FR2956728A1 - Heat solar collector for transmitting solar energy received by heat exchange coolant, has closing unit comprising actuating unit with shape memory alloy to open closing unit beyond preset temperature of collector - Google Patents

Abstract

The collector has an air-knife (4) i.e. lower air blade, comprising a ventilation opening (6) that is closed or opened by a closing unit i.e. trap door (10). The closing unit comprises an actuating unit with shape memory alloy to open the closing unit beyond preset temperature of the collector. The shape memory alloy is selected among titanium nickel based alloy or copper based alloy, where the shape memory alloy comprises phase changing temperature ranging at 15 degree Celsius. An independent claim is also included for a method for ventilating a heat solar collector.

Description

The invention relates to a solar thermal collector, and a heating device comprising at least one such solar thermal collector. Finally, it also relates to a method of ventilation of a solar thermal collector.

A solar thermal collector makes it possible to transmit a portion of the solar energy received to a heat transfer fluid by heat exchange. The thermal efficiency of solar energy transfer to the coolant depends on many factors. In particular, when the temperature of a sensor subjected to constant radiation increases, its thermal efficiency decreases and then vanishes at a temperature called stagnation temperature. In an extreme situation for which the solar radiation received by a solar thermal collector is important while the energy requirement is low, that is to say that the heat transfer fluid is not or little solicited, the temperature of the solar thermal collector increases sharply. up to the stagnation temperature for which no energy is finally transmitted to the coolant. Such an increase in temperature of the solar thermal collector is not only useless at the energy level but also leads to its accelerated aging and the degradation of its future performance.

To avoid reaching such situations of temperature rise of the solar thermal collectors when this is undesirable, called overheating situations, it is known to provide a ventilation mechanism of the sensor to reduce its temperature.

A first solution of the state of the art is for example described in the document US4150659. It is based on a solar thermal collector whose geometry favors natural convection ventilation. For this, the sensor is equipped with a hatch whose actuation depends on the temperature of the sensor, on the basis of a piston comprising a low-boiling point liquid and a return spring. The phase change of this liquid, which must correspond to a temperature of the sensor not to be exceeded, induces the actuation of the hatch which allows the implementation of a natural ventilation which cools the sensor. However, this solution has a high inertia between the phase change reaction and the increase in pressure of the actuator of the door, which causes a desynchronization between the temperature variation of the sensor and the implementation of ventilation.

We must then try to anticipate the opening of the hatch to really prevent overheating of the sensor, which is complex to develop. Finally, as the opening of the hatch is very progressive with such actuation, it starts early and extends over a large temperature range of the order of several tens of degrees to reach a satisfactory opening at the temperature of overheating of the sensor. Following the above remarks, this solution does not allow to obtain a high accuracy of the cooling by ventilation of the solar thermal collector.

A second solution of the state of the art, described in document WO8100613, implements a ventilation of a solar thermal collector on the basis of ventilation hatches whose opening is controlled by a wax actuator, which expands and increases in pressure with the temperature until inducing actuation of the hatch. However, this expansion is small in magnitude and proportional to the variation in temperature. The opening of the trap is therefore over a very wide temperature range and the mechanism of the opening remains very limited. Thus, this solution also does not make it possible to obtain a high accuracy of the cooling by ventilation of a solar thermal sensor. Thus, a general object of the invention is to propose an improved solution for ventilating a solar thermal collector. to avoid overheating and increase its performance over time and its life. More specifically, the invention seeks to achieve all or part of the following objects:

A first object of the invention is to provide a ventilation solution 10 of a solar thermal collector which allows a precise and synchronized implementation with the temperature of the solar thermal collector.

A second object of the invention is to provide an inexpensive solution for ventilation of a solar thermal collector. To this end, the invention is based on a solar thermal collector comprising an air slit comprising at least one ventilation orifice, which can be closed or opened by a sealing means, characterized in that the shut-off means comprises an actuating means comprising a shape memory alloy (AMF) so as to open the shutter means beyond a predefined temperature of the solar thermal sensor to prevent it from overheating.

The shape memory alloy may be an alloy based on nickel titanium or copper-based.

The shape memory alloy can have a phase change temperature in a range of 15 degrees Celsius, the upper bound of this range being between 65 and 160 degrees Celsius.5 The shape memory alloy (AMF) ) may be part of a blade, rod or coiled spring component cooperating with a shutter to induce a closed position of the cold-phase shutter of the AMF and an open position of the hot-phase shutter of the AMF.

