EP2111521A2

EP2111521A2 - Tube collector with variable thermal conductivity of the coaxial tube

Info

Publication number: EP2111521A2
Application number: EP07857896A
Authority: EP
Inventors: Maik Schedletzky
Original assignee: SCHEDLETZKY, Maik
Current assignee: LEIPZIGER SOLARGESELLSCHAFT MBH
Priority date: 2006-12-19
Filing date: 2007-12-19
Publication date: 2009-10-28
Also published as: US8191549B2; DE202007003441U1; US20100018522A1; WO2008074852A3; WO2008074852A2

Abstract

Collector tube for a solar collector, having an envelope tube, an absorber tube which is arranged within the envelope tube and into whose interior a heat carrier medium can be carried, characterized by an inner tubular element which is arranged within the absorber tube and has a thermal conductivity which is variable. Distributor segment for at least one collector tube which is designed in particular according to one of the preceding claims, having at least one first opening for supplying a heat carrier medium into the at least one collector tube, at least one second opening for carrying the heat carrier medium away from the at least one collector tube, a channel for supplying the heat carrier medium from outside the at least one collector tube into the at least one collector tube, a channel for carrying the heat carrier medium away from the collector tube to outside the at least one collector tube, with the supply channel and the output channel being arranged such that the distributor segment can be directly coupled to at least one further identical distributor segment in a heat carrier medium circuit.

Description

Tubular collector with variable thermal conductivity of the coaxial tubes

The present invention relates to a collector tube, a collector tube for a collector tube and a tube collector.

There are known tube collectors for the absorption of sunlight, in which the collector tubes each comprise a transparent cladding tube and an absorber tube. Fig. 15a, b shows such a collector tube of the prior art. Cladding tube 1 and absorber tube 2 are closed at one end and fused together at the other end. Between the tubes 1, 2 is vacuum or a gas with low thermal conductivity, so that a structure - similar to a thermos - with a cavity 3 is formed. The absorber tube 2 is used for light absorption and is provided for this purpose with an absorber layer. The light 29 passes through the transparent cladding tube 1 located on the vacuum from Ab sorber layer 2. The resulting heat in the Ab absorber layer is transferred to a heat conducting 33, which rests against the inside of the absorber tube 2 and the cavity 3 of the collector tube lined. To transfer the heat to the heat transfer medium 4, 4a, the heat conducting plate 33 is connected to a U-shaped bent tube 35 in which the heat transfer medium to be heated 4, 4a flows. Air gaps or oxidation layers between Wärmeleitblech 33 and U-shaped bent tube 35 and absorber tube lead to heat transfer resistance and deteriorate the collector efficiency. In relation to the absorber surface, the amount of heat transfer medium should not be too large, so that the heat transfer medium can heat up quickly and the collector does not react too slow. Reflectors are used because there is less light on the side of the collector that faces away from the light than on the front. These reflect radiation between the tubes and the reflector. tor hits, on the side of the collector tubes which faces away from the light. With direct direct sunlight and a reflector width equal to twice the tube diameter, the backs of the collector tubes receive approximately as much light as the front sides. In diffused light conditions, the tubes partially shadow the reflector, so much less light can be reflected on the back of the tubes. In Germany, for example, the annual proportion of diffuse light is around 50% of global radiation. The consequence of this is that the reflector in diffused light does not contribute significantly to the increase in yield. In direct light, the reflector causes a power increase of the collector. In case of stagnation, eg with full storage or pump failure, if the heat from the collector can not be removed, the additional radiation through the reflector has a negative effect on the operational safety. Because at temperatures between 250 to 300 ⁰ C, the formation of steam can lead to damage to the equipment and aging of the antifreeze. Expensive, which supply the heat transfer medium to the collector tubes or dissipate, are therefore usually made of copper, which can withstand these temperatures. To reduce heat losses, the distributors are covered with high-temperature-resistant insulating materials. To fix the collector tubes as well as all other collector components, aluminum housings are usually used. Due to the large number of collector components, the assembly effort is great and causes high production costs in connection with the materials used.

The object of the invention is therefore to provide elements for a solar collector which make it possible to limit the maximum temperature and in particular also the use of materials with low temperature resistance in order to achieve a reduction in the variety of components with new production methods. Furthermore, a high efficiency should be achieved. This object is achieved by the collector tube having the features of claim 1, by the distributor segment having the features of claim 20, or by a tube collimator. Lektor solved with the features of claim 24. Advantageous developments of the invention are defined in the respective subclaims.

Considering the aspects of high efficiency, the invention proposes a collector tube which brings about a reduction in the standstill temperature. According to the invention, the heat transfer medium does not flow through a U-shaped bent tube, but directly along the inner wall of the absorber tube. As a result, heat transfer resistances between absorber tube, heat conducting sheet and U-shaped bent tube are eliminated and the efficiency of the collector is increased. In addition, the volume of the heat transfer medium to be heated is minimized to reduce the reaction time of the collector. For this purpose, a coaxial tube is inserted into the cavity of each collector tube. The coaxial tube separates the inflowing cold heat transfer medium from the heated heat transfer medium. The cold heat transfer medium flows inside the coaxial tube to the lower end of the cavity of the collector tube and flows back for heat absorption between the outside of the coaxial tube and the inside of the absorber tube. The coaxial tube is arranged eccentrically in the cross section of the cavity of the collector tube. The eccentricity of the coaxial tube is oriented to the light side of the collector tube. This reduces the volume of the heat transfer medium to be heated on the side facing away from the light and at the same time increases on the side facing the light. In this way, the heat transfer medium on the side facing away from the light, despite lower light irradiation, heated just as fast as on the light-facing side. The reflector can be made smaller in relation to the tube diameter. In diffuse light conditions, the smaller reflector has only a negligible effect, but ensures that the standstill temperature increases less in the case of direct vertical irradiation.

