Patent application title: Device for the efficient conversion of compressed gas energy to mechanical energy or thrust
Henry M. Gerard (Capistrano Beach, CA, US)
IPC8 Class: AB63H1102FI
Class name: Power plants reaction motor (e.g., motive fluid generator and reaction nozzle, etc.) motive fluid principally liquid
Publication date: 2010-07-01
Patent application number: 20100162681
A mechanical device efficiently converts energy stored in a highly
compressed gas, such as air in a pipeline or SCUBA tank, to mechanical
energy, such as might be used to drive an electrical generator or to
propel a water craft.
1. Apparatus for converting energy from a compressed gas into propulsion
of a non-compressible fluid; the apparatus comprising:a housing having a
first flow path in which said compressed gas is introduced and a second
flow path in which said non-compressible fluid is introduced, said first
and second flow paths being isolated from one another;at least one
rotatable member having blades in said first flow path and having fluid
propulsion units in said second flow path, interaction between said
blades and said compressed gas causing said member to rotate and causing
said propulsion units to rotate and impart propulsion to said
2. The apparatus recited in claim 1 wherein said compressed gas and said non-compressible fluid flow in opposed directions.
3. The apparatus recited in claim 1 comprising at least two of said rotatable members.
4. The apparatus recited in claim 3 wherein said at least two rotatable members rotate concurrently in opposite directions.
5. The apparatus recited in claim 1 wherein said compressed gas is air and said non-compressible fluid is water.
6. Apparatus for converting energy from a compressed gas into electrical energy; the apparatus comprising:a housing having a flow path in which said compressed gas is introduced;at least one turbine having blades in said flow path for rotating said turbine;said turbine having an electrical generator responsive to rotation of said turbine for producing electrical energy.
7. The apparatus recited in claim 6 comprising at least two of said turbines.
8. The apparatus recited in claim 7 wherein said at least two turbines rotate concurrently in opposite directions.
9. The apparatus recited in claim 8 wherein each of said at least two turbines having oppositely oriented blades.
10. The apparatus recited in claim 6 wherein said compressed gas is air.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application takes priority from U.S. Provisional Application Ser. No. 61/192,645 filed Sep. 20, 2008.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of energy conversion and specifically to the use of compressed gas (e.g., air) to transmit energy to a non-compressible fluid (e.g., water), or to an electrical generator.
2. Background Art
The use of gas compression is a known method for storing energy as in, for example, the application to air-brake systems. This mode of energy storage has at least two important advantages over other mechanical modes, e.g., using springs or flywheels; namely: 1. The compressed gas stored energy system is relatively safe because the accidental release of the stored energy is less likely to cause harm by hurling a massive, mechanical projectile. 2. The compressed gas storage system is comparatively lightweight and inexpensive because, being hydraulic; it is relatively easy to manipulate forces.
While it is quite easy to store energy compactly by compressing a gas, it is relatively difficult to efficiently recover this stored energy to perform useful work. This difficulty arises from the same aspect that makes compressed gas safe for energy storage; namely, that while high gas velocities may readily occur accidentally, as through a leak, there is a relatively insignificant amount of mass in the high velocity gas, itself, with which to do work, or damage.
This invention utilizes well-known gas turbine techniques with fluid propulsion techniques to efficiently extract energy from the high pressure gas and transfer it to the fluid. This is of major significance because the configuration facilitates the gradual, controlled extraction of the compressed gas energy in sequential stages. Furthermore, it also facilitates the gradual, controlled transmission of this energy to a non-compressible fluid, or to integral electrical generators. The stored energy is, thereby, rendered readily available to perform useful mechanical work.
Unlike gas, the non-compressible fluid has significant mass. Consequently, by being transferred to the fluid, the (potential) energy stored in the compressed gas becomes more easily used to perform further mechanical work, such as driving the rotating shafts of electrical generators or to propel a vehicle.
Roughly 20 years ago, the inventor herein was asked to develop a practical means of powering a small recreational watercraft, such as a surfboard. Because the product drivers for this application include low cost, simplicity, durability and effective propulsion, this problem proved quite formidable. Solutions based on mechanical energy storage or employing reciprocating pistons proved impractical because they typically involve valves, (often) electronics and frequently the consumption of fuel. All of these factors pointed toward an inappropriate level of weight, complexity, cost and risk. For example, the mechanical storage of sufficient energy to propel the mass of a person on a surfboard would require a massive spring or flywheel that would be large, heavy, expensive and, most troubling of all, unrealistically dangerous for a toy. Storing and extracting the fuel to energize such a mechanical apparatus also seemed rather impractical and risky for a compact mobile lightweight sea-going platform, particularly one destined for use in the random and forceful environment of breaking waves!
