Patent Publication Number: US-9853301-B2

Title: Thermal conditioning fluids for an underwater cryogenic storage vessel

Description:
CROSS-REFERENCE OF RELATED APPLICATIONS 
     This application is a division of co-pending U.S. application Ser. No. 12/552,136, filed on Sep. 1, 2009, entitled, “Thermal Conditioning Fluids For An Underwater Cryogenic Storage Vessel”, which is related to U.S. application Ser. No. 14/162,188, filed on Jan. 23, 2014, entitled “Underwater Cryogenic Storage Vessel and Method of Using Same,” and is also related to U.S. Pat. No. 8,651,313, issued on Feb. 18, 2014, entitled, “Underwater Cryogenic Storage Vessel”, which is expressly incorporated herein by reference in its entirety. 
    
    
     GOVERNMENT RIGHTS 
     This invention was made with Government support under contract number HR0011-06-C-0073 awarded by the United States Navy. The government has certain rights in this invention. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to fuel systems, and in particular to thermal conditioning cryogenic fluids associated with fuel systems for underwater vehicles. 
     BACKGROUND 
     Some vehicles, such as underwater vehicles, have a fuel system that uses a fuel cell to provide power to the vehicle. Typically, these fuel cells are supplied with kerosene and oxygen to produce power. These fuel cells also produce carbon dioxide as an effluent. In such power systems, the oxygen supplied to the fuel cell is stored in storage tanks, which are connected to the fuel cell. The resulting carbon dioxide is collected and stored in separate storage tanks. 
     In existing power systems of such vehicles, the oxygen is stored as a liquid in storage tanks arranged adjacent to each other. Before supplying the oxygen to the fuel cell, the liquid oxygen in these tanks may need to be boiled off, such that the oxygen supplied to the fuel cell is in a gaseous state. However, the heat supplied to one of the tanks for boiling off the oxygen may dissipate to the other tanks in the vicinity, thereby increasing the temperature and consequently, the pressure in the storage tanks adjacent to the tank that is being supplied with heat. 
     In an attempt to reduce the effect of the dissipated heat on the other tanks located in the vicinity, the tanks are conventionally made with insulated vacuum gaps to reduce the amount of heat that may leak into the unused tanks. However, because of the insulated gaps, these tanks take up a larger volume. Further, because there may still be some heat leak into the storage tanks despite the insulated gaps around the storage tanks, the fluids in the tanks may expand due to an increase in pressure. In order to account for the possibility of fluid expansion, these conventional tanks are typically only partially-filled, thereby requiring tanks with greater volume to store the amount of fuel desired. 
     It is with respect to these and other considerations that the disclosure made herein is presented. 
     SUMMARY 
     Technologies are described herein for thermal conditioning fluids associated with a fuel system. According to one aspect of the disclosure, a fuel system includes a fuel cell and a storage vessel. The storage vessel is configured to store a first fluid that is supplied to the fuel cell and a second fluid that is supplied by the fuel cell. The first fluid includes a liquid first fluid and a gaseous first fluid, and the second fluid includes a liquid second fluid and a gaseous second fluid. The fuel system also includes a thermal conditioning module that is configured to receive the gaseous first fluid from the storage vessel and also to receive the gaseous second fluid from the fuel cell. The gaseous first fluid stored in the storage vessel is conditioned by absorbing heat from the gaseous second fluid, such that the fuel cell receives the gaseous first fluid from the thermal conditioning module. The gaseous second fluid received from the fuel cell is converted to the liquid second fluid. The liquid second fluid is then stored in the storage vessel. 
     In another aspect of the present disclosure, a fuel system includes a thermal conditioning module. The thermal conditioning module is configured to receive a gaseous first fluid from a storage vessel and a gaseous second fluid from a fuel cell. The gaseous first fluid from the storage vessel is conditioned by absorbing heat from the gaseous second fluid to create a conditioned gaseous first fluid. A first portion of the conditioned gaseous first fluid is provided to the fuel cell, while a second portion is provided back to the storage vessel. The gaseous second fluid from the fuel cell is converted to a liquid second fluid and provided to the storage vessel. 
     In yet another aspect, a fuel system includes a fuel cell, a storage vessel, and a thermal conditioning module. The storage vessel includes two storage tanks, each configured to store a first fluid to be supplied to the fuel cell. The storage vessel also includes a storage compartment configured to store a liquid second fluid supplied by the fuel cell. The thermal conditioning module receives the first fluid from the storage vessel and receives a gaseous second fluid from the fuel cell. The first fluid is conditioned by absorbing heat from the gaseous second fluid from the fuel cell to create a conditioned first fluid. A portion of the conditioned first fluid is provided to the fuel cell and a second portion is provided back to the storage vessel. The gaseous second fluid from the fuel cell is converted to a liquid second fluid and provided to the storage compartment for storage. 
     It should be appreciated that the above-described subject matter may also be implemented in various other embodiments without departing from the spirit of the disclosure. These and various other features will be apparent from a reading of the following Detailed Description and a review of the associated drawings. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended that this Summary be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a fuel system comprising a fuel cell, a thermal conditioning module, and a storage vessel, according to embodiments described herein; 
         FIG. 2  is a cut-open view of the storage vessel, according to embodiments described herein; 
         FIG. 3  is a partial cut-open view and partial bottom view of the storage vessel, according to embodiments described herein; 
         FIG. 4  is a line diagram illustrating the flow of fluids within the storage vessel, according to embodiments described herein; 
         FIG. 5  is a block diagram illustrating a thermal conditioning module of a fuel system, according to embodiments described herein; 
         FIG. 6  is a logical flow diagram illustrating a routine for operating the fuel system, according to embodiments described herein; 
         FIG. 7  is a logical flow diagram illustrating a routine for storing an effluent in a storage tank of the storage vessel, according to embodiments described herein; and 
         FIG. 8  is a logical flow diagram illustrating a routine for conditioning the storage tank of the storage vessel, according to embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is directed to technologies for conditioning fluids that are and will be stored in a storage vessel. In the following detailed description, references are made to the accompanying drawings that form a part hereof, and which are shown by way of illustration, specific embodiments, or examples. Referring now to the drawings, in which like numerals represent like elements through the several figures, a fuel system according to the various embodiments will be described. As described above, the fuel system may be utilized to provide power to an underwater vehicle, wherein the fuel system includes a fuel cell and a thermal conditioning module configured to receive stored fuel and to condition the fuel before supplying the fuel to the fuel cell. 
