U.S. patent application number 12/509558 was filed with the patent office on 2010-12-02 for radiation heat collection device.
Invention is credited to Marco Antonio Carrascosa Perez, Abel Garcia-Mijan Gomez, Manuel Julian Luna Sanchez, Fernando Rueda Jimenez.
Application Number | 20100300431 12/509558 |
Document ID | / |
Family ID | 41134668 |
Filed Date | 2010-12-02 |
United States Patent
Application |
20100300431 |
Kind Code |
A1 |
Carrascosa Perez; Marco Antonio ;
et al. |
December 2, 2010 |
RADIATION HEAT COLLECTION DEVICE
Abstract
This invention relates to a device that comprises at least one
collection unit (11), equipped with a collection tube (21) placed
on supports (23), which is formed by an inner absorber tube (31)
shaped as a continuous tube and an outer envelope tube (33). The
collection unit (11) also comprises reflectors (15) that direct the
radiation toward the collection tube (21). Moreover, the device
comprises means (41, 43) designed to maintain the collection tube
(21) space between the absorber tube (31) and the envelope tube
(33) at a pressure of between 510.sup.-1-510.sup.-2 mbar. The main
advantages of the invention include the reduction in the breaking
of glass due to the lower stresses to fatigue, an increase in the
effective collection surface (97%-98%) and active management of the
vacuum, which makes it possible to monitor the evolution thereof at
all times.
Inventors: |
Carrascosa Perez; Marco
Antonio; (Madrid, ES) ; Luna Sanchez; Manuel
Julian; (Madrid, ES) ; Garcia-Mijan Gomez; Abel;
(Madrid, ES) ; Rueda Jimenez; Fernando; (Madrid,
ES) |
Correspondence
Address: |
MOORE & VAN ALLEN PLLC
P.O. BOX 13706
Research Triangle Park
NC
27709
US
|
Family ID: |
41134668 |
Appl. No.: |
12/509558 |
Filed: |
July 27, 2009 |
Current U.S.
Class: |
126/652 ;
126/664; 126/694; 126/708 |
Current CPC
Class: |
Y02E 10/40 20130101;
Y02E 10/44 20130101; F24S 23/74 20180501; F24S 80/30 20180501; F24S
10/45 20180501; F24S 40/80 20180501 |
Class at
Publication: |
126/652 ;
126/664; 126/694; 126/708 |
International
Class: |
F24J 2/14 20060101
F24J002/14; F24J 2/50 20060101 F24J002/50; F24J 2/24 20060101
F24J002/24 |
Foreign Application Data
Date |
Code |
Application Number |
May 26, 2009 |
EP |
098382082.7 |
Claims
1. Radiation heat collection device that comprises at least one
collection unit (11) equipped with a collection tube (21) placed on
supports (23) and reflectors (15), wherein the collection tube is
formed by an inner absorber tube (31) and an outer envelope tube
(33), the reflectors (15) direct the radiation toward the
collection tube (21), and wherein said radiation heat collection
device comprises means (41, 43) designed to maintain the collection
tube (21) space between the inner absorber tube (31) and the outer
envelope tube (33) at a pressure of between
5.times.10.sup.-1-5.times.10.sup.-2 mbar when the device is
operative.
2. Device, as claimed in claim 1, wherein the inner absorber tube
(33) is shaped as a continuous tube.
3. Device, as claimed in claim 1, wherein the outer envelope tube
(33) is formed by multiple segments united by joints (51, 81, 95,
95') that include support and slide means (65) for the inner
absorber tube (31).
4. Device, as claimed in claim 1, wherein the collection tube (21)
supports (23) are shaped as a rigid structure and fixed to a
bearing structure of the collection unit (11).
5. Device, as claimed in claim 19, wherein each collection unit
(11) is formed by two semi-collectors (13, 13') and are connected
by vacuum pumps at a central part (41) and at an end (43).
6. Device, as claimed in claim 5, wherein the device further
comprises an element (45) that is connected to the central part of
each collection unit (11), designed for the introduction of a gas
that allows to drag the hydrogen present in the collection tube
(21) space between the inner absorber tube and the outer envelope
tube (33), in collaboration with the vacuum pumps (43) connected to
the ends of each collection unit (11).
