MEASURING DEVICE FOR DETERMINING A DISTRIBUTION OF A HEAT TRANSFER MEDIUM AND METHOD FOR DETERMINING A DISTRIBUTION OF A HEAT TRANSFER MEDIUM

A measuring device for determining a distribution of a heat transfer medium on an inner wall of a shaftless container which rotates when used to heat the heat transfer medium with concentrated solar radiation in a solar thermal power plant or as a rotary kiln includes a distance measuring device for determining a thickness of a film of the heat transfer medium on the inner wall of the container. The distance measuring device includes at least one optical device for detecting at least one height profile along at least one measurement line projected onto the inner wall and at least one position transducer for determining a current rotational position of the respective measurement line on the inner wall. A method for determining a distribution of a heat transfer medium on an inner wall of a shaftless container is also provided.

BACKGROUND AND SUMMARY

The invention relates to a measuring device for determining a distribution of a beat transfer medium in a receiver device for solar radiation in a solar thermal power plant and to a method for determining a distribution of a heat transfer medium.

DE 102010062367 A1 describes a device for receiving solar radiation. The device comprises a container with an inner wall and a rotational drive device, by which the container is rotated about an axis of rotation. The container has an axis which is oriented parallel or at an acute angle to the direction of gravity. A heat transfer medium is guided through the container along the inner wall to form a heat transfer medium film. Particles or a liquid, for example, are proposed as the heat transfer medium in DE 102010062367 A1.

In experiments with the device described, there were indications of an inhomogeneous distribution of the film and thus of the heat transfer medium on the inner wall of the device. A possible reason for this can be that the surface of the inner wall of the container can change during operation due to the high thermal load of solar radiation and thermal cycles between times with solar radiation and times without solar radiation, so that a homogeneous distribution of the film may no longer be given.

In order to recognize this, a simulation of the film thickness of the heat transfer medium is usually carried out, which however involves many simplifications and assumptions that are not fully validated.

It is desirable to create a measuring device for determining a distribution of a heat transfer medium in a receiver device for solar radiation in a solar thermal power plant, which provides meaningful data.

It is also desirable to specify methods for determining a distribution of a heat transfer medium using such a measuring device.

A measuring device is proposed for determining the distribution of a heat transfer medium on an inner wall of a shaftless container that rotates when used as intended, which is provided in particular to heat the heat transfer medium with concentrated solar radiation in a solar thermal power plant or as a rotational kiln. The measuring device includes a distance measuring device for determining a thickness of a film of the heat transfer medium on the inner wall of the container. The distance measuring device comprises at least one optical device for detecting at least one height profile along at least one measurement line projected onto the inner wall and at least one position transducer for determining a current rotational position of the respective measurement line on the inner wall relative to a rotational position of the container.

The container is in particular a so-called particle receiver in a solar thermal power plant. In a particle receiver, solar rays are concentrated in the interior and a particulate heat transfer medium is heated, the particles of which are distributed along the inner wall of the particle receiver when the particle receiver is rotated. The particles form a particle film essentially parallel to the inner wall of the particle receiver. The particle film moves from an inlet into the particle receiver to an outlet from the particle receiver.

The film thickness can advantageously be measured. A possibly incorrect calculation or simulation of the film thickness can be omitted. The film thickness can not only be assessed qualitatively, whether there are gaps in the film, for example, but a reliable statement can be made about the film thickness on the inner wall of the container in the measured region.

The measuring device is particularly suitable for so-called centrifugal receivers, also known as particle receivers, in receiver devices for solar radiation in solar thermal power plants and for rotational kilns.

According to an advantageous configuration of the measuring device, the distance measuring device can be designed to detect distance data directly on the inner wall of the container along the measurement line in order to create the height profile.

A statement about the height profile on the entire surface of the inner wall or on regions of the inner wall that are of interest can be obtained if, for example, a large number of measurement lines lying next to one another are detected one after the other. The container can expediently be set in rotation for this purpose, so that a region or the entire surface of the inner wall can be measured.

According to an advantageous configuration of the measuring device, the distance measuring device can be designed to detect distance data directly on the film of the heat transfer medium on the inner wall of the container along the measurement line in order to create the height profile.

