EP1459022A1

EP1459022A1 - Method and installation for predicting the temperature of articles passing through a cooling chamber

Info

Publication number: EP1459022A1
Application number: EP20020800627
Authority: EP
Inventors: Bernard Delpuech; Pascal Favier; Sylvain Fourage
Original assignee: Air Liquide SA; LAir Liquide SA a Directoire et Conseil de Surveillance pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2001-10-05
Filing date: 2002-10-03
Publication date: 2004-09-22
Also published as: FR2830608A1; CA2462399A1; US20040237547A1; FR2830608B1; WO2003031891A1; JP2005504952A

Abstract

The invention relates to a method of predicting the temperature of articles (P) passing through the chamber (2) of a cooling installation using a coolant (4), said method comprising a step whereby the temperature of articles (P) exiting said chamber (2) is predicted. Said prediction is calculated from the characteristic quantities in relation to the operation of said chamber (2), the thermodynamic and physical characteristics of said chamber (2) and the thermodynamic and physical characteristics of said articles (P). The invention is suitable for controlling quick-freezing tunnels for food.

Description

Method and installation for predicting the temperature of articles passing through a cooling enclosure

The present invention relates to a method for predicting the temperature of articles undergoing thermal cooling. The invention applies for example to installations for freezing food articles.

Known deep-freezing installations comprise, for example, an enclosure or tunnel, of deep-freezing crossed right through by a belt conveyor on which the articles to be frozen are deposited, the conveyor circulating continuously or sequentially through the deep-freezing tunnel.

A cryogenic tunnel uses an inert fluid at low temperature which exchanges heat directly by contact with the products to be frozen.

Conventionally, a cryogenic tunnel uses either dry ice (-80 ° C), or liquid air, or liquid nitrogen (-196 ° C) as a vector of cold. Dry ice allows the transport of fresh or frozen products without fear of breaking the cold chain. Nitrogen and liquid air allow either individual freezing of food products or the hardening of fragile, deformable or sticky products (such as ice cream ...).

If we examine the system consisting of the tunnel and the product load, several parameters can influence the temperature of the product at the output: the production rate which, for a given loading rate, implies a variation of the time of stay in the enclosure, the flow rate of the fluid which acts on the temperature profile, the inlet temperature of the product, the convective profile of the enclosure, and the loading rate. The system is therefore a multivariable system and a cooling process cannot take these elements into account in a simple feedback loop.

The main difficulty in correcting setpoint deviations is related to the fact that there is no commercially available sensor capable of continuously measuring the internal temperature of products today.

In the methods of prediction of the state of the art, in order to treat monovariable systems, we have been led to consider the convective profile and the loading rate as constant, and to fix the production rate, the temperature of the products entering the deep-freezing chamber as well as the other operating parameters of the installations.

One then acts for example on the flow rate of the cryogenic fluid in order to define the average profile of the temperatures of the fluid in the tunnel and thus to regulate the temperature of the product at the outlet.

The operating conditions and regulation instructions are defined in recipes created experimentally. A recipe memorizes the tuning parameters for a given production.

If the production conditions vary, we leave very little autonomy to the operator to modify the parameters, he can only load a new recipe.

An existing system described in French patent FR-A-2 760 272 implements a method allowing the temperature of the articles leaving the enclosure to be predicted. However, this prediction is based on a value representative of the quantity of articles treated and on the quantity of cryogenic fluid with which the articles are brought into contact. Such a prediction is therefore very approximate.

It appears that the existing methods exhibit a certain instability in operation, significant adjustment difficulties and a low capacity for adaptation to operating conditions.

The present invention aims to remedy these problems. To this end, it relates to a method for predicting the temperature of articles passing from an inlet to an outlet, an enclosure of a cooling installation, which uses a cooling fluid, which method comprises a step of predicting of the temperature of articles leaving said enclosure, characterized in that said prediction is calculated on the basis of operating characteristic quantities of said enclosure, of thermodynamic and physical characteristics of said enclosure and of thermodynamic and physical characteristics of said articles.

