Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02755477 2011-10-18
A DECOUPLED, FLUID DISPLACER, STERLING ENGINE
Cross Reference to Related Application
This application claims priority from Canadian Patent Application No.
2,717,839 filed October 18, 2010, entitled LOGIC CONTROLLED DE-COUPLED
DISPLACEMENT-TYPE STIRLING ENGINE.
Field of the Invention
This invention relates to the field of devices utilizing Sterling engines and
in
particular to a de-coupled fluid displacing Sterling engine.
Background of the Invention
Sterling engines have been around for over two hundred years. Recently,
efficiencies of operation have increased where low temperature differential
Sterling engines
now routinely operate at temperature differentials of five degrees Celsius.
These temperature
differentials may be found in geo-thermal applications where in summer an
above ground
temperature is five degrees higher an underground temperature, and vice-versa
in winter.
In the present invention a low temperature differential Sterling engine has
portion of the engine underground, i.e. the hot side in the winter season, and
the remainder of
the engine on the surface, i.e. the cold side in winter. In this scenario, the
displacer would
have to travel a great distance, and would be very heavy. A mechanical
linkage, of such a
typical mechanism, from a driven flywheel to the displacer would be very
cumbersome. It is
consequently one object of the present invention use the Sterling engine to
displace fluid over
a distance to provide for pressurized actuation of an actuator such as a
piston.
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Summary of the Invention
In the summary, the mechanically decoupled, fluid displacing Sterling engine
according to one aspect of the present invention may be characterized as
including:
(a) hollow first and second containers, each of the containers having
opposite upper and lower ends;
(b) first and second fluid conduits mounted to, so as to extend between in
fluid communication with, the first and second containers;
(c) a selectively actuable fluid pump mounted in cooperation with the
second conduit, the fluid pump adapted to selectively pump fluid between the
containers;
(d) a processor cooperating with the fluid pump, the processor adapted to
control the pumping by the fluid pump;
(e) a third fluid conduit having opposite first and second ends, the first end
of the third conduit extending into the lower end of the second container, a
fluid
motivated actuator mounted to, in fluid communication with, the second end of
the third conduit,
The first conduit only extends into the upper ends of the containers, and the
second conduit extends into the lower ends of the containers. The first and
second containers
contain an actuating volume of an actuating fluid. The balance of the volume
of the containers
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contains a working gas. The gas is expandable and contractable upon heating
and cooling of
the gas respectively. The actuating volume of the actuating fluid is
sufficient for pumping of
the fluid between the containers and for actuation of the fluid along the
third conduit, whereby
the expanding of the gas urges a power stroke translation of the actuator, and
the volume of the
containers is pressurized upon a temperature differential being applied to the
first and second
containers to cause the expansion of the gas. Advantageously the temperature
differential is a
geothermal temperature differential. The pumping displaces the actuating fluid
between the
containers so as to correspondingly displace the gas for heating or cooling to
provide the
temperature differential to the gas.
In a preferred embodiment the containers are hot and cold chambers of a
Sterling engine, wherein the first chamber is adapted to be installed in-
ground, and the second
container is adapted to be mounted above ground. During a cold season the
second container
is the cold chamber and the first container is the hot chamber. During a warm
season the first
container is the cold chamber and the second chamber is the hot chamber. The
processor is
adapted to cause the pump to pump the actuating fluid into the cold chamber to
thereby drive
the gas into the hot chamber to increase the pressurization and the actuation
of the actuator in
the power stroke and to pump the actuating fluid into the hot chamber to
thereby drive the gas
into the cold chamber to reduce the pressurization and permit a reverse
retracting translation
of the actuator, whereby a net gain in work as between the power stroke and
the pumping of
the fluid is achieved.
In one embodiment the first conduit has opposite ends which are oriented so as
to direct a flow of the gas from each the end against an adjacent wall of the
container so as to
increase a rate of heat exchange between the flow and the adjacent wall. For
example, the
containers may have curved interior surfaces and the ends of the first conduit
direct the flow at
an acute angle against the curved interior surfaces. Depending on the shape of
the containers,
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CA 02755477 2011-10-18
the flow may advantageously induce a swirling flow in the containers. The ends
may be
nozzles, and the containers may be cylindrical.