A statement about the height profile on the entire surface of the inner wall or on regions of the inner wall that are of interest can be obtained if, for example, a large number of measurement lines lying next to one another are detected one after the other. The container can expediently rotated for this purpose, so that a region or the entire surface of the inner wall can be measured.

A light section can advantageously be used to detect the height profile. The light section is a known method of optical 3D measurement technology, with which a height profile can be measured along a projected line of light and is based on the principle of triangulation. The optical device can in particular be a light section sensor, which includes a line projector, usually with a laser as the light source, which projects a line that is as narrow and bright as possible onto the measurement object, and an electronic camera, which detects the projection of the measurement line on the object, in this case the clean inner wall or the film on the inner wall. The displacement of the measurement line in the camera image can be converted into 3-D coordinates using the methods of photogrammetry that are known per se. Measuring devices that use this method are known, for example, as so-called profile scanners.

Profile scanners measure a height profile along a projected line of light, which represents the measurement line. The distance is not measured continuously. There is a certain number of measuring points along the height profile, each of which generates its own measured value for the distance.

In the case of film thickness measurement in the solar radiation receiver, a profile scanner can be held in the container by means of a holder and a height profile of the particle film can be measured along the longitudinal axis of the container, also known as the receiver. This height profile is initially only a 2D profile. If the container now also rotates and the measurement of the previously measured height profile is continuously repeated, a 3D height profile of the film of the heat transfer medium is created.

In the case of a perfect cylinder, the thickness of the particle film could be calculated from the 3D height profile and the determined distance of the profile scanner to the inner wall of the receiver. However, since the container is not a perfect cylinder, the measurement of the 3D profile alone does not provide any information about the actual thickness of the particle film.

In order to determine this thickness, a reference measurement of the empty container without heat transfer medium can also be carried out. The inner wall of the container, also referred to as the inliner, is measured in the same way as the film of the heat transfer medium on the inner wall and a 3D height profile of the inner wall is created. The two height profiles can then be subtracted from one another. The result is the actual thickness of the film of the heat transfer medium.

In order to be able to correctly subtract the two height profiles from one another, information about the rotational position of the two height profiles or the respective measurement line in relation to this rotational position of the container is also required. The rotational position of the measurement line correlates closely with the rotational position of the container, in particular the rotational position of the measurement line can be equal to the rotational position of the container. This allows the measurement points of both height profiles to refer to the same real point in the container.

This information can be provided by the position transducer, also known as an encoder or encoder. This is a rotation angle sensor that can be used to determine the rotational position of the container.

This rotational position can be transferred to the profile scanner so that the individual measuring points along the respective measurement line can be saved with the information about the associated rotational position of the container. Alternatively or additionally, the rotational position of the container can be transferred to a computing device, which can accordingly assign the measurement points to the information about the rotational position and the height profile of the associated measurement line.

A transfer to the profile scanner can take place via an interface, for example via an RS-422 interface, which can be connected directly from the position transducer to the profile scanner. The measurement data on the rotational position can then be stored at the same time as the measurement data regarding the distance and can be transmitted to the computing device and processed.

The heat transfer medium can advantageously consist of or comprise particles, for example bauxite particles. The height profile is measured on a surface of a film of the heat transfer medium in the form of a particle bed. It turns out that even a porous bed with the absorptive material of the bauxite particles reflects enough light.

According to an advantageous embodiment of the measuring device, the measurement line can extend parallel to a longitudinal axis of the container. The measurement line consists of or comprises a number of individual measurement points along the length of the measurement line, in which the optical device determines the distance between the measurement object and the sensor for each measurement point, for example via a transit time measurement.

The profile scanner can have a variable measuring range transverse to the longitudinal axis in the direction of the surface normal of the inner wall of the container. The measuring range can be adjusted depending on how different the distances to be measured are, for example due to non circular running or eccentricity of the container. With small changes in distance, the measuring range can be very small. If there are larger differences, the range can be chosen larger, for example if the circularity is not perfect or if there is an eccentricity.

The measuring frequency of the profile scanner depends on the size of the measuring range. The smaller this range, the fewer measuring points have to be read out on the sensor and the faster measurements can be taken. Accordingly, it is desirable to keep this range small.

