Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
11328~9
SOLAR TRACKING CONCENTRATOR
BACKGROUND OE' THE INVENTION
The invention relates generally to solar energy
utilization systems and particularly to an improved solar
tracking concentrator which admirably lends itself to
incorporation into a solar thermal energy collection and
transport subsystem which may form part of a solar energy
electrical power generation system.
It seems to be commonly assumed or agreed that one
of the most pressing problems facing the nation at this time
in history is that of en~rgy and, more particularly, locating
feasible energy sources that are economically competitive
alternatives to traditional fuels, such as fossil fuels.
There has been much research and development effort and
activity directed at the development of solar central receiver
electrical power generation systems. In one such system, a
large field or array of individually driven and controlled
mirror-like devices forming part of heliostats reflect the
sun's rays to a common, focal, heat absorbing zone, i.e. the
central receiver, which may be part of a boiler/superheater.
The central receiver is a target for the reflected sun's rays,
which are highly concentrated at the central receiver and may
be collected at high temperatures in excess of 500 degrees
Centigrade and subsequently used through known systems, such
as steam-turbine driven electrical generating plants, to
produce electricity or otherwise to provide thermal energy
for other systems. Another system employs a plurality of
distributed point focusing solar thermal concentra~ors which
1132~9
convert solar energy to steam and transport it to a central
power conversion subsystem. Both government and industry
recognize that before a solar energy electrical power
generating system becomes a practical reality, it must be
economically feasible, i.e. the cost of generation of a unit
of electricity must be in a cost range that is comparable to
or better than that of contemporary electrical power
generating systems. Studies have indicated that the cost of
heliostats, be they of the type used in central or point
focusing receiver systems, is the largest factor in the
overall cost of such a system. It has been concluded that
the development of an operationally acceptable solar tracking
point focusing concentrator which lends itself to ease of
manufacture in quantity production, ready shipment to site,
easy assembly and installation at site, and low cost
maintenance over the expected life of the system, is highly
desirable. Such an improved concentrator must produce or
contribute to a significant reduction in initial cost and
maintenance costs over the prospective life of the system.
SUMMARY OF THE INVENTION
A heliostat is a device which includes an optical
reflective surface that is appropriately mounted, driven and
controlled so as to continuously track the sun during the
course of the day and reflect the sun's rays to a receiver.
Although a complete heliostat comprises an assembly of
components which includes the reflective surface, support
structure therefor, a drive and control system therefor, and
a means to protect particularly the reflective surface from
injurious environmental conditions, such as wind, sand, snow
and rain, likely to be encountered at the site of installation,
11328~9
this invention deals primarily with the provision of an
improved solar tracking point focusing concentrator and some
closely related components, which permit and contribute to
the design of an overall improved heliostat.
Solar tracking point focusing concentrators
according to the invention herein are extremely simple, light
weight, use cost effective materials, made of few parts,
permit the use of low cost mass production techniques,
eliminate shipping problems to the installation site and lend
themselves to semiautomatic and easy installation at the site
with minimum labor. The aforesaid attributes provide an
extremely low initial cost concentrator and result from
applicant's unique parabolic reflector configuration and
- mounting, which produces or permits: (1) near optimal opticalperformance; (2) minimum volume within the concentrator's
enclosure required for elevational and azimuth movement of
the reflector; (3) an inherently balanced design which
obviates the need for counter weights and the resultant heavy
duty reflector drive means, and (4) a solar heat receiver-
exchange device rigidly mounted at the focus of the reflector
and secured to the pedestal and piping in permanently fixed
position thereby obviating the need for movable joints in the
high temperature, high pressure piping system. Applicant's
unique parabolic reflector configuration and mounting comprises
providing a reflector of dished parabolic configuration
having a rim angle of approximately 109 , and mounting the
reflector for rotation about horizontal and vertical axes to
effect angular adjustments in elevation and azimuth,
respectively, which axes intersect at the focal point of the
paraboloid.
