阅读说明：本技术 利用双通道式次级热交换器和机舱压力辅助的环境控制系统 (Environmental control system with dual channel secondary heat exchanger and cabin pressure assist ) 是由 L·J·布鲁诺 于 2017-04-21 设计创作，主要内容包括：提供一种系统。所述系统包括入口,所述入口提供第一介质；压缩装置,所述压缩装置包括压缩机；以及至少一个热交换器,所述至少一个热交换器位于所述压缩机的下游。所述压缩装置与提供所述第一介质的所述入口连通。所述至少一个热交换器包括第一通道和第二通道。所述至少一个热交换器的所述第一通道的出口与所述压缩机的入口流体连通。(A system is provided. The system includes an inlet that provides a first medium; a compression device comprising a compressor; and at least one heat exchanger downstream of the compressor. The compression device is in communication with the inlet for providing the first medium. The at least one heat exchanger includes a first channel and a second channel. An outlet of the first passage of the at least one heat exchanger is in fluid communication with an inlet of the compressor.)

1. A system, comprising:

an inlet providing a first medium;

an inlet providing a second medium;

a compression device, the compression device comprising a compressor,

wherein the compression device is in communication with the inlet providing the first medium; and

at least one heat exchanger downstream of the compressor,

wherein the at least one heat exchanger comprises a first channel and a second channel, and

wherein the second media are mixed at the inlet of the second channel of the at least one heat exchanger.

2. The system of claim 1, wherein the second medium comprises recirculated air.

3. The system of claim 1, wherein the inlet providing the first medium is in communication with and receives the first medium from a fresh air source.

4. The system of claim 1, wherein the first medium comprises exhaust air.

5. The system of claim 1, wherein the first medium is received by the inlet providing the first medium from a low pressure portion of an engine or an auxiliary power unit.

6. The system of claim 1, wherein the at least one heat exchanger is a ram air heat exchanger.

Background

Generally, with respect to current air conditioning systems for aircraft, cabin pressurization and cooling are powered by the engine discharge pressure during cruise. For example, pressurized air from the engines of an aircraft is provided to the cabin by a series of systems that vary the temperature and pressure of the pressurized air. To power this preparation of pressurized air, the only source of energy is the pressure of the air itself. Therefore, current air conditioning systems require relatively high pressures at cruise. Unfortunately, in view of the general trend in the aerospace industry towards more efficient aircraft, relatively high pressures provide limited efficiency with respect to engine fuel combustion.

Disclosure of Invention

According to one embodiment, a system is provided. The system includes an inlet that provides a first medium; a compression device comprising a compressor; and at least one heat exchanger downstream of the compressor. The compression means is in communication with an inlet for providing said first medium. The at least one heat exchanger includes a first channel and a second channel. The outlet of the first passage of the at least one heat exchanger is in fluid communication with the inlet of the compressor.

Additional features and advantages are realized through the techniques of the embodiments herein. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features, refer to the description and to the drawings.

Drawings

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

fig. 1 is a schematic diagram of an environmental control system, according to an embodiment;

FIG. 2 is an example of operation of an environmental control system according to an embodiment; and is

FIG. 3 is an example of the operation of an environmental control system according to another embodiment.

Detailed Description

A detailed description of one or more embodiments of the disclosed apparatus and methods is presented herein by way of illustration, not limitation, with reference to the figures.

Embodiments herein provide an environmental control system utilizing a two pass heat exchanger patent that includes a quench circuit and recirculation air that is mixed between the two passes to provide cabin pressurization and cooling with high engine fuel combustion efficiency using low pressure engine exhaust air.

In general, embodiments of the environmental control system can include one or more heat exchangers and compression devices. The medium discharged from the low-pressure location of the engine flows into the compartment through one or more heat exchangers. Turning now to fig. 1, a system 100 is shown, the system 100 receiving media from an inlet 101 and providing a conditioned form of the media to a chamber 102. The system 100 includes a compression device 120 and a heat exchanger 130. The elements of the system are connected by valves, pipes, conduits, etc. A valve is a device that regulates, directs, and/or controls the flow of a medium by opening, closing, or partially obstructing various passageways within the pipes, ducts, etc. of the system 100. The valve may be operated by an actuator so that the flow rate of the medium in any part of the system 100 may be adjusted to a desired value.

