U.S. patent application number 11/721946 was filed with the patent office on 2008-08-07 for solar energy collection apparatus and method.
This patent application is currently assigned to SHEC LABS - SOLAR HYDROGEN ENERGY CORPORATION. Invention is credited to Maurice J. Tuchelt.
Application Number | 20080184990 11/721946 |
Document ID | / |
Family ID | 36585840 |
Filed Date | 2008-08-07 |
United States Patent
Application |
20080184990 |
Kind Code |
A1 |
Tuchelt; Maurice J. |
August 7, 2008 |
Solar Energy Collection Apparatus and Method
Abstract
An apparatus for collecting heat from a solar concentrator has
an isothermal body defining an elongated cavity with a circular
opening having a diameter equal to a diameter of a focus of the
solar concentrator, the cavity having a reflective walls such that
solar rays contacting the walls are substantially reflected. The
circular opening is located at the focus of the solar concentrator
and perpendicular to a principal axis of the solar concentrator,
and the axis of the cavity is aligned with the principal axis of
the solar concentrator. The heat generated in the isothermal body
is absorbed by the heat sink. The length of the cavity is
sufficient to absorb a desired proportion of the energy in the
solar rays entering the cavity and is about 5 to 9 times the
diameter of the opening of the cavity. Depending on material used,
the isothermal body can be enclosed in a reducing atmosphere to
maintain reflectivity of the cavity walls.
Inventors: |
Tuchelt; Maurice J.;
(Regina, CA) |
Correspondence
Address: |
STANDLEY LAW GROUP LLP
495 METRO PLACE SOUTH, SUITE 210
DUBLIN
OH
43017
US
|
Assignee: |
SHEC LABS - SOLAR HYDROGEN ENERGY
CORPORATION
Saskatoon
CA
|
Family ID: |
36585840 |
Appl. No.: |
11/721946 |
Filed: |
December 15, 2005 |
PCT Filed: |
December 15, 2005 |
PCT NO: |
PCT/CA05/01900 |
371 Date: |
September 26, 2007 |
Current U.S.
Class: |
126/684 |
Current CPC
Class: |
F24S 2023/88 20180501;
F24S 20/20 20180501; Y02E 10/40 20130101; F03G 6/06 20130101; Y02E
10/46 20130101 |
Class at
Publication: |
126/684 |
International
Class: |
F24J 2/10 20060101
F24J002/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 2004 |
CA |
2490207 |
Claims
1. An apparatus for collecting heat from a solar concentrator and
for transferring the collected heat to a heat sink, the apparatus
comprising: an isothermal body defining an elongated cavity with a
substantially circular opening having a diameter substantially
equal to a diameter of a focus of the solar collector, the cavity
having reflective walls such that solar rays contacting the walls
are substantially reflected; wherein the isothermal body is adapted
to be oriented such that the circular opening is located
substantially at the focus of the solar collector and substantially
perpendicular to a principal axis of the solar concentrator, and
such that an axis of the cavity is substantially aligned with the
principal axis of the solar concentrator; wherein the isothermal
body is adapted for thermal connection to the heat sink such that
heat generated in the isothermal body is absorbed by the heat sink;
and wherein a length of the cavity is sufficient to absorb a
desired proportion of the energy in the solar rays entering the
cavity.
2. The apparatus of claim 1 wherein the proportion of the energy in
the solar rays entering the cavity that is absorbed increases as
the length of the cavity increases.
3. The apparatus of claim 1 wherein the length of the cavity is
about 5 to 9 times the diameter of the circular opening.
4. The apparatus of claim 3 wherein the length of the cavity is
between 6.5 to 7.5 times the diameter of the circular opening.
5. The apparatus of claim 1 wherein the cavity is substantially
cylindrical.
6. The apparatus of claim 1 wherein the isothermal body is made
from a reflective material such that the walls of the cavity are
reflective.
7. The apparatus of claim 1 comprising a liner made of reflective
material between the isothermal body and the cavity and operative
to provide the reflective walls of the cavity.