The actuator may be a piston. The actuating fluid may be a liquid. The cold
chamber may include heat radiating members, for example, fins.
The engine may further include a flywheel cooperating with, so as to be driven
by, the piston. Sensors may be provided cooperating with the flywheel. The
sensors are
adapted to detect angular positions and/or angular displacement of the
flywheel and to
communicate corresponding data, corresponding to the angular positions and/or
the angular
displacement, to the processor. The engine may further include a generator
cooperating with
the flywheel for generation of electricity. The electricity may be used to
power the processor
and the pump.
Brief Description of the Drawings
Figure 1 is, in cross sectional view, a sealed a container containing fluid
and
having a conduit passing through the container from the fluid to an actuator.
Figure 2 is a sectional view through two sealed containers wherein one of the
containers is the container of figure 1 modified to include a further conduit
extending in fluid
communication between the upper ends of the two sealed containers, and wherein
only the
container having the actuator contains fluid.
Figure 3 is the cross sectional view of the figure 2 wherein the fluid has
mostly
been displaced from the container having the actuator into the second
container.
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Figure 4 is the cross sectional view of figure 3 of a further conduit
extending
in fluid communication between the two containers, this fluid communicating
conduit
extending to the lower ends of the containers in the manner of the actuating
conduit connected
to the actuator, and wherein the fluid communication has a pump cooperating
with the conduit
for pumping the fluid between the two containers.
Figure 5 is a partially cutaway view of a further embodiment of one of the
containers showing the use of an angled nozzle at the end of the gas
communicating conduit
extending between the upper ends of the two containers.
Figure 6 is a partially cutaway view of another embodiment of a container
showing a further inclined nozzle for inducing a swirling pattern of gas
passing through the
gas communicating conduit.
Figure 7 is the container of figure 6 having cooling fins mounted in radially
spaced array around the container.
Figure 8 is, in perspective view, a piston driven flywheel cooperating with a
electrical generator.
Detailed Description of Embodiments of the Invention
The following is a description of one embodiment of a mechanism according to
the present invention. The theory of operation for such a mechanism will be
built up from
basic principles, symbolically represented by glass jars, starting at figure
one, although it is
intended that the representation of glass jars is not to be limiting as other
containers, including
containers having different sizes and shapes would also work.
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Figure one shows an enclosed container 10 with an elongate actuating conduit
12 mounted into it. The container has fluid 14 inside of it. Above the fluid
is a high pressure
gas 16. This gas 16 pushes on the fluid 14 sufficiently such that the fluid is
pushed into the
actuating conduit 12.
If the container is heated from some initial temperature, the heated gas will
expand and push on the fluid, causing the piston 18 inside the actuator
housing to be moved in
an outward direction A.
If the temperature of the container is brought back to its initial condition,
the
gas will contract forming a slight vacuum on the fluid and cause the piston to
move back or
retract to its initial position.
Figure two shows the same setup as figure one apart from the high pressure gas
being placed in a separate container 20. If this separate container is heated
or cooled, the piston
18 will move as described above. The upper ends of the two containers are in
fluid (gas)
communication through conduit 22. In the claims hereto, container 20 may be
referred to as
the first container and container 10 may be referred to as the second
container.
For this description container 20 will be considered to be heated and
container
10 will be considered to be cooled. The mechanism as shown would put the
piston 18 in its
outmost position.
In Figure three much of the fluid 14 which was in container 10 in figure two
has been transferred into the heated container 20. In this condition, the
average gas
temperature is near the temperature of the cooled container 10. At this low
temperature, the
piston 18 will be at its most retracted position, having retracted in
direction B.
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The engine of Figure four includes a means to pump fluid back and forth from
the containers. An in-line pump 24 on conduit 26 is illustrated by way of
example. The
piston 18 can be moved inwardly and outwardly, i.e. extended or retracted, as
desired by
pumping fluid 14. The moving fluid 14 displaces the working gas 16 and the
working gas is
then heated or cooled.
