FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
1. Title of the invention
A SOLAR HEATING SYSTEM
2. Applicants)
Name Nationality Address
TATA CHEMICALS LTD INDIA BOMBAY HOUSE, 24 HOMI MODI STREET,
MUMBAI-400001
3. Preamble to the description
COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it is
to be performed.

The invention relates to solar water heaters. In particular, the invention relates to solar water heating systems having a coating of nano particles.
BACKGROUND
Global warming and the impact of global energy requirements have assumed significant importance in the global economy. The last decade has witnessed countries introduce laws making use of solar energy mandatory for certain applications. Solar heating is particularly favored as a means for heating water required for domestic and industrial purposes.
Solar water heating systems comprise of a substrate that is used to absorb the incident solar radiation and pass on the heat absorbed to water flowing in pipes thermally connected to the substrate. A flat plate is the most common type of solar thermal collector, and is usually used as a solar hot water panel to generate hot water. A weatherproofed, insulated box containing a black metal absorber sheet with built in pipes is placed in the path of sunlight. Solar energy heats up water in the pipes carising it to circulate through the system by natural convection, or using external power. The absorber sheet may for example include a copper sheet coated with copper chromate. With increasing copper prices cost efficiency of solar water heaters is also adversely affected. SUMMARY
The invention relates to a solar heating system comprising a substrate capable of absorbing incident radiation, at least one fluid conduit thermally connected to the
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substrate, and a coating of metal nano particles on the substrate; at least some of the nano particles having an anisotropic shape and capable of absorption of solar radiation.
The invention also relates to a solar heating system comprising a substrate capable of absorbing incident radiation, at least one fluid conduit thermally connected to the substrate, and a coating of metal nano particles on the substrate; at least some of the nano particles having a triangular shape and capable of absorption of solar radiation.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The accompanying drawings illustrate the preferred embodiments of the invention and together with the following detailed description serve to explain the principles of the invention.
FIG. 1 is an optical photograph of a copper plate before the coating (A) and after a coating (B) in accordance with an embodiment of the invention.
FIG. 2 illustrates the results of measurements of temperature of the copper substrate before and after coating of a sample of silver nano triangles in sunlight, in accordance with an embodiment.
FIG. 3 illustrates the results of measurements of temperature of the copper substrate before and after coating of a sample of gold nano triangles in sunlight, in accordance with an embodiment.
DESCRIPTION OF PREFERRED EMBODIMENTS
To promote an understanding of the principles of the invention, reference will be made to the embodiment illustrated in the drawing and specific language will be used to
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describe the same. It will nevertheless be understood that no limitation of scope of the invention is thereby intended, such alterations and further modifications in the illustrated system and such further applications of the principles of the inventions as illustrated therein being contemplated as would normally occur to one skilled in art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
A solar water heating system is described comprising an absorber substrate with at least one fluid conduit thermally connected to the substrate. The absorber substrate is provided with a coating of nano metal particles. The nano particles preferably have an anisotropic shape and are capable of absorption of solar radiation. The nano particles are also preferably of a triangular shape and are capable of absorption of solar radiation.
The absorber substrate may be for any solar water heating system including flat plate systems; evacuated tube systems or parabolic systems. The absorber substrate may be metal, glass or polymer. In accordance with an embodiment, the substrate is a copper plate.
The absorber substrate may have one or more fluid conduits thermally connected to the substrate such that heat absorbed by the substrate is conveyed to the fluid in the conduits. In accordance with an embodiment, the fluid conduits are copper and the fluid is water,
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The size of the metal nano particles coated on the substrate may be of any size. The nano particles may be in the range of 2 nm to 500 nm and sometimes even larger. The size of the metal nano particles coated on the substrate is preferably in the range of 10 to 500 nm.
The metal nano particles may be any of silver or gold.
The metal nano particles are preferably anisotropic in shape. The metal nano particles may be prepared by any known processes for the preparation of anisotropic shaped nano particles. Anisotropic shaped particles are found to exhibit greater efficiency in solar water heating applications. Anisotropic particles include prisms, triangular and generally refer to particles having properties that are directionally oriented.
In accordance with an aspect the metal nano particles are preferably triangular in shape. The metal nano particles may be prepared by any known process for the preparation of triangular shaped nano particles. By way of specific example, a method of preparation of silver nano particles in an aqueous medium is described.
The process of synthesizing triangular shaped silver nano particles comprises preparing a silver nitrate solution, more specifically 100 mL of 0.008 M Silver nitrate solution is prepared using distilled water. A second solution of chitosan is prepared; more specifically a chitosan solution of 1 wt % is prepared in 5 wt % citric acid. A third solution of chitosan is prepared; more specifically a chitosan solution of 1 wt % is prepared in 5 wt % Ascorbic acid. 1 mL of the second solution is added to the 100 mL silver nitrate solution and stirred for five minutes at room temperature. To this solution
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200 to l000 µl of the third solution is added and the reaction mixture is stirred for 30 minutes. Silver nanoparticles are formed in the solution. The UV-visible spectroscopy illustrates the triangular shaped silver nano particles.
By way of specific example, a method of preparation of gold nano particles in an aqueous medium is described.