After the mechanical approach was rejected, several years passed before the inventor noticed a neighborhood boy playing with a toy rocket powered by compressed air. The body of the rocket was an inverted plastic pop bottle which was partially filled with water. Air was pumped in through a hole in the cork stopper, which bubbled up through the water and was trapped and compressed in the bottle. At the appointed time, the cork was pulled, allowing the compressed air to push water downward from the now open bottle. In reaction to the expulsion of the water, the bottle shot high into the air until all the water was expelled. This was a remarkable example of compressed air energy being transferred to water to produce safe, simple, inexpensive and significant kinetic energy. It was also quite clear that without the use of water, the compressed air energy could barely lift the rocket from the ground!
The combination of compressed air and water made a sufficiently impressive demonstration to motivate the application of the configuration to the surfboard-propulsion problem. In running the applicable equations, however, it quickly became clear that this approach was not effective because it required transporting too much water (in addition to the weight of a passenger) for compressed air to accelerate. Too much energy was simply wasted in accelerating the water before it was "pumped" out to drive the vehicle; there was insufficient energy to move the passenger fast enough or far enough. Clearly, a better method was needed which utilized water for producing thrust, but did not require carrying and accelerating the water!
Recently, it became clear that the compressed gas could be made to drive water that was not onboard only if the water and compressed gas were confined to separate chambers. In this configuration, compressed, low mass gas could readily be carried on-board as the energy storage medium, while the necessary, more massive water, could be readily acquired from and expelled to the environment, as needed.
SUMMARY OF THE INVENTION
This invention utilizes few moving parts, no inputs of electricity and does not require chemical fuel. Though the design optimization of the turbine and impeller blades is technically challenging, both technologies are understood. However, the novel combination of these in the sequential turbine/impeller sections is a key attribute of this invention. The configuration is rugged in construction and the manufacturing is relatively simple and inexpensive. Because this invention may be constructed entirely from non-metallic materials, the characteristics of the material(s) from which the component parts are fabricated are also a critical element of the invention. For the use as a propulsion engine, the configuration of the underwater housing is also a key attribute.
In researching issued U.S. patents for fluid propulsion systems that employ energy from turbines as a source, several disclosures were found in which hot gas turbine exhaust was the source of energy that created pressure in the fluid. This invention differs in principle from those. This invention does not involve mixing (or contact) between the high-pressure gas and the non-compressible fluid.
In the preferred embodiment hereof, the high-pressure gas is controlled by a pressure regulator and used to drive blades of a turbine, causing a rotation which then drives attached impeller blades that are integral to the turbine section.
The high-pressure gas and the non-compressible fluid are confined to separate chambers.
The impeller blades are driven by the rotation of the turbines and thereby transmit energy to a non-compressible fluid, such as water, thereby increasing the fluid pressure along the axial direction toward the fluid jet outlet.
This invention includes the use of several turbine/impeller sections in sequence, (as well as only a single section, if desired) that are directly coupled by gas and fluid flows so as to enable efficient energy extraction from the compressed gas to the fluid. As the gas pressure drops after transferring energy to one turbine section (and thereby, coupling some energy to the pumped fluid) the lower pressure gas out-flow then drives the subsequent turbine/impeller section (and thereby, contributing more energy to further increase fluid pressure).
Through the action of one or more turbine/impeller sections, energy extracted from the high pressure gas flow produces a jet of high pressure fluid that is ejected at the fluid outlet to produce thrust or to drive another energy-consuming machine, e.g., an impact turbine, positioned at the high pressure fluid output.
A principal feature of this invention is that the mass of the ejected fluid is far greater than the mass of the compressed gas that stores the energy. Thus, the resulting thrusting force is correspondingly far greater than if the compressed gas is directly ejected to generate a reactive thrust.
A second important feature of this invention is that it contains multiple turbine/impeller sections thereby permitting concurrent extraction of energy at different compressed gas pressures.
A third important feature of this invention is that the turbine/impeller sections are configured to permit independent rotation of the sections; thereby allowing the sections to have different rotational velocities. This facilitates the design optimization of each section (and all sections) so as to extract maximum energy from the gas and couple it to the fluid, thus maximizing the conversion efficiency.
