Patent Application
20120137950
The present invention relates generally to power generation and propulsion systems, and more particularly, to power generation and propulsion by harvesting hydrostatic pressure.
Undersea Unmanned Vehicles (UUVs) are utilized for a variety of applications including both commercial and military operations. However, providing such vehicles with sufficient fuel and/or power storage means necessary to propel the UUV and its payload for extended periods of time have been problematic.
High-speed sprint capabilities in UUVs may also be desirable for various applications, for example, for military applications. Underwater rocket engines and impulse water-jet engines may be used in UUVs for achieving high-speed sprints. Impulse water-jet engines use hydrogen and oxygen gases as fuel to propel the UUVs. However, hydrogen and oxygen gases need to be pressurized above the ambient hydrostatic pressure for effective operation of the impulse water-jet engines. For example, if a UUV is at a depth of about 800 meters (m), the ambient hydrostatic pressure may be about 80 atm. Pressurization of hydrogen and oxygen gases to a pressure greater than 80 atmospheric pressure (atm) in a UUV using conventional compressor systems may be so energy-intensive as to render such systems impractical. Improved power generation and sprint-propulsion systems for UUVs would prove beneficial.
As described herein, a method for harvesting ambient hydrostatic pressure in a compressed gas system in an underwater vehicle includes the step of pressurizing a gas in a first gas tank in the underwater vehicle using a high ambient hydrostatic pressure encountered by the underwater vehicle during a submerged state of the underwater vehicle within a body of water. At least some of the pressurized gas is transferred from the first gas tank to a second gas tank in the underwater vehicle. At least some amount of the pressurized gas is transferred from the second gas tank to a prime mover in the underwater vehicle for performing mechanical work. The method further includes the step of storing the gas expressed by the prime mover in a third gas tank in the underwater vehicle. At least some amount of gas is transferred from the third gas tank to the first gas tank in the underwater vehicle using a low ambient hydrostatic pressure encountered by the underwater vehicle during the submerged state in the water body.
According to another embodiment of the invention, a compressed gas system for harvesting ambient hydrostatic pressure for an underwater vehicle operative to descend within a water body to a given depth and to ascend from the given depth of the water body to a lesser depth cyclically or in an alternating fashion includes a first gas tank and a second gas tank in fluid communication with the first gas tank. A third gas tank is in fluid communication with the second gas and the first gas tank. A first valve controls a gas flow between the second gas tank and the third gas tank. A second valve controls a gas flow between the third gas tank and the first gas tank. The gas stored in the third gas tank is selectively subjectable to the ambient hydrostatic pressure during a submerged state of the underwater vehicle within the water body.
According to an embodiment of the invention, the compressed gas system further includes a first differential valve operatively coupled to the third gas tank and configured to be selectively actuated when the ambient hydrostatic pressure is lower than the gas pressure in the third gas tank to selectively subject the gas stored in the third gas tank to the ambient hydrostatic pressure. A second differential valve operatively coupled to the third gas tank is configured to be selectively actuated when the ambient hydrostatic pressure is higher than the gas pressure in the third gas tank to selectively subject the gas stored in the third gas tank to the ambient hydrostatic pressure.
According to an embodiment of the invention, the compressed gas system further includes a first heat exchanger configured to extract heat energy from the gas stored in the first gas tank, and a second heat exchanger configured to transfer heat energy into the gas stored in the second gas tank.
According to an embodiment of the invention, a method for pressurized electrolysis of fresh water in an underwater vehicle includes the step of storing fresh water in a first water tank in the underwater vehicle. The fresh water in the first water tank is pressurized using the ambient hydrostatic pressure when the underwater vehicle is in a submerged state within a water body. The pressurized water is electrolyzed to release hydrogen and oxygen gases. The method further includes the step of storing the released hydrogen gas and the oxygen gas in a first hydrogen tank and a first oxygen tank respectively.
According to an embodiment of the invention, the method further includes the step of cooling the stored hydrogen gas in the first hydrogen tank, thereby reducing the pressure of the stored hydrogen gas in the first hydrogen tank. The method also includes the step of cooling the stored oxygen gas in the first oxygen tank, thereby reducing the pressure of the stored oxygen gas in the first oxygen tank.
In an embodiment of the invention, the method further includes the steps of pressurizing the fresh water stored in the first water tank using the ambient hydrostatic pressure and transferring the pressurized water from the first water tank to a second water tank. The hydrogen gas and the oxygen gas released in the electrolyzing step are stored in a second hydrogen tank and a second oxygen tank, respectively, before storing the hydrogen gas and the oxygen gas in the first hydrogen tank and the first oxygen tank, respectively. The method includes the steps of pressurizing the hydrogen gas and the oxygen gas stored in the second hydrogen tank and the second oxygen tank respectively using the ambient hydrostatic pressure in the submerged state of the underwater vehicle within the water body and transferring the pressurized hydrogen gas and the oxygen gas from the second hydrogen tank and the second oxygen tank, respectively, to the first hydrogen tank and the first oxygen tank, respectively.
