Patent Description:
A decrease in temperature of a first pressure vessel segment downstream from a fill port is explained by adiabatic expansion of the gas. Some gases also experience the Joule-Thomson effect, which describes the isenthalpic expansion of gases. As gas expands from a high-pressure reservoir to the lower-pressure conformable pressure vessel, the gas cools. This cooling occurs without heat being transferred to the surrounding conformable pressure vessel; rather, the cooling is due to expansion caused by the decrease in pressure. A last pressure vessel segment upstream from an outlet of the conformable pressure vessel experiences an increase in temperature because, unlike the first pressure vessel segment which encounters adiabatic cooling, the gas in the last pressure vessel segment only experiences an increase in pressure. Therefore, as the gas in the last pressure vessel segment is compressed, the temperature of the gas rises due to heat of compression.

<CIT> discloses a conformable pressure vessel, comprising: pressure vessel segments defined by a cavity disposed within a liner, the pressure vessel segments configured to receive and store a gas in a compressed state, and each of the pressure vessel segments including a first section of the liner having a first diameter and a second section of the liner having a second diameter smaller than the first diameter; a reinforcement layer surrounding the liner; an inlet in fluid communication with the cavity of the liner, the inlet configured to receive the gas from a gas source; an outlet in fluid communication with the cavity of the liner, the outlet configured to output the gas from the pressure vessel segments; and a connecting tube in fluid communication with the inlet and the outlet, the connecting tube configured to receive the gas from the outlet and to supply the gas from the outlet to the inlet so that the gas is recirculated through the pressure vessel segments in response to the inlet receiving the gas from the gas source.

<CIT> discloses the use of phase changing materials as a component of the liner.

The present invention relates to the feature combination of the independent claim(s). Preferable embodiments are provided in the dependent claims.

This disclosure relates to conformable pressure vessel including pressure vessel segments defined by a cavity disposed within a liner. The pressure vessel segments receive and store a gas in a compressed state, and each of the pressure vessel segments includes a first section of the liner having a first diameter and a second section of the liner having a second diameter smaller than the first diameter. The conformable pressure vessel includes a reinforcement layer surrounding the liner and an inlet in fluid communication with the cavity of the liner. The inlet receives the gas from a gas source. The conformable pressure vessel further includes an outlet in fluid communication with the cavity of the liner, and the outlet outputs the gas from the pressure vessel segments. The conformable pressure vessel includes a connecting tube in fluid communication with the inlet and the outlet, and the connecting tube receives the gas from the outlet and to supply the gas from the outlet to the inlet so that the gas is recirculated through the pressure vessel segments in response to the inlet receiving the gas from the gas source.

The inlet may include a nozzle having a first end downstream of the gas source, a second end downstream of the first end and upstream of the pressure vessel segments, and a middle portion between the first end and the second end. The middle portion may have a cross-sectional area smaller than a cross-sectional area of the first end and a cross-sectional area of the second end. When the gas flows across the middle portion, the middle portion may increase velocity of gas flow as the gas source pushes the gas to the inlet. The connecting tube may include an entry end connected with the outlet and an exit end connected with the second end of the nozzle. When the gas flows from the nozzle to the inlet, from the inlet through the pressure vessel segments, and to the outlet out the connecting tube, a temperature of the conformable pressure vessel may be equalized. An interior profile of the connecting tube may be shaped to enable flow of the gas through the connecting tube from the outlet to the inlet and to prevent the flow of the gas through the connecting tube from the inlet to the outlet. The connecting tube may include a tesla valve so that temperature of the conformable pressure vessel is equalized as the gas flows across the pressure vessel segments, the connecting tube, or both.

