FR2786556A1 - METHOD OF MONITORING THE EVOLUTION OF DRYING AND DEVICE FOR IMPLEMENTING IT - Google Patents

Abstract

The dryer of the invention comprises a drum (29) connected to a drying circuit comprising an air heating device (30), a fan (33) and a measuring probe (35). This probe has a capacitive relative humidity sensor (36) which alternately receives the drying air (valve 40 closing the orifice 38) and the ambient air (orifice 38 open) .The degree of drying of the laundry is thus determined. very precisely.

Description

1. The present invention relates to a method for monitoring

  the evolution of drying and a device for implementing this process.

  In a drying device, such as a dryer, monitoring the drying by hot air makes it possible to determine the end of the drying process, and therefore the stop of the device. Of course, the drying process must be optimized, in order to obtain a determined degree of drying of the laundry for the lowest possible energy expenditure. This drying monitoring is generally done either by analyzing the change in the temperature of the air passing through the products to be dried, or by analyzing the change in the resistivity of these products. In addition, there is no humidity sensor

  adapted to the requirements of household appliances.

  The known methods do not make it possible to determine the end of the drying process with sufficient precision to carry out said optimization. Indeed, the result of the measurement (of temperature or resistivity) varies greatly depending on variations of at least one of the following parameters: mains voltage, power of the heating element for drying air, the temperature of the ambient air, the quantity of product to be dried and its nature, the precision of the temperature measurement ... The existing measurement devices meet very specific needs, specific to the precision required for a given application. Their cost is therefore prohibitive for mass production and for

universal employment.

  The subject of the present invention is a process for monitoring the drying progress of wet products placed in an enclosure through which a stream of drying air passes, a process which makes it possible to provide faithful indications on the state of drying of the products, which is reliable both for a low humidity environment and for a high humidity environment, for a wide range of ambient temperatures (for example from 0 to 100 C), for a stable and / or unstable drying air flow, process which provides results independent of the operating conditions and location of the drying machine, and which adapts to

  open or closed drying, with evacuation or with condensation.

  The present invention also relates to a device for monitoring the evolution of drying of products in an enclosure traversed by a current of drying air, inexpensive device, simple, robust, standard, modular, reliable, universal (usable for different devices or for various models of the same device, without modification or with the minimum

  possible modifications), affecting neither the measurement nor the expected result.

  The method of the invention consists in measuring at least several times during drying the difference in relative humidity between the air flow circulating in the enclosure and the ambient air, in monitoring the convergence of these two types of measurements. and stop the process when their gap reaches a

determined value.

  Measurements can be made either using two paired and isothermal sensors, or using a single sensor

  alternately subjected to the two types of air.

  The present invention will be better understood on reading the

  detailed description of several embodiments, taken as

  of nonlimiting examples and illustrated by the appended drawing, in which: FIG. 1 is a block diagram of a measuring device, with two sensors, for implementing the method of the invention, - FIG. 2 is a block diagram of a measurement device with a single sensor, for the implementation of the method of the invention, - Figure 3 is a diagram of evolution of relative humidity as measured according to the method of l invention, - Figure 4 is a simplified diagram of a sensor, similar to that of Figure 2, equipped with a valve, - Figures 5 and 6 are simplified diagrams of an example of use of the sensor Figure 4, - Figure 7 is a simplified diagram of a sensor, similar to that of Figure 2, equipped with a filter, - Figures 8 and 9 are simplified views of an example of use of a sensor according to the invention, respectively in the measurement phase of the air inside the drying circuit, and of my ure of air outside this circuit, - Figures 10 to 12 are simplified sectional views of different embodiments of the sensor according to the invention, and Figures 13 to 15 are simplified diagrams of three embodiments of a drying circuit implementing the method of the invention. The present invention is described below with reference to a dryer, but it is understood that it is not limited to this single application, and that it can be implemented in other fields, such as

  than drying raw materials, food ...

  There is shown in Figure 1, in a very simplified manner, a sheath 1, forming part of a dryer drying circuit, downstream of the drying drum. In this sheath 1 circulates an air current charged with the moisture taken from the load of laundry placed in the drum. This air is one

  temperature higher than that of the ambient air (near the machine).

  In the sheath 1, there is a first relative humidity sensor 2, and at

  outside the sheath 1, there is a second relative humidity sensor 3.

