Patent Application
20110162641
The present invention relates to an absorber, in particular for a solar collector, and a method for manufacturing the same.
Solar collectors comprise a housing having an upper cover, preferably a glass pane, and a lower cover, preferably made of a sheet metal, and an absorber, which is disposed in the housing and is designed for converting sunlight and solar energy into heat The absorber includes an absorber plate and pipes in the form of lines for a heat transfer medium for transporting energy by carrying heat.
A solar collector of this kind is described in DE 20 2006 003 399, which discloses a so-called hybrid collector having specially designed heat-conducting plates.
Furthermore, a wide variety of absorbers for solar collectors are known from the prior art. These known absorbers usually include absorber plates, which are coated on the side that is oriented toward the sun and below which pipes are disposed for conveying a fluid, that is to say, a gas or a liquid. The pipes, which are usually made of a heat-conducting metal, in particular copper, are preferably formed as a meander (one pipe) or a so-called harp (several connected pipes).
Different processes are known from the prior art for connecting the copper pipes to the absorber plates.
It was thus attempted to use welded and soldered connections, which however necessitate pipes and absorber plates of the same material for achieving a good connection between them, and leave marks on that visible surface of the absorber plates that is oriented toward the sun. Another disadvantage of such connections is that they become entirely or partially loose as a result of thermal stresses. The loosening of these connections can occur particularly when different materials having variably high expansion coefficients are used.
It has been suggested in DE 20 2006 003 399 to hold the pipes below the absorber plate with the aid of so-called heat-conducting plates. This solution has indeed proved to be useful per se, but it requires the use of additional material and also leaves room for further optimization with respect to heat transfer from the absorber plate to the pipe.
Adhesive bonds between the plates for holding the pipes have also been described in the prior art. But the disadvantage of adhesive bonds is usually that they have a relatively low heat conductance value since the adhesive usually has an insulating effect. An additional known problem is that the bonded joints can be destroyed as a result of the varying thermal expansion of the plates and the pipes embedded therein.
The adhesive bonds known from the prior art also suffer from the shortcoming that even the pipes are glued to the plates, which can result in additional thermal stresses.
On the whole, the heat transfer from the absorber plate to the heat transfer medium via the pipes can still be improved further in the solutions suggested by the prior art described above. Furthermore, the outer side of the absorber must have a flawless appearance.
It is the object of the present invention to solve the two problems last mentioned.
According to the invention, an absorber is provided, which includes an at least partly flat absorber plate, on which at least one metallic pipe, through which a heat transfer medium for carrying heat can flow and which likewise has a partly flat surface resting against the flat surface of the absorber plate, is disposed with the aid of at least one heat-conducting plate.
By virtue of the fact that the absorber plate rests flatly, particularly directly against the pipe/s, an excellent heat transfer is achieved easily between these two elements of the absorber, without impairing the appearance of the absorber in this construction.
The flat surfaces of the at least one pipe and the absorber plate are preferably located parallel to each other.
The invention also provides for a method for manufacturing an absorber, in which the pipe and the heat-conducting plates are combined and the partly flat surface of the metallic pipe is then molded in a non-cutting forming work process on this arrangement consisting of the at least one pipe and the at least one heat-conducting plate.
This method ensures, in a particularly easy and uncomplicated manner, that the heat-conducting plate rests positively against the pipe, while the pipe is flattened in a forming process at least in certain sections or over its entire axial length.
Furthermore, the pipe rests directly against the absorber plate in the forming work step so that a precise contact of these two elements with each other is also ensured easily in a single work process.
By virtue of the fact that the pipes are enclosed over their entire circumference, it is possible to use pipes having a particularly thinner wall thickness, ranging between 0.2 and 0.5 mm, preferably 0.3 mm.
By virtue of the particularly good heat transfer, the length of the pipes can be reduced while maintaining the same effectiveness (which makes it possible to cut down on the material and costs involved).
It is possible to hold the pipes between the heat-conducting plate and the absorber plate for displacement in the longitudinal direction in order to compensate for thermal stresses.
The method of the invention also makes it possible to manufacture an absorber for such a solar collector particularly easily and cost-effectively.
The invention provides for a method in which a heat-conducting plate is connected to an absorber plate such that the round pipe, which is arranged in-between, is provided with a flat surface extending parallel to the absorber plate and the entire circumference of the pipe is in direct contact with the plates. This consequently simplifies the production of the absorber while still achieving the excellent heat transfer cited above.
The heat-conducting plate is preferably glued below the absorber plate. Additional advantageous features are suggested below that are aimed at improving the heat transfer of the adhesive layer.
