Patent Description:
In aeronautical fuel cell propulsion systems, hydrogen most commonly is stored in a liquid hydrogen tank, cooled to -<NUM> (cryogenic liquefied hydrogen). In this storage form, the hydrogen occupies less volume than in gas form, and volume is scarce in aircrafts. In order to function in a fuel cell, the hydrogen needs to be heated up to approximately room temperature (RT). This heating needs to be carried out between the liquid hydrogen (LH2) and the fuel cell.

<CIT> presents a pipe heating system for an aircraft.

The object of the invention is to provide a device for converting cryogenic liquefied gas into gas that can be provided for a fuel cell propulsion system.

To achieve this object, the invention provides a pipe according to claim <NUM>. A pipe system, a fuel cell propulsion system, and a method for producing a pipe are subject-matter of the parallel claims.

Advantageous embodiments of the invention are subject-matter of the dependent claims.

In one aspect, the invention provides a pipe for heating a cryogenic liquefied gas, the pipe having a peripheral wall including a ply of one or more electrically conductive carbon fibers, the ply being configured and electrically connectable to a power supply in such a way that the one or more carbon fibers are heated when power is supplied to the ply.

Preferably, the one or more carbon fibers are coated with an electrically non-conductive material.

Preferably, the one or more carbon fibers are coated with a polymer resin.

Preferably, the one or more carbon fibers are coated with an epoxy resin.

Preferably, the peripheral wall further comprises a graphene layer.

Preferably, the graphene layer is arranged between an inner pipe region of the pipe and the ply.

Preferably, the one or more carbon fibers are arranged disconnected between end portions of the one or more carbon fibers.

Preferably, the end portions are electrically connectable to the power supply.

Preferably, the end portions extend out of the ply.

Preferably, the end portions of a plurality of carbon fibers are electrically connected into a bundle.

Preferably, the one or more carbon fibers are at least partially embedded in a matrix.

Preferably, the one or more carbon fibers that are embedded in the matrix, build a carbon fiber-reinforced polymer.

Preferably, the one or more carbon fibers are arranged in a substantially longitudinal direction of the pipe.

Preferably, the ply includes a plurality of carbon fibers arranged substantially in parallel to each other.

Preferably, the ply extends radially over the peripheral wall.

Preferably, the one or more carbon fibers are arranged at and/or around a circumference of the pipe.

Preferably, the ply is a part of a laminate that includes at least a further ply.

Preferably, the further ply includes one or more carbon fibers.

Preferably, the pipe is configured for converting cryogenic liquefied gas into gas.

Preferably, the pipe is configured for conducting gas and cryogenic liquefied gas.

Preferably, the cryogenic liquefied gas is cryogenic liquefied hydrogen.

In another aspect, the invention provides a pipe system including the pipe and a power supply electrically connected to the ply.

Preferably, the pipe system includes an electrical element for regulating an electric current through the ply.

Preferably, the pipe system includes a temperature measuring means for measuring a temperature of the pipe.

In another aspect, the invention provides a fuel cell propulsion system, including the pipe system, the pipe being in fluid connection with a tank and a fuel cell device.

Preferably, the fuel propulsion system further includes a heat exchanger for transferring heat that is produced by the fuel cell device to the pipe system.

In another aspect, the invention provides an aircraft including the pipe, the pipe system and/or the fuel propulsion system according to any of the preceding embodiments.

In another aspect, the invention provides a method for producing a pipe for heating a cryogenic liquefied gas, the method comprising the steps:.

Preferably, the method further comprises the step:
Coating the carbon fibers with an electrically non-conductive material.

Preferably, the method further comprises the step:
Coating the carbon fibers with a polymer resin.

Preferably, the method further comprises the step:
Coating the carbon fibers with an epoxy resin.

Preferably, the method further comprises the step:
At least partially embedding the carbon fibers in a matrix.

Preferably, the method further comprises the step:
Building a carbon fiber-reinforced polymer.

Preferably, the method further comprises the step:
Arranging the one or more carbon fibers disconnected between end portions of the one or more carbon fibers.

Preferably, the method further comprises the step:
Arranging a plurality of carbon fibers substantially in parallel to each other.

Preferably, the method further comprises the step:
Folding the ply such that the one or more carbon fibers are arranged in a substantially longitudinal direction of the pipe.

Preferably, the method further comprises the step:
Arranging the one or more carbon fibers at and/or around a circumference of the pipe.

Preferably, the method further comprises the step:
Adding a graphene layer on the ply.

Preferably, the graphene layer is added by spraying graphene flakes and/or by applying a buckypaper on the ply.

Preferably, the method further comprises the step:
Electrically connecting end portions of a plurality of carbon fibers into a bundle.

Preferably, the method further comprises the step:
Electrically connecting the ply, a bundle and/or end portions of the one or more carbon fibers to a power supply.