7. Device, as claimed in claim 3, wherein said joints (51)
comprise: flanges (53, 53') with co-operating means (55, 59; 55',
59') with the ends (57, 57') of each pair of segments of the outer
envelope tube (33); a ring (61) placed between said flanges (53,
53'), fixed to a support (23); sealing bands (63, 63') placed in
openings of said ring (61) adjacent to said ends (57, 57'); an
insulation crown (62) with inner radial teeth (64) designed for the
support and sliding of the inner absorber tube (31) joined to said
ring (61); and axial tightening means designed to bring said ends
(57, 57') close to the ring (61).
8. Device, as claimed in claim 3, wherein said joints (81)
comprise: flanges (83, 83') fixed to a support (23); an insulation
crown (85) with lateral slots (87, 87') designed for the reception
of each pair of segments (35, 35') of the outer envelope tube (33)
between pairs of sealing bands (89, 89'); and inner radial teeth
(86) designed for the support and sliding of the inner absorber
tube (31) and radial tightening means for said flanges (83,
83').
9. Device, as claimed in claim 1, wherein each collection unit is
formed by multiple groups of segments (36, 37) of the outer
envelope tube (33), wherein the segments (36, 37) of each group are
united by joints (95) fixed to supports (23), and the ends of each
group are united by pairs of joints (95') supported in a
displaceable manner on supports (23) with an intermediate bellows
device (97), said joints (95, 95') comprising: flanges (101, 101')
with co-operating means (105, 109; 105', 109') with the ends (107,
107') of each pair of segments (36, 37) of the outer envelope tube
(33); a ring (111) placed between said flanges (101, 101'); sealing
bands (113, 113') placed in openings of said ring (112) adjacent to
said ends (107, 107'); an insulation crown (112) with inner radial
teeth (114) designed for the support and sliding of the inner
absorber tube (31) joined to said ring (111); and means designed to
maintain said ends (107, 107') and the ring (111) immobilized.
10. Device, as claimed in claim 1, wherein said outer envelope tube
(33) is made of glass, or of polymethylmethacrylate (PMMA).
11. Device, as claimed in claim 10, wherein the outer envelope tube
(33) is made of glass and wherein the thickness of said outer
envelope tube is between 2.5 and 3.5 mm.
12. Device, as claimed in claim 1, wherein the inner absorber tube
(31) has a circular cross-section and a diameter of between 70 and
90 mm.
13. Device, as claimed in claim 1, wherein said inner absorber tube
(31) has an oval cross-section.
14. Device, as claimed in claim 1, wherein the useful collection
surface of the collection tube (21) is between 97%-98% of its total
length.
15. Device, as claimed in claim 1, wherein the focal length is
between 1,700 mm and 1,900 mm.
16. Device, as claimed in claim 1, wherein the length of the
segments of the outer envelope tube (33) united by the joints (51,
81, 95, 95') is between 4 and 6 m.
17. Device, as claimed in claim 1, wherein the length of the
segments of the inner absorber tube (31) joined by welds is between
12 and 16 m.
18. Device, as claimed in claim 1, wherein the solar radiation is
collected by means of parabolic reflectors.
19. Device, as claimed in claim 1, wherein said means comprise
vacuum pumps.
20. Device, as claimed in claim 10, wherein the means designed to
maintain said ends (107, 107') and the ring (111) immobilized
include encapsulated traction springs (104, 104').
Description
FIELD OF THE INVENTION
[0001] This invention relates to a radiation heat collection device
and, more particularly, to a heat collection device which uses a
parabolic reflector that focuses the solar heat radiation onto an
absorber tube.
BACKGROUND OF THE INVENTION
[0002] The solar heat collection devices that use
cylindrical-parabolic concentrators known in the state of the art
are based on the developments arising from the construction of
thermoelectric plants called "Segs", which were implemented in the
United States in the 1980s.
[0003] The known designs use structures that act as supports for
the reflector elements that make up the parabolic reflector profile
and the absorber tube located on the theoretical focal line of the
parabolic cylinder formed by the reflectors. These structures are
usually formed by inter-connected modules and equipped with an
orientation mechanism that makes it possible to collect the maximum
possible radiation by following the sun.
[0004] The reflector elements may be composed of different
materials, made using different processes and supported in
different ways, but, in any event, the objective is to obtain the
maximum possible reflectivity and the maximum geometric precision
such that, following the optical laws of reflection and refraction,
the reflected beam interception deviation with respect to the
theoretical focal point is as small as possible.