The conformable pressure vessel may further include a shell enclosing the pressure vessel segments, and the inlet and the outlet may be integrated in walls of the shell so that the gas is movable between the pressure vessel segments and the outlet or the inlet. The conformable pressure vessel may further include heat pipes extending perpendicularly along the pressure vessel segments, and the heat pipes may allow heat to flow between the pressure vessel segments. The pressure vessel segments may be stacked within the shell in a row so that the heat pipes are laying across the pressure vessel segments. The conformable pressure vessel may further include thermally conductive materials surrounding the reinforcement layer at a top-most pressure vessel segment and a bottom-most pressure vessel segment, and the thermally conductive materials may assist creating an equilibrium of temperature between the pressure vessel segments. The inlet and the outlet each may include a stem creating a fluid connection between the pressure vessel segments and the connecting tube; and a cap securing the liner, the reinforcement layer, and the stem so that fluids are movable between the cavity and the inlet or the outlet.

The disclosure further relates to a conformable pressure vessel including a liner defining a cavity and pressure vessel segments formed along the liner in first sections having a first diameter and second sections having a second diameter smaller than the first diameter. The conformable pressure vessel includes an inlet in fluid communication with the cavity of the liner through the second section of a first pressure vessel segment, and the inlet receives a gas from a gas source. The conformable pressure vessel includes an outlet in fluid communication with the cavity of the liner through the second section of a second pressure vessel segment, and the outlet outputs the gas from the liner. The conformable pressure vessel includes a connecting tube facilitating fluid communication between the inlet and the outlet so that the gas flows from the outlet to the inlet and is recirculated through the liner in a way that distributes heat throughout the pressure vessel segments, and the connecting tube receives the gas from the gas source. The conformable pressure vessel includes a reinforcement layer surrounding the liner and a phase change material coating an interior surface of the liner.

The phase change material may coat every one of the pressure vessel segments so that the heat is distributed throughout the conformable pressure vessel. The phase change material may absorb energy and at least partially melt so that temperature of the conformable pressure vessel is equalized. The conformable pressure vessel may further include a nozzle having a first end connected with a middle portion and connect with the gas source and a second end connected with the middle portion and the connecting tube, and the middle portion may have a cross-sectional area smaller than a cross-sectional area of the first end and a cross-sectional area of the second end. The connecting tube may be connected with the outlet or the inlet, and when the connecting tube is connected with the outlet, the second end of the nozzle may space the connecting tube from the inlet. When the connecting tube is connected with the inlet, the second end of the nozzle may space the connecting tube from the outlet.

The disclosure further relates to a conformable pressure vessel including pressure vessel segments, and each pressure vessel segment defines a cavity that is adjacent to a narrow portion. The pressure vessel segments couple together at the respective narrow portions so that the respective cavities are fluidly coupled and the pressure vessel segments form a continuous structure. The conformable pressure vessel includes an inlet in fluid communication with the cavities of the pressure vessel segments through the narrow portion of an entry pressure vessel segment, and the inlet receives a gas from a gas source. The conformable pressure vessel includes an outlet in fluid communication with the cavities of the pressure vessel segments through the narrow portion of an exit pressure vessel segment, and the outlet outputs the gas from the pressure vessel segments. The conformable pressure vessel includes heat pipes extending perpendicularly between stacked pressure vessel segments, and the heat pipes allow heat to flow between the pressure vessel segments.

The conformable pressure vessel may further include a reinforcement layer positioned between the heat pipes and the pressure vessel segments, and the reinforcement layer may surround each of the pressure vessel segments. The conformable pressure vessel may further include a thermally conductive material surrounding the reinforcement layer and/or coupling two or more pressure vessel segments so that the heat pipes and the thermally conductive material distribute heat throughout the conformable pressure vessel. The conformable pressure vessel may further include a shell enclosing the thermally conductive material, the heat pipes, and the pressure vessel segments so that the thermally conductive material, the heat pipes, and the pressure vessel segments are protected from an outside environment. The heat pipes may extend from the entry pressure vessel segment to the exit pressure vessel segment so that each heat pipe contacts at least two pressure vessel segments.

The thermal management methods disclosed herein are configured to manage the thermal gradient that arises due to pressurizing a conformable pressure vessel including pressure vessel segments.

Heat gradients typically do not develop within the interior of traditional gas storage tanks because the gas is mixed throughout the entire storage tank instead of split between pressure vessel segments. The gas has the freedom to move and mix, so any rise in temperature is diffused evenly throughout the storage tank. Unlike conformable pressure vessels, traditional storage tanks are not sectioned, so there is no beginning or end.