If a collector is oriented to the south, the largest part of the heat transfer medium to be heated is located on the south side of this arrangement - A -

Collector tubes and is directly irradiated by the sun. If the sun shines obliquely on the collector in the mornings or evenings, it is advantageous if then also the largest amount of the heat transfer medium to be heated is at the points of highest light intensity. For this purpose, the coaxial tube is displaced laterally in the collector tube. In this way, the heat transfer medium to be heated, for example, at southeast radiation on the opposite side - namely in the northwest direction - the lowest and on the directly irradiated side, the largest volume of the heat transfer medium to be heated. The lateral displacement of the coaxial tube is carried out according to the respective position of the sun. For the realization of the lateral displacement of the coaxial tube in the collector tube preferably components made of materials are used, which change their shape and / or their volume when the temperature changes. For example, these components are locked between the absorber tube and the coaxial tube in such a way that they are heated simultaneously with the heat transfer medium. If there is a different degree of heating of the heat transfer medium, for example, between the east and west side due to lateral solar radiation, the component is deformed more on the warmer side than on the dark side. With the deformation of the component, the coaxial tube is displaced laterally, until the different volumes of the heat transfer medium to be heated result in compensation for the different radiation and temperature equalization.

According to the invention, the coaxial tube is variable in its thermal conductivity. Since hot and cold heat transfer medium - separated by the coaxial pipe - flow past each other in countercurrent, the thermal conductivity of the coaxial tube should be as low as possible in normal operation, to prevent heat from the hot is transferred to the cold heat transfer medium. In the case of an accident, however, it is advantageous if the thermal conductivity of the coaxial tube is as large as possible, so that the heat is transferred unhindered to the incoming cold water, which in this case represents a cold reservoir, and the standstill temperature is lowered. Realized is the variable thermal conductivity of the Koaxialrohrs advantageously through a double-walled glass tube in which there is a small amount of liquid and a gas or gas mixture. This type of coaxial tube is referred to below as a convection balloon.

The variable thermal conductivity of the coaxial tube can also be achieved in a further embodiment of the invention that materials such as bimetals or shape memory materials change their shape and thereby form thermal bridges in the double-walled coaxial tube. Even materials in which a variable thermal conductivity is caused by a change in the molecular structure, are possible. A further variant according to the invention consists in that a double-walled coaxial tube is used, which is equipped with special layers for the emission and absorption of thermal radiation. The outer tube of the double-walled coaxial tube is provided on the inside with a variable selective layer. This layer emits little or no thermal radiation at low temperatures, as they prevail in normal operation of the collector. Only at high temperatures, such as occur in stagnation case, or when exceeding a threshold temperature, the variable-selective layer is able to radiate heat. In order to avoid reflections of the inner coaxial tube, the outer side of the inner coaxial tube can be provided with an absorption layer. The heat is transferred to the cold reservoir after absorption by the inner coaxial tube. Inner and outer coaxial tube are preferably connected together at the ends, so that a cavity is formed. Since the emission and absorption layers are located in the cavity of the coaxial tube, they do not come into contact with the heat transfer medium and are protected against abrasion, deposits and chemical changes. The location of the inner coaxial tube in the outer coaxial tube may be concentric or eccentric. Particularly suitable for the absorbent layer of the inner coaxial tube are ceramic layers having an absorption maximum in the infrared range of the light spectrum. To prevent heat transfer in the coaxial tube even at low temperatures by heat conduction, the cavity of the coaxial tube can be evacuated.

The operation of the coaxial tube according to the invention with variable thermal conductivity will be explained in more detail with reference to the convection balloon.

The convection balloon consists of a double-walled coaxial tube with the ends of the tubes joined together to create a cavity between the inner and outer tubes in which convection can take place.

The cavity is filled with a small amount of a medium which evaporates at a certain temperature. This medium is called convection medium.

In normal operation, the cold and the warm heat transfer medium are separated by the coaxial tube or the convection balloon. The heat transfer medium rises along the absorber wall and heats up. In the lower tube area, the heat transfer medium is still cold, so that the convection medium in the convection balloon is in the liquid state of aggregation. The upper portion of the convection balloon contains a gas or gas mixture with low thermal conductivity. For example, various noble gases are particularly suitable. Even a low pressure reduces the thermal conductivity. The relatively low thermal conductivity of the gas ensures that little heat is transferred to the cold heat transfer medium inside. At standstill, the heat transfer medium between the absorber tube and the convection balloon is heated along the entire length to the lower area, where the convection medium is located in the convection balloon. If the temperature of the heat transfer medium exceeds the boiling point of the convection medium, it changes to the vaporous state of matter. The resulting vapor rises on the outer wall of the convection balloon and continues to absorb heat from the heat transfer medium. The convection medium condenses on the inside of the convection balloon, transferring heat to the cold heat transfer medium. The condensed convection medium flows down. The convection of the convection medium creates a cycle in which heat is transferred from the absorber layer to the inside of the convection balloon to the cold reservoir. In this way, on the one hand, the heat transfer medium on the outside of the convection balloon is prevented from overheating and causing damage. On the other hand, the collector yield is increased because the heat radiation is minimized to the outside by a low collector temperature and the heat transported into the interior is not lost. Depending on the convection fluid used, such as ethanol, water or a mixture of substances and the prevailing pressures in the convection balloon, the boiling point and thus the start of the heat transfer can be defined. In order to achieve an abrupt increase in the heat transfer through the convection, it is advantageous to seal the convection medium with a second substance with respect to the overlying gas space of the convection balloon. This ensures that evaporation of the convection medium and thus convection only begin to a considerable extent when the convection medium has been heated to the boiling point. The sealing substance should advantageously not be miscible with the convection medium, have a higher boiling point and have a lower specific gravity. By way of example, water can be used as convection medium and oil or paraffin for sealing.

