VOLUMETRIC ENERGY RECOVERY DEVICE AND SYSTEMS
RELATED APPLICATIONS
[0001] This application is being filed on 28 February 2013, as a PCT
International Patent application and claims priority to U.S. Patent Application Serial
No. 61/604,929 filed on 29 February 2012, the disclosure of which is incorporated
herein by reference in its entirety.
TECHNICAL FIELD
[0001] The present disclosure relates to a volumetric fluid expander used for
power generation in the Rankine cycle.
BACKGROUND
[0002] The Rankine cycle is a power generation cycle that converts thermal
energy to mechanical work. The Rankine cycle is typically used in heat engines,
and accomplishes the above conversion by bringing a working substance from a
higher temperature state to a lower temperature state. The classical Rankine cycle is
the fundamental thermodynamic process underlying the operation of a steam engine.
[0003] In the Rankine cycle a heat "source" generates thermal energy that brings
the working substance to the higher temperature state. The working substance
generates work in the "working body" of the engine while transferring heat to the
colder "sink" until the working substance reaches the lower temperature state.
During this process, some of the thermal energy is converted into work by exploiting
the properties of the working substance. The heat is supplied externally to the
working substance in a closed loop, wherein the working substance is a fluid that has
a non-zero heat capacity, which may be either a gas or a liquid, such as water. The
efficiency of the Rankine cycle is usually limited by the working fluid.
[0004] The Rankine cycle typically employs individual subsystems, such as a
condenser, a fluid pump, a heat exchanger such as a boiler, and an expander turbine.
The pump is frequently used to pressurize the working fluid that is received from the
condenser as a liquid rather than a gas. Typically, all of the energy is lost in
pumping the working fluid through the complete cycle, as is most of the energy of
vaporization of the working fluid in the boiler. This energy is thus lost to the cycle
mainly because the condensation that can take place in the turbine is limited to about
10% in order to minimize erosion of the turbine blades, while the vaporization
energy is rejected from the cycle through the condenser. On the other hand, the
pumping of the working fluid through the cycle as a liquid requires a relatively small
fraction of the energy needed to transport the fluid as compared to compressing the
fluid as a gas in a compressor.
[0005] A variation of the classical Rankine cycle is the Organic Rankine cycle
(ORC), which is named for its use of an organic, high molecular mass fluid, with a
liquid-vapor phase change, or boiling point, occurring at a lower temperature than
the water-steam phase change. As such, in place of water and steam of the classical
Rankine cycle, the working fluid in the ORC may be a solvent, such as n-pentane or
toluene. The ORC working fluid allows Rankine cycle heat recovery from lower
temperature sources such as biomass combustion, industrial waste heat, geothermal
heat, solar ponds, etc. The low-temperature heat may then be converted into useful
work, which may in turn be converted into electricity.
SUMMARY
[0006] A volumetric or positive displacement expander configured to transfer a
working fluid and generate useful work includes a housing. The housing includes an
inlet port configured to admit relatively high-pressure working fluid and an outlet
port configured to discharge relatively low-pressure working fluid. The expander
also includes first and second twisted meshed rotors rotatably disposed in the
housing and configured to expand the relatively high-pressure working fluid into the
relatively low-pressure working fluid. Each rotor has a plurality of lobes, and when
one lobe of the first rotor is leading with respect to the inlet port, one lobe of the
second rotor is trailing with respect to the inlet port. The expander additionally
includes an output shaft configured to be rotated by the relatively high-pressure
working fluid as the working fluid undergoes expansion.
[0007] Another embodiment of the disclosure is directed to a system used to
generate useful work via a closed-loop Rankine cycle, wherein the system includes
the volumetric expander described above.
[0008] Yet another embodiment of the disclosure is directed to a vehicle
including a power-plant and employing the above system to augment the power
generated by the power-plant.
[0009] The above features and advantages, and other features and advantages of
the present disclosure, will be readily apparent from the following detailed
description of the embodiment(s) and best mode(s) for carrying out the described
invention when taken in connection with the accompanying drawings and appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIGURE 1 is a schematic depiction of a system employing a Rankine
cycle for generating useful work and having features that are examples of aspects in
accordance with the principles of the present disclosure.