According to other characteristics:

- At least part of said quantities characteristic of the operation of said installation is entered manually; - At least part of said quantities characteristic of the operation of said installation is automatically detected;

at least thermodynamic characteristics of said cooling fluid and said thermodynamic and physical characteristics of said enclosure are used to make a prediction of the behavior of said enclosure based on the resolution of thermal balances on elementary slices of the volume of said enclosure;

- Said prediction of the behavior of said enclosure also uses, said quantities characteristic of the operation of said installation; - said quantities characteristic of the operation of said installation represent at least one of the elements chosen from the group consisting of:

- The speed of a conveyor for transporting said articles through said enclosure; - the loading rate; and

- ventilation of the atmosphere of said enclosure;

- Said prediction of the behavior of said enclosure is corrected on the basis of experimental readings of the temperature profile which prevail in said enclosure; - At least said thermodynamic and physical characteristics of said articles are used to make a prediction of the behavior of said articles based on the resolution of the discretized heat conservation equation and applied to a network of spatial and temporal points constituting a mesh of said articles; said prediction of the behavior of said articles also uses said quantities characteristic of the operation of said installation;

- Said quantities characteristic of the operation of said installation include the temperature of said articles entering said enclosure; - Said prediction of the behavior of said articles is optimized by calculations of modification of said mesh of said articles according to mathematical sequences;

- said prediction of the behavior of said articles is optimized by removing prediction calculations for spatial and temporal points of said mesh of said articles for which the enthalpy variations are less than a predetermined threshold;

- Said prediction of the temperature of said articles leaving said enclosure is based on said prediction of the behavior of said enclosure as well as on said prediction of the behavior of said items;

- said prediction of the temperature of the articles takes into account an experimental measurement of this temperature.

The present invention also relates to a method for cooling articles passing from an inlet to an outlet, an enclosure of a plant for cooling said articles (P) which uses a cooling fluid, characterized in that it includes a step of predicting the temperature of said articles according to the invention;

According to another characteristic of the invention, said prediction is carried out by a reiteration of the prediction of the behavior of said enclosure and the prediction of the behavior of said articles, said method comprising a step of modifying at least one of the parameters chosen in the group consisting of:

- the flow rate of said cooling fluid;

- the residence time of said articles in said enclosure; - the flow of gas extracted from said enclosure;

- the speeding up of gases;

- gas recirculation; and

- The balance between the air inlets and the gas outlets, until a theoretical value for the temperature of said articles at the outlet of said enclosure is obtained, close to a set point.

The present invention also relates to a device for predicting the temperature of articles passing through an installation, comprising a cooling enclosure which uses a cooling fluid comprising means for predicting this temperature, characterized in that said predicting means comprise calculation means which use quantities characteristic of the operation of the installation, thermodynamic and physical characteristics of said enclosure and thermodynamic and physical characteristics of said articles. The present invention also relates to an installation for cooling articles comprising an enclosure for cooling said articles which uses a cooling fluid, characterized in that it comprises a device for predicting the temperature of said articles according to the invention. According to other characteristics of the invention:

- Said cooling fluid is injected into said enclosure and exchange of heat with said articles by direct contact;

- Said cooling fluid circulates in a heat exchange device included in said enclosure, and indirectly exchanges heat with said articles through said heat exchange device.

The invention will be better understood on reading the description which follows, given solely by way of example and made with reference to the appended drawings, in which:

- Fig.1 shows a block diagram illustrating an installation implementing a method according to the invention;

- Fig.2 illustrates the numerical modeling of the articles to be treated;

- Fig.3 illustrates the digital modeling of the cooling enclosure; and

- Fig.4 shows the flowchart of the coupling of the enclosure model and the items model.

In Figure 1, there is shown a food article processing installation equipped to implement a method according to the invention.

This installation comprises a cryogenic enclosure or tunnel 2, of the conventional type, allowing the freezing of food articles P by bringing them into contact with a cryogenic fluid 4 conveyed by a supply line 5, from any source.

For example, tunnel 2 has the shape of a rectangular parallelepiped.

As mentioned above, the cryogenic fluid 4 used can be, for example, dry ice or liquid nitrogen. This tunnel 2 is associated with a conveyor 6 of the conventional type, allowing the articles P to be introduced into the enclosure 2 and their extraction and operating either sequentially or continuously.

The installation is equipped with measuring means 8 of characteristics relating thereto. They deliver for example the temperature profile in enclosure 2 and the conveyor unwinding speed 6. This last piece of information linked to the length of enclosure 2 makes it possible to obtain the residence time of the products P in enclosure 2.

The installation is furthermore equipped with input means 10 by an operator of operating parameters, such as for example the temperature of entry into the enclosure 2 of the products P.

In another version of the installation, the cited operating parameters, namely the temperature profile, the residence time or the unwinding speed, and the inlet temperature of the products P, are distributed differently between the measurement. and manual entry.

We can also have the case where all the operating parameters are measured and the case where all are entered manually.