8. The apparatus of claim 7 further comprising a low-emissivity
shield covering an end of the isothermal body between the opening
of the cavity and outer edges of the isothermal body.
9. The apparatus of claim 1 further comprising an enclosure
enclosing the isothermal body, and a reducing atmosphere inside the
enclosure operative to substantially prevent oxidation of the
reflective walls of the cavity and thereby maintain reflectivity of
the reflective walls.
10. The apparatus of claim 9 wherein the reflective walls comprise
OFHC copper and wherein the reducing atmosphere contains hydrogen
and a filler gas.
11. The apparatus of claim 9 further comprising insulation in walls
of the enclosure.
12. An apparatus for collecting heat from the sun and for
transferring the collected heat to a heat sink, the apparatus
comprising: a solar concentrator; an isothermal body defining an
elongated substantially cylindrical cavity with a substantially
circular opening having a diameter substantially equal to a
diameter of a focus of the solar collector, the cavity having
reflective walls such that solar rays contacting the walls are
substantially reflected; wherein the isothermal body is oriented
such that the circular opening is located substantially at the
focus of the solar collector and substantially perpendicular to a
principal axis of the solar concentrator, and such that an axis of
the cavity is substantially aligned with the principal axis of the
solar concentrator; wherein the isothermal body is adapted for
thermal connection to the heat sink such that heat generated in the
isothermal body is absorbed by the heat sink; and wherein a length
of the cavity is about 5 to 9 times the diameter of the circular
opening.
13. The apparatus of claim 12 further comprising a low-emissivity
shield covering an end of the isothermal body between the opening
of the cavity and outer edges of the isothermal body.
14. The apparatus of claim 12 further comprising an enclosure
enclosing the isothermal body, and a reducing atmosphere inside the
enclosure operative to substantially prevent oxidation of the
reflective walls of the cavity and thereby maintain reflectivity of
the reflective walls.
15. The apparatus of claim 14 wherein the reflective walls comprise
OFHC copper and wherein the reducing atmosphere contains hydrogen
and a filler gas.
16. A method for collecting heat from a solar concentrator for
transfer to a heat sink, the method comprising: providing an
isothermal body defining an elongated cavity with a substantially
circular opening having a diameter substantially equal to a
diameter of a focus of the solar collector, the cavity having
reflective walls such that solar rays contacting the walls are
substantially reflected; orienting the isothermal body such that
the circular opening is located substantially at a focus of the
solar collector and substantially perpendicular to a principal axis
of the solar concentrator, and such that an axis of the cavity is
substantially aligned with the principal axis of the solar
concentrator; reflecting solar rays that contact a reflective wall
from a first contact point on the reflective wall to a second point
on a reflective wall and to a plurality of subsequent contact
points on the reflective walls until a desired proportion of the
energy contained in the solar rays is absorbed by the reflective
walls; thermally connecting the heat sink to the isothermal body
such that heat generated in the isothermal body by the absorbed
energy of the solar rays is absorbed by the heat sink.
17. The method of claim 16 wherein the proportion of the energy in
the solar rays entering the cavity that is absorbed increases as
the length of the cavity increases.
18. The method of claim 16 wherein the cavity is substantially
cylindrical and the length of the cavity is about 5 to 9 times the
diameter of the opening of the cavity.
19. The method of claim 16 comprising enclosing the isothermal body
in an enclosure and providing a reducing atmosphere inside the
enclosure operative to substantially prevent oxidation of the
reflective walls of the cavity and thereby maintain reflectivity of
the reflective walls.
20. The method of claim 19 wherein the reflective walls comprise
OFHC copper and wherein the reducing atmosphere contains hydrogen
and a filler gas.
Description
[0001] This invention is in the solar energy field and in
particular the collection of concentrated solar radiation for the
purpose of driving a thermo-chemical, thermo-mechanical or other
thermal process.
