Solar collector and method for producing a light-absorbing surface

Abstract

A solar collector is provided that has a base material and a nanostructured layer integrated into the base material so as to form a light-absorbing surface. The nanostructured layer has nanoparticles of an inorganic material.

Claims

1. A solar collector having a light-absorbing surface comprising: a base material having a surface; and a nanostructured layer that is integrated in a total area of the surface of the base material thereby forming the light-absorbing surface, wherein the nanostructured layer has nanoparticles of an inorganic material, and wherein the nanostructured layer additionally includes a flux, a binder and a thixotropic agent.

2. The solar collector according to claim 1, wherein the inorganic material of the nanoparticles has a greater degree of heat absorption than the base material.

3. The solar collector according to claim 1, wherein inorganic material comprises titanium and/or at least one titanium compound.

4. The solar collector according to claim 1, wherein the base material comprises aluminum, metal, or glass.

5. A method for producing a light-absorbing surface, the method comprising: providing a base material having a surface; coating the surface with a layer of nanoparticles of an inorganic material; and heating the surface so that the layer of nanoparticles forms a nanostructured layer that is integrated in the surface in order to form the light-absorbing surface, wherein the layer of nanoparticles additionally includes a flux, a binder, and a thixotropic agent.

6. The method according to claim 5; wherein the layer of nanoparticles is sprayed onto the surface.

7. The method according to claim 5, wherein the heating of the surface is done via a soldering process.

8. The method according to claim 5, wherein the base material includes aluminum, and the inorganic material comprises titanium and/or at least one titanium compound.

9. The method according to claim 5, wherein the layer of nanoparticles comprises titanium dioxide nanoparticles.

10. The method according to claim 5, wherein the layer of nanoparticles comprises a controlled atmosphere brazing flux, a nano titanium dioxide suspension, a polyurethane binder suspension, a polyurethane thickener suspension, and fully deionized water.

11. The method according to claim 10, wherein the layer of nanoparticles is composed of 25-40% CAB flux, 10-20% nano titanium dioxide suspension, 5-20% polyurethane binder suspension, 1-10% polyurethane thickener suspension, and 30-45% fully deionized water.

12. The solar collector according to claim 1, wherein the layer of nanoparticles comprises a controlled atmosphere brazing flux, a nano titanium dioxide suspension, a polyurethane binder suspension, a polyurethane thickener suspension, and fully deionized water.

13. The solar collector according to claim 12, wherein the layer of nanoparticles is composed of 25-40% CAB flux, 10-20% nano titanium dioxide suspension, 5-20% polyurethane binder suspension, 1-10% polyurethane thickener suspension, and 30-45% fully deionized water.

14. The solar collector according to claim 13, wherein the layer of nanoparticles is composed of 32% CAB flux, 15% nano titanium dioxide suspension, 12% polyurethane binder suspension, 5% polyurethane thickener suspension, and 36% fully deionized water.

15. The method according to claim 11, wherein the layer of nanoparticles is composed of 32% CAB flux, 15% nano titanium dioxide suspension, 12% polyurethane binder suspension, 5% polyurethane thickener suspension, and 36% fully deionized water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 is a schematic representation of a solar collector according to an embodiment of the invention; and

(3) FIG. 2 is a flow chart of a method according to an embodiment of the invention.

DETAILED DESCRIPTION

(4) In the following description of preferred exemplary embodiments of the present invention, like or similar reference characters are used for the elements that are shown in the different drawings and have similar effects, with a repeated description of these elements being omitted.

(5) FIG. 1 shows a schematic representation of a solar collector having a base material 101 and a light-absorbing surface 103, according to an exemplary embodiment of the present invention. The light-absorbing surface 103 is integrated in the base material. The light-absorbing surface is nanostructured. Consequently, nanoparticles of an inorganic material, for example of a metal, can be embedded in the surface of the material 101 over the entire area.

(6) The solar collector can be implemented as a thin-walled heat exchanger in which aluminum is used as the base material 101.