The installation finally comprises means 12 for controlling the quantity of cryogenic fluid 4 injected into the enclosure 2. These means 12 comprise means 14 for controlling the flow of cryogenic fluid 4. For example, the control means 14 are constituted by solenoid valve systems or proportional valves of the conventional type, arranged on the cryogenic fluid supply line 5.

The fluid 4 is injected at one or more places in the enclosure 2. The control means 14 are controlled by the output of comparison means 16, which are connected as input to input means 18 of a setpoint relating to the temperature of the articles leaving the enclosure 2 and to means 20 for predicting this temperature.

Control of the flow rate of cryogenic fluid 4 injected into an installation such as that described, on the basis of a comparison between a setpoint and a prediction of the outlet temperature of the articles, is considered to be known and will not be described further. in detail.

Advantageously, the installation also includes a gas ventilation system controlling the gas flows and the ventilation of the atmosphere of the enclosure 2.

For example, this system is made up of specific fans enabling gas to speed up, fans controlling gas recirculation and a combination of fans and movable doors controlling the balance between air inlets and outlets. gas. In the context of the invention, the means 20 for predicting the temperature of the articles P at the outlet of the enclosure 2, comprise means for predicting or predicting 22 the behavior of the enclosure 2, and means for predicting or predicting 24 of the behavior of the articles P. The predictive means 22 of the behavior of the enclosure 2 make it possible to predict by calculation, as described below with reference to FIG. 3, the theoretical profile of the temperatures of the cryogenic fluid 4 to inside the enclosure 2.

The results delivered by the prediction means 22 depend on the thermodynamic characteristics of the cryogenic fluid 4, on the convective characteristics of the enclosure 2, as well as on the characteristics of the means for injecting the cryogenic fluid 4 into the enclosure 2, on the characteristics of the system. ventilation and physical characteristics of the enclosure 2.

In the described version of the invention, the prediction means 20 also include means 26 for correcting the predictor 22 of the behavior of the enclosure 2.

These correction means 26 make it possible to take into account, in the calculations of the predictor 22, elements characteristic of the operation of the installation, such as for example the speed of the conveyor 6, temperature readings inside the enclosure 2, the temperature of the cryogenic fluid 4 recovered after the treatment of articles P, or the thermal losses of enclosure 2. The data injected into the predictor 22 using the correction means 26 can be entered manually through the means of input 10 or measured by the measurement means 8. For example, there is a series of probes inside the enclosure 2 which make it possible to establish an experimental profile of the temperatures of the cryogenic fluid 4 in the enclosure 2 .

These results are then compared to the theoretical results and the diagram of a calibration curve is defined which makes it possible to adjust the theoretical values delivered by the predictor 22 of the behavior of the enclosure 2.

The means 24 of predicting the behavior of the articles P, make it possible to determine by calculation, as described below with reference to FIG. 2, the variations in enthalpy of the articles P as a function of their external environment and their initial temperature . The results delivered by the predictor 24 depend on the physical and thermodynamic characteristics of the P products.

In the described version of the invention, the prediction means 20 also include means 28 for optimizing the predictor 24 calculations of the behavior of the products P, the operation of which is described below with reference to FIG. 2.

Coupling means 30, described in more detail with reference to FIG. 4, make it possible to link the results delivered by the predictor 22 of the behavior of the enclosure 2 and those delivered by the predictor 24 of the behavior of the articles P and to deliver a theoretical temperature of the items P leaving the enclosure 2.

Thus, the prediction implemented by the means 20 for predicting the temperature of the articles P leaving the enclosure 2 takes into account the thermodynamic and physical characteristics of the enclosure 2 and of the products P, as well as the quantities characteristics of the operation of the installation.

Therefore, the determination of the temperature of the articles P at the outlet of the enclosure 2 is dynamic, easily configurable and easily adaptable to the operating conditions of the installation.

In Figure 2, there is shown an example of a mesh of a food item P.

The thermodynamic and physical characteristics of the articles P are taken into account in the cooling process by the predictor 24 of the behavior of the articles P, and is based on a modeling of the articles P to which the heat conservation equation is applied. discrete.

Indeed, the equation of heat conservation cannot be solved at any point in space and at all times, by a simple integral function.

The method used consists in discretizing this equation so that it is solved only on spatial and temporal points called nodes and designated by the general reference 32.

After definition of a mesh of the article P, one applies the equation of conservation of heat to each of the nodes 32. One thus obtains a system of equation which must be solved in order to know the thermal state of the article P in time and in space.

