DE102011102281A1 - Cooking oven for preparing food products, has static device comprising region with narrowed cross-section, where flow rate of gases is related with flow rate of air with pressure, temperature and vapor concentration in cooking chamber - Google Patents

Abstract

The oven (1) has a measuring device comprising a static device i.e. venturi tube, which is inserted into a pipe (3) for connecting a furnace chamber with outer atmosphere. The static device comprises a region (4) with a narrowed cross-section, which increases velocity of gas with reduced pressure. Surrounding air is mixed with withdrawing gases transported along the pipe. Flow rate of gases is related with flow rate of air with respect to pressure, temperature and vapor concentration in a cooking chamber (2). A flowmeter (8) is arranged at another pipe (7) sucking air. An independent claim is also included for a method for measuring flow rate of gases.

Description

The present invention relates to a food cooking oven having a device for measuring the flow rate of the gases exiting the oven, having the features of the preamble of the main claim 1.

The invention also relates to a measuring method by which the aforesaid device operates to measure the flow rate of gases exiting the furnace.

More particularly, the invention relates to the art of cooking food ovens, which are typically provided with a device for producing or supplying steam and / or with a device for supplying ambient air into the cooking chamber of the oven, and which are also provided with a hole connecting the cooking chamber to the outside atmosphere to allow the gases and vapors supplied to the cooking chamber and / or within the cooking chamber to escape. The supply or production of steam and / or ambient air is used in so-called steam cooking processes (maximum concentration of steam) or in those where a controlled concentration of steam is required. During these cooking processes, it is necessary to introduce or generate steam and / or introduce ambient air into the cooking chamber to regulate the concentration of the steam itself. This supply or generation of steam or ambient air, along with the possible generation of vapor by the foodstuffs, causes gas to escape from the hole connecting the chamber to the outside atmosphere of the oven. The escaping gas can be composed as follows:

• - 100% steam, in the case when cooking is done with 100% steam, or if the food being boiled contains a large amount of water that evaporates during cooking, or
• - A mixture of steam and air, in the case when the cooking is carried out with a concentration of less than 100% and / or ambient air is introduced into the furnace to reduce the concentration of the vapor within the same.

Depending on the type of cooking additionally escape, together with the gas, other substances, such as swaths of organic substances such. As fats that develop during cooking.

In order to be able to control the flow rate of the supplied or generated steam and / or the flow rate of the ambient air fed into these cooking ovens, it would be advantageous to be able to measure the flow rate of the gas exiting the cooking chamber and to use this signal to move the device to regulate the supply of air and the supply or generation of steam in the cooking chamber.

Especially in steam cooking processes where the steam concentration should be maximum, regulating the flow rate of the steam supplied to the cooking chamber or generated in the cooking chamber to the necessary minimum would allow a high energy saving potential due to the high heat output needed to produce the excess steam , In these cases, steam generation is currently provided in practice which is much larger than the necessary minimum.

Unfortunately, this measurement is very complicated because of the high temperatures of the gas exiting the cooking chamber and because of its tendency to easily contaminate and / or add the flow velocity measuring devices because of the predominantly organic substances produced during cooking ,

Devices and / or methods are known which measure this flow rate directly or indirectly, but these have many disadvantages, including cost, reliability and accuracy.

The problem underlying the present invention is to provide a furnace with a measuring device that is structurally and functionally designed to overcome the limitations of said prior art.

The problem is solved by the invention by means of a furnace with a measuring device according to claim 1 and a method for measuring the flow rate of the gas exiting the furnace according to claim 6. The subclaims disclose preferred developments of the invention.

Further features and advantages of the invention will become more apparent from the following detailed description of a preferred embodiment, given by way of non-limitative example with reference to the accompanying drawings, in which:

1 is a schematic view of a furnace according to the present invention, which is equipped with a device for measuring the flow velocity of the gases leaving the furnace,

2 a schematic view of a detail of 1 in a possible alternative embodiment, and

3 a schematic view of a detail of 1 in a possible further alternative embodiment.

With reference to the drawings mentioned is with 1 an oven for food called and shown only schematically, the inside with a cooking chamber 2 equipped to accommodate food to be cooked.