As shown in fig. 1, media may flow through the system 100 from the inlet 101 to the chamber 102, as indicated by the solid arrows A, B. In the system 100, the medium may flow through the compression device 120, through the heat exchanger 130, from the compression device 120 to the heat exchanger 130, from the heat exchanger 130 to the compression device 120, and so on. Further, the medium may be recirculated from the chamber 102 to the system 100, as indicated by the dash-dot-dash arrow D (and may then flow back to the chamber 102 and/or to the exterior of the system 100).

Typically, the medium may be air, while other examples include a gas, a liquid, a fluidized solid, or a slurry. When media is provided from the chamber 102 of the system 100, the media is referred to herein as recirculated air. When the medium is provided by an engine connected to the system 100 (such as from the inlet 101), the medium may be referred to herein as exhaust air. With respect to the exhaust air, the low pressure location of the engine (or auxiliary power unit) may be used to provide the medium at an initial pressure level that is close to the pressure of the medium within the cabin 102 once the medium is at (e.g., cabin pressure).

For example, continuing the aircraft example described above, air may be supplied to the environmental control system by "bleeding" from the compressor stage of the turbine engine. The temperature, humidity and pressure of such exhaust air varies widely depending on the rpm of the compressor stage and turbine engine. Because of the low pressure location of the engine, the air may be slightly above or slightly below the cabin pressure (e.g., the pressure in the cabin 102). Discharging air from low pressure locations at such low pressures causes less fuel to burn than discharging air from higher pressure locations. However, because the air begins at this relatively low initial pressure level and because a pressure drop may occur across one or more heat exchangers, the pressure of the air may drop below the cabin pressure as it flows through the plurality of heat exchangers 130. When the pressure of the air is lower than the cabin pressure, the air will not flow into the cabin to provide pressurization and temperature regulation. To achieve the desired pressure, the exhaust air may be compressed as it passes through the compression device 120.

The compression device 120 is a mechanical device that controls and manipulates the medium (e.g., increases the pressure of the exhaust air). Examples of compression devices 120 include air cycle machines, three-wheel machines, four-wheel machines, and the like. The compression may include a compressor, such as a centrifugal, diagonal or mixed flow, axial, reciprocating, ionic liquid piston, rotary screw, rotary vane, scroll, diaphragm, bubble compressor, or the like. Further, the compressor may be driven by an electric motor or medium (e.g., exhaust air, cabin exhaust air, and/or recirculation air) through the turbine.

Heat exchanger 130 is a device configured for efficient heat transfer from one medium to another. Examples of heat exchangers include twin-tube, shell and tube, plate and shell, adiabatic wheel, plate fin, pillow plate and fluid heat exchangers. Air propelled by the fan (e.g., by a push or pull method) may be blown through the heat exchanger under a variable cooling airflow to control the final air temperature of the exhaust air.

In view of the aircraft example, the system 100 of FIG. 1 will now be described with reference to FIG. 2. Fig. 2 depicts a schematic view of the system 200 (e.g., an embodiment of the system 100) when the system 200 is installed on an aircraft.

The system 200 will now be described with respect to a conventional bleed air driven environmental control system for an aircraft that utilizes a current cabin three-wheel air conditioning system. Conventional bleed air driven environmental control systems receive bleed air at a pressure between 30 pounds per square inch (abs) (e.g., during cruise) and 45 pounds per square inch (abs) (e.g., on the ground). In conventional bleed air driven climate control systems, the centrifugal compressor of the air cycle machine receives nearly all of the bleed air flow at a pressure of about 45 pounds per square inch (abs) during hot day ground operation. Further, during hot day cruise operation, the centrifugal compressor of the air cycle machine receives only a portion of the exhaust air flow at a pressure of 30 pounds per square inch (abs). The remaining portion of the bleed air bypasses the centrifugal compressor through the air cycle machine bypass valve and is routed to the nacelle.