X, Y and Z are axes defining an orthonormal spatial reference frame around the article P. T is the temperature of the article P expressed in kelvin (K), and C its specific heat expressed in watt per kilogram and by Kelvin (W / (Kg ^* K)).

Food items P that are frozen are generally made up of different bodies.

This means that the phase change is accompanied by a temperature variation and that the heat conservation equation can still apply.

On the other hand, if one is brought to treat a pure body, the equation is no longer continuous. In this case, the problem is simplified by modifying the enthalpy table of the pure body so that the change in size generates a small variation in temperature.

The discretization is made thanks to the mathematical method of the finite differences in variable mode.

In known manner, this can be carried out in two ways.

The first, implicit discretization, has the advantage of being stable whatever the spatial and temporal configuration. At a given instant, it makes it possible to determine the temperature of a node 32 as a function of the temperature of the neighboring nodes at the same instant. However, it implies constant boundary conditions and a matrix resolution of the equation system formed by each of the nodes 32. The second, explicit discretization, makes it possible to directly determine the temperature of a node 32 at an instant T + ΔT d ' after the conditions at time T. The result is immediate, on the other hand, it is necessary to choose a suitable time step so as to avoid the instability of the model.

The first method is recommended in the case where it is sought mainly to obtain the surface temperature of a product, which corresponds to the operation commonly called the "crusting" operation. The second is recommended when you want to freeze and know the core temperature of a product. The mesh of the product P, is a crucial problem. On this directly depends the simplicity of further processing and the accuracy of the results.

A large number of nodes brings great precision in the result but imposes a high computation time. It is a question of finding a compromise between precision and calculation time.

For example, for the case of a food product with external dimensions 100 x 60 x 10 mm with a regular mesh every millimeter, it takes more than 17000 knots and as many equations to define the behavior of article P. In the described version of the invention, there are optimization means 28 of the calculations which make it possible to optimize the mesh which is carried out in the predictor 24 of the behavior of the articles P.

For example, in the case of crusting, the solidification of a thin product skin is more particularly monitored by phase change. We therefore need a dense network at the periphery and wider at heart.

To not manually enter the coordinates of each of the nodes and to keep simple relationships between the nodes and facilitate processing, one solution is to distribute nodes in each direction of space using for example a geometric progression , as shown in Figure 2.

For example, on the X axis, we distribute the nodes as follows: we consider Δx the value of the first term which corresponds to the abscissa of the first node, and r the reason, different from 1, of the geometric sequence set implemented. The value of the n ^th term is: Δx ^* r ^{n "1.} , This corresponds to the position on the X axis of the n ^th node. The sum of the first n terms is: î -"

S = Ax + £ - ir Figure 2 represents the positioning of the nodes according to this mesh on a parallelepipedic article P where one imposed a condition of parity on the number of nodes so as to simplify the resolution. This gives a value corresponding to the dimension of article P along the X axis: with R ι- _r

1 +;

With I which corresponds to the abscissa of the central node on this length

The imprecision on the X axis is then expressed in the following manner

\ -2 - 1

To achieve simple calculations, the inaccuracies on the three axes are fixed at the same value. This induces an error on the dimensions of the article P which is acceptable in the case where one is only interested in the temperatures on a thin skin thickness and the core temperatures vary little, as is the case in the crusting operations.

In the case of deep-freezing operations where it is sought to determine the core temperature of the product, a corrective term can be inserted in the formulas. In the case of the X axis, the following corrective term is inserted:

Ax '= M)

Another possible optimization method consists in reducing the processing time by omitting certain calculations.

Indeed, on each node, we add the heat flux to the six faces of its elementary volume. However, there are areas where thermal effects can be likened to one-dimensional problems.

To exploit this particularity, the treatment is broken down by no longer summing up the heat fluxes on each face, but in each direction. On each direction, one solves, for a time step ΔT, the equations with the nodes while going from the border towards the heart, until the va- enthalpy is considered to be negligible because it is below a predetermined threshold.

By carrying out this operation in each direction, one defines a volume of the product P including all the nodes for which the enthalpy variations will be negligible, and therefore for which no calculation will be made.

This can save computing time, especially in the first moments of the exchange.

In the case where the article P is of complex shape, it can be broken down into a set of elementary forms to which the mesh defined above or any other mesh adapted to the shape of the article P is applied.

The means 24 for predicting the behavior of the articles P as well as the means 28 for optimizing the calculations are, for example, implemented by software means.

