Patent Description:
Feeding a saturated liquid from a tank to a consumer or another component through a pump, the pressure inside the tank decreases and cavitation in the pump becomes more probable. Such a saturated liquid may be liquid hydrogen, which may be stored in a storage tank inside an aircraft for feeding hydrogen to a consumer using a pump, or in a land transport vehicle for liquefied gases or marine transportation and feed systems or a stationary tank.

The challenges of pumping saturated liquids is known from aviation, marine and land vehicles and stationary applications. There are several approaches to increase the net positive suction pressure upstream a pump, which includes increasing pressure in the tank using vapor or other gases, heating vapor in the tank, changing a position of the pump to take benefit from hydrostatic pressure, using a pre-pump or subcooling the liquid at a pump inlet by low pressure evaporation and venting the gas over board, in particular in space applications. However, these solutions increase the complexity of the pump arrangement and may require particular effort in using a particular heater or evaporator, non-condensable gases to be carried along and be released /captured during refilling of the tank, instable stratification, and high additional weight and complexity or limiting the usability in space applications.

<CIT> discloses a fuel gas supply system having a liquid gas-storage tank, a fuel gas supply line and a heat exchange circuit with a working medium. The fuel gas supply line has a tank outlet pipe for liquid gas, a fuel gas pump for pressurizing fuel gas to a fuel gas supply pressure for a combustion engine and an end heat exchanger. The fuel gas pump is arranged outside the liquid gas-storage tank, and is connected by the tank outlet line for liquefied gas.

It is thus an object of the invention to propose an alternative pump arrangement for pumping a saturated liquid, which allows an increase of net positive suction pressure of a pump with a high efficiency, a low weight and without the above-identified drawbacks.

This object is met by a pump arrangement having the features of claim <NUM>. Advantageous embodiments and further improvements may be gathered from the subclaims and the following description.

A pump arrangement for providing a saturated liquid is proposed, comprising a tank for saturated liquid having a tank outlet, a heat exchanger for cooling the saturated liquid, the heat exchanger having a liquid inlet, a liquid outlet, a coolant inlet and a coolant outlet, a pump having a pump inlet and a pump outlet, an expansion valve having an expansion valve inlet and an expansion valve outlet, and a pump arrangement output downstream the pump outlet for feeding saturated liquid to a consumer, wherein the tank outlet is in fluid communication with the liquid inlet of the heat exchanger, such that saturated liquid stored inside the tank is able to flow into the heat exchanger, wherein the heat exchanger is designed to sub-cool the saturated liquid, wherein the liquid outlet of the heat exchanger is in fluid communication with the pump inlet, wherein the expansion valve outlet is in fluid communication with the coolant inlet of the heat exchanger, and wherein the expansion valve inlet is arranged downstream the liquid outlet of the heat exchanger or the tank for receiving and expanding a fraction of liquid flowing through the pump arrangement and routing it into the coolant input to at least partially evaporate and receive evaporation enthalpy of the liquid to be subcooled.

The pump arrangement according to the invention allows the increase of net positive suction pressure (NPSP) for a pump for a saturated liquid, wherein the disadvantages explained above are avoided. It is to be understood that the NPSP is the difference between the total pressure of the liquid to be pumped and the vapor pressure at a given temperature. The core features of the pump arrangement is explained in detail below.

The tank is a receptacle for receiving the saturated liquid. Depending on the liquid to be stored, the tank may be designed for mechanically withstanding a certain pressure. Furthermore, the tank may be thermally insulated for minimizing a heat transfer into the interior of the tank. For example, a saturated liquid may be liquid hydrogen, which is usually stored at cryogenic temperatures, wherein the tank is usually thermally insulated. However, tanks for liquefied petroleum gas (LPG), hydrocarbons and condensates may not necessarily be thermally insulated and the pump arrangement according to the invention is not limited to a certain liquid.

The tank may comprise a tank inlet that may be arranged at a top, a side or a bottom surface of the tank. It may be used for feeding saturated liquid into the tank. However, the tank inlet may also be used for feeding vapor or gas into the tank, as explained further below. The tank outlet may preferably be arranged at a bottom surface to further optimize the NPSP.