1~328~9
The extremely light weight solar tracking
concentrator constructed in accordance with the invention
lends itself to being supported by a simple pipe pedestal
assembly which can be automatically inserted into the ground,
and driven by a low cost, mass produced, linear stepping
motor drive system which, in turn, lends itself to being
controlled by accurate positioning microprocessors, which
can be mass produced and operate on electronic position pulse
- counting techniques. Further, all elements of the drive and
control systems can be factory installed and mounted on the
pedestal frame assemblies.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a light
weight, inexpensive solar tracking concentrator that permits
low cost mass production techniques to be employed for its
manufacture; part and subassembly sizes small enough for
conventional shipping; semiautomatic and simple installation,
and easy maintenance.
It is a further object of the invention to provide
an improved parabolic solar tracking concentrator which:
~1) provides near optimal optical performance; (2) requires
minimum room for elevational and azimuth movement of its
reflector; (3) provides an inherently balanced mounting of
the reflector, and (4) permits the mounting of a fixed heat
receiver at the focus of the reflector.
It is a still further object of the invention to
provide an improved light weight solar tracking concentrator
that lends itself to being supported on a simple pipe pedestal
assembly which permits automatic insertion into the ground by
a machine, and driven and controlled by light weight drive and
113Z869
control components that are factory installed and mounted on
the reflector and pedestal assembly of the concentrator.
It is another object of the invention to provide an
improved light weight solar tracking concentrator that lends
itself to being driven and controlled to track the sun by
highly accurate potentially low cost mass produced electronic
microprocessors and linear stepping motor drives.
Other and more particular objects of the invention
will in part be obvious and will in part appear from a -
perusal of the following description of the preferred
embodiment of the invention and the claims, taken together
with the drawings.
DRAWINGS
FIGURE 1 is a sketch of a small solar energy power
generation plant which incorporates the improved solar
tracking concentrators of the invention;
FIGURE 2 is a side elevational view of an improved
solar tracking concentrator installed for operation on site
within a protective enclosure, with a portion of the enclosure
~0 broken away for clarity;
FIGURE 3 is an enlarged, side elevational view of
the improved solar concentrator, by i~self, with a portion of
the reflector broken away and some of the pipe pedestal
assembly shown in cross section for clarity;
FIGURE 4 is a front elevational view of the improved
solar concentrator of Figure 3 looking from the right thereof;
. FIGVRE 5 is an enlarged view of the pipe pedestal,
reflector support post and drive therefor;
FIGURE 6 is a perspective front view of the
Figures 3 and 4 improved solar concentrator;
11328~9
FIGURE is a sectional view taken through the
central portion of the reflector to show an assembly detail;
FIGURE 8 is a schematic view showing the geometry
of the paraboloid configuration and mounting relative to its
axes of rotation, focal point and the heat receiver
disposition;
FIGURE 9 is a perspective view, with portions
broken away for clarity, of a heat receiver-boiler that may
be used in conjunction with my improved solar concentrator;
FIGURE 10 is a central longitudinal sectional view
of the heat receiver-boiler of Figure 9 on an enlarged scale;
FIGU~E 11 is a sectional view taken on line 11-11
of Figure 10, and
FIGURE 12 is an enlarged view of a portion of
Figure 10 showing the detailed construction of the heat pipe,
boiler monotube interface.
DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1 comprises a sketch of an aesthetic low
profile deep set back one megawatt solar power plant which is
well suited to incorporate my improved solar tracking
concentrator. The Figure 1 power plant is for illustrative
purposes only and will be only generally described herein.