BACKGROUND
[0002] There exists today considerable interest in harnessing
renewable solar thermal energy for a multitude of heat driven
processes. These may include thermo-mechanical as in sterling
engine or steam turbine power generation systems, thermo-chemical
reforming, thermal-cracking, process heating, general heating,
materials processing etc. Solar collection systems are usually
placed in locations where sunlight is readily available. In a
typical system mirrors either flat-segmented, or curved, are
arranged in a parabolic or trough configuration to concentrate
incident solar radiation on a predefined target. Tracking control
systems or preprogrammed algorithms maintain the required optical
geometry by moving the mirror as the sun transverses the sky.
[0003] The target is usually some form of cavity or shallow dish
into which the concentrated light cone is directed. The cavity is
commonly disposed with a plurality of tubes into which a coolant is
flowed to convey absorbed heat to the working process. Some cavity
designs as in U.S. Pat. No. 5,113,659 incorporate a series of hot
shoes inside a cavity to conduct thermal energy to a plurality of
free piston sterling generators. In some solar thermo-chemical
processing the image fireball is employed to directly heat catalyst
beds in transparent process tubes often resulting in hotspots,
causing catalyst sintering and poor process temperature
control.
[0004] In all these collection schemes, the spot size and shape
must be tailored for the heat exchange and cavity parameters. To
avoid local overheating effects the fireball is often defocused or
multiple fireball images are skewed to provide a homogenous heat
zone into which the process heat exchange tubes are displaced. This
results in a less than optimal focus of the solar fireball on the
target and an increase in radiation losses due to the enlarged
solar image size with the accompanying increased area of hot
radiating surfaces.
[0005] Scaling and the costs of solar collection technology will be
dictated to a large part by overall product conversion efficiency,
therefore the goal of any solar collection system is the maximum
product production for the smallest possible solar collection area.
A key factor in achieving this goal is the minimization of
parasitic losses due to target re-radiation.
[0006] The required process temperatures dictate the collection
means, be it trough reflectors for low-grade heat applications or
parabolic concentrators for higher temperatures. Steam systems may
be operated at moderate temperatures of less than 800 K, whereas
thermo-chemistry in an effort to obtain high equilibrium constants
in some endothermic reactions may require substantially higher
temperatures. Unfortunately as process temperatures increase,
parasitic radiation loss follows Stefan's Law
(Pr=.sigma..epsilon.AT.sup.4) such that losses due to thermal
radiation increase sixteen fold for each doubling of the absolute
temperature of the target, which is at the process temperature. It
follows that minimum radiation loss can be realized by utilizing
the smallest possible fireball image or the highest solar
concentration in conjunction with an optimized cavity receiver
configuration in which the blackbody area equals the focused solar
image.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide a solar
heat collecting apparatus and method that overcomes problems in the
prior art.
[0008] In a first embodiment the invention provides an apparatus
for collecting heat from a solar concentrator and for transferring
the collected heat to a heat sink. The apparatus comprises an
isothermal body defining an elongated cavity with a substantially
circular opening having a diameter substantially equal to a
diameter of a focus of the solar collector, the cavity having
reflective walls such that solar rays contacting the walls are
substantially reflected. The isothermal body is adapted to be
oriented such that the circular opening is located substantially at
the focus of the solar collector and substantially perpendicular to
a principal axis of the solar concentrator, and such that an axis
of the cavity is substantially aligned with the principal axis of
the solar concentrator. The isothermal body is adapted for thermal
connection to the heat sink such that heat generated in the
isothermal body is absorbed by the heat sink. The length of the
cavity is sufficient to absorb a desired proportion of the energy
in the solar rays entering the cavity.
[0009] In a second embodiment the invention provides an apparatus
for collecting heat from the sun and for transferring the collected
heat to a heat sink. The apparatus comprises a solar concentrator,
and an isothermal body defining an elongated substantially
cylindrical cavity with a substantially circular opening having a
diameter substantially equal to a diameter of a focus of the solar
collector, the cavity having reflective walls such that solar rays
contacting the walls are substantially reflected. The isothermal
body is oriented such that the circular opening is located
substantially at the focus of the solar collector and substantially
perpendicular to a principal axis of the solar concentrator, and
such that an axis of the cavity is substantially aligned with the
principal axis of the solar concentrator. The isothermal body is
adapted for thermal connection to the heat sink such that heat
generated in the isothermal body is absorbed by the heat sink and a
length of the cavity is about 5 to 9 times the diameter of the
circular opening.