[0011] FIGURE 2 is a schematic perspective top view of an expander used in the
system shown in Figure 1.
[0012] FIGURE 3 is a schematic cross-sectional side view of the expander
shown in Figure 2.
[0013] FIGURE 4 is a diagram depicting the Rankine cycle employed by the
system shown in Figure 1.
[0014] FIGURE 5 is a schematic depiction of the system shown in Figure 1
being used in a vehicle having an internal combustion (IC) engine as a vehicle
power-plant.
[0015] FIGURE 6 is a schematic depiction of the system shown in Figure 1
being used in a vehicle having a fuel cell as a vehicle power-plant.
[0016] FIGURE 7 is a side view of a configuration of an expander usable in the
system shown in Figure 1.
[0017] FIGURE 8 is a cross-sectional view of the expander shown in FIGURE 7
taken along the axial centerline of the expander.
[0018] FIGURE 9 is a schematic showing geometric parameters of the rotors of
the expander shown in FIGURE 7.
[0019] FIGURE 10 is a schematic cross-sectional view of the expander shown in
FIGURE 7.
DETAILED DESCRIPTION
[0020] Referring to the drawings wherein like reference numbers correspond to
like or similar components throughout the several figures. Figures 1-10 illustrate a
system in which a volumetric energy recovery device 20 having dual interleaved
twisted rotors extracts energy from a waste heat stream from a power source that
would otherwise be wasted, such as an exhaust air stream from an internal
combustion engine 52. As configured, the volumetric energy recovery device 20
returns the extracted energy back to the engine 52 via an output shaft 38 of the
device 20. In one embodiment, a gear reducer 19 is utilized to transfer energy
between the output shaft 38 and a power input location of the engine 52, such as the
engine drive shaft. Accordingly, the volumetric energy recovery device 20 operates
to increase the overall efficiency of the engine 52.
[0021] In some embodiments, an intermediate working fluid 12-1 is utilized to
transfer energy between the engine exhaust and the device 20. Referring to Figure
1, a system 10 is schematically presented in which the working fluid 12-1 is utilized
in a Rankine cycle. Generally, the Rankine cycle uses a working substance,
typically a fluid, in a closed loop to operate power generation systems and heat
engines for converting thermal energy to mechanical work. In the Rankine cycle a
heat "source" generates thermal energy that brings the working substance to an
elevated temperature state. The working substance generates work in the "working
body" of the heat engine while transferring thermal energy to the colder "sink" until
the working substance reaches the lower temperature state. During this process,
some of the thermal energy is converted into mechanical work by exploiting the
properties of the working substance.
[0022] As shown schematically in Figure 1, the system 10 employs a working
fluid 1 as the working substance for closed loop circulation while using the
Rankine cycle to generate mechanical work. The system 0 includes a condenser 14
configured to compress or condense the working fluid 12. The system 10 also
includes a fluid pump 16. The pump 16 is configured to receive the working fluid
12 from the condenser 14 and pressurize the condensed working fluid 12. The
system 10 also includes a heat exchanger 18. The heat exchanger 18 is configured
to receive the working fluid 2 from the pump 6 and boil the working fluid. The
system 10 additionally includes a volumetric rotary expansion device or expander
20. The expander 20 is configured to receive the working fluid 12 from the heat
exchanger 18, generate the work, and complete the loop in the Rankine cycle by
transferring the working fluid back to the condenser 14.
Volumetric Energy Recovery Device - General
[0023] In general, the volumetric energy recovery device 20 relies upon the
kinetic energy and static pressure of the working fluid 12-1 to rotate an output shaft
38. Where the device 20 is used in an expansion application, such as with a Rankine
cycle, additional energy is extracted from the working fluid via fluid expansion. In
such instances, device 20 may be referred to as an expander or expansion device, as
so presented in the following paragraphs. However, it is to be understood that the
device 20 is not limited to applications where a working fluid is expanded across the
device.
