and is therefore unsuitable for use in cooking appliances.

From the WO 97/38776 A1 a fused filter membrane device is provided with which a purified sample gas for a gas analyzer can be generated. For this purpose, porous membranes are used which separate a gas stream from solid and liquid particles. The device thus serves only to separate a sample gas from solid and liquid particles and is not suitable for filtering organic silicon compounds.

Porous filter structures and their methods of manufacture are known from DE 103 61 571 A1 , of the US 6,027,796 and the DE 10 2006 015 386 A1 known. These known filters are made of ceramic materials.

The known filter systems are therefore not for various reasons suitable for, volatile organic silicon compound effectively from a hot gas to filter out of a cooking chamber. Filter systems of organic Compounds usually do not have the necessary heat resistance, around for an insert in a cooking appliance to be considered. Membranes, filters made of fibers or filters with coarse pores do not have sufficient reaction areas to the organic silicon compounds to be filtered out with the to remove necessary efficiency from the sample gas. Other filters, such as B. activated carbon filter are again not selective enough, since they would also remove other components from the gases.

Of the The invention is therefore based on the object, the generic cooking device such to further develop that the Disadvantages of the prior art are overcome. Especially is to filter passivating organic silicon compounds be selective and effective, but without other organic compounds restrain the filtering being both low maintenance and heat resistant at the same time should.

These Task is inventively characterized solved, that the Filter device at least one mesoporous filter with a middle Pore radius between 1 nm and 50 nm, the material of the filter Silica and / or silicate to selectively with the filter gaseous To filter silicon compounds from a sample gas of the cooking chamber atmosphere.

It is preferred that the material of the filter consists of silicon oxide and / or silicate and / or the filter has mesopores with an average pore radius of approximately 10 nm, and / or the specific surface area of the filter is approximately 1000 m ² / g.

With The invention also proposes that the filter be detachable, in particular in a housing, is attached, wherein preferably the housing at one of the cooking space delimiting Wall in the area of an opening in said wall, preferably detachable, attachable.

there can be provided that the Gas sensor, in particular detachable, at least partially in the housing is arranged, preferably opposite to the opening.

With The invention further proposes that the filter in a network and / or a gauze, wherein preferably the network and / or the Gauze on the case, especially solvable, is appropriate.

there can be provided that the Net and / or gauze made of polytetrafluoroethylene (PTFE) and / or Stainless steel exists or exists.

With The invention is also proposed that the housing at least on his cooking chamber contactable surfaces made of stainless steel and preferably in the form of a stainless steel cylinder is trained.

Furthermore, it is proposed that the filter device additionally comprises a coarse filter which is arranged between the filter and the cooking chamber to protect the filter and the gas sensor from particles, such as solids, fat and / or liquid droplets, the coarse filter preferably made of stainless steel is formed and / or releasably connected to the Ge housing and / or the cooking chamber wall is mounted in the region of the opening.

Cooking appliances according to the invention can also be characterized be by at least one pump and / or Blower, which supplies at least the gas sensor cooking chamber atmosphere.

there can be provided that the Pump and / or blower device the cooking space atmosphere at least partially through the filter before it becomes a gas sensor arrives.

Prefers Furthermore, a control or regulating device is in operative connection with the heating device, the gas sensor, the filter device, the pump and / or blower device, a cooking chamber circulation means, an operating device and / or a display device is provided.

moreover can at least one seal between the door or the lid and the cooking chamber and / or at least one cable sheath comprising organic silicon compounds, in particular silicone elastomers, be provided.

Finally will with the invention also proposed that the gas sensor at least one semiconductor gas sensor comprises and / or the conductivity the gas sensor detectable and on the display device, in particular as a function of time, displayable is.