[0010] In a third embodiment the invention provides a method for
collecting heat from a solar concentrator for transfer to a heat
sink. The method comprises providing an isothermal body defining an
elongated cavity with a substantially circular opening having a
diameter substantially equal to a diameter of a focus of the solar
collector, the cavity having reflective walls such that solar rays
contacting the walls are substantially reflected; orienting the
isothermal body such that the circular opening is located
substantially at a focus of the solar collector and substantially
perpendicular to a principal axis of the solar concentrator, and
such that an axis of the cavity is substantially aligned with the
principal axis of the solar concentrator; reflecting each solar ray
that contacts a reflective wall from a first contact point on the
reflective wall to a second point on a reflective wall and to a
plurality of subsequent contact points on the reflective walls
wherein a portion of the energy contained in each solar ray is
absorbed by a reflective wall at each contact point until a desired
proportion of the energy contained in the solar ray is absorbed by
the reflective walls; thermally connecting the heat sink to the
isothermal body such that heat generated in the isothermal body by
the absorbed energy of the solar rays is absorbed by the heat
sink.
[0011] The solar radiation is converted to heat by multiple
internal reflections within the reflective cavity disposed in the
isothermal body, and this cavity receiver assembly is thermally
coupled to the required heat process or heat sink. the isothermal
body has significant mass to integrate thermal fluctuations and
provide the coupled process with a substantially consistent
temperature regardless of minor insulation or fireball image
deviations.
[0012] The cavity opening is positioned at the focus of a parabolic
solar concentrator on the principal optical axis such that the
light cone is at its minimum diameter at the cavity entrance.
[0013] The mechanical configuration resembles a thick walled hollow
cylinder clad with or constructed wholly of a chemically reducible
material such as, but not limited to, copper. The isothermal body
is thermally coupled to a heat process while the open end of the
cavity intercepts the light cone at the foci from a solar
concentrator. Solar flux enters the cavity and undergoes multiple
internal reflections while evenly dispersing and gradually reducing
the radiation to heat which is absorbed by the isothermal body of
the receiver and conducted to the process. Reflectivity of the
cavity walls is maintained by an inert or reducing local
atmosphere.
DESCRIPTION OF THE DRAWINGS
[0014] The aforementioned objects and advantages of the present
invention as well as additional objects and advantages thereof will
be more fully understood herein as a result of a detailed
description of preferred embodiments of the invention when taken in
conjunction with the following drawings where like components in
the drawings are assigned like designators and where:
[0015] FIGS. 1 and 2 are schematic views of a prior art solar heat
collection system configured to drive a Sterling to electrical
converter,
[0016] FIG. 3 depicts the target irradiance profile of a radially
skewed solar collector used in the prior art to reduce solar
concentration to an acceptable level;
[0017] FIG. 4 is a graph of the radial flux distribution of the
prior art and the current invention;
[0018] FIG. 5 is a graphical representation of blackbody thermal
radiation loss in relation to target temperature and area;
[0019] FIG. 6 is a schematic sectional side view of an embodiment
of the present invention employed in a Sterling engine driven
generator system;
[0020] FIG. 7 is a schematic sectional side view of an alternate
embodiment of the invention in a superheating application;
[0021] FIGS. 8 and 9 are schematic sectional side views of an
embodiment of the present invention employed in a thermo-chemical
reactor system;
[0022] FIG. 10 is a schematic isometric view of an isothermal body
of the invention defining a co-axial cavity and illustrating a
single ray path and the basic principals of the cavity
operation;
[0023] FIG. 11 is an end view of the thermally conductive body of
FIG. 10 illustrating the internal ray path.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0024] FIGS. 1 and 2 schematically illustrate a prior art system of
solar heat collection driving a heat engine and electric generator
combination. Solar heat collection systems are used to provide heat
for a wide variety of purposes in which the collected heat is
transferred to a heat sink, such as the illustrated heat engine,
that essentially consumes the heat. The operating temperature will
vary depending on the purpose, and the system will be designed such
that all the collected heat will be drawn away by the heat sink
once the operating temperature is at the desired temperature which
can vary from about 100.degree. C. to 1400.degree. C. or more.