The closure means may be a trap comprising a movable shutter in rotation, of flat or curved shape, and may comprise an AMF blade connected on the one hand to the solar thermal collector and on the other hand to the shutter so that power actuate.

The closure means may comprise a shutter movable in translation, and an AMF spring connected on the one hand to the solar thermal collector and on the other hand to the shutter so as to be able to actuate it.

The air gap can be between an absorber and an insulating element of the solar thermal collector.

The shape memory alloy (AMF) can be single direction and associated with a stress spring or two-way.

The invention also relates to a heating device characterized in that it comprises at least one solar thermal collector as defined above.

The invention also relates to a method of ventilating a solar thermal collector, characterized in that it comprises a step of opening a shutter closing a ventilation orifice of the thermal solar collector 30 automatically by an actuation obtained by the change of property of a shape memory alloy to a predefined temperature.

These objects, features and advantages of the present invention will be set forth in detail in the following description of a particular embodiment made in a non-limiting manner in relation to the appended figures among which:

Figure 1 schematically illustrates a sectional view of a solar thermal collector according to an embodiment of the invention.

Figures 2 and 3 show a sectional view of a ventilation flap of a solar thermal collector according to the embodiment of the invention respectively in a closed and open configuration. FIG. 4 represents the kinematic diagram of the operation of the ventilation flap of the solar thermal collector according to the embodiment of the invention.

Figure 5 shows the phase change temperature ranges of some shape memory alloy materials used by the embodiment of the present invention.

Figure 6 schematically shows a sectional view of the ventilation flap 25 of a solar thermal collector according to the embodiment of the invention in an open configuration.

Figure 7 schematically shows a sectional view of the ventilation flap of a solar thermal collector with a shutter according to a variant of the embodiment of the invention in an open configuration.

Figures 8 and 9 show a sectional view of a ventilation flap of a solar thermal collector according to a variant of the embodiment of the invention respectively in a closed and open configuration.

FIG. 1 represents a solar thermal collector according to an embodiment of the invention. This sensor comprises a glazed surface 1, an upper air gap 2, an absorber 3, a lower air gap 4 at least 10 mm thick and an insulator 5. According to an essential element of the invention, the sensor further comprises a ventilation means which rests on ventilation holes 6 which can be opened or closed by a closure means using the properties of at least one shape memory alloy (AMF). For this, ventilation openings 6 are provided on the lateral faces of the sensor, at the level of the lower air gap 4. These ventilation holes 6 are open or closed by at least one closure means comprising a means of ventilation. actuation, which is a hatch 10 in the embodiment shown.

Figures 2 and 3 show the hatch 10 can close or open a ventilation port 6 according to the embodiment of the invention. The hatch 10 comprises a shutter 11 rotatably mounted about an axis 12 positioned in its upper part within the absorber 3 of the sensor. A blade comprising at least one shape memory alloy (AMF), more simply called AMF blade 13, is connected to the shutter 11 on the one hand and to the absorber 3 on the other hand, and positioned inwardly of the sensor, at a ventilation port 6 of the sensor. A leaf spring 14 is connected to the shutter 11 on its outer face, and also bears on an external extension of the absorber 3. These two blades 13, 14 are connected to the shutter 11 and the absorber 3 by a flat bearing connection 15 and a recessed connection 16, as shown in FIGS. 2 and 3.

The operation of the hatch 10 of the invention will now be explained. Figure 2 shows the hatch 10 in a closed position, when the sensor temperature is said to be "low". In this closed position, the shutter 11 occupies a substantially vertical position, extends over the entire height of the ventilation opening 6 and bears against a stop 17 provided on the lateral face of the insulator 5. In this configuration, the air present in the lower air gap 4 remains enclosed and without contact with the outside, possibly in closed convection movement, as illustrated by the arrow F. Note, the AMF material is advantageously positioned to the inside of the sensor, so that its temperature in the closed position of the shutter 11 is very close to the temperature of the sensor, more precisely of the absorber 3, which makes it possible to better synchronize its reaction as a function of the temperature of the solar thermal collector.

Beyond a certain temperature of the solar thermal collector, the AMF blade 13 changes its physical property, as will be explained below. This change induces a rotation of the shutter 11 about its axis 12, to obtain the opening of the hatch 10. In this open configuration of the hatch 10, shown in Figure 3, a natural convection is established, in which a hot air flow S leaves the lower air space 4 of the sensor while a cold air flow E enters. This natural air flow causes the cooling of the solar thermal collector.