[0024] The expansion device 20 has a housing 22 with a fluid inlet 24 and a
fluid outlet 26 through which the working fluid 12-1 undergoes a pressure drop to
transfer energy to the output shaft 38. The output shaft 38 is driven by
synchronously connected first and second interleaved counter-rotating rotors 30, 32
which are disposed in a cavity 28 of the housing 22. Each of the rotors 30, 32 has
lobes that are twisted or helically disposed along the length of the rotors 30, 32.
Upon rotation of the rotors 30, 32, the lobes at least partially seal the working fluid
12-1 against an interior side of the housing at which point expansion of the working
fluid 12-1 only occurs to the extent allowed by leakage which represents and
inefficiency in the system. In contrast to some expansion devices that change the
volume of the working fluid when the fluid is sealed, the volume defined between
the lobes and the interior side of the housing 22 of device 20 is constant as the
working fluid 12-1 traverses the length of the rotors 30, 32. Accordingly, the
expansion device 20 may be referred to as a "volumetric device" as the sealed or
partially sealed working fluid volume does not change. It is noted that, and as will
be clear to one skilled in the art upon learning of this disclosure, the described
geometry and construction of the expander 20 is dissimilar from the geometry and
construction of a typical roots-type compressor.
[0025] The expander 20 is shown in detail in Figures 2 and 3. The expander 20
includes a housing 22. As shown in Figure 2, the housing 22 includes an inlet port
24 configured to admit relatively high-pressure working fluid 12-1 from the heat
exchanger 8 (shown in Figure 1). The housing 22 also includes an outlet port 26
configured to discharge working fluid 12-2 to the condenser 14 (shown in Figure 1).
It is noted that the working fluid discharging from the outlet 26 is at a relatively
higher pressure than the pressure of the working fluid at the condenser 14. Referring
to Figure 8, the inlet and outlet ports 24, 26 may be provided with connectors 25, 27,
respectively, for providing a fluid tight seal with other system components to ensure
the working fluid 12-1, 12-2, which may be ethanol, does not dangerously leak
outside of the expander 20.
[0026] As additionally shown in Figure 3, each rotor 30, 32 has four lobes, 30-1,
30-2, 30-3, and 30-4 in the case of the rotor 30, and 32-1, 32-2, 32-3, and 32-4 in the
case of the rotor 32. Although four lobes are shown for each rotor 30 and 32, each
of the two rotors may have any number of lobes that is equal to or greater than two,
as long as the number of lobes is the same for both rotors. Accordingly, when one
lobe of the rotor 30, such as the lobe 30-1 is leading with respect to the inlet port 24,
a lobe of the rotor 32, such as the lobe 30-2, is trailing with respect to the inlet port
24, and, therefore with respect to a stream of the high-pressure working fluid 12-1.
[0027] As shown, the first and second rotors 30 and 32 are fixed to respective
rotor shafts, the first rotor being fixed to an output shaft 38 and the second rotor
being fixed to a shaft 40. Each of the rotor shafts 38, 40 is mounted for rotation on a
set of bearings (not shown) about an axis XI , X2, respectively. It is noted that axes
XI and X2 are generally parallel to each other. The first and second rotors 30 and
32 are interleaved and continuously meshed for unitary rotation with each other.
With renewed reference to Figure 2, the expander 20 also includes meshed timing
gears 42 and 44, wherein the timing gear 42 is fixed for rotation with the rotor 30,
while the timing gear 44 is fixed for rotation with the rotor 32. The timing gears 42,
44 are configured to retain specified position of the rotors 30, 32 and prevent contact
between the rotors during operation of the expander 20.
[0028] The output shaft 38 is rotated by the working fluid 12 as the working
fluid undergoes expansion from the relatively high-pressure working fluid 12-1 to
the relatively low-pressure working fluid 12-2. As may additionally be seen in both
Figures 2 and 3, the output shaft 38 extends beyond the boundary of the housing 22.