Thus, the heat transfer of the adhesive bond can be improved by admixing heat-conducting substances, particularly metal splinters or metal fibers, to the adhesive.
It is also feasible to improve the heat transfer by partly arranging metal strips or a heat-conductive paste between the heat-conducting plate and the absorber plate.
Likewise, that surface of the heat-conducting plate that comes in contact with the absorber plate can be disposed at a different level, the heat-conducting plate being provided with portions of direct contact to the absorber plate that alternate with the adhesive portions.
Preferably, a plastic-bonding adhesive is used, which can be rolled on both sides with an adhesive effect, and can be applied to or rolled on individual strips of the heat-conducting plates in the method of the invention.
According to the invention, there is preferably no adhesive between the pipe and the absorber plate or between the heat-conducting plate and the pipe. The advantage of the absence of adhesive in the regions cited above is that the pipe can be displaced freely between the plates in the case of thermal elongation. This prevents stresses and damages of the components involved.
In a preferred embodiment, the heat-conducting plates taper toward the ends. This measure improves heat flow.
For cost reasons, an aluminum material is selected for the absorber plate and the heat-conducting plate in contrast to the commercially available copper pipes.
The non-cutting forming process is very preferably a pressing process, the at least one pipe, the at least one heat-conducting plate and preferably also the absorber plate being inserted together into a compression mold. Alternately, it is also easy and uncomplicated if the non-cutting forming process is a pressure-rolling process.
According to a preferred variant of the method of the invention, (a) at least one channel is initially formed in the at least one heat-conducting plate, (b) the pipe is then inserted into this channel and (c) the arrangement from step b) is covered by the absorber plate, and (d) the arrangement from step c) is then subjected to the forming process. Production as suggested by this method ensures, in particular, that the appearance of the absorber is not impaired by the manufacturing process.
It is advantageous if the channel has a larger diameter than the pipe inserted therein.
Since the copper pipes are enclosed approximately over their entire circumference, they can be designed with a thinner wall thickness considering that the absorber plate and the heat-conducting plate(s) are also used for absorbing pressure. This makes it possible to cut down on the cost of materials.
As a result of optimum heat transfer, the relative pipe length can be reduced, thus leading to further material savings.
The at least one pipe-preferably has the cross-sectional shape of a circle, the circumference of which is partly flattened, the flattened region forming the flat surface, which rests against the absorber plate, and the heat-conducting plates positively bordering the remaining circular outer circumference of the at least one pipe. Alternately, the at least one pipe can have the cross-sectional shape of an oval, the circumference of which is partly flattened, the flattened region forming the flat surface, which rests against the absorber plate, and the heat-conducting plates positively bordering the remaining oval-shaped outer circumference of the at least one pipe.
It is advantageous if strip-shaped sheet-metal pieces are initially cut to length i.e., from a sheet-metal roll for forming the heat-conducting plates, and the channel is then stamped in these sheet-metal pieces, the diameter of the channel being larger than that of the initial pipe.
According to another particularly preferred variant of the method, (a) the cut-to-length heat-conducting plates that are preferably already provided with the channel are rolled or coated with the adhesive of the invention, (b) the heat-conducting plates are inserted into a compression mold, (c) the bent copper pipe (meander or serpentine-shaped) or the copper pipes (harp-shaped) is/are then inserted into the channels of the heat-conducting plates, (d) the absorber plate is then placed on the pipes, and (e) the absorber plate is subsequently pressed onto the pipes using a smooth punch so that the pipes expand in the channels of the heat-conducting plates during the forming process.
In order to ensure particularly good heat transfer, the channels of the heat-conducting plates and the pipe diameter are configured to match each other such that the pipes almost completely fill out the intermediate space remaining finally between the absorber plate and the heat-conducting plate, and the absorber plate and the heat-conducting plate are pressed together.
A plurality of pipes and/or a plurality of heat-conducting plates and the absorber plate are particularly preferably interconnected in accordance with one or more steps of the preceding processes.
The method of the invention also ensures very short production times since preferably only one pressing process is carried out. However, it is also possible to carry out multiple pressing processes.
The channels of the heat-conducting plates and the pipe diameter are preferably configured to match each other such that the pipes almost completely fill out the intermediate space remaining finally between the absorber plate and the heat-conducting plate, and the absorber plate and the heat-conducting plate are pressed together properly.
The bent pipe ends or the pipe ends intended for additional connecting elements are preferably not stamped or flattened, thus allowing for thermal expansion in these regions and the mounting of connecting pipes.
