Power supply for underwater vehicles and sensors

Abstract

The present invention relates to a power supply system for underwater vehicles, in particular to a power supply system for autonomous underwater vehicles, to underwater vehicles equipped with such power supply systems and to a method of operating an underwater vehicle. The power supply system for underwater vehicles comprises a hydrogen fuel cell, which on the one hand is in fluid contact with a metal hydride storage tank, and on the other hand, with a membrane module that is capable of extracting dissolved oxygen from water. By combining the above mentioned components, the energy necessary to support the AUV operation and the operation of its sensors can be provided, replacing in an efficient and sustainable way the currently employed battery energy systems. For the operation of gliders, a weight compensating mechanism could also be implemented.

Claims

1. An underwater vehicle equipped with a power supply system, the power supply system comprising a hydrogen fuel cell, a metal hydride storage tank and a membrane module, wherein the hydrogen fuel cell is in fluid contact with said metal hydride storage tank and with said membrane module, the membrane module employing an oxygen selective membrane in the form of a thin film composite membrane, capable of harvesting dissolved oxygen from an aqueous environment.

2. The underwater vehicle of claim 1, wherein the hydrogen fuel cell is a proton-exchange membrane (PEM) fuel cell.

3. The underwater vehicle of claim 1, wherein the fuel cell is a fuel cell operating at a temperature between 60° C. and 120° C.

4. The underwater vehicle of claim 3, wherein the fuel cell is a fuel cell operating at a temperature between 60° C. and 80° C.

5. The underwater vehicle of claim 1, wherein the membrane module comprises a membrane of a material selected from the group consisting of polyolefins; polysilicones; polysilanes, polysiloxanes, and fluorinated polyolefins.

6. The underwater vehicle of claim 5, wherein the membrane material is selected from cross-linked poly(dimethylsiloxane) (PDMS) and poly(octylmethylsiloxane) (POMS).

7. The underwater vehicle of claim 1, wherein the membrane is of a flat sheet geometry or a hollow geometry.

8. The underwater vehicle of claim 1, wherein the metal hydride is selected from those having a desorption temperature of from 20° C. to 100° C. at 500 kPa.

9. The underwater vehicle of claim 1, wherein the heat of operation of the fuel cell is at least partially transferred to the metal hydride tank.

10. The underwater vehicle of claim 1, which is an autonomous underwater vehicle (AUV).

11. The underwater vehicle of claim 10, which is an autonomous underwater vehicle (AUV) of the type of a glider.

12. The underwater vehicle of claim 1, wherein the underwater vehicle has a vehicle shell, a nose, a shoulder, a top, a bottom and hydrofoils, and wherein the membrane module is positioned at the nose of the underwater vehicle, the shoulder, the top or bottom of the underwater vehicle shell, or the hydrofoils of the underwater vehicle.

13. The underwater vehicle of 12, wherein the membrane module is positioned at the nose of the underwater vehicle.

14. A method of operating an underwater vehicle, wherein power is supplied by a power supply system comprising a hydrogen fuel cell, metal hydride storage tank and a membrane module, wherein the hydrogen fuel cell is in fluid contact with said metal hydride storage tank and with said membrane module, the membrane module employing an oxygen selective membrane capable of harvesting dissolved oxygen from an aqueous environment.

15. The underwater vehicle of claim 5, wherein the polysiloxanes are poly(dimethylsiloxane) (PDMS) or poly(octylmethylsiloxane) (POMS).

16. The underwater vehicle of claim 5, wherein the fluorinated polyolefins are poly(tetrafluoroethylene) (PTFE) or poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene] (Teflon AF 2400).

Description

(1) The invention is now described in an exemplary manner with reference to the appended figures, wherein

(2) FIG. 1 is a schematic representation of the invention; and

(3) FIG. 2 is an illustration of an AUV having installed a membrane module at its nose, and exhibiting a surrounding shell and two hydrofoils which can also act as potential membranes housings.

(4) FIG. 1 is a schematic representation of the invention. It shows a fuel cell 10 located within the body, nose part or another location in an underwater vehicle 1. The fuel cell 10 is in flow connection with a metal hydride tank 12, which delivers hydrogen (H.sub.2) to operate the fuel cell 10. The fuel cell 10 is also in flow connection with a membrane module 14, wherein a plurality of membranes is arranged in a way that provides water flow for reduction as much as possible of the formation of boundary layer zones.

(5) The membranes in the membrane module 14 extract dissolved oxygen (O.sub.2) from water as a permeate stream. A permeate stream from the membrane module 14 is present in the form of an O.sub.2 rich gas, which may contain amounts of other gases such as nitrogen (N.sub.2), argon (Ar), carbon dioxide (CO.sub.2) and/or water vapour. The permeate stream is guided in a loop system 15a from the membrane module 14 to the fuel cell 10 and the O.sub.2 in the permeate stream is consumed therein. O.sub.2 depleted gas may be recirculated in the loop system 15b from the fuel cell 10 to the membrane module 14 to maintain a gas flow between the membrane module and the fuel cell.

(6) As H.sub.2 and O.sub.2 are consumed in the fuel cell, water (H.sub.2O) is produced. The H.sub.2O produced in the fuel cell—and also H.sub.2O which has co-permeated through the membrane as water vapour—may be released to the environment. For this purpose, a heat exchanger 16 may be provided that will condense the water and a pumping system connected to the heat exchanger 16 will release the condensed water into the environment. Part of the H.sub.2O produced may, however, be used for buoyancy control in the underwater vehicle. The fuel cell 10 produces the energy necessary to operate the underwater vehicle 1 and the sensors therein.

(7) FIG. 2 illustrates an underwater vehicle 1 having a body part 4 which is surrounded by a shell 6 and which is fitted with hydrofoils 8a, 8b. Such hydrofoils 8a, 8b are typical for gliders that allow the gliders to glide forward while descending or ascending through the water. The nose of the underwater vehicle is equipped with a membrane module 10 comprising an array of membranes. In FIG. 2, the membrane module 10 incorporates an array of membranes 10, and is attached to the nose of the underwater vehicle 1. The membranes are arranged within the membrane module 10 so as to allow for contact of the membranes with ambient water. The membranes allow oxygen gas (O.sub.2) to permeate from the water flow into the gas stream and the oxygen rich permeate stream will be conveyed to a fuel cell with which the membrane module is in contact. The surrounding shell 6 and the hydrofoils 8a, 8b can also be considered as potential housings for the membranes.

(8) As shown in FIG. 2, the membrane module may be placed on the nose of an underwater vehicle. However, other locations such the top and bottom, and the hydrofoils, of the underwater vehicle may be suitable locations as well.

(9) In FIG. 2, the body part 4 of the underwater vehicle 1 hosts the fuel cell and the metal hydride tank (both not shown), as well as the sensor equipment and buoyancy control equipment (also not shown).

EXAMPLE

(10) An ocean glider, a low power AUV, requires about 3-5 W and operates typically for about 5 weeks. Using a 10 W commercially available fuel cell, this means that it is necessary to use 50 mol of oxygen and 100 mol of hydrogen. For the efficient storage and transport of hydrogen, ca. 12 kg of commercial hydride, e.g., Hydralloy® C. are necessary. A simple mass transfer model indicates that for the extraction of 50 mol of oxygen from water, 2-5 m.sup.2 of polymer membrane based, e.g., on the polymer poly(octylmethylsiloxane) (POMS) is sufficient. During the 5 weeks operation 1.8 kg water is produced, of which 1.6 kg is to be purged from the vehicle to maintain its weight while the glider reaches the surface of the water and the pressure will be equilibrated.