Background and Summary of the Invention
The present invention relates to solar evaporators for thermal engines
and, more particularly, to solar evaporators for Stirling engines in which temperatures
in different parts of the evaporator tend to be equalized.
Evaporators for thermal or Stirling engines are utilized to heat
a medium, ranging from cryogenic gases such as hydrogen to liquid metals such as
sodium, and transport the medium from an evaporator to a condenser to provide
energy to run the engine. Various types of evaporators and condensers exist in
the art. One type, illustrated in U.S. Patent No. 4,523,636, assigned to the assignee
of the present invention, the specification of which is herein incorporated by
reference, illustrates a heat fin configuration coupled with a heat pipe to transport
the medium from the evaporator to the condenser.
The above art generally requires an external heat source such as
heated air or the like to heat the fins to vaporize the medium and cause it to
flow through the heat pipe. The present invention enables solar energy to heat
the evaporator to in turn heat the medium and cause it to flow between the evaporator
and the condenser. Devices which utilize solar energy to heat evaporators for thermal
or Stirling engines are illustrated in U.S. Patent Application Serial No.019,651,
filed February 27, 1987, entitled "Solar Powered Stirling Engine", assigned to
the assignee of the present invention, the specification of which is herein incorporated
by reference. It is desirable to maximize the solar energy to heat the evaporator
to transport the heated medium and to reduce problems resulting from unequal temperatures
in spaced parts of the evaporator due to uneven distribution of solar heat on the
receiving face of the evaporator.
Accordingly, the present invention provides a solar evaporator which
enables the medium to be heated to substantially even temperatures and the flow
transported equally from the evaporator through each pipe into each condenser
chamber. Thus, the present invention provides a solar evaporator which maximizes
the sun's energy.
The present invention provides a new and improved solar evaporator.
The solar evaporator of the present invention is utilized with thermal engines
which have at least two heat pipes and a corresponding number of condenser chambers
communicating with each heat pipe. The evaporator includes a parabolic dish shape
disk for receiving reflected rays of the sun and constructed so as to include a
pair of side-by-side chambers in heat exchange relation with the face which receives
the solar heat. The chambers communicate with the heat pipes. Wicks adapted to
transport the heating medium fluid are disposed within the chambers in engagement
with the walls to transport fluid between the chambers and the heat pipes.
In one embodiment of the invention, an auxiliary body extends between
the evaporator chambers and includes a wick structure in heat exchange relation
with the wicks in the chambers so that the temperatures in the chambers are equalized
even though the heat flux distribution on the face of the disk is uneven. If one
chamber is hotter it heats the mecium in the wick in the auxilary body. The medium
in the body in turn heats the medium in the chamber which was cooler, and this
exchange continues until the chamber temperatures are substantially equal.
In a second embodiment of the invention, the chambers are separated
by a common wall and wicks are arranged on opposite sides. When one chamber is
hotter than the other the medium in the wick in that chamber that is engaged with
the common wall will heat the corresponding medium in the other chamber. This process
of heating and cooling as the distribution of solar heat flux on the receiving
face of the disk continues to change continually equalizes the temperature in the
From the subsequent description and the appended claims taken in
conjunction with the accompanying drawings, additional advantages and features
of the present invention will become apparent to those skilled in the art.
Brief Description of the Drawings
Detailed Description of the Preferred Embodiment
- Figure 1 is an elevational view of a Stirling engine including a solar evaporator
in accordance with the present invention;
- Figure 2 is an enlarged side elevation view partially in cross-section of the
solar evaporator shown in Figure 1;
- Figure 3 is a front view of the solar evaporator shown in Figure 2;
- Figure 4 is a rear view, partly broken and shown partially in cross-section,
of the solar evaporator shown in Figure 2;
- Figure 5 is a side elevation view, like Figure 2, of a modified form of the
evaporator of this invention; and
- Figure 6 an elevational view of a dish collector module and a Stirling engine
equipped with the evaporator of this invention and mounted on the collector module
so as to receive reflected solar energy from the collector, and illustrating the
directional and seasonal orientation of the collector.
Referring to the drawings, particularly Figure 1, the solar evaporator
of this invention, indicated generally at 10, is illustrated in combination with
a Stirling engine 12. The Stirling engine 12 includes heat pipes 14 communicating
the evaporator 10 with the condenser chamber 16 of the engine 12.
Turning to Figures 2 through 4, it can be seen that the evaporator
10 includes first 18 and second 20 chambers positioned adjacent to one another
forming the overall dish shape evaporator 10. The chambers 18 and 20 are formed
by a parabolic disc shape body 21 having a concave front wall with upper and lower
halves 24 and 26, respectively, separated by an air gap 22. The front walls 24
and 26 are of a concave configuration and have outer solar heat receiving faces
28 6 and 30 and the rear walls 36 and 38 are spaced rearwardly from the front
walls. The interior surfaces 40 and 42 of the chambers 18 and 20 are lined with
a wick 44 and coarse porous material 46 is engaged with the wick 44 to maintain
it in heat exchange engagement with the body walls.