  S15 This sensor 3 is placed inside the machine, but outside the entire drying air circulation circuit. The two sensors 2 and 3 are connected to a computer 4, such as a microcontroller. These sensors are paired and brought to the same temperature: sensor 2 is, in fact at the temperature of the drying air circulating in the sheath 1, while sensor 2 is heated to the same temperature by a heating resistor for example . The computer 4 determines the difference between the measurements of the sensors 2 and 3, that is to say the difference in relative humidity between the inside of the sheath 1 and the outside, that is to say the relative humidity difference between the inside of the sheath 1 and the outside, that is to say the difference between the amount of water conveyed by the drying air flow and that contained in the ambient air, which is justified by the fact that the measurements are carried out at the same temperature. According to the embodiment of FIG. 2, a single sensor 5 is used which receives alternately drying air and ambient air. In this figure 2, we have omitted the means for circulating these two air flows (means described below). The sensor 5 is a component called "humidity", which essentially comprises a capacitor or a resistor 6 arranged inside a housing 7 open at its ends. In the case where this component comprises a capacitor, its dielectric is the air present inside the housing 7. Its capacity varies as a function of the relative humidity of the air which represents its dielectric. The housing 7 is fixed to the sheath I so that one of its end openings communicates with the ambient air, and the other with the air circulating in the sheath. The sensor 5 can therefore be traversed alternately by the air in the sheath 1 and by the ambient air. It is connected, as in the case of Figure 1, to

a computer 4.

  Figure 3 relates to a dryer whose fan of the drying circuit rotates in both directions of rotation, but whose volute

  is made so that the air flow always flows in the same direction.

  A high air flow corresponds to one direction of rotation of the fan, and a low air flow to the other direction. The respective durations of rotation in one direction and in the other are different, for example 40 seconds at high flow and a

  ten seconds at low speed.

  Thus, the air flow in the drying circuit takes

  alternately two different values, for example 40m3.h and 150 m3.h.

  This makes it possible, in combination with the alternation of the directions of rotation of the drum in which the laundry to be dried is arranged, to improve the drying efficiency by loosening the laundry (these alternations of direction of rotation of the

  fan and drum can be synchronized with each other).

  Curve 8 represents the evolution of the capacity of the capacitor constituting the relative humidity sensor 7, this capacity being an inverse function of the relative humidity of the air passing through the sensor. This curve 8 includes maxima 8A, corresponding to the measurement of the relative humidity of the ambient air and minima 8B corresponding to the measurement of the relative humidity of the drying air, (higher than that of the ambient air), downstream of the drum, at low air flow, as well as intermediate maxima 8c, corresponding to the relative humidity measurement of the drying air at high flow. FIG. 3 shows the curves 8D and 8E constituting the envelopes of curve 8, and which are the geometric locations of the maxima 8A and the minima 8B, respectively. It can be seen that these curves 8D and 8E, which are substantially rectilinear, tend to converge at the end of the process, and that both are increasing, owing to the fact that as the laundry dries, the air temperature of drying increases, and, to a lesser extent, that of the ambient air (the ambient air is that inside

of the machine body).

  FIG. 3 also shows the curve 9 of evolution of the mass of linen ML, expressed as a percentage by mass of water contained in the linen: the reference 0% corresponds to the mass of linen before washing and drying, this linen being very slightly charged by the humidity of the ambient air of the room in which it is stored (for example about 2% more mass due to this ambient humidity). This curve 9, calculated

  from curves 8D and 8E, is, of course, constantly decreasing.

  The initial value of curve 9 (instant TO) is, for the example shown, around 55%. When curve 9 passes through a determined value, for example 10% (instant T1), the maximum flow rate of the drying air and / or the heating power of this drying air is reduced. At time T2, curve 9 passes through the value 0%, then passes through slightly negative values, corresponding to a complete drying of the laundry (which, before washing, was, as specified above, slightly loaded with water , therefore not completely dry). The drying process can be stopped at an instant T3, slightly after T2, or before T2, depending on the

user requirements).

  FIG. 4 shows a probe 10 comprising the sensor 7 having, at one of its open ends, a sleeve 11, the free end of which is provided with a valve 12 capable of closing or leaving open this free end, under the control of the computer 4 (or of a mechanical or electromechanical device). There is shown, in simplified manner, in Figures 5 and 6 an example of use of the probe 10 of Figure 4. This probe 10 is fixed, by its end opposite to that provided with the valve 12, on the pipe 13 of a drying circuit, downstream of the products to be dried. In FIG. 5, the valve 12 is open, and the outside air is sucked in by the vacuum created in the pipe 13 by the flow of drying air (arrow 14), passing through the sensor 7. In FIG. 6, the valve 12 is closed, and therefore only the air

  of the drying circuit goes through sensor 7 (arrow 15).