In one example, a conformable pressure vessel includes seven pressure vessel segments. A last pressure vessel segment is capped with a plug and a first pressure vessel segment is connected to a valve to fill the conformable pressure vessel. Gas continuously enters the first pressure vessel segment and then gets pushed into the following pressure vessel segments as more gas enters. There is a pressure drop occurring in each consecutive pressure vessel segment because gas must flow through a section of each pressure vessel segment having a lesser diameter to reach the next pressure vessel segment. Therefore, the gas in the last pressure vessel segment is at a lower pressure than the gas in the first pressure vessel segment. Pressure tends to equalize throughout a traditional storage tank, but due to the pressure vessel segments included in the conformable pressure vessel, this equilibrium takes longer to achieve. Therefore, the pressure of the gas in the last pressure vessel segment will always lag behind the pressure of the gas in the first pressure vessel segment.

A magnification of this phenomenon occurs when the fill rate of the conformable pressure vessel is increased. Adding gas at a faster rate causes the temperature difference between pressure vessel segments to be much greater and leads to heat building up within the conformable pressure vessel more quickly. This increase in heat within the conformable pressure vessel occurs because more gas molecules are compressed in a smaller amount of time.

To manage the thermal gradient present during fill or extraction of gas from conformable pressure vessels, several methods are disclosed. The first method involves using thermal conductive materials in the conformable pressure vessel. Thermal conductive materials leverage the increased surface to volume ratio of the pressure vessel to transfer heat between the different parts of the pressure vessel to achieve a thermal equilibrium and avoid extreme temperatures within the conformable pressure vessel. Another method recirculates the gases in the conformable pressure vessel. Another method uses phase change materials within the conformable pressure vessel.

Thermally conductive material transfers heat from the pressure vessel segments having a higher temperature to the pressure vessel segments having a lower temperature due to heat transfer caused by conduction and convection. Each pressure vessel segment is defined by a liner material (e.g. a thermoplastic liner). A reinforcement layer surrounds the liner. The reinforcement layer can be surrounded by a thermally conductive material, such as a thermally conductive foam. A shell encloses the thermally conductive foam. Thermally conductive material, such as a heat pipe, can couple two or more pressure vessel segments. Thermal conduction allows for more thermal consistency throughout the conformable pressure vessel, where heat transfer can reduce the temperature extremes and achieve faster thermal equilibrium.

The method of recirculating the gas is accomplished by connecting different pressure vessel segments to allow the gas to travel in a continuous loop through the conformable pressure vessel. To enable this continuous gas flow, the pressure vessel may include a connecting tube connecting an outlet of the conformable pressure vessel to an inlet. The connecting tube may include a Tesla valve, which is a valve allowing unidirectional flow. Continuous gas flow through the pressure vessel segments enables temperature diffusion throughout the conformable pressure vessel as hot gas flows from the last pressure vessel segment into the cooler first pressure vessel segment. Simulations using this method show that, compared to conformable pressure vessels lacking continuous flow, the temperature of the first pressure vessel segment increases, and the temperature of the last pressure vessel segment decreases to reach a state of thermal equilibrium between the pressure vessel segments.

Another method includes using a phase change material (PCM) applied to the liner of the conformable pressure vessel. PCMs have been widely studied as thermal energy storage options in gas storage tanks. PCMs absorb heat generated during fueling of gas storage tanks in the form of latent heat. As the PCM absorbs heat, it begins to melt, but it does not heat up. In one example, the PCM includes paraffin wax embedded with a graphite matrix. The PCM works most efficiently when the mixture is applied to the inside of the liner. This configuration allows a faster fill rate of the conformable pressure vessel. The PCM also reduces the degree of pre-cooling required for a given fill time by <NUM> - <NUM>.