In contrast to conventional bleed air driven climate control systems that utilize current cabin three-wheel air conditioning systems, system 200 is an example of an aircraft's climate control system that provides air supply, thermal control, and cabin pressurization to aircraft crewmembers and passengers with high engine fuel burn efficiency. The system 200 shows exhaust air flowing at an inlet 201 (e.g., shutting off an engine of an aircraft at an initial flow rate, pressure, temperature, and humidity), which in turn is provided to a cabin 202 (e.g., cabin, cockpit, pressurized space (volume), etc.) at a final flow rate, pressure, temperature, and humidity. Exhaust air may be recirculated from the cabin 202 back through the system 200 (cabin exhaust air and recirculated air are represented herein by dash-dot lines D1 and D2, respectively, in fig. 2) to drive and/or assist the system 200.

The system includes a housing 210 for receiving ram air and directing the ram air through the system 200. It should be noted that, based on the embodiment, exhaust gas from the system 200 may be routed to an outlet (e.g., released into the ambient air through the housing 210).

System 200 also shows valves V1-V8, heat exchanger 220, air cycle machine 240 (which includes turbine 243, compressor 244, turbine 245, fan 248, and shaft 249), condenser 260, water extractor 270, and recirculation fan 280, each of which are connected by piping, tubing, or the like. It should be noted that heat exchanger 220 is an example of heat exchanger 130 as described above. Further, in an embodiment, the heat exchanger 220 is a secondary heat exchanger located downstream of the primary heat exchanger (not shown). It should also be noted that the air cycle machine 240 is an example of the compression device 120 as described above.

Air cycle machine 240 extracts or performs work on the media by increasing and/or decreasing pressure and by increasing and/or decreasing temperature. The compressor 244 is a mechanical device that raises the pressure of the discharge air received from the inlet 201. Turbines 243, 245 are mechanical devices that drive compressor 244 and fan 248 via shaft 249. The fan 248 is a mechanical device that propels air through the housing 210 by a push or pull method, thereby crossing the secondary heat exchanger 220 with a variable flow of cooling air. Thus, the turbines 243, 245, the compressor 244 and the fan 248 together for example show: the air cycle machine 240 may operate as a four-wheel air cycle machine that utilizes air recirculated or discharged from the cabin 202 (e.g., in an embodiment, the air cycle machine 240 utilizes cabin discharge air to perform a compression operation, as indicated by the dash-dot-dash line D1).

The condenser 260 is a particular type of heat exchanger. The water extractor 270 is a mechanical device that performs the process of temporarily or permanently taking water from any source, such as exhaust air. Recirculation fan 280 is a mechanical device that may propel air recirculation into system 200 (as indicated by dashed line D2) by a propelling method.

In the high pressure mode of operation of system 200, high pressure, high temperature air is received from inlet 201 through valve V1. The high pressure, high temperature air enters the compressor 244. The compressor 244 pressurizes and heats high pressure, high temperature air in the process. This air then enters the first channel of the heat exchanger 220 and is cooled by the ram air. The air exiting the first pass of the heat exchanger 220 then enters the second pass of the heat exchanger 220 to produce cooled, high pressure air. This cooled high pressure air passes through valve V7 into condenser 260 and water extractor 270 where the air is cooled and moisture is removed in the condenser 260 and water extractor 270. The cooled high pressure air enters a turbine 243, where the cooled high pressure air expands and work is extracted. Work from the turbine 243 may drive both the compressor 244 and the fan 248. The fan 248 is used to pull the ram air flow through the heat exchanger 220. Also, the turbine 243 generates cold exhaust air by expanding the cooled high-pressure air and extracting work therefrom. After exiting the turbine 243, the cold exhaust air is mixed at a mixing point with recirculation air D2 provided by fan 280 through valves V6 and V8. In this case, the mixing point may be located downstream of the compression device 240. This type of mixing point may also be referred to as being downstream of the compressor 244 and downstream of the turbine 243. By mixing the cold exhaust air with the recirculation air D2, the system 200 utilizes the recirculation air (which is warm and humid) to level the cold exhaust air (e.g., to raise the temperature). This leveled exhaust air in turn enters the low pressure side of the condenser 260, cools the exhaust air on the high pressure side of the condenser 260, and is routed to condition the cabin 202.