[0025] In this example solar radiation 1 is reflected by the solar
concentrator 2 in solar rays 7 of a solar beam and focused on a
target 8 positioned in a cavity 11 at the focus of a parabolic
concentrator 2. The target 8 consists of a plurality of metal tubes
3 arranged symmetrically about the principal axis 9 of the
parabolic solar concentrator 2 to intercept the light cone. To
reduce thermal convection losses a quartz window 5 covers the
target 8. A coolant flows through the tubes 3 to remove heat
generated by the absorption of radiation on the tubes 3 and
transfer this heat to the heat engine 4 by conduction.
[0026] The mechanical energy converted by the heat engine in this
example is communicated by a shaft 10 to a generator 6, which
converts the mechanical energy to electrical energy. In this
example, the flux distribution directed at target 8 conforms to an
annular ring as shown in FIG. 3 by skewing multiple fireball images
on the tubular heat exchange structure in an effort to reduce solar
flux intensity levels to the heat exchange design limits. In FIG.
4, curves W graphically illustrate the resulting radial flux
distribution at the target 8 caused by the superimposed and skewed
fireball images of FIG. 3. As seen in FIG. 3, an approximately
circular portion in the middle of the target is substantially not
exposed to the solar rays 7. The concentration of the solar beam 7
on the target 8 is thus reduced by increasing the radiated target
area.
[0027] Solar concentration is typically measured in units of
"suns". One sun represents the energy incident upon a unit area
normal to the sun, which is about 1000 watts per square meter
(W/m.sup.2). Further for example, while the solar concentration
possible at the focus might be about 5500 suns, the heat exchange
tubing 3 will not withstand the heat developed at that
concentration. Given the heat capacity and mass flow of the
coolant, along with thermal transfer parameters of the heat
exchange, the maximum safe solar concentration in this example is
limited to about 877 suns or 877000 W/m.sup.2. To reduce the solar
concentration the mechanism is arranged, by skewing the parabolic
concentrator 2 for example, so that a larger area is radiated, and
the solar concentration is thus reduced, to effect the required
thermal transfer while maintaining the temperature of the exchanger
within design limits.
[0028] Increasing the target size however also increases the
radiation losses at a given temperature and reduces the efficiency
of the solar collector. As shown in FIG. 5, the magnitude of energy
loss at an emissivity of 1.0 due to target re-radiation is
substantially affected by the process temperature and the radiant
area of the target. In the example above in FIGS. 1 and 2, the
diameter of the target 8 would be about 15 inches and the solar
concentration is 877 suns on a target area of about 177 square
inches (including the circular portion in the middle of the target
that is substantially not exposed to the solar rays 7). By
rearranging the parabolic solar concentrator 2 to concentrate a
single fireball at the focus, the target can have a diameter of
about 6 inches so that the solar concentration is 5500 suns on a
target area of about 28 square inches at the focus. Thus the target
area is reduced by a factor of about 6.25 and the concentration
correspondingly increases by a factor of 6.25.
[0029] As seen in FIG. 5, by decreasing the target size to six
inches from 15 inches, the radiation loss can be reduced from 13%
to 2% where the process operating temperature is 850.degree. C. As
seen in FIG. 5, the radiation losses for the larger target increase
dramatically as the operating temperature rises, while the
radiation losses for the smaller target increase much less. These
data are thermodynamic realities consistent with any blackbody
solar receiver design at the indicated temperatures. The much
higher solar concentration however is problematic when actually
building a collector of such a small diameter.