An eccentrically running, rotating component can be problematic, since the measuring range would actually have to be quite large in order to be able to detect everything precisely. This can be solved using software technology by evaluating the data from the position transducer, which can be connected to the profile scanner and/or to the computing unit, together with the data of the height profiles of the profile scanner.

In this case, a reference measurement can first be carried out in order to detect deviations in the circularity of the container. The information from the reference measurement can then be used to shift the measuring range according to the imperfect circularity of the container in the height profile. This has the advantage that the measuring range can be selected to be quite small, which results in a higher measuring frequency. Nevertheless, the distance information can be recognized with sufficient accuracy, since the measuring range is shifted according to the lack of roundness

According to an advantageous embodiment of the measuring device, the position transducer can be coupled to the container, in particular attached to the container, and detect a rotational position of the container. In particular, the profile scanner can detect a rotational position of the container, which is supplied by the position transducer, synchronously with the projected measurement line. Alternatively or additionally, the position transducer can forward the rotational position to a computing unit, which combines the projected measurement line and the respective rotational position. The position transducer can advantageously have a magnetic tape that is placed around the container. In particular, the rotational position of the container can be determined using a magnetic tape with a number of magnetic poles, which are read out by a sensor of the position transducer that moves over the magnetic tape.

A container, in particular a particle receiver, for heating the heat transfer medium of a receiving device for solar radiation or a rotational kiln usually does not have a shaft around which the container can rotate. Rather, it is driven by a chain. Therefore, conventional position transducers cannot be used to determine the rotational position of the particle receiver. Advantageously, the rotational position can be determined by means of a magnetic tape placed around the container with a specific number of poles, which can be read by a sensor. This combination of sensor and magnetic tape can then be used to determine the rotational position of a shaftless container, in particular a particle receiver, with great accuracy.

It is particularly advantageous to use a combination of a magnetic tape placed around the container and a sensor arranged above it for detecting a rotational position of a shaftless rotating particle receiver in a solar thermal power plant or in a rotational kiln. The sensor may be placed at a fixed angular position with respect to the container. While the container rotates, the sensor does not rotate. The distance between the sensor and the magnetic tape is suitably between about 1 mm and about 3 mm. Optionally, the sensor can be mounted so that it can be moved radially in order to ensure an even distance to the receiver or the magnetic tape. This is advantageous if, for example, the container is not running circularly or is eccentric, or if the distances between the magnetic tape and the sensor can fluctuate.

According to an advantageous embodiment of the measuring device, a computing device can be coupled to the distance measuring device and/or the position transducer.

Advantageously, the computing device can carry out a corresponding assignment of the measuring points to the information about the rotational position of the container and the distance according to the height profile of the associated measurement line. In particular, in this case, height profile data from a measurement of the inner wall of the empty container without a heat transfer medium and from a measurement with a film of the heat transfer medium can be processed. The two height profiles can then be subtracted from one another. The result is the actual thickness of the film of the heat transfer medium.

According to an advantageous configuration of the measuring device, the distance measuring device can protrude into the container on a holder. In particular, a plurality of the optical devices of the distance measuring device can protrude into the container on a holder. If the distance measuring device has only one optical device, in particular in the form of a profile scanner, this can be arranged to be displaceable along and/or with the holder so that the container can be measured over its entire length.

If the distance-measuring device has a plurality of optical devices, in particular in the form of profile scanners, their number can expediently be selected such that the entire axial extent of the container can be detected with adjacent measurement lines.

According to a further aspect of the invention, a method is proposed for determining a distribution of heat transfer medium on an inner wall of a shaftless container that rotates when used as intended, in particular in which the heat transfer medium of a receiver device for solar radiation in a solar thermal power plant or a rotational kiln is heated, by means of a measuring device, which comprises at least one optical device for detecting at least one height profile along at least one measurement line projected onto the inner wall and at least one position transducer for determining a current rotational position of the respective measurement line on the inner wall.

The distance measuring device detects at least one height profile along at least one measurement line projected onto the inner wall using the at least one optical device, and the at least one position transducer determines a current rotational position of the container and thus the rotational position of the respective measurement line on the inner wall.

