WO2011069062A1

WO2011069062A1 - Integral multi-staging of oscillating vane machines

Info

Publication number: WO2011069062A1
Application number: PCT/US2010/058882
Authority: WO
Inventors: Jedd N. Martin; Bradley R. Fierstein; Stephen M. Chomyszak
Original assignee: Mechanology, Inc.
Priority date: 2009-12-03
Filing date: 2010-12-03
Publication date: 2011-06-09

Abstract

The present disclosure relates to multi-staging within an Oscillating Vane Machine (OVM), in particular, to multi-staging within a single OVM and controlling inter-stage pressure ratios therein.

Description

Inventors: Jedd N. Martin, Bradley R. Fierstein, Stephen M. Chomyszak

INTEGRAL MULTI-STAGING OF OSCILLATING VANE MACHINES

RELATED APPLICATIONS

This application is a combined utility conversion of and claims the benefit of,

U.S. Provisional Application No. 61 /266,371 ('371 ), filed December 3, 2009, and U.S. Provisional Application No. 61 /266,385 ('385), filed December 3, 2009. The entire teachings of the above applications -are incorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure relates to multi-staging within an Oscillating Vane

Machine (OVM), in particular, to multi-staging within a single OVM and controlling inter-stage pressure ratios therein.

BACKGROUND OF THE INVENTION

Oscillating Vane Machines have been described, for example, in US Patent Publication US 2009-0081061 by Chomyszak et al., which is incorporated herein by reference. The benefits of multi-staging in compression or expansion processes are well documented and known to those skilled in the art. For compression, multi- staging with inter-cooling significantly reduces the amount of energy required to compress the fluid or gas, thus improving efficiency. Typically, there is a significant additional equipment cost associated with multi-staging as an additional machine or machines are required. While the '061 application describes the use of multi-staging and intercooling, improvements are still desirable.

SUMMARY OF THE INVENTION

To overcome the limitations of the prior art, the present disclosure includes novel methods for multi-staging within an Oscillating Vane Machine (OVM), and controlling inter-stage pressure ratios therein. Specifically, the disclosure describes improvements wherein, one, two or more chambers within an OVM may be used as a first stage to feed a second stage chamber within the same OVM. Further described is an intercoo!er or intercooling chamber that provides for fluid cooling either internally or externally to the OVM. The disclosure also provides methods for varying the volumetric flow and compression frequency of individual chambers, which provides optimization of conditions within an OVM for a given working fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 shows the stator, chambers and vanes for a multistage configuration for a four vane OVM.

FIG. 2 shows a gear driven crank-rocker mechanism for a multistage OVM. FIG. 3 shows a gear driven crank-rocker mechanism for a multistage OVM, wherein the gear ratios for the chambers are different.

DETAILED DESCRIPTION OF THE INVENTION

While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Integral multi-staging within an OVM can be done with as few as two chambers - one chamber acting as the first stage and one chamber acting as the second stage. The invention provides improvements in such OVMs, including optimization of the thermodynamics, pressures, flow rates and pressure ratios. To determine the first stage pressure ratio in an integral two stage OVM, we use the combined gas law. The relationship between pressure, temperature and volume of the first and second stage can be written as:

where V\, p_\, T_\ are the first stage displaced volume, inlet pressure and inlet temperature and ₂, /¾ j are the second stage displaced volume, inlet pressure and inlet temperature. For example, in a four chamber, two stage OVM, wherein three chambers act as a first stage and one chamber acts as a second stage, the displaced volume of the first stage is three times the displaced volume of the second stage or

combining and rearranging equations 1 and 2 yields the following equation for the first stage pressure ratio

As seen in the equation, if the first stage discharge gas is cooled (e.g., via an intercooler) to match the first stage inlet temperature, the first stage pressure ratio equals three. By adjusting the amount of cooling and the displaced volumes of the first and second stages, the first stage pressure ratio can be controlled as desired by the OVM designer. The displaced volumes can be modified by changing the number of first stage chambers ported in to the second stage or by having different vane and chamber dimensions in the first and second stages. Similarly the pressure ratios of a three stage or more OVM can be determined and optimized.

In actual dynamic operation of an OVM compressor, the displaced volumes discussed above are, in reality, volumetric flow rates determined by the amount of displaced volume and the frequency with which the volume is displaced. As such, the method of controlling inter-stage pressure as a function of the displaced volumetric flow rate of each sta e (Equation 2 can be generalized as:

where p, Q, and T represent pressure, volumetric flow rate, and temperature respectively.