For the purposes of achieving a one megawatt capacity for an
approximate 0.4 load factor capability, the power plant
comprises a field of 150 distributed air supported plastic
bubble enclosures E, each of which houses one of my improved
solar tracking concentrators. The enclosures are desirably
machine installed on forty foot centers and utilize in situ
soil as part of their foundation structure. A tract of just
under eleven acres, which may be totally fenced and graded
1132869
for local drainage specifications, is utilized. A perimeter
set back of 100 feet may be employed to provide for aesthetic
appeal, security considerations and a perimeter access drive-
way. In operation, each of the solar concentrators produces
at its individual location superheated steam for power
generation purposes which must be transported from the individ-
ual distributed concentrators to a central power conversion
subsystem, e.g. a steam operated electrîcal power generating
station. The steam effectively may be conveyed through a
manually installed above ground vacuum insulated piping network
that connects the field of concentrators with the power
conversion subsystem. The piping network also provides a
feedwater supply for the boilers located at each of the
concentrators, and may also conveniently carry the electrical
wiring for powering the control-drive means for the control
and driving of the solar reflectors of the concentrators.` In
Figure 1, the piping network may be generally understood. It
comprises transverse pipes P for tying in the boilers of the
concentrators. Pipes P communicate with main header H which,
in turn, communicates with the power conversion subsystem PCB.
The pipes P and header H internally carry feedwater supply and
superheated steam conduits. The conduits must be thermally
insulated so they and/or the pipes and header are appropriately
insulated. Particularly effective insulated piping networks are
disclosed and claimed in the copending application of Daryl L.
Renschler and Horton being filed concurrently herewith. The
subsystem PCB includes the turbine generator set, condenser,
pumps, valves,steam accumulator, water conditioning subsystem,
feedwater heater, master control and computer. An energy
storage subsystem, such as a battery unit, may optionally be
employed when load factors above 0.4 are selected. If so,
the energy storage submodule EB may be employed. A cooling
tower subsystem CT is employed for known purposes. The
- 7 -
113Z8~9
foregoing represents a very general description of a small
solar power generating plant in which my improved solar
energy tracking point concentrators may be employed.
In Figure 2 the improved concentrator is ~enerally
designated C and shown as housed within a protective
enclosure E which protects the concentratOr from environmental
conditions. The protective enclosure generally includes a
plurality of transparent plastic segments S and a foundation
~. The specific construction of enclosure E forms no part of
my invention being described and claimed in this application
for it is described and claimed in the U.S. Pat. No.
~283,887 dated ~U~st /8, 1981 entitled Solar
Heliostat Enclosure, Enclosure Foundation And Installation
Method And Machine Therefor of J. Zdeb ànd Horton The
detailed construction and operation of the enclosure is set
forth in the referred to application. It may be briefly
characterized as a low cost air supported bubble enclosure
which includes a plurality of zipper connected panels of
clear plastic material that are supported by air supplied ~y
a blower unit provided for each enclosure. The foundation is
ring shaped and connected to lower portions of the panels.
The foundation is filled with in situ soil excavated at each
enclosure location. Means is provided for personnel to have
access to the interior of the enclosure for assembly,
maintenance and repair. An internal rigid frame built of
metal pipes is provided for lightning protection and for
support of the bubble during nonpowered air support periods,
such as on calm days.
My improved solar concentrator C comprises a
collector assembly generally indicated as CA that is supported
8 --
113Z8~9
on a pipe pedestal assembly generally indicated as PA. The
collector assembly is mounted on the pedestal assembly so as
to be adjustable in azimuth and elevation angles and to be
automatically controlled and driven for tracking the sun from
sunrise to sunset. It is the improved concentrator
construction to which my invention primarily addresses itself.
With particular reference to Figures 3, 4 and 5, the collector
assembly CA will be understood. The collector assembly CA
comprises a light weight segmented structure parabolic dish
reflector 10. The broad concept of the reflector construction
was conceived by NASA in 1963 during its work to develop and
demonstrate for space applications a thirty-two foot diameter
aluminum honeycomb segmented structure parabolic dish. The
dish reflector 10 is an assemblage of segmented leaves 12,
each made of one-half inch thick aluminum honeycomb sandwich
construction. The surfaces of the segments are stretch
formed aluminum bonded to the core with thermosetting
adhesive. The concave surface of the dish reflector 10 is
coated with aluminized mylar so as to be reflective. The
segments are formed soasto provide a central opening 14 in the
dish reflector to facilitate assembly of the reflector segments
by clip means. One or more of the segments which is located
at the bottom of the assemblage of the dish reflector are
formed so as to provide a rectangular slot 16. The slot
permits a portion of the pipe pedestal assembly PA to extend
through the reflector so as to permit vertical movement of
the reflector 10 when its elevational angle is adjusted
during operation. A pair of horizontally aligned openings 13
are formed in two segments to permit ends of a xeflector
supporting yoke to extend through the reflector as part of its
mounting.