A further variant according to the invention of the coaxial tube with variable heat capacity consists in that the coaxial tube is made up of at least two nested tubes. A coaxial tube with several "layers" is formed, the tubes are open at both ends, and the openings of the tubes located further inwards are preferably smaller on the inflow side of the cold heat transfer medium than the opening of the outer tube cold heat transfer medium in the outer layer of the coaxial tube, between the outer tube and the nearest inner tube, heat transferred through the wall of the outer tube to the cold heat transfer medium is drawn to the outflow side of the coaxial tube. transported alrohrs. Thereafter, the heat transfer medium flows in the gap between the inside of the absorber tube and the outside of the coaxial tube back up, where it is further heated. Since the heat is transported away from the outer Koaxialrohrschicht, gets in normal operation, little heat to the cold reservoir inside the coaxial tube. The heat transfer can be further reduced by further similar layers of the coaxial tube. The ratio of the volume flows of the heat transfer medium through the layers of the coaxial tube is determined by the ratio of the tube openings between the layers.

At standstill, when no heat transfer medium circulates in the collector, the removal of heat from the outer and the further inside arranged Koaxialrohrschichten is interrupted. Heat is then transferred through the walls of the coaxial tube from layer to layer to the interior of the coaxial tube, the cold reservoir. By dissipating the heat from the absorber tube to the cold reservoir, overheating is prevented.

Of importance for the standstill temperature is the ratio of the absorber surface to the volume of the heat transfer medium. The larger the volume in relation to the absorber surface, the lower the standstill temperature, since the light intensity and sunshine duration of a day is limited. In contrast to conventional solar panels, in which at the level of the standstill temperature as much heat is radiated to the environment as light energy radiates, with the device according to the invention, the non-removed heat is stored for the most part in the collector. It is released slowly to the environment and is also available after sunset. The heat transfer medium in the gap between the coaxial tube and the absorber tube gradually cools down without further supply of light - depending on the quality of the selective coating and the vacuum. The release of the heat stored in the cold reservoir is carried out according to the invention via the coaxial tube. At temperatures in the cold reservoir, which are above the boiling point of the convection medium, the Heat dissipation fast, since the coaxial tube has a high thermal conductivity. It results in the convection balloon from a convection in the reverse direction in which heat is transported from the inside out. With increasing cooling, the convection fluid condenses more and more and the thermal conductivity of the convection balloon decreases. The residual heat from the cold reservoir is released increasingly slowly to the environment. This has the advantage that on the one hand this heat can be used over a longer period of time. On the other hand, the period of one night is long enough for the heat transfer medium to cool down to such an extent that it also provides a sufficiently large cold reservoir on the following day in order to be able to limit the standstill temperature. In other variants of the coaxial tube or can be expected that the heat transfer medium for large volumes and warm nights not fully cooled, as may be the case in southern countries, ensures a device that the heat not only through the coaxial tube to the Environment is given, but the convection of the heat transfer medium itself gets going. For this purpose, a connection with a valve is created between the headers for the hot and cold heat transfer medium. The valve opens and closes a circuit between cold and warm heat transfer medium. If the valve opens, the warm heat transfer medium rises from the interior of the coaxial tube. On the outside of the coaxial tube or via an intermediate cooler, it is cooled, sinks down and flows from below into the interior of the coaxial tube. In this way, the high heat transfer resistance of the coaxial tube is bypassed and also a large heat transfer volume can be completely cooled so that it can absorb a corresponding amount of energy on the following day.

The large diameter of the coaxial tubes offers advantages for easy venting of the collector system, as air bubbles in the coaxial tube can rise without being entrained by the heat carrier flow. The unproblematic way of venting offers the possibility of coupling the collector to a drain-back system in which the heat transfer medium is at a standstill is drained. This offers another possibility to cool the heat transfer medium overnight. However, it also has the advantage that at very low temperatures in winter the heat transfer medium already reaches the collector at a relatively high temperature level (room temperature) and no energy is required to bring the heat transfer medium from minus temperatures to this temperature level.

Devices that completely or partially shade the collector during the summer at mid-summer help to limit the standstill temperature. Advantageously, a transparent cover of the collector, for example in the form of a glass sheet, which is arranged so that it comes in the sun in the summer at noon for reflection. The direct light is reflected so that it does not reach the collector. In the remaining times, the light can reach the collector largely unhindered.

When filled, the collectors of the invention have a much higher weight than conventional, which in freestanding assembly -. on flat roofs - is advantageous in terms of wind loads, because there is no need to provide additional weights.

By limiting the standstill temperatures, it is possible to completely dispense with the construction of the collector on expensive metals such as aluminum or copper and instead advantageously to use plastic. On the one hand, the use of plastic enables new less expensive production techniques, such as injection molding. On the other hand, the functions of several collector components, such as the distributor of the inflowing cold heat carrier medium or the effluent hot heat transfer medium and the thermal insulation, locking the collector tubes, the manifold housing and the collector mounting device can be integrated into a single component. However, integrating different functions in a component poses problems when there are hot and cold zones are that expand differently and lead to the deformation of the component. This is the case, for example, if the distributors for cold and hot heat transfer medium are provided in one component. The solution to this problem is a segmentation of the distributor. Each segment has the same or similar functions, with different length expansions within a segment being compensated by flexible elements between the segments. The size of a segment is determined by how large the expected maximum temperature differences within a segment are and which length differences can be tolerated.