       FIG. 1  illustrates a fuel system  100  that includes a fuel storage vessel  101 , a fuel cell  102 , a thermal conditioning module  104  and an electronic controller  114 . The electronic controller  114  may be a computer, a processor, or any other hardware and/or software component that is configured to control the various components associated with the fuel system  100 . In various embodiments, the electronic controller  114  may not be a part of the fuel system  100  but may still be configured to control the various components associated with the fuel system  100 . 
     According to embodiments, the fuel cell  102  may be configured to receive a first fluid, such as gaseous oxygen, as a reactant from the thermal conditioning module  104 , and to produce a gaseous second fluid, such as gaseous carbon dioxide as an effluent, which is then supplied to the thermal conditioning module  104 . In some embodiments where the venting of gases may be undesirable, the first fluid may be stored as a liquid in the storage vessel  101 . In embodiments, the first fluid may be stored in liquid form and in gas form, such that the gaseous first fluid is supplied from the storage vessel to the thermal conditioning module  104 . Further, the gaseous second fluid produced by the fuel cell  102  may be conditioned by the thermal conditioning module  104 , such that the gaseous second fluid is converted to a liquid second fluid and stored in the same or different storage vessel. In various embodiments, the fuel cell  102  utilizes gaseous oxygen and kerosene to generate energy and produces gaseous carbon dioxide as an effluent. It should be appreciated that the kerosene, or any other reactant of the fuel cell  102 , may be supplied to the fuel cell  102  from a reactant source (not shown). 
     The thermal conditioning module  104  may be configured to receive the gaseous first fluid stored in the storage vessel  101  via at least one of a plurality of fluid exit ports  112 , which may route fluids stored in the storage vessel  101  to the thermal conditioning module  104 . The thermal conditioning module  104  may also condition the gaseous first fluid as the gaseous first fluid travels through the thermal conditioning module  104 , after which the thermal conditioning module  104  supplies the conditioned gaseous first fluid to the fuel cell  102 . The fuel cell  102  may receive the conditioned gaseous first fluid from the thermal conditioning module  104  via a passage  106 . Upon receiving the conditioned gaseous first fluid, the fuel cell  102  may produce the gaseous second fluid, which is supplied to the thermal conditioning module  104  via a passage  108 . The thermal conditioning module  104  may be configured to condition the gaseous second fluid to the liquid second fluid as the second fluid passes through the thermal conditioning module  104 . Upon conditioning the gaseous second fluid to liquid second fluid, the thermal conditioning module  104  may deliver the liquid second fluid to the storage vessel  101  via a plurality of fluid entry ports  110 . The liquid second fluid is then stored in a location of the storage vessel from where the first fluid is not being supplied. Further details regarding the thermal conditioning module  104  will be described in regard to  FIGS. 5-8 . 
     The passage  106  may be configured to supply the conditioned gaseous first fluid from the thermal conditioning module  104  to the fuel cell  102 . The passage  108  may be configured to supply the unconditioned gaseous second fluid from the fuel cell  102  to the thermal conditioning module  104 . In addition, the fuel system also includes a plurality of fluid entry ports  110  that may be configured to allow fluids to flow from the thermal conditioning module to the storage vessel. Similarly, the fuel system also includes a plurality of fluid exit ports  112  that may be configured to allow fluids to flow from the storage vessel to the thermal conditioning module. Details regarding the plurality of fluid entry ports  110  and the fluid exit ports  112  will be described in regard to  FIGS. 2-4 . 
     Referring now to  FIGS. 2-4 , details regarding the storage vessel  101  are shown.  FIG. 2  illustrates the storage vessel  101  that includes storage tanks  202 ,  204 ,  206  and a storage compartment  208  that is positioned adjacent to one end of the storage tanks  202 ,  204 ,  206 . It should be appreciated that the storage vessel  101  may include any number of storage tanks and any number of storage compartments within the storage vessel  101 . In one embodiment, the storage vessel  101  may not include any storage compartments. In embodiments where there is more than one storage compartment, the storage compartments may also be arranged concentrically or in any other fashion. The storage compartment may be located anywhere within the storage vessel  101 , and may store the same or different fluid as the storage tanks  202 ,  204 ,  206 . 
     In the present embodiment, the storage vessel  101  includes the first storage tank  202 , the second storage tank  204  and the third storage tank  206  concentrically arranged such that the first storage tank  202  is surrounding the second storage tank  204 , and the second storage tank  204  is surrounding the third storage tank  206 . The first storage tank  202  may include a first fluid entry port  220  and a first fluid exit port  222 . The second storage tank  204  may include a second fluid entry port  224  and a second fluid exit port  226 , and the third storage tank  206  may include a third fluid entry port  228  and a third fluid exit port  230 . In addition, the storage compartment  208  may also include a compartment fluid entry port  232  and a compartment fluid exit port  234 . The plurality of fluid entry ports  110  (shown in  FIG. 1 ) may include at least the first fluid entry port  220 , the second fluid entry port  224 , the third fluid entry port  228 , and the compartment fluid entry port  232 . The plurality of fluid entry ports  112  (shown in  FIG. 1 ) may include at least the first fluid exit port  222 , the second fluid exit port  226 , the third fluid exit port  230 , and the compartment fluid exit port  234 . Details of the plurality of fluid entry ports  110  and the plurality of fluid exit ports  112  will be described in detail below in regard to  FIG. 3 . 