Of the Invention is thus the surprising finding underlying that the volatile organic silicon compounds that arise during the operation of a cooking appliance, effective with a mesoporous Silica or a mesoporous silica-based filter from the cooking chamber atmosphere can be filtered out, a gas sensor for determining the chemical state of the cooking chamber atmosphere and thus a Garegrads a food in the oven is supplied. Other organic Components that escape from the food are not from the mesoporous Silicon oxide filter held. This will make the measurements of the gas sensor not falsified, by other volatile components of the cooking chamber atmosphere, the for determining the chemical state of the cooking chamber atmosphere and thus of the food are important, removed or reduced.

The Use of silica is not just for the high temperatures that occur in cooking appliances, suitable, but also advantageous because the volatile Silicon compounds on the surfaces of the filter to silica be oxidized and thus the surface of the filter in the long term is not passivated by the filtering. The mesopores put sure that the Filter a big one surface at the same time, however, the pores are large enough to be with the Pass gas sensor to be measured organic compounds. The cooking appliance according to the invention ensures that the existence Gassen sor, which is a part of the cooking appliance, not by the im Cooking appliance occurring organic silicon compounds is impaired.

Further Features and advantages of the invention will become apparent from the following Description of an embodiment a cooking appliance according to the invention based schematic drawings. Showing:

1 the structure of a cooking appliance according to the invention in a sectional view,

2 the sensitivity of two gas sensors in a cooking appliance without filters and against poisoning with organic silicon compounds, in the form of their conductivity as a function of time, and

3 the sensitivity of the two gas sensors in a cooking appliance with and without filters and before and after a poisoning with organic silicon compounds, again in the form of their conductivity as a function of time.

1 shows the schematic structure of a cooking appliance according to the invention 1 with a cooking space 3 in which a food is 6 on a food support 9 is placed. The cooking space 3 is on all sides by furnace walls 12 limited. On one side of the cooking chamber 3 is one through a door 15 closable opening provided. Between the door 15 and the furnace walls 12 is a seal 18 attached, which is a tight closing of the cooking chamber 3 through the door 15 allows.

During operation of the cooking appliance 1 with the door closed 15 is the air in the cooking chamber 3 with the help of a fan 21 behind a baffle 24 attached, circulated. With the help of a heater 27 that the fan wheel 21 Surrounds the atmosphere in the oven 3 be heated. The heat is transferred through the fan 21 circulated air on the food 6 , With increasing heating of the food 6 also change the by the food 6 released organic substances that accumulate in the cooking chamber atmosphere.

These substances are combined with a gas sensor 30 measured. At the gas sensor 30 it is usually a semiconductor gas sensor that is housed in a housing 33 is attached and over an opening 36 with the cooking space 3 of the cooking appliance 1 connected is. With the help of a pump (not shown) can the gas sensor 30 Atmosphere from the oven 3 be supplied. The by the food 6 released substances can thus from the gas sensor 30 be measured.

In addition to the food 6 but also the seal 18 the door 15 heated. The seal 18 must therefore be made of a temperature-resistant material, which should have in addition to the temperature resistance but also flexible properties such as rubber. Silicone elastomers as well as other organic silicon compounds are particularly suitable as material for such applications. In addition to the seal 18 can in the oven 3 even more components with organic silicon compounds may be present. An example of this is a core temperature probe (not shown) constructed via a flexible cable having an outer jacket containing organic silicon compounds. Due to the circulated cooking chamber atmosphere, the food to be cooked 6 , the seal 18 and other components heated. When these materials are heated, volatile organic silicon compounds are formed, which accumulate in the cooking chamber atmosphere. These organic silicon compounds also reach the gas sensor via the cooking chamber atmosphere 30 , An example of such a silicon compound is z. For example hexamethyldisiloxane. These compounds settle on the surface of the gas sensor 30 and are oxidized there. In semiconductor gas sensors, the volatile silicon compounds decompose on the hot sensor surface and form silicon oxide there. This covers the sensitive layer of the gas sensor 30 and thus worsens the sensor properties, up to a complete destruction of the gas sensor 30 , Since all soft materials, such. B. the door seal 18 of the cooking chamber 3 , Made of such silicone elastomers, from which escape the volatile silicon compounds when heated, this places a significant burden on the gas sensor 30 Silicone elastomers are preferred in cooking appliances because they are both heat resistant and food safe.