In Figure 3, there is shown schematically the enclosure for processing food articles.

The thermodynamic and physical characteristics of the enclosure 2 are taken into account in the cooling process by the predictor 22 of the behavior of the enclosure 2, and is based on a modeling of the enclosure 2 in the form of elementary slices . As described above with reference to FIG. 1, the cooling enclosure 2 is associated with a conveyor 6. It is supplied with cryogenic fluid 4 via a supply line 5. The enclosure 2 is assimilated to a rectangular parallelepiped.

To determine the theoretical profile of the temperatures of the fluid 4, the method implemented by the predictor 22 of the behavior of the enclosure 2 consists in carrying out a succession of local heat balances.

For this purpose, we consider a modeling of the thermodynamic system of tunnel 2, in steady state, in the form of elementary sections 34ι to 34 _n , perpendicular to the length of the enclosure 2. The sum of these elementary sections 34τ to 34 _n , represents the internal volume of enclosure 2.

For each elementary section 34ι to 34 _n , the balance of the heat transfers is carried out in order to determine the enthalpy of the fluid 4 and therefore its temperature.

This assessment must take into account: - heat losses with the outside of tunnel 2;

- cryogenic liquid 4 injected into the spraying zones; and

- exchanges between the products P and the fluid 4.

In the case of section 34j of the tunnel of dimensions LTh, the heat balance results in the following equation:

In this equation: _m corresponds to the enthalpy of the cryogenic fluid 4 at the outlet of the elementary section 34j expressed in joules per kilogram (J / Kg); H _M e, corresponds to the enthalpy of the cryogenic fluid 4 at the input of the elementary section 34j expressed in joules per kilogram (J / Kg); corresponds to the liquid enthalpy of the cryogenic fluid 4 injected expressed in joules per kilogram (J / Kg);

] - [corresponds to the enthalpy of article P at the input of section 34j expressed in joules per kilogram (J / Kg);

H corresponds to the enthalpy of the article P at the outlet of the section

34d expressed in joules per kilogram (J / Kg);

] ζ _τ corresponds to the heat exchange coefficient of tunnel 2 with the outside expressed in watt per square meter and per kelvin (W / (m ² K)); m __ corresponds to the mass flow rate of cryogenic fluid 4 vaporized in section 34j expressed in kilograms per second (Kg / s); _j jl corresponds to the mass flow rate of cryogenic fluid 4 entering the section 34ι expressed in kilograms per second (Kg / s);

YYl corresponds to the mass flow rate of products to be treated expressed in kilograms per second (Kg / s); ¹ _Amb corresponds to the ambient temperature expressed in kelvin; and y corresponds to the temperature of the cryogenic fluid 4 at the input of the unit 34 | expressed in Kelvin.

FIG. 3 also shows the heat flows: th _r H _t ^is represented P ^ar ' ^{a letter} A;

rh _m H _M O ^{is re} ^BSB has P ^{ar the lΘttre B:} H m _m _m ^is represented by the letter C;

_. m H _{e (P} ^r ^{is re} ESENTE with the letter D, and

m H _d) ^is represented by the letter E;

From experience, we know that under certain operating conditions (production flow too low or temperature of the cryogenic fluid 4 too low), the cryogenic liquid 4 injected is only partially vaporized and a fraction of the liquid flows towards the inlet. of enclosure 2.

If one wishes to take this phenomenon into account, it is preferable to resolve the local assessments starting with the elementary section located at the exit of the tunnel. The calculations are therefore made in the opposite direction of the path of the products P, ie along the axis X as shown in FIG. 3. In this sense, in fact, the fraction of non-vaporized liquid can be transferred to the next one and so on. until reaching the ventilation zones where the injected flows are zero and where the liquid surpluses are vaporized.

To determine the fraction of cryogenic liquid 4 not vaporized in an elementary slice, an enthalpy of the limiting fluid is designated, below which a liquid content will appear.

This is equivalent to setting a minimum gaseous fluid temperature in the tunnel.

The non-vaporized liquid title at the outlet of the elementary section 34j corresponds to χ _{L (i)} and is expressed in the following form:

_. - WlfLtqV)

Ytt fs (i)

If the calculations are simplified by considering that the enthalpy of this liquid fraction is substantially equal to the enthalpy of the cryogenic fluid 4 injected, the expression of the title of the following liquid is obtained:

In this equation, fj _{J m} corresponds to the limit enthalpy of formation of a liquid title in an elementary section of the tunnel 2.

