FR2492956A1 - Large-evacuated solar heat collector panel - formed by flat box with glass surfaces and contg. finned tube coated with heat absorbing substance such as black chromium - Google Patents

Abstract

The collector consists of a large, flat and rectangular box sealed to air so a hard vaccum can be maintained in the box, where the top and/or bottom main surfaces of the box are transparent. Inside the box is a U-tube provided with large flat fins, and through which a heat transfer fluid is circulated. The two ends of the U-tube pass through one end wall of the box, which has a main surface of ca. 0.8-1.3 sq. metres. The box contains partitions, which support the U-tube and divide the box into compartments which each have an area of 1/8th to 1/12 th of a aq. metre, and each contain two diametrically-opposed fins fixed to the U-tube. The fins are coated with a substance which selectively absorbs heat. The box withstands a hard vacuum, and the collector is inexpensive.

Description

 Large vacuum solar energy collector.

 The present invention relates to a vacuum solar energy collector, large dimensions allowed by a structure and special materials.

 The vacuum sensors that we know today show two common characteristics - they are in the form of a tube / glass "PYREX" (borosilicate), generally7 and - their dimensions are small: the glass tube (which contains the absorber) has a diameter of 8-10 cm and a length of about 2 m. The active surface per tube is therefore very small, of the order of 1/10 m2, which means that several tubes have to be combined to form a sensor whose total active surface is of the order of 1 m2.

 There are also known sensors with two concentric tubes, the directory space being under vacuum and containing the absorbent surface.

 Naturally, in this case - the number of glass-to-metal welds is numerous, therefore the price of labor is increased, for manufacturing, - the tubes are connected together in series or in parallax, which represents a significant junction piping costs, - the tubes must each be placed in a vacuum in an oven for an hour and a half, at 4000 C. This operation is also very expensive.

 It is easy to see the very high cost of such a sensor, all the more since the "PYREX" tubes are very expensive.

 It should be noted that the two above characteristics of known sensors, which entail many drawbacks, one of the most serious of which is a very high price, are both made necessary by the use of vacuum: - we know in fact that a cylindrical or spherical structure withstands the enormous pressure constraints caused by a high internal vacuum much better than a flat structure for example; and - it is also known that said pressure stresses are in relation to the surface exposed to the vacuum, which therefore tends to reduce.

 In particular, attempts have been made, according to the invention, to reduce the price of "vacuum collectors" in a considerable proportion, which has not been attempted to date, despite the obvious advantage of such a reduction in price.

 The Applicant has achieved this result by seeking to develop, despite the enormous pressure effects which it knew had to appear, and which the known sensors aim precisely to avoid, a large vacuum sensor making it possible to avoid the disadvantages of the association of several smaller sensors.

In order to further reduce the cost of the device, the
The Applicant has also opted for a planar shape despite the poor capacity - known - of vacuum resistance of such structures.

The sensor according to the invention consists - by a plane absorber - contained in a parallelepiped "box" of which at
the less the face facing the sun is transparent.

 To obtain sensors of useful surface reaching approximately 1 m2, it was necessary to combat the total pressure of the order of 10 tonnes exerted on such a surface, while being obliged, for obvious reasons, to use weak materials (glass) and thin. It was also necessary to prevent the risk of dislocation of the sensor appearing due to the expansion constraints as soon as a complex structure is used (a problem which does not arise, or is easy to solve, with tubular sensors).

 The Applicant has managed to reconcile these different contradictory imperatives.

pour sa plus
grande facilité de fabrication ; dans tout ce
qui suit, l'expression "tube en U" désigne
ces deux variantes notamment) dans lequel
circule un fluide caloporteur, le contact étant
réalisé sur toute la longueur du tube, sensi
blement, - et contenu dans une boîte parallzlépipédique étanche à
l'air, dont au moins une face est transparente , - les deux extrémités du tube en U se prolongeant à
l'extérieur d'au moins une des faces latérales de ladite
boite, avec un joint étanche à l'air et résistant aux
fortes pressions placé en chacun des points de traversée
de la paroi par ledit tube, qui se trouvent sensiblement
à mi-hauteur - un vide poussé étant établi et maintenu à l'intérieur de ladite boite et est caractérisé en ce que ladite surface absorbante plane représente environ 0,8 m2 à 1,3 m2, en ce que l'on dispose à l'intérieur de ladite boîte des éléments dont la hauteur est égale à la hauteur interne de la boîte, qui partagent la surface interne de la boîte en plusieurs "surfaces réduites" d'environ 1/8 à 1/12 m2 chacune, la surface absorbante étantelle-même partagée en "ailettes" de nombrelde forme, de positionnement et de dimensions correspondant à chacune de ces "surfaces réduites", ou de dimensions légèrement inférieures, lesdits éléments comportant de plus des dispositifs sur lesquels l'absorbeur vient reposer par le tube en U et/ou les ailettes, sensiblement à mi-hauteur de la boîte.The sensor according to the invention is characterized by: - a flat absorber constituted by
. a flat absorbent surface t
. in contact with a "U" tube (preferably a tube in