<FIG> shows a cutaway perspective view of a conformable pressure vessel <NUM>. The conformable pressure vessel <NUM> contains seven connected pressure vessel segments <NUM> configured to receive and store a gas in a compressed state. Each of the pressure vessel segments <NUM> includes a liner (e.g. a thermoplastic liner) underneath a reinforcement layer (e.g. a fiber layer). The pressure vessel segments <NUM> are surrounded by a thermally conductive material, in this example, a thermally conductive foam <NUM>. The pressure vessel segments <NUM> and the thermally conductive foam <NUM> are enclosed by a shell <NUM>. <FIG> also shows an end fitting including a cap <NUM> and a stem <NUM>. The end fittings connect the conformable pressure vessel <NUM> to valves, adapters, plugs, or couplings, and assist in containing the pressurized gas within the conformable pressure vessel <NUM>. There is an end fitting on each end of the pressure vessel segments <NUM> that reaches outside the shell <NUM>.

<FIG> shows a sectional view of the same seven-segment conformable pressure vessel <NUM>. Each pressure vessel segment <NUM> includes a liner <NUM> that defines a cavity <NUM>. The liner <NUM> can include a thermoplastic liner. Each liner <NUM> includes a first section <NUM> having a first diameter and a second section <NUM> having a second diameter smaller than the first diameter. The pressure vessel segments <NUM> are coupled together at the respective second sections <NUM> of the liner <NUM> such that the cavities <NUM> of each liner <NUM> are fluidly coupled. The conformable pressure vessel <NUM> includes an inlet <NUM> in fluid communication with the cavities <NUM> of the pressure vessel segments <NUM> through the second section <NUM> of a first pressure vessel segment <NUM>. The inlet <NUM> is configured to receive a gas from a gas source. The conformable pressure vessel <NUM> also includes an outlet <NUM> in fluid communication with the cavities <NUM> of the pressure vessel segments <NUM> through the second section <NUM> of a second pressure vessel segment <NUM>. The outlet <NUM> is configured to output the gas from the pressure vessel segments <NUM>. Though the outlet <NUM> is shown as being in fluid communication with the last pressure vessel segment in the seven-segment conformable pressure vessel <NUM> (i.e., the second pressure vessel segment <NUM>) in this example, either the inlet <NUM> or the outlet <NUM> could be fluidly coupled with alternate pressure vessels segments.

A reinforcement layer <NUM> surrounds the liner <NUM>. The reinforcement layer <NUM> can include a fiber reinforcement layer. The thermally conductive foam <NUM> surrounds the reinforcement layer <NUM>. The shell <NUM> encloses the thermally conductive foam <NUM> and the pressure vessel segments <NUM>. One cap <NUM> connects to the liner <NUM> and the reinforcement layer <NUM> at the inlet <NUM>. Another cap <NUM> connects to the liner <NUM> and the reinforcement layer <NUM> at the outlet <NUM>. The caps <NUM> function to attach the stems <NUM> to the respective pressure vessel segments <NUM>. The thermally conductive foam <NUM> and the shell <NUM>, which provide structure, support, and protection for the pressure vessel segments <NUM>, are also shown.

Materials such as plastic and high strength fibers typically used in lightweight and high-pressure gas storage tanks and conformable pressure vessels do not have high thermal conductivities. However, by using thermally conductive materials such as thermally conductive foams and heat pipes as indicated herein, the high surface to volume ratio in conformable pressure vessels can be used to transfer heat from areas of high temperature to areas of low temperature. This can significantly reduce temperature extremes within the conformable pressure vessel. An example is described in reference to <FIG>.

<FIG> is a side view of a six-segment pressure vessel <NUM>. The pressure vessel <NUM> includes the pressure vessel segments <NUM>. The pressure vessel segments <NUM> are connected by heat pipes <NUM>, also referred to as thermally conductive members. The heat pipes <NUM> allow heat to flow between the pressure vessel segments <NUM>. In this configuration, when different pressure vessel segments <NUM> are heated or cooled to different temperatures, the heat pipes <NUM> can assist in creating temperature equilibrium between the different pressure vessel segments <NUM>. The heat pipes <NUM> are connected to thermally conductive materials <NUM> which are disposed around the top-most and bottom-most pressure vessel segments <NUM> in the example of <FIG>. The thermally conductive materials <NUM> can further assist in creating the temperature equilibrium between the pressure vessel segments <NUM>. Though the heat pipes <NUM> are shown as extending between first and last pressure vessel segments <NUM>, the heat pipes <NUM> can be applied between any respective pressure vessel segments <NUM> in the same pressure vessel <NUM> to achieve temperature equilibrium. Additionally, though the thermally conductive materials <NUM> are shown as surrounding the first and last pressure vessel segments <NUM>, the thermally conductive materials <NUM> can surround any of the pressure vessel segments <NUM> in the pressure vessel <NUM>.