According to an advantageous embodiment of the method, a rotational position of the two height profiles with and without a heat transfer medium on the inner wall of the container can be determined in relation to a rotational position of the container. As a result, the film thickness of the heat transfer medium on the inner wall of the container can be determined with precise positioning by subtracting the data.

According to an advantageous embodiment of the method, the distance can be measured without solar radiation entering the container. Conventional components that do not tolerate high temperatures can advantageously be used.

According to an advantageous embodiment of the method, a difference between the distance data of the film and the distance data of the inner wall can be formed and from this a location-dependent distribution of the film of the heat transfer medium on the inner wall of the container can be determined. As a result, reliable measured values can be provided.

According to an advantageous embodiment of the method, a measuring frequency of the position transducer can be adapted to a length of the measurement line in the direction of the longitudinal axis of the container. As a result, an exact measurement can be carried out even in the case of larger changes in distance, namely in the case of a profiled surface with a correspondingly pronounced height profile.

According to an advantageous embodiment of the method, a reference measurement can be carried out to determine an eccentricity and/or lack of circularity of the container and a length of the measurement lines can be adjusted in the direction of the longitudinal axis of the container. The determination of the distribution of heat transfer medium on the inner wall of the container can advantageously be adapted to the actual state of the container.

According to an advantageous embodiment of the method, the determination of the distribution of heat transfer medium on the inner wall can be carried out repeatedly and changes in the distribution can be detected. This allows a reliable quality check to be carried out during the service life of the solar radiation receiver.

According to an advantageous embodiment of the method, a maintenance requirement can be indicated if permissible tolerances of the changes are exceeded. Timely maintenance or repair can favorably enable reliable operation of the solar radiation receiver.

According to a further aspect of the invention, a use of a measuring device is proposed for determining a distribution of a heat transfer medium on an inner wall of a container which is designed to heat the heat transfer medium with concentrated solar radiation in a solar thermal power plant, comprising a distance measuring device for determining a thickness of a film of the heat transfer medium on the inner wall of the container, wherein the distance measuring device comprises at least one optical device for detecting at least one height profile along at least one measurement line projected onto the inner wall and at least one position transducer for determining a current rotational position of the respective measurement line on the inner wall, wherein the position transducer has a combination of a magnetic tape and a sensor arranged thereabove for detecting a rotational position of the shaftless rotating container.

The container is in particular a particle receiver, also known as a centrifugal receiver, in a solar thermal power plant. Optionally, the combination can also be used to detect a rotational position of a rotational kiln.

According to an advantageous embodiment, the magnetic tape can be arranged on the container and can rotate with the container, while the sensor is arranged above the magnetic tape. The magnetic tape can surround the container, in particular on the outer circumference, and the sensor can be arranged at a small radial distance from it. The sensor may be placed at a fixed angular position with respect to the container. While the container rotates, the sensor does not rotate. The distance between the sensor and the magnetic tape is suitably between about 1 mm and about 3 mm. Optionally, the sensor can be mounted so that it can be moved radially in order to ensure an even distance to the receiver or the magnetic tape. This is advantageous if, for example, the container is not running circularly or is eccentric, or if the distances between the magnetic tape and the sensor can fluctuate.

Optionally, the magnetic tape can also be arranged on the inside, in particular on the inner wall, of the container and the sensor can be arranged correspondingly inside the container at a small radial distance from it.

According to an advantageous embodiment, the magnetic tape can be arranged on the container and can rotate with the container, while the magnetic sensor is arranged above the container or magnetic tape. The sensor can be arranged on the outside of the container, in particular on the outer circumference, and the magnetic tape can be arranged at a small radial distance from it. Optionally, the magnetic tape can also be arranged on the inside, in particular on the inner wall, of the container and the sensor can be arranged correspondingly inside the container at a small radial distance from it.

Optionally, the two alternative embodiments can also be combined on one container, wherein the measuring accuracy can be increased by two such combinations of sensor and magnetic tape.

According to a further aspect of the invention, use of a combination of a magnetic tape and a sensor arranged above it is proposed for detecting a rotational position of a shaftless rotating container. The container is in particular a particle receiver, also known as a centrifugal receiver, in a solar thermal power plant. Optionally, the combination can also be used to detect a rotational position of a rotational kiln.