[0005] One of the main elements of the device is the tube in charge
of absorbing the maximum possible energy of that reflected from the
reflector surface and transmitting it as efficiently as possible to
the heat-transfer fluid used. In order to prevent losses by thermal
convection, the absorber tube, normally made of a metallic material
with a suitable selective-layer coating, is surrounded by a glass
envelope tube, and the intermediate space is subjected to high
vacuum, which requires hermetic glass-metal joints and high-quality
metal-metal welds subjected to vacuum. U.S. Pat. No. 6,705,311
describes specific solutions in this regard.
[0006] On the other hand, configuration of the device with
completely airtight segments with high vacuum requirements has
favoured the use of Getter systems for hydrogen absorption, such as
that disclosed in US 2004134484.
[0007] The disadvantages of the solar collection devices known in
the state of the art include the following: [0008] High cost of the
absorber tubes. [0009] Breaking of the glass-metal joints, with the
consequent loss of vacuum and, therefore, of yield. [0010] Breaking
of the glass tube at the joint areas. [0011] Need to perform costly
temperature and vacuum degasification processes that allow to
activate the getter system. [0012] Undetectability of the loss of
vacuum in a tube or great uncertainty of the tracers specified,
with low confidence regarding the information prior to the failure.
[0013] Possible saturation of H2 in the getter system through time
for temperatures below the working temperature, which would cause a
significant loss of yield. [0014] Impossibility to easily measure
the vacuum during the device's operating life. [0015] Need to use
materials such as glass for the envelope tube and glass-metal
joints due to the high level of vacuum required. [0016] High
replacement cost in the event of breakage. [0017] Impossibility to
repair the replaced element. [0018] Limited useful surface due to
the need to absorb the differential dilations between the inner
tube and the outer cover by means of bellows and connecting
elements.
[0019] This invention is intended to overcome these
disadvantages.
SUMMARY OF THE INVENTION
[0020] One object of this invention is to provide robust,
controllable thermoelectric plants that ensure a minimum level of
inoperativity, caused by the breaking of their components and the
need for complex maintenance operations to replace them, during
their operating life.
[0021] Another object of this invention is to provide
thermoelectric plants that allow for flexible, cost-optimized
production and exploitation.
[0022] Another object of this invention is to provide
thermoelectric plants that make it possible to increase the
interception factor and, consequently, the yield thereof.
[0023] Another object of this invention is to provide
thermoelectric plants that make it possible to increase the
effective surface in the absorber element, and, consequently, the
yield thereof.
[0024] These and other objects are achieved by means of a heat
collection device that comprises at least one collection unit
equipped with a collection tube, formed by an inner absorber tube
and an outer envelope tube, and reflectors that direct the
radiation to the collection tube, wherein: [0025] The inner
absorber tube is shaped as a continuous tube. [0026] The outer
envelope tube is formed by multiple segments united by joints that
include support and slide means for the inner absorber tube. [0027]
The collection tube supports have a rigid structure and are fixed
to the collection unit's bearing structure. [0028] There are means
available to maintain a pressure of between 510.sup.-1-510.sup.-2
mbar in the collection tube space between the inner absorber tube
and the outer envelope tube when the device is operative.
[0029] In a preferred embodiment of this invention, the heat
collection device collects solar radiation by means of a parabolic
reflector, amongst other elements.
[0030] In a preferred embodiment of this invention, said heat
collection device also comprises means for introducing gas into the
collection tube which allow for hydrogen drag. Jointly with the
vacuum production means, this leads to a device that makes it
possible to monitor and control the vacuum level and the presence
of hydrogen in the intermediate space between the inner absorber
tube and the outer envelope tube, which contributes to optimizing
the yield of the device.
[0031] In a preferred embodiment of this invention, the joints of
all the segments making up the outer envelope tube are fixed to the
collection tube supports. This provides for a very robust heat
collection device.
[0032] In a preferred embodiment of this invention, part of the
joints of all the segments making up the outer envelope tube are
supported in a displaceable manner on the collection tube supports.
This provides for a heat collection device wherein maintenance
operations are reduced.
[0033] In a preferred embodiment of this invention, the outer
envelope tube is made of glass, with a thickness of between 2.5 and
3.5 mm. This provides for a heat collection device with a very
optically efficient collection tube.