A fourth important feature of this invention is that the principles of operation remain unchanged if combustion of fuel is utilized as a source of the high-pressure gas, so as to increase the "on-board" energy beyond the constraints of passive compressed gas.
In summary, high-pressure gas is caused to flow past a series of optimally designed turbine sections causing these sections to rotate. This rotation causes the rotation of optimally designed impellers that are integral to each section, which, like pump stages, increase the pressure of the non-compressible fluid stream flowing through them. The overall effect is that "environmentally clean" low pressure (spent) gas is expelled to the atmosphere, while a high pressure fluid jet, carrying the energy extracted from the gas is ejected for propulsion, or supplies mechanical energy, in a more useful and practical form, for other work-performing purposes.
One application for this invention is in enabling the use of a low-cost, environmentally safe readily renewable, relatively physically small-sized and lightweight energy source (e.g., high pressure gas) to propel a craft through a relatively dense fluid, such as water.
Another application is as a novel and efficient means for the transfer of energy stored in a compressed gas to a denser medium, whereby the energy becomes more practically available to perform work.
BRIEF DESCRIPTION OF THE DRAWINGS
The aforementioned objects and advantages of the present invention, as well as additional objects and advantages thereof, will be more fully understood herein after as a result of a detailed description of a preferred embodiment when taken in conjunction with the following drawings in which:
FIG. 1A illustrates a configuration of this invention, which is intended for the production of thrust, and identifies the principal elements;
FIG. 1B illustrates a configuration of this invention, which is intended for the production of electricity, and identifies the principal elements;
FIG. 2 shows the Gas Expansion Cavity which must be analytically designed to result in optimum energy conversion efficiency;
FIG. 3, comprising FIGS. 3A and 3B, illustrates a preferred implementation of the mechanism by which rotational energy of a turbine/impeller section is converted to increase pressure of the non-compressible fluid; and
FIG. 4 shows one technique, namely reversing blade curvature for adjacent turbines that may be employed to preserve laminar (i.e., non-turbulent) flow in the gas region.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
FIGS. 1A and 1B illustrate the configuration of this invention and identify principal elements.
FIG. 1A shows a housing 10 with two cylindrical chambers 14 and 18 through which pressure regulated (throttled) compressed gas flows from a High Pressure Inlet 16, through a gas distribution manifold in the outer chamber 18, to a Low Pressure Outlet 20; and non-compressible fluid (that provides the thrust) flows from a Low Pressure Inlet 22 through the inner chamber 14 to the fluid output 24. Subsequently, the housing design was modified to its current configuration which is streamlined. In this configuration, the rotating element is called the Turbine/Impeller Section.
FIG. 1B also shows a housing 30 with two cylindrical chambers 34 and 38 through which pressure regulated (throttled) compressed gas flows from a High Pressure Inlet 36, through a gas distribution manifold in the outer chamber 38, to a Low Pressure Outlet 40. Here, however, the inner chamber 34 houses electrical generators 35, one per turbine section, that are driven by the rotating turbines. No non-compressible fluid is involved; instead, the electrical power produced by each generator is fed by cables 42 to an electrical power-combining network 44. In this configuration, the rotating element is called the Turbine/Generator Section.
Turbine/Impeller Section (External Surface) (FIG. 1a):
Within the chamber 14, two turbine/impeller sections are shown which are representative of a series of such sections. The outer surface of the toroidal section contains turbine blades 25 that are shaped to efficiently extract energy from the gas stream using conventional aerodynamic principles, such as those commonly used to design an airplane wing or a boat sail. Critical elements of this design include "angle of attack" and radius of curvature; and it is well-known that high-energy extraction, or "lift", is achieved in a high-velocity stream, when the angle of attack and curvature are relatively small. Similarly, for low velocity streams, greater angle of attack and curvature provides for better energy coupling. Thus, it is desirable for improved energy extraction as the gas pressure drops along the direction of gas flow owing to the extraction of energy by the preceding sections, to modify the blade shape for each section. It is worth noting that the force on the (Reaction-Type) turbine blade, as illustrated, is produced as a reaction (per Newton's Third Law) to the streamline gas flow over the curved turbine blades. With respect to pumping the fluid, where a second turbine is working with a flow of more massive molecules such as water or pressurized steam, alternative (Impulse-Type) turbine blade designs (whereby the force may be produced by the direct impact of the fluid stream against the blade surface, per Newton's Second Law) may transfer energy more efficiently. Depending on the intended use, either a propeller (which is a Reaction-Type turbine) or an impeller (which is an Impact-Type turbine) method, or a combination of both, may be used for optimization of the turbine blade design for increasing the pressure of the fluid stream. Thus impellers may be used in this invention to pump the non-compressible fluid through turbine action, while propeller type turbine blades are preferable for extracting energy from the compressed gas.
