Power plants – Motor operated by expansion and/or contraction of a unit of... – Unit of mass is a gas which is heated or cooled in one of a...
Reexamination Certificate
2000-03-02
2002-05-07
Nguyen, Hoang (Department: 3748)
Power plants
Motor operated by expansion and/or contraction of a unit of...
Unit of mass is a gas which is heated or cooled in one of a...
C060S523000, C060S524000
Reexamination Certificate
active
06381958
ABSTRACT:
TECHNICAL FIELD
The present invention pertains to improvements to thermal components of a Stirling cycle heat engine and more particularly to the heater head and combustion chamber assembly and regenerator.
BACKGROUND OF THE INVENTION
Stirling cycle machines, including engines and refrigerators, have a long technological heritage, described in detail in Walker,
Stirling Engines
, Oxford University Press (1980), incorporated herein by reference. The principle underlying the Stirling cycle engine is the mechanical realization of the Stirling thermodynamic cycle: isovolumetric heating of a gas within a cylinder, isothermal expansion of the gas (during which work is performed by driving a piston), isovolumetric cooling, and isothermal compression.
Additional background regarding aspects of Stirling cycle machines and improvements thereto are discussed in Hargreaves,
The Phillips Stirling Engine
(Elsevier, Amsterdam, 1991) and in co-pending U.S. patent applications Ser. No. 09/115,383, filed Jul. 14, 1998, and Ser. No. 09/115,381, filed Jul. 14, 1998, which reference and both of which applications are herein incorporated by reference.
The principle of operation of a Stirling engine is readily described with reference to
FIGS. 1
a-
1
e
, wherein identical numerals are used to identify the same or similar parts. Many mechanical layouts of Stirling cycle machines are known in the art, and the particular Stirling engine designated generally by numeral
10
is shown merely for illustrative purposes. In
FIGS. 1
a
to
1
d
, piston
12
and a displacer
14
move in phased reciprocating motion within cylinders
16
which, in some embodiments of the Stirling engine, may be a single cylinder. A working fluid contained within cylinders
16
is constrained by seals from escaping around piston
12
and displacer
14
. The working fluid is chosen for its thermodynamic properties, as discussed in the description below, and is typically helium at a pressure of several atmospheres. The position of displacer
14
governs whether the working fluid is in contact with hot interface
18
or cold interface
20
, corresponding, respectively, to the interfaces at which heat is supplied to and extracted from the working fluid. The supply and extraction of heat is discussed in further detail below. The volume of working fluid governed by the position of the piston
12
is referred to as compression space
22
.
During the first phase of the engine cycle, the starting condition of which is depicted in
FIG. 1
a
, piston
12
compresses the fluid in compression space
22
. The compression occurs at a substantially constant temperature because heat is extracted from the fluid to the ambient environment. The condition of engine
10
after compression is depicted in
FIG. 1
b
. During the second phase of the cycle, displacer
14
moves in the direction of cold interface
20
, with the working fluid displaced from the region of cold interface
20
to the region of hot interface
18
. This phase may be referred to as the transfer phase. At the end of the transfer phase, the fluid is at a higher pressure since the working fluid has been heated at constant volume. The increased pressure is depicted symbolically in
FIG. 1
c
by the reading of pressure gauge
24
.
During the third phase (the expansion stroke) of the engine cycle, the volume of compression space
22
increases as heat is drawn in from outside engine
10
, thereby converting heat to work. In practice, heat is provided to the fluid by means of a heater head
100
(shown in
FIG. 2
) which is discussed in greater detail in the description below. At the end of the expansion phase, compression space
22
is full of cold fluid, as depicted in
FIG. 1
d
. During the fourth phase of the engine cycle, fluid is transferred from the region of hot interface
18
to the region of cold interface
20
by motion of displacer
14
in the opposing sense. At the end of this second transfer phase, the fluid fills compression space
22
and cold interface
20
, as depicted in
FIG. 1
a
, and is ready for a repetition of the compression phase. The Stirling cycle is depicted in a P-V (pressure-volume) diagram as shown in
FIG. 1
e.
Additionally, on passing from the region of hot interface
18
to the region of cold interface
20
, the fluid may pass through a regenerator
134
(shown in FIG.
2
). Regenerator
134
is a matrix of material having a large ratio of surface area to volume which serves to absorb heat from the fluid when it enters hot from the region of hot interface
18
and to heat the fluid when it passes from the region of cold interface
20
.
Stirling cycle engines have not generally been used in practical applications due to several daunting engineering challenges to their development. These involve such practical considerations as efficiency, lifetime, and cost. The instant invention addresses these considerations.
SUMMARY
0
F THE INVENTION
In accordance with preferred embodiments of the present invention, there is provided a thermal cycle engine of the type having a piston undergoing reciprocating linear motion within an expansion cylinder containing a working fluid heated by heat from an external source that is conducted through a heater head. The thermal cycle engine has a heat exchanger for transferring thermal energy across the heater head from a heated external fluid to the working fluid, the heat exchanger comprising a set of heat transfer pins, wherein each heat transfer pin has an axis directed away from the cylindrical wall of the expansion cylinder. In accordance with alternate embodiments of the invention, the axis of each heat transfer pin may be substantially perpendicular to the cylindrical wall of the expansion cylinder. In accordance with further alternate embodiments of the invention, the heat exchanger may comprise a set of fins substantially aligned with the axis of the expansion cylinder. The thermal cycle engine may further include a plurality of dividing structures for spatially separating the set of heat transfer pins into subsets of heat transfer pins, and the heat transfer pins of each subset of heat transfer pins may have axes that are substantially parallel to each other.
In accordance with other embodiments of the invention, a subset of the set of heat transfer pins, up to the entirety thereof, may include heat transfer pins extending from the heater head into the external fluid. A pin backer may be provided for guiding the heated external fluid past the set of heat transfer pins. A dimension of the pin backer perpendicular to the heater head may decrease in the direction of the flow path, and the surface area of the heat transfer pins transverse to the flow path may increase in the direction of the flow path. The heat transfer pins may have a population density that increases in the direction of the flow path, and the height and density of the heat transfer pins may vary with distance in the direction of the flow path.
In accordance with another aspect of the present invention, a method is provided for manufacturing a heat exchanger for transferring thermal energy across a heater head from a heated external fluid to the working fluid. The method has the steps of casting at least one array of heat transfer pins integrally cast onto a panel, bonding the array of heat transfer pins to the heater head. The step of bonding may include mechanically attaching the panel to the heater head and may also include brazing the panel of the array of heat transfer pins to the heater head.
A method for manufacturing a heat exchanger in accordance with further embodiments of the invention provides the steps of fabricating a plurality of perforated rings, stacking the perforated rings in contact with a heater head, and bonding the perforated rings to the heater head. The step of fabricating may include stamping the rings out of a sheet of metal.
In accordance with yet a further aspect of the invention, a thermal sensor is provided for measuring a temperature of the heater head of a thermal cycle engine at a point of maximum temperature of
Gurski Thomas Q.
Kamen Dean L.
Langenfeld Christopher C.
LaRocque Ryan Keith
Norris Michael
Bromberg & Sunstein LLP
New Power Concepts LLC
Nguyen Hoang
LandOfFree
Stirling engine thermal system improvements does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Stirling engine thermal system improvements, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Stirling engine thermal system improvements will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2914567