[0034] In a preferred embodiment of this invention, the outer
envelope tube is made of Polymethylmethacrylate (PMMA). This
provides for a heat collection device with a less expensive
collection tube.
[0035] In a preferred embodiment of this invention, the inner
absorber tube has an oval cross-section. This provides for a heat
collection device with a collection tube that improves the
utilization of solar radiation.
[0036] In different preferred embodiments of this invention, inner
absorber tubes with a circular cross-section are used, with a
diameter between 70 and 90 mm and/or configurations with focal
lengths Fl between 1,700 mm and 1,900 mm. This provides for more
efficient heat collection devices.
[0037] In different preferred embodiments of this invention, the
segments of the outer envelope tube have a length of between 4 and
6 m, and the segments of the inner absorber tube have a length of
between 12 and 16 m. This provides for easy-to-assemble heat
collection devices.
[0038] Other characteristics and advantages of this invention will
arise from the detailed description of an embodiment that
illustrates the object thereof in relation to the accompanying
figures.
DESCRIPTION OF THE FIGURES
[0039] FIG. 1 is a perspective view of a collection unit of a heat
collection device in accordance with this invention.
[0040] FIG. 2 schematically shows the directioning of radiation
toward the collection tube of a solar heat collection device in
accordance with this invention.
[0041] FIG. 3 is a perspective view of the final part of the
collection tube of a heat collection device in accordance with this
invention.
[0042] FIG. 4 is a schematic diagram that illustrates the vacuum
formation process in a heat collection device in accordance with
this invention formed by four collection units.
[0043] FIG. 5 is a schematic diagram that illustrates the gas drag
in a heat collection device in accordance with this invention
formed by four collection units.
[0044] FIG. 6 is a diagram that shows the relationship between heat
losses and pressure in the intermediate space between the outer
envelope tube and the inner absorber tube for air and hydrogen.
[0045] FIG. 7 is a figure similar to FIG. 2, except that the inner
absorber tube of the collection tube has an oval cross-section.
[0046] FIG. 8 is a perspective view of a first embodiment of the
segment joint of the outer envelope tube in a heat collection
device in accordance with this invention.
[0047] FIG. 9 is a partial-section perspective view of said first
embodiment of the joint, and FIGS. 9a and 9b are detailed views of
two areas of the joint.
[0048] FIG. 10 is a cross-section view of the insulation crown of
the joint illustrated in FIG. 9.
[0049] FIG. 11 is a partial-section perspective view of a second
embodiment of the segment joint of the outer envelope tube in a
heat collection device in accordance with this invention.
[0050] FIG. 12 is a partial view of a longitudinal section of the
joint of FIG. 11.
[0051] FIG. 13 is a perspective view of the insulation crown of the
joint illustrated in FIGS. 11 and 12.
[0052] FIG. 14 is a cross-section view of the joint illustrated in
FIGS. 11-13.
[0053] FIG. 15 is a partial elevation view of a heat collection
device in accordance with this invention using a third embodiment
of the segment joint of the outer envelope tube.
[0054] FIG. 16 is a detailed view of the area of FIG. 17 with two
joints and an intermediate bellows.
[0055] FIG. 17 is a partial-section perspective view of the joint
of FIGS. 15-16.
[0056] FIG. 18 is a partial view of a longitudinal section of the
joint of FIG. 17.
DETAILED DESCRIPTION OF THE INVENTION
[0057] FIG. 1 represents a collection unit 11 of a heat collection
device formed by two semi-collectors 13, 13' with reflectors 15,
15' that reflect the radiation toward collection tube 21, which
extends along the focal line of said reflectors 15, 15' and is
placed on supports 23 fixed to the bearing and guiding structure of
collection unit 11. Central area 17 of said structure also contains
components 19 of the vacuum and gas drag systems whereto we will
refer further below. Oil or another fluid circulates through
collection tube 21; it is heated by the radiation and transmitted
to a heat exchanger or directly to a turbine in the event that
Water-Steam is used as the heat-transfer fluid in order to, for
example, produce electrical energy, or to another device designed
to utilize the fluid's calorific energy. As shown in FIG. 2,
collection tube 21, which receives the beams reflected by a
reflector 15, comprises an inner absorber tube 31 and an outer
envelope tube 33 with an intermediate space that, as we shall see,
is subjected to controlled vacuum when collection unit 11 is
operative.