_ g _
113Z8~9
The reflector 10 is formed and supported by a frame
comprising a plurality of support rings 18, 20 and 22 which
are axially spaced, of circular coniguration and of
different diameters. Support ~ing 18 is the smallest central
one disposed adjacent re~lector central opening 14. The
support rings are supported in predetermined positions to
form a cage-like support frame for the reflector 10 by a
; plurality of arcuate radial brackets 24 which are secured to
the support rings to form a sturdy cage-like ~rame for the
reflector 10. To maintain the reflector and frame in
assembled position, clips 26 are employed to secure the inner
ends of the segments 12 at the opening 14 to the ring 18.
When fully assembled, the reflector 10 and its support frame
comprise the collector assembly CA, a functianally unitary
structure which includes the dish-like reflec~or 10 of
paraboloid configuration. The collector assembly CA is mounted
on pipe pedestal assembly PA for controlled movement about
horizontal and vertical axes to permit adjustment of the
paraboloid reflector in either elevation or azimuth to aim at
and track the s~un. As the collector assembly is of light
weight, it may be supported by a light weight supporting pipe
pedestal assembly PA.
The pipe pedestal assembly PA is predicated generally
on the single support pipe pedestal concept disclosed and
claimed in the U.S. Patent No. y,~oq, ?36 dated ~lU~ lq8O
of J. Zdeb and Horton, entitled Solar Central
Receiver Heliostat Reflector Assembly. Because of the ~
consciously designed light weight collector assembly employed
in my concentrator, a light weight pipe pedestal assembly may
be used to support the collector assembly and its control and
-- 10 --
11328~9
drive systems. The pipe pedestal assembly PA also serves the
additional function of providing a rigid mounting for the
reflected radiated solar heat receiver-boiler B with the heat
receiver BB at the focal point of my improved concentrator.
It also provides support for the feedwater and steam conduits
that are operatively associated with the boiler BO of the
receiver-boiler B.
The pipe pedestal assembly is formed by securely
installing an insert 40 for mounting the assembly into the
ground at the site, as by employing a conventional drilling
machine adapted for this purpose. The insert 40 comprises a
rugged pipe section of suitable length for the soil conditions
to be encountered at the site, which is hardened at its earth
entry end for drilling and flared with a Morse taper socket at
the other end. After the insert 40 is mounted, the remainder
of the pipe pedestal assembly is simply and totally installed
by manually inserting a matching Morse taper end on the main
pedestal support post pipe 42 into the ground insert 40. A
clamping device optionally may be used to additionally secure
the assemblage. The pedestal assembly may be assembled and
tested at the factory. It comprises the pipe 42, which is
formed at its lower end with the Morse taper to facilitate
mounting, centrally with means to rotatably support a
reflecting yoke, and at its upper end with means to support
the receiver-boiler B in fixed position. Pipe 42 supports
an arm 44 which extends upwardly, is slightly inclined from
the vertical and its upper end rigidly supports the receiver-
boiler B in fixed position, as by a detachable pipe fitting
flanged connection. As will be subsequently described in
detail, the configurational and dispositional relationship of
-- 11 --
11328~9
the concentrator components is such that the solar heat
receiver ball BB of the heat receiver-boiler B is disposed in
fixed position at the focal point of the paraboloid reflector
10 .