According to an advantageous embodiment, the magnetic tape can be arranged on the container and can rotate with the container, while the sensor is arranged above the magnetic tape. The sensor may be placed at a fixed angular position with respect to the container. While the container rotates, the sensor does not rotate. The distance between the sensor and the magnetic tape is suitably between about 1 mm and about 3 mm. Optionally, the sensor can be mounted so that it can be moved radially in order to ensure an even distance to the receiver or the magnetic tape. This is advantageous if, for example, the container is not running circularly or is eccentric, or if the distances between the magnetic tape and the sensor can fluctuate.

The magnetic tape can surround the container, in particular on the outer circumference, and the sensor can be arranged at a small radial distance from it. Optionally, the magnetic tape can also be arranged on the inside, in particular on the inner wall, of the container and the sensor can be arranged correspondingly inside the container at a small radial distance from it.

According to an advantageous embodiment, the sensor can be arranged on the container and can rotate with the container, while the magnetic sensor is arranged above the sensor. The sensor can be arranged on the outside of the container, in particular on the outer circumference, and the magnetic tape can be arranged at a small radial distance from it. Optionally, the magnetic tape can also be arranged on the inside, in particular on the inner wall, of the container and the magnetic tape can be arranged inside the container at a small radial distance from it.

Optionally, the two alternative configurations can also be combined on one container, wherein the measuring accuracy can be increased by two such combinations of sensor and magnetic tape.

DETAILED DESCRIPTION

In the figures, identical or identically acting components are identified by the same reference signs. The figures only show examples and are not to be understood as limiting.

Before the invention is described in detail, it should be pointed out that it is not limited to the respective components of the device and the respective method steps, since these components and methods can vary.

The terms used herein are only intended to describe particular embodiments and are not used in a limiting manner. Furthermore, if the singular or indefinite articles are used in the description or in the claims, this also applies to the plural of these elements, unless the overall context clearly indicates otherwise.

The directional terminology used in the following with terms such as “left”, “right”, “above”, “below”, “in front of”, “behind”, “after”, and the like only serves for better comprehension of the figures and is in no way intended to restrict the generality. The components and elements shown, their design and use can vary according to the considerations of a person skilled in the art and can be adapted to the respective applications.

FIG.1shows an exemplary embodiment of a container120of a solar radiation receiver100which is driven by a chain (not shown).

The container120is double-walled and has an inner wall130on which a film152of a heat transfer medium150, for example bauxite particles, moves through the container120during intended operation. Along the axial extent162of the container120, the film152is strongly heated by the solar radiation112entering through the aperture126for radiation input. The heat transfer medium150is fed in, for example, via the medium inlet124on the opposite side of the container120in a manner known per se and is distributed by the rotation of the container120on its inner wall130.

The longitudinal axis160of the container120can be inclined at an angle114with respect to gravity g.

In order to determine the thickness of the film152, a distance measuring device10is used, which comprises at least one optical device30with a transmitter32and a receiver34. The optical device30is advantageously designed as a profile scanner, with which a measurement line40(FIG.2) is directed onto the object to be measured, for example the inner wall130with or without film152.

FIG.2shows a schematic representation of the detection of a height profile by a distance measuring device10on a measurement line40, whileFIG.3shows a schematic representation of the detection of a height profile on a region42of measurement lines40following one another in a circumferential direction140in accordance withFIG.2.

The transmitter32is conveniently a laser and the receiver34is conveniently an electronic camera. The transmitter32of the optical device30radiates a laser beam onto the inner wall150, and the receiver34measures at points along a measurement line40the distances between the optical device30and points on the measurement line40.

During the measurement, the optical device30is rigidly mounted, while the container120can move in the direction of rotation170under the measurement line40. If the measurement line40or the region42of measurement lines40is positioned above a step in the film152, the height difference154is detected, so that a height profile can be detected with the measurement line40.

A height profile of the inner wall130without the film152and a height profile of the inner wall130with the film152of heat transfer medium150can be detected. From the difference in values, the thickness of the film152can be determined. A rotational position of the container120is determined for each measurement line40, so that the thickness of the film152can be determined with positional precision.