Preferably, the method further comprises the step:
Adding further plies in order to build a laminate.

Preferably, the further plies are added by filament winding.

Embodiments of the invention preferably have the following advantages and effects:
Embodiments of the invention preferably provide a method and a device for heating liquid hydrogen in carbon fiber-reinforced polymer (CFRP) pipes to a temperature, reaching gas form, and to room temperature (RT), for use in a fuel cell, without any external heating source outside the pipe.

Preferred embodiments of the invention are advantageous, in particular, when main engines are electric and are obtaining their energy from a fuel cell that has not yet reached its operating temperature, such as at cold start of the fuel cell.

The heating of the liquid hydrogen can be achieved by one or more coated carbon fibers in the inside of a ply of the pipe, in which electric current can be running.

The heat can be transferred to the hydrogen via a graphene cover layer, that can transmit heat via surfaces the best.

It is preferred that the pipe is sufficiently tight to suppress permeation.

In preferred embodiments, the innermost layer of graphene can have multiple functions, such as:.

Embodiments of the invention preferably have the following advantages:.

Embodiments of the invention are now explained in more detail with reference to the accompanying drawings of which.

<FIG> shows a comparative embodiment of a fuel cell propulsion system <NUM>.

The fuel cell propulsion system <NUM> includes a tank <NUM>, a pipe <NUM>, a fuel cell device <NUM>, a heat exchanger <NUM>, and an electric motor <NUM>.

The tank contains a fuel <NUM> in form of a cryogenic liquefied gas <NUM>.

The cryogenic liquefied gas <NUM> is preferably liquid hydrogen <NUM>, but other cryogenic liquefied gases <NUM> which can be used as fuel <NUM> in the fuel cell device <NUM> are within the scope of the invention.

The pipe <NUM> is in fluid connection with the tank <NUM> and the fuel cell device <NUM>.

In operation, the fuel cell device <NUM> converts the chemical energy of the fuel <NUM> and an oxidizing agent <NUM> into electricity. Heat is produced by the fuel cell device <NUM>.

The oxidizing agent <NUM> in the case shown in <FIG> is oxygen <NUM> in gas form. The electricity is provided for the electric motor <NUM>.

For operation, the fuel <NUM> that is provided for the fuel cell device <NUM>, needs to be in gas form.

In the comparative embodiment of <FIG>, a heat exchanger <NUM> transfers the heat produced by the fuel cell device <NUM> via a hot liquid pipe <NUM> to the pipe <NUM>, so that in the pipe <NUM> the liquid hydrogen <NUM> is converted into hydrogen <NUM> in gas form.

Provided the liquid hydrogen <NUM> can obtain the energy from a heat source, this works well. However, if the fuel cell device <NUM> is cold, at start, no heat is produced by the fuel cell device <NUM> for several minutes. However, to function, the fuel cell device <NUM> needs hydrogen <NUM> warmed up to room temperature (RT).

<FIG> shows a comparative embodiment of a pipe system <NUM>.

The pipe system <NUM> includes the pipe <NUM>, a heating spiral <NUM>, and a power supply <NUM>.

The heating spiral <NUM> includes an electrically conductive wire <NUM>, for instance a copper wire, that is clamped on top of the pipe <NUM> by clamps <NUM>.

The heating spiral <NUM> is electrically connected to the power supply <NUM> via an electric cable <NUM>.

When power is supplied to the heating spiral <NUM>, the wire <NUM> is heated. The heat is transferred to the pipe <NUM>, which, in turn, warms up the liquid hydrogen <NUM> in the pipe <NUM>.

The heating spiral <NUM> includes a straight piece of the electrically conductive wire <NUM>. Thus, the pipe <NUM> is heated mainly at one side thereof. The overall efficiency of this pipe system <NUM> is reduced.

<FIG> shows a fuel cell propulsion system <NUM> according to an embodiment of the invention.

In the embodiment shown in <FIG>, the fuel cell propulsion system <NUM> includes the tank <NUM>, a pipe system <NUM>, and the fuel cell device <NUM>.

The fuel cell propulsion system <NUM> can additionally include a heat exchanger <NUM>.

The fuel cell device <NUM> includes a block <NUM> for distributing hydrogen <NUM>, a polar/bipolar plate <NUM>, an anode <NUM>, a membrane <NUM>, a cathode <NUM>, and another polar/bipolar plate <NUM>.

The pipe system <NUM> includes a pipe <NUM> and a power supply <NUM> (not shown).

<FIG> shows a sectional view of the pipe <NUM> according to an embodiment of the invention. The cross-section is taken from line IV-IV in <FIG>.

The pipe <NUM> includes a peripheral wall <NUM> surrounding an inner pipe region <NUM>.

The peripheral wall <NUM> includes a laminate <NUM>. In the present case, the laminate <NUM> is designed as a carbon fiber-reinforced polymer <NUM>.