The pipe 42 and the arm 44 are hollow and in
communication. At the upper end of the arm 44 they communicate
with the interior of the receiver-boiler B, and at their lower
end they communicate with a horizontally extending hollow
pipe 46. The pipe 42, arm 44 and pipe 46 are thermally
insulated as by being vacuum jacketed, and house a feedwater
conduit 48 and a steam conduit 50 (see Figure 5). In operation,
feedwater from a source is supplied through the conduit 48 to
the boiler 52, where steam is generated because of the heat
transfer from the heat pipe 54, as will be more fully explained,
and the steam exits out the steam conduit 50 which preferably
is lead through an insulated piping network of the type which
forms the subject of the copending application of Daryl L.
Renschler and myself, to a power conversion station and
ultimately utilized for generating electricity. Of course,
the steam may be otherwise directed to a steam utilization
means, if desired.
The pipe pedestal assembly PA also serves to support
on its main pipe 42 the reflector 10 for adjustment in azimuth
and elevation. To achieve this mounting, a rigid bracket 56
~5 is secured to the pipe 42. It includes an upwardly facing end
bearing 57 and a laterally extending arm 58 which at its end
supports a linear stepping motor 60. Rotatably mounted
concentrically about a vertically central portion of the pipe
42 is a reflector support tube 62 which is supported at its
lower end by end bearing 57, and at its upper end integxally
1~3Z869
carries a V-shaped yoke 64 which, in turn, supports the
collector assembly CA. At its lower end, tube 62 has a
rigidly secured drive wheel 66 that is operationally associated
with the linear stepping motor 60. Linear stepping motors and
drive wheels are known.
The collector assembly CA is carried by the yoke 64
in such a configurational and dispositional relationship that
the common vertical axis of the pipe 42 and the tube 62 extend
through the focal point of the paraboloid reflector. Therefore,
rotation of the tube 62 about pipe 42 changes the azimuth
angle of the reflector 10. The rotation of tube 62 is effected
by the linear stepping motor 60 operating with the drive wheel
66 to rotate support tube 62 with its connected yoke 64 and the
supported reflector 10 relative to pipe 42 about a vertical
axis in either direction in a predetermined controlled manner
as required to track the sun. Light weight, sun tracking
microprocessor controls operating linear stepping motors are
known.
The yoke 64 comprises a pair of upwardly oppositely
extending inclined arms 68. The yoke, when the collector
assembly is connected to it in operational position, is
disposed within the confines of the paraboloid reflector 10,
except for its opposite ends 70 which extend on a common
horizontal axis through aligned openings 13 formed in two of
the segments 12 forming the reflector 10. The yoke ends 70
extend through openings 13 to the exterior of the reflector
10. Each end 70 carries a radially extending arm 72 which at
its free end supports a linear stepping motor 74 which, in
turn, is operationally associated with a semicircular drive
wheel 76. There are two drive wheels 76 rigidly secured to
- 13 -
1~3Z8~9
the support ring 20 of the collector assembly and extending
rearwardly on the central rear exterior of the reflector.
The arrangement is such that there is an operatively associated
linear stepping motor 74 and drive wheel 76 at each lateral
side of the collector assembly. Therefore, the reflector 10
may be selectively controllably adjusted in elevation by
actuation of the stepping motors 74 in a known predetermined
controlled manner to track the sun. The configuration and
mounting of the reflector 10 is such that rotation of the
reflector relative to the yoke occurs about a horizontal axis
that passes through the focal point of the paraboloid
reflector. Reflector elevational adjustments are made about
a horizontal axis which passes through the focal point and, as
previously described, azimuth adjustments are made about a
vertical axis that passes through the focal point. Hence, the
horizontal and vertical axes of rotation of the reflector
intersect at right angles at the focal point. Further, as
previously described, the solar heat receiver BB of the
receiver-boiler B is mounted at the top of pedestal arm 44 in
position to be disposed at the focal point of the paraboloid
reflector. This, of course, is a position which exposes it
to the maximum amount of radiated solar energy reflected by
the reflector 10. Also, it requires the minimum amount of
room for movement of the reflector in its enclosure.