[0058] In the installations known in the state of the art, inner
tube 31 has a diameter of about 70 mm and the focal length, Fl, is
located at about 1,700 mm; as is well known, these magnitudes are
determined by the characteristics of the parabolic concentrators
for purposes of optimizing the interception factor of the reflected
beams.
[0059] Inner absorber tube 31 and outer envelope tube 33 may be
made of the same type of materials used in the thermoelectric
plants known in the state of the art, typically metal coated with
selective layers for the absorber tube and glass for the envelope
tube.
[0060] In a preferred embodiment of the invention, the thickness of
outer envelope tube 33, made of glass, is between 2.5 and 3.5 mm,
and, preferably, 3 mm for borosilicates.
[0061] Outer envelope tube 33 may also be made of other suitable
transparent materials, such as Polymethylmethacrylate (PMMA).
[0062] In a preferred embodiment of the invention, inner absorber
tube 31 is formed by welded segments with lengths of between 12 and
16 meters, and outer envelope tube 33 is formed by segments with
lengths of between 4 and 6 meters. The segment joints of outer
envelope tube 33 are placed on supports 23 and shaped, as shown
further below, to fulfill a three-fold purpose: that the
intermediate space between outer envelope tube 33 and inner
absorber tube 31 may be subjected to vacuum, that the segments of
outer envelope tube 33 may dilate/contract due to an
increase/reduction in the temperature without compromising its
integrity nor the airtightness of said intermediate space, and that
they provide a support and slide base for inner absorber tube 31
such that it may freely dilate/contract thereon.
[0063] Consequently, inner absorber tube 31 freely dilates
independently from outer envelope tube 33 and the dilations of the
latter are absorbed at the joints of the segments that compose it;
therefore, the intermediate space between both, which extends along
the entire device, may act as a vacuum chamber. In the final part
of each collection tube 21, a bellows 25 (see FIG. 3) accumulates
the total dilations of inner absorber tube 31 with respect to the
last support 23, without transmitting a cyclised load to envelope
tube 33. Thus, bellows 25 are the closing elements of the
above-mentioned vacuum chamber.
[0064] FIGS. 4 and 5 schematically illustrate the vacuum and gas
drag systems of a heat collection device in accordance with the
invention composed of four collection units 11, each formed by two
semi-collectors 13, 13'.
[0065] The vacuum system comprises a central vacuum pump 41 and two
end vacuum pumps 43 for each collection unit 11. FIG. 4 illustrates
the air flow with all the pumps 41, 43 under operating
conditions.
[0066] The gas drag system comprises a gas-dispensing element 45
connected to the central part of each collector 11. FIG. 5
illustrates the gas flow when the system is started with dispensing
elements 45 and end pumps 43 under operating conditions.
[0067] The operation of the heat collection device in accordance
with this invention may be described as follows:
[0068] The device receives direct radiation by orientation toward
the radiation source in one or two axes, preferably one axis for
thermoelectric production applications, by heating the surface of
inner absorber tube 31, which causes heating of the oil circulating
inside. Right before the device is oriented toward the radiation
heat source, vacuum pumps 41, 43 begin to create a vacuum in the
intermediate space between inner absorber tube 31 and outer
envelope tube 33 until a maximum pressure, of between 510.sup.-1
and 510.sup.-2 mbar, is achieved along the entire length. This
pressure is sufficient to almost completely eliminate heat losses
through the vacuum chamber when the material inside it is primarily
air; this is not the case when the gas is hydrogen, as may be seen
in FIG. 6, in curves 27, 29 that show the relationship between heat
losses and pressure for, respectively, air and hydrogen. This
Figure is taken from "Technical Report: Heat transfer analysis and
Modeling of a Parabolic Trough Solar Receiver Implement in
Engineering Equation Solver. R. Forristel". The joints of outer
envelope tube 33, whereto we will refer in more detail further
below, make it possible to achieve that vacuum level, such that it
is not necessary to implement high-vacuum tubes with hermetic
seals, GTMS welds and Getter systems. As the heating takes place,
the temperature of inner absorber tube 31 increases to its maximum,
between 400.degree. C. and 600.degree. C., thereby increasing the
length, sliding along the support and positioning means placed on
the joints, which are designed for point contact. Supports 23 of
outer envelope tube 33 are fixed and, therefore, will remain in the
specified position during said operation.