It is likewise advantageous that meander-shaped or harp-shaped pipe structures can be produced easily from the round initial pipes. This would hardly be possible in case of pipes having flattened regions.
Wherever reference is made herein to at least one pipe, absorber plate or heat-conducting plate, this is also understood to include the possibility of designing and arranging a plurality of these elements in the manner described.
A plurality of pipes and/or a plurality of heat-conducting plates and the absorber plate are preferably interconnected in accordance with embodiments of the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
a, b; 9a, b show additional views of portions of the absorber according to the invention.
According to the exemplary embodiment of
Commercially available metal pipes, particularly copper pipes of round cross-section, which can be bent relatively easily and to the ends 5 of which standard connecting elements can be joined, are preferably used as the initial work piece for manufacturing the absorbers. The pipe 3 is held below the absorber plate 2 with the aid of at least one heat-conducting plate, preferably a plurality of straight, profile-like heat-conducting plates 4. According to a particularly preferred embodiment, the heat-conducting plates 4 are each laid out in the form of strips, one strip-shaped heat-conducting plate being preferably assigned to each straight pipe section of the meander in the longitudinal direction, and the pipe ends 6, which are each bent around 180°, not being covered by the heat-conducting plates 4. The advantage of this arrangement is that there is no build-up of stresses in the case of thermal expansion: the pipes 3 are force-locked in such a way between the absorber plate 2 and the heat-conducting plate 4 that they allow an axial displacement. The heat-conducting plates 4 are therefore always shorter than the absorber plate 2 in their longitudinal orientation.
A pipe 3 (referred to as “deformed pipe section”), which is formed during the assembly of the absorber in a non-cutting forming process and which has a flat surface 8a continuously or at least partly over its axial length, is disposed below the absorber plate 2. This flat surface 8a of the pipe 3 is oriented toward the absorber plate 2 and rests directly against a corresponding flat surface 8b of the absorber plate 2. This flat surface 8a of the pipe 3 (which is preferably larger than ⅓ of the pipe circumference) is in direct contact with the absorber plate 2, thereby resulting in optimized direct heat transfer.
The heat-conducting plate 4 is glued to the absorber plate 2 and it encloses the approximately semicircular circumference of the pipe 3. As a result, heat is likewise dissipated from the absorber plate 2 via the pipe 3 to the heat transfer medium such as water, for example. It can be seen clearly that almost the entire circumference of the pipe 3 is in contact with the absorber plate 2 and the heat-conducting plate 4. There is no adhesive present between the pipe and the plates.
A pressure that is higher relative to the wall thickness of the pipe can prevail in the pipe 3 by virtue of the fact that the pipe 3 is enclosed over the entire circumference thereof. As a result, it is possible to provide the pipe wall with a very thin thickness, preferably 0.3 mm, thereby facilitating the deformation process and economizing on the material used.
An aluminum sheet having a thickness of 0.5 mm is preferably used for the absorber plate 2 and the heat-conducting plate 4, it being possible to select a special design for the heat-conducting plate 4 as described below in more detail.
The preferred adhesive bond between the absorber plate 2 and the heat-conducting plate 4 is formed such that it is particularly thin in order to achieve the best possible heat transfer despite the insulating effect of the adhesive. For further improving the heat transfer, it is suggested to admix metal splinters or metal fibers to a commercially available adhesive known per se.
As another alternative, the heat-conducting plate 4, as illustrated in
As an additional option,
The individual process steps for manufacturing the absorber of the invention are explained with reference to
The channel 13, which is provided with an arcuate or semicircular shape, and the diameter of which is clearly larger than that of the pipe 3, is disposed at the center of the heat-conducting plate 4. The lateral arms of the heat-conducting plate 4 are then coated with an adhesive over their entire width or in part. The pipe 3, bent preferably in the form of a meander, is inserted into the channel 13 of the heat-conducting plate, which facilitates production due to the large lateral tolerances.
The pre-formed heat-conducting plate 4, the at least one pipe 3 and the absorber plate 2 are then layered on top of each other in this order, the absorber plate 2 lying on the pipes 3; that is to say, without coming into contact with the adhesive material on the heat-conducting plate 4.
The deformation of the pipe 3 and a gluing process take place in the subsequent pressing process. Here, the pipe 3 is deformed in such a way that it forms a flat contact surface toward the absorber plate 2 and completely fills out the channel 13 of the heat-conducting plate. Furthermore, the pipe ends preferably have a round and not a flattened cross-section in order to enable the mounting of standard connecting elements.
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