Then, under a certain temperature, the hatch returns to its original shape shown in FIG. 2. The optional leaf spring 14 assists the return of hatch 10 in its closed configuration of FIG.

Figure 4 illustrates the kinematic principle described above.

A shape memory material (AMF) undergoes a crystallographic phase transformation, i.e. a change in its crystalline structure, when it is carried beyond a certain temperature. It presents a first state called "low temperature", also called martensitic phase, and a second state called "high temperature", also called austenitic phase. Between these two phases, the AMF changes in particular stiffness, having a lower rigidity in its low temperature state. The embodiment described above exploits this feature. At low temperature, the spring return blade 14 exerts a force sufficient to deform the AMF blade 13 and push the shutter 11 in the closed position against the stop 17. At high temperature, the AMF blade 13 has a higher rigidity in which the the force exerted by the leaf spring 14 is no longer sufficient for its deformation: it then resumes a different shape as shown in Figure 3, causing the shutter 11 in the open position.

This property of the AMF material thus makes it possible to form a means for actuating a hatch associated with a ventilation orifice of a solar thermal collector, as explained above. The use of an AMF material has the advantage of a high precision of the actuation of a hatch due to its phase change which is carried out over a reduced temperature range, which extends over at most 15 hours. degrees, and which can be advantageously reduced to less than 10 degrees.

This makes it possible to achieve a high accuracy and reactivity of the hatch according to the temperature of the sensor and to form an accurate ventilation solution.

The AMF material used may be of different kinds. This choice is mainly a function of the temperature at which it must change phase. This phase change also depends on the stress applied to the element in AMF material, which causes a shift of 1 degree Celsius for 7 MPa. This consideration makes it possible to accurately determine the phase change temperature of an element comprising an AMF material for each arrangement envisaged. The material will then be chosen so that the upper limit of its phase change range, which may be of the order of 15 degrees Celsius as previously explained, corresponds to the stagnation temperature of the solar thermal collector.

For application in a polymer-type thermal solar collector having an air stagnation temperature of 124 degrees Celsius and an AMF material actuation means subjected to a stress of 150 MPa, the selected AMF material will be a carbon-based alloy. nickel and titanium (NiTi) or a copper-based AMF material. Preferably, an AMF NiTi material will be chosen because it has a better endurance property. For the above conditions, an AMF whose phase change temperature is between 85 degrees Celsius and 100 degrees Celsius at rest will be fine. Indeed, as the temperature rises, the sensor opening will be between 105 degrees Celsius and 120 degrees Celsius, and its closing will be between 100 degrees Celsius and 85 degrees Celsius. This difference obtained by the hysteresis principle of the phase transformation of the AMF makes it possible to compensate for the difference in temperature between the absorber of the sensor and the AMF when the hatch is open. As an indication, Figure 5 shows the phase change temperatures of the nickel-titanium and copper based AMF materials. As is apparent from the figure, it is possible to obtain alloys with different properties while remaining composed of NiTi or copper, which allow their use over a wide temperature range. More generally, an AMF material will be chosen whose phase change temperature is between 65 and 160 degrees Celsius.

It should be noted that an AMF material has sufficient mechanical characteristics to allow efficient actuation of the hatch, according to the principle described above. As an example of implementation of this principle, a NiTi alloy AMF blade with a dimension of 40 × 30 × 0.25 mm can be chosen, according to a geometry forming an angle α without stress in the austenitic phase, as represented in FIG. such a blade may have a Young's modulus of 22.5 GPa in the martensitic phase and 60 GPa in the austenitic phase. For a shutter of 50 g, a stiffness stress spring 0.011 N / degree makes it possible to position the shutter in the closed position against its stop in cold martensitic phase of the AMF blade.

With the previous values, the angle e is therefore 90 degrees below the temperature of overheating of the sensor and then 70 degrees from the temperature of overheating. This opening of 20 degrees is adapted to obtain sufficient ventilation of the sensor. Note, the shutter 11 may alternatively have a curved shape that provides an opening of constant section with its single rotation of 20 degrees in the open position, as shown schematically in Figure 7.

The embodiment described above uses an AMF material in the form of a blade. Alternatively, the AMF material may be integrated into any other element, which may be in the form of a rod, wire, or helical or torsion spring, etc.