Turbine/Generator Section (external surface): The outer surface of the Turbine/Generator Section of FIG. 1B is the same as that described, above, for the Turbine/Impeller Section of FIG. 1A.
Gas Expansion Cavity:
FIG. 2 shows the Gas Expansion Cavity which must be analytically designed to result in optimum energy conversion efficiency. In general, the geometry of the Gas Expansion Cavity is related to the details of desired working pressure range and the configuration and dynamics of the turbine blades and impellers. Two basic principles guide the design; namely
1. The need to conserve mass and non-turbulent flow, as the gas interacts with the turbine blades; and
2. The compressed gas and non-compressible fluid both interact efficiently with the turbine blades and the impellers, as they flow through their respective cavities, as illustrated, inside the Housing.
While the compressed gas tank pressure may be well over 200 atm, the gas flowing into the gas expansion chamber may be regulated by means of a pressure regulator (not shown) to limit the working pressure to a lesser range. For purposes of discussion, we consider the case of a design for operation over a pressure range of 20:1; i.e., the regulator might be set for about 20 atm so that when fully-expanded, the gas would have about 1 atm pressure and, in principle, have little energy remaining for further extraction, before the gas was vented to the atmosphere. The regulated compressed gas experiences a pressure-drop as it couples (interacts) with the High Pressure Turbine Blades (see the FIG. 2 illustration). The pressure reduction is a manifestation of the energy extracted, and coupled to the non-compressible fluid by the rotating turbine/impeller section. Having lowered pressure, the compressed gas exiting from the first section must flow into a greater volume of cavity (shown by increased cross-sectional area), to ensure conservation of mass-flow of the gas. The amount of the volume increase is related to the aerodynamics of the blades and the loading corresponding to the impeller action. Similar considerations apply as the compressed gas interacts with subsequent turbine/impeller sections while flowing toward the final section of low pressure (see FIG. 2). Because the compressed gas is transformed from high pressure to low, the gas expansion cavity is shown to increase in cross-sectional area along the direction of gas flow, and the turbine blades are shown to increase in blade area in this direction. With sequentially diminishing gas pressure, the progressive increase in blade area works to improve the energy extraction efficiency of the lower pressure sections. Well-known, but relatively complex aerodynamic formulas can be employed to determine the effect of each turbine section upon the gas flow, and to ensure that gas pressure and energy remains at appropriate levels (described by the well-known Bernoulli's equation) to ensure laminar flow through the gas expansion cavity. In principle, the force on the turbine blades decreases with gas stream velocity, which itself, decreases as gas pressure drops. Therefore, there is usually a point of diminishing returns, beyond which it is not practical to employ additional turbine/impeller sections. Based on this consideration and that of the hydrostatic pressure at the Housing surface, the "spent" compressed gas may well be at some pressure above or below atmospheric when vented (thereby, possibly sacrificing or saving some energy conversion efficiency).
Turbine/Impeller Section (Internal Surface):
The interior of each turbine/impeller section contains impellers that are driven by the rotation of the section. As is the case for turbine design, the impeller design should be optimized using conventional hydrodynamic techniques to maximize the efficiency of converting the rotational energy to pressure of the non-compressible fluid flowing along the axis of the section. The objective of this transfer of energy to the fluid is to increase the pressure of the fluid as it passes through the section by the process of "pumping". In broad generality, a propeller may be used to replace the impeller. In such case, the design optimization of turbine blade and propeller are similar in that angle of attack and curvature are optimization parameters that change as pressures and velocities vary along the axial direction of the invention.
It is possible that interchanging the outer (gas) and inner (non-compressible fluid) chambers may offer an advantage in optimizing for efficient energy conversion and/or economical manufacturing. Indeed, it is also possible that improvements may be achieved, from an increase in complexity, by utilizing more than one chamber for gas and/or non-compressible fluid flow. These alternatives are within the scope of this disclosure.