for his more
great ease of manufacture; in everything
which follows, the expression "tube in U" indicates
these two variants in particular) in which
circulates a heat transfer fluid, the contact being
carried out over the entire length of the tube, sensi
- and contained in a waterproof rectangular box
air, at least one side of which is transparent, - the two ends of the U-shaped tube extending
the exterior of at least one of the lateral faces of said
box, with an airtight seal and resistant to
strong pressures placed at each crossing point
from the wall by said tube, which are located substantially
at mid-height - a high vacuum being established and maintained inside said box and is characterized in that said planar absorbent surface represents approximately 0.8 m2 to 1.3 m2, in that there is available at l inside said box elements whose height is equal to the internal height of the box, which divide the internal surface of the box into several "reduced surfaces" of about 1/8 to 1/12 m2 each, the absorbent surface being itself divided into "fins" of numerous shape, positioning and dimensions corresponding to each of these "reduced surfaces", or of slightly smaller dimensions, said elements further comprising devices on which the absorber comes to rest by the tube in U and / or the fins, substantially halfway up the box.

According to a first embodiment, said "elements" form a system of partitions perpendicular to each other and to the walls of the boot, the common height of which is equal to the internal height of the boot, and the length of which is substantially equal, or slightly lower (a clearance of about 1 inm is provided to allow expansion), either to the width or to the length of the box, said partitions having 1) devices allowing their assembly in the
box, without exceeding its internal height,
so as to divide the internal surface of the box
in several reduced areas, preferably identi
ques, from about 1/8 to 1/12 m2; and 2) notches adapted to support sensitive
halfway up, in the box, the branches of the
tube in t'U ", and said absorbent surface is itself divided into as many parts or" fins "as one has delimited reduced surfaces, and so that each of these" fins1 can take place, when the the tube in l, u "is deposited in the notches which support it, in each of the internal volumes of the box delimited by said reduced surfaces.

 According to a second embodiment, said "elements" consist of the combination of glass cylinders, of height slightly less than the internal height of the box, with graphite "pads" intended to support the faces of the box, and which have a shape and dimensions allowing them to adapt to each free end of said cylinder, the height of the cylinder + pads combination being equal to the internal height of the box, said cylinders + pads combination being arranged at regular intervals on the " trace "partitions in the previous embodiment, and comprising substantially at mid-height at least one protrusion serving as support for the adjacent" fins ". Preferably, supports will be placed on each side of the absorber tube.

 The flat absorber can easily be made of normal steel (in order to have a low material cost) or of copper-plated steel, stainless steel or copper.

 The use of normal steel is possible because, since the absorber is in a vacuum, there is no possibility of corrosion by oxidation due to air (which is not the case with normal sensors which must either be made of stainless steel (high colt) or include protection (galvanization, electrolytic nickel offset, etc.).

 The sensor being intended to work at high temperature (up to 3000 C) it is important that the emission coefficient is as low as possible at the high operating temperatures that we envisage.

We must remember that - the coefficient 8 increases with temperature, - the term t S w ~ T 4 is the only one which intervenes in
the loss of a vacuum sensor, because there is
no conductivity in a vacuum, hence the interest
to have a very low - the yield is directly linked to the coefficient 8 of the
sensor.

 For the purposes of the invention, it is essential that is less than 0.1 to 2000 C.

 On the other hand, the value of the coefficient is less essential.

One can easily obtain such a coefficient Spar the use - of a deposit by electrolysis
. either black chromium (under chromium oxide)
. either black nickel (under Ni oxide) - a chemical reaction
. either copper dendrite
. either tungsten dendrite.

In order to further reduce the coefficient, we must have a very shiny and very smooth undercoat, also called mirror polish t for this we can make - on iron, copper, copper-plated iron, a thin deposit
electrolytic nickel or molybdenum (called
still Flash) - on stainless steel, electropolishing.

 These techniques are well known and of a fairly low cost.

