Title of Invention

"A GLASS LAMINATED PARABOLIC TROUGH REFLECTORS AND PROCESS OF MANUFACTURE THEREOF"

Abstract

This invention relates to a glass laminated parabolic trough reflector characterized in:- a laminated glass sheets wherein the glass sheets comprises a front moulded glass sheet (9) of parabolic shape having thickness of for example 2 mm and a gear moulded glass sheet (14) identical to said front moulded glass sheet; the convex unit of the front moulded glass sheet is provided with a silver reflective coating (10) and two protective layers (11, 12} of copper; the glass sheets are disposed with a polyvinyl butyral film (13) there between and the convex side of the rear moulded glass sheet is provided with an enamel coating. Further according to this invention there is provided a method of manufacture of glass laminated parabolic trough reflector comprising steps of: a. providing silver reflective coating on the convex side of a first parabolic shaped moulded glass sheet for example of 2 mm thickness followed by coating with two layers of copper; laminating the coated moulded glass thus obtained by step (a) with second identical moulded glass sheet for example of 2 mm thickness by fusing a polyvinyl film between the rear side of the coated first moulded glass sheet as obtained by a step (a) and the front side of the said second moulded glass sheet by subjecting the assembly to heating between 140-150°C in a vacuum chamber thereby achieving hermetic sealing without any air/humidity pockets in between the laminated glass sheets followed by an enamel coating on the convex side of the said rear moulded glass sheet obtaining the desired glass laminated parabolic trough reflector. (Fig: 2)