The distributor segment according to the invention can receive one or more collector tubes.

In the distributor segment according to the invention are channels for the heat transfer medium. In the upper channel flows the cold and in the lower the warm heat transfer medium. The collector tube is fixed from below in an opening of the channel for the warm heat transfer medium and sealed with seals. The coaxial tube, which is located in the collector tube, is fixed in an opening of the channel for the cold heat transfer medium and also sealed with seals. In this way, the cold heat transfer medium from the channel of the distributor can flow into the coaxial tube, leave the inside of the coaxial tube at the bottom, flow up between the absorber tube and the outside of the coaxial tube and open in the manifold in the channel for the warm heat transfer medium. According to the supply and discharge channels are arranged such that a plurality of distributor segments in a heat transfer medium circuit directly, ie without hoses, pipe sections or the like, can be coupled together. In this way, any tube collector arrangement can be formed with one type of distributor segments. Moreover, directly at the place of use of the tube collector, the arrangement can be changed by inserting or removing distributor segments (and collector tubes connected thereto), if, for example, it should turn out that the system is incorrectly positioned. was dimensioned. Several distributor segments are held together by fasteners. As connecting elements are, for example, mounting frames, brackets or threaded rods. For endless assembly, threaded rods are preferably used, on which the distributor segments are lined up with corresponding holes. Between the distributor segments seals are arranged as flexible elements to compensate for the thermal expansion and for sealing.

A particularly advantageous embodiment of a segment for a collector tube and coaxial tube is made of heat-resistant plastic by injection molding. This type of production allows low unit costs, makes moreover the segmentation of the manifold advantage, since in this way the difference in thermal expansion within a component can be compensated easiest.

The openings for the collector tube and for the coaxial tube are offset from each other so that this results in the correct eccentric position of the coaxial tube in the cavity of the collector tube. Hollow chambers, which can be arranged around the heat transfer channels, serve for thermal insulation. These can also be filled with heat-insulating materials.

If the connections for inflow and outflow of the heat transfer medium are located on a collector side, it is provided in an advantageous development of the invention to integrate into the distributor housing another channel to achieve a uniform distribution of pressure losses within a collector by a so-called Tichelmannverschaltung , It is advantageous to dimension the channel cross sections of a distributor segment for inflow and outflow of the heat transfer medium into or out of the collector tubes so that the pressure losses of inflow and outflow of the heat transfer medium including the pressure losses in the tubes are the same. In this way it is possible to line up any number of distributor segments and to vary the collector size variably. stallten. If collector tubes are used in which the heat transfer medium to be heated is separated from the cold incoming heat transfer medium, as is the case for example with the use of coaxial tubes, an advantageous development of the distributor segment is that between the channels for cold and hot heat transfer medium a valve is integrated. The valve creates a connection between the cold and hot heat transfer medium, creating a gravity driven cycle. The circuit may serve to transfer heat from the absorber layer into the cold reservoir to avoid high standstill temperatures or to transfer heat in the reverse direction from the heated cold reservoir to the absorber layer where it is gradually radiated at night. The distributor segments can be designed so that a veneer can be used as a design element or as UV and weather protection.

The distributor segment with the connecting elements and sealing elements thus forms a kind of modular system with a minimum number of different components, from which almost any tube collector systems can be assembled and changed. Especially the small number of different components is attractive for use in the area, where warehousing and procurement are a significant factor.

The invention also includes a tube collector having at least one of the components according to the invention.

In the drawings, advantageous embodiments of the invention are shown. It shows

1 shows a cross section of a Sydneyröhre with eccentrically mounted coaxial tube. Figure 2 is a side view of a Sydneyröhre with eccentrically mounted coaxial tube. 3 shows a side view of a sideline tube with eccentrically mounted convection balloon and liquid convection medium in normal operation;

4 shows a side view of a sideline tube with an eccentrically mounted convection balloon and vaporized convection medium at a standstill;

5 shows the heat release from the heated cold reservoir via the convection balloon;

6 shows the heat release from the heated cold reservoir via the convection of the heat transfer medium; Figure 7 is a longitudinal section of a distributor segment with a Sydneyröhre and coaxial tube.

Fig. 8 is a cross-section of a distributor segment with a sydney tube and coaxial tube;

9 shows the flow of the heat transfer medium in a longitudinal section through a collector consisting of several distributor segments with sydney tubes;

10a a collector consisting of four distributor segments;

Fig. 10b, the endless assembly of a collector of distribution segments with

Connection elements; 10c shows the arrangement of connecting elements of an endless mounted collector;

11 shows the structure of a curved collector field;

FIG. 12 shows the heat transfer to the cold reservoir by means of heat radiation; FIG.

Fig. 13 shows the displacement of the coaxial tube in the collector tube; FIG. 14a shows the regulation of heat transfer to the cold reservoir via thermal bridges of shape memory materials in the cold state; FIG.

14b shows the regulation of the heat transfer to the cold reservoir via thermal bridges of shape memory materials in the warm state;

Fig. 15a shows a Sydney tube in cross-section according to the prior art; Fig. 15b shows the Sydney tube according to the prior art in longitudinal section;

16 shows the connection to a drain-back system in normal operation;

17 shows the connection to a drain-back system when the collectors are emptied; 18 shows the construction and the function of a coaxial tube of several layers in normal operation. and

Fig. 19 shows the function of the coaxial tube of several layers at a standstill.