The heat exchanger is provided for subcooling the saturated liquid. For this, the saturated liquids can enter the heat exchanger through its liquid inlet and flow through one or a plurality of cooling channels created inside the heat exchanger. Afterwards, the subcooled liquid exits the heat exchanger at its liquid outlet. For providing the cooling function, a coolant inlet is provided, through which a two-phase flow of the saturated liquid is routed. Thus, the coolant function is provided by a part of the liquid in form of a two-phase flow. The two-phase flow is created by feeding a fraction of the saturated liquid that flows through the pump arrangement, into the expansion valve, such that it expands upstream of the coolant inlet. This leads to a partial evaporation at strongly reduced saturation temperature relative to the tank saturation temperature and the fluid reaching the coolant inlet is a mixture of liquid and vapor. Inside the heat exchanger the expanded liquid receives evaporation heat through the cooling channels, further evaporates and flows out through the coolant outlet. Resultantly, the liquid is subcooled and a flow of vapor is created. The expansion valve may be a throttle valve, which may be set to an expansion behavior through a fixed orifice geometry or similar, or which may be actively controlled. Also, the expansion valve may be a simple, switchable valve that is followed by one or more expansion nozzles.

As explained further below, the vapor may either be used for increasing the pressure inside the tank or it may be vented to the environment, depending on the embodiment of the pump arrangement according to the invention. By subcooling the saturated liquid, the NPSP at the pump inlet is increased and the pump may reliably pump the saturated liquid to a respective consumer. The risk of cavitation is decreased. The saturated or subcooled liquid is provided at the pump arrangement output, which is downstream the pump. In most embodiments described below, the pump arrangement output is directly connected to the pump outlet.

For the sake of completeness it is indicated that the expansion valve inlet may also be directly connected to the tank outlet.

In an advantageous embodiment, the pump arrangement further comprises a compressor coupled with the coolant outlet. The vapor created by vaporizing the saturated liquid enters the compressor and is pressurized. In some embodiments, the pressure of the vapor is increased above a tank pressure, such that the pressurized vapor, i.e. the pressurized gas, can be fed into the tank inlet to increase the tank pressure. In other embodiments, the vapor pressure is increased above the atmospheric pressure, such that the vapor can be vented to the atmosphere. The compressor allows to generate a lower pressure for evaporation in the heat exchanger for enabling a lower temperature on the coolant side.

In an advantageous embodiment, the expansion valve is connected to a fluid line downstream the pump and upstream the coolant inlet. Hence, a part of the saturated liquid flowing out of the pump outlet is tapped from a supply flow for a consumer of the saturated liquid and fed back into the expansion valve for being at least partially evaporated. This utilizes the pressure difference created by the pump and the feedback for the fraction of liquid into the expansion valve is simplified.

In an advantageous embodiment, the expansion valve is connected to a fluid line upstream the pump and upstream the coolant inlet. The expansion valve may be designed differently than an expansion valve fed with the saturated liquid tapped from a point downstream the pump. However, the pressure differential between the tank and the liquid outlet of the heat exchanger is sufficient for feeding the fraction of saturated liquid into the expansion valve. The overall efficiency of the pump arrangement may be slightly increased compared to the above-mentioned solution, as the fraction of the saturated liquid is not additionally pressurized before being expanded again.

In an advantageous embodiment, the compressor is connected to a tank inlet. The compressor generates the suction pressure to reduce the saturation pressure below the saturation pressure of the liquid within the tank and the vaporized liquid is fed into the tank inlet. Thus, the pressure inside the tank is increased, while no other gas from a separate gas source or a dedicated device are required for this purpose. The compressor is preferably designed to increase the pressure of the evaporated liquid to just slightly above the pressure inside the tank. The pressure difference can be made to depend on the respective saturated liquid and the required mass flow. The compressor as well as a pressure sensor downstream or inside the compressor may be connected to a control unit, which is able to control the compressor to provide a predetermined pressure increase.

In an advantageous embodiment, the compressor or coolant outlet is in fluid communication with the environment, i.e. the surrounding of the pump arrangement, which may be the atmosphere or the space that surrounds a vehicle, in which the pump arrangement is installed. The compressor may thus be capable of increasing the pressure of the vaporized liquid to a level above atmospheric pressure. A dedicated control of the compressor is not absolutely required as long as the pump arrangement is capable of always being able to vent the vaporized liquid into the atmosphere. This makes the pump arrangement capable of being operated under atmospheric pressure. If the coolant outlet is in fluid communication with the environment, the pump arrangement may be dedicated for space or high atmospheric altitude operation, e.g. in a cruise flight phase of a commercial aircraft at an altitude of about <NUM> or more.