Accordingly, the output shaft 38 is configured to capture the work or power
generated by the expander 20 during the expansion of the working fluid 12 that takes
place in the rotor cavity 28 between the inlet port 24 and the outlet port 26 and
transfer such work as output torque from the expander 20. Although the output shaft
38 is shown as being operatively connected to the first rotor 30, in the alternative the
output shaft 38 may be operatively connected to the second rotor 32. The output
shaft 38 can be coupled to the engine 52 such that the energy from the exhaust can
be recaptured. As shown in Figure 1, a gear reducer is provided to provide a
better match between rotational speeds of the engine 52 and the shaft 38.
Expander - Geometry
In one aspect of the geometry of the expander 20, each of the rotor lobes 30-
1 to 30-4 and 32-1 to 32-4 has a lobe geometry in which the twist of each of the first
and second rotors 30 and 32 is constant along their substantially matching length 34.
As shown schematically at Figure 9, one parameter of the lobe geometry is the helix
angle HA. By way of definition, it should be understood that references hereinafter
to "helix angle" of the rotor lobes is meant to refer to the helix angle at the pitch
diameter PD (or pitch circle) of the rotors 30 and 32. The term pitch diameter and
it's identification are well understood to those skilled in the gear and rotor art and
will not be further discussed herein. As used herein, the helix angle HA can be
calculated as follows: Helix Angle (HA) = ( 180/.pi.* arctan (PD/Lead)), wherein:
PD = pitch diameter of the rotor lobes; and Lead = the lobe length required for the
lobe to complete 360 degrees of twist. It is noted that the Lead is a function of the
twist angle and the length LI, L2 of the lobes 30, 32, respectively. The twist angle
is known to those skilled in the art to be the angular displacement of the lobe, in
degrees, which occurs in "traveling" the length of the lobe from the rearward end of
the rotor to the forward end of the rotor. As shown, the twist angle is about 120
degrees, although the twist angle may be fewer or more degrees, such as 160
degrees.
[0029] In another aspect of the expander geometry, the inlet port 24 includes an
inlet angle 24-1, as can be seen schematically at Figure 2, and in the embodiment
shown at Figure 7. In one embodiment, the inlet angle 24-1 is defined as the general
or average angle of an inner surface 24a of the inlet port 24, for example an anterior
inner surface as shown at Figure 8. In one embodiment, the inlet angle 24-1 is
defined as the angle of the general centerline of the inlet port 24, for example as
shown at Figure 2. In one embodiment, the inlet angle 24-1 is defined as the general
resulting direction of the working fluid 12-1 entering the rotors 30, 32 due to contact
with the anterior inner surface 24a, as can be seen at both Figures 2 and 8. As
shown, the inlet angle 24-1 is neither perpendicular nor parallel to the rotational axes
XI, X2 of the rotors 30, 32. Accordingly, the anterior inner surface 24a of the inlet
port 24 causes a substantial portion of the working fluid 12-1 to be shaped in a
direction that is at an oblique angle with respect to the rotational axes XI, X2 of the
rotors 30, 32, and thus generally parallel to the inlet angle 24-1.
[0030] Furthermore, and as shown at both Figures 2 and 8, the inlet port 24 may
be shaped such that the working fluid 12-1 is directed to the first axial ends 30a, 30b
of the rotors 30, 32 and directed to the rotor lobe leading and trailing surfaces
(discussed below) from a lateral direction. However, it is to be understood that the
inlet angle 24-1 may be generally parallel or generally perpendicular to axes XI, X2,
although an efficiency loss may be anticipated for certain rotor configurations.
Furthermore, it is noted that the inlet port 24 may be shaped to narrow towards the
inlet opening 24b, as shown in both Figures 2 and 8. Referring to Figure 10, it can
be seen that the inlet port 24 has a width W that is slightly less than the combined
diameter distance of the rotors 30, 32. The combined rotor diameter is equal to the
distance between the axes XI and X2 plus the twice the distance from the centerline
axis XI or X2 to the tip of the respective lobe. In some embodiments, width W is
the same as or more than the combined rotor diameter.