Fluid Impeller Pumping:
FIG. 3, comprising FIGS. 3A and 3B illustrates a preferred implementation of the mechanism by which rotational energy of a turbine/impeller section is converted to increased pressure of the non-compressible fluid. Other means for such conversion of rotational energy include the use of propellers, such as are commonly used to power watercraft, instead of impellers. As mentioned earlier, the impeller implementation being an impact class of turbine may be superior to the propeller, a reactive class, because of the sensitivity of efficiency of the latter to preservation of laminar flow. Thus, it may be possible to readily achieve higher conversion efficiency using the impeller than with the propeller.
FIG. 3A illustrates a representative turbine/impeller section 50, shown in both isometric (FIG. 3A) and cross-sectional views (FIG. 3B). Also shown in both views are representative turbine blades. Support/bearings 53, are structures that provide support for the turbine/impeller sections. These hold the sections in place with respect to the housing 10 and allow them to rotate independently with low friction and prevent mixing (leaking) between the gas and fluid streams. The cross-sectional view (FIG. 3B) illustrates the fluid path from the Fluid Inlet, through the input orifices 55 and into the impeller chambers 54. Centrifugal force in the rotating section forces the fluid outward toward the exit orifices of the impeller chambers 56; through the space between sectors and into the input orifices of the subsequent impellers. The rotating impellers pump the fluid from the Fluid Input to the Fluid Output Jet, sequentially increasing fluid pressure in each rotating section.
The turbine/impeller sections are typically held in place while permitting their free rotation by means of support rings 53 in FIG. 3B. The cylindrical section of the ring is fitted into circular slots in the two adjacent turbine/impeller sections with sufficient clearances to permit axial rotation with minimal frictional loss, but not excessive clearances that may cause leakage. The cylindrical supporting rings are held in place by their connection to the internal surface of the outer chamber of the housing.
Other Hydrodynamic Considerations for Achieving Efficient Energy Transfers:
A fundamental principle which guides the design of all elements of this invention, including the gas and fluid chambers, the multiple turbine/impeller sections and the supported cylindrical rings, is the need to preserve non-turbulent flow in the compressed gas and in the non-compressible fluid. If either flow is permitted to become turbulent, the ability of the gas to transfer energy to the turbine blades and/or the ability of the impellers to increase the fluid pressure is reduced! The illustration in FIG. 4, shows one technique, namely reversing blade curvature for adjacent Reaction-Type turbines, that may be employed to preserve laminar (i.e., non-turbulent) flows.
Preserving Streamlined (Laminar) Flow:
In the example shown in the FIG. 4, the direction of angle of attack and curvature of the turbine blades is reversed for adjacent turbine/impeller sections. This change causes the direction of rotation to alternate for the adjacent sections, and may necessitate corresponding changes in the impeller configuration so that the efficiency of fluid pressure increase is maintained for each section. The alternating of turbine blade curvatures is used to compensate for the changes in gas stream direction caused by action of the up-stream turbine blades, and serves to bend the gas stream back toward the axis of the assembly.
A second aspect of the illustrated configuration that is intended to comply with aero- and hydrodynamic flow constraints is the selective placement of the high speed and the high torque turbine/impeller sections. The larger turbine blades are positioned to drive the impellers of the lower pressure region of fluid flow. Thus, the pressure in the non-compressible fluid increases as it moves toward the smaller sections. In this manner, the opening of the compressed gas pressure regulator valve (not shown) acting as a throttle, causes low velocity gas to flow past the "up-stream" turbine blades, that could be designed to best couple only to high velocity flow. There, the angle of attack and blade curvature is relatively flat so as not to cause turbulence in the low velocity gas as it bypasses blades and flows on toward the blades of the lower pressure sections that are designed to match the aerodynamics for lower velocity gas flow. Similarly, the impellers that are "upstream" (with respect to the gas flow) are designed to efficiently pump the relatively low-pressure fluid arriving from the lower gas velocity sections. As gas pressure is throttled up, the blades of the high pressure sections start to couple more efficiently and, by action of their impellers, begin to produce increased pressure all along the fluid stream. At full throttle, all turbine/impeller sections are efficiently driven because of progressive energy extraction from the gas flow, which progressively reduces gas velocity to match the design ranges of "down-stream" turbine blades, and maximum fluid pressure is achieved in the sequence of impeller pumps.