In addition, the shutter has been described as a rotatable member.

However, it could be in another form and have a different degree of freedom than the illustrated rotation, to close or open a ventilation port 6. For example, it can be in the form of a movable drawer in translation by a slide connection, as illustrated below, or any valve, flap or movable cover according to any pivot movement, or any other movement as a combination of translation and rotation.

Figures 8 and 9 illustrate for example an alternative embodiment of the embodiment of the invention, wherein the shutter means is a slide 20 movable in translation. It comprises a shutter 21 movable in translation between two stops 27, 28 front and rear connected to the absorber 3. A first spring of AMF material 23 is positioned between the inner stop 27 and the shutter 21 and a second stress spring 24 is positioned between the shutter 21 and the outer stop 28.

In the closed position shown in FIG. 8, the slide is in a position such that its shutter 21 extends from the insulating element 5 to the absorber 3 to close the ventilation orifice 6. When the spring temperature AMF 23 exceeds the predefined threshold value, the AMF material changes phase and becomes more rigid, so as to oppose the force exerted by the bias spring 24. This change induces the translation of the slide towards the outside of the sensor thermal solar, showing an orifice 22 in its lower part which connects the outside air with the air layer 4 of the solar thermal sensor: as before, a natural ventilation is established then. The operating principle of this shutter means is therefore the same as before.

According to another embodiment of the shutter means, not shown, an AMF element with a so-called "double-sense" property could be used. In such a case, the stress spring would no longer be necessary, the AMF material being sufficient for actuating the shutter in both directions. As a matter of remark, such a two-way AMF material has two memorized geometrical shapes and automatically switches from one to the other reversibly around a threshold temperature, without the need for a spring or any other element of equivalent constraint. This variant can be combined with the two previous embodiments illustrated by FIGS. 2 and 8, respectively.

The closure means described above is particularly well suited to a flat solar thermal collector comprising an air gap between an absorber and an insulator, and which may be of polymer type. However, it remains more generally applicable to the ventilation of any solar collector, which does not necessarily have the structure described in connection with Figure 1. In addition, the invention also relates to equivalent constructions, wherein the actuating means comprising the AMF would be linked to the solar thermal collector or to the shutter in a different way, for example.25

Claims (10)

Revendications1. Solar thermal collector comprising an air gap (4) comprising at least one ventilation opening (6), which can be closed or opened by a shutter means, characterized in that the shutter means comprises a means for actuation comprising a shape memory alloy (AMF) so as to open the shutter means beyond a preset temperature of the solar thermal sensor to prevent overheating. 2. Solar thermal collector according to the preceding claim, characterized in that the shape memory alloy is an alloy based on nickel titanium or copper-based. 3. solar thermal collector according to claim 1 or 2, characterized in that the shape memory alloy has a phase change temperature in a range of 15 degrees Celsius, the upper limit of this range being between 65 and 160 degrees Celsius. Thermal solar collector according to one of the preceding claims, characterized in that the shape memory alloy (AMF) is part of a blade-shaped component (13), rod or spring (23) helical cooperating with a shutter (11; 21) to induce a closed position of the cold-phase shutter of the AMF and an open position of the hot-phase shutter of the AMF. 5. Solar thermal collector according to the preceding claim, characterized in that the closure means is a door (10) comprising a shutter (11) movable in rotation, flat or curved shape, and comprises a blade AMF (13) connected to on the one hand to the solar thermal collector and on the other hand to the shutter (11) so as to be able to actuate it. 6. Solar thermal collector according to claim 4, characterized in that the closure means comprises a shutter (21) movable in translation, and an AMF spring (23) connected firstly to the solar thermal collector and secondly to the shutter (21) so that it can be actuated. 7. solar thermal collector according to one of the preceding claims, characterized in that the air gap (4) is between an absorber (3) and an insulating element (5) of the solar thermal collector. 8. Solar thermal collector according to one of the preceding claims, characterized in that the shape memory alloy (AMF) is single-direction and associated with a stress spring (14; 24) or two-way. 9. Heating device characterized in that it comprises at least one solar thermal collector according to one of the preceding claims. 20 10. A method of ventilating a solar thermal collector, characterized in that it comprises a step of opening a shutter (11; 21) closing a ventilation orifice (6) of the solar thermal collector automatically by an actuation obtained. by changing the property of a shape memory alloy at a predefined temperature.