[0069] During operation of the heat collection device, the vacuum
action will be maintained only as long as necessary, due to the
degasification produced by the surface of the components of inner
absorber tube 31. Everyday operation will provide for a direct
degasification system in the installation, such that it is not
necessary to perform said operation in each inner absorber tube
prior to assembling it. In the event that the heat losses increase
due to the presence of hydrogen, a drag operation will be performed
which consists of introducing a given gas, such as dry air, CO2 or
others with a conduction coefficient equal to or lower than that of
air, into the vacuum chamber by means of dispensing elements 45,
controlling either the flow rate, the temperature of the gas
introduced, or both, in order to prevent potential thermal shocks,
in the event that glass outer envelope tubes 33 are used, and the
subsequent discharge by means of the vacuum system. The previous
operation will make it possible to control, whenever necessary, the
partial pressure of hydrogen and, therefore, the rate of heat loss
due to the existing gas mixture and the vacuum chamber pressure. If
outer envelope tube 33 is made of a suitable transparent plastic
material, such as Polymethylmethacrylate (PMMA), there is no risk
of said thermal shocks.
[0070] The vacuum and gas drag systems are electronically
programmable and controllable systems designed to operate the
dynamic vacuum on the basis of the needs at each time, without the
complexity that the presence of thousands of tubes designed to last
25 years with 10.sup.-4 mbar vacuums entails.
[0071] The independence between inner absorber tube 31 and outer
envelope tube 33 also makes it possible for inner tube 31 to have,
as shown in FIG. 7, an oval geometry with the major semi-axis
oriented in the direction of the axis of the parabola, in order to
improve the interception factor of the reflected beams,
particularly at the ends of parabola 15, where there is the maximum
probability of separation in the focal area. Due to the difference
in the distance from the parabola to the focus at the different
points thereof, the probability distribution of reflected beams at
a given point of the parabola translates into an angular aperture
.beta., the linear aperture "a" whereof will be a function of
distance "d" to the focus of the point in question. FIG. 7 shows
the variation of linear aperture a1 and a2 for points p1 and p2
positioned around the centre and the end of parabola 15 at
distances d1 and d2, respectively. The oval geometry of inner
absorber tube 31 makes it possible to increase the yield of the
system using a smaller quantity of material than that necessary to
cover the same area with a circular geometry. Similarly, the
lateral section subject to losses by radiation will be lower than
the circular equivalent.
[0072] As regards the segment joints of outer envelope tube 33,
below we will describe a first embodiment of this invention, in
accordance with FIGS. 8-10.
[0073] Each joint 51 comprises: [0074] Two flanges 53, 53' with
axial tightening means (FIGS. 8 and 9 do not show the typical bolts
used in this type of flanges, but they do show the flange
openings), the configuration whereof includes sloping surfaces 55,
55', which co-operate with enlarged edges 57, 57' of the ends of
segments 35, 35' of envelope tube 33 through contact elements 59,
59'; these have a high elasticity and a low hardness in order to
prevent the generation of local stresses in the glass. [0075] A
ring 61, placed between flanges 53, 53', with two hermetic sealing
bands 63, 63' designed to maintain the vacuum, with a fixation base
69 on a support 23. [0076] An insulation crown 62 bound to ring 61,
and support and slide means for inner absorber tube 31, consisting
of inner radial teeth 64 which provide point contacts with inner
absorber tube 31 and allow it to slide with a suitable tribologic
behaviour that minimizes friction and wear. Insulation crown 62
also fulfils a thermal insulation function in order to minimize
losses by conduction. Preferably, it is made of a ceramic
material.
[0077] As already mentioned, ends 55, 55' of segments 35, 35' of
envelope tube 33 have an enlarged configuration in order to
collaborate with flanges 53, 53' and, furthermore, their final area
56 is protected against concentrated IR and solar radiation.
[0078] This configuration of joint 51 takes advantage of the
dilation of outer envelope tube 33 due to the increase in
temperature, since it generates an added compression effect on
sealing bands 63, due to the fixed position, as base 69 of ring 61
is fixed to support 23.