In Figure 1, the cross section of a collector tube consisting of a cladding tube 1 and an absorber tube 2 is shown with eccentrically mounted coaxial 6.

Between the cladding tube 1 and the absorber tube 2 is vacuum 3. Das

Heat transfer medium 4 absorbs the heat of the absorber tube 2, in which it flows in a gap with different width between absorber tube and coaxial along. The cold incoming heat transfer medium 5 is located inside the coaxial tube and forms a cold reservoir 5. On the sun-facing side of the collector is a reflector 10. This reflects the

Light on the solar side facing away from the collector tube 1, 2.

Figure 2 shows the longitudinal section of the collector tube consisting of a cladding tube 1 and an absorber tube 2 with eccentrically mounted coaxial 6. The cold incoming heat transfer medium 5 flows according to the arrows

9 down. Between absorber tube 2 and coaxial 6, it then flows upwards. If light is absorbed by the absorber tube 2, the still cold heat transfer medium 4a gradually heats up and leaves the tube as a warm heat transfer medium 4 at the upper end of the collector tube 1, 2.

As can be seen in FIG. 3, the coaxial tube 6 can also be designed as a double-walled tube, so that a convection balloon 6a is formed. The convection balloon 6a forms a closed system containing a convection medium 7. In addition, the convection balloon 6a may be filled with gases 38 having a low thermal conductivity. In normal operation at relatively low conditions the convection medium 7 is liquid and collects at the lower end in the cold region of the heat transfer medium 5, 4a of the collector tube 1, 2. The convection medium 7 may be compared to the gas chamber 38 sealed with a sealing substance 37, so that the convection 7 only in larger Scope evaporates when its boiling point is reached.

In contrast, Figure 4 shows a state in which the convection medium 7, 7a is evaporated. This state is reached when the removal of the warm heat transfer medium 4 is hindered, so that the lower region of the collector tube 1, 2, 4 5a also heats up. The evaporating convection medium 7a rises upward. It continues to absorb heat from the heat transfer medium 4 via the outer wall of the convection balloon 6a. This heat is transmitted to the cold reservoir 5 on the inside of the convection balloon. The convection 11 in the convection balloon 6a according to the arrow direction continues until the temperatures between the heat transfer medium 4 and the cold reservoir 5 are balanced or are below the boiling temperature of the convection medium 7, 7a.

FIG. 5 shows the process of heat release from the cold reservoir 5a. In the dark, no heat is transferred from the absorber tube 2 to the heat transfer medium 4, 4a. The heat transfer medium 4, 4 a cools gradually, since heat is radiated to the environment 12. If the temperature in the cold reservoir 5a is above the boiling temperature of the convection medium 7, 7a, the convection flow direction in the convection balloon reverses. Evaporated convection medium 7a rises on the inside of the convection balloon 6a upwards, thereby absorbs heat from the cold reservoir 5a and transfers the heat to the heat transfer medium 4, 4a. The more the cooling reservoir 5a cools, the less heat is given to the environment via the convection balloon 6a. The heat release decreases sharply when the temperature in the cold reservoir 5a falls below the boiling temperature of the convection medium 7, 7a. If the heat release from the cold reservoir 5a is accelerated independently of the convection balloon 6a, which may be the case when large volumes of the cold reservoir 5a have to be cooled, the convection of the heat transfer medium 5, 5a, 4, 4a as in FIG shown used. For this purpose, a valve 22 is opened, so that the heat transfer medium 5, 5a, 4, 4a can circulate. The heat transfer medium 4, 4a cools between the absorber tube 2 and the outer wall of the convection balloon 6a by Wärmeab radiation 13 or via a separate consumer. As a consumer, for example, cooler or memory, which are arranged in a suitable position to the collector. During cooling, the density of the heat transfer medium 4, 4a increases so that it sinks down and warm heat transfer medium 5a flows from the cold reservoir 5a into the gap between the absorber tube 2 and outer wall of the convection balloon 6a or into a separate consumer.

FIG. 7 shows the structure of a distributor segment 18 in longitudinal section. The collector tube 1, 2 is locked by an opening 4 d in the distributor segment 18 that it opens in the distribution channel 4 c. The coaxial tube 6, 6a opens in the distributor channel 4b through an opening 4e in the distributor segment 18. The opening 4e represents the inflow of the (cold) heat carrier medium from the distributor segment 18 into the coaxial tube 6. The opening 4d represents the outflow of the (FIG. The cold heat transfer medium 4a flows from a distribution channel 4b in the coaxial tube 6 and moves according to the flow direction 9 between the coaxial tube 6 and absorber tube 2 again in the direction of distributor, where it in a Distribution channel 4c opens. In order to achieve a uniform flow through the collector tubes 1, 2 and a coaxial tube 6 with the heat transfer medium 4, 4a, it is expedient to evenly distribute the pressure losses within a collector field by a Tichelmannverschaltung. Distribution channel 15 serves to transport the heat transfer medium to the end of the collector field, so that the sum of the distance from inflow and outflow of the heat transfer medium for each collector tube is the same size. For thermal insulation, the distribution channels 16 provided, which can also be filled with suitable materials. Between the distribution channel 4b for cold heat transfer medium and 4c for warm heat transfer medium, a distribution valve 22a can be integrated to analogous to the valve 22 in Fig. 6 a circulation of the heat transfer medium 5, 5a, 4, 4a to ermögli- chen.

