Vane-type Compressors and Expanders with Minimal Internal Energy Losses

Abstract

Current piston based air-conditioning system compressors only have isentropic efficiencies near 50%. Making internal leakage and friction negligible, via detailed design of the vane machine, would almost halve power consumption. In addition, by recovering expansion energy that is normally wasted via an expander, the system Coefficient of Performance COP can be improved up to an additional 30%.

Description

FIELD OF INVENTION

The field of invention is related to vane-type compressors, expanders, and the integral compressor/expander.

SUMMARY OF INVENTION

Virtually all of the existing air-conditioning, heat pump, and refrigeration systems operate on a thermodynamic cycle using a compressor, condenser, expansion valve or expansion-device, and evaporator. System efficiency (Coefficient-of-Performance COP) is largely dependent on the compressor efficiency.

Now currently, piston-based auto air-conditioning system compressors are the most commonly used, even though they typically have only isentropic efficiencies of about 55%, the other 45% corresponding to wasteful internal energy losses of largely leakage and friction.

Devising detailed ways to minimize the huge 45% losses is the subject of this patent. In addition, a suitable expander can recover expansion energy normally wasted, leading to significant reduction in power consumption.

North American auto air-conditioning, for one example, consumes over 27 Billion dollars worth of fuel annually, with commensurate global warming effect from CO2 produced, so doubling compressor efficiency could have huge effects. Range limitation in electric vehicles is another huge issue, indicating the need for vastly improved air-conditioning systems, and heat pumps.

Vane-type compressors have the potential to reach high efficiency. Studies have shown which internal leakage and friction losses are most significant. Minimizing these losses by careful detail design is outlined, and collectively are the key to raising isentropic compressor efficiency significantly.

Similar solutions can be applied to vane-type expanders, and in particular the integral compressor/expander. A well-designed vane-type expander can recover expansion energy that is normally wasted passing through the expansion valve or device. System COP can be improved by up to ˜30% with current refrigerant fluids.

The first major region of significant energy loss is the rotor-flat-end/casing clearance. Traditionally this is reduced to only about one thousandth of an inch clearance, yet must accommodate thermal expansion. Refrigerant vapor leakage, and oil suppression of leakage must be adjusted for minimal net energy loss. Vapor leakage increases with clearance, and oil flow with clearance cubed, while oil-shearing friction is inversely proportional to clearance. Oil viscosity can vary significantly due to refrigerant solubility and local temperature. A further complication is due to the factor-of-ten speed variation, typical of belt driven auto air-conditioning compressors.

One solution is to eliminate the large leaking area of the conventional rotor-flat-end clearance and replace by some suitable low-friction seal. The key is the type of seal, and use of a seal consisting of a wearable thermoplastic ring, mounted in the static casing and pressed onto essentially hardened discs at the rotor ends via an elastomeric ring achieves requirements. The same refrigerant fluid exists on either side of the seal, so slight leakage is acceptable, making this type of seal viable.

Additional seal features are a cut, or lap joint, in the ring to allow for thermal expansion, and means to locate the cut at a suitable radial location for minimal local pressure difference and hence local leakage. An alternative consists of an uncut ring with sealing at a fine shaped deformable tip. Local oiling on the high-pressure side, or sides, of the seal suppresses leakage from imperfections and lubricates. Increasing clearance, and minimizing the area adjacent to the seal under oil shear, can reduce this local friction loss significantly compared to other designs. Seal friction can be made even less, by promoting hydrodynamic lubrication, and the limiting rpm increased.

A second region of significant leakage is at the minimum clearance, where the rotor almost touches the casing, separating high-pressure refrigerant fluid from low-pressure fluid. Here again clearance in current machines is about a thousandth of an inch, and thermal expansion must be accommodated. Viscous oil injection can inhibit refrigerant vapor leakage, but oil flow must not lead to excessive out-gassing and heating of the inlet refrigerant fluid, or complete loss of oil in the sump due to excessive oil flow.

In the case of auto units, that are belt driven, the rpm can vary from about 600 to 6000 rpm depending on engine speed, creating problems using a shaft driven oil pump. In addition oil viscosity can vary by three orders of magnitude, depending on temperature and refrigerant solubility. The oil can be supplied to the clearance either via a pumped jet arranged to largely flood the clearance, or pushed ahead of the vanes if supplied at lower pressure.

The solution, in the case of pumped oil, is to keep the oil supply pressure steady, irrespective of rpm, via a relief valve. An additional reduction in oil flow can be achieved by cooling the oil to increase its viscosity.