[0030] FIG. 6 illustrates an embodiment of an apparatus of the
invention for collecting heat from a solar concentrator and for
transferring the collected heat to a heat sink. The heat sink in
the illustrated embodiment is a Sterling engine-generator similar
in design to that of FIGS. 1 and 2 with a collection apparatus of
the present invention. Here, instead of skewing the concentrator,
solar radiation 1 concentrated by a parabolic solar concentrator 2
is sharply focused to a single fireball image at the entrance
opening of elongated cavity 13. Here the solar concentration is
greatest, and the diameter of the target, the entrance opening of
the cavity 13, is smallest. In FIG. 4, curve S graphically
illustrates the resulting radial flux distribution at the target 8
with a single fireball image.
[0031] The opening of the cavity 13 is circular having a diameter
substantially equal to the diameter of the focus of the solar
collector 2. The cavity 13 is oriented such that the circular
opening is located at the focus of the solar collector 2 and
substantially perpendicular to a principal axis 9 of the solar
concentrator 2, and such that an axis of the cavity 13 is
substantially aligned with the principal axis 9.
[0032] The cavity 13 is defined in an isothermal body 12 made from
stainless steel, or the like. The cavity 13 is lined with a metal
liner 32 such as copper exhibiting good reflectivity in a
chemically reduced state and excellent thermal conductivity.
Alternatively, the isothermal body 12 may be constructed wholly of
a chemically reducible and thermally conductive material such as
but not limited to copper. In any event the cavity 13 has
reflective walls such that solar rays 7 contacting the walls are
substantially reflected. Multiple reflections of the light beam
within the cavity 13 transform the energy from the solar rays to
heat in the walls of the cavity 13 that is transferred by
conduction to the isothermal body 12 increasing its temperature and
making this heat energy available to the heat sink process.
[0033] By reflecting solar rays 7 that contact a reflective wall
from a first contact point on the reflective wall to a second point
on a reflective wall and to a large plurality of subsequent contact
points on the reflective walls the effective area of the receiver
is increased from the area of the opening of the cavity to the area
of the walls of the cavity. Since the cavity is elongated compared
to the opening of the cavity, the proportion of solar rays that
reflect from wall to wall and then out through the opening before
being absorbed is small.
[0034] The proportion of solar energy absorbed can be increased by
increasing the length of the cavity. Total absorption of the beam
is unrealistic, however if the length of the reflective cavity 13
is about 5-9 times the diameter of the cavity entrance opening the
length of the cavity will generally be sufficient to absorb a
desired significant proportion of the solar rays entering the
cavity. Tests have shown a very good approximation of a blackbody
absorber is realized with minimal blackbody area where the length
of the reflective cavity 13 is about 7 times the diameter of the
cavity entrance opening. With such a configuration about 95% of the
solar energy is absorbed.
[0035] Increasing the length of the cavity 13 will increase the
proportion of solar rays absorbed, however the length of the
isothermal body 12 is also increased. As the size of the isothermal
body 12 increases, conductive heat losses from the isothermal body
increase as well and gains in radiation reduction are offset by
conduction losses through the enlarged surface area of the
isothermal body 12. Decreasing the length of the cavity 13 will
result in a reduced proportion of the energy in the solar rays 7
being absorbed, as a greater proportion of the rays will be
reflected out of the cavity 13 and lost.
[0036] The cavity 13 is maintained in a reducing local atmosphere
for the chemical reduction of exposed metallic components whose
reflectivity would decrease if oxidized and thus reduce the
effectiveness of the apparatus.
[0037] FIGS. 10 and 11 illustrate the isothermal body 12 and cavity
13 of the present invention excluding any heat extraction means
where a single ray path of the solar beam 7 is traced through the
entrance 20 of the cavity 13 and encounters the reflective wall of
the cavity 13. The solar ray 7 or photon in this example undergoes
many reflections before finally being absorbed by the cavity wall
where its energy is transferred to the isothermal body 12 thus
increasing its internal energy or temperature. The path followed by
the photon in FIGS. 10 and 11 is but one of a myriad of paths
possible, depicted for illustrative purposes only. Focused light
energy with a Gaussian beam profile directed at the cavity entrance
would follow every possible path within the cavity evenly
distributing the heat therein.