FIG. 8 shows a cross-section of a distributor segment 18 with a vacuum tube 1, 2 and a coaxial tube 6. A reflector 10 marks the back of the collector tube 1, 2. The collector tube 1, 2 and the coaxial tube 6 are fixed and sealed by tube seals 17 in the openings 4d, 4e. In order to connect a plurality of distributor segments 18 to one another, corresponding bores 21 are provided, into which connecting elements 20, such as threaded rods, can be inserted. The bores 21 can advantageously be mounted in pairs in order to allow the construction of an arbitrarily long collector field. A mounting device 36 allows the attachment of the collector to a frame or an elevation.

Figure 9 shows the structure of a collector array consisting of a plurality of distributor segments 18, each with a collector tube 19. By juxtaposing a plurality of distributor segments channels 4b, 4c, 15, which are flowed through by the heat transfer medium 4, 4a corresponding to the arrows 9.

FIGS. 10a to 10c show how the individual distributor segments 18 can be joined together to form a collector field. FIG. 10 a shows a field of cooperation of four distributor segments 18. The distributor segments 18 are connected to one another by connecting elements 20. FIG. 10b shows by way of example how further distributor segments 18 can be added to a collector array comprising four distributor segments 18. In this case, further connecting elements 20 are fastened in the parallel openings 21 of the last distributor segment. On these connecting elements 20 alternately seals 17b and distributor segments 18 are plugged and hydraulically sealed. In FIG. 10 c shows how an arbitrarily long collector field can be built up by alternating use of the pairwise bores 21 for the connecting elements 20.

FIG. 11 shows how the collector according to the invention can be adapted to a curved mounting surface. The collector field is shown from above. In order to achieve a curvature of the collector field, conical seals 17a or special cones are used in the assembly of the collector field. Due to different material thicknesses of the seals 17a, the curvature can be adapted to the requirements.

FIG. 12 shows the heat transfer from the warm heat transfer medium 4 to the cold reservoir 5. In this case, a variable selective layer 23, which is located on the inside of the outer coaxial tube, is heated by the warm heat transfer medium 4. At low temperatures, as prevail in the normal operation of the collector, the variably selective layer 23 does not emit heat radiation 25. Only at high temperatures, as they occur in the case of stagnation, or when exceeding a threshold temperature, the variable selective layer 23 is able to radiate heat 25. The outer side of the inner coaxial tube can advantageously be provided with an absorber layer 24, which absorbs the heat radiation 25 and transfers it to the cold reservoir 5. To prevent heat transfer in the coaxial tube, even at low temperatures by heat conduction, the coaxial tube can be evacuated.

The displacement of the coaxial tube in the collector tube is shown in FIG. Components or components of a component 27, 28, which change their shape and / or their volume when heated, are located between absorber tube 2 and coaxial tube 6. If one of these components or components 27, 28 is heated more strongly by the irradiation of the sun 29 as the other 27, it moves the coaxial tube laterally and thereby increases the gap between the absorber tube 2 and Coaxial tube 6. On the side facing the sun, a gap is formed with the largest volume of the heat transfer medium 30 to be heated. On the side facing away from the sun, a gap with the smallest heat transfer volume 31 arises.

FIGS. 14a and 14b show how the heat transfer in the coaxial tube 6 from the warm heat transfer medium 4 to the cold reservoir 5 takes place. In normal operation, the heat transfer medium 4 is not warm enough to change the shape of the shape memory material 32 so much that a thermal bridge is formed. The shape memory material abuts only on the side of the passing heat transfer medium 4, while the inside of the coaxial tube 6 is not touched to the cold reservoir 5. This condition is shown in Fig. 14a. If the heat transfer medium 4 heats up beyond the normal operating temperature, the shape memory material 32a deforms to such an extent that, as shown in FIG. 14b, it also bears against the inside of the coaxial tube 6 and transfers heat from the heat transfer medium 4 to the heat transfer medium 4 Cold reservoir 5a transfers.

FIG. 15 a shows a Sydney tube according to the prior art with heat-conducting laminates in cross-section and in FIG. 15 b in a longitudinal section. In this case, the incident light 29 is absorbed in the absorber tube 2. The resulting heat must be transferred to a Wärmeleitblech 33 and then to a U-shaped bent tube 35. The occurring heat transfer resistors 34 have a negative effect on the collector efficiency.

In Fig. 16, the coupling of the collector 18, 19 according to the invention is shown to a drain-back system in the normal operation of the solar system. The heat transfer medium 4a to be heated flows out of the heat accumulator 39 via the valve 42 into the collector. The valve 42 is opened according to the indicated arrows. The branch to the drain-back tank 40 is closed. After flowing through the collector 18, 19, the warm heat transfer medium flows over the valve 41 back into the heat accumulator 39. The valve 41 is opened according to the indicated arrows. The branch to the drain-back tank 40 is closed.