<FIG> shows a side view of a conformable pressure vessel <NUM> with six pressure vessel segments employing one thermal-mitigation method, recirculation. While gas is circulating through the conformable pressure vessel <NUM>, a pressure drop can occur in sections of the pressure vessel segments having a lesser diameter because these sections can restrict flow between the pressure vessel segments. During a fill event, the last pressure vessel segment, that is, the pressure vessel segment furthest downstream from the location of an inlet, is therefore at a lower pressure than the first pressure vessel segment. Pressure tends to equalize throughout gas storage tanks, but due to the segmented nature of the conformable pressure vessel <NUM>, this equilibrium can take some time to achieve.

The method of recirculation can be used to more quickly achieve a pressure and/or temperature equilibrium in the conformable pressure vessel <NUM>. This method involves connecting the first pressure vessel segment and the last pressure vessel segment. This connection can include a heat pipe connected to the first pressure vessel segment and the last pressure vessel segment to permit the transfer of heat between the pressure vessel segments. This connection can also include a passage for gas to flow between the first and the last pressure vessel segments. In embodiments of the conformable pressure vessel <NUM> including the passage, gas is able to flow from the last pressure vessel segment into the first pressure vessel segment. This makes the conformable pressure vessel <NUM> act as if it were one continuous segment. The increase in temperature of the conformable pressure vessel <NUM> is diffused throughout the entire pressure vessel as hot gas flows from the warmer last pressure vessel segment into the cooler first pressure vessel segment.

In <FIG>, an arrow shows gas entering the conformable pressure vessel <NUM> in the bottom right corner. The gas leaves the valve of its reservoir and travels through a connector <NUM>, through the stem <NUM> of the end fitting and into the first pressure vessel segment <NUM> of the conformable pressure vessel <NUM>. Gas then circulates through each pressure vessel segment and out of the last pressure vessel segment <NUM> until it reaches the elbow <NUM>. The elbow <NUM> attaches to a connecting tube <NUM>. The connecting tube <NUM> is in fluid communication with an inlet <NUM> of the first pressure vessel segment <NUM> and with an outlet <NUM> of the last pressure vessel segment <NUM>. The connecting tube <NUM> is configured to receive gas from the outlet <NUM> and to supply the gas from the outlet <NUM> to the inlet <NUM>. In this configuration, the gas is recirculated through the pressure vessel segments in response to the inlet <NUM> receiving gas from a gas source (e.g., gas traveling from a reservoir and through the connector <NUM>).

For gas to flow in the direction desired, the last pressure vessel segment <NUM> must be at a higher pressure than the first pressure vessel segment <NUM>. To achieve this pressure differential, the conformable pressure vessel <NUM> may include a pressure delta to help motivate flow from the last pressure vessel segment <NUM> to the first pressure vessel segment <NUM>. In one example, the pressure delta includes a nozzle.

<FIG> shows a sectional view of a nozzle <NUM> used to create a pressure differential in the conformable pressure vessel <NUM> of <FIG>. The nozzle <NUM> includes a first end <NUM> downstream from a gas source and a second end <NUM> downstream from the first end <NUM> and upstream from the pressure vessel segments. The nozzle <NUM> includes a middle portion <NUM> between the first end <NUM> and the second end <NUM>. A cross-sectional area of the middle portion <NUM> is smaller than cross-sectional areas of the first end <NUM> and the second end <NUM>. The nozzle <NUM> can replace the connector <NUM> shown in <FIG>. Gas enters from the right side of the nozzle <NUM>, as shown by the arrow. As the gas moves further through the nozzle <NUM>, the cross-sectional area through which the gas travels decreases. By the principle of mass conservation, the mass flow rate must remain constant throughout the entire nozzle <NUM>. Since mass flow rate is equal to density times velocity times cross-sectional flow area, velocity and cross-sectional area are inversely proportionate.