Other elements (not shown) can be included to maintain laminar flow in the gas and, if needed, in the fluid streams. These include non-rotating vanes, called "stators", which are positioned between the rotating turbine/impeller sections. The stators help to deflect the gas and fluid flows back toward the axis of the channels, and thereby inhibit turbulent flow.
Also not shown, is the ability to vary the width and impeller length along the non-compressible fluid chamber (i.e., cavity cross-section), as an additional design variable that can be used in the optimized embodiment to adjust gas flow velocity and fluid pressure at each turbine/impeller section.
Turbine/Generator Section (Internal Surface):
The exterior of the section contains turbine blades that are identical to those in the Turbine/Impeller configuration, but the interior employs a conventional electrical generator instead of the Impeller used in the alternative configuration. The generators provide loading on the rotating turbine sections in the same manner as described for the Impellers. The design optimization requirements for the turbine blades are analogous to those described for the Turbine/Impeller configuration.
Because the individual sections rotate independently, the use of Direct Current (DC) generators may be advantageous compared to Alternating Current (AC) generators as DC provides the simplification of eliminating the need for phase and frequency matching in the Electrical Power-Combining Network.
Electrical Power-Combining Network:
The electrical power-combining network uses conventional circuit design techniques to conduct and combine the electrical power, generated by the individual rotating Turbine/Generator sections, to a common output for delivery to the user.
1. Recreational Propulsion (Turbine/Impeller Configuration):
a) Powered Surfboard: This invention, (along with compressed air storage tanks), may be integrated into the design of a surfboard, or smaller "Boogie" board. The rider controls the speed of the board through the water by adjusting the (regulated) air pressure at the `High Pressure Inlet`. The benefits of this compressed air powered propulsion include aiding the recreational user in effortlessly moving further and more quickly through the water. The limitations of paddling, the need for fins and even for beginning the ride from a prone position, are eliminated.
b) SCUBA Propulsion: This invention may be integrated into the design of a harness which permits the diver to route a portion of the `on-board` compressed air supply for use in underwater, or surface, propulsion. This, for example, might enhance the underwater dive experience and also provide a useful aid for returning to the beach, or dive boat, at the end of a dive.
c) Small Craft Propulsion: The invention may be fitted to a small boat or float-craft, along with an (electrical) solar cell, an (electrical) air compressor, and a storage tank for the compressed air. After several hours of floating off-shore, the solar cell, driving the air compressor, builds up a charge of compressed air in the storage tank. This collected energy is then fed into this invention and used to propel the craft back to shore. Such an assembly would be particularly useful in remote locations, or other places where the management of combustible fuel is problematical.
2. Energy Retrieval Form Compressed Air Energy Storage (CAES) in Solar Energy System (Turbine/Generator Configuration):
There is a concept for storing solar energy for use during the night by compressing it into vast underground caverns. Recovery is implemented, by the use of a pair of turbines; paralleling the configuration disclosed herein, in that the sequential turbines are built for "High Pressure" and "Low Pressure, respectively. It is worth noting that there is "pre-heating" of the compressed gas prior to injection into the turbines. The present invention eliminates this wasteful use of energy by requiring that the turbine blades, themselves, be designed to couple (match) the pre-existing pressure of the compressed gas. The Turbine/Impeller Configuration of this invention is a critical component for enabling the wide-spread adoption of Solar Energy as a replacement for power generation from fuels that are in dwindling supply, which also produce the undesired by-products of Greenhouse gases.
3. Spark-less Propulsion (Turbine/Impeller Configuration):
a) Explosion-Sensitive Marine Environments: Similar to SCUBA Propulsion application, described above.
b) Submarine Stealth Drive: Through the use of compressed air as an energy source, combined with a non-metallic implementation of this invention, The present `non-reciprocating` form of engine, driving an internally-powered jet of (propulsion) water, could provide a quiet `Stealth-Drive` for a submerged vehicle.
c) Light Weight, Low Cost Torpedo Drive: Similar to `Stealth Drive`, described above.
Sample Stored Energy Calculation:
Two important questions bearing on the effectiveness of this invention as a means of marine propulsion using a compressed air tank as the source of stored energy are:
1. How much energy can safely stored in a practical-sized tank?
2. How much transport can this energy provide?
Calculation of Stored Energy:
We will use a modern High Pressure SCUBA tank as the reference for the safe storage of compressed air. This tank is certified for storing 107 cubic feet (volume at 1.0 atmosphere pressure) at a pressure of 3442 psi (234.2 atmospheres). This tank has a volume of 0.457 cubic feet. (Recent H2 powered vehicle technology has increased max. pressure limit by about 3×.)