According to an embodiment of the invention, the method further includes the step of heating the stored hydrogen gas and the stored oxygen gas in the first hydrogen tank and the first oxygen tank respectively, thereby increasing the pressures of the stored hydrogen gas and the stored oxygen gas in the respective first tanks. According to an embodiment, the heating step includes transferring of at least some quantity of heat energy to the first hydrogen tank and the first oxygen tank from a combustor, wherein the pressurized hydrogen gas and the pressurized oxygen gas are combusted.
According to an embodiment of the invention, a system for pressurized electrolysis of fresh water in an underwater vehicle includes a first fresh water tank and an electrolyzer in fluid communication with the first fresh water tank. The electrolyzer is configured to electrolyze fresh water to release hydrogen and oxygen gases. The system further includes a first hydrogen tank and a first oxygen tank in fluid communication with the electrolyzer for, respectively, storing the hydrogen gas and the oxygen gas released by the electrolyzer. A first pressure transfer system is adapted to exert the ambient hydrostatic pressure on the water stored in the first fresh water tank.
According to an embodiment of the invention, the system further includes a first one-way differential valve interposed between the electrolyzer and the first hydrogen tank to regulate the flow of the hydrogen from the first hydrogen tank to the electrolyzer. A second one-way differential valve is interposed between the electrolyzer and the first oxygen tank to regulate the flow of the oxygen from the first oxygen tank to the electrolyzer.
According to an embodiment of the invention, the pressurized electrolysis system further includes a second fresh water tank in fluid communication with the first fresh water tank via a third one-way differential valve, and with the electrolyzer via a first valve. A second hydrogen tank is in fluid communication with the electrolyzer via a second valve, and with the first hydrogen tank via the first one-way differential valve. A second oxygen tank is in fluid communication with the electrolyzer via a third valve, and with the first oxygen tank via the second one-way differential valve. A second pressure transfer system is adapted to exert the ambient hydrostatic pressure on the hydrogen stored in the second hydrogen tank in the submerged state of the underwater vehicle within the water body. A third pressure transfer system is adapted to exert the ambient hydrostatic pressure on the oxygen stored in the second oxygen tank, in the submerged state of the underwater vehicle within the water body.
According to an embodiment of the invention, the system further includes a combustor configured to receive, from the first hydrogen tank, the pressurized hydrogen gas, and, from the first oxygen tank, the pressurized oxygen gas for combustion therein.
According to an embodiment of the invention, the system further includes a heat transfer system configured to transfer at least some quantity of heat, generated in the combustor due to the combustion of the pressurized hydrogen gas and the pressurized oxygen gas therein, to the first hydrogen tank and the first oxygen tank, thereby raising the temperatures and the pressures of the pressurized hydrogen gas and the pressurized oxygen gas stored in the respective first hydrogen and oxygen tanks.
Understanding of the present invention will be facilitated by consideration of the following detailed description of the exemplary embodiments of the present invention taken in conjunction with the accompanying drawings, in which like numerals refer to like parts and in which:
It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, many other elements found in such underwater unmanned vehicles and clathrate gliders. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. The disclosure herein is directed to all such variations and modifications known to those skilled in the art.
It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. Furthermore, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the scope of the invention.
One or more figures show block diagrams of systems and apparatus embodying aspects of the invention. One or more figures show flow diagrams illustrating systems and apparatus for such embodiments. However, it is to be understood that the operational and process flows described herein may be performed by embodiments of systems and apparatus other than those discussed with reference to the block diagrams, and embodiments discussed with reference to the systems/apparatus could perform operations different from those discussed with reference to the accompanying flow diagrams.
Although the following description refers to water bodies, sea, and seawater, such terms are for illustrative purposes only and are not intended to limit the scope of the invention. The compressed gas system described herein may be implemented in a system operative in any other liquid where the requisite pressure difference between the gas in the compressed gas system and the ambient pressure encountered by the system in a submerged state within a liquid body is available. Similarly, the pressurized electrolysis system described herein may be implemented in any other liquid where the requisite pressure difference between the fresh water in the water tank and the ambient pressure encountered by the system in a submerged state within a liquid body is available. The use of the terms such as “sea,” “seawater,” and “ambient water” are solely for illustrative purposes and should not be construed as limiting the scope of the invention.