FIG. 4 shows the operation of the means 20 for predicting the temperature of the articles P at the outlet of the enclosure 2.

In order to be able to predict the temperature of the articles P at the outlet of enclosure 2, the cooling process involves predicting the behavior of enclosure 2 implemented by the predictor 22 of the behavior of enclosure 2 and the prediction of the behavior of the articles implemented by the predictor 24 of the behavior of the articles P.

In the installation described with reference to FIG. 1, this step is implemented by the coupling means 30.

We start by implementing the predictor 22 of the behavior of the enclosure 2, during a step 40. This delivers the heat losses 42 by elementary section which are reintroduced into the predictor 22.

After repeating this operation a certain number of times, we obtain the total thermal losses 44 as well as the profile 46 of the temperatures of the fluid 4 in the enclosure 2. To calculate the thermal balance of each slice, the predictor 22 requires the enthalpic variations of articles P. In fact, during the first iteration, the temperature profile of the fluid 4 in the enclosure 2 cannot be calculated, it is fixed arbitrarily.

The predictor 24 of the behavior of the items P is then implemented during a step 50. This delivers the enthalpy 52 of the product P at the outlet of the enclosure 2, ie its temperature.

Optionally, the predictor 24 of the behavior of the articles P also delivers the enthalpy variations 54 of an article P for each elementary section of the enclosure 2. In this case, this information is returned to the behavior predictor 22 of the enclosure 2 which inserts it into the heat balance of each elementary section. The enthalpy 52 of the product P at the outlet of the enclosure 2 as well as the profile 46 of the temperatures of the fluid 4 in the enclosure 2 and the total thermal losses 44, are put in relation in order to determine the total flow rate of the fluid, at step 60.

Optionally, the flow rate 62 injected into each elementary section is also obtained. In this case, this information is returned to the behavior predictor 22 of the enclosure 2 which inserts it into the heat balance of each elementary section.

It is then checked whether the temperature profile of the fluid 4 in the enclosure 2 is stable, in step 80. For example, the profile of the fluid temperatures is considered to be stable if it meets the following criteria twice:

In this equation, dif_profil is a constant fixed by the operator. On the first pass, the profile is considered unstable. As long as the profile is considered unstable, we return to step

40 and we start again the succession of operations making it possible to define a profile.

Once a stable profile has been obtained, it is checked whether the setpoint entered by the input means 10 for a setpoint relating to the temperature of the products P at the outlet of the enclosure 2 has been reached, in step 80. If the setpoint has been reached, the last profile of the temperatures of the fluid 4 inside the enclosure 2 is implemented, in a conventional manner, by the control of the means 14 for controlling the flow of fluid 4, step 90.

If the setpoint has not been reached, in step 100, a correction 102 is applied to the flow rate of the fluid 4 before repeating the algorithm. Optionally, a correction 104 is also applied directly to the temperature profile of the fluid 4, which is injected into the predictor 22 of the behavior of the enclosure 2.

In this example, the prediction of the temperature of the articles leaving the enclosure is used to perform automated control of a cryogenic enclosure 2 by influencing the flow rate of the fluid 4 injected.

We can similarly influence the residence time of the articles P in the enclosure 2 by modifying the speed of the conveyor 6 or the downtime in the case of a sequential conveyor. We can also act on the speed gas extraction or on the loading rate, or on a combination of these parameters.

Similarly, it is possible to influence the balance between the air inlets and the gas outlets, the gas extraction speed, the gas speed up, or even the gas recirculation by influencing the elements. control of these parameters.

One can imagine that the algorithm is constantly reiterated in order to ensure continuous monitoring of the operating conditions and allow the adjustment of the profile of the temperatures of the fluid. One can also imagine the implementation of the algorithm following the detection of a modification of the operating parameters.

Furthermore, the method of the invention is implemented in an installation having non-contact sensors for the temperature of the items being output, for example sensors based on thermal radiation or the infrared image, or even on a measurement by microwave thermometry (TMO), such as the sensor described in patent FR-A-2,771,552.

The results delivered by the means for predicting the temperature of the articles leaving the enclosure according to the invention are then cross-checked with the measurements delivered by these sensors. In this case, one or the other of the information is used to check the other, or an average of the two values for the operation of the installation.

In another situation, the information delivered by the sensor is used to correct the prediction. Advantageously, the measurement frequency is lower than the frequency of delivery of a prediction. Although a particular embodiment has been described, it is not considered to limit the scope of the present invention.