Thus, the constraints imposed on pressure ratio by volume and temperature as described previously are still appropriate, but by expanding the definition to be in terms of displaced volumetric flow rate, the additional control variable of independent stage compression frequency is introduced. Compression frequency of any chamber of an OVM is dictated by the speed at which the vane oscillates. This additional control greatly expands the flexibility of a given OVM frame such that it can most effectively meet the pressure ratio requirements of various fluid compression applications, while enabling the primary OVM components (stator, vane, vane shaft, seals etc.) to remain the same.

An integral multi-stage OVM has significant cost and package advantages over multi-staging with multiple machines. The footprint of the integral two-stage OVM will be significantly smaller than an equivalent first stage and second stage OVM coupled together. As with footprint, the cost of the integral two-stage OVM will be significantly lower than a two OVM array since less material and fewer parts would be required. Combined with the inherent power density of the OVM geometry, an integral two-stage OVM has the potential to deliver high flows and high pressures from a remarkably small package.

Furthermore, since each chamber of a peripherally pivoted OVM acts independently of one another, each chamber could be a different stage or even process a different fluid.

FIG . 1 shows the stator and chambers with vanes for a multi-stage configuration for a four vane OVM. In this preferred embodiment, three of the chambers 3 within the stator 1 receive fluid through at least one intake port 4 disposed within each chamber 3. Actuation of the vane 2 at a known frequency within the chamber 3 compresses the fluid from a first stage pressure to a desired inter-stage pressure. The fluid output of each of the three first stage chambers 3 flows from at least one exhaust port 5 disposed within each first stage chamber 3 into an intercooler, such as an external heat exchanger, which is in fluid communication with at least one exhaust port 5 of each first stage chamber 3 and at least one intake port 4 of a second stage chamber 3. The fluid then flows through an intake port 4 of a second stage chamber 3 and is compressed to the final desired pressure.

An alternative embodiment to that just described includes a means for cooling the fluid as it flows through the intercooler. In one embodiment, the cooling occurs within the OVM. This can be accomplished for example, through use of water or other fluid jackets, cooling fins or other means.

It may be desirable for a variety of reasons to retain control over inter-stage pressure ratio such that division of work between stages can be thermodynamically optimized, without altering the geometry of the chambers or altering the effectiveness of inter-cooling to achieve a different volume ratio. Altering the geometry would likely cause asymmetry in the OVM components, particularly the stator, vane, seals, etc., increasing part count, manufacturing cost and other undesirable attributes for a product line. Inter-cooling to a specific temperature as a control over inter-stage pressure ratio is inefficient and impractical.

Consider a four chamber machine, consisting of three chambers serving as the first compression stage, and the fourth chamber serving as the second compression stage. Assuming the compression chambers and linkage mechanisms are geometrically identical, and are arranged in a two-stage configuration as mentioned above, the displaced volumetric flow rate through the three first-stage chambers will be three times that of the single second-stage chamber. Assuming perfect inter-cooling, this means that the inter-stage pressure ratio will be forced to accommodate for the mismatch in volumetric flows according to the Combined Gas Law in Equation 2, and will drive the inter-stage pressure ratio to 3 to 1 . It follows that if the displaced volume of the individual chambers was not the same then the volume ratio, and consequently the pressure ratio would not remain at 3 to 1 . An embodiment of the above concept is shown in Fig. 2. Each compression chamber 3 is driven by an independent crank-rocker mechanism 22. Each crank rocker mechanism 22 is geared to a central drive shaft 21 , with identical gear sizes for each compression chamber 3, meaning that each compression chamber 3 is operating at the same speed (and consequently the same volumetric flow rate) as described above. However, since inter-stage pressure is governed by volumetric flow rate per Equation 2, it is straightforward to achieve various inter-stage pressure ratios by varying the speed, and consequently the volumetric flow rate, of the individual compression chambers. In the current embodiment, this could simply imply a different gear ratio to match the desired volumetric flow rates for each chamber. In this way, volumetric flow, Q, through a given compression chamber n, can be defined as,

(l ) Q_n = r_gear - f - AV_n where r_gear is the gear ratio for chamber n,f is the drive shaft frequency (speed) in Hz, and A V_n is the displacement volume of the chamber. To determine inter-stage pressure ratio for any given configuration, the total volumetric flow rate of each stage would need to be calculated by Equation 3. Assuming perfect inter-cooling, Equation 2 can be simplified to

where ί represents the stage of interest, ₊ / / represents the inter-stage pressure ratio, and V is the total volumetric flow rate for the indicated stage.