It should be noted that when operating in the high pressure mode, it is possible for the air exiting the compressor 244 to exceed the auto-ignition temperature of the fuel (e.g., 400F for steady state and 450F for transient state). In this case, air from the outlet of the first pass of the heat exchanger 220 is ducted by valve V2 to the inlet of the compressor 244. This reduces the inlet temperature of the air entering the inlet of the compressor 244, and thus the air exiting the compressor 244 is below the auto-ignition temperature of the fuel.

The high pressure mode of operation may be used under flight conditions when engine pressure is sufficient to drive the cycle or when the temperature of the cabin 202 requires. For example, conditions such as ground slow, taxi, take-off, climb, and hold conditions will cause the air cycle machine 240 to operate in a high pressure mode. Additionally, ultra high temperature high altitude cruise conditions may cause air cycle machine 240 to operate in a high pressure mode.

In the low pressure mode of operation, exhaust air from inlet 201 bypasses air cycle machine 240 through valve V1 and passes directly through the first pass of heat exchanger 220. After exiting the first channel, the exhaust air is then mixed at a mixing point with recirculation air D2 provided by fan 280 through valves V6 and V8 to produce mixed air. In this case, the mixing point may be located downstream of the compressor 244 and/or upstream of the second pass of the heat exchanger 220. The mixed air enters the second channel of the heat exchanger 220, in which it is cooled by the ram air to the temperature required for the cabin 202 in order to produce cooling air. The cooled air then passes directly into the chamber 202 through valve V7. In addition, cabin discharge air D1 is used to keep air cycle machine 240 rotating at a minimum speed. That is, cabin discharge air D1 flowing from the cabin 202 through valves V4 and V5 enters the turbine 245 and expands on the turbine 245 so that work is extracted. This work is utilized to rotate air cycle machine 240 at a minimum speed, such as about 6000 rpm. The air exiting turbine 245 is then discarded overboard through housing 210.

The low pressure mode may be used at flight conditions where the pressure of the exhaust air entering the air cycle machine 240 is approximately 1 psi above cabin pressure (e.g., cruise conditions at an altitude above 30,000 feet and conditions at or near standard ambient day types).

In a boost pressure mode of operation, exhaust air from the inlet 201 enters the compressor 244 where it is compressed and heated in the compressor 244. The compressed and heated air from the compressor 244 passes through the first pass of the heat exchanger 220 and then mixes at a mixing point with the recirculation air D2 provided by the fan 280 through valves V6 and V8 to produce mixed air. In this case, the mixing point may be located downstream of the compressor 244 and/or upstream of the second pass of the heat exchanger 220. The mixed air enters the second channel of the heat exchanger 220, in which it is cooled by the ram air to the temperature required for the cabin 202 in order to produce cooling air. The cooled air then passes directly into the chamber 202 through valve V7. Additionally, cabin discharge air D1 is used to provide energy to pressurize the discharge air entering compressor 244. That is, cabin discharge air D1 flowing from the cabin 202 through valves V4 and V5 enters the turbine 245 and expands on the turbine 245 so that work is extracted. The amount of work extracted by turbine 245 is sufficient to rotate air cycle machine 240 at the speed required by compressor 244 to raise the pressure of the exhaust air to a value that can drive the exhaust air through heat exchanger 220 and into compartment 202.

The boost pressure mode may be used at flight conditions where the pressure of the exhaust air entering the air cycle machine 240 is as low as 2.5 pounds per square inch below cabin pressure (e.g., cruise conditions where the altitude is above 30,000 feet and conditions at or near standard ambient day types).

In view of the aircraft example, the system 100 of FIG. 1 will now be described with reference to FIG. 3. Fig. 3 depicts a schematic view of the system 300 (e.g., an embodiment of the system 100) when the system 300 is installed on an aircraft. For ease of explanation, components of system 300 similar to system 200 are reused using the same identifier and are not repeated. Alternative components of the system 300 include a valve V9, a reheater 350, a condenser 360 and a water extractor 370, and an alternative path for recirculating air is indicated by the dashed line D3.