In another version, the installation is equipped with means for determining the value representative of the quality and / or quantity of articles treated, which means are connected to the means for predicting the temperature of the articles leaving according to the invention.

In addition, the cooling method of the invention can also be applied in a mechanical cooling installation having an indirect heat exchange device. The invention has been described in the case of cooling food articles, however it can also be applied to other types of articles, in particular metallic articles.

In addition, the term cooling also covers systems aimed at maintaining and controlling a temperature lower than the initial temperature of an article.

Furthermore, the invention has been described in the context of a cooling installation. However, the temperature prediction method can be implemented independently of the enclosure control means, for example in the context of temperature control.

The invention makes it possible in particular to ensure the traceability of the articles during acquisition and storage operations with a view to providing a quality guarantee.

Claims

1. Method for predicting the temperature of articles (P) passing from an inlet to an outlet, an enclosure (2) of a cooling installation which uses a cooling fluid (4), which method comprises a step of prediction of the temperature of articles (P) at the outlet of said enclosure (2), characterized in that said prediction is calculated on the basis of operating characteristic quantities of said enclosure (2), of thermodynamic and physical characteristics of said enclosure ( 2) and of thermodynamic and physical characteristics of said articles (P).

2. Method according to claim 1, characterized in that at least part of said quantities characteristic of the operation of said installation is entered manually.

3. Method according to claim 1 or 2, characterized in that at least a portion of said quantities characteristic of the operation of said installation is detected automatically.

4. Method according to any one of claims 1 to 3, characterized in that at least thermodynamic characteristics of said cooling fluid (4) and said thermodynamic and physical characteristics of said enclosure (2), are used to make a prediction of the behavior of said enclosure (2) based on the resolution of thermal balances on elementary slices of the volume of said enclosure (2).

5. Method according to claim 4, characterized in that said prediction of the behavior of said enclosure (2) also uses said quantities characteristic of the operation of said installation.

6. Method according to claim 5, characterized in that said quantities characteristic of the operation of said installation represent at least one of the elements chosen from the group consisting of:

- The speed of a conveyor (6) for transporting said articles (P) through said enclosure (2); - the loading rate; and

- ventilation of the atmosphere of said enclosure (2).

7. Method according to any one of claims 4 to 6, characterized in that said prediction of the behavior of said enclosure (2) is correct. based on experimental readings of the temperature profile prevailing in said enclosure (2).

8. Method according to any one of claims 1 to 7, characterized in that at least said thermodynamic and physical characteristics of said articles (P) are used to make a prediction of the behavior of said articles (P) based on the resolution of the 'heat conservation equation discretized and applied to a network of spatial and temporal points constituting a mesh of said articles (P).

9. Method according to claim 8, characterized in that said prediction of the behavior of said articles (P) also uses, said quantities characteristic of the operation of said installation.

10. Method according to claim 9, characterized in that said quantities characteristic of the operation of said installation include the temperature of said articles (P) at the inlet of said enclosure (2).

11. Method according to any one of claims 8 to 10, characterized in that said prediction of the behavior of said articles (P) is optimized by calculations of modification of said mesh of said articles (P) according to mathematical sequences.

12. Method according to any one of claims 8 to 11, characterized in that said prediction of the behavior of said articles (P) is optimized by suppressing prediction calculations for spatial and temporal points of said mesh of said articles (P) for which the enthalpy variations are less than a predetermined threshold.

13. Method according to claims 4 and 8 taken together, characterized in that said prediction of the temperature of said articles (P) at the outlet of said enclosure (2) is based on said prediction of the behavior of said enclosure (2) as well as on said prediction of the behavior of said articles (P).

14. Method according to any one of claims 1 to 13, characterized in that said prediction of the temperature of the articles (P) takes into account an experimental measurement of this temperature.

15. Method for cooling articles (P) passing from an inlet to an outlet, an enclosure (2) of an installation for cooling said articles (P) which uses a cooling fluid (4), characterized in that 'it comprises a step of predicting the temperature of said articles (P) according to any one of claims 1 to 13.

16. Method according to claim 15, characterized in that said prediction is carried out by a reiteration of the prediction of the behavior of said enclosure (2) and of the prediction of the behavior of said articles (P), said method comprising a step of modifying '' at least one of the parameters chosen from the group consisting of:

- the flow rate of said cooling fluid (4);

- the residence time of said articles (P) in said enclosure (2); - the flow of gas extracted from said enclosure (2);

- the speeding up of gases;

- gas recirculation; and

- The balance between the air inlets and the gas outlets, until a theoretical value for the temperature of said articles (P) at the outlet of said enclosure (2) is obtained, close to a set point.