[0038] As the temperature of the isothermal body 12 increases, the
exposed face 14, depending on its emissivity and area, will radiate
energy contributing to the total parasitic loss. It is advantageous
therefore to construct a shield 30 of a similar reducible material
such as copper, as illustrated in FIGS. 6-9, to cover this or any
exposed face of the isothermal body 12 between the opening of the
cavity and the outer edges of the isothermal body in an effort to
reduce the thermal radiation loss by reducing surface emissivity.
Chemically reducible and similar shields can be used to cover any
exposed components at the process temperature.
[0039] FIG. 7 shows a superheating arrangement used for steam or
working fluids of a heat process. Solar energy as described in the
aforementioned is absorbed by the mechanism of multiple internal
cavity reflections and absorption, which heat the isothermal body
12 to the process temperature required. The working fluid enters
the receiver at 18 and is circulated cyclically through passages
17, symmetrically located in the isothermal body 12, absorbing
energy from the body and exiting to the required process at 19.
[0040] In the embodiments of FIGS. 6 to 9, a sealed enclosure 16 is
provided which serves to contain a reducing atmosphere 15 as well
as any required insulation. A window 5 allows entry of solar
radiation to the reflective cavity 13 and also provides a gas seal
for the enclosure 16. The enclosure 16 is filled with a reducing
atmosphere, such as 5% hydrogen and the balance a filler gas that
is inert at the operating temperature. Nitrogen is a good choice
since it is cheap and inert at higher operating temperatures. Other
inert gases such as argon, etc, could be used as well. The reducing
atmosphere maintains the reducible metals, for example oxygen free
high conductivity (OFHC) copper or other like metallic compounds,
in their required metallic form. In this state, the reflective
surfaces of the liner 32 of reflective cavity 13 and shield 30
maintain a low emissivity thereby fulfilling their function in this
invention.
[0041] To reduce heat loss the enclosure 16 containing the reducing
gas is insulated.
[0042] In FIGS. 6-9, as solar radiation heats the cavity 13,
thermal expansion of the metal cavity liner 32 forming the metallic
walls of the cavity 13 causes high compression forces against the
interior walls of the isothermal body 12. Intimate contact between
these components decreases the thermal resistance of the metallic
boundary between the liner 32 and the isothermal body 12 enhancing
thermal transfer to the heat receiving isothermal body 12,
increasing the maximum rated flux density of the cavity by making
the cavity liner and receiver assembly substantially
isothermal.
[0043] FIGS. 8 and 9 illustrate a thermo-chemical solar reactor
where concentrated solar beam 7 enters a gas sealed enclosure 16
through a quartz window 5 where, through multiple cavity
reflections, the energy of the solar beam 7 is absorbed by the
isothermal body 12 and converted to heat. Reactant gas is admitted
to the feed line 22 and preheat channel 24. The hot reactant, on
exiting the preheater channels 24, enters the reaction beds 25
within the isothermal body where a catalyzed endothermic reaction
occurs. The products in these examples exit the isothermal body at
tubes 23.
[0044] Other embodiments of the examples depicted in FIGS. 6
through 9 would include a solid isothermal body constructed of a
reducible metal or ceramic thereby eliminating the need for a
reflective cavity liner or shield. Other means of inhibiting
oxidation of these key components such as other reducing gasses or
varying concentrations of the prescribed gasses are contemplated
within the scope of this invention.
[0045] The apparatus of the present invention is suitable for use
with higher operating temperatures where radiation losses represent
a significant portion of collected solar energy. At lower operating
temperatures, the radiation losses are less significant and use of
the apparatus will not typically provide significant benefits.
[0046] Thus the foregoing is considered as illustrative only of the
principles of the invention. Further, since numerous changes and
modifications will readily occur to those skilled in the art, it is
not desired to limit the invention to the exact construction and
operation shown and described, and accordingly, all such suitable
changes or modifications in structure or operation which may be
resorted to are intended to fall within the scope of the claimed
invention.
* * * * *