The furnace is provided with a heat generating means, not shown, for example with electrical resistors or a heat exchanger connected to a fuel gas burner. A device (not shown) for generating or supplying steam or reducing its concentration is additionally provided, for. B. by means of the supply of steam generated by a steam generator outside the cooking chamber, or by introducing water into the cooking chamber to increase the concentration of the steam, which is suitable for the cooking process, or by the introduction of ambient air in the cooking chamber to reduce the concentration of the steam.

reference numeral 3 denotes a pipe that has a hole 3a with the interior of the chamber 2 is connected, and that connects the chamber to the outside atmosphere, to the gases that are generated in the chamber after the supply or generation of steam or ambient air in the chamber itself, together with the generated by the food itself during the cooking steam to the outside to transport. It should be noted that, depending on the type of cooking, other substances along with the gases over the pipe 3 can escape, for. B. swaths of organic substances, such as fats, which develop during cooking.

More precisely, the tube has 3 a T-shape with a first area 4 who left the chamber 2 exit, and move into a second area 5 and a third area 6 extends, which extend in extension to each other, as in 1 is clearly shown. From the free end of the range 6 the gases can escape. A second pipe 7 is in the area 5 used. This has a smaller diameter than the area 6 of the pipe 3 on. The pipe 7 extends over the central connection point of the areas 4 to 6 out into a part of the area 6 ,

The passage cross section for the gas between the pipe 6 and the tube 7 represents a constriction of the passage cross section of the tube 7 which is the narrowing to the end 7a the pipe 7 extends. Thereafter, the passage cross section again has the dimension of the cross section of the area 6 of the pipe 3 on.

The aforesaid narrowing of the cross-section creates a static device in which an increase in velocity (in the narrowed section) is created which is locally associated with a corresponding decrease in the pressure of the gas flowing through the device.

Due to the reduced pressure, preferably with pressures below atmospheric pressure, at the end 7a of the pipe 7 is generated by increasing the velocity of the gas (caused by the narrowing of the cross-section), a flow of ambient air from the opposite end 7b of the pipe 7 , which opens to the outside atmosphere, sucked. This stream of ambient air, along the pipe 7 is sucked, can be easily measured, for example by means of a flow meter only schematically illustrated 8th who is on the pipe 7 is arranged.

In practice, the static device uses the known principle known as the Venturi effect (the pressure of a fluid stream increases as the velocity drops and vice versa). It is known to use the Venturi tube to measure the flow rate of a fluid by measuring the pressure of the fluid itself at two points of the tube at different cross-sections / speeds. When a Venturi tube, which is made with a geometry to produce a pressure below the atmospheric pressure in the region where an increase in velocity arises, in the outlet pipe 3 for the gases coming from the cooking chamber 2 of the furnace, is inserted, and the pipe which opens to the atmosphere is connected to this area, then the ambient air will flow to the inside of the venturi pipe.

• – Geometrie des Venturi-Rohrs und des Rohrs, das den Niederdruckbereich des Venturi-Rohrs mit der Atmosphäre verbindet,
• – Temperatur T (gleich der der Garkammer 2) und Konzentration C des Dampfes des Gases, das durch das Venturi-Rohr strömt,
• – Atmosphärentemperatur T und einen Druck p',

besteht eine doppelt-eindeutige Korrelation zwischen dem Gasstrom, der aus der Garkammer 2 austritt, und dem Luftstrom, der vom Venturi-Rohr angesaugt wird. Die Korrelation, die die Strömungsgeschwindigkeit der angesaugten Umgebungsluft und die Strömungsgeschwindigkeit des Gases, das aus dem Ofen entweicht, verbindet, kann theoretisch (unter Verwendung bekannter Gleichungen, die Phänomene wie z. B. der Satz des Bernoulli, das Universalgesetz der Gase usw. beschreiben) oder experimentell bestimmt werden. Sobald die Korrelation zwischen der Strömungsgeschwindigkeit der Umgebungsluft und der Strömungsgeschwindigkeit des Gases bei verschiedenen der vorgenannten Variablen bestimmt wurde, kann durch Messen der Strömungsgeschwindigkeit der Umgebungsluft die Strömungsgeschwindigkeit der Gase bestimmt werden.For a certain

• Geometry of the Venturi tube and tube connecting the low pressure area of the Venturi tube to the atmosphere,
• - Temperature T (equal to the cooking chamber 2 ) and concentration C of the vapor of the gas flowing through the Venturi tube,
• Atmospheric temperature T and a pressure p ',

There is a double-definite correlation between the gas flow coming out of the cooking chamber 2 exit, and the airflow that is drawn in by the Venturi tube. The correlation connecting the flow rate of the intake ambient air and the flow rate of the gas escaping from the furnace can theoretically (using known equations) describe phenomena such as Bernoulli's theorem, the universal law of gases, and so forth ) or determined experimentally. Once the correlation between the flow velocity of the ambient air and the flow velocity of the gas has been determined for various of the aforementioned variables, by measuring the flow rate of the ambient air, the flow rate of the gases can be determined.