In order for a system like this to be efficient, the working gas must be
heated
and cooled quickly. This problem may be solved by injecting the working gas
into the
containers in an efficient manner. Such a manner is demonstrated in figure
five by way of
example.
The working gas in Figure 5 is injected through nozzle 22a into the container
10 shown as direction C, tangentially, to the container wall 10a. As well the
flow should be
angled downwardly. The same applies to container 20 and the opposite end of
conduit 22. If
the gas is injected in this manner, the flowing gas will travel in a helical
path D (dotted
outline) continuously contacting the container wall 10a. As the gas travels,
it transfers heat to
and from the container.
The question is, can the piston 18 perform more work than was done by the
pump 24?
In the claims hereto, with reference to Figure 4 by way of example, the first
conduit is conduit 22, the second conduit is conduit 26 and the third conduit
is conduit 12.
The first end of conduit 12 is the lowermost end which, by way of example, may
be %2 inch
from the bottom of container 10. Container 10 may be the above ground chamber
of the
engine, and thus container 20 may be the under-ground chamber. The fluid
motivated actuator
is, by way of example, piston 18, although as would be known to those skilled
in the art, many
other forms of actuator may be actuated by a pressurized fluid, be it a gas or
liquid.
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CA 02755477 2011-10-18
The following is a mathematical development to show the work on the piston
verses the work to move the fluid.
The ideal gas law for a system of two temperatures and the same number of
moles is,
P, 1-71 = nRT1 = PV; = n.RT;
If we assume that there is a constant load, on the piston. Then we would have
a
constant pressure. Therefore P1 would equal P2. We can factor these out, along
with n and R,
and simplify yielding,
1., V.
Ti Tr
Solving for the new expanded volume yields, ~y
V2 V1 l f
The change in volume is,
A17 V,
Substituting for the expanded volume yields,
AT' = t71 =) - 'i
f1
Factoring the initial volume to the left yields,
The stroke length of the cylinder is,
ate
aF =
A
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Where "A" is the cross sectional area of the piston,
Substituting for the change in volume yields, r 1
AL Ti it
L
Work on a cylinder is known to be
1'; = FAAL
Substituting the cylinder stroke length yields, IT2
Canceling out the cylinder cross sectional area yields, 11
11 =PviLT`-1]
1
Now let's generate an equation for the work on the fluid.
L1 = FD
The force is equal to the density of the fluid times the volume. Therefore,
1' = pV1 D
Let's now evaluate the net work on the system.
AW = YGJ - T'
Substituting the derived work equations yields, r 1
A11~~ =1'1iT-iJ-p1'1,
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This equation shows that as the operating pressure increases, the work to move
the fluid
becomes less and less significant.
To show this more conclusively, let's calculate the fraction of the work to
move
the fluid over the net work. This is as follows,
R_
}+-p
T'1D
a
As the operating pressure increases, the fraction of the fluid moving work,
"R"
is reduced asymptotically.
The mechanical advantage of the work provided by the pump to the work
produced by the system is as follows,
11f1-1
P~ ~ T
ptiD
The following are a few notes about the operation of this system. The cylinder
performing work has been described as a hydraulic one. This is because
Hydraulic cylinders
tend to work better at very high operating pressures. This is not to say that
a pneumatic
cylinder could not be used. The hydraulic cylinder may be attached to the cold
chamber by
way of a hydraulic hose. Likewise, the hot and cold chambers may be connected
to each other
by way of pneumatic and hydraulic lines. The operation of this system is
dependent on some
form of logic controller to control the reversible pump.
For a system to produce work from geothermal energy during a cold season the
hot chamber, figure 6, would be buried under ground, while the cold chamber,
figure 7, would
be on the surface, connected to a piston 28, flywheel 30 , and generator
assembly 32, such as
CA 02755477 2011-10-18
seen in figure 8. The cold chamber on the surface may have heat radiation fins
34 on its
surface to enhance rapid cooling. To say the surface chamber is the cool
chamber implies
operation in the winter. During summer operation, the surface chamber would
become the hot
chamber while the ground chamber would become the cool chamber. This would not
affect the
operation of the system.