Friction is the third major energy loss, and it has been shown that the friction of the vane tip rubbing on the casing is the dominant friction loss. The solution is to provide an oil film on the casing inside surface that promotes vane skidding on oil. The coefficient-of-friction drops from about 0.1 to 0.001 for one hundredth the friction with hydrodynamic lubrication. Data for journal bearings indicate the effect of rpm, viscosity and pressure effects to a first approximation. Supplying a radius to the vane tip, and casing covering of adequately viscous oil is indicted for minimal friction.

A fourth effect, on reducing the system power consumption, is achieved via an expander mounted on the compressor drive shaft. Similar internal details are needed to make the expander leakage and friction negligible. An efficient unit can recover up to 20% of ideal compressor power that is conventionally wasted as pressure drops through the expansion valve. System COP improvement can reach almost 30% with current refrigerants.

A fifth leakage area is past the edges of the vanes but is usually of small value. By supplying oil to a slight recess in the vane edge, this loss can be minimized.

U.S. Pat. Nos. 5,819,554, 5,769,617, and 7,823,398B2 discussed vane-type expanders, and integral compressor/expander designs. The detailed compressor energy minimization techniques above can obviously also be applied to individual expanders and integral compressor/expanders, and to circular rotor and elliptical casing designs.

Heating and cooling can be achieved via a reversible heat pump system. In the case of a compressor with energy recovery expander, the use of an additional 6-way reversing valve leads to viability.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 shows an axial cross section through a compressor. This could also apply to an expander.

FIG. 2 shows a radial section through a compressor.

FIG. 3 shows a typical seal.

FIG. 4 shows an axial section through an integral compressor/expander.

FIG. 5 shows a radial section through an expander.

FIG. 6 shows a radial section through a compressor with two minimal clearance areas.

FIG. 7 shows a typical oil system used to seal key internal leakage areas.

FIG. 8 shows a compressor and expander heat pump system operating in air-conditioning mode.

FIG. 9 shows the compressor and expander heat pump system operating in heat pump mode.

DETAILED DESCRIPTION

FIG. 1 consists of an axial section through a vane-type compressor, and can be read in conjunction with FIGS. 2 and 3.

A casing 1, contains a rotor 2, mounted on a shaft 3, supported in bearings 4, and connected to an external drive system via the shaft end 5, the rotor being positioned in the casing such that a minimal clearance 6 occurs at one position, the low pressure refrigerant fluid enters at port 28 leading to inlet volume 7, where it is compressed as the rotor rotates to a high pressure region 8, the rotor having a plurality of slots 9, containing substantially rectangular vanes 10, which have profiled tips 11, the rotor having hardened cylindrical discs 12, on which seals 13 (see FIG. 3) rub, the seal consisting of a sleeve 14 of good wearing material such as thermoplastic, rubbing on the rotor discs 12, the sleeve having a cut or lap joint 15 to allow for thermal expansion, and tab or alternative 31 to locate the cut at a suitable position for minimal leakage, or if uncut a deformable shaped tip 54, the sleeve 14 is pressed against the disc 12 via a suitable elastomeric ring 16 (shown cut out for clarity), thrust bearings 17 align the casing 1 with rotor 2 and vanes 10, a pump 18 increases oil pressure, shaft seal 19 inhibits leakage externally, and an integral oil-separator/sump region 20 collects refrigerant fluid and oil passing through the reed valves 21 via ducts (not shown), and sealing oil is injected 33 on the high pressure side of minimal clearance 6 and to lubricate seals 13, lubricate vane tips 35, and vane edges 36 via ducts not shown for clarity.

FIG. 4 shows an axial section through an integral compressor/expander, and should be read with FIGS. 2,3,5.

Reading FIG. 4 with compressor section XX of FIG. 2 we get: A casing 1, contains a rotor 2, mounted on a shaft 3, supported in bearings 4, and connected to an external drive system via the shaft end 5, the rotor being positioned in the casing such that a minimal clearance 6 occurs at one position, the low pressure refrigerant fluid enters at port 28 leading to inlet volume 7, where it is compressed as the rotor rotates to a high pressure region 8, the rotor having a plurality of slots 9, containing substantially rectangular vanes 10, which have profiled tips 11, the rotor having hardened cylindrical discs 12 and 27, on which seals 13 (see FIG. 3) rub, the seal consisting of a sleeve 14 of good wearing material, rubbing on the rotor discs 12 and 27, the sleeve having a cut or lap joint 15 to allow for thermal expansion, and tab or alternative 31, to locate the cut at a suitable position for minimal leakage, or if uncut a deformable shaped tip 54, the sleeve 14 is pressed against the disc 12 via a suitable elastomeric ring 16 (shown cut out for clarity), thrust bearings 17 align the casing 1 with rotor 2 and vanes 10, a pump 18 increases oil pressure, shaft seal 19 inhibits leakage externally, and an integral oil-separator/sump region 20 collects refrigerant fluid and oil passing through the reed valves 21 via ducts (not shown), and sealing oil is injected 33 on the high pressure side of minimal clearance 6 and to lubricate seals 13, lubricate vane tips 35, and vane edges 36 via ducts not shown for clarity.