FIG.4shows a measuring device100according to an exemplary embodiment of the invention, in which a distance measuring device10has an optical device30that can be displaced on or with a holder20.

The distribution of heat transfer medium150on the inner wall130of the container120can be determined with the measuring device100. The measuring device100comprises the distance measuring device10, which in this exemplary embodiment comprises an optical device30for detecting at least one height profile along at least one measurement line40projected onto inner wall130, and at least one position transducer50for determining a current rotational position of the respective measurement line40on the inner wall130with respect to the rotational position of the container120.

The measurement line40extends parallel to a longitudinal axis160of the container120. If the container120rotates, adjacent measurement lines40form a region42, as schematically shown inFIG.3.

The position transducer50is attached to the container120and detects the rotational position of the container120, in particular synchronously with the projected measurement line40in a measuring position. The position transducer50can forward the position values to the distance measurement device10or, as indicated in the figure, to a computing device90, which links the distance measurement values and the position values.

It goes without saying that the measured values can be transmitted from the position transducer50to the optical device30and/or to the computing unit90, as indicated by dot-dashed lines inFIGS.4and5, by wire via data cables or also wirelessly.

Since the container120cannot be driven by a shaft the angular position of which could be detected when the container120rotates, the position transducer50has a magnetic tape52which is placed around the container120. In order to determine the rotational position, the magnetic tape52has a number of magnetic poles, which are read out by a sensor54of the position transducer50.

In order to also detect the distribution of the heat transfer medium150on the entire inner wall130of the container120in the direction of the longitudinal axis160, the optical device30can be shifted parallel to the longitudinal axis of the container120to a new measurement position.

FIG.5shows a measuring device100according to an exemplary embodiment of the invention, in which, in contrast to the exemplary embodiment inFIG.4, a distance measuring device10has a plurality of optical devices30, in this example three optical devices30. The number of optical devices30can be advantageously selected such that their measurement lines40projected onto the inner wall130or the film152adjoin one another in the direction of the longitudinal axis160of the container120and cover the entire axial extension162thereof. The optical devices30can then remain at their respective measuring point when determining the distribution of the heat transfer medium150on the inner wall130.

FIG.6shows a perspective view of a container120in a framework200with a position transducer50on the container120according to an exemplary embodiment of the invention.FIG.7shows a detailed view of an arrangement of a magnetic tape52of the position transducer50according toFIG.6on a bearing flange132of the container120.FIG.8shows a detailed view of an arrangement of the position transducer50with sensor54and magnetic tape52according toFIG.6.

The container120has no shaft for the rotation of the container120during normal operation. The container120is driven, for example, by a chain drive, for which purpose the container120in this example has a flange134with a crown gear136, into which a chain (not shown) can engage in order to rotate the container20. A bearing flange132is arranged on the container120at an axial distance therefrom.

The container120is mounted and guided in the framework200by the bearing flange132. For example, the container120has the bearing flange132at one axial end and the flange134with the crown gear136at the opposite axial end.

The magnetic tape52can be arranged on the bearing flange132of the container120with which the container120is supported in the framework200.

The magnetic tape54can be fastened to the bearing flange132on an outer side of a suitably bent holding sheet plate60, for example made of aluminum, and enclose the container120on its outer side. The holding sheet plate60can be arranged, for example, in a free space on the inside of the bearing flange132.

The holding sheet plate60can consist of or comprise individual parts that are bent on a bending machine. The holding sheet plate60can then be fastened to the inside of the bearing flange132, for example by gluing. Then the magnetic tape52can be fastened to the holding plate60, for example by gluing, or fixed with a tightening strap or in another suitable manner.

The sensor54is mounted at a small distance from the magnetic tape52. An advantageous distance is in particular between 1 mm and 3 mm. For this purpose, the sensor54can be arranged on a holding arm56which points towards the magnetic tape52and is fixed to the framework200(FIG.6). In this way, the sensor54can be positioned in a stable and reproducible manner in relation to the magnetic tape52.

The connections of holding arm56and sensor54to the framework200can advantageously be detachable and can be designed, for example, as screw connections.

FIG.9shows a detailed view of a magnetic tape52of a position transducer50on a drive flange134of a container120according to an exemplary embodiment of the invention.FIG.10shows a detailed view of the position transducer50on the drive flange134of the container120according toFIG.9.