One example that controls inter-stage pressure ratio in this fashion is shown in FIG. 1 and FIG. 2. In this case, it is desired to increase the inter-stage pressure ratio from 3 to 1 , which would occur naturally if the individual chambers were operating at the same speed, to 4.69 to 1. This is accomplished by "slowing down" the second stage chamber, decreasing the volumetric flow rate of the second stage such that a higher inter-stage pressure ratio is imposed on the first stage. In the example shown in the first stage chambers are geared with a ratio of 1.25, meaning the first stage crank rocker mechanisms move 25% faster than the drive shaft, while the second stage has a gear ratio of 0.80, or 20% slower than the drive shaft speed. Since all of the chambers are driven off of the same drive shaft, and the chamber geometries are identical, these terms cancel, and the ratio of volumetric flow rates from Equation 4 can be stated as,

i r_gear<2 - - A V . .

. . ^ = 4.69

The inter-stage pressure ratio of 4.69, assuming perfect inter-cooling and no irreversibilities, would be the theoretical thermodynamically optimal division of work between two stages for an overall pressure ratio of 4.69² = 22 to 1. By changing the speed of the second stage, it is possible to achieve the same effect as though the second-stage chamber were geometrically smaller in volume compared to the first-stage chambers by a ratio of 0.8/1.25.

This control over inter-stage pressure ratio is obviously not limited to a four- chamber OVM configured for two-stage operation. The same theory can be applied to OVMs of any plurality of chambers, and any desired number of stages.

FIG. 3 shows an alternative embodiment comprising a four-stage configuration of a four-chamber OVM. In this case, the vane 2 of each chamber 3 is rotating at a different speed with the intent that each chamber 3 operates as an individual stage, where the gear ratios between each successive stage dictate the pressure ratio achieved.

In the geared embodiments described, different gear ratios are accomplished by the use of multiple gear planes/where each set of gear ratios rotates in its own plane orthogonal to the drive shaft, thus preventing interference between gears. The additional incremental cost to configure an OVM in this manner is relatively small and is particularly appealing for applications such as industrial air compression where it is desirable to have a single compressor frame that covers a wide variety of pressure ratios. Another alternative embodiment comprises a belt driven crank-rocker mechanism, or many of the various OVM drive mechanisms covered in U.S. patent application number 1 1 /858,963 filed September 21 , 2007; and U.S. patent application number 1 1 /858,951 filed September 21 , 2007, and in U.S. patent application number 12/235,291 filed September 22, 2008.

Yet another embodiment might have the geared cranks could instead be driven by individual position-sensing electrical motors, or servomotors, which would then drive the crank rocker mechanism. This would allow not only for complete control over compression speed of each chamber, but would allow the compression speed to be varied during normal operation of the OVM, consequently altering inter-stage pressure ratio to meet the desired conditions at any time. In addition the servomotor driven OVM would have benefits for capacity control, or limiting gas delivery during operation to save energy when demand is lower, by altering the speed of all of the chambers simultaneously. This method would also · enable the chamber "firing" or synchronization pattern to be altered during use in response to changing conditions or requirements for the OVM, such as chamber deactivation, where it would be desirable to maintain mechanical and fluidic balance for the active chambers.

As a further embodiment of that just described, the servo-driven OVM concept can be taken even one step further by eliminating the crank rocker (or other drive mechanism) entirely, and coupling the vane shafts directly to individual servomotors. This would allow the entire vane shaft motion profile to be electronically controlled, in addition to speed and synchronization described above.

It is understood that there are myriad alternative OVM designs and configurations to which the teachings of this disclosure would be applicable, though they are not discussed explicitly in this document.

Claims

CLAIMS What is claimed is:

1. An integral multi-staging Oscillating Vane Machine (OVM), the OVM

comprising: a stator;

a first stage, the first stage comprising at least one chamber within the stator and wherein each of the at least one chambers feature a vane oscillating at a fixed frequency, at least one intake port and at least one exhaust port;

a second stage, the second stage comprising at least one chamber within the stator and wherein the at least one chamber features a vane oscillating at a fixed frequency, at least one intake port and at least one exhaust port; and

at least one intercooler being in fluid communication with the at least one exhaust port of each of the at least one chamber of the first stage and the at least one intake port of the at least one chamber of the second stage.

2. The integral multi-staging OVM of claim 1 wherein the intercooler is an externally disposed heat exchanger.

3. The integral multi-staging OVM of claim 2 wherein the at least one

intercooler is internal to the at least one stator.

4. The integral multi-staging OVM of claim 1 further comprising at least one driving mechanism that individually controls the frequency at which each vane oscillates within each chamber.

5. The integral multi-staging OVM of claim 4 wherein the driving mechanism comprises a gear driven crank-rocker. The integral multi-staging OVM of claim 4 wherein the driving mechanism comprises a variable speed motor driven crank-rocker.

The integral multi-staging OVM of claim 4 wherein the driving mechanism comprises a position-sensing motor directly driving each vane.

The integral multi-staging OVM of claim 4 wherein the oscillating speed of the at least one vane in the at least one second stage chamber is less than the oscillating speed of the at least one vane in the at least one second stage chamber.