The reheater 350 and the condenser 260 are a particular type of heat exchanger. The water extractor 370 is a mechanical device that performs the process of taking water from any source, such as exhaust air. The reheater 350, condenser 260 and/or water extractor 370 may be combined together into a high pressure water separator.

In the high pressure mode of operation, high pressure, high temperature air is received from inlet 201 through valve V1. The high pressure, high temperature air enters the compressor 244. The compressor 244 pressurizes high pressure, high pressure air and heats the high pressure, high temperature air in the process. This air then enters the first channel of the heat exchanger 220 and is cooled by the ram air. The air exiting the first pass of the heat exchanger 220 then enters the second pass of the heat exchanger 220 to produce cooled, high pressure air. This cooled high pressure air enters the reheater 350 through valve V7, where the cooled high pressure air is cooled in the reheater 350; through the condenser 360, the cooled high pressure air is cooled in the condenser 360 by the air from the turbine 243; by the water extractor 370, moisture in the air is removed in the water extractor 370; and re-enters the reheater 350 where the air is heated almost to the inlet temperature at valve V7. The warmed, high pressure and now dry air enters the turbine 243, where it expands and work is extracted 243. Work from the turbine 243 may drive both the compressor 244 and the fan 248. The fan 248 is used to pull the ram air flow through the heat exchanger 220. After exiting the turbine 243, the cold air (typically below freezing) cools the warmed humid air in the condenser 360. Downstream of the condenser 360, the cold air exiting the air cycle machine 240 is mixed at a mixing point with recirculation air D3 provided by a fan 280 through a valve V9 to produce mixed air. In this case, the mixing point may be located downstream of the compression device 240. This type of mixing point may also be referred to as being downstream of the compressor 244 and downstream of the turbine 243. This mixed air is then sent to the conditioning chamber 202.

When operating in the high pressure mode, it is possible for the air exiting the compressor 244 to exceed the auto-ignition temperature of the fuel (e.g., 400F for steady state and 450F for transient). In this case, air from the outlet of the first pass of the heat exchanger 220 is ducted by valve V2 to the inlet of the compressor 244. This reduces the inlet temperature of the air entering the inlet of the compressor 244, and thus the air exiting the compressor 244 is below the auto-ignition temperature of the fuel.

The high pressure mode of operation may be used under flight conditions when engine pressure is sufficient to drive the cycle or when the temperature of the cabin 202 requires. For example, conditions such as ground slow, taxi, take-off, climb, and hold conditions will cause the air cycle machine 240 to operate in a high pressure mode. Additionally, ultra high temperature high altitude cruise conditions may cause air cycle machine 240 to operate in a high pressure mode.

In the low pressure mode of operation, exhaust air from inlet 201 bypasses air cycle machine 240 through valve V1 and passes directly through the first pass of heat exchanger 220. After exiting the first channel, the exhaust air is then mixed at a mixing point with recirculation air D2 provided by fan 280 through valve V6 to produce mixed air. In this case, the mixing point may be located downstream of the compressor 244 and/or upstream of the second pass of the heat exchanger 220. The mixed air enters the second channel of the heat exchanger 220, in which it is cooled by the ram air to the temperature required for the cabin 202 in order to produce cooling air. The cooled air then passes directly into the chamber 202 through valve V7. In addition, cabin discharge air D1 is used to keep air cycle machine 240 rotating at a minimum speed. That is, cabin discharge air D1 flowing from the cabin 202 through valves V4 and V5 enters the turbine 245 and expands on the turbine 245 so that work is extracted. This work is utilized to rotate air cycle machine 240 at a minimum speed, such as about 6000 rpm. The air exiting turbine 245 is then discarded overboard through housing 210.

The low pressure mode may be used at flight conditions where the pressure of the exhaust air entering the air cycle machine 240 is approximately 1 psi above cabin pressure (e.g., cruise conditions at an altitude above 30,000 feet and conditions at or near standard ambient day types).