A unique feature of my invention is the selection
of the 109 rim angle for the paraboloid. See Figure 8 for a
diagram of the geometry of a paraboloid having a 109 rim
angle. This rim angle, under the geometry of a paraboloid
structure inherently results in the center of gravity of the
structure being at the focal point. Thus, the weight of the
- 14 -
1~328~9
reflector 10 is balanced about its rotating axes in all
directions. Therefore, only the lowest torque requirements
are necessary for the drive system for the reflector, which
permits the use of light weight components. This avoids the
heavy high capacity motors required by prior art devices that
employ counterweights to balance their reflectors. This rim
angle also produces optimum optical efficiency for a collector
assembly.
It will, therefore, be understood that my reflector
configuration and mounting is such as to produce reflector
rotational axes that intersect at the focal point of the
reflector, as well as a reflector center of gravity at the
focal point. Hence, the focal point is coincident with the
center of gravity and the rotational axes intersection. The
arrangement is highly desirable in that: (1) it produces a
reflector with near optimal optical performance, (2) it
produces an inherently balanced reflector without counter-
weights, (32 it requires minimum enclosure volume for
reflector movement in normal operation, and (4) it permits
stationary mounting of a solar heat receiver at the focus of
the reflector.
One of the advantages of the unique configuration
and mounting of the reflector is to permit locating the solar
heat receiver, i.e. spherical boiler BB, at the focus of the
reflector. Although it could be part of a variety of solar
heat apparatus, the spherical boiler BB may conveniently form
a part of the solar heat receiver-boiler B. The detailed
construction of heat receiver-boiler B is shown in Figures 9 -
12, which illustrate a highly effective construction. The
solar heat receiver portion BB is a spherical ball and
- 15 -
:113Z869
substantially totally unshielded to permit maximum utilization
of the reflected radiated rays of the sun which, due to 109
rim angle of the reflector, are reflected and impinge on
substantially the entire spherical surface of ball BB. The
only ball portion that the sun's rays do not contact is the
portion of the ball BB that is connected to the boiler portion
BO of the receiver-boiler B. This arrangement is nearly
optimum optically.
The boiler portion BO is essentially elongated and
cylindrical shaped and has its longitudinal axis disposed at
an angle of 40 from the vertical (see Figure 8) which is
considered to be a most effective disposition as it invokes
the force of gravity to aid in refluxing of the vaporizable
working fluid used in the receiver-boiler. The receiver-boiler
functions to absorb reflected solar radiated heat concentrated
by the reflector 10 on the heat receiver ball BB, and to
transfer this heat through a heat pipe to the feedwater that
is disposed in the boiler of receiver-boiler. A desirable
boiler is a helically coiled monotube once-through steam
generator that surrounds the condenser portion of a potassium
heat pipe to generate superheated steam, which may thereafter
be utilized as steam power. The boiler portion BB is formed
by cylindrical metal casing 80 that at one end has a conicai
portion 82 which is attached to the ball BB. The other end of
casing 80 is closed by end wall 84. The potassium heat pipe
designated 54 is formed by a metal envelope that has a portion
86 that is generally correspondingly shaped to the casing 80
and disposed concentrically within it. The envelope includes
a conical reduced portion 88 and an integrally formed
essentially spherical body 90 which forms the heat receiving
ball BB. Ball BB comprises the evaporation region of the heat
- 16 -
i~3Z8~9
pipe 54. The envelope has an elongated cylindrical portion 92
disposed around the condenser region of the heat pipe 54 that i5
thermally coupled to the helically coiled monotube once-through
steam generator 52 by conduction and radiation across a helium
filled helical gap 94 (see Figure 12). The elongated cylindrical
portion 92 of the heat pipe forming envelope comprises the
condenser region-heat sink portion thereof. The steam generator
52 is helically wrapped around the heat sink portion 92 and
disposed in a helical corrugated groove 96 formed in the envelope
wall forming the heat sink portion 92 of the heat pipe. The gap
94 is formed by the groove 96 and a helically grooved enclosing
copper jacket 106, which is hermetically sealed to heat sink
portion 92. Enclosing the steam generator 52 and heat sink
portion 92 of the heat pipe is an annular hermetically-sealed
multifoil superinsulation capsule 98. The feedwater and super-
heated steam conduits 48 and 50, which are insulated, as by
encapsulated multifoil wrappings, are connected to opposite ends,
i.e. input and output, respectively, of the monotube generator,
and extend to and from the receiver-boiler. They extend out through
the boiler portion BO at a location near its lower end, and through
the hollow support arm 44 of the pipe pedestal assembly. Arm 44
may be vacuum jacketed to further insulate the conduits 48, 50.