Where, ṁ is the mass flow rate, ρ is the density of the fluid and v is the velocity of the fluid. This means that as the cross-sectional area decreases in the middle of the nozzle, the velocity increases to conserve mass flow.

Then, by the Venturi Effect, when the velocity of a fluid or gas increases in a nozzle, pressure decreases. That means that at point <NUM>, the middle of the nozzle <NUM> in <FIG>, where the cross-sectional area is the smallest, velocity is largest, and pressure is lowest according to Bernoulli's Principle. Assuming the fluid experiences a negligible change in height while travelling through the nozzle, Bernoulli's equation can be re-written to say that pressure plus (one half times density times velocity squared) remains constant throughout the nozzle <NUM>. This means that if velocity increases, pressure must decrease so that the equation still equals the same constant. Therefore, a low-pressure area can be created in the middle of the nozzle <NUM>. As the gas moves past the middle portion <NUM> of the nozzle <NUM>, the gas expands and the pressure remains low. This location was selected as the connection point between the first pressure vessel segment <NUM> and the last pressure vessel segment <NUM> in the conformable pressure vessel <NUM> of <FIG> to maintain the validity of the narrow cross-section in the middle of the nozzle <NUM>.

<FIG> shows a partial sectional view of a pressure vessel <NUM> similar to the conformable pressure vessel <NUM> shown in <FIG>. The gas comes out of a valve and enters the assembly at the bottom right as shown by the arrow. The gas goes straight through the nozzle <NUM> toward the first pressure vessel segment. While the gas travels through the nozzle <NUM>, the gas reaches its lowest pressure in the middle of the nozzle <NUM>, where the cross-section is smallest. The gas then travels through each consecutive pressure vessel segment, though only the first and last pressure vessel segments are shown in <FIG>. Once the gas reaches the end of the last pressure vessel segment and enters the elbow <NUM>, the low-pressure area inside the nozzle <NUM> causes the gas to flow down through the connecting tube <NUM> toward the nozzle <NUM>. The nozzle <NUM> connects back to the first pressure vessel segment, so the gas is recirculated throughout the entire pressure vessel <NUM>. During the recirculation, the gas diffuses the heat, allowing the pressure vessel <NUM> as a whole to reach one equilibrium temperature.

Additionally and/or alternatively, one or more other devices may be used to enable recirculation of gas through the pressure vessel in a preferred flow direction. For example, an interior profile of the connecting tube <NUM> shown in <FIG> can be shaped to enable flow of gas through the connecting tube <NUM> from the outlet <NUM> to the inlet <NUM> and to prevent flow of the gas through the connecting tube <NUM> from the inlet <NUM> to the outlet <NUM>. This interior profile may be achieved using a Tesla valve, shown in <FIG>. The Tesla valve causes gas to flow preferentially one way, shown by the arrow <NUM>. For example, in the sectional view shown in <FIG>, if gas enters the valve from the left side, when it reaches the first intersection, some of the gas splits to follow the top channel and some goes down through the lower channel. The gas that travelled up then follows the path around and ends up looping so far as to be re-directed leftward. This tendency of a fluid or gas to follow the shape of a convex object it contacts is known as the Coanda Effect. This effect causes the gas to interfere with the rest of the flow that was initially travelling from left to right. This occurs at every junction, so the overall flow from left to right is slowed. However, if gas enters the valve from the right side, it experiences a different path. In this case, there are no junctions, due to the angle of the shapes and channels within the cavity of the Tesla valve, so the gas does not split and interfere with its own flow.

The Tesla valve <NUM> is shown incorporated into the pressure vessel in <FIG>. It is oriented so that gas flows preferentially from the last pressure vessel segment to the first pressure vessel segment. This configuration causes the gas to recirculate throughout the conformable pressure vessel and therefore diffuse the thermal gradient that would otherwise form. This may be used independently of or in conjunction with another device used to create a pressure delta, such as the nozzle <NUM> shown in <FIG>.

