Vacuum tube solar collector with overheating protectionby means of a rotating reflector

Abstract

The aim is to add a device to vacuum-tube solar collectors so as to prevent overheating thereof. FIG. 1 shows an illustration summarizing the invention applied, in this case, to a vacuum-tube collector of the type consisting of a single glass tube ( 1 ) with heat pipe ( 2 ) centred inside the glass tube ( 1 ) and making contact with heat-absorbing fins ( 6 ). The invention is characterized in that the part of the inner wall of the glass tube ( 1 ) which is hidden from the sun incorporates a curved reflector ( 3 ) with a small thickness along the entire length of the glass tube ( 1 ), which reflector is secured by means of various rings ( 4 ) and is able to rotate while being operated by means of a nitinol or bi-metal torsion spring ( 5 ) which is screwed in and makes good thermal contact with the evaporator tube of the heat pipe ( 2 ) so that, when the temperature of the evaporator tube of the heat pipe ( 2 ) increases beyond a certain value, it causes the nitinol spring to change form, rotate and cause rotation of the reflector ( 3 ), protecting the heat-absorbing fins ( 6 ) from the solar radiation and preventing overheating of the collector and the solar installation. Rotation is reversed when the temperature of the evaporator tube ( 2 ) drops, the collector remaining in the normal heat supply condition. This invention is applicable, with certain modifications, to any type of vacuum-tube solar collector according to the accompanying description. Thus not only is overheating prevented in solar installations, but also the collectors are made more efficient due to the reflection of the radiation heat losses of the fins back towards themselves by means of the reflector.

1 . Solar collector of the type of vacuum tubes consisting of two concentric glass tubes( 1  and  14 ) between which vacuum has been made, that transmits the sun's radiant energy to the working fluid by means of a heat transfer tube( 2 ) in thermal contact with the inner glass tube( 14 ) by means of aluminum molded fins( 23 ), characterized by it incorporates a curved reflector( 3 ) of small thickness, located between the two concentric glasses along almost all their length, hidden from the sun, and being of arc less or equal to 180 degrees, and diameter something less that the outer glass( 1 ), and surrounded by rings( 4 ) fixed to the reflector by several tabs( 7 ) or by pressure parts, so that the reflector can rotate between the glasses pushed by a bimetal or nitinol (or any other alloy that changes shape with temperature) torsion spring, coiled around the heat transfer tube( 2 ). The sprig, in turn, is connected with s north magnet( 16 ) located in the inner wall of the inner glass( 14 ), that attracts another south magnet( 17 ), located in the outer wall of the inner glass( 14 ). A temperature increase inside the inner glass( 14 ) rotates the nitinol spring( 5 ) and this, in turn, rotates the reflector( 3 ) due to the magnets. The rotation of the reflector( 3 ) covers the inner glass( 14 ) from the solar radiation, preventing the overheating of the working fluid and it is reversible in function of the temperature of the inner glass( 14 ) so that in a normal situation of the collector supplying heat, the reflector( 3 ) returns to its original position below the inner glass hidden from the solar radiation, by itself in case of using a bimetal of nitinol spring with two memory shapes, or by means of another steel spring( 11 ) in case of a nitinol spring( 5 ) (or any other alloy that changes shape with temperature) of a single shape memory. In addition to the overheating protection, this invention is intended to increase the collector performance when the reflector( 3 ) is located in its normal lower position of supplying heat, below the inner glass( 14 ) reflecting the radiation heat loss of the inner glass( 14 ) towards itself, being optimum the increasing in performance due to the fact that the reflector( 3 ) is not in contact with the glass tube( 1 ), existing a separation, in vacuum, created by the rings( 4 ) interposed between the inner wall of the glass tube( 1 ) and the reflector. 
     
     
         2 . Solar collector according to  claim 1  characterized in that the heat transfer tube is a heat pipe, centered in the inner glass tube( 14 ). 
     
     
         3 . Solar collector according to  claim 1  characterized in that the heat transfer tube is an off center heat pipe and because the bimetal or nitinol spring( 5 ) is coiled and hooked at an axis of a copper or aluminum part( 20 ) with good thermal contact, hold by pressure or welded with the heat pipe( 2 ). 
     