In one configuration, one or both of the compressed gas system and the pressurized electrolysis system described herein may be deployed in Clathrate Powered Undersea Unmanned Vehicles (CPUUVs), such as those disclosed in the commonly owned, pending United States patent applications having Ser. No. 12/557,143, filed Sep. 10, 2009, and Ser. No. 12/017,966, filed Jan. 22, 2008, which applications are incorporated by reference herein in their entireties. It is understood that, although the following description of the various embodiments of the invention may refer to a CPUUV, the described embodiments may also be deployed in other UUVs and underwater gliders. The terms UUV and CPUUV may, therefore, be used interchangeably without limiting the scope of the disclosure. Such variations in the described embodiments are intended to be within the scope of the invention. The CPUUVs, as described in the '143 and the '966 applications, can traverse the ocean driven by a thermodynamic buoyancy modulation cycle that operates by ascending into warm surface water and descending into cold deep water, as described in further detail below. The deepest depth of the modulation cycle exceeds the depth of the known underwater sprint propulsion vehicles.
As described in detail in the '143 and the '966 applications, the CPUUV descends in a water body, as the warm surface water starts melting the clathrate ice stored in a clathrate bladder in the CPUUV. The melting of the clathrate ice in the bladder causes a contraction in the volume of the bladder. The bladder contraction in turn causes an increase in the volume of the adjacent ballast tanks, which then receive ambient seawater. As the CPUUV stores the seawater in the ballast tanks, its buoyancy decreases causing the CPUUV to descend into the water body. At the conclusion of its descent, the CPUUV is surrounded by relatively cold ambient seawater. The relatively cold ambient seawater is utilized to extract heat from the molten clathrate ice in the clathrate bladder, thereby initiating the freezing of the clathrate in the bladder. As the clathrate ice freezes, its volume increases, thereby expanding the clathrate bladder. The expansion of the clathrate bladder causes the seawater stored in the ballast tanks to be expelled. As the seawater is expelled from the ballast tanks, the buoyancy of the CPUUV increases. As its buoyancy increases, the CPUUV starts its ascent in the water body. When the CPUUV culminates its ascent, the clathrate in the clathrate bladder has reverted to its frozen state. The CPUUV is now surrounded by relatively warm surface water again, ready to initiate its descent after the warm surface water is permitted to substantially melt the frozen clathrate ice or hydrate in the clathrate bladder. Thus, the buoyancy of the CPUUV is modulated thermodynamically by utilizing the difference in temperatures of the ambient seawater at the surface, which temperature is generally higher than the melting temperature of the clathrate and the temperatures of the ambient seawater at the depths, where the temperatures are generally lower than the freezing point of the clathrate.
Referring to
Prime mover 140 drives a device 180, which device 180 may take the form of any of device which may be driven by prime mover 140. Some non-limiting examples of device 180 are briefly discussed below. The term “prime mover” is intended to cover any machine, such as, but not limited to, a turbine that transforms pressure energy of a fluid (e.g., a gas) to mechanical work or electrical energy. Other non-limiting examples of prime mover 140 include a rudder driver, which may include a gas cylinder and a piston that drives a rod to drive a rudder (an example of device 180) or a control surface such as a submarine foil (another example of device 180) for controlling the UUV's degrees of freedom during the UUV's operation in the water body; a mass balance driver, which may include a mass on a screw (yet another example of device 180) that is driven by a compressed gas piston and a cam for adjusting the center of gravity of the UUV; a ballast regulator, which may include a gas bladder (yet another example of device 180) in a ballast tank for driving the ballast; a maneuvering thruster, which may include a gas bladder in a small ballast tank having a fixed nozzle for creating, for example, a water jet; a micro-turbine configured to power a generator; a micro-turbine for powering a propeller; and a micro-turbine for powering a seawater impellor configured to pump seawater over a heat exchanger.
High pressure gas tank 130 is in fluid communication with prime mover 140 through a control or check valve 135. Control valve 135 may be selectively actuated to control the flow of a pressurized gas from high pressure gas tank 130 to prime mover 140. For instance, if the gas pressure exceeds a predetermined pressure threshold in high pressure gas tank 130, valve 135 may be actuated (e.g., either self-actuated or actuated by controller 170) to permit the pressurized gas to flow from high pressure gas tank 130 to prime mover 140. Prime mover 140 is in fluid communication with low pressure gas tank 110 such that the gas flowing out from prime mover 140 is stored in low pressure gas tank 110. Low pressure gas tank 110 is in fluid communication with recirculation or intermediate gas tank 120. A control or check valve 115 controls the flow of the gas from low pressure gas tank 110 to recirculation tank 120. For example, if the gas pressure in low pressure gas tank 110 exceeds a predetermined pressure threshold, valve 115 may be actuated (e.g., either self-actuated or actuated by controller 170) to permit the gas to flow from low pressure gas tank 110 to recirculation tank 120. Recirculation tank 120 is in fluid communication with high pressure gas tank 130. A control or check valve 125 controls the flow of the gas from recirculation tank 120 to high pressure gas tank 130. If the gas pressure in recirculation tank 120 exceeds a predetermined pressure threshold, valve 125 may be actuated (e.g., either self-actuated or actuated by controller 170) to permit the gas to flow from recirculation tank 120 to high pressure gas tank 130.