[0031] In another aspect of the expander geometry, the outlet port 26 includes an
outlet angle 26-1, as can be seen schematically at Figure 2, and in the embodiment
shown at Figure 7. In one embodiment, the outlet angle 26-1 is defined as the
general or average angle of an inner surface 26a of the outlet port 26, for example as
shown at Figure 8. In one embodiment, the outlet angle 26-1 is defined as the angle
of the general centerline of the outlet port 26, for example as shown at Figure 2. In
one embodiment, the outlet angle 26-1 is defined as the general resulting direction of
the working fluid 12-2 leaving the rotors 30, 32 due to contact with the inner surface
26a, as can be seen at both Figures 2 and 8. As shown, the outlet angle 26-1 is
neither perpendicular nor parallel to the rotational axes XI, X2 of the rotors 30, 32.
Accordingly, the inner surface 26a of the outlet port 26 receives the leaving working
fluid 12-2 from the rotors 30, 32 at an oblique angle which can reduce backpressure
at the outlet port 26. In one embodiment, the inlet angle 24-1 and the outlet angle
26-1 are generally equal or parallel, as shown in Figure 2. In one embodiment, the
inlet angle 24-1 and the outlet angle 26-1 are oblique with respect to each other. It is
to be understood that the outlet angle 26-1 may be generally perpendicular to axes
XI, X2, although an efficiency loss may be anticipated for certain rotor
configurations. It is further noted that the outlet angle 26-1 may be perpendicular to
the axes XI, X2. As configured, the orientation and size of the outlet port 26-1 are
established such that the leaving working fluid 12-2 can evacuate each rotor cavity
28 as easily and rapidly as possible so that backpressure is reduced as much as
possible. The output power of the shaft 38 is maximized to the extent that
backpressure caused by the outlet can be minimized such that the working fluid can
be rapidly discharged into the lower pressure working fluid at the condenser.
[0032] The efficiency of the expander 20 can be optimized by coordinating the
geometry of the inlet angle 24-1 and the geometry of the rotors 30, 32. For example,
the helix angle HA of the rotors 30, 32 and the inlet angle 24-1 can be configured
together in a complementary fashion. Because the inlet port 24 introduces the
working fluid 12-1 to both the leading and trailing faces of each rotor 30, 32, the
working fluid 12-1 performs both positive and negative work on the expander 20.
[0033] To illustrate, Figure 3 shows that lobes 30- 1, 30-4, 32- 1, and 32-2 are
each exposed to the working fluid 12-1 through the inlet port opening 24b. Each of
the lobes has a leading surface and a trailing surface, both of which are exposed to
the working fluid at various points of rotation of the associated rotor. The leading
surface is the side of the lobe that is forward most as the rotor is rotating in a
direction Rl , R2 while the trailing surface is the side of the lobe opposite the leading
surface. For example, rotor 30 rotates in direction Rl thereby resulting in side 30- a
as being the leading surface of lobe 30-1 and side 30-1 b being the trailing surface.
As rotor 32 rotates in a direction R2 which is opposite direction Rl, the leading and
trailing surfaces are mirrored such that side 32-2a is the leading surface of lobe 32-2
while side 32-2b is the trailing surface.
[0034] In generalized terms, the working fluid 12-1 impinges on the trailing
surfaces of the lobes as they pass through the inlet port opening 24b and positive
work is performed on each rotor 30, 32. By use of the term positive work, it is
meant that the working fluid - 1 causes the rotors to rotate in the desired direction:
direction Rl for rotor 30 and direction R2 for rotor 32. As shown, working fluid 12-
1 will operate to impart positive work on the trailing surface 32-2b of rotor 32-2, for
example on surface portion 47. The working fluid - 1 is also imparting positive
work on the trailing surface 30-4b of rotor 30-1, for example of surface portion 46.
However, the working fluid 12-1 also impinges on the leading surfaces of the lobes,
for example surfaces 30-1 and 32-1, as they pass through the inlet port opening 24b
thereby causing negative work to be performed on each rotor 30, 32. By use of the
term negative work, it is meant that the working fluid 12-1 causes the rotors to rotate
opposite to the desired direction, Rl , R2.