To the volatile silicon compounds of the gas sensor 30 fed Probegas from the oven 3 to disconnect is in the case 33 a mesoporous silica filter 39 built-in. The filter 39 This is done between two stainless steel gazes or nets 42 accommodated. Alternatively, such a network 42 but also made of PTFE. In cooking appliance technology, however, it has proven itself, components, with the cooking chamber 3 to be made of stainless steel. Accordingly, the housing is 33 preferably a stainless steel cylinder.

The filter 39 is like that on the stove wall 12 of the cooking chamber 3 attached so that the gases from the oven 3 first through the filter 39 through before they become the gas sensor 30 reach. The filter material consists of mesoporous silica with a pore radius of approximately 10 nm. The filter material selectively filters out the volatile silicon compounds and allows the target gases out of the cooking chamber 3 to the gas sensor 30 happen. The volatile silicon compounds settle on the surfaces of the mesopores of the silicon dioxide filter and are oxidized there. As a result, new silicon oxide compounds are formed on the surface of the pores, so that the filter itself is not passivated. Clogging of the pores can only be expected after a very long time. In addition, the silicon dioxide is completely insensitive to the temperatures of the gases from the cooking chamber. This is how it succeeds, the gas sensor 30 to protect against poisoning by the volatile silicon compounds.

The 2 and 3 show measurements of conductances of two gas sensors, which on a furnace wall of a cooking chamber of a cooking appliance (similar 1 ) are mounted. The gas sensors are mounted in operative connection with the cooking chamber so that they can detect gas from the oven. During the measurements, a defined amount of octanal was introduced into the oven after about 4 minutes (240 seconds). Octanal is a typical target gas, which is also produced when cooking meat. After approximately 14 minutes (820 seconds), the supply of octanal was stopped. The beginning and end of Octanalzufuhr is in the 2 and 3 with the dashed lines A (beginning of Octanalzufuhr) and B (end of Octanalzufuhr).

2 shows the measurement of two gas sensors, which were connected without the interposition of a filter to the cooking chamber of the cooking appliance. The individual measuring points of the first sensor are shown with squares, the measurements of the second sensor with circles. The measurements show that both sensors react identically without filters and without poisoning by organic silicon compounds. It can be clearly seen how the conductivity of the two semiconductor gas sensors increases when octanal is added to the cooking chamber atmosphere.

3 shows in each case a series of measurements with the two sensors before and after a poisoning by organic silicon compounds. The first sensor was equipped with a filter (measuring points denoted by squares and triangles with tip above) and the second sensor without filter (measuring points indicated by circles and triangles with tip pointing downwards). The measurements after poisoning by organic silicon compounds are in 3 marked by triangles. To the poisoning process, which nor Usually, very slowly, to accelerate, a seal was placed in the cooking chamber of a cooking device, in which a particularly large number of organic silicon compounds were liberated. The conductivity of the sensors is a measure of their reactivity. It can be seen that before the poisoning the sensor without filter (measuring points with circles) has a slightly higher sensitivity than the sensor with filter (measuring points with squares). This results from the fact that the filter inhibits the target gases and thus slightly reduces the sensitivity of the sensor system. After the poisoning one sees clearly that the sensor reacts only very weakly to the Octanal without filter (measuring points with triangles, point downwards). The response of the sensor with filter, however, is virtually unchanged (measuring points with triangles, top tip). This shows that the sensor with a mesoporous silica filter can be very well protected from the harmful effects of volatile organic silicon compounds.

The mesopores (mesopore radius 1 to 50 nm) cause a very high specific surface area (up to about 1000 m ² per gram) of the silicon oxide. Silicon oxide filters out the volatile silicon compounds with high selectivity and allows the compounds to be detected to pass through to a high degree. This makes it possible to filter out particularly large amounts of volatile silicon compounds without severely impairing the diffusion time of the target gases.