In one configuration, recirculation tank 120 is in fluid communication with a fluid decoupler 150. System 100 further includes a low pressure one-way differential valve 145 and a high pressure one-way differential valve 155 in fluid communication with fluid decoupler 150. In an embodiment of the invention, fluid decoupler 150 may take the form of a seawater bellows. In another configuration, fluid decoupler 150 and recirculation tank 120 may be combined into a unitary structure, as will be described below in further detail.
In an exemplary embodiment, heat exchanger 112 may be configured to receive ambient seawater therein to effect heat transfer between low pressure gas tank 110 and the ambient seawater. Likewise, heat exchanger 132 may be configured to receive ambient seawater therein to effect heat transfer between high pressure gas tank 130 and the ambient seawater. In another embodiment, heat exchanger 132 may be configured to collect and transfer heat, such as heat generated by the electronics present in the UUV (i.e., dissipation or “waste” heat) and transfer the same to high pressure gas tank 130 to selectively increase the temperature of the gas stored in high pressure gas tank 130. It will be understood that system 100 further includes pumps and valves for regulating the flow of coolant and/or ambient seawater through heat exchangers 112, 132. However, since such heat exchanger systems are known in the art, they are not described in further detail for the sake of brevity.
Referring also to
Second compartment 144 is in fluid communication with high pressure differential valve 155 and low pressure differential valve 145. The ambient water, for example the seawater, may be received by second compartment 144 via high pressure differential valve 155, responsive to a difference in the pressure of the gas stored in first compartment 142 and the ambient hydrostatic pressure. Conversely, the received seawater may be ejected from second compartment 144 via low pressure differential valve 145, responsive to a difference in the pressure of the gas stored in first compartment 142 and the ambient hydrostatic pressure. Piston 146 may move responsive to the difference in the pressures of the ambient seawater and the gas stored in recirculation gas tank 120 and resulting actuation of high pressure differential valve 155 and low pressure differential valve 145 as explained below. It will be understood that piston 146 is so arranged between first compartment 142 and second compartment 144 as to substantially prevent any leakage of the gas stored in first compartment 142 into second compartment 144 as well as any leakage of the water stored in second compartment 144 into first compartment 142.
High pressure differential valve 155 serves to selectively subject the gas in the fluid decoupler 150 to an ambient hydrostatic pressure 160 (of
Low pressure differential valve 145, on the other hand, serves to discharge pressure from recirculation gas tank 120 via fluid decoupler 150 when ambient hydrostatic pressure 160 (of
Referring again to
An advantage of controller 170 controlling the actuation of high pressure differential valve 155 and low pressure differential valve 145 is that differential valves 155, 145 may be selectively actuated only when needed to pressurize or depressurize the gas in system 100. Mechanical self-actuating differential valves 155, 145, on the other hand, may remain actuated based on the difference in the pressures of the gas stored in first compartment 142 and/or recirculation gas tank 120, regardless of the need of the system. Such prolonged actuation of differential valves 155, 145 may expose valves 155, 145 to ambient seawater for prolonged periods of time. Increased exposure to ambient seawater may, in turn, lead to bio-fouling issues, for example. It is further understood that bio-fouling may be addressed using ozone purge or chlorine purge techniques known in the art.