     In various embodiments, the third storage tank  206  may be nested inside the second storage tank  204 , which may be nested inside the first storage tank  202 . Each of the first, second, and third storage tanks  202 ,  204 ,  206  have a bottom end, which is adjacent the storage compartment  208 . In some embodiments, each of the three storage tanks  202 ,  204 ,  206  and the storage compartment  208  may contain the same volume of fluid or may contain different volumes of fluid. 
     According to various embodiments, the storage vessel  101  may store one fluid or more than one fluid. In some embodiments, the first storage tank  202  may store a first fluid, the second storage tank  204  may store a second fluid, and the third storage tank  206  may store a third fluid. Further, the storage compartment  208  may be used to store the same or a different fluid as the storage tanks. In some embodiments, the three storage tanks  202 ,  204 ,  206  and the storage compartment  208  are sealed, such that the fluid from one of the storage tanks  202 ,  204 ,  206  and the storage compartment  208  may not flow into another storage tank  202 ,  204 ,  206  or the storage compartment  208 . 
     In the present embodiment, as described above, the storage vessel  101  may be utilized for storing liquid oxygen and liquid carbon dioxide. Because of the very low boiling points of these liquids, it is important that the storage tanks  202 ,  204 ,  206  that store these liquids maintain low temperatures, such that the liquids do not boil off to gas and thereby increase the pressure inside these tanks  202 ,  204 ,  206 . Therefore, it may be desirable to protect the storage tanks  202 ,  204 ,  206  from external environmental conditions by covering them with insulating materials and/or a vacuum gap. The vacuum gap may be a gap between two storage tanks that is a vacuum. The vacuum gap may serve as an insulator, such that the amount of heat exchange between the two storage tanks is reduced. 
     The external environmental conditions for a particular storage tank may include conditions that exist outside that particular storage tank. Specifically, these external environmental conditions may include environmental conditions, such as the temperature, pressure, and illumination of the environment around the storage tanks. In some embodiments, the storage vessel may be used to store cryogenic liquids, such as liquid oxygen, which has a boiling point of around −290° F. and liquid carbon dioxide, which has a boiling point of around −60° F. Therefore, if the storage vessel  101  is placed in normal environmental conditions, for example, at 45° F., the temperature inside the storage vessel  101  is significantly lower than the environmental conditions external to the storage vessel  101 . Further, because the storage tanks  202 ,  204 ,  206  are concentrically arranged, the external conditions of the first storage tank  202  may be influenced by the external environmental conditions, such as the temperature outside the storage vessel  101  on one side, and by the temperature inside the second storage tank  204 . It should be appreciated that the conditions external to a particular storage tank  202 ,  204 ,  206  or storage compartment  208  may influence the conditions inside the storage tank or storage compartment. 
     According to embodiments, the storage vessel  101  may utilize insulating material such as a multi-layer insulation in a vacuum gap, evacuated powder insulation or foam insulation, to protect the storage vessel  101  from external environmental conditions. Each storage tank  202 ,  204 ,  206  may be surrounded by an insulating material to protect each storage tank  202 ,  204 ,  206  from external environmental conditions that exist in the remaining storage tanks  202 ,  204 ,  206  and storage compartment  208 . In some embodiments where space is limited, it may be desirable to utilize a smaller amount of space for insulating the storage tanks. Therefore, the insulating material may be a thin layer of multi-layer insulation, which surrounds each of the storage tanks  202 ,  204 ,  206 . In various embodiments, the bottom end of the storage tanks  202 ,  204 ,  206  is also surrounded by insulating material, such that the conditions present in the storage compartment  208  may not affect the fluid in the storage tanks  202 ,  204 ,  206 . By insulating the storage tanks  202 ,  204 ,  206 , the fluid stored in the storage tanks  202 ,  204 ,  206  may be protected from conditions that may be present in the remaining storage tanks  202 ,  204 ,  206 . 
     In one embodiment, each storage tank  202 ,  204 ,  206  may be surrounded by a vacuum jacket, which serves as an insulator for the storage tank it surrounds. Similar to the vacuum gap, the vacuum jacket may surround a storage tank such that a vacuum surrounds the storage tank, which serves as an thermal insulator to reduce the amount of heat exchange between the storage tank and the external environment surrounding the storage tank. 
     According to embodiments, the first storage tank  202  may be surrounded by a first insulating material  210 , which may be configured to protect the first storage tank  202  and the contents inside the first storage tank  206  from the external environmental conditions that may influence the conditions, such as the temperature, inside the first storage tank  202 . Similarly, the second storage tank  204  may be surrounded by a second insulating material  212 , which may be configured to protect the second storage tank  204  and the contents inside the second storage tank  204  from the external environmental conditions exposed to the surface of the second storage tank  204  that is in contact with the second insulating material  212 , such as the environmental conditions inside the first storage tank  202 . It should be appreciated that the second insulating material  212  may also protect the first storage tank  202  from the environmental conditions present in the second storage tank  204 . The third storage tank  206  may be surrounded by a third insulating material  214 , which may be configured to protect the third storage tank  206  and the contents inside the third storage tank  206  from the external environmental conditions exposed to the surface of the third storage tank  204  that is in contact with the third insulating material  214 . It should further be appreciated that the third insulating material  214  may also protect the second storage tank  204  from the environmental conditions present in the third storage tank  206 . Hence, the insulating material may protect each storage tank from the external environmental conditions that surround that particular storage tank. As a result, any change in environmental conditions, such as a change in temperature that occurs in a particular storage tank may be isolated to that particular storage tank. 