In an advantageous embodiment, the pump arrangement further comprises a jet pump having a primary inlet, a secondary inlet, and a jet pump outlet, wherein the expansion valve is arranged downstream of the liquid outlet of the heat exchanger, wherein the pump is coupled with the primary inlet, wherein the coolant outlet is coupled with the secondary inlet. The jet pump is fed with a pressurized flow of subcooled liquid as the primary flow. A secondary flow in the form of evaporated liquid is suctioned into the primary flow through the secondary inlet. Both flows mix and exit the jet pump outlet together.

In an advantageous embodiment, the jet pump outlet is coupled with a tank inlet. Consequently, the primary inlet of the jet pump is only provided with a part of a flow that exits the pump. It may provide a mixture of evaporated liquid and saturated liquid at the tank inlet to increase the pressure inside the tank.

In an advantageous embodiment, the pump arrangement output is downstream the pump and upstream the primary inlet of the jet pump. In line with the above, the main part of the flow exiting the pump outlet is fed to a consumer. Only a fraction is fed into the primary inlet of the jet pump.

In an advantageous embodiment, the pump arrangement output is connected to the jet pump outlet. As an alternative to the above, the jet pump outlet delivers the total mass flow for the consumer.

In an advantageous embodiment, the expansion valve has a variable cross-section for controlling the fraction of saturated liquid flowing through the expansion valve. As explained above, the expansion valve may then be controlled to provide a desired evaporation behavior and/or a required pressure drop.

In analogy to the above, the invention relates to a method for providing a saturated or subcooled liquid, comprising the steps of feeding the saturated liquid from a tank through a tank outlet to a liquid inlet of a heat exchanger to sub-cool the liquid, feeding a fraction of the sub-cooled liquid or the saturated or subcooled liquid from the tank to an expansion valve inlet of an expansion valve to evaporate it thereby at reduced temperature relative to the tank liquid temperature at least partially, and feed it to a coolant inlet of the heat exchanger for receiving evaporation enthalpy from the liquid flowing into the liquid inlet to substantially evaporate completely, feeding the sub-cooled liquid from a liquid outlet of the heat exchanger to a pump inlet of a pump, and pumping the sub-cooled liquid to a pump arrangement output downstream the pump outlet for feeding saturated liquid to a consumer.

In an advantageous embodiment, a compressor or a jet pump reduces the pressure of the coolant flow below the according tank saturation pressure.

In an advantageous embodiment, the method may further comprise the step of feeding the evaporated liquid into a tank inlet of the tank for increasing the pressure inside the tank.

In addition and in further analogy to the above, one, a plurality or all further steps may be provided. These may include compressing the evaporated liquid flowing out of the coolant outlet by means of a compressor. The compressed gas may be fed into the tank inlet or into the environment. The sub-cooled liquid may be fed to the expansion valve from downstream or upstream the pump.

Also, the sub-cooled liquid may be pumped into a primary inlet of a jet pump and the evaporated liquid flowing out of the coolant outlet may be fed into a secondary inlet of the jet pump, wherein a jet pump outlet supplies a pump arrangement output with sub-cooled liquid. In an alternative, the pump arrangement output is supplied with sub-cooled liquid from downstream the pump and upstream of the jet pump, wherein the primary inlet of the jet pump is provided with a fraction of sub-cooled liquid and wherein the secondary inlet of the jet pump is provided with the evaporated liquid flowing out from the coolant outlet, and wherein the jet pump delivers sub-cooled liquid and gas to the tank inlet.

If the compressor or the jet pump feed the coolant into the tank, the saturation pressure, i.e. the evaporation pressure, of the coolant is reduced below the saturation pressure of the liquid within the tank. This is particularly beneficial for operation of the pump arrangement at atmospheric pressures, which are above the saturation pressure of the coolant.

The method steps mentioned above are to be understood as defining a continuous process and the steps are conducted at the same time.

The invention further relates to a vehicle comprising at least one pump arrangement according to the above and at least one consumer coupled with the pump arrangement output of the at least one pump arrangement.

In an advantageous embodiment, the vehicle is an aircraft, wherein the at least one consumer comprises a fuel cell and/or a device for conducting a combustion.

In the following, the attached drawings are used to illustrate exemplary embodiments in more detail. The illustrations are schematic and not to scale. Identical reference numerals refer to identical or similar elements. They show:.

<FIG> shows a pump arrangement <NUM> in a first exemplary embodiment. Here, a tank <NUM> is provided, which stores a saturated liquid, such as liquid hydrogen, at saturation conditions. The tank <NUM> comprises a tank inlet <NUM> and a tank outlet <NUM>. The pump arrangement <NUM> is designed to store and provide the saturated liquid from the tank <NUM> to a consumer <NUM>. It may comprise a thermal insulation, which is not shown in detail herein. For example, the saturated liquid may be liquid hydrogen.