Referring now to
UUV 330 starts its descent into the water body towards a bed 320 of the water body. During stage B, as UUV 330 descends further in the water body, ambient hydrostatic pressure 160 increases. Once ambient hydrostatic pressure 160 exceeds beyond a predetermined threshold, high pressure differential valve 155 is actuated. The seawater enters second compartment 144 and causes piston 146 to pressurize the gas contained in first compartment 142. As a result, the gas contained in recirculation gas tank 120 is pressurized. As the gas pressure in recirculation gas tank 120 exceeds a predetermined threshold, valve 125 is actuated to permit the flow of the gas from recirculation gas tank 120 to high pressure gas tank 130. As the mass of the gas flowing into high pressure gas tank 130 increases, the gas pressure in high pressure gas tank 130 also increases. Thus, high ambient hydrostatic pressure 160 is harvested and stored in form of the gas pressure in high pressure gas tank 130. In one configuration, once a predetermined gas pressure in high pressure gas tank 130 is achieved, valve 125 is actuated to cut off further flow of the gas from recirculation gas tank 120 to high pressure gas tank 130. Similarly, once a predetermined gas pressure in recirculation gas tank 120 is achieved, high pressure differential valve 155 is actuated to cut off further flow of the seawater into the second compartment 144. In an exemplary embodiment, controller 170 may dynamically actuate differential valves 125, 135, to optimally harvest the ambient hydrostatic pressure, based on the parameters such as the ambient hydrostatic pressure, gas pressures in low pressure gas tank 110, recirculation gas tank 120, high pressure gas tank 130, the depth of UUV 330 and the velocity of UUV 330 as measured by the respective pressure sensors, temperature sensors, the depth sensors and the velocity sensors associated with UUV 330.
According to an embodiment of the invention, a method for harvesting ambient hydrostatic pressure in a compressed gas system in an underwater vehicle thus includes a step of storing a gas at a given pressure in a first tank within the underwater vehicle. The method further includes a step of pressurizing the gas in the first tank using an ambient pressure associated with the water body encountered by the UUV when in a submerged state, wherein the ambient pressure is higher than the given pressure.
As is known in the art, for a constant volume and a constant mass, a decrease in temperature results in a decrease in the pressure of a gas, per the ideal gas law. As UUV 330 is descending during stage B, the temperature of ambient seawater surrounding UUV 330 decreases. The relatively colder ambient seawater flowing through heat exchanger 132 may be used to cool high pressure gas tank 130. The cooling of high pressure gas tank 130 results in a reduction in pressure of the gas stored therein. In an exemplary embodiment, valve 125 may be periodically actuated to permit further flow of high pressure gas from recirculation tank 120 to high pressure gas tank 130. In an embodiment, valve 125 may self-actuate, depending on the pressure difference between the gas stored in recirculation gas tank 120 and high pressure gas tank 130. In another embodiment, valve 125 may be dynamically actuated by controller 170 based on the pressures in tanks 120, 130, as measured by the respective pressure sensors associated with tanks 120, 130. Similar reduction in the pressure of the gas stored in low pressure gas tank 110 due to the cooling of low pressure gas tank 110 further enhances its capacity to receive more quantity of gas emitted from prime mover 140.
Further, when prime mover 140 is in operation, the gas expressed from prime mover 140 and received by low pressure gas tank 110, increases the pressure and the temperature of the gas stored in low pressure gas tank 110. The relatively colder ambient seawater flowing through heat exchanger 112 may be used to cool low pressure gas tank 110, to mitigate the rise in the temperature and the pressure of gas stored in low pressure gas tank 110, when prime mover 140 is in operation. Thus, the lower temperatures of ambient seawater advantageously may be used to store higher quantities of high pressure gas in high pressure gas tank 130 as well to receive higher quantities of gas in low pressure gas tank 110 during the operation of the prime mover 140. In an exemplary embodiment, controller 170 may regulate the flow of the ambient seawater in heat exchangers 112, 132 based on the temperatures of the ambient seawater, the gas stored in low pressure gas tank 110, and the gas stored in high pressure gas tank 130.
At stage C, UUV 330 reaches a target depth (e.g., the maximum design depth) in the water body. Valve 135 may be actuated to permit the flow of pressurized gas from high pressure gas tank 130 to prime mover 140. Prime mover 140 converts the pressure energy of the pressurized gas into another form of energy, for example, mechanical energy. For instance, prime mover 140 may power one or more propellers to impart motion to UUV 330. In a CPUUV, prime mover 140 powering a propeller may reduce the consumption of scarce stored electrical energy for forward propulsion. Prime mover 140 also propels the CPUUV at a speed sufficient to maintain the required flow of seawater within the CPUUV for the formation of the clathrate hydrate. Prime mover 140 may also be used to shift the center of gravity of UUV 330 to change its orientation from a nose down orientation to a horizontal orientation on reaching stage C. Prime mover 140 may also be used to pump the ambient seawater through various heat exchangers present in UUV 330, for example to cool the gas stored in high pressure gas tank 130, in an exemplary configuration.