[0035] Accordingly, it is desirable to shape and orient the rotors 30, 32 and to
shape and orient the inlet port 24 such that as much of the working fluid 12-1 as
possible impinges on the trailing surfaces of the lobes with as little of the working
fluid 12-1 impinging on the on the leading lobes such that the highest net positive
work can be performed by the expander 20.
[0036] One advantageous configuration for optimizing the efficiency and net
positive work of the expander 20 is a rotor lobe helix angle HA of about 35 degrees
and an inlet angle 24-1 of about 30 degrees. Such a configuration operates to
maximize the impingement area of the trailing surfaces on the lobes while
minimizing the impingement area of the leading surfaces of the lobes. In one
embodiment, the helix angle is between about 25 degrees and about 40 degrees. In
one embodiment, the inlet angle 24-1 is set to be within (plus or minus) 15 degrees
of the helix angle HA. In one embodiment, the helix angle is between about 25
degrees and about 40 degrees. In one embodiment, the inlet angle 24-1 is set to be
within (plus or minus) 15 degrees of the helix angle HA. In one embodiment, the
inlet angle is within (plus or minus) 10 degrees of the helix angle. In one
embodiment, the inlet angle 24-1 is set to be within (plus or minus) 5 degrees of the
helix angle HA. In one embodiment, the inlet angle 24-1 is set to be within (plus or
minus) fifteen percent of the helix angle HA while in one embodiment, the inlet
angle 24-1 is within ten percent of the helix angle. Other inlet angle and helix angle
values are possible without departing from the concepts presented herein. However,
it has been found that where the values for the inlet angle and the helix angle are not
sufficiently close, a significant drop in efficiency (e.g. 10-15% drop) can occur.
Rankine Cycle Operation
[0037] Figure 4 shows a diagram 48 depicting a representative Rankine cycle
applicable to the system 10, as described with respect to Figure 1. The diagram 48
depicts different stages of the Rankine cycle showing temperature in Celsius plotted
against entropy "S", wherein entropy is defined as energy in kilojoules divided by
temperature in Kelvin and further divided by a kilogram of mass (kJ/kg*K). The
Rankine cycle shown in Figure 4 is specifically a closed-loop Organic Rankine
Cycle (ORC) that may use an organic, high molecular mass working fluid, with a
liquid-vapor phase change, or boiling point, occurring at a lower temperature than
the water-steam phase change of the classical Rankine cycle. Accordingly, in the
system 10, the working fluid 12 may be a solvent, such as ethanol, n-pentane or
toluene.
[0038] In the diagram 48 of Figure 4, the term "Q" represents the heat flow to or
from the system 10, and is typically expressed in energy per unit time. The term "W
" represents mechanical power consumed by or provided to the system 10, and is
also typically expressed in energy per unit time. As may be additionally seen from
Figure 4, there are four distinct processes or stages 48-1, 48-2, 48-3, and 48-4 in the
ORC. During stage 48-1, the working fluid 12 in the form of a wet vapor enters and
passes through the condenser 14, in which the working fluid is condensed at a
constant temperature to become a saturated liquid. Following stage 48-1, the
working fluid 12 is pumped from low to high pressure by the pump 6 during the
stage 48-2. During stage 48-2, the working fluid 12 is in a liquid state.
[0039] From stage 48-2 the working fluid is transferred to stage 48-3. During
stage 48-3, the pressurized working fluid 12 enters and passes through the heat
exchanger 18 where it is heated at constant pressure by an external heat source to
become a two-phase fluid, i.e., liquid together with vapor. From stage 48-3 the
working fluid 12 is transferred to stage 48-4. During stage 48-4, the working fluid
12 in the form of the two-phase fluid expands through the expander 20, generating
useful work or power. The expansion of the partially vaporized working fluid 12
through the expander 20 decreases the temperature and pressure of the two-phase
fluid, such that some additional condensation of the two-phase working fluid 12 may
occur. Following stage 48-4, the working fluid 1 is returned to the condenser 14 at
stage 48-1, at which point the cycle is then complete and will typically restart.