The drive flange134is part of the container120itself. In this embodiment, the magnetic tape52is attached to the outside of the drive flange134, for example by gluing.

The sensor54is mounted at a small distance from the magnetic tape52. An advantageous distance is in particular between 1 mm and 3 mm. For this purpose, the sensor54can be arranged on a holding arm56which points towards the magnetic tape52and which is fixed to the framework200(FIG.10). In this way, the sensor54can be positioned in relation to the magnetic tape52in a stable and reproducible manner.

The connections of the holding arm56and the sensor54to the frame200can advantageously be detachable and can be designed, for example, as screw connections.

It goes without saying that the magnetic tape52can also be arranged at a different location on the container120.

FIG.11shows a cut-out perspective view of a container120in a framework200with an optical device30of a distance measuring device10on a holder20according to an exemplary embodiment of the invention.

The holder20protrudes into the interior of the container120with an arm22pointing in the axial direction of the container120. The optical device30is fastened to the arm22, for example by screwing, tying, clamping or the like.

The arm22is attached to a crossbeam24located in front of the aperture126of the container120and attached to the framework200. Typically, during the operation of the container120, solar radiation is directed into the container120through the aperture126.

In particular, the crossbeam24can extend from one side of the framework200to the other side and cover the aperture126.

The optical device30can be arranged to be displaceable along the arm22. Alternatively or additionally, the arm22can be arranged to be displaceable on the crossbeam24.

Alternatively or additionally, the arm22can also be designed as a telescopic arm.

All connections of the arm22are expediently designed as detachable connections, so that the aperture126can be freed again after the measurements.

FIG.12shows a flow chart for carrying out a method according to an exemplary embodiment of the invention.

The method for determining a distribution of heat transfer medium150on an inner wall130of a container120starts with step S100.

In a first sequence S200, a first measurement takes place, in which the inner wall130of the container120is measured. In step S202, the optical device30of the distance measuring device10measures the distances between the optical device30and points on the measurement line40on the inner wall130, point by point along a measurement line40, while the position transducer50measures the rotational position of the container120(step S204). A first three-dimensional point cloud is generated in step S206by linking distance and rotational position. The respective distance in relation to the respective measurement line40results in a height profile of the inner wall130both in the direction of the longitudinal axis160of the container120and, since the container120rotates, in the circumferential direction140.

A second measurement takes place in a second sequence S300, in which the film152of the heat transfer medium150, which is distributed on the inner wall130, is measured. In step S302, the optical device30of the distance measuring device10measures the distances between the optical device30and points on the measurement line40on the film152, point by point along a measurement line40, while the position transducer50measures the rotational position of the container120(step S304).

A further three-dimensional point cloud is generated in step S306by linking distance and rotational position. The respective distance in relation to the respective measurement line40results in a height profile of the film152on the inner wall130both in the direction of the longitudinal axis160of the container120and, since the container120rotates, in the circumferential direction140.

It goes without saying that the measurement on the inner wall130can also be carried out after the measurement on the film152, so that the two sequences S200and S300can be swapped.

In step S402, in sequence S400, a difference between the distance from the measurement on the inner wall130of the container120without heat transfer medium150and the distance from the measurement on the film152on the inner wall130is formed for each measuring point. In step S404a corrected point cloud is provided.

After sequence S400, in step S500, measured values for the thickness of the film152corresponding to the distribution of the heat transfer medium150on the inner wall130are provided at a defined number of measuring points. The thickness of the film152or the distribution of the heat transfer medium150on the inner wall130can be determined with high spatial resolution.

The method ends in step S600.

The distance measurements are made without solar radiation entering the container120. The measurements are expediently carried out at comparable temperatures.

Furthermore, corrections can be made during a reference measurement and during the measurement on the film152if the container120has deviations from circularity and/or an eccentricity. In particular, the measurement lines40can be adapted.

The determination of the distribution of heat transfer medium150on the inner wall130can be carried out repeatedly at time intervals for quality control and any changes in the distribution can be detected. If permissible tolerances of the changes are exceeded, a maintenance requirement can be indicated.

LIST OF REFERENCE NUMERALS