The receiver-boiler B is mounted on the arm 44 in an inclined
stationary position, with the center of its heat receiver body 90
disposed at the lower end at the focal point of the reflector 10.
Solar radiation is reflected and focused by the
reflector 10 on the surface of the heat receiver body 90, which
is the heat input surface of the evaporation region of the heat
pipe 54. ~ody 90 forms a part of an overall heat pipe 54, which
is a metal envelope outlined by cylindrical heat pipe wall 86,
conical portion 88 and spherical body 90. The surface of the
body 90 is selected to maxi~ize high solar radiation absorption
activity consistent with long life of the body. A quantity 100
- 17 - ~
1~3Z8~9
of vaporizable working fluid, perferably potassium in liquid
form, is disposed within and partially fills the envelope
forming the heat pipe 54. A wick 102 having capillary
formations to transport working fluid is disposed within the
heat pipe 54 and substantially throughout the entire inner
surface of the metal envelope that forms heat pipe 54. As the
potassium liquid disposed in the portion of the wick adjacent
the inner wall of body 90 is heated, it vaporizes and flows
through an elongated vapor duct in the envelope that extends
through the constricted neck 104 of the envelope ~etween the
body 90 and heat sink portion 92. Potassium vapor tra~els
through the vapor duct from within the body 90 to the interior
of the heat sink portion 92 where it condenses on the inner
surface of the corrugated wall portion of the heat sink portion
lS 92. It is cooled by conduction and radiation of its heat
across the helium filled gap 94 to heat the steam generator `
coil 52. Thereafter, it refluxes back through the wick 102 to
the interior of the body 90. Gravity, due to the inclined
orientation of the receiver-boiler, strongly assists refluxing.
The wick 102 may conveniently consist of several layers of 100
mesh stainless steel wire cloth and performs the following
functions: One, it distributes liquid potassium over the inner
surface of the body 90 in a thin film from which it is
evaporated out of the wick pores without delet~rious bubble
formation. As the sun is tracked, the solar heated area o~ the
heat absorbing surface of body 90 moves. This requires good
working fluid distribution, which is accomplished through the
capillary action of the wick. Two, it distributes working
fluid over the inclined inner surfaces of the heat pipe
following snutdown preparatory to start up. Three, it distributes
- 18 -
~13Z8~9
a thin film condensate over the inner surface of the heat sink
portion 92 to assure high thermal conduc~ance and well
distributed return of condensate to the evaporator region in
body 90. Four, it constrains capillary forces of the refluxing
condensate in the reduced neck portion 104 where vapor velocity
is high to avoid entrainment in the vapor streamr i.e.
undesirable foaming of the working fluid.
The heat pipe envelope is attàched to the outer
casing 80 within the thermal insulating capsule 98. Lateral
support for the heat pipe is provided by a sliding joint 108
between adjacent ends of the heat pipe envelope and the insulating
capsule at one end of the heat receiver-boiler assembly. The
sliding joint support as such is not to constrain relative
axial thermal expansion of the heat pipe envelope within the
casing 80. The monotube steam generator helix 52 is positioned
between the helically grooved corrugated wall 96 of the heat
pipe envelope and copper cap fin pieces 106 which are brazed
to the corrugated wall portion 96 and form a helically grooved
jacket that cooperates with wall 96 to form the gap 94 for
housing the monotube boiler and which is helium filled. For
the latter prupose, spacers are provided to maintain an
approximately uniform helium filled gap between the heated
heat sink wall surfaces and the monotube steam generatorr thus
ensuring a moderate circumferentially uniform flux on the
steam generator tube surface and permitting freedom for
independent expansion of the heat pipe envelope and the boiler
generator coil through wind-unwind motion of the coil in its
loosely confined mounting. The insulating structure enclosing
the monotube steam generator may be Linde nickel foil-refrasil
encapsulated in a vacuum. At the upper end of the heat receiver-
-- 19 --
'113ZB~9
boiler B, seal off tubes 110 and 112 arè provided for
evacuation anq filling of the heat pipe 54 with potassium and
the helical gap~4 with helium, respectively. The access opening
for these tubes in the end of outer casing is covered by an
insulation cap 114.