     The insulating material may be any type of insulation known to those skilled in the art. Because the storage tanks may store cryogenic liquids, the insulating material should be able to insulate the storage tanks even at very low temperatures. In one embodiment, vacuum jackets may surround the storage tanks. A vacuum jacket may include multi-layer insulation, powder insulation, or foam insulation within the jacket, which serves as an insulator. 
     In order to maintain the pressure inside the storage vessel  101 , and the individual storage tanks  202 ,  204 ,  206  and the storage compartment  208 , a seal  236  may be placed at the top end of the storage vessel  101 . Those skilled in the art may appreciate that the seal  236  may allow the fluid entry ports  220 ,  224 ,  228 ,  232  and fluid exit ports  222 ,  226 ,  230 ,  234  of the three storage tanks  202 ,  204 ,  206  and storage compartment  208  to pass through the seal  236 , such that there is no leakage present between the fluid entry ports  220 ,  224 ,  228 ,  232  and fluid exit ports  222 ,  226 ,  230 ,  234  and the seal  236 . It should be appreciated that the seal  236  may be made from a variety of materials that are known to those skilled in the art. It may be desirable to select a seal that may operate under the conditions in which the storage vessel will be utilized. For instance, in embodiments where the storage vessel  101  is being used to store liquid oxygen, a seal that is capable of operating under extremely cold temperatures may be used. Further details regarding the seal  236  will be described below in regard to  FIG. 3 . 
     Referring now to  FIG. 3 , the storage vessel  101  may include fluid entry ports  220 ,  224 ,  228 ,  232  and fluid exit ports  222 ,  226 ,  230 ,  234 . In various embodiments, fluid entry ports  220 ,  224 ,  228 ,  232  and fluid exit ports  222 ,  226 ,  230 ,  234  extend out of the storage vessel  101  at the top end of the storage vessel  101 , where they may be attached to the thermal conditioning module  104  or a fluid source. 
     According to embodiments, the first storage tank  202  may include the first fluid entry port  220 , which may be used to supply fluid from the thermal conditioning module  104  to be stored in the first storage tank  202 . The first storage tank  202  may also include the first fluid exit port  222 , which may be configured to route the stored fluid from the first storage tank  202  to the thermal conditioning module  104 . 
     Similarly, the second storage tank  204  may include the second fluid entry port  224 , which may be used to supply fluid from the thermal conditioning module  104  to be stored in the second storage tank  204 . The second storage tank  204  may also include the second fluid exit port  226 , which may be configured to route the stored fluid from the second storage tank  226  to the thermal conditioning module  104 . In addition, the third storage tank  206  may also include the third fluid entry port  228 , which may be used to supply fluid from the thermal conditioning module  104  to be stored in the third storage tank  206 . The third storage tank  206  may also include the third fluid exit port  230 , which may route the stored fluid from the third storage tank  206  to the thermal conditioning module  104 . 
     In various embodiments, the compartment fluid entry port  232  may extend from outside the storage vessel  101 , pass through the inner most storage tank, and into the storage compartment  208 . In some embodiments, the inner most storage tank may be the third storage tank  206 . The compartment fluid entry port  232  may be used to supply a fluid from the thermal conditioning module  104  to the storage compartment  208 . Further, the storage vessel  101  may include the compartment fluid exit port  234 , which similar to the compartment fluid entry port  232 , may extend from outside the storage vessel  101 , and pass through the inner most storage tank to the storage compartment  208 . In various embodiments, the fluid passing through the compartment fluid entry port  232  and compartment fluid exit port  234  may be affected by the conditions present inside the inner most storage tank. In order to reduce the effects caused by the conditions present inside the inner most storage tank, the compartment fluid entry port  232  and compartment fluid exit port  234  may be surrounded by insulating material as well. 
     As described above, the seal  236  may be configured to receive the fluid entry ports  220 ,  224 ,  228 ,  232  and fluid exit ports  222 ,  226 ,  230 ,  234 , while also be configured to maintain the pressure inside each of the storage tanks  202 ,  204 ,  206  and the storage compartment  208 . The seal  236  may include a first seal  237 A configured to maintain the pressure inside the first storage tank  202 , a second seal  237 B configured to maintain the pressure in the second storage tank  204  and a third seal  237 C configured to maintain the pressure in the third storage tank  206 . 
     Referring now to  FIG. 4 , the storage vessel  101  may further include a plurality of sensors  402 ,  404 ,  406 ,  408  that may be configured to monitor the environmental conditions within various parts of the storage vessel  101 . The first sensor  402  may be positioned within the first storage tank  202 , and configured to monitor at least one of the temperature and pressure inside the first storage tank  202 . Similarly, the second sensor  404  may be positioned within the second storage tank  204 , the third sensor  406  may be positioned within the third storage tank  206 , and the compartment sensor  408  may be positioned within the storage compartment  208  of the storage vessel  101 . The second sensor  404 , the third sensor  406 , and the compartment sensor  408  may all be configured to monitor at least one of the temperature and pressure inside the second storage tank  204 . It should be appreciated that any number of sensors may monitor any number of conditions inside each of the storage tanks  202 ,  204 ,  206  and storage compartment  208  of the storage vessel  101 . Further, although not shown in the drawings, it should be understood that the sensors may be in direct or indirect communication with the electronic controller  114  that is configured to control the operation of the fuel system  100 . For the sake of clarity, the fluid entry ports  220 ,  224 ,  228 ,  232  and fluid exit ports  222 ,  226 ,  230 ,  234  are marked with dotted lines. 