In another configuration, prime mover 140 may convert the pressure energy of the pressurized gas into electrical energy. In an exemplary configuration, if UUV 330 includes a critical power load, such as an active sonar pulse, prime mover 140 may briefly power a generator to charge up a capacitor to store sufficient electrical energy to power the sonar amplifiers. In another embodiment, prime mover 140 may power a generator to recharge a battery (not shown). In yet another embodiment, prime mover 140 and a generator (not shown) powered therewith may supply electric energy to electrolyze pressurized fresh water to provide pressurized hydrogen and pressurized oxygen, as described further below.
The amount of power or energy generated by prime mover 140 is determined by the capacity and/or pressure characteristics of low pressure gas tank 110. The gas expressed from prime mover 140 is received by low pressure gas tank 110. As the mass of the gas flowing from high pressure gas tank 130 to prime mover 140 increases, the mass of the gas in low pressure gas tank 110 also increases, thereby increasing the gas pressure in low pressure gas tank 110. The higher the quantity of the gas low pressure gas tank 110 is able to store therein, the more the power generated by prime mover 140. Likewise, the higher the pressure low pressure gas tank 110 is able to withstand, the more the power generated by prime mover 140. Therefore, the capacity of low pressure gas tank 110 determines the amount of power or energy generated by prime mover 140. UUV 330 begins its ascent in the water body during stage D.
As UUV 330 continues its ascent from a given depth in the water body, ambient hydrostatic pressure 160 decreases. When ambient hydrostatic pressure 160 drops below a first predetermined pressure threshold, low pressure differential valve 145 is actuated. The first predetermined pressure threshold is lower than the gas pressure in recirculation gas tank 120. The actuation of low pressure differential valve 145 causes the gas from recirculation tank 120 to enter first compartment 142 of fluid decoupler 150 and push piston 146 toward second compartment, thereby expelling the seawater from second compartment 144. The gas flow from recirculation gas tank 120 to first compartment 142 depressurizes recirculation gas tank 120 as the volume available for the gas in first compartment 142 increases.
As the gas pressure in the recirculation gas tank 120 falls below a second predetermined pressure threshold, valve 115 is actuated to permit the flow of the gas from low pressure gas tank 110 to recirculation gas tank 120. The second predetermined pressure threshold is lower than the gas pressure in low pressure gas tank 110. The actuation of valve 115, thus, depressurizes low pressure gas tank 110, as the gas flows from low pressure gas tank 110 to recirculation gas tank 120. Thus, when UUV 330 reaches stage E, the low pressure gas tank 110 is depressurized and a bulk of the gas in system 100 is stored in the recirculation tank 120. It will be understood that at stage E, when low pressure gas tank 110 is depressurized, the seawater is expelled from second compartment 144, thereby reducing the ballasting effect of second compartment 144. Thus, it may be advantageous to maneuver UUV 330, after depressurizing at or near surface 310, because the relatively lighter weight of UUV 330 requires relatively less energy to accelerate UUV 330. Likewise, during stage B, maneuvering of UUV 330 may be more energy cost-efficient if performed before the pressurization of high pressure gas tank 130 because the seawater has not yet entered second compartment 144.
During the ascent of UUV 330, during stage D, the temperature of the ambient seawater tends to increase as the UUV 330 approaches surface 310 of the water body. The relatively warmer seawater may be used to increase the temperature of the gas stored in low pressure gas tank 110. As is known in the art, for a constant mass and a constant volume, an increase in temperature of a gas results in an increase in the pressure of a gas, per the ideal gas law. Thus, as the temperature of the gas stored in low pressure gas tank 110 increases, the pressure of the stored gas also increases. Valve 115 may be selectively actuated to depressurize low pressure gas tank 110 by permitting the gas to move from low pressure gas tank 110 to recirculation gas tank 120. Further, if prime mover 140 is operated during stages D and E, the pressure of the gas drops in high pressure gas tank 130, as the high pressure gas stored therein is allowed to move from high pressure gas tank 130 to prime mover 140. The relatively warmer ambient surface seawater flowing through heat exchanger 132 may be used to heat the remaining gas in high pressure gas tank 130, thereby raising the temperature and the pressure of the remaining gas in high pressure gas tank 130. Additionally, the heat generated by the electronics in UUV 330 may also be used to raise the temperature of the gas stored in high pressure gas tank 130. Thus, the relatively higher ambient seawater temperatures may be advantageously used to move higher quantities of gas from low pressure gas tank 110 to recirculation gas tank 120.