The process of synthesizing triangular shaped gold nano particles comprises of preparing a chloroauric acid solution, more specifically preparing 100ml of 10-3 M chloroauric acid solution in distilled water. A lemon grass extract was prepared in 500 mL distilled water. 50 gm of lemon grass was washed with distilled water, dried in air at room temperature and cut into small pieces. To the cut pieces of lemon grass 500 mL of distilled water was added and heated in autoclave at ~ 120 °C at 20 psi pressure for 20 min. The solution so obtained was cooled solution to room temperature and filtered using filter paper.
To l0mL of chloroauric acid solution 2mL of lemon grass extract was added and kept at room temperature for 12 to 16 hours. Chloroaurate ions are reduced by lemon grass extract to form gold nano triangles in the solution. In accordance with an aspect the amount of lemon grass extract solution can be varied from 0.5 mL to 2.5 mL to increase the number of triangles in the solution and hence the NIR absorption. The gold and silver nano particles so prepared may include some nano particles having shapes other than triangular.
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By way of specific example, in the example of preparation of gold nano particles described above, some spherical nano particles may also be formed along with the triangular nano particles. The presence and amount of spherical gold nano particles varies with the amount of lemon grass extract used for the reduction. However, the amount of such other shaped particles nano particles is preferably under 30 percent of the total amount of nano particles.
Method of Coating:
The nano particles may be applied to a substrate by any conventional methodology. In accordance with an embodiment, one method of coating the metal nano particles on to a substrate is provided. By way of specific example, a coating of silver nano particles is provided on an absorber substrate made of copper. 20 mL of silver nano particles solution synthesized was used for the coating. The silver nano particles were coated on a 40 sq. cm area of copper substrate. The copper substrate is heated to approximately 170 °C. The silver nano particles solution was spray dried on the hot copper substrate at the flow rate of 2 mL/min. The solvent was evaporated and the nano particles were coated on the copper surface.
By way of a specific example 25 to 50mg of silver nanoparticles are required to coat 100 sq. cm area of copper substrate. By way of specific example 5 to 10 mg of gold nano particles are required to coat l000sq. cm are of copper substrate.
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INDUSTRIAL APPLICAPABILITY
The metal nano particles coated on the absorber substrate absorb in an enhanced manner the incident solar radiation. The anisotropic metal nano particles, particularly the triangular shaped metal nano particles, absorb more heat in the form of near infra red radiations and hence the temperature of fluid flowing through the fluid conduit thermally connected to the absorber substrate also increases. The increase in heat absorption allows a smaller size collector and particularly a smaller size absorber substrate such as copper. A smaller size absorber substrate reduces cost of the solar water heating system. The increase in heat absorption is also useful for space saving and higher demand applications.
By way of a specific example the temperature of the copper substrate before and after coating of a sample of silver nano triangles was measured in sunlight. Figure 2 tabulates the result of measurements that were carried out at Pune, India on 29th February 2008 at 2.50pm 1ST. As can be seen from the figure there has been a significant increase in the temperature of the absorber substrate after it has been coated with triangular silver nanoparticles.
By way of a specific example the temperature of the copper substrate before and after coating of a sample of gold nano triangles was measured in sunlight. Results of measurements that were carried out at Pune, India on 30th November 2007 at 12.55 pm 1ST are tabulated in Figure 3. As can be seen from the figure there has been a significant
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increase in the temperature of the absorber substrate after it has been coated with triangular gold nanoparticles.

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We claim:
1. A solar heating system comprising:
a substrate capable of absorbing incident radiation; at least one fluid conduit thermally connected to the substrate; and a coating of metal nano particles on the substrate; at least some of the nano particles having an anisotropic shape and capable of absorption of solar radiation.
2. A solar heating system comprising:
a substrate capable of absorbing incident radiation; at least one fluid conduit thermally connected to the substrate; and a coating of metal nano particles on the substrate; at least some of the nano particles having a triangular shape and capable of absorption of solar radiation.
3. A solar heating system as claimed in claim 1 or 2 wherein the substrate is copper.
4. A solar heating system as claimed in claim 1 or 2 wherein the substrate is glass or polymer.
5. A solar heating system as claimed in claim 1 or 2 wherein the metal nano particles are silver or gold.
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6. A solar heating system as claimed in claim 5 wherein the process of preparing silver nano particles comprises reducing a silver precursor in the presence of a stabilising agent to obtain capped silver nano particles.
7. A solar heating system as claimed in claim 5 wherein the process of preparing gold nano particles comprises preparing a chloroauric acid solution; preparing a lemon grass extract solution and adding the lemon grass extract solution to the chloroauric acid solution.
8. A solar heating system as claimed in claim 1 or 2 wherein the size of the nano particles is in the range of 2 to 500 nm and preferably in the range of 10 to 500 nm.
9. A method of manufacturing a solar heating system comprising a substrate capable
of absorbing incident radiation; at least one fluid conduit thermally connected to
the substrate; the method comprising:
coating on the substrate metal nano particles, at least some of the nano particles having an anisotropic shape and capable of absorption of solar radiation.
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10. A method as claimed in claim 9 wherein anisotropic particles includes triangular nano particles.
11. A method as claimed in claim 9 or 10 wherein the coating is applied by spray deposition of the nano particle solution on a heated substrate.
12. A solar heating system substantially as herein described with reference to and as illustrated by the accompanying drawings.
13. A method of manufacturing a solar heating system substantially as herein described with reference to and as illustrated by the accompanying drawings.
(Essenese Obhan Of Obhan & Associates Agent for the Applicant
Dated this 30th day of October 2008
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