  Whatever the configuration, the valve 12 ensures ventilation of the sensor to prevent the formation of condensate which would make

  impossible to measure relative humidity.

  According to the embodiment of FIG. 7, a filter 16 is integrated into the probe 10, this filter being for example placed between the sleeve 11 and the body of the sensor 7. This filter makes it possible to prevent possible deposition of particles (particles of laundry) which can lead to the obstruction of the pipes crossed by the drying air flow, and / or which can alter the sensor itself. This filter can be defined to induce a loss of

  load used to control the air flow rate of the flow created by the ventilation.

  According to the embodiment of FIG. 8, the sensor 17 (sensor of FIG. 4 or of FIG. 7) can be immersed inside the line 18 of drying air and measure the relative humidity which prevails there. when the air flow in this line is low or zero. An outside air intake is formed upstream of the sensor 17 thanks to an auxiliary pipe 19. The outlet of the pipe 19 is located inside the pipe 18, is directed in the same direction as the circulating air flow in the pipe 18 and opens opposite the input of the sensor 17. The entry of the pipe 19 opens outside the pipe 18. When the air flow rate in the pipe 18 is high (FIG. 9), there creates a vacuum at the outlet of line 19, and therefore sucks in air

  outside which is sent to sensor 17.

  Conversely, according to a variant not shown, the sensor 17 can be arranged outside the pipe 18, and it cooperates with an auxiliary pipe, the inlet of which, located inside the pipe 18, is directed in the direction reverse of the drying air flow, and whose outlet opens opposite the sensor inlet. Thus, when the drying air flow is high, air from the pipe 18 is sent by overpressure to the sensor, while when this flow is low or zero, the sensor does not receive

  practically more than the air outside the pipe 18.

  According to FIG. 10, there is integrated into the sensor 20 (which may be that of FIG. 4 or of FIG. 7) a local fan 21 which directs either the flow of outside air, or the flow of interior air towards the sensor 20 , depending on its direction of rotation: the assembly 20 + 21 may, for example, be arranged in a manner similar to that shown in FIG. 2, being open at its two ends, or else be arranged in one media (inside or outside the drying circuit) and be connected to the other medium by a pipe taking air from this other medium by switching on the fan (which

  only rotates in one direction of rotation).

  As shown in FIG. 11, a sensor 22, a flap sleeve 23 and a filter 24 can be integrated in a single component. Or, as shown in FIG. 12, a sensor 25, a fan 26 can be integrated in a single component. , a valve sleeve 27 and a filter 28. Of course, if the machine has two probes, the components 16 and / or 21 and / or 23 and / or 23 and / or 24 and / or 26 and / or 27 can be integrated into each one and / or 28. Thanks to such a device, in the case of machines with two flows (large and small air flow in the drying air circuit, the signal representing the true relative humidity can be amplified. In this case , the sensor is brought to low temperature by the coldest flow. Thus, the measurement of the other flow will be made at a temperature lower than its true temperature (due to the thermal inertia of the sensor, cooled by the flow coldest), and the measured relative humidity will be higher than the actual relative humidity. ispositif is particularly suitable for monitoring the evolution of the drying of low loads or drying cycles at low power

of heating.

  It is understood that the cooling of the sensor can be carried out by any other means than the coldest flow: for example by an auxiliary flow other than one of the two flows to be measured, or by a Peltier effect module ... There is shown in FIG. 13 the simplified diagram of a drying circuit of the exhaust type (evacuation to the outside of the drying air after passing through the drum of laundry to be dried), with "pull flow" (suction turbine drying air, located near the outlet of the drying circuit). This drying circuit comprises a drum 29 in which the laundry to be dried is arranged. Upstream of the drum 29, an air heating device 30 is connected to the drum by a pipe 31. The heating device 30 receives ambient air by an inlet pipe 30A. At the outlet of the drum 29, a pipe 32 connects it to a suction turbine 33

  whose outlet pipe 34 discharges the humid air thus sucked out.

  A probe 35 is fixed to the pipe 32. This probe 35 comprises a tubular body 36, fixed to the pipe 32, in which is disposed a sensor such as the sensor 7. One of the ends of the body 36 opens out inside of the pipe 32. On the other end of the body 36 is fixed a sleeve 37 having two orifices 38, 39. The orifice 38 communicates directly with the ambient air. A movable valve 40, disposed in the sleeve 37, can selectively close the orifice 38 or the orifice 39. In the embodiment of the

  FIG. 13, the orifice 39 is constantly blocked by a plug 41.