The Sterling cycle is characterized by isobaric heating, isothermal expansion,
isobaric cooling, and finally isothermal contraction. The steps of operation
of this cycle are as
follows.
Starting with all the fluid in the cold chamber, the heated working gas
expands
and pushes on the fluid in the cold chamber, thereby pushing strongly on the
piston.
After a time, the logic controller causes the pump to pump the fluid from the
cold chamber to the hot chamber. This displaces the working gas from the hot
chamber to the
cold chamber. The working gas in the cold chamber cools down. The cooled
working gas
pushes weakly on the fluid and thereby the piston. The piston may then
retract.
Again after a time, the logic controller (not shown) causes the pump 24 to
pump
the fluid from the hot chamber to the cold chamber. This displaces the working
gas from the
cold chamber to the hot chamber. The working gas in the hot chamber heats up.
The heated
working gas pushes strongly on the fluid and thereby the piston.
The following is an example of how much work could be done by a system like
this.
Let's start with the input variables.
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1. The hot working chamber dimensions are 24 inches Diameter by 24 inches long
which equals 10,851 cubic inches.
2. The cold working chamber dimensions are 24 inches Diameter by 24 inches
long which equals 10,851 cubic inches.
3. The system is pressurized to move a load of 1400 pounds through a 1 inch
square piston. This requires an operating pressure of 1400 pounds per square
inch.
4. The low operating temperature is 273 degrees Kelvin.
5. The high operating temperature is 278 degrees Kelvin.
6. The density of hydraulic fluid is 0.03168 pounds per cubic inch.
7. The distance to move the working fluid is 480 inches.
Let's calculate the net work. l
T2-1J-pVD
AW=P17, R-
A W = (1400)(10051) - 1J - (0.03168)(10651)(480')
[273
lid' = 227,393 Joules
If this work occurred in twenty seconds, we have 11,370 watts.
Let's evaluate the fraction of the total work used to move the working fluid.
1 D
R=
i - 1]+pi', D
R (0.0 3169)(1 OSS 1)(480)
=
(140a3(10851) [~73 - 1] + (0.03168X10851)460)
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R = 0.372
R 37%
Next let's evaluate the mechanical advantage of the system.
P. 1i
E=
p D
(1400 )(10851) [ 3 -1]
(0..0316x)(10851 ){480)
E=1.69
Consider the operation of a system using a flywheel. The orientation of the
flywheel when the cylinder is at full contraction is considered to be zero
degrees.
At zero degrees the fluid is in the cold chamber. Therefore the working gas is
at
its highest temperature. Since the working gas is at its highest temperature,
the pressure on the
piston is at its highest. The piston applies the highest torque to the
flywheel at this stage.
When the flywheel rotates ninety degrees, the pump starts moving fluid out of
the cold chamber, into the hot chamber. By the time the flywheel is at one
hundred and eighty
degrees, all the fluid has been moved. This moved fluid displaces the working
gas to the cold
chamber. The cooler gas applies a reduced pressure on the remaining fluid and
piston. Inertia
maintains rotation of the flywheel, against the reduced force, until the
flywheel is back at zero
degrees.
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When the flywheel rotates two hundred and seventy degrees, the pump starts to
pump the working fluid out of the hot chamber. By the time the flywheel is
back at zero
degrees, all of the working fluid has been moved into the cold chamber were
the sequence
starts all over again.
Sensor markers (not shown) are placed on the radial edge of the flywheel at
positions 0 degrees, 90 degrees, 180 degrees, and finally 270 degrees. A
sensor (not shown)
detects the sensor markers as they pass, and communicates this information to
the logic
controller. The logic controller evaluates the angle of the flywheel and
controls the working
fluid pump 24 to maintain steady state operation.
Some of the electricity that is generated by generator 32 is stored, for
example
by a power management system, for use by the hydraulic pump and the logic
controller.
The flywheel obtains, in a properly designed system, enough momentum to
operate a load such as a generator. For the generator to obtain a high angular
velocity for
operation, a gear ratio may be employed from the flywheel to the generator
drive shaft.
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