Reading FIG. 4 with FIG. 5 (the expander region) we get: A minimum clearance 22, an inlet high pressure refrigerant fluid region 23 (i.e. fluid downstream of conventional valve returning to evaporator), supplied via the expander inlet port 29, the low pressure expanded fluid region 24 leading to outlet port 30, the rotor containing a plurality of slots 25, containing essentially rectangular expander vanes 26, profiled vane tips 32, circular discs 27 and 12, and seals 13, and sealing oil 34 injected on the high pressure side of minimal clearance 22, and to lubricate seals 13, lubricate vane tips 32, and vane edges 37 via ducts not shown for clarity.

FIG. 6 shows a casing 1, with two minimum clearances 6, other components being as FIG. 1, or FIG. 3.

An individual expander would have an axial section as FIG. 1, and radial section as FIG. 5.

FIG. 7 shows the outline of the oil sealing and lubrication system, as applied to the compressor/expander of FIG. 4. Oil leaves the base of the sump/separator 20 via duct 38, and enters the pump suction 39, discharging at higher pressure 40. A relief valve 41 keeps the supply header pressure fairly constant irrespective of compressor speed. The oil is injected to key sealing and lubrication areas as shown for the compressor in FIG. 2 points 33, 35, 36 and FIG. 7 point 43, and for the expander of FIG. 5 points 34 and 37 and FIG. 7 point 42. Not shown is oil cooling to increase viscosity by passing through cool regions of the apparatus, and ducts for bearing oiling.

FIGS. 8 and 9 show how the reversible type heat pump based on a compressor and expander can be operated in cooling or heating mode via the addition of a 6-way valve 47.

FIG. 8 shows the heat pump in cooling mode, with arrows showing flow direction. The high-pressure refrigerant leaves the compressor 44 via a conventional 4-way valve 45 before entering the heat exchanger 46 that acts as a condenser here. Thereafter the fluid passes through 6-way valve 47, then by-passes the conventional heating cycle expansion device 48 by passing through check valve 49, before passing through cooling cycle expansion device 51 (it's thermal bulb attached to evaporator outlet not shown). The fluid then passes through the 6-way valve 47 before entering the expander 52. Thereafter the fluid is directed via the 6-way valve to the heat exchanger 53, which acts as an evaporator here, providing desired cooling.

FIG. 9 shows the heat pump in heating mode. By changing the flow connections in 4-way valve 45 and 6-way valve 47, the heating cycle expansion device 48 functions, and heat exchanger 46 becomes the evaporator, while exchanger 53 becomes the condenser supplying desired heat.

Claims

1. A rotating vane compressor operating on an air-conditioning, heat pump, or refrigeration cycle, wherein compression of a refrigerant fluid occurs within a stationary casing having a circular profile, and that contains a cylindrical rotor with essentially flat end faces, said rotor being driven via a shaft supported in bearings that receives power from an external energy source, said rotor being mounted in said casing such that a minimal clearance occurs at one point separating the inlet low pressure region and high pressure discharge region, said rotor containing a plurality of radial slots containing substantially rectangular vanes having a close fitting arrangement with adjacent components, and a profiled tip where touching said casing, said rotor being composed of hardened cylindrical discs mounted on the flat rotor ends that have a circular outer diameter on which a seal mounted in said casing rubs, said seal consisting of a circular sleeve having good wear properties with a fine cut or lap joint or if uncut a deformable shaped tip, pressed against said rotor mounted disc by a squeezed elastomeric ring, axial alignment of said rotor and said vanes with said casing being controlled via thrust bearings.

2. A rotating vane machine operating on an air-conditioning, heat pump, or refrigeration cycle, wherein compression occurs in a compressor section and at least part of the expansion step occurs in an expander section, said compressor and expander sections being located axially relative to each other within a casing machined to provide separate compressor and expander cavities on assembly and having a smooth internal profile, said casing containing a cylindrical rotor being driven by a shaft supported in bearings that receives power from an external energy source, said rotor being mounted in said casing such that a minimal clearance occurs at one point for compressor and expander sections separating high pressure refrigerant fluid from low pressure refrigerant respectively, said rotor containing a plurality of radial slots containing substantially rectangular compressor and expander vanes having a close fitting arrangement with adjacent components and profiled tips where touching said casing, said rotor being composed of hardened cylindrical discs mounted on the flat rotor ends and another separating compressor and expander sections, on which seals mounted in said casing rub, said seals consisting of a circular sleeve having good wear properties with a fine cut or lap joint or if uncut a deformable shaped tip, pressed against said rotor circular discs by a squeezed elastomeric ring, axial alignment of said rotor and vanes with said casing being controlled via thrust bearings.