In a CPUUV, the buoyancy modulation system modulates the buoyancy of the CPUUV by regulating the amount of seawater in the ballast tank. Since the ambient water is also accumulated in, and displaced out of, second compartment 144, second compartment 144 also acts as a ballast as the total CPUUV mass increases and decreases with the movement of the seawater in and out of second compartment 144. However, this increase and decrease in the total CPUUV mass may operate either to amplify or to counter the buoyancy modulation by the CPUUV's primary buoyancy modulation system during different stages of operation of the CPUUV. For example, when the CPUUV ascends in the water body (during stage D of
When the CPUUV is starting its ascent (stages C and D of
Referring now to
In an exemplary embodiment, prime mover 140 may be coupled to an impeller (not shown) mounted on the exterior of UUV 330. As UUV 330 is ascending or descending in a water body, responsive to the buoyancy modulation by the primary buoyancy modulation system of UUV 330, the impeller would be driven by the motion of UUV 330 through the water. In an exemplary configuration, the impeller may be operatively coupled to a compressor (not shown) in fluid communication with low pressure gas tank 110 and high pressure gas tank 130. The compressor may pressurize and transfer at least some amount of gas from low pressure gas tank 110 to high pressure gas tank 130.
An advantage of compressed gas system 100 (of
Referring to
In an exemplary embodiment, system 500 further includes a heat exchanger 565 associated with high pressure hydrogen gas tank 560, a heat exchanger 575 associated with high pressure oxygen gas tank 570, a heat exchanger 585 associated with combustor 580 and a coolant pump 587. Heat exchangers 565, 575, 585 and pump 587 are interconnected (via appropriate piping systems) to define a closed loop system. A coolant may be circulated by pump 587 in the closed loop such that heat is extracted from combustor 580, thereby cooling down combustor 580. The extracted heat is transferred by the coolant to high pressure hydrogen tank 560 and high pressure oxygen tank 570 via heat exchangers 565, 575, respectively, thereby heating the gas stored in tanks 560, 570. In an exemplary embodiment, coolant pump 587 may be driven by battery 550 or prime mover 140 (of
In one configuration, battery 550 may store the electrical energy generated by prime mover 140 (of
In an exemplary embodiment, high pressure hydrogen tank 560, high pressure oxygen tank 570 and pipes connecting electrolyzer 540 and high pressure gas tanks 560, 570 may be fabricated using strong, light weight carbon composites. In one configuration, high pressure hydrogen tank 560 and the pipe connecting electrolyzer 540 to tank 560 may be coated with a metal on their interior surfaces to prevent leakage of the hydrogen gas through the walls of tank 560 and the pipes connected thereto.
Operation of system 500 is described with reference to
With the aid of battery 550, the pressurized fresh water is electrolyzed in electrolyzer 540 to produce pressurized hydrogen gas and pressurized oxygen gas. As will be understood by one skilled in the art, the pressurized hydrogen gas and the pressurized oxygen gas will be at a pressure slightly less, for example, about five percent (5%) less than the pressure of the pressurized fresh water due to the pressure losses associated with, for example, fluid decoupler 520, variable pressure fresh water tank 530 and other components of system 500. One-way differential valves 562, 572 are actuated to permit the flow of pressurized hydrogen gas and oxygen gas from electrolyzer 540 to high pressure hydrogen tank 560 and high pressure oxygen tank 570 respectively. The pressurized hydrogen gas and oxygen gas are then stored in the respective tanks 560, 570.
As is known in the art, as a result of electrolysis, the pressurized hydrogen and oxygen gases are at a higher temperature than the fresh water which was electrolyzed to produce these gases. In an embodiment of the invention, the pressurized hydrogen and oxygen gases stored in respective high pressure gas tanks 560, 570 may be cooled to reduce their temperatures. In one configuration, cold ambient seawater at the stage C, for example, of UUV 330 may be used to extract heat energy from the pressurized hydrogen and oxygen gases stored in respective tanks 560, 570. In another configuration, a coolant may be circulated in thermal coupling with tanks 560, 570 to extract heat energy from the pressurized hydrogen and oxygen gases stored therein. The coolant may be circulated using pumps powered by prime mover 140 (of
Referring now to
In one configuration, the pressurized hydrogen and oxygen gases may be fed to a propulsion system, such as described in commonly owned U.S. Pat. No. 7,128,624, issued Oct. 31, 2006, which is incorporated by reference herein in its entirety. In the open cycle underwater propulsion system described in the '624 patent, the pressurized hydrogen and oxygen gases are fed into a combustion chamber to initiate a combustion reaction, which generates high-pressure steam. The high-pressure steam may be cooled with the injection of seawater, as well as due to the expansion of the steam. High-pressure water is then ejected out of the combustor in the form of a water jet, thereby generating thrust for the underwater vehicle. The steam pressure drops due to the expansion of the steam as well as due to the condensation of the steam. As the pressure in the seawater barrel drops, the flapper valve opens to fill the seawater barrel with the ambient seawater.