The liquid is tapped from the tank <NUM> through the outlet <NUM> and is provided to a liquid inlet <NUM> of a heat exchanger <NUM>. Here, one or more cooling channels, which are not shown in detail, are provided, through which the liquid flows. The liquid is discharged at a liquid outlet <NUM>. The heat exchanger <NUM> further comprises a coolant inlet <NUM> and a coolant outlet <NUM>. A two-phase flow, i.e. the liquid and evaporated liquid explained further below, enters the coolant inlet <NUM>. By flowing through the heat exchanger <NUM>, it receives evaporation enthalpy, such that it preferably evaporates completely. Afterwards, it exits the coolant outlet <NUM> mainly in the form of gas. At the same time, the liquid that exits the liquid outlet <NUM> is sub-cooled.

The sub-cooled liquid enters a pump inlet <NUM> of a pump <NUM> and is then fed from a pump outlet <NUM> to a pump arrangement output <NUM> for feeding the consumer <NUM> with the saturated liquid. At a junction <NUM> downstream the pump <NUM> and upstream of the pump arrangement output <NUM>, a fraction of the sub-cooled liquid is tapped and fed to an expansion valve <NUM> through an expansion valve inlet <NUM>. Here, the liquid is expanded and partially evaporates to create the above two-phase flow. The two-phase flow exits an evaporation valve outlet <NUM> and enters the coolant inlet <NUM> directly downstream. The expansion valve <NUM> comprises a variable cross-section to enable the control of the fraction of liquid tapped at the junction <NUM>.

Vaporized liquid, i.e. the gas flowing out from the coolant outlet <NUM>, is fed to a compressor inlet <NUM> of a compressor <NUM>. Here, the gas is pressurized and fed to the tank inlet <NUM> through the compressor outlet <NUM>. Hence, the pressure inside the tank <NUM> this increased. By increasing the tank pressure as well as by sub-cooling the saturated liquid at the pump arrangement output <NUM>, the NPSP is clearly improved. This configuration also allows to chill down and prime the pump <NUM> to its operational temperature through the compressor <NUM> and does not require a mass flow to chill down the pump <NUM> to be vented.

<FIG> shows a pump arrangement <NUM>, which is based on the previously explained pump arrangement <NUM> and comprises a slight modification. Here, the expansion valve inlet <NUM> is connected to a junction <NUM>, which is downstream of the liquid outlet <NUM> and upstream of pump inlet <NUM>. Thus, the mass flow handled by the pump <NUM> and thus the required power for the pump <NUM> is slightly decreased. Furthermore, the pressure differential between the expansion valve inlet <NUM> and the expansion valve outlet <NUM> may be slightly smaller than in the pump arrangement <NUM> shown in <FIG>. For increasing the tank pressure as much as in pump arrangement <NUM> of <FIG>, the compressor <NUM> may need to provide a slightly higher compression.

<FIG> shows a pump arrangement <NUM>, which is another modification of the pump arrangement <NUM> shown in <FIG>. Here, the compressor outlet <NUM> is not connected to the tank <NUM>, but to the atmosphere <NUM>. Hence, the compressor <NUM> is merely adapted for increasing the pressure of the vaporized liquid to a pressure that is slightly above the atmospheric pressure. This allows to vent the vaporized liquid into the atmosphere <NUM>. This reduces the complexity of the pump arrangement <NUM> and may eliminate the need for controlling the compressor <NUM>.

<FIG> shows a further pump arrangement <NUM>, which includes the modifications of pump arrangement <NUM> of <FIG> and pump arrangement <NUM> of <FIG>. Here, a fraction of the sub-cooled liquid is tapped from junction <NUM> upstream of the pump <NUM> and is fed to the expansion valve <NUM> through the expansion valve inlet <NUM>. Furthermore, the compressor outlet <NUM> is connected to the atmosphere <NUM>. Consequently the pump <NUM> may require slightly less power than with tapping the fraction of sub-cooled liquid from junction <NUM> downstream the pump <NUM>. The compressor <NUM> may not need to be controlled and may not require providing a compression ratio as high as in the embodiments of <FIG> and its power consumption may thus be lower.

<FIG> shows a pump arrangement <NUM>, which is based on the pump arrangement <NUM> shown in <FIG>, but does not comprise a compressor <NUM>. This variant may exemplarily be used in space applications or in applications where the pressure reached at the coolant outlet <NUM> is higher than the atmospheric pressure.