[0040] Typically a Rankine cycle employs a turbine configured to expand the
working fluid during the stage 48-4. In such cases, a practical Rankine cycle
additionally requires a superheat boiler to take the working fluid into superheated
range in order to remove or evaporate all liquid therefrom. Such an additional
superheating process is generally required so that any liquid remaining within the
working fluid will not collect at the turbine causing corrosion, pitting, and eventual
failure of the turbine blades. As shown, the ORC of Figure 4 is characterized by the
absence of such a superheat boiler and the attendant superheating process needed to
evaporate all liquid from the working fluid. The preceding omission is permitted by
the fact that the expander 20 is configured as a twin interleafed rotor device which is
not detrimentally impacted by the presence of a liquid in the working fluid 12.
Furthermore, the expander 20 benefits from the presence of such a liquid, primarily
because the remaining liquid tends to enhance the operational efficiency of the
expander by sealing clearances between the first and second rotors 30, 32, and
between the rotors and the housing 22. Accordingly, when useful work is generated
by the expander 20 in the system 10, the working fluid 12 within the expander is
present in two phases, i.e., as a liquid-vapor, such that conversion efficiency of the
ORC is increased. However, it is to be understood that the recovery device 20 can
be used in configurations involving a superheated gas.
[0041] Additionally, a smaller size expander may be used in the system 10 to
achieve the required work output. The efficiency will never be above the Carnot
efficiency of 63% because that is the maximum Caarnot efficiency eff = 1-Tcold/
Thot. The working fluid will likely be ethanol which has a max temp of 350c before
it starts to break down. The expander efficiency will be less than the peak efficiency
of a turbo but the efficiency islands are considerably larger over a greater flow range
then than the turbo expander so an overall efficiency for a cycle is larger.
[0042] As shown in Figure 5, the system 0 may be used in a vehicle 50 having
an internal combustion (IC) engine 52 as a vehicle power-plant. As shown, the C
engine 52 includes an exhaust system 54. The exhaust system 54 may further
include an exhaust gas recirculation (EGR) feature. According to the present
disclosure, the EGR of the exhaust system 54 may operate as the heat exchanger 8
of the Rankine cycle of the system 10. Additionally, as shown in Figure 6, the
system 10 may be used in a vehicle 56 that includes a fuel cell 58 such as a solid
oxide fuel cell configured to operate as the vehicle power-plant. Each of the
vehicles shown in Figure 5 and 6 may directly connect the work energy through a
pulley or gear drive 19 or may include a load storage device 60, such that the work
generated by the expander 20 may be accumulated in the load storage device 60 for
subsequent release on demand. It is also noted that the load storage device 60 may
be an accumulator wherein the recovery device 20 provided shaft power to a pump
or other type of device known in the art.
[0043] The detailed description and the drawings or figures are supportive and
descriptive of the invention, but the scope of the invention is defined solely by the
claims. While some of the best modes and other embodiments for carrying out the
claimed invention have been described in detail, various alternative designs and
embodiments exist for practicing the invention defined in the appended claims.

CLAIMS
1. A system used to generate useful work via a closed-loop Rankine
cycle, the system comprising:
a condenser configured to condense a working fluid;
a fluid pump configured to pressurize the working fluid;
a heat exchanger configured to heat the working fluid; and
a volumetric fluid expander configured to receive the working fluid from the
heat exchanger, generate the work, and transfer the working fluid to the condenser,
the expander including:
a housing having an inlet port configured to admit relatively highpressure
working fluid and an outlet port configured to discharge into relatively lowpressure
working fluid;
first and second twisted meshed rotors rotatably disposed in the
housing and configured to expand the relatively high-pressure working fluid into the
relatively low-pressure working fluid, wherein each rotor has a plurality of lobes;
and
an output shaft operatively connected to one of the first and second
rotors and rotated by the working fluid as the working fluid undergoes expansion.
2. The system of claim 1, being characterized by the absence of a
superheat boiler provided to take the working fluid into superheated range and
evaporate all liquid from the working fluid.