Phase change materials (PCMs) may also be implemented in a conformable pressure vessel to further mitigate the development of temperature gradients. PCMs can store and release large amounts of latent heat energy. As the PCM changes phase, its temperature remains constant even as it absorbs heat. This is because the heat absorbed by the PCM energizes molecules of the PCM to a point where the PCM changes phase. PCMs, such as paraffin wax, can be used to coat an interior of the liner of the conformable pressure vessel. Then, as the coated pressure vessel segment is filled with gas and the temperature rises, the PCM will absorb the heat, preventing the temperature from rising. As the PCM absorbs heat, it begins to melt, but does not heat up. When the area surrounding the PCM becomes cool, the PCM releases the heat, moderating the temperature of the conformable pressure vessel. A PCM may coat an interior surface of the liner of one or more pressure vessel segments. For example, the PCM may coat an interior surface of the liner of every pressure vessel segment individually or may coat the liner of only a first pressure vessel segment and a second (e.g. last) pressure vessel segment. Coating an interior surface of the liner of the first and last pressure vessel segments may assist to moderate the temperature of the conformable pressure vessel since the temperature is most extreme in these segments.

To verify that the methods discussed above are effective, a study was done using physics modeling and pressure and temperature simulations. A first analysis was done to establish a baseline pressure vs. temperature curve for a pressure vessel having seven pressure vessel segments. The first and last pressure vessel segments were not connected, and no additional temperature mitigation device was included aside from the thermal conductivity of the pressure vessel itself, which includes thermally conductive foam. A fill rate of <NUM> grams per second was used. The results of this analysis are shown in <FIG> and <FIG>.

<FIG> includes a graph of pressure vs. temperature curves for the first pressure vessel segment of different conformable pressure vessels including various temperature mitigation devices for the first <NUM> seconds of gas fill. Separate curves are shown to indicate performance of pressure vessels having the following features: a baseline pressure vessel including thermally conductive foam; a gas recirculating pressure vessel similar to that shown in <FIG>; a heat pipe; a gas recirculating pressure vessel including a Tesla valve similar to that shown in <FIG>; a pressure vessel including a phase change material (PCM); and a pressure vessel including all of these listed features.

<FIG> includes a graph of pressure vs. temperature curves for the last pressure vessel segment of the same conformable pressure vessels described with respect to <FIG>. for the first <NUM> seconds of gas fill.

Table <NUM> shows the minimum temperature of the first pressure vessel segment and the maximum temperature of the last pressure vessel segment of each conformable pressure vessel described with respect to <FIG> and <FIG>.

In the baseline pressure vessel including thermally conductive foam, the temperature of the first pressure vessel segment cooled from an initial temperature of <NUM> to a minimum temperature of <NUM>. The temperature of the last pressure vessel segment increased from <NUM> to a maximum temperature of <NUM>. These temperatures exceed the maximum capabilities of most materials used in typical gas storage tanks and would result in insufficient fill due to post-fill cooling.

In another tested configuration, a series of heat pipes were connected to the first and last pressure vessel segments. This modification significantly reduced the temperature gradient between the first and last pressure vessel segments. As shown in <FIG>, the maximum temperature of the last pressure vessel segment was reduced from the baseline of <NUM> to <NUM>.

The next method evaluated was a recirculation method, for example, the recirculation method shown in <FIG>, where the last pressure vessel segment is connected to the first pressure vessel segment with a connecting tube. The pressure vessel segments form a continuous chain, and hot gas from the last pressure vessel segment mixes with cooler gas in the first pressure vessel segment. <FIG> and <FIG> show the pressure vs. temperature curves for the recirculation method in the first and last pressure vessel segments relative to the baseline. While the maximum temperature of the last pressure vessel segment was reduced from <NUM> to <NUM>, the minimum temperature of the first pressure vessel segment of <NUM> was not significantly changed. The recirculation method does allow the gases from the first and last pressure vessel segments to mix and provides some temperature mitigation; however, the recirculation method does not prevent the inflowing gas from initially traveling in the unintended direction from the first pressure vessel segment, through the connecting tube, and to the last pressure vessel segment. This extends the time required to establish a circulating flow path within the conformable pressure vessel.