<FIG> shows a further pump arrangement <NUM>, which is based on the pump arrangement <NUM> shown in <FIG>. However, the extension valve <NUM> is supplied with a fraction of sub-cooled liquid from junction <NUM> upstream of the pump <NUM>, as shown in <FIG> and <FIG>.

<FIG> shows a pump arrangement <NUM>, which comprises a jet pump <NUM> having a primary inlet <NUM> and a secondary inlet <NUM>. Sub-cooled liquid exiting the pump outlet <NUM> is fed to the primary inlet <NUM> of the jet pump <NUM>. Evaporated liquid, i.e. the gas exiting the coolant outlet <NUM>, is fed to the secondary inlet <NUM> of the jet pump <NUM>. Due to the flow of the sub-cooled liquid into the primary inlet <NUM>, the gas is suctioned into the secondary inlet <NUM> and is mixed with the primary flow. The resulting combination flow out through a jet pump outlet <NUM>. The pump arrangement output <NUM> in this embodiment is located downstream of the jet pump outlet <NUM> and feeds the liquid to the consumer <NUM>. The use of a jet pump <NUM> is beneficial, as it is a passive device capable of increasing the pressure of the already expanded and evaporated liquid from the coolant outlet <NUM> to feed it to the consumer <NUM>.

The heat exchanger <NUM> is connected to the tank <NUM> through the liquid inlet <NUM> and the sub-cooled liquid flows out through the liquid outlet <NUM>. Here, a junction <NUM> is provided, from which a main flow of sub-cooled liquid is fed to the pump inlet <NUM>. A fraction of the flow is fed to the expansion valve inlet <NUM> to be expanded in the expansion valve <NUM>. Afterwards, it is fed to the coolant inlet <NUM> through the expansion valve outlet <NUM>.

<FIG> shows a pump arrangement <NUM>, which is based on the pump arrangement <NUM> shown in <FIG>. However, in this exemplary embodiment, the pump arrangement output <NUM> is connected to a junction <NUM>, which is located downstream the pump outlet <NUM> and upstream of the primary inlet <NUM> of the jet pump <NUM>. Thus, only a fraction of the sub-cooled liquid flowing out from the pump outlet <NUM> is fed to the primary inlet <NUM> of the jet pump <NUM>.

Here, the evaporated liquid, i.e. the gas exiting the coolant outlet <NUM>, is fed to the secondary inlet <NUM> and is suctioned through the action of the primary jet pump flow into the secondary inlet <NUM>. The jet pump outlet <NUM> in turn is coupled with the tank inlet <NUM> in order to feed a part of the saturated liquid as well as the evaporated liquid back into the tank <NUM> for increasing the pressure inside the tank <NUM>.

Claim 1:
Pump arrangement (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) for providing a saturated or subcooled liquid, comprising:
- a tank (<NUM>) for saturated liquid having a tank outlet (<NUM>),
- a heat exchanger (<NUM>) for cooling the saturated liquid, the heat exchanger (<NUM>) having a liquid inlet (<NUM>), a liquid outlet (<NUM>), a coolant inlet (<NUM>) and a coolant outlet (<NUM>),
- a pump (<NUM>) having a pump inlet (<NUM>) and a pump outlet (<NUM>),
- an expansion valve (<NUM>) having an expansion valve inlet (<NUM>) and an expansion valve outlet (<NUM>), and
- a pump arrangement output (<NUM>) downstream the pump outlet (<NUM>) for feeding saturated or subcooled liquid to a consumer (<NUM>),
wherein the tank outlet (<NUM>) is in fluid communication with the liquid inlet (<NUM>) of the heat exchanger (<NUM>), such that saturated liquid stored inside the tank (<NUM>) is able to flow into the heat exchanger (<NUM>),
wherein the heat exchanger (<NUM>) is designed to sub-cool the saturated liquid,
wherein the liquid outlet (<NUM>) of the heat exchanger (<NUM>) is in fluid communication with the pump inlet (<NUM>),
wherein the expansion valve outlet (<NUM>) is in fluid communication with the coolant inlet (<NUM>) of the heat exchanger (<NUM>), and
wherein the expansion valve inlet (<NUM>) is arranged downstream the liquid outlet (<NUM>) of the heat exchanger (<NUM>) or the tank (<NUM>) for receiving and expanding a fraction of liquid flowing through the pump arrangement (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and routing it into the coolant input (<NUM>) to evaporate at reduced saturation temperature at least partially and receive evaporation enthalpy of the liquid to be sub-cooled.