In Fig. 17, the coupling of the collector 18, 19 according to the invention to a drain-back system after emptying of the collector 18, 19 is shown. In this case, the valve 41 is brought into a position in which the heat transfer medium from the collector 18, 19 flows according to the arrow in the drain-back tank 40. The connection of the valve 41 to the heat accumulator 39 is closed. If the drain-back container 40 is located below the collectors 18, 19, the heat transfer medium can flow independently by gravity into the drain-back container 40. If this is not the case, the heat transfer medium is pumped out by the pump 43. To ventilate the collectors 18, 19, the valve 42 is brought into a position in which air from the drain-back container 40 passes into the collector in the direction of the arrow. The connection of the valve 42 to the heat accumulator 39 is closed. An emptying of the collector tubes 19 is possible up to the level 46, is sucked in the air. The filling of the collector 18, 19 by means of pump 43 which pumps the heat transfer medium from the drain-back tank 40 via the valve 41 in the collector 18, 19. The escaping from the collector 18, 19 air is passed through the valve 42 into the drain-back tank 40. After filling the collector 18, 19, the valves 41, 42 are brought into a position in which the drain-back container 40 is closed and the heat transfer medium 4, 4a between the collector 18, 19 and heat accumulator 39 can circulate. In a further advantageous embodiment, the function of the drain-back container 40 can be integrated into the heat accumulator 39.

FIG. 18 shows a coaxial tube which consists of several layers through which the inflowing cold heat transfer medium 5 flows. Through the outer layer of the coaxial tube 50, the majority of the inflowing cold heat transfer medium 5, since the opening 54 of the outer tube 49th is greater than the opening 55 of the second tube of the coaxial tube 51. The heat transfer medium flows according to the indicated arrows to the other end of the coaxial tube and takes the heat transmitted through the outer tube 49 with. A second tube of the coaxial tube 52 is formed with a third tube of the coaxial tube 53. Less heat carrier medium 5 flows through the second layer of the coaxial tube 52 than through the outer layer of the coaxial tube 50 , but more than into the interior of the third tube of the coaxial tube 53 passes, because only a part of the heat transfer medium passed into the tube 51 flows through the opening 56 of the tube 53. The heat transfer medium passes through the openings 54, 55, 56 - possibly over other similar, not shown layers - with increasingly smaller volume flows more and more into the interior of the coaxial tube to the cold reservoir 5. Also in the layer 52 and each other, not shown layer of the coaxial tube Heat, which has been transmitted through the walls of the tubes 49, 51, 53 and other unillustrated tubes, is transported to the other end of the coaxial tube. The openings 54, 55, 56 simultaneously serve to ventilate the coaxial tube layers 50, 52, the cold reservoir 5 and further, not shown, layers of the coaxial tube.

FIG. 19 shows the heat transfer through the coaxial tube consisting of several layers 50, 52 at standstill. Since no heat with the volume flow of the heat transfer medium 5 from the layers 50, 52 and other, not shown layers is removed, heat from the absorber layer corresponding to the thermal conductivity of the heat transfer medium and the tubes 49, 51, 53 and other not shown pipes in Inside the coaxial tube transferred to the cold reservoir 5a.

The invention further comprises a distributor or a distributor element for a collector tube, the sole characterizing feature of which is that it is made of plastic, preferably by injection molding. List of reference numbers used

1 cladding tube

2 absorber tube

3 vacuum

4 warm heat transfer medium

4a to be heated cold heat transfer medium 4b distribution channel for cold heat transfer medium

4c distribution channel for warm heat transfer medium

4d second opening (drain)

4e first opening (inflow)

5 inflowing cold heat transfer medium, cold reservoir 5a heated heat transfer medium in the cold reservoir

6 coaxial tube

6a convection balloon

7 liquid convection medium

7a vaporized convection medium 8 protective cap

9 flow direction of the heat transfer medium

10 reflector

11 Confection in convection balloon

12 Heat transfer via convection balloon 13 Heat emission through convection of the heat transfer medium

14 Convection of the heat transfer medium

15 Distribution channel for Tichelmann interconnection

16 cavity for thermal insulation

17 tube seal 17a conical seal

17b manifold gasket 18 distributor segment

19 Collector tube with coaxial tube

20 Connecting element for distributor segments

21 hole for connecting element

22 valve

22a distribution valve

23 variable selective layer of the outer coaxial tube

24 From the sorber layer of the inner coaxial tube

25 heat radiation

26 Vacuum of the coaxial tube

27 cold component for displacement of the coaxial tube

28 warm component for displacement of the coaxial tube

29 Direction of irradiation of the sun

30 point of the largest heat carrier volume

31 position of the smallest heat carrier volume

32 shape memory material cold state

32a shape memory material warm condition

33 heat-conducting sheet

34 heat transfer resistances

35 U-shaped tube for heat transfer medium

36 Mounting device

37 Sealing substance

38 gas in the convection balloon

39 heat storage

40 drain-bucket containers

41 Valve for emptying and filling the collector tubes with heat transfer medium

42 Valve for venting and bleeding the collector tubes

43 Pump for filling the collector tubes

44 Fill level in the drain-back tank during operation of the solar system

45 Fill level in the drain-back tank when collectors are empty 46 Level of the collector tubes after emptying

47 Flow direction of the heat transfer medium when emptying the collectors

48 Air flow with ventilation of the collectors

49 outer tube of the coaxial tube 50 outer layer of the coaxial tube

51 second tube of the coaxial tube

52 second layer of the coaxial tube

53 third tube of the coaxial tube

54 opening of the outer tube 55 opening of the second tube

56 Opening of the third pipe

57 Heat transfer through the layers of the coaxial tube at standstill

Claims

claims

1. Collector tube for solar collector, comprising: a cladding tube (1), an absorber tube (2), which is arranged within the cladding tube (1) and in the interior of which a heat transfer medium (4, 5) can be guided,

characterized by an inner tube member (6, 6a; 49, 51, 53) disposed within the absorber tube

(2) is arranged and has a thermal conductivity which is variable.

2. Collector tube according to claim 1, characterized in that the thermal conductivity is variable depending on the flow.