Fundamental Equation for Stored Energy: The energy in a closed system is calculated as the sum of differential amounts of energy, dU, where,
Where, δq is the infinitesimal amount of heat added to the system and SW is the infinitesimal amount of work done by the system.
Converting to Extensive Variables: The symbol, "δ", denotes an intensive variable; that depends on the detailed properties of the system. The symbol, "d", denotes an extensive variable; one that depends on the overall state of the system. For a reversible process,
Where, T is the system temperature (Kelvins), and S is the entropy.dU can be written in terms of extensive variables as,
Where P is the pressure and V is the volume.
To solve for the total energy added to a tank by compressed gas, we will assume that heat flow into or out of the tank accounts for a negligible amount of energy. This adiabatic assumption means,
Equation for Total Energy: The total energy change in terms of work done by the system is calculated by integrating the differential, dU, contributions from the start, to the end of the process. The total energy change is thus,
ΔU=-∫PdV. Equation 1
Pressure-Volume Equation for an Ideal Gas: To a close approximation, most gasses follow a pressure, volume, temperature equation (the Ideal Gas Law) given by,
PV=nRT. Equation 2
Here, n is the number of moles of gas and R is a universal gas constant.
Inserting Equation 2 into Equation 1 leads to,
This integrates to,
Uf-Ui=-nRT ln(Vi/Vf). Equation 3
Ui and Uf are the initial and final energies, respectively.
Evaluation of Work Done by the System: We can now calculate the work done by the system when 107 cubic feet of gas is compressed into the 0.457 cubic foot tank. This is the negative of the work done on the system in this compression process; and (by the conservation of energy), this is equal to the amount of energy that can be delivered from the compressed gas tank when the ejected gas returns to the state of P=1 atmosphere and V=107 cubic feet. From Equation 3 we find that the work done by the system (during compression) is,
Substituting from Equation 2 leads to:
Which we can evaluate using P and V as the initial pressure and volume of the uncompressed gas; namely, 1 atmosphere and 107 cubic feet, respectively; leading to,
Uf-Ui=-107 ln(107/0.457)cubic foot atmospheres.
By transforming to metric units we get,
Uf-Ui=-107×28.3 ln(107/0.457)liter atmospheres.
In still more familiar units of energy we find that the work done by the system is,
Uf-Ui=-107×28.3×74.7 ln(107/0.457)foot pounds. Equation 4
Total Stored Energy: Finally, we evaluate Equation 4 to calculate the available energy, Ua, that can be delivered from the compressed gas tank to perform work; namely,
Ua=-(Uf-Ui)=1,244,095 ft pounds.
To get a better feel for this amount of energy, we can convert to still other units; namely,
Ua=0.628 horsepower hour;
Or, Ua is the total amount of energy that can be supplied by the combustion of 1.5 fluid ounces of gasoline!
Estimation of Maximum Range of Marine Craft: In the ideal case where we ignore the actual energy conversion loss in this invention (which is, as yet, unknown) and the energy loss to drag, or friction with the water (also unknown), we can estimate the maximum range, dmax, by hypothesizing that the invention is used to deliver, for example, 20 pounds of thrust, ft. This is perhaps approximately what a passenger could deliver by using swim fins for propulsion. For this example, the range, given by,
For ft=20 pounds, dmax=62,205 feet or 11.8 miles!
Conclusion: While ignoring the actual energy conversion efficiency that this invention can achieve, as well as drag force (that varies with design of he craft), the potential achievable range at 20 pounds thrust is sufficient to strongly suggest that this invention can be an effective source of propulsion for a small watercraft (e.g., a surfboard), or a SCUBA diver returning to his boat.
In both the propulsion and generator applications, it is desirable to maximize the conversion of energy taken from the compressed gas. For a practical turbine design, this implies: (1) that the gas temperature is not changed in the energy extraction process; and (2) that the system is designed for minimal stream velocity of the exhausted gas.
Having thus disclosed embodiments of the present invention in the form of a propulsion device and in the form of an electrical generator for use with compressed air or other gases, it will now be evident that the invention has a number of novel aspects that provide useful and advantageous results. Therefore, such aspects are recited in the following claims and may be protected by the scope thereof which may exceed the limited examples of the provided description.
Patent applications by Henry M. Gerard, Capistrano Beach, CA US