3. A rotating vane compressor, or compressor component of a compressor/expander assembly, operating on an air-conditioning, heat pump, or refrigeration cycle, wherein compression of a refrigerant fluid occurs within a stationary casing having a non-circular profile, and that contains a cylindrical rotor with essentially flat end faces, said rotor being driven via a shaft supported in bearings that receives power from an external energy source, said rotor being mounted in said casing such that two minimal clearances occur separating the inlet low pressure region and high pressure discharge regions, said rotor containing a plurality of radial slots containing substantially rectangular vanes having a close fitting arrangement with adjacent components, and a profiled tip where touching said casing, said rotor being composed of hardened cylindrical discs mounted on the flat rotor ends that have a circular outer diameter on which a seal mounted in said casing rubs, said seal consisting of a circular sleeve having good wear properties with a fine cut or lap joint or if uncut a deformable shaped tip, pressed against said rotor mounted disc by a squeezed elastomeric ring, axial alignment of said rotor and said vanes with said casing being controlled via thrust bearings.

4. A rotating vane expander operating on an air-conditioning, heat pump, or refrigeration cycle, wherein expansion of a refrigerant fluid occurs within a stationary casing having a circular profile, and that contains a cylindrical rotor with essentially flat end faces, said rotor providing energy to a shaft supported in bearings that gives power to an external energy system, said rotor being mounted in said casing such that a minimal clearance occurs at one point separating the inlet high pressure region and low pressure discharge region, said rotor containing a plurality of radial slots containing substantially rectangular vanes having a close fitting arrangement with adjacent components, and a profiled tip where touching said casing, said rotor being composed essentially of cylindrical discs mounted on the flat rotor ends that have a circular outer diameter on which a seal mounted in said casing rubs, said seal consisting of a circular sleeve having good wear properties with a fine cut or lap joint or if uncut a deformable shaped tip, pressed against said rotor mounted disc by a squeezed elastomeric ring, axial alignment of said rotor and said vanes with said casing being controlled via thrust bearings.

5. The vane-type compressor of claim 1, in which the minimal clearance, vane edges, and clearance adjacent to the seals with elastomeric ring, is flooded by oil supplied from a shaft driven pump via orifices, said oil being controlled at a steady pressure via an appropriate relief valve that can allow for rpm changes of about a factor of ten, and where the oil can be cooled as needed to increase viscosity thus limiting excessive oil flow, and where sufficient oil is spread over the casing interior to promote hydrodynamic lubrication of vane tips for minimal friction.

6. The vane-type compressor with integral expander of claim 2, in which the minimal clearance, vane edges, casing interior on which the vanes rub, and clearance adjacent to the seals with elastomeric ring, of both the compressor section and expander section, are flooded by oil supplied from a shaft driven pump via orifices, said oil being controlled at a steady pressure via an appropriate relief valve that can allow for rpm changes of about a factor of ten, and where the oil can be cooled as needed to limit excessive oil flow, and where sufficient oil is spread over the casing interior to promote hydrodynamic lubrication of vane tips for minimal friction.

7. The vane-type compressor of claim 3, in which the minimal clearance, vane edges, casing interior on which the vanes rub, and clearance adjacent to the seals with elastomeric ring, is flooded by oil supplied from a shaft driven pump via orifices, said oil being controlled at a steady pressure via an appropriate relief valve that can handle rpm changes of about a factor of ten, and where the oil can be cooled as needed to limit excessive flow, and where sufficient oil is spread over the casing interior to promote hydrodynamic lubrication of vane tips for minimal friction.

8. The vane-type expander of claim 4, in which the minimal clearance, vane edges, casing interior on which the vanes rub, and clearance adjacent to the seals with elastomeric ring, is flooded by oil supplied from a shaft driven pump via orifices, said oil being controlled at a steady pressure via an appropriate relief valve that can handle rpm changes of about a factor of ten, and where the oil can be cooled as needed to limit excessive flow, and where sufficient oil is spread over the casing interior to promote hydrodynamic lubrication of vane tips for minimal friction.

9. A reversible heat pump with a compressor and expander, containing a 6-way reversing valve enabling the unit to function as a cooler or heater, as desired.