3. The system of claim 2, wherein when useful work is generated during
the Rankine cycle, the working fluid is present in two phases within the expander,
such that conversion efficiency of the Rankine cycle is increased via the working
fluid sealing internal clearances between the first and second rotors, and between the
rotors and the housing.
4. The system of claim 1, wherein the system is used in a vehicle having
an internal combustion engine with an exhaust system, and wherein the heat
exchanger is in fluid communication with the exhaust system.
5. The system of claim 1, wherein the system is used in a vehicle having
a solid oxide fuel cell.
6. The system of claim 1, further comprising a load storage device,
wherein the mechanical work generated by the expander is accumulated in the load
storage device for subsequent release on demand.
7. The system of claim 6, wherein the load storage device is one of an
pneumatic accumulator, a hydraulic accumulator, and an electric battery.
8. The system of claim 1, wherein the inlet port includes an inlet angle
of incidence relative to the trailing lobe that is substantially parallel to the surface
plane of the trailing lobe when the trailing lobe is rotated and presented to the
working fluid.
9. The system of claim 1, wherein the expander includes first and
second meshed timing gears fixed relative to the first and second meshed rotors,
respectively, that are configured to prevent contact between the rotors.
10. A volumetric fluid expander configured to transfer a working fluid
and generate useful work, the expander comprising:
a housing having an inlet port configured to admit relatively high-pressure
working fluid and an outlet port configured to discharge into relatively low-pressure
working fluid;
first and second twisted meshed rotors rotatably disposed in the housing and
configured to expand the relatively high-pressure working fluid into the relatively
low-pressure working fluid, wherein each rotor has a plurality of lobes defining a
helix angle; and
an output shaft having a rotational axis that is configured to be rotated by the
relatively high-pressure working fluid as the working fluid undergoes expansion;
wherein the helix angle is between about 25 degrees and about 40 degrees
and the inlet angle is both oblique with respect to the shaft rotational axis and has a
value that is within about 5 degrees of the helix angle.
11. The fluid expander of claim 0, wherein the inlet angle is about 30
degrees.
1 . The fluid expander of claim 10, wherein the helix angle is about 35
degrees.
13. The fluid expander of claim 11, wherein the inlet angle is about 30
degrees.
14. The fluid expander of claim 13, wherein each of the rotors has a twist
angle of about 120 degrees.
15. The fluid expander of claim 10, wherein the inlet angle is oblique
with respect to a rotational axis of the output shaft.
16. The fluid expander of claim 10, wherein the outlet port is includes an
outlet angle that is oblique with respect to a longitudinal axis of the rotors.
17. An energy recovery system:
a power source that generates a waste heat stream, the power source having a
power input location;
a volumetric energy recovery device configured to transfer energy from the
waste heat stream to the power input location, the volumetric energy recovery device
including:
a housing having an inlet port and an outlet port;
first and second twisted meshed rotors in fluid communication with
the inlet and outlet ports, the rotors being rotatably disposed in the housing wherein
a first rotational axis of the first twisted rotor is parallel to a second rotational axis of
the second twisted rotor;
an output shaft operatively connected to one of the first and second
rotors and to the power input location of the power source, the output shaft being
rotated by power from the waste heat stream.
18. The energy recovery system of claim 17, wherein the waste heat
stream is in fluid communication with a working fluid and wherein the working
fluid is in fluid communication with the volumetric energy recovery device via the
inlet and outlet ports.
19. The energy recovery system of claim 17, wherein the working fluid is
an organic fluid.
20. The energy recovery system of claim 19, wherein the working fluid is
subjected to a Rankine cycle in which at least a portion of the working fluid is
expanded from a liquid state to a vapor state within the energy recovery device.
2 1. The energy recovery system of claim 17, wherein the power source is
an internal combustion engine and the waste heat stream is an engine exhaust
stream.
22. The energy recovery system of claim 17, wherein the power input
location is a load storage device.
23. The energy recovery system of claim 22, wherein the load storage
device is a fuel cell.
24. The energy recovery system of claim 17, wherein the power input
location is an engine output shaft.