A sensor device (not shown) may also be suitably provided to measure the concentration C of the vapor in the chamber and / or the temperature T of the cooking chamber and / or the ambient temperature T and / or the atmospheric pressure p '.

It is also clear that the static device alternative embodiments to the in 1 may have shown. For example, a Venturi tube may be used in the 2 and 3 shown embodiments are selected as a possible alternative embodiment.

In addition, provision may also be made for a moderate flow rate Q 'of the ambient air into the tube 7 is forced, for example by means of a ventilation device (not shown), regardless of the existence of the gas from the cooking chamber 2 escapes. In this case, when there is gas leakage, the flow rate of the air sucked by the static device due to the reduced pressure is added to the flow rate Q '. The flow rate Q 'can be easily determined because it is related to the characteristic of the ventilator (eg, proportional to the speed of rotation of the fan by which the ventilator is generated).

In operation of the flow velocity measuring device of gases exiting the furnace, the method by which it operates basically sees measuring the flow velocity of the ambient air along the tube 7 in the range of the reduced pressure of the static device through which the gases leaving the cooking chamber are recycled, and obtaining a measurement of the flow rate of the gas leaving the cooking chamber via the correlation between the flow rate of the gas and the flow rate of the ambient air due to the geometry of the static device, the temperature, the pressure and the vapor concentration of the exiting gas from the chamber.

The invention thus solves the problem posed, offering many advantages.

A first advantage lies in the fact that the measurement of the flow rate of the air takes place at ambient temperature and not at the temperature of the cooking chamber.

A second advantage is associated with the fact that the intake ambient air does not contain the substances (for example cooking fats) which can pollute and / or clog the measuring device.

Yet another advantage is that the pipe remains clean for the intake of ambient air, since it always has a lower pressure with respect to the point of the Venturi pipe to which it is connected.

Claims (6)

Food cooking oven comprising a cooking chamber, means for supplying or generating steam in the cooking chamber, and / or means for supplying ambient air into the cooking chamber, a first pipe for connecting the cooking chamber to the outside atmosphere, gases or vapors contained in the cooking chamber supplied to the cooking chamber and / or generated in the cooking chamber to escape, a device for measuring the flow velocity of the gas emerging from the cooking chamber, wherein the chamber is subject to certain conditions of temperature, pressure and concentration of the steam, characterized in that the measuring device comprises a static device inserted into the first tube for connecting the furnace chamber to the outside atmosphere, the static device comprising a region of reduced cross-section suitable for increasing the velocity of the gas with consequent cross-section Reducing the pressure of the gas by itself, and in that the device comprises a second tube suitable for communicating the external atmosphere with the area of the restricted cross-section in which a reduction in pressure takes place, the ambient air being suitable with the exiting ones Gases, which are transported along the first tube from the furnace, to be mixed, is returned via the second tube, wherein the flow rate of the exiting gases with the flow velocity of the air, which is recycled along the second tube, as well as with the conditions of pressure the temperature and vapor concentration present in the chamber. Oven according to claim 1, wherein on the second tube, which is suitable, the outside atmosphere To connect with the region of reduced pressure of the static device, a device for measuring the flow velocity of the air flowing through the second tube, is provided. A furnace according to claim 1 or claim 2, wherein the static device is a Venturi tube. The furnace of claim 1, wherein the value of the pressure in the region of the static reduced pressure device is less than the atmospheric pressure. Oven according to one of the preceding claims, wherein a sensor device for measuring the concentration of the vapor in the chamber and / or the temperature of the cooking chamber and / or the ambient temperature and / or the pressure of the cooking chamber is provided. A method of measuring the flow rate of gases exiting the cooking chamber of a food oven equipped with a flow rate measuring device according to one or more of the preceding claims, the method comprising the steps of: Determining the flow rate of the ambient air which is recycled along the second tube in the region of reduced static pressure of the static device through which the gases leaving the cooking chamber are returned, Obtaining a measurement of the flow velocity of the gas leaving the chamber via a correlation between the flow rate of the gas and the flow rate of the ambient air according to the geometry of the static device, the temperature, the pressure and the vapor concentration of the gases leaving the chamber.

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