The wick 44, capable of transporting liquid with capillary action,
is mounted on the internal surfaces of the evaporator 10 including the inner faces
32, 34, of the front walls 24, 25, and the inner faces 37, 39 of the rear walls
36 and 38 of the chambers 18 and 20.
Generally, the coarse porous material 46 is sandwiched between the
front and back parts of the wick 44 to maintain the wick 44 against the inner faces
32, 34, 37 and 39 of the body 21. The coarse porous material 46 can be comprised
of stainless steel gauze or other materials sufficiently porous to allow vaporous
heat transport medium to flow therethrough with a minimum of obstruction to flow
while providing compressive strength.
An auxiliary body 50 is coupled with the chambers 18 and 20 so as
to bridge the air bap 22. The auxiliary body 50 includes a wall 52 which is coupled
to the rear walls 36 and 38 of chambers 18 and 20. The auxiliary body 50 is hollow
and includes a wick 54 which engages and is in heat exchange relation with the
walls 36 and 38 along its entire length to enable transport of fluid heating medium
from one end of the body 50 to the other along the length of the wick 54.
As the concave disk evaporator 10 is heated with solar energy, the
liquid medium within the evaporator begins to "heat up". As the medium heats, heated
vapor bebins to travel from the chambers 18 and 20 into the heat pipes 14. However,
the heat on the concave face of the evaporator will probably not be uniform so
the temperature in the chambers 18 will not be equal.
Figure 6 shows a dish collector module 60 comprising a parabolic
reflecting dish 62 which is supported for azimuthal and elevational motions. The
dish 62 is illustrated supported on the outer end of an arm 64 that is pivotally
supported at its inner end on a bracket 66 for up and down movement about an axis
D. Arm 64 can be moved up and down angularly about the horizontal axis D. The bracket
66 is also rotatably supported on an upwardly inclined leg 68 of fixed support
70 so that the dish module 60 can be rotated about axis T.
Appropriate motive means are used to impart rotational motion to
the dish 62 about axis T and to the arm 64 about axis D and there are suitable
controls associated with the motive means for causing the dish to track the sun
as it travels across the sky. Such motive means and controls are conventional and
will not be explained in further detail here. Suffice is to say that the controls
operate to keep the dish axis pointed at the sun, parallel with the direction
of incident sunlight.
The dish 62 serves to concentrate the solar rays which are incident
upon it by reflecting them to the focal point at which the dish shape body 21 in
the evaporator 10 is located. The evaporator 10 is connected to the Stirling engine
12 by heat pipes 14 as shown in Figure 1 and the combination is supported by suitable
structural framework 72 on the collector module 60. It can thus be seen from Figure
6 that inequality of heat on the chambers 18 and 20 is due to the movement of
the sun and is to be expected.
Assume that one chamber 18 or 20 is hotter than the other chamber
18 or 20. The wick portion of 54 in heat exchange relation with the hot chamber
will become hotter than the wick 54 opposite the cooler chamber. This will cause
a flow of heated medium in the wick 54 to a position opposite the cooler chamber
where it will give up heat to the cooler chamber until the temperatures of the
chambers are equalized.
Thus, as the vaporous heated fluid medium flows into the four heat
pipes 14, the flow rate in each heat pipe will be substantially equal to the flow
rate in the other heat pipes.
As the medium is condensed in the condensing chambers 16, the wick
44 draws the liquid medium from the condenser chambers into the evaporator chambers
18 and 20.
The return of the medium to the evaporator 10 enables the medium
to "heat up" and repeat the process of vaporization, return to the condenser,be
condensed, and continue to cycle, powering the Stirling engine.
In the modified form of the evaporator 10 shown in Figure 5, and
indicated generally at 10a, like numerals with the suffix "a" are used to indicate
like parts in the evaporator 10. In the evaporator 10a, the inner and outer walls
80 and 82, respectively, of the evaporator body 21a are continuous so the air gap
22 is eliminated. The walls 80 and 82 are of parabolic disc shape having different
curvatures so that only a single peripheral weld 84 and an internal diametrically
extending wall 86 are required to form the side-by-side chambers 18a and 20a.
Wickling 88 is engaged with the inner side of the front wall 80,
wickling 90 is engaged with the inner side of the back wall 82 and wicking 92 is
engaged with opposite sides of the divider wall 86. As one chamber 18a or 20a
becomes hotter than the other, the medium in the wick 92 26 in the hotter chamber
will become heated. This heated wick 92 will give up heat to the wall 86 which
will in turn heat the medium in the wick 92 in the cooler chamber resulting in
raising the temperature in the cooler chamber until it is equal to the temperature
in the hotter chamber.
It can thus be seen that the improved solar evaporator 10 of this
invention enables efficient and continued use of solar power to drive the engine
12 so long as heat from the sun is available.