[0079] The thermal insulation system causes the temperatures in the
areas of sealing bands 63, 63' not to exceed 100.degree. C.;
consequently, different materials with the adequate specifications
may be used. The mean temperature of outer envelope tube 33 will be
a function of the material used, but, in any event, the limited
dilation thereof will be absorbed by sealing bands 63, 63'. The
tightening and contact elements of segments 35, 35' of outer
envelope tube 33 must have sufficient flexibility to maintain them
in a radial position during the displacements thereof. Sloping
surfaces 55, 55' of flanges 53, 53' have been designed for this
purpose. The angle .OMEGA. to be used is a function of the
elasticity of the tightening system and the load per empty weight
to be borne by said system, which will generate a normal component
that is a function of said angle .OMEGA..
[0080] Furthermore, insulation crown 62 is intended to connect the
vacuum or insulation chamber with the adequate conductivity by
means of a design that allows for an adequate difference in
pressure between the endpoints of the vacuum chamber defined
between absorber tube 31 and outer tube 33, the maximum pressure
being lower than 5*10.sup.-1 mbar at all times. To this end, the
hydraulic diameter of the cross-section must be at least greater
than 75% of that corresponding to the annular section defined by
the inner diameter of outer envelope tube 33 and the outer diameter
of inner absorber tube 31.
[0081] In a second embodiment, as may be observed in FIGS. 11-14,
joints 81 comprise: [0082] Two clamp-flanges 83, 83' with radial
tightening means (not shown) that join to frames 84, 84', which are
fixed on supports 23. [0083] An insulation crown 85 with, on the
one hand, slots 87, 87' designed to receive the pair of segments
35, 35' of outer envelope tube 33, with sufficient clearance to
this end, and, on the other hand, support and slide means for inner
absorber tube 31 consisting of inner radial teeth 86 which provide
point contacts for inner absorber tube 31 and allow it to slide
with a suitable tribologic behaviour that minimizes friction and
wear. Insulation crown 85 also fulfils a thermal insulation
function in order to minimize losses by conduction. Preferably, it
is made of a ceramic material. [0084] Two pairs of sealing bands
89, 89' placed on lateral openings of insulation crown 85, on the
edges of said slots 87, 87', such that said segments 35, 35' remain
between them and, consequently, a vacuum is maintained in the
intermediate space between inner absorber tube 31 and outer
envelope tube 33.
[0085] Between flanges 83, 83' and insulation crown 85, an
intermediate part 88 is placed, made of an elastomer material
designed to homogenize the effect of tightening flanges 83, 83' on
insulation crown 85. The dilations of segments 35, 35' are absorbed
with small deformations of sealing bands 89, 89'.
[0086] Although joints 51 and 81 are constructively different, they
may be considered to be functionally equivalent.
[0087] In a third embodiment of the invention, illustrated in FIGS.
15-18, a group of two segments 36, 37 of outer envelope tube 33 is
united by means of a joint 95 fixed onto a support 23 and the ends
of that group are united to other adjacent groups by means of pairs
of joints 95' supported in a displaceable manner on a support 23
with an intermediate bellows device 97 which, in turn, facilitates
welding of the components of inner absorber tube 31 between two
joints 95' by the contraction of bellows 97 and the subsequent
assembly thereof.
[0088] As observed in FIG. 15, the group formed by segments 36 and
37, which has a length L of, for example, 12 m, is centrally united
by a joint 95 fixed onto a support 23 and, on the ends, by joints
95' supported in a displaceable manner on supports 23. In turn, end
joints 95' of each group are connected by means of a bellows 97.
The arrows, f, indicate the displacements of the end joints as a
consequence of the dilations of segments 36, 37 of outer envelope
tube 33.
[0089] The axial dilation of segments 36, 37 of a glass envelope
tube 23 may be calculated to be about 2 mm every 6 m for a maximum
temperature difference of 100.degree. C.; for this reason, supports
23 of the ends of each group of segments 36, 37 may allow for
displacements of joints 95' of about 3 mm.
[0090] Bellows 97 fulfils the three following functions: [0091] It
absorbs the axial movement of adjacent glass segments, which, on
the basis of the above, may be considered to be less than 6 mm.
[0092] It gives continuity to the vacuum chamber defined between
inner absorber tube 31 and outer envelope tube 33. [0093] It makes
it possible to disassemble the components of the inner absorber
tube in order to repair them, if necessary.