A suitable material for the heat pipe,wicking, the
external casing and the monotube steam generator coil is
ustenitic. The advantages of this material include excellent
fabricability and weldability, good strength and corrosion
resistance at the operating temperatures contemplated, a
- thermal expansion coefficient matching that of copper, which
is used for the corrugated jacket fin structure, and well
proven compatibility with potassium. The major disadvantage
of this material is relatively low thermal conductivity, which
is objectionable insofar as the relatively high input wall
temperature drop to the body 90 is concerned.
The monotube steam generator 52 functions to transform
feedwater supplied at approximately 400 F. into superheated
- steam at approximately 950 F. as a result of the transfer of
the solar thermal energy supplied by the heat pipe at 1250 psia
by one pass through a single continuous boiler tube. The
monotube configuration minimizes a number of boiler tube
connections which enhances reliability. The once-through
feature eliminates the high pressure recirculating pump, the
steam drum and the liquid separators employed in recirculating
boilers, further increasing simplicity and reliability, as
well as significantly reducing cost. By positioning the steam
generator tubing in the helium filled space, significant thermal
stress problems affecting the generator tubing, if it were
directly exposed to the heat pipe fluid or attached directly
to tne heat pipe itself, are eliminated.
- 20 -
~i~2B69
With the reflector configuration and mounting
described, it will be understood that the reflector 10 will
be automatically driven to track the sun and will reflect the
sun's rays over most of the surface of the solar heat
receiver ball BB formed by body 90. The reflected solar
energy impinging on the outer surface of the body 90 during
tne course of the day is conducted to its inner surface, the
evaporator region, where it vaporizes potassium liquid in the
wick which ~lows out through the reduced neck portion 104 to
within cylindrical heat sink portion 92, the condenser region,
where it condenses in the wick 102 disposed on the inner
surface thereof, on transfer of its heat across the helium
filled space 94 to the monotube generator 52 to heat the
feedwater therein. The condensed potassium then refluxes,
i.e. flows through the wicking to the interior of the ~ody
90, where the solar heat transfer process resulting in
, . .. .
potassium vaporization continues. The feedwater is supplied
to the monotube generator 52 from a source through feedwater
supply conduit 48, and after being transformed into
superheated steam, it exits through the steam conduit 50.
The pipe pedestal assembly support tube 42 and conduits 48
and 50 are insulated to minimize heat losses. The feedwater
tube 48 and steam tube 50, which may be encapsulated in
multifoil insulation, both laterally exit out a lower portion
of the support pipe 42 into a horizontal transfer pipe 46,
which preferably is also insulated. The conduits 48, 50 are
housed, thereafter, in the insulated piping network including
piping P and header H to direct the steam to the power
conversion station PCB. It will be understood that both the
feedwater supply conduit and the steam conduit (48, 50)
113Z8~9
extend throughout the piping network to a source of feedwater
supply and the steam utilization means of the power conversion
station, respectively. It will also be understood tnat the
piping network may also support electrical cables from a
S source to provide electrical energy for the reflector control
and drive means which form a part of the solar energy
concentrators that are distributed about the field in their
xespective enclosures.
In view of the foregoing, it should be apparent
that I have achieved the objects of this invention. As will
be apparent to those skilled in the art, various changes and
modifications of the invention can be made without departing
from the spirit and scope of the invention, which is limited
only by the following claims.
- 2~ -