Full Text

FIELD OF INVENTION This invention relates to glass laminated parabolic trough reflectors and process of manufacture thereof. The parabolic trough reflectors find applications in process heat and solar thermal power generation. PRIOR ART Parabolic trough reflectors/collectors are solar devices that concentrate solar radiations on to the focal line of the mirror. The device converts direct solar radiation into thermal energy and is ideal for working in the 150°C- 400°C temperature range. A parabolic trough reflector is basically made up a parabolic trough shaped mirror which is silver polished on the convex side of parabola and which reflects direct solar radiation, concentrating it on a receiver tube located in the focal line of the parabola. This concentrated radiation heats the fluid that circulates through the tube thus transforming the solar radiation into thermal energy. Conventional parabolic trough reflectors (fig.l) comprise of a moulded glass sheet (1) generally of 4mm thickness having a silver reflective surface (2) on its convex side. This silver surface is protected by two copper layers (3,4). The said copper layers are protected by two synthetic material layers (5,6) which are further protected by two enamel paint layers (7,8). Such a parabolic trough reflector concentrates solar radiations on a heat receiver tube located on the focal line of the parabola. Such concentrated heat radiations heat the fluid that circulates through the heat transfer tube, thus transforming solar radiations into thermal energy. A disadvantage of the above parabolic trough reflectors is these are breakable in nature. The broken pieces of the parabolic mirror fall apart from the supporting plate and fall on the lower half of glass surface of the parabolic trough reflector (PTR) and damage it. These broken pieces sometimes fall on the glass surface of Heat Collection Element/absorber tube and cause damage to it, which in turn results in loss of solar heat. The breakage of the parabolic trough reflectors is generally caused by thermal stress, high wind, vibrations during earthquake, repeated hitting by peacocks by their beaks, after their seeing their image in mirror and impact on account of solid objects during cleaning. Another disadvantage of the above type of mirrors is that the silver reflecting surface on the convex side of the parabola gets peeled-off over a period of time due to ingress of moisture through the scratch points on the silver polished surface of the mirror. Still another disadvantage of the above-type of mirrors is that during transportation or mounting of the reflectors, scratches occur on the reflective surface of mirror which ultimately dead to peeling of the polish due to ingress of moisture through the scratches thus caused. Further drawback of the above type of PTR is that the glass generally used in these PTRs is a naturally cooled glass which is more fragile due to invisible micro-cracks. US Patent No. 4,297,003 discloses a solar collector module comprising an extended width parabolic trough collector supported from pylons. The collector is formed by a center module and two wing modules which are joined together along abutting edges by connecting means. A drawback of the above patent is that the parabolic trough collector comprises of a single glass mirror and has therefore same disadvantages as described above. US Patent No. 4,427,838 discloses a high concentration solar energy reflector which collects direct solar radiation as well as diffused solar radiation. A reflector focuses direct radiation on to a first collector and reflects a substantial portion of the diffused radiation on to a second collector positioned near the focus of the reflector. However, the above reflector is also made of single glass reflecting surface and is therefore attended to with the disadvantages described for conventional reflectors. US Patent No. 3,985,119 discloses a solar energy collector system providing a mechanically oriented parabolic trough direct radiation collector having along the focal line a portion of a first fluid conduit system and outside the focal line, a portion of a second fluid conduit system. A second collector system is provided to conserve heat at the fluid conduit systems and a glass-front enclosure is provided over the parabolic trough collector. However, the above parabolic trough collector is based on a single glass reflecting surface which is vulnerable to breakage due to thermal stresses, vibrations, unintentional hits or hits by beaks of peacocks etc. leading to the disadvantages as described above. OBJECTS OF THE PRESENT INVENTION An object of the present invention is to propose a glass laminated parabolic trough reflector which is non-breakable. Another object of the present invention is to propose a glass laminated parabolic trough reflector wherein reflective surface comprises two glass surfaces which are laminated together with polyvinyl butyral film in between. Such lamination enhances strength of the glass surface by 2 to 3 times and does not allow the cracked pieces to fall apart. The lamination works as a damper to vibrations of impact. This immmizes the breakage of Heat Collection Element (HCE) and reflectors which is caused in conventional parabolic trough reflectors/collectors by falling pieces from the broken glass surface of the parabolic trough reflector. Still another object of the present invention is to propose a glass Laminated parabolic trough reflector which has 2-3% more efficiency than the conventional parabolic trough reflectors. Further object of the present invention is to propose a glass laminated parabolic trough reflector wherein the drawback of peeling off/scratching of polished surface is overcome by the laminated of two glass surfaces with a polyvinyl butyral film in between. STATEMENT OF INVENTION According to this invention there is provided a glass laminated parabolic trough reflector characterized in:- a laminated glass sheets wherein the glass sheets comprises a front moulded glass sheet (9) of parabolic shape having thickness of 1-2 mm and a rear moulded glass sheet (14) identical to said front moulded glass sheet having thickness 2-3 mm; the convex unit of the front moulded glass sheet is provided with a silver reflective coating (10) and two protective layers (11, 12) of copper; the glass sheets are disposed with a polyvinyl butyral film (13) there between and the convex side of the rear moulded glass sheet is provided with a conventional enamel coating. Further according to this invention there is provided a method of manufacture of