     
         4 . Solar collector according to  claim 1  characterized in that the heat transfer tube is a concentric pipe where the water to be heated flows through. 
     
     
         5 . Solar collector according to  claim 1  characterized in that the heat transfer tube is an “U” shape pipe( 18 ) that runs inside the inner glass( 14 ) in all its length, and which water to be heated flows through, and because the bimetal or nitinol spring( 5 ) is coiled and hooked at an axis of a copper or aluminum part( 19 ) with good thermal contact, hold by pressure or welded with the “U” shape pipe( 2 ). 
     
     
         6 . Solar collector according to  claim 1  characterized in that the heat transfer tube is the inner glass tube( 14 ) itself, that acts as a heat pipe, with a small amount of liquid inside the inner glass tube( 14 ), that evaporates when the temperature increases and ascends through the tube up to its top end, and that protrudes from the outer glass as a heat pipe condenser in contact with the water to be heated, and because nitinol springs and the magnets are secured and rotate freely over the axis of a part hooked by pressure inside the inner tube, immersed in the vapor that ascends along the tube. 
     
     
         7 . Solar collector according to  claim 2  characterized in that the aluminum molded fins( 23 ) are multiple, three or more, with a radial section. The radius of the aluminum fins( 23 ) may be curved or straight, although it is preferable curved, especially when their number is low, six or eight, with the aim of allow a separation between them for a better heat absorption inside the inner tube( 14 ). 
     
     
         8 . Solar collector according to  claims 1  to  7  Characterized in that the reflector incorporates four cylinders( 22 ) with tip, made of iron or a material with high content in iron, that substitutes the surrounding rings and that can rotate freely hold by its tips to the reflector, two of them located at the same height near the end of the outer tube, and the other two also at the same height, but near the opposite end, and that are rotated by the magnetic field through the inner glass( 14 ) of the two magnets( 21 ) with a “V” shape located at the same height as the cylinders, that in turn are rotated by two bimetal or nitinol springs. 
     
     
         9 . Solar collector of the type of a single glass vacuum tube( 1 ) that transmits the sun's radiant energy to the working fluid by means of a heat-absorbing fins( 6 ) in contact with a heat transfer tube( 2 ), characterized by it incorporates a curved reflector( 3 ) of small thickness along the glass tube( 1 ), of arc something less or equal to 180 degrees and diameter something less than the inner wall of the inner glass tube( 1 ), hidden from the sun and surrounded by rings( 4 ), and fixed to it by several tabs( 7 ) or by pressure parts, so that it can be rotated inside the glass tube( 1 ) pushed by a bimetal or nitinol (or any other alloy that changes shape with temperature) torsion spring( 5 ) coiled around the heat pipe( 2 ) with good thermal contact and hooked to the reflector( 3 ) by its long end( 8 ) and to the heat pipe( 2 ) by its short end( 9 ) by a clamp( 10 ) or a pressure ring or welded. A temperature rise of the heat pipe( 2 ) rotates the nitinol spring( 5 ) and this, in turn, rotates the reflector( 3 ). This rotation of the reflector( 3 ) covers the absorbing fins( 6 ) from the solar radiation preventing the overheating of the working fluid, and it is reversible in function of the temperature of the heat pipe( 2 ), so that in a normal situation of the collector supplying heat, the reflector( 3 ) returns to its original position below the absorbing fins hidden from the solar radiation, by itself in case of using a bimetal of nitinol spring with two memory shapes, or by means of another steel spring( 11 ) in case of a nitinol spring( 5 ) (or any other alloy that changes shape with temperature) of a single shape memory. In addition to the overheating protection, this invention is intended to increase the collector performance when the reflector( 3 ) is located in its normal lower position of supplying heat, below the fins( 6 ), reflecting the radiation heat loss of the fins( 6 ) towards itself, being optimum the increasing in performance due to the fact that the reflector( 3 ) is not in contact with the glass tube( 1 ), existing a separation, in vacuum, created by the rings( 4 ) interposed between the inner wall of the glass tube( 1 ) and the reflector. 
     
     
         10 . Solar collector according to  claim 9  Characterized in that the heat transfer tube is a heat pipe. 
     
     
         11 . Solar collector according to  claim 9  Characterized in that the heat transfer tube is a concentric pipe where the water to be heated flows through.