     Referring now to  FIG. 5 , details regarding the thermal conditioning module  104  will now be described. It should be appreciated that the thermal conditioning module  104  described herein may be utilized for conditioning fluids in a wide variety of applications. However, for the sake of clarity, the present disclosure will describe the thermal conditioning module  104  as it is utilized within the fuel system  100  that utilizes gaseous oxygen as a reactant, and produces gaseous carbon dioxide as an effluent. The thermal conditioning module  104  may be configured to receive and condition gaseous oxygen, such that it is in a suitable condition for being supplied to the fuel cell  102 . Further, the thermal conditioning module  104  may also be configured to receive and condition gaseous carbon dioxide such that it is in a suitable condition for being stored in the storage vessel. 
     According to embodiments, the thermal conditioning module  104  may include a first storage tank entry valve  510 , configured to control the flow of the oxygen from the thermal conditioning module  104  to the first storage tank  202  via the first fluid entry port  220 . A first storage tank exit valve  512  may be configured to control the flow of oxygen from the first storage tank  202  to the thermal conditioning module  104  via the first fluid exit port  222 . Similarly, the thermal conditioning module  104  may also include a second storage tank entry valve  514 , configured to control the flow of the oxygen from the thermal conditioning module  104  to the second storage tank  204  via the second fluid entry port  224 . A second storage tank exit valve  516  may be configured to control the flow of oxygen from the second storage tank  204  to the thermal conditioning module  104  via the second fluid exit port  226 . The thermal conditioning module  104  may also include a third storage tank entry valve  518 , configured to control the flow of the oxygen from the thermal conditioning module  104  to the third storage tank  206  via the third fluid entry port  228 . A third storage tank exit valve  520  may be configured to control the flow of oxygen from the third storage tank  206  to the thermal conditioning module  104  via the third fluid exit port  230 . In addition, the thermal conditioning module  104  may also include a storage compartment entry valve  522  configured to control the flow of fluids to the storage compartment  208  via the compartment fluid entry port  232  (shown in  FIG. 4 ) and a storage compartment exit valve  508  configured to control the flow of fluids from the storage compartment to the thermal conditioning module  104  via the compartment fluid exit port  234  (shown in  FIG. 4 ). 
     The thermal conditioning module  104  may also include other valves, such as a first effluent valve  524 , a second effluent valve  526 , a first recycling valve  528  and a second recycling valve  530 . The first effluent valve  524  may be configured to control the flow of the effluent from the fuel cell  102  into the first storage tank  202  of the storage vessel  101 . When the first effluent valve  524  is open, the effluent is able to flow into the first storage tank. Similarly, the second effluent valve  526  may be configured to control the flow of the effluent from the fuel cell  102  into the second storage tank  204  of the storage vessel  101 . When the second effluent valve  526  is open, the effluent is able to flow into the second storage tank  204 . The rate at which the effluent is able to flow into the first storage tank  202  and the second storage tank  204  may be controlled by the electronic controller  114 , which may be capable of opening and closing the first effluent valve  524  and second effluent valve  526 , respectively. Further, the first recycling valve  528  may be configured to control the flow of fluid flowing through the first fluid exit port  222  back into the first storage tank  202 . The second recycling valve  530  may be configured to control the flow of fluid flowing through the second fluid exit port  226  back into the second storage tank  204 . The amount of fluid that may flow through the first recycling valve  228  and the second recycling valve  230  may be controlled by the electronic controller  114 . Details regarding these valves and others are described below. 
     Further, the thermal conditioning module  104  may also include back-up valves that may operate in the event of a failure of another valve, and may also include various check valves, pressure release valves and other types of valves that may be utilized to improve the operation of the thermal conditioning module  104 . In addition, the thermal conditioning module  104  may include a variety of regulators that may be utilized to regulate the flow of fluids to reduce any back pressure buildup and to supply the fluids at a desired pressure. 
     It should be appreciated that the valves, regulators, and other components utilized during the operation of the fuel system  100  may be controlled by the electronic controller  114 . Further, the sensors described above in  FIG. 4  and additional sensors positioned throughout the fuel system  100  that may monitor various operating conditions, may communicate information with the electronic controller  114 , which may provide the electronic controller  114  with information to make decisions regarding the operation of the fuel system  100 . Further details of the electronic controller  114  will be described later. 
     The thermal conditioning module  104  may also include a first heat exchanger  540 , a second heat exchanger  542 , a compressor  544  and a plurality of heating elements, such as a first heating element  532 , a second heating element  534 , and a storage tank heating element  548 . Further, the thermal conditioning module  104  may include a boil off fan  546  that is electronically controlled by the electronic controller  114 . It should be appreciated that the thermal conditioning module  104  may include other parts, components and/or module, such as regulators, valves, and fans that are not shown in  FIG. 5 . Details regarding the operation of the components associated with the thermal conditioning module  104  will be described in detail along with the operation of the fuel system  100  with regard to  FIGS. 6-8 . 
     According to embodiments, the thermal conditioning module  104  utilizes the heat exchangers  540 ,  542  to condition the carbon dioxide. Because of the temperature difference that exists between the gaseous oxygen and gaseous carbon dioxide, passing the two gases through the heat exchangers  540 ,  542  allows the gaseous oxygen to absorb the heat of the carbon dioxide. The gaseous oxygen that enters the storage vessel  101  may be slightly higher than −290° F., which is the boiling point of liquid oxygen. The gaseous carbon dioxide entering the thermal conditioning module  104  from the fuel cell  102  may be at around 60° F. Therefore, due to the large temperature difference between the two gases, efficient heat exchange may take place. 