(7) Titanium compounds are suitable as nanoparticles. Thus, black titanium compounds have the highest degree of absorption as absorbers in comparison to other materials. Thus, Ti.sub.2O.sub.2N has the values A.sub.=0.95, T.sub.=0, R.sub.=0.05 in the visible range, and has the values A.sub.=0.05, T.sub.=0, R.sub.=0.95 in the infrared range. In comparison, black nickel has the values A.sub.=0.88, T.sub.=0, R.sub.=0.12 in the visible range and the values A.sub.=0.07, T.sub.=0, R.sub.=0.93 in the infrared range, black chrome has the values A.sub.=0.87, T.sub.=0, R.sub.=0.13 in the visible range and the values A.sub.=0.09, T.sub.=0, R.sub.=0.91 in the infrared range, and aluminum grating has the values A.sub.=0.70, T.sub.=0, R.sub.=0.30 in the visible range and the values A.sub.=0.07, T.sub.=0, R.sub.=0.93 in the infrared range.

(8) FIG. 2 shows a flowchart of a method for producing a light-absorbing surface according to an exemplary embodiment of the present invention. The first step 201 provides a base material having a surface. This can be an aluminum heat exchanger. The surface can be the surface that later on is intended as an absorption surface, for example for solar radiation. Next, in a step 203, a coating of the surface with a layer of nanoparticles of an inorganic material takes place. To this end, a solution that includes the nanoparticles can be applied to the surface, for example. In order to integrate the nanoparticles into the surface, a heating of the surface takes place in a step 205. In this way, the layer of nanoparticles can interact with the surface and form a nanostructured, light-absorbing surface. The heating can take place in a brazing process.

(9) In this way, a strongly light-absorbing coating based on titanium and/or titanium compounds need not be applied to the surface post-production, for example, but instead can be generated in situ in the uppermost layers of the aluminum base material during the production (soldering) of the aluminum heat exchanger. The light absorption thereby takes place directly in the uppermost aluminum layers themselves, and is thus transferred faster and more efficiently to a coolant.

(10) According to an exemplary embodiment, in order to produce a light-absorbing aluminum surface, the aluminum heat exchanger for solar engineering can be sprayed, prior to the soldering process, with a suspension of (Nocolok) CAB flux to which a certain percentage of titanium dioxide nanoparticles has been added. In addition, this suspension contains a binder and a thixotropic agent in order to fix the solids of the suspension to the surface until the reaction temperature is reached in the CAB soldering furnace.

(11) When the reaction temperature is reached, a chemical reaction occurs with the aluminum surface, the nitrogen atmosphere, and the nano titanium dioxide particles, with black titanium compounds then being produced that are then incorporated into the melting aluminum surface with the (Nocolok) flux.

(12) In this way, a very intensely black and matte inorganic surface can be produced that strongly absorbs light.

(13) Preferably, 11-20% titanium nanoparticles relative to the solids are added to the (Nocolok) CAB flux.

(14) A preferred formula for aluminum surfaces with solder plating comprises 32.0% CAB flux, 15.0% nano titanium dioxide suspension, 12.0% polyurethane binder suspension, 5.0% polyurethane thickener suspension, and 36.0% fully deionized water.

(15) Heating of the surface can take place during brazing of individual parts for heat exchangers, so no additional step for heating is necessary. Aluminum or aluminum alloys can be used as the base material for the heat exchangers. A suitable soldering process is so-called Nocolok soldering, which uses a flux based on potassium fluoroaluminates with the empirical formula K.sub.1-3AlF.sub.4-8 that is commercially available under the name Nocolok. This Nocolok flux remains on the surface after soldering, and can coat it with a crystalline layer.

(16) The light-absorbing surface can include elementary Ti and Ti in a bonding state, for example TiO and/or nitride, as a component. In addition, the surface can include moieties in tetravalent form and compounds such as K.sub.2TiF.sub.6. It is possible here that Ti is not detectable in the surface region, but instead is only detectable after 60 min argon ion etching, corresponding to a removal of approximately 280 nm SiO.sub.2 equivalent layer thickness.

(17) The exemplary embodiments described are chosen merely by way of example and may be combined with one another.

(18) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.