 Other suitable techniques can, of course, be applied to the treatment of the surface of the absorber.

 The absorber can easily be produced with a tube bent into a pin (U) or with three U-shaped branches.

 The absorbent plates are then welded (or brazed) to the tube.

 The realization is simple and the worker has a surface of the order of m2.

 The manufacturing operations (bending, welding, selective surface treatment) are identical to other vacuum sensors.

 It can therefore be seen that the labor cost for manufacturing the absorber is divided by about 10.

The flat box can easily be made in 3 ways
a) Glass box
The material may be very inexpensive normal ice glass.

 You can operate with two windows, on the two sides of the sensor, and 4 strips on the four sides.

 One can also operate with a mold having the shape of a parallelepiped and making it possible to give the glass the shape of a half box (such as a television screen). We then take 2 half boxes to make a completely transparent sensor; or a box and a lid.

 The welding of glass elements is very well known and is done using a pyroceram sintering technique identical to that used for the manufacture of color TV tubes.

 Two glass-to-metal welds of the conventional type are provided in this area at the level of the pipe passages (reduction in the number of glass-to-metal welds and the cost price of the sensor, since only 2 welds per m2 instead of 20 for example) .

 b) the box is made with the upper and lower face made of ice glass.

 The four sides are made of stainless steel, Kovar (Fe Co Ni alloy) or any other metal having an expansion identical to glass.

 The glass-metal junction is made, either with pyroceram, or by conventional glass-metal welding by fusion, with a torch or by infrared.

 c) The box is made with the bottom and sides in stainless steel or in 'Kovar, or any other metal with coefficient of expansion identical to glass.

The upper side is made with ice glass.

 The following combinations can in particular be used - stainless steel / "90 frit" / ice glass - "NoVAR" (Fe Co Ni alloy) / "50 frit" / PYREX.

The "KOVAR" can be replaced with corresponding adaptation by the "INVAR" or "DILVER" products. These alloys are sold by the company METALIMPHY,
PARIS.

The glass which can be used has a thickness of 4 to 10 mm, preferably 7 mm, for the
box, and especially for the upper sides and
lower.

For side walls, and partitions
support interior, you can use a glass less
thick, but for reasons of standardization, we
will take the same glass.

If the box has metal walls,
especially steel, the thickness of these walls will be
preferably about 2 mm.

In solutions b) and Xc) the pipe passages are made using a conventional weld or an argon weld
In solutions a) and b) it is possible to adapt a reflective cylindroparabolic or paraboloid surface behind the sensor in order to obtain on the rear face a concentration effect of solar radiation to obtain a higher operating temperature of the sensor.

 In all cases, a glass or metal tube is provided, called "Queusot" and used to connect the vacuum ponpe when the unit is placed under vacuum.

 This vacuuming operation (temperature rise in an oven at 3800 C, pumping of the sensor to degas all materials (glass, steel, etc.) for 1 1/2 hours) is very expensive. It can therefore be seen that the sensor according to the invention considerably reduces the price of m2 by this parameter also.

 An essential point of the invention consists in installing inside the box supports or partitions whose ralle is - to share the surfaces and to support them, in order to delimit portions of sensors and to have only small surfaces in depression, - to support the absorber, while allowing it a free expansion.

 The invention therefore provides for installing between each fin of the absorber a support which prevents the bringing together and the implosion of all the materials working in compression.

 It is easy to see that these supports are an essential point of the invention; without them, it is out of the question to put the sensor under vacuum.

 Other characteristics and advantages of the invention will be better understood on reading the description which follows, and with reference to the appended drawings in which - Figure 1 shows in perspective a sensor according to the invention - Figure 2 shows a section of the sensor of Figure 1 along II-II.

- Figure 3 shows a model of longitudinal partitions (Figure 3a) and transverse (Figure 3h3 usable according to the invention (first embodiment); - Figure 4 shows a variant "with graphite pads" of the partitions shown in Figure 3 (FIG. 4a: longitudinal partition; FIG. 4b: transverse partition; FIG. 4c: cross section of one of the partitions of FIG. 4a or 4b); - FIG. 5 represents the second embodiment of a sensor according to the invention, of the type with "verregraphite cylinders": top view (FIG. 5a) and cross-sectional view (FIG. 5b).

 In the appended drawings, the same references have the same meanings, which are as follows: 1. parallelepiped box.

2 (2 ') upper face of the box (lower); 3. side face in which the
passages of the absorber tube.

4. absorber tube, in 5. absorber fins.