     The thermal conditioning module  104  may be configured to efficiently cool down and liquefy the carbon dioxide produced by the fuel cell  102  using the gaseous oxygen supplied by the storage tank. Therefore, the gaseous carbon dioxide that enters the thermal conditioning module  104  is at 60° F. at 15 psi, and may need to be conditioned, such that the gaseous carbon dioxide is liquefied and stored in the storage vessel at below −60° F. at 100 psi. In order to obtain this, the thermal conditioning module  104  receives the gaseous oxygen and passes it through the first heat exchanger  540 . Some of the gaseous oxygen is then passed through to the second heat exchanger  542  before it enters the fuel cell  102 . 
     The gaseous carbon dioxide produced by the fuel cell  102  is initially supplied to the second heat exchanger  542  at about 60° F. at 15 psi, where the heat of the gaseous carbon dioxide is absorbed by the gaseous oxygen, thereby cooling the gaseous carbon dioxide to about −60° F. at 15 psi. The cooled gaseous carbon dioxide is then supplied to a compressor  544 , which compresses the cooled carbon dioxide from 15 psi to 100 psi. It may be desirable to compress the carbon dioxide after cooling it, as it may be more energy efficient to do so. Next, the pressurized carbon dioxide is supplied to the second heat exchanger  542  at −60° F. at 100 psi, where it is further cooled and liquefied to liquid carbon dioxide at less than −60° F. As the pressurized carbon dioxide passes through the first heat exchanger  540 , the gaseous oxygen that was supplied by the storage vessel  101  absorbs the heat of the pressurized carbon dioxide, hence cooling the carbon dioxide enough to liquefy it to liquid carbon dioxide. 
       FIGS. 6-8  describe various routines utilized by the fuel system  100  during operation. However, before the various routines are performed by the fuel system  100  during operation, the fuel system  100  performs various routines for preparing the fuel system  100  prior to use. For instance, the storage vessel  101  may need to be filled with liquid oxygen at a specific temperature and pressure. In one embodiment, the liquid oxygen is stored in all three storage tanks  202 ,  204 ,  206 . Some gaseous oxygen may be present inside the three storage tanks  202 ,  204 ,  206  as well. Also, gaseous oxygen is stored in the storage compartment  208  at −60° F. and 100 psi, to prevent the liquid carbon dioxide from freezing and to reduce any adverse performance issues due to back pressure being generated in the fuel system  100 . Further, the valves that control the flow of fluid from the storage tanks  202 ,  204 ,  206  to the thermal conditioning module  104  are closed. 
     Referring now to  FIG. 6 , a routine  600  for operating the fuel system  100  is described. The routine  600  begins at operation  602 , where the fuel cell  102  is initiated. As the fuel cell  102  is initiated at operation  602 , the routine  600  proceeds to operation  604 , where the electronic controller  114  may open the first storage tank exit valve  512 . As the first storage tank exit valve  512  is opened, unconditioned gaseous oxygen present in the first storage tank  202  may flow through the first fluid exit port  222 , through the first storage tank exit valve  512 , and into the first heat exchanger  540 . 
     From operation  604 , the routine  600  proceeds to operation  606 , where the unconditioned gaseous oxygen is supplied to the first heat exchanger  540 . As described above, the gaseous oxygen absorbs some of the heat of the pressurized carbon dioxide that is partially conditioned by the second heat exchanger  542  and the compressor  544 . As the gaseous oxygen and the pressurized carbon dioxide pass through the first heat exchanger  540 , the unconditioned gaseous oxygen is warmed by absorbing the heat of the pressurized carbon dioxide. From operation  606 , the routine  600  proceeds to split to operation  608 , and operation  612 . 
     At operation  608 , a portion of the warmed oxygen is supplied to at least one boil off fan, such as the boil off fan  546 . At operation  608 , some of the warmed gaseous oxygen is routed back towards the storage vessel  101 . In the present embodiment, the warmed gaseous oxygen is routed back to the storage tank  101  that is supplying the gaseous oxygen to the thermal conditioning module, which according to the present embodiment, is the first storage tank  202 . The boil off fan  546  may be utilized to build a pressure difference, such that some of the warmed gaseous oxygen coming out of the first heat exchanger  540  is rerouted back to the first storage tank  202 . 
     From operation  608 , the routine  600  proceeds to operation  610 , where the warmed gaseous oxygen is routed through the storage tank heating element  548 , such that the warmed gaseous oxygen may be warmed further before entering the first storage tank  202 . The conditioned gaseous oxygen may then pass through at least one of the storage tank fluid entry valves  510 ,  514 ,  518 . The fuel system  100  may determine the storage tank from which to receive the gaseous oxygen, and may therefore open the valve associated with the fluid entry port of that particular storage tank. As described above, the first storage tank  202  is being used to supply the oxygen and therefore, the electronic controller  114  may open the first storage tank fluid entry valve  510 , allowing the conditioned gaseous oxygen from the storage tank heating element  548  to be routed back to the first storage tank  202 , where the conditioned gaseous oxygen may bubble through the liquid oxygen stored in the first storage tank  202 . 
     It may be appreciated that the boil off fan  546  may operate at a fixed speed to generate a fixed flow rate or may be operated at a higher or lower speed to either increase or decrease the flow rate of gaseous oxygen being routed to the first storage tank, respectively. It should be appreciated that depending upon the amount of power demanded, the electronic controller  114  may vary the speed of the one boil off fan  546  accordingly. For instance, when the fuel cell  102  needs to produce more power, the electronic controller  114  may increase the speed of the boil off fan speed  546 , thereby routing more gaseous oxygen through the boil off fan  546  and thus, more gaseous oxygen through the first storage tank  202 , and eventually to the fuel cell  102  via the conditioning process described herein. 