17. Device for predicting the temperature of articles (P) passing through an installation comprising a cooling enclosure (2) which uses a cooling fluid (4) comprising means (20) for predicting this temperature, characterized in that said prediction means (20) include calculation means (22,24) which use variables characteristic of the operation of the installation, thermodynamic and physical characteristics of said enclosure (2) and thermodynamic and physical characteristics of said articles (P).

18. Device according to claim 17, characterized in that it comprises manual input means (10) of at least part of said quantities characteristic of the operation of said installation.

19. Device according to claim 17 or 18, characterized in that it comprises means (8) for measuring at least part of said quantities characteristic of the operation of said installation.

20. Device according to any one of claims 17 to 19, characterized in that said predicting means (20) comprise an enclosure predictor (22) adapted to predict the behavior of said enclosure (2) from the resolution thermal balances on elementary slices of the volume of said enclosure (2), which enclosure predictor (22) receives as input, thermodynamic characteristics of said cooling fluid (4) and said thermodynamic and physical characteristics of said enclosure (2).

21. Device according to claim 20, characterized in that said enclosure predictor (22) also receives at input, said quantities characteristic of the operation of said installation.

22. Device according to claim 21, characterized in that said quantities characteristic of the operation of said installation represent at least one of the elements chosen from the group consisting of:

- the speed of a conveyor (6) for transporting said articles (P) through said enclosure (2);

- the loading rate; and

- ventilation of the atmosphere of said enclosure (2).

23. Device according to any one of claims 20 to 22, characterized in that said enclosure predictor (22) is associated with correction means (26) based on experimental readings of the temperature profile prevailing in said enclosure ( 2).

24. Device according to any one of claims 18 to 23, characterized in that the prediction means (20) comprise an article predictor (24) adapted to predict the behavior of said articles (P) from the resolution of the discretized heat conservation equation applied to a network of spatial and temporal points constituting a mesh of said articles (P), which article predictor (24) receives as input at least said thermodynamic and physical characteristics of said articles (P ).

25. Device according to claim 24, characterized in that said article predictor (24) also receives as input, said quantities characteristic of the operation of said installation.

26. Device according to claim 25, characterized in that said quantities characteristic of the operation of said installation include the temperature of said articles (P) at the inlet of said enclosure (2).

27. Device according to any one of claims 24 to 26, characterized in that said article predictor (24) is associated with means for optimizing calculations by modifying said mesh of said articles (P) according to mathematical sequences.

28. Device according to any one of claims 24 to 27, characterized in that said item predictor (24) is associated with calculation optimization means by eliminating prediction calculations for spatial and temporal points of said mesh said articles (P) for which the enthalpy variations are less than a predetermined threshold.

29. Device according to claims 20 and 24 taken together, characterized in that the prediction means (20) comprise coupling means (30) of said enclosure predictor (22) and said article predictor (24).

30. Installation for cooling articles (P) comprising an enclosure (2) for cooling said articles (P) which uses a cooling fluid (4), characterized in that it includes a device for predicting the temperature said articles (P) according to any one of claims 17 to 29.

31. Installation according to claim 30, characterized in that it comprises coupling means (30) which perform a repetition of the implementation (40) of the enclosure predictor (22) and of the implementation (50 ) of the article predictor (24) and of the comparison means (16) which are connected at input to input means (18) of a temperature set point of said articles (P) at output from said enclosure (2) and to said prediction means (20), and are connected at the output to control means (12) comprising control means (14) adapted to modify at least one of the parameters chosen by the group consisting of:

- the flow rate of said cooling fluid (4);

- the speeding up of gases;

- gas recirculation; and

- the balance between the air inlets and the gas outlets, until a theoretical value for the temperature of said articles (P) at the outlet of said enclosure (2) is obtained close to the setpoint entered using said means for entering (18) a temperature setpoint.

32. Installation according to any one of claims 30 or 31, characterized in that said cooling fluid (4) is injected into said enclosure (2) and exchange of heat with said articles (P) by direct contact.

33. Installation according to any one of claims 30 or 31, characterized in that said cooling fluid circulates in a heat exchange device included in said enclosure, and indirectly exchanges heat with said articles (P) through of said heat exchange device.

34. Installation according to any one of claims 30 to 33, characterized in that it comprises means for measuring the temperature of said articles (P) at the outlet of said enclosure (2) which deliver information taken into account by the predictive means (20).