In a boost pressure mode of operation, exhaust air from the inlet 201 enters the compressor 244 where it is compressed and heated in the compressor 244. . The compressed and heated air from the compressor 244 passes through the first pass of the heat exchanger 220 and then mixes at a mixing point with the recirculated air D2 provided by the fan 280 through the valve V6 to produce mixed air. In this case, the mixing point may be located downstream of the compressor 244 and/or upstream of the second pass of the heat exchanger 220. The mixed air enters the second channel of the heat exchanger 220, in which it is cooled by the ram air to the temperature required for the cabin 202 in order to produce cooling air. The cooled air then passes directly into the chamber 202 through valve V7. Additionally, cabin discharge air D1 is used to provide energy to pressurize the discharge air entering compressor 244. That is, cabin discharge air D1 flowing from the cabin 202 through valves V4 and V5 enters the turbine 245 and expands on the turbine 245 so that work is extracted. The amount of work extracted by turbine 245 is sufficient to rotate air cycle machine 240 at the speed required by compressor 244 to raise the pressure of the bleed air to a value that can drive the exhaust air through heat exchanger 220 and into compartment 202.

The boost pressure mode may be used at flight conditions where the pressure of the exhaust air entering the air cycle machine 240 is as low as 2.5 pounds per square inch below cabin pressure (e.g., cruise conditions where the altitude is above 30,000 feet and conditions at or near standard ambient day types).

In view of the above, one or more embodiments may include a system comprising: an inlet providing a first medium; a compression device comprising a compressor, wherein the compression device is in communication with an inlet providing a first medium; and at least one heat exchanger downstream of the compressor, wherein the at least one heat exchanger comprises a first channel and a second channel, and wherein an outlet of the first channel of the at least one heat exchanger is in fluid communication with an inlet of the compressor.

One or more embodiments may also include the above system comprising a second inlet for providing a second medium, wherein the second media are mixed at the inlet of the second channel of the at least one heat exchanger.

One or more embodiments may also include any of the above systems, wherein the second medium comprises recirculated air.

One or more embodiments may also include any of the above systems, wherein the second medium is received from the pressurized space by an inlet providing the second medium.

One or more embodiments may also include any of the systems described above, wherein the inlet providing the first medium is in communication with and receives the first medium from a fresh air source.

One or more embodiments may also include any of the above systems, wherein the first medium comprises exhaust air.

One or more embodiments may also include any of the above systems, wherein the first medium is received by the inlet providing the first medium from a low pressure portion of the engine or the auxiliary power unit.

One or more embodiments may also include any of the above systems, wherein the at least one heat exchanger is a ram air heat exchanger.

One or more embodiments may also include any of the above systems, wherein the aircraft includes the system.

In view of the above, one or more embodiments may include a system comprising: an inlet providing a first medium; an inlet providing a second medium; a compression device comprising a compressor, wherein the compression device is in communication with an inlet providing a first medium; and at least one heat exchanger located downstream of the compressor, wherein the at least one heat exchanger comprises a first channel and a second channel, and wherein the second media is mixed at an inlet of the second channel of the at least one heat exchanger.

One or more embodiments may also include the system described above, wherein the second medium comprises recirculated air.

One or more embodiments may also include any of the above systems, wherein the second medium is received from the pressurized space by an inlet providing the second medium.

One or more embodiments may also include any of the systems described above, wherein the inlet providing the first medium is in communication with and receives the first medium from a fresh air source.

One or more embodiments may also include any of the above systems, wherein the first medium comprises exhaust air.

One or more embodiments may also include any of the above systems, wherein the first medium is received by the inlet providing the first medium from a low pressure portion of the engine or the auxiliary power unit.

One or more embodiments may also include any of the above systems, wherein the at least one heat exchanger is a ram air heat exchanger.

One or more embodiments may also include any of the above systems, wherein the aircraft includes the system.

Aspects of embodiments are described herein with reference to flowchart illustrations, schematic illustrations, and/or block diagrams of methods, apparatus, and/or systems according to embodiments of the invention. Furthermore, the description of the various embodiments has been presented for purposes of illustration, but is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvements to the technology found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The flow chart depicted herein is just one example. There may be many variations to this type of diagram or the steps (or operations) described therein without departing from the spirit of the invention. For example, the steps may be performed in a differing order, or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention.

While the preferred embodiment to the invention has been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.