The in the foregoing description, the drawings and the claims disclosed features of the invention both individually and in any combination for the realization be essential to the invention in its various embodiments.

1

Cooking appliance

3

oven

6

be cooked

9

food support

12

furnace wall

15

door

18

poetry

21

fan

24

Air baffle

27

heater

30

gas sensor

33

casing

36

opening

39

filter

42

Gauze / Network

Claims (13)

Cooking appliance ( 1 ), comprising one over a door ( 15 ) or a lid closable cooking space ( 3 ), into the food ( 6 ), a heating device ( 27 ) at least one with the cooking space ( 3 ) operatively connected gas sensor ( 30 ) for determining the chemical state of the cooking chamber and one between the cooking chamber ( 3 ) and the gas sensor ( 30 ), characterized in that the filter device comprises at least one mesoporous filter ( 39 ) with an average pore radius between 1 nm and 50 nm, the material of the filter ( 39 ) Comprises silica and / or silicate. Cooking appliance according to claim 1, characterized in that the filter ( 39 ) Mesopores having an average pore radius of about 10 nm, and / or the specific surface area of the filter ( 39 ) is about 1000 m ² / g. Cooking appliance according to claim 1 or 2, characterized in that the filter ( 39 ) detachable, in particular in a housing ( 33 ), wherein preferably the housing ( 33 ) at one of the cooking chamber ( 3 ) bounding wall ( 12 ) in the region of an opening ( 36 ) in said wall ( 12 ), preferably releasably attachable. Cooking appliance according to claim 3, characterized in that the gas sensor ( 30 ), in particular detachably, at least partially in the housing ( 33 ) is arranged, preferably the opening ( 36 ) opposite. Cooking appliance according to one of the preceding claims, characterized in that the filter ( 39 ) in a net and / or gauze ( 42 ), wherein preferably the net and / or the gauze ( 42 ) on the housing ( 33 ), in particular detachably, is attached. Cooking appliance according to claim 5, characterized in that the net and / or the gauze ( 42 ) consists of polytetrafluoroethylene (PTFE) and / or stainless steel or exist. Cooking appliance according to one of claims 3 to 6, characterized in that the housing ( 33 ) is made of stainless steel at least on its contactable with Garraumatmosphäre surfaces and is preferably formed in the form of a stainless steel cylinder. Cooking appliance according to one of the preceding claims, characterized in that the filter device additionally comprises a coarse filter which is located between the filter ( 39 ) and the cooking chamber ( 3 ) is arranged around the filter ( 39 ) and the gas sensor ( 30 ) from particles, such as solids, fat and / or liquid droplets to protect, wherein the coarse filter is preferably made of stainless steel and / or detachable to the housing ( 33 ) and / or the cooking chamber wall ( 12 ) in the region of the opening ( 36 ) is attached. Cooking appliance according to one of the preceding claims, characterized by at least one pump and / or blower device which at least the gas sensor ( 30 ) Supplies cooking chamber atmosphere. Cooking appliance according to claim 9, characterized in that the pumping and / or blowing device at least partially through the filter ( 39 ) before it becomes a gas sensor ( 30 ). Cooking appliance according to one of the preceding claims, characterized by a control or regulating device in operative connection with the heating device ( 27 ), the gas sensor ( 30 ), the filter device ( 39 ), the pumping and / or blowing device, a cooking chamber atmosphere circulation device ( 21 ), an operating device and / or a display device. Cooking appliance according to one of the preceding claims, characterized by at least one seal ( 18 ) between the door ( 15 ) or the lid and the cooking chamber ( 3 ) and / or at least one cable sheath comprising organic silicon compounds, in particular silicone elastomers. Cooking appliance according to one of the preceding claims, characterized in that the gas sensor ( 30 ) comprises at least one semiconductor gas sensor, and / or the conductivity of the gas sensor ( 30 ) can be detected and on the display device, in particular as a function of time, can be displayed.