3. collector tube according to claim 2, characterized in that the inner tube element (49, 51) is designed as a double-walled tube.

4. collector tube according to claim 2 or 3, characterized in that the inner tube member (49, 51, 53) has at least one further tube (53) which is arranged concentrically to the inner tube member (49, 51).

5. collector tube according to claim 2 to 4, characterized in that the flows in the inner tube member (49, 51, 53) are different, in particular in an outer tube (49) is greater than in an inner tube (51, 53).

6. collector tube according to one of claims 2 to 5, marked thereby, that the inner tube member (49, 51, 53) openings on both sides

(55, 56).

7. collector tube according to claim 1, characterized in that the thermal conductivity is temperature-dependent variable.

8. collector tube according to claim 1 or 7, characterized in that the heat transfer medium (4, 5) through the interior of the Innenrohrelement- elements (6, 6a) can be supplied and on the outside of the inner tube member (6, 6a) can be discharged.

9. Collector tube according to one of claims 1, 7 or 8, characterized in that the inner tube element (6, 6a) as a double-walled tube (6,

6a) is formed, in which a medium (7, 7a) is included, which causes the temperature-dependent variable thermal conductivity.

10. collector tube according to claim 9, characterized in that the variable thermal conductivity is caused by evaporation of the medium (7, 7a) during heating.

11. The collector tube according to claim 10, characterized in that in the double-walled tube (6, 6a) a substance (37) is present, which the evaporation of the medium (7, 7a) below the boiling point of the medium

(7, 7a) substantially prevented.

12. The collector tube according to claim 11, characterized in that the substance (37) has a higher boiling point than the medium (7, 7a) and / or a lower specific gravity than the medium (7, 7a) and / or not with the medium (7, 7a) is miscible.

13. collector tube according to claim 7 or 8, characterized in that the inner tube member (6, 6a) is double-walled and having parts (32, 32a) with shape memory, which depends on the temperature the thermal conductivity of the inner tube element (6, 6a) is changed by the formation of thermal bridges.

14. Collector tube according to claim 1 or 7, characterized in that the inner tube element (6, 6a) consists of a material which changes its thermal conductivity with a temperature-induced change in the molecular structure.

15. Collector tube according to claim 1 or 7, characterized in that the inner tube element (6) as a double-walled tube (6) is formed, wherein the outer tube is provided on the inside with a selective coating (23), which at higher Temperatures of the light emission (25) is used and in which the inner tube is provided on the outside with a selective coating (24), which serves the light absorption.

16. Collector tube according to one of the preceding claims, characterized in that the inner tube element (6, 6a; 49, 51, 53) is arranged eccentrically to the absorber tube (1), preferably in the direction of lichtein- radungsabge side facing.

17. Collector tube according to claim 16, characterized by means which make the eccentricity of the inner tube member (6, 6a, 49, 51, 53) adjustable.

18. Collector tube according to one of the preceding claims, characterized in that devices are provided which shade the collector tube at least partially.

19. Collector tube according to claim 18, characterized in that the shading is effected by reflection of the incident light.

20. Distribution segment for at least one collector tube, which is configured in particular according to one of the preceding claims, comprising: at least a first opening (4e) for supplying a heat transfer medium into the at least one collector tube, at least one second opening (4d) for discharging the heat transfer medium of the at least one collector tube, a channel (4b) for supplying the heat transfer medium from outside the at least one collector tube into the at least one collector tube, a channel (4c) for discharging the heat transfer medium from the

Collector tube to the outside of at least one collector tube, wherein the feed channel (4b) and the discharge channel (4c) are arranged such that the distributor segment with at least one other similar distribution segment in a heat transfer medium circuit is directly verkoppelbar.

21. distributor segment according to claim 20, characterized in that it is made of plastic.

Distributor segment according to claim 20 or 21, characterized in that the first opening (4e) and the second opening (4d) are arranged to communicate with the eccentric tubes (6, 6a) of a collector tube (1, 2) according to a of claims 1 to 19 are connectable.

23. Distributor segment according to one of claims 20 to 22, characterized in that provisions (16) for thermal insulation of the heat transfer medium.

24. distributor segment according to one of claims 20 to 23, characterized in that it is in one piece.

25. distributor segment according to one of claims 20 to 24, characterized in that it comprises means for fixing the collector tube.

26. Distributor segment according to one of claims 20 to 25, characterized in that it comprises means (20, 21) for coupling a plurality of distributor segments to each other.

27. distributor segment according to one of claims 20 to 26, characterized in that it comprises means for fixing a Mahrzahl of distri lersegmenten together.

28 distributor segment according to one of claims 20 to 27, characterized in that it comprises a channel (15) for the realization of a Tichelmann interconnection of a plurality of collector tubes.

29. distributor segment according to one of claims 20 to 28, characterized in that seals (17b) are present between two distributor segments and / or at one end of a distributor segment.

30. Distributor segment according to claim 29, characterized in that the seals (17a) are conical.

31. distributor segment according to one of claims 20 to 30, characterized in that the distributor segment can be provided with a veneer.

32. distributor segment according to one of claims 20 to 31, characterized in that valve means (22) is provided, via which the heat transfer medium (4, 4a) can be cooled by means of a separate cooler.

33. Distributor segment according to one of claims 20 to 32, characterized in that it has holding means for a fastening device of the distributor segment.

34. Tubular collector with at least one collector tube according to one of claims 1 to 19.

35. Tubular collector according to claim 34 with at least one distributor segment according to one of claims 20 to 33.

36. tube collector according to claim 34 or 35 with a connection option to a drain-back system.