glass laminated parabolic trough reflector comprising the steps of: a. providing silver reflective coating on the convex side of a first parabolic shaped moulded glass sheet of 1-2 mm thickness followed by coating with two layers of copper; b. laminating the coated moulded glass thus obtained by step (a) with second identical moulded glass sheet of 2-3 mm thickness by fusing a polyvinyl film between the rear side of the coated first moulded glass sheet as obtained by a step (a) and the front side of the said second moulded glass sheet by subjecting the assembly to heating between 140-150°C in a vacuum chamber thereby achieving hermetic sealing without any air/ humidity pockets in between the laminated glass sheets followed by a conventional enamel coating on the convex side of the said rear moulded glass sheet obtaining the desired glass laminated parabolic trough reflector. DESCRITPION OF FIGURES The invention is illustrated with accompanying drawings which are intended to illustrate an embodiment of the present invention. These drawings are not intended to be taken restrictively to imply any limitation on the scope of the present invention. In the accompanying drawings: - Fig. 1:- shows the conventional parabolic trough reflector/collector; Fig.2:-shows the Glass Laminated Parabolic Trough Reflector of the present invention. DESCRIPTION OF INVENTION W.R.T. DRAWINGS Referring to fig.2, the glass laminated parabolic reflector of present invention comprises of a parabolic shaped front moulded glass sheet (9). This front glass sheet may be of thickness 2mm (as shown in fig.2) preferably 1mm {as shown fig. 3). The convex side of the said front glass sheet is polished with silver reflective coating (10). This silver coating is protected by two copper layers (11,12). A rear moulded glass sheet (14) is provided which is identical in shape to the said front moulded glass sheet. The thickness of the rear glass sheet is 2mm if the thickness of front glass sheet is taken as 2mm. Preferably the thickness of said front glass sheet is 1mm and the thickness of said rear glass sheet is 3mm. A polyvinyl butyral film (PVB) (13) is fused between the front curved glass surface of the said rear moulded glass sheet and the rear side of the said front moulded glass sheet after being coated as above. The arrangement is heated in a vacuum chamber at temperature between 140-150°C which melts the PVB film and hermetically seals the said rear moulded glass sheet with the said coated front moulded glass sheet. This step eliminates any humidity/air pockets. This assembly of laminated glass sheets is given a further protective enamel coating (15) on the convex side of the said rear moulded glass sheet. Method of Manufacture The glass laminated parabolic trough reflectors of the present invention are prepared by the process comprising following steps: (a) 2 Nos. of identical glass sheets having thickness of 2mm each, preferably front glass sheet of 1mm thickness and rear glass sheet of 3mm thickness, are sagged as per design on the die, in a temperature controlled furnace gradually upto the sagging temperature of the glass sheets in one go; (b) After proper sagging of both the glass sheets, these are cooled down gradually or choosing prescribed heat strengthing/toughning of glass sheet, method, upto the ambient temperature; (c) Both the moulded/sagged glass sheets are cleaned and one glass sheet on its convex side is silver coated and then two layers of copper protective surfaces are coated over it; (d) Poly vinyl Butyral (PVB) film is fused in between both the curved glass sheets obtained by step (c) in a vacuum chamber at temperature between 140-150°C, so that the laminated glass sheets get hermatically sealed, ensuring no humidity or air pockets between the two glass sheets. It is to be understood that the glass laminated parabolic trough reflectors and process of manufacture thereof, as per the present invention is susceptible to modifications, changes and adaptations by those skilled in the art. Such variant embodiments are intended to be within the scope of the present invention, which is further set forth under the following claims: WE CLAIM: 1. A glass laminated parabolic trough reflector characterized in:- a laminated glass sheets wherein the glass sheets comprises a front moulded glass sheet (9) of parabolic shape having thickness of 1-2 mm and a rear moulded glass sheet (14) identical to said front moulded glass sheet having thickness 2-3 mm; the convex unit of the front moulded glass sheet is provided with a silver reflective coating (10) and two protective layers (11, 12) of copper; the glass sheets are disposed with a polyvinyl butyral film (13) there between and the convex side of the rear moulded glass sheet is provided with a conventional enamel coating. 2. A glass laminated parabolic trough reflector as claimed in claim 1, wherein the said front moulded glass sheet has thickness preferably of 1 mm. 3. A glass laminated parabolic trough reflector as claimed in claim 1, wherein said rear moulded glass sheet has thickness of preferably 3 mm. 4. A method of manufacture of glass laminated parabolic trough reflector as claimed in claim 1, comprising the steps of: a. providing silver reflective coating on the convex side of a first parabolic shaped moulded glass sheet of 1-2 mm thickness followed by coating with two layers of copper; b. laminating the coated moulded glass thus obtained by step (a) with second identical moulded glass sheet of 2-3 mm thickness by fusing a polyvinyl film between the rear side of the coated first moulded glass sheet as obtained by a step (a) and the front side of the said second moulded glass sheet by subjecting the assembly to heating between 140-150°C in a vacuum chamber thereby achieving hermetic sealing without any air/humidity pockets in between the laminated glass sheets followed by a conventional enamel coating on the convex side of the said rear moulded glass sheet obtaining the desired glass laminated parabolic trough reflector.

Documents:

1140-del-2004-abstract.pdf

1140-DEL-2004-Claims-(06-03-2012).pdf

1140-del-2004-claims-(cancelled).pdf

1140-del-2004-claims.pdf

1140-del-2004-complete specification(granted).pdf

1140-DEL-2004-Correspondence Others-(06-03-2012).pdf

1140-del-2004-correspondence-others.pdf

1140-del-2004-correspondence-po.pdf

1140-del-2004-description (complete).pdf

1140-del-2004-drawings.pdf

1140-del-2004-form-1.pdf

1140-del-2004-form-19.pdf

1140-del-2004-form-2.pdf

1140-del-2004-form-3.pdf

1140-del-2004-gpa.pdf

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