[0094] Joints 95, 95' comprise: [0095] Two flanges 101, 101', with
first tightening means 103, 103' and second tightening means 104,
104' consisting of encapsulated traction springs, the configuration
whereof includes sloping surfaces 105, 105', which co-operate with
enlarged edges 107, 107' of the ends of segments 36, 37 of envelope
tube 33 through contact elements 109, 109', made of a material with
a medium hardness and a low elasticity constant, such as Teflon.
[0096] A ring 111, placed between flanges 101, 101' with two
hermetic sealing bands 113, 113' designed to maintain the vacuum,
with a support base 119 on a support 23. Due to the action of
tightening means 103, 103'; 104, 104', sealing bands 113, 113',
which are made of an elastomer material with suitable coatings to
maintain their characteristics during their estimated lifetime,
always have a pre-determined degree of compression, for example 20%
of the diameter thereof, regardless of the working temperature of
the heat-transfer fluid and, therefore, of the temperature of outer
envelope tube 33 and of inner absorber tube 31. In joints 95,
support base 119 is united to support 23 and, in joints 95', it is
supported on support 23, such that it may slide thereon. [0097] An
insulation crown 112 joined to ring 111 with support and slide
means for inner absorber tube 31, consisting of inner radial teeth
114 that provide point contacts for inner absorber tube 31 and
allow it to slide with a suitable tribologic behaviour that
minimizes friction and wear. It also includes inner protectors 121
in the form of a "cooking pan", in order to protect sealing bands
113, 113' and contact elements 109, 109' against the concentrated
radiation produced by the reflector mirrors which might reach them
as a result of optical errors. Insulation crown 112 also fulfils a
thermal insulation function in order to minimize losses by
conduction. Preferably, it is made of a ceramic material.
[0098] The collection device in accordance with this invention
makes it possible to surpass the magnitudes of the parabolic solar
concentrators known in the state of the art in, at least, the
following aspects: [0099] The diameter of circular absorber tubes
31, which may be between 70-90 mm and equivalent dimensions in the
case of absorber tubes with an oval cross-section or tubes with
other types of cross-sections. [0100] Focal length Fl, which may be
between 1,700-1,900 mm.
[0101] This is basically due to the greater optical precision that
may be achieved with rigid supports 23 and the absence of
significant movements of collection tube 21. The current systems
absorb axial dilations by the rotating displacement of the rigid
supports, thereby causing a loss of position of the absorber tube
with respect to the theoretical position, of 12 mm on average and
24 mm maximum, exclusively calculated on the basis of the design
concept, without taking into consideration manufacturing and
assembly precisions.
[0102] Furthermore, it allows to improve the useful collection
surface of collection tube 21, which may be estimated to be between
97%-98% of the total length, thanks to the absence of both
glass-metal joints and intermediate bellows for the compensation of
thermal dilations, estimated to be 25 mm every 6 m as the
differential dilation between the inner tube and the outer cover,
as a consequence of using a continuous absorber tube 31.
[0103] The advantages of the heat collection device in accordance
with the invention with respect to the solar heat collection
devices known in the state of the art include the following: [0104]
Absence of GTMS welds. [0105] Less shaded space per meter. Greater
effective surface. [0106] Absence of Getter for hydrogen control.
[0107] Potentially higher optical yield due to the possibility of
fixed supports. Dilation absorbed in the end. [0108] Possibility to
use absorber tubes with a non-cylindrical geometry and, in
particular, an oval geometry, which improve the yield. [0109] Ease
of assembly and process. Gasifications are not required for high
vacuum levels. [0110] No need for highly airtight joints. [0111]
Reduced breaking of glass due to lower stresses to fatigue. [0112]
Possibility to reduce the thickness of the glass outer envelope
tube since GTMS welds are not required and lower stresses are borne
at the ends. Improved optical yield due to better transmittance.
[0113] Active management of the vacuum and the presence of hydrogen
make it possible to know the location at each time and monitor the
evolution thereof, unlike in the case of hermetically closed
systems. [0114] Ease of manufacturing. [0115] Reduced vacuum
requirements. [0116] Elimination of the need to use Getter systems
and vacuum control elements in the closed chamber. [0117] Greater
precision of the position of the absorber tube with respect to the
theoretical focal point, since it may move on fixed supports during
dilation.
[0118] Regarding the embodiments of the invention described, those
modifications included within the scope defined by the following
claims may be introduced.
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