6. longitudinal partition (s).

7. transverse partition (s).

8. absorber support notch.

9. notches for assembling the partitions (6) and (7)
between them.

h box height hi internal box height.

10. passage notch for the bent part of the tube
in "U". (allows dilation).

11. graphite "skates".

12. glass cylinder.

13. "clip" for holding the absorber.

First embodiment
(Figures 1, 2, 3 and 4).

 The supports are preferably made of glass. They can be produced by casting in a mold or, for small series, with a diamond saw.

 The partitions interlock at a right angle by the adapted notches (9), in known manner.

 According to an entirely preferred variant of this first embodiment, the upper and lower parts of each partition are provided with "pads" (11) in graphite, in the shape of a "U" of dimensions adapted to the partition. <the total height of partition + skids must be equal to hi).

 It has in fact been discovered that graphite allows, thanks to its lubricating properties, to envisage different expansions of the elements without risk of damage to the sensor. Graphite makes it possible, during expansion, to avoid in particular the appearance of scratches which would constitute as many weak points on the glass. A rectification just before assembly is easily possible. In addition, the pads increase the bearing surface of the faces on the partitions, and therefore reduce the risk of implosion.

Second embodiment (Figures Sa and 5b).

-------------------------------------
The cylinder / graphite combinations are placed on the "trace" -, in the previous embodiment, partitions (6) and (7).

 Neither the shape nor the material of the interior supports is limiting.

 We can design stainless steel, KOUkR glass, copper steel glass, steel graphite, etc.

The essential point of the invention is that these
supports allow to consider an important flat surface
aunt, under vacuum, without risk of implosion.

Another interesting point of the invention is
the use of graphite for its lubricating properties.

I1 is likely that only graphite allows
to consider different dilations without risk of
damage to the sensor.

To our knowledge, this is the first time that
graphite is used in vacuum techniques
to secure and hold a vacuum assembly.

GET
The sensor must, of course, be fitted with a getter (a sort of small pump which adsorbs the last molecules present in a vacuum chamber. TV tubes and tubular vacuum sensors are fitted with this).

 The getter can be of two kinds - activatable by high frequency.

 These are kinds of rings that are placed under the absorber because there is a risk of Barium spite on the lower ice. This Getter being very inexpensive, one can also place several in the sensor.

- activatable by electric current.

 It then suffices to provide for the passage of two wires through the glass. This kind of Getter will preferably be placed near the Queusot.

 The advantage of such a Getter is its possibility of reactivation after 10 years for example.

 In both cases, the Getters are calculated to adsorb the degassing for at least 20 years.

The previously described sensor allows applications that conventional sensors do not allow
- due to lack of efficiency at high temperature,
- by the fact that they are too sensitive to
outside temperature and they don't allow
not recovering calories in case of
diffuse sun.

Among the applications
- heating existing installed habitats
with radiators working at high temperature
(80-900 C),
- seawater desalination by flash process
or multi-story,
- the production of electricity through
of a thermodynamic cycle <on this subject, the sensor
provides thermodynamic efficiency
higher for lower cost than power plants
already known, in turn and mirror or concentra
tion).

On the other hand, electricity production can
continue in winter, which is not the case
of current plants.

- pumping water with thermodynamic circuit,
- air conditioning with absorption machine,
- the production of low pressure steam for
industry (stationery, food, industry
chemical, etc.),
- coupling with geothermal and thermo pump for
district heating operations.

I1 allows, of course the applications already known to the traditional sensor
- domestic hot water production (ratio 1 to
2 over the year, in terms of calorie intake),
- low temperature heating of new homes
provided for such a system (report 1 to 5 on the
heating season, in terms of intakes of
calories),
- agricultural application: heating of greenhouses,
drying hay or fruit.

 The following examples illustrate the invention without, however, limiting its scope.

EXAMPLE 1
A sensor was produced as shown in Figure 1, but comprising 8 fins (including 2 fins at the bent part of the tube).

 Each "reduced surface" has the dimensions 300 x 300 mm, each fin 276 x 276 mm.

 The height h is equal to 60 mm.

 Diameter of the absorber tube: 14 mm.

 Absorbent surface: the best results have been obtained thanks to a spite of black chromium (0.3, u) with dendritic structure (= 0.06 at 200C C) on copper coated with an electrolytic deposit "Flash" (about 10 s ) 2.5 y thick.

- weight of the sensor produced: 47 kg / m2 - stagnation temperature: 250-300 C under 1000 W - with graphite pads, no problem of expansion
never arose.