     From operation  606 , the routine  600  also proceeds to operation  612 , where the remaining warmed gaseous oxygen that passed through the first heat exchanger  540  may be received by the second heat exchanger  542 . As described above, the remaining warmed gaseous oxygen is further conditioned by absorbing heat from the unconditioned carbon dioxide supplied by the fuel cell  102  that also passes through the second heat exchanger  542 . 
     From operation  612 , the routine  600  proceeds to operation  614 , where the conditioned remaining gaseous oxygen is supplied to the fuel cell  102 . It may be appreciated that the conditioned gaseous oxygen passes through a pressure regulator (not shown) prior to being supplied to the fuel cell  102  via passage  106 . The pressure regulator may reduce the pressure at which the conditioned remaining gaseous oxygen is being supplied to the fuel cell  102 . The routine  600  continues to operate until the electronic controller  114  determines that the first storage tank  202  is not supplying enough gaseous oxygen for the desired functioning of the fuel cell  102 . 
     Referring now to  FIG. 7 , a routine  700  for conditioning the gaseous carbon dioxide produced by the fuel cell  102  is described. The routine  700  begins at operation  702 , where the thermal conditioning module  104  receives the unconditioned gaseous carbon dioxide from the fuel cell  102  via passage  108 . From operation  702 , the routine  700  proceeds to operation  704 , where the unconditioned carbon dioxide received from the fuel cell  102  is cooled by passing the unconditioned carbon dioxide through the second heat exchanger  542 . As described above, cooler oxygen supplied from the first heat exchanger  540  passes through the second heat exchanger  542  as well, and absorbs some of the heat of the unconditioned carbon dioxide. 
     From operation  704 , the routine  700  proceeds to operation  706 , where the cooled gaseous carbon dioxide is pressurized by passing the cooled carbon dioxide through the compressor  544 . From operation  706 , the routine  700  proceeds to operation  708 , where the pressurized carbon dioxide then passes through the first heat exchanger  540 , where the pressurized carbon dioxide is converted to liquid carbon dioxide. As described above, the unconditioned gaseous oxygen supplied from at least one of the storage tanks  202 ,  204 ,  206  absorbs the heat of the pressurized carbon dioxide as it passes through the first heat exchanger  540 , liquefying the carbon dioxide. 
     From operation  708 , the routine proceeds to operation  710 , where the electronic controller  114  determines where the liquefied carbon dioxide is to be stored. Initially, the electronic controller  114  may open the compartment fluid entry valve  522  to store the liquefied carbon dioxide in the storage compartment  208 . However, once the storage compartment  208  is filled with the liquefied carbon dioxide and the thermal conditioning module  104  has conditioned the first storage tank  202 , such that the first storage tank  202  may store the liquefied carbon dioxide, the electronic controller  114  may close the compartment fluid entry valve  522  and open the first storage tank fluid entry valve  510 . 
     From operation  710 , the routine  700  proceeds to operation  712 , where the liquid carbon dioxide is routed to the desired storage location of the storage vessel  101 . In the present embodiment, the desired storage location of the storage vessel is the location whose fluid entry valve is open. In various embodiments, once the first storage tank is also filled with liquid carbon dioxide, the electronic controller  114  may close the first storage tank fluid entry valve  510  and open the second storage tank fluid entry valve  514 , such that the liquefied carbon dioxide may be stored in the second storage tank  204 . From operation  712 , the routine  700  proceeds to operation  714 , where the pressure of the carbon dioxide tank being filled is controlled to a safe pressure by relieving the pressure periodically and venting the oxygen (and carbon dioxide) gases in the tank through the storage compartment exit valve  508 , the first storage tank exit valve  512 , or the second storage tank exit valve  516  to the stream entering the first heat exchanger  540 . 
     Referring now to  FIG. 8 , a routine  800  for receiving gaseous oxygen from the second storage tank  204  after the first storage tank  202  is not supplying enough gaseous oxygen to the fuel cell  102  and conditioning the first storage tank  202  for storing liquid carbon dioxide is described. The routine  800  begins at operation  802 , where the thermal conditioning module  104  is routing unconditioned gaseous oxygen from the first storage tank to the first heat exchanger  540  via the first fluid exit port valve  512 . From operation  802 , the routine  800  proceeds to operation  804 , where the electronic controller  114  determines that the first storage tank  202  is not supplying enough gaseous oxygen. The electronic controller  114  utilizes the first sensor  402 , amongst other components to gather information such as the remaining liquid oxygen volume to determine if more gaseous oxygen can be supplied by the first storage tank  202 . Upon determining that the first storage tank  202  cannot supply enough gaseous oxygen, the electronic controller  114  may open the second storage tank fluid exit valve  516 . Depending upon how much gaseous oxygen is being supplied by the first storage tank  202 , the electronic controller  114  may controllably open the second storage tank fluid exit valve  516  of the second storage tank  204  to provide enough gaseous oxygen from the second storage tank  204  to make up the difference between the gaseous oxygen supply demanded by the fuel cell  102  and that being supplied by the first storage tank  202 . As the first storage tank  202  supplies less unconditioned gaseous oxygen, the electronic controller  114  may gradually open the second storage tank fluid exit valve  516  further, thereby increasing the flow rate of the unconditioned gaseous oxygen being supplied from the second storage tank  204 . 