  The circuit of FIG. 13 works as follows: when the valve 40 closes the orifice 38, the turbine only sucks air from the heating device 30, and the sensor placed in the body 36 measures the relative humidity of this air, after its passage through the drum 29. It is the same if the turbine 33 is stopped. On the other hand, when the valve 40 no longer closes the orifice 38, and the turbine 33 sucks drying air, the ambient air is sucked through the orifice 38, and the sensor therefore measures the humidity relative of

this ambient air.

  In FIG. 14, a variant of the drying circuit of FIG. 13 has been shown, still for a machine of the discharge type, but with a "pushed" flow. In this FIG. 14, the same elements as those in FIG. 13 are assigned the same reference numbers. The turbine 33 is no longer disposed between the pipes 32 and 34, but upstream of the heating device 30, to which it is connected by a pipe 42 in a "T" shape, one branch of which is connected by a pipe 43 to the orifice 38 of the probe 35. The turbine 33 draws ambient air through an inlet pipe 33A. The measurements are carried out when the turbine 33 is operating. When the valve 40 closes the orifice 38, the sensor measures the relative humidity of the drying air circulating in the duct 32, and when the valve 40 does not close the orifice 38, the turbine 33 "pushes" I outside air, drawn in via line 33A, not only to the heating device, but also, via line 43 to the sensor of the

  probe 35. The sensor then measures the relative humidity of the ambient air.

  FIG. 15 relates to a machine with a condensation drying circuit. This drying circuit cooperates with a drying drum 44, and it comprises: a heating device 45, the outlet of which is connected by a pipe 46 to the drum 44, and the inlet of which is connected by a pipe 47 to a turbine 48; a condenser 49, the inlet of which is connected by a pipe 50 to the drum 44 and the outlet of which is connected by a pipe 51 to the turbine 48. A probe 35A, similar to the probe 35, is fixed on the pipe 50, of the same as the probe 35 on the pipe 32. The only notable difference between the probes 35 and 35A is that the probe 35A does not have a cap closing its orifice 39. The orifice 38 communicates with the ambient air, while the the orifice 39 is connected by a line 52 to the line 51. When the valve 40 closes the orifice 38, part of the drying air coming from the drum 44 through the line 50 passes into the probe 35A (arrow 53) and is sucked, via line 52, by the turbine 48. The sensor then measures the relative humidity of the drying air. When the valve 40 closes the orifice 39, the ambient air is sucked in via the orifice 38 and passes through the probe A to go towards the condenser 49 (arrow 54). The sensor then measures the relative humidity of the ambient air.

  Of course, for all the embodiments described above

  above, the air flow through the probe is significantly lower than the drying air flow, so as not to significantly disturb the drying process.

Claims (11)

  1. Method for monitoring the evolution of drying of wet products placed in an enclosure traversed by a current of drying air, characterized in that it consists in measuring at least several times during drying the difference in relative humidity between the air flow circulating in the enclosure and the ambient air, to monitor the convergence of these two types of measurements and   to stop the process when their deviation reaches a determined value.   2. Method according to claim 1, characterized in that the   measurements are carried out using two paired and isothermal sensors.   3. Method according to claim 1, characterized in that the measurements are carried out using a single sensor alternately subjected to both types of air.   4. Method according to one of the preceding claims,   characterized in that at the start of the process, the drying air is heated to the maximum expected power, and that when said deviation reaches another determined value, greater than that triggering the stopping of the process,   decreases the heating power and / or the drying air flow.   5. Device monitoring the evolution of the drying of drying products of wet products arranged in an enclosure (29, 44) traversed by a current of drying air, characterized in that it comprises a device for measuring the difference d relative air humidity   drying and ambient air (2, 3, 4, 7, 10, 17, 20, 22, 25, 35, 35A).   6. Device according to claim 5, characterized in that the measuring device comprises two sensors (2, 3) connected to a computer,   one of these sensors receiving ambient air, and the other the drying air.   7. Device according to claim 5, characterized in that the measuring device comprises a single sensor receiving alternately   drying air and ambient air.   8. Device according to claim 7, characterized in that a valve (40) makes it possible to alternate the arrival of drying air and ambient air on the sensor.   9. Device according to one of claims 5 to 8, characterized in   what the sensor (s) is (are) a capacitive component (s) or   resistive (s) referred to as "humidity".   10. Device according to one of claims 5 to 9, characterized in   what the sensor (s) is (are) associated (s) (each) with a filter (16).   11. Device according to one of claims 5 to 10, characterized in   what the sensor (s) is (are) associated (each) with a local fan (21, 26).