As the pressurized hydrogen and oxygen gases from their respective tanks 560, 570 are injected into combustor 580, the pressures of the remaining hydrogen and oxygen gases in the respective tanks 560, 570 start to decline. Once the pressures of the hydrogen and oxygen gases in their respective tanks 560, 570 fall below a predetermined threshold, further injection of hydrogen and oxygen gases into combustor 580 would not produce steam sufficiently pressurized to effectively operate water-jet engine 600. Therefore, when the pressures of the hydrogen and oxygen gases in their respective tanks 560, 570 fall below a predetermined threshold, water-jet engine 600 ceases to operate. If, however, the pressure of the hydrogen and oxygen gases remaining in their respective tanks 560, 570 can be increased, the quantities of the hydrogen and oxygen gases that can be usefully injected into combustor 580 may also be increased, thereby increasing the efficiency of system 500 and prolonging the operational times of water-jet engine 600.
In an exemplary embodiment, the hydrogen and oxygen gases remaining in their respective tanks 560, 570 may be further pressurized by heating the stored hydrogen and oxygen gases in their respective tanks 560, 570. As is known in the art, at a constant mass and a constant volume, an increase in temperature results in an increase in pressure for a gas, per the ideal gas law. In one configuration, such heating of the stored hydrogen and gases in their respective tanks 560, 570 may be achieved by transferring heat from combustor 580. Such a transfer of heat from combustor 580 also advantageously cools down combustor 580, thereby reducing the operational stresses thereon and prolonging the operational life of combustor 580. Since heat transfer systems for transferring heat from such a combustor 580 to tanks 560, 570 are known in the art, they are not described in any detail for the sake of brevity.
Referring now to
Referring to
An advantage of system 500 is that ambient hydrostatic pressure is harvested to pressurize the freshwater, which, when electrolyzed, produces pressurized hydrogen and oxygen gases. Therefore, the need for pumping energy generally required to pressurize the hydrogen and oxygen gases is eliminated. Another advantage of system 500 is that sufficient thrust power may be generated to enable UUV 330 to sprint at a speed of about forty (40) knots. UUV 330 equipped with system 500 may be capable of sprints ranging from about 1 kiloyard (kyd) to about 5 kyd. However, system 500 may be used for electrolysis only when the ambient hydrostatic pressure exerted on the fresh water is sufficiently high to produce pressurized hydrogen and oxygen gases. Thus, system 500 may be effective only at depths below a threshold depth. Furthermore, as the size of UUV 330 (of
Referring now to
As shown in
Variable pressure fresh water tank 530 is in fluid communication with a high pressure fresh water tank 810 via a one-way differential water valve 835. Similarly, variable pressure hydrogen tank 820 is in fluid communication with high pressure hydrogen tank 560 via a one-way differential gas valve 562 and variable pressure oxygen tank 830 is in fluid communication with high pressure oxygen tank 570 via one-way differential gas valve 564. High pressure water tank 810 is in fluid communication with electrolyzer 540 via a check valve 845 (e.g., either self-actuated or controlled by a controller). Check valve 845 regulates the flow of the pressurized water from high pressure water tank 810 to electrolyzer 540. Electrolyzer 540 is in fluid communication with each of variable pressure hydrogen tank 820 and variable pressure oxygen tank 830. Variable pressure hydrogen tank 820 and variable pressure oxygen tank 830 are in fluid communication with high pressure hydrogen tank 560 and high pressure oxygen tank 570 respectively.
Pressure transfer system 805 may be actuated to exert ambient hydrostatic pressure 510 on the fresh water stored in variable pressure fresh water tank 530. Once the water pressure in variable pressure fresh water tank 530 exceeds a predetermined threshold, one-way differential valve 835 may be actuated to permit the flow of pressurized water to high pressure water tank 810. One-way differential valve 835 prevents the reverse flow of pressurized water from high pressure water tank 810 to variable pressure water tank 530. In this embodiment, high pressure water is available for electrolysis even when UUV 330 (of
The hydrogen and oxygen gases released from the electrolysis of high pressure water in electrolyzer 540 are stored in variable pressure hydrogen tank 820 and variable pressure oxygen tank 830 respectively. When UUV 330 (of
An advantage of system 800 is that electrolysis of fresh water may be performed continuously regardless of the depth of UUV 330 (of
While the foregoing invention has been described with reference to the above-described embodiment, various modifications and changes can be made without departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims. Accordingly, the specification and the drawings are to be regarded in an illustrative rather than a restrictive sense. The accompanying drawings that form a part hereof, show by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. This Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled.
Such embodiments of the inventive subject matter may be referred to herein, individually and/or collectively, by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations of variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.