- without graphite pads, there were some scratches
on the upper side.

EXAMPLE 2
The partitions were replaced by glass cylinders with a diameter of 30 mm (thickness 4 mm) with graphite pads.

 The same results were obtained as in Example 1.

Claims (9)

 of said enclosure; characterized in that said enclosure consists of an airtight parallelepiped box, at least one upper or lower face of which is transparent, in that said crossing points are located substantially halfway up one of the lateral faces of said box, in that the dimensions of said box are such that said planar selective absorbent surface that the box contains represents an area of about 0.8 m2 to 1.3 m2, in that there is inside said box of elements, the height of which is equal to the internal height of the box, which divide the internal surface of the box into several "reduced surfaces" of approximately 1/8 to 1/12 m2 each, the absorbent surface being itself shared in 1, fins "of number, shape, positioning and dimensions corresponding to each of these" reduced surfaces ", or of slightly smaller dimensions, said elements further comprising devices on which the absorber comes to rest by the tub e in Uou Li and / or the fins, substantially halfway up the box.  the enclosure by said tube, - a high vacuum being established and maintained inside  at each of the crossing points of the wall of  airtight seal remaining at high pressures  outside of said enclosure, with at least one  less partially transparent; - the two ends of the U or H tube extending  produced substantially over the entire length of the tube, - and contained in an airtight and airtight enclosure  circulates a heat transfer fluid, the contact being  . in contact with a U or U tube, in which  . a plane selective absorbent surface, : 1. Solar vacuum collector, which includes - a flat absorber consisting of 2. Sensor according to claim 1, characterized in that said elements form a systole of partitions perpendicular to each other and to the walls of the box, whose common height is equal to the internal height of the box, and whose length is substantially equal to, or less aberrantly (a clearance of about 1 mm is provided to allow expansion), either to the width or to the length of the box, said partitions having 1) devices allowing their assembly in the  box, without exceeding its internal height,  so as to divide the internal surface of the box  in several reduced surfaces, preferably identical,  about 1/8 to 1/12 m2 and 2) notches adapted to support sensitive  halfway up, in the box, the branches of the tube in "U" or LEZ, - and said absorbent surface is itself divided into  as many parts or "fins" as defined  reduced areas, and mandore that each of these  "fins" can take place, when depositing  the tube in l, u "or U in the notches which support it  tent, in each of the internal volumes of the box  delimited by said reduced areas. 3. Sensor according to claim 2, characterized in that the height of the partitions is slightly less than the internal height of the box, and in that one engages at the upper part and at the lower part of said partitions of the graphite pads in the shape of an inverted U, covering substantially the entire length of each of the partitions1 except at the locations of the various devices and notches, the dimensions of said pads being such that the total height of each of the partitions provided with these lower and upper pads is equal to the height internal of the box. 4. Sensor according to claim 1, characterized in that said elements consist of the combination of glass cylinders, of height slightly less than the internal height of the boot, with graphite "pads" intended to support the faces of the box , and which have a shape and dimensions allowing them to adapt to each free end of said cylinder, the height of the combination cylinder + pads being equal to the internal height of the box, said combinations cylinders + pads being arranged at regular intervals on the "trace" of partitions as described in claim 2, and comprising substantially at mid-height at least one protuberance serving as support for the adjacent "fins". 5. Sensor according to claim 4, characterized in that, on said trace, there is at least a portion of the cylinders on each side of each of the branches of said tube. 6. Sensor according to any one of claims 1 to 5, characterized in that the dimensions of each of the reduced surfaces is 300 x 300 mm and in that the dimensions of each of the fins is 276 x 276mm, the sensor comprising twice 4 reduced surfaces and the height being 60 mm 7. Sensor according to any one of claims 1 to 6, characterized in that the selective absorbent surface consists of a selective absorbent deposit carried out on a metal plate itself coated with a primary layer deposited by an electrolysis process " Flash". 8. Sensor according to claim 7, characterized in that the metal constituting said plate is chosen from iron, copper and copper-plated iron, in that said primary layer is made of nickel or molybdxne, and in that said selective deposition consists of black chrome or black nickel dendrites. 9. Sensor according to claim 8, characterized in that said plate is made of copper, said primary layer consists of molybdenum, and said selective deposit consists of dendritesde black chromium.  lo. Sensor according to any one of Claims 7 to 9, characterized in that the thicknesser of the said primary layer is approximately 2 to 3 P and in that the thickness of the said selective deposit is approximately 0.3 lu.