     From operation  804 , the routine  800  proceeds to operation  806 , where the electronic controller  114  may close the first storage tank fluid exit port valve  512  and open the first reconditioning valve  528 . By doing so, the gaseous oxygen within the first storage tank  202  may now circulate through the first storage tank  202 . The gaseous oxygen may leave the first storage tank  202  through the first fluid exit port  222 , the first reconditioning valve  528 , the first heating element  532 , the first fluid entry port  510 , and circulate back into the first storage tank  202 . The first heating element  532  may be configured to heat the gaseous oxygen as it circulates around the storage tank, thereby supplying heat to the first storage tank  202 . It should be appreciated that the amount of heat supplied by the first heating element  532  may be controlled by the electronic controller  114 , such that if the temperature in the first storage tank  202  needs to be quickly increased, the first heating element  532  may operate at a higher heat level. As the gaseous oxygen is being heated during the cycle, the temperature of the first storage tank  202  is increasing. The conditioning process may continue until the first storage tank  202  is ready to receive liquid carbon dioxide. Upon completely conditioning the first storage tank, the first reconditioning valve  428  may be closed. It may be appreciated that the first storage tank is conditioned to a prespecified temperature such that the first storage tank is in condition to receive the liquid effluent. In various embodiments, the prespecified temperature should be greater than the melting point of the effluent and less than the boiling point of the effluent such that the effluent does not freeze or boil inside the conditioned first storage tank. 
     From operation  806 , the routine  800  proceeds to operation  808 , where the warmed gaseous oxygen from the second storage tank  204  is passed through the first heat exchanger  540 . From operation  808 , the routine  800  splits and proceeds to operation  810  and operation  812 . At operation  810 , the warmed gaseous oxygen from the second storage tank  204  is rerouted back to the storage vessel  101  via the boil off fans. As described above, the warmed gaseous oxygen is rerouted back to the second storage tank  204 , causing the second storage tank  204  to supply more gaseous oxygen to the first heat exchanger  540 . 
     From operation  808 , the routine  800  also proceeds to operation  812 , where the remaining warmed gaseous oxygen is further conditioned by passing the warmed gaseous oxygen through the second heat exchanger  542 , similar to operation  612 , as described above. The routine  800  then proceeds to operation  814 , where the conditioned gaseous oxygen is supplied to the fuel cell  102 . Finally, the routine  800  then proceeds to operation  816 , where the gaseous carbon dioxide is conditioned and supplied to the storage vessel  101 . Details of how the gaseous carbon dioxide produced from the fuel cell  102  is conditioned to liquid carbon dioxide stored in the storage vessel has been described above in  FIG. 7 . From operation  816 , the routine  800  then proceeds to operation  818 , where the liquid carbon dioxide is stored in the conditioned first storage tank  202 . In various embodiments, the electronic controller  114  may determine that the storage compartment  208  is full via the sensor positioned within the storage compartment  208 . Upon determining that the storage compartment  208  is full, the electronic controller  114  may close the compartment fluid entry port valve  522  and open the first storage tank fluid entry valve  510 , rerouting the liquid carbon dioxide to the conditioned first storage tank  202 . The routine  800  then ends. 
     It should be appreciated that the size of the storage vessel  101  and the size of the respective storage tanks  202 ,  204 ,  206  and storage compartments  208  are designed according to the particular application they are utilized for. For instance, in the present embodiment, the fuel system  100  may be configured to accommodate enough liquid carbon dioxide produced by the fuel cell  102  from the time the fuel cell  102  is initiated up to the time the first storage tank  202  no longer contains enough liquid oxygen to supply to the fuel cell  102  and the time it takes for the fuel system  102  to condition the first storage tank  202 , such that it may be able to store the liquid carbon dioxide. Additionally, the storage compartment  208  may be configured to store a prespecified amount of the liquid carbon dioxide even after the thermal conditioning module begins to receive the gaseous oxygen from the second storage tank  204 . The prespecified amount of carbon dioxide may be the amount of carbon dioxide produced by the fuel cell  102  from the time the first storage tank  202  begins to start supplying gaseous oxygen to the thermal condition module  104  up to the time the first storage tank  202  stops supplying gaseous oxygen to the thermal conditioning module  104 , and the amount of carbon dioxide produced by the fuel cell  102  from the time the second storage tank  204  starts supplying gaseous oxygen to the thermal conditioning module  104  up to the time the first storage tank  202  is conditioned and ready to store liquid carbon dioxide. 
     According to various embodiments, the mass, volume and density of the storage vessel  101  may be an important consideration during the construction and application of the storage vessel  101 . For instance, in a fuel system for an underwater vehicle, the density of the fuel system and its individual components may be a consideration for maintaining the buoyancy of the vehicle. In such embodiments, the mass of the fluid being stored in the storage tanks  202 ,  204 ,  206 , the mass of the empty storage vessel  101 , and the mass of the fluid being stored in the storage compartment  208  may all be relevant in determining the mass and dimensions of the storage vessel  101 . In addition, the material used, the thickness of insulation, and the thickness of the walls of the storage tanks  202 ,  204 ,  206  may be considerations that may be taken into account before construction of the storage vessel  101  begins. 
     It should be appreciated that that the present disclosure is not limited to a fuel system  102 , but to any technology that may be utilized for conditioning fluids. Further, those skilled in the art will appreciate that the scope of the present disclosure includes, but is not limited to applications for conditioning a first fluid by absorbing the heat of a second fluid, wherein the second fluid has a higher boiling point than the first fluid. 
     The subject matter described above is provided by way of illustration only and should not be construed as limiting. Various modifications and changes may be made to the subject matter described herein without following the example embodiments and applications illustrated and described, and without departing from the true spirit and scope of the present invention, which is set forth in the following claims.