By including a Tesla valve in the connecting tube, the initial flow of gases in the unintended direction is reduced, and a recirculation flow can be more quickly established in the conformable pressure vessel. As shown in <FIG>, after an initial increase in temperature of the last pressure vessel segment, recirculating flow moved hot gases from the last pressure vessel segment to mix with the incoming cool gas from the fill port. This resulted in a maximum temperature of the last pressure vessel segment of only <NUM>. Additionally, the minimum temperature of the first pressure vessel segment increased from <NUM> of the baseline to <NUM>. This further demonstrates that hot gases from the last pressure vessel segment mixed with the cool gases in the first pressure vessel segment.

In another tested configuration, a PCM was used to coat the liner of the baseline conformable pressure vessel. As shown in <FIG>, the maximum temperature of the last pressure vessel segment was reduced to <NUM>. As shown in <FIG>, the minimum temperature of the first pressure vessel segment was increased to <NUM>.

Finally, a final gas recirculating pressure vessel model including heat pipes, a Tesla valve, thermally conductive foam, and a PCM was tested. As shown in <FIG>, the minimum temperature of the first pressure vessel segment increased to <NUM>. As shown in <FIG>, the maximum temperature of the last pressure vessel segment was <NUM>.

Claim 1:
A conformable pressure vessel (<NUM>, <NUM>, <NUM>, <NUM>), comprising:
pressure vessel segments (<NUM>) defined by a cavity (<NUM>) disposed within a liner (<NUM>), the pressure vessel segments (<NUM>) configured to receive and store a gas in a compressed state, and each of the pressure vessel segments (<NUM>) including a first section (<NUM>) of the liner (<NUM>) having a first diameter and a second section (<NUM>) of the liner (<NUM>) having a second diameter smaller than the first diameter;
a reinforcement layer (<NUM>) surrounding the liner (<NUM>);
an inlet (<NUM>) in fluid communication with the cavity (<NUM>) of the liner (<NUM>) at a first of the pressure vessel segments (<NUM>) and configured to receive the gas from a gas source, the inlet having a first end (<NUM>) downstream of the gas source, a second end (<NUM>) downstream of the first end (<NUM>), and a middle portion (<NUM>) between the first end (<NUM>) and the second end (<NUM>), the middle portion (<NUM>) having a cross-sectional area smaller than a cross-section area of the first end (<NUM>) and a cross-sectional area of the second end (<NUM>); and
an outlet (<NUM>) in fluid communication with the cavity (<NUM>) of the liner (<NUM>) at a last of the pressure vessel segments (<NUM>) and configured to output the gas from the pressure vessel segments (<NUM>), the outlet (<NUM>) configured to fluidly communicate with the second end (<NUM>) of the inlet (<NUM>) through a connecting tube (<NUM>) having an interior profile shaped to enable flow of the gas through the connecting tube (<NUM>) from the outlet (<NUM>) to the inlet (<NUM>) and to prevent the flow of the gas through the connecting tube (<NUM>) from the inlet (<NUM>) to the outlet (<NUM>);
wherein when the gas flows across the middle portion (<NUM>) of the inlet (<NUM>), a velocity of gas flow increases to create a low-pressure area in the inlet (<NUM>),
wherein the low-pressure area in the inlet (<NUM>) and the interior profile of the connecting tube (<NUM>) are configured to motivate flow from the last of the pressure vessel segments (<NUM>) to the first of the pressure vessel segments (<NUM>) to recirculate the gas through the pressure vessel segments (<NUM>) in response to the inlet (<NUM>) receiving the gas from the gas source, and
wherein recirculating the gas through the pressure vessel segments (<NUM>) equalizes a temperature of the conformable pressure vessel (<NUM>, <NUM>, <NUM>, <NUM>).