<FIG> shows an enlarged view of the peripheral wall <NUM> of the pipe <NUM>. The enlarged view is taken from the box of <FIG>.

The laminate <NUM> includes a (CFRP) ply <NUM> that is preferably arranged at an innermost region <NUM> of the peripheral wall <NUM>.

The laminate <NUM> may include further (CFRP) plies <NUM> arranged in an outside region <NUM> of the peripheral wall <NUM>.

The (innermost) ply <NUM> of the laminate <NUM> includes a plurality of carbon fibers <NUM>. However, within the scope of the invention, the ply <NUM> may also include only a single carbon fiber <NUM>.

The carbon fibers <NUM> are embedded in a matrix <NUM>.

<FIG> shows an embodiment of one of the plurality of carbon fibers <NUM> of <FIG>.

The one or more carbon fibers <NUM> are coated with an electrically non-conductive material <NUM>. In the present case, the one or more carbon fibers <NUM> are coated with a polymer resin <NUM>, namely an epoxy resin <NUM>.

The carbon fiber <NUM> is electrically conductive, while the epoxy resin <NUM> is non-conductive.

The coated carbon fiber <NUM> can withstand temperatures of over <NUM>. The epoxy resin <NUM> allows transmission of ions, but not of electrons. Thus, the epoxy resin <NUM> avoids short-circuits or current leakage, when a plurality of coated carbon fibers <NUM> could come into contact.

The carbon fibers <NUM> that are embedded in the matrix <NUM>, build the carbon fiber-reinforced polymer <NUM>.

The peripheral wall <NUM> further comprises a graphene layer <NUM> that is arranged between the inner pipe region <NUM> and the ply <NUM>.

The graphene layer <NUM> can have multiple effects. It can conduct heat, it can contribute to suppress permeation, and/or it can contribute to avoid static electricity when the pipe <NUM> is filled fast with liquid hydrogen <NUM>.

<FIG> shows a pipe system <NUM> according to an embodiment of the invention.

In contrast to the heating spiral <NUM> in <FIG>, the ply <NUM> radially extends over the peripheral wall <NUM> of the pipe <NUM>.

The ply <NUM> may also be radially extending over the entire peripheral wall <NUM>.

In other words, the ply <NUM> may surround the inner pipe region <NUM> of the pipe <NUM>.

The carbon fibers <NUM> of the ply <NUM> are thus arranged at and/or around a circumference <NUM> of the pipe <NUM>.

In the embodiment shown in <FIG>, the carbon fibers <NUM> are arranged in a longitudinal direction (LD) of the pipe <NUM>. However, the carbon fibers <NUM> may also be arranged in any other direction, for example in a transversal direction of the pipe <NUM>.

The carbon fibers <NUM> respectively include end portions <NUM>.

The end portions <NUM> are located at opposite sides 69a, 69b of the carbon fibers <NUM>.

The carbon fibers <NUM> are arranged disconnected between the end portions <NUM>. Thus, no short-circuit is produced.

The end portions <NUM> may extend out of the ply <NUM>.

The end portions <NUM> of some of the plurality of carbon fibers <NUM> are electrically connected into a bundle <NUM>.

The bundles <NUM> are electrically connected to the power supply <NUM> such that the ply <NUM> is electrically connected to the power supply <NUM>.

When power is supplied to the ply <NUM>, the carbon fibers <NUM> are heated. Thus, the pipe <NUM> can heat the liquid hydrogen <NUM> to room temperature (RT). This may be advantageous especially at cold start of the fuel cell device <NUM>.

When the fuel cell device <NUM> operates, a heat exchanger <NUM> may additionally transfer the heat that is produced by the fuel cell device <NUM> to the pipe <NUM>. Due to the heated carbon fibers <NUM>, the heat exchanger <NUM> may be reduced in size and weight.

In the following, a method for producing the pipe <NUM> according to an embodiment of the invention is described.

First, the plurality of carbon fibers <NUM> is provided and arranged disconnected between the end portions <NUM> and/or substantially in parallel to each other. This means, that the carbon fibers <NUM> are arranged in such a way that short-circuits are avoided in the ply <NUM>.

The carbon fibers <NUM> are then coated with the polymer resin <NUM>, for example with epoxy resin <NUM>.

The carbon fibers <NUM> may be at least partially embedded in the matrix <NUM>. The carbon fiber-reinforced polymer <NUM> is built and the ply <NUM> is produced.

The ply <NUM> is then covered with the graphene layer <NUM>. This can be achieved by spraying graphene flakes on the ply <NUM>, by applying a buckypaper on the ply <NUM> or by any other suitable method producing a graphene layer <NUM> on the ply <NUM>.

The ply <NUM> is then folded up to the pipe <NUM>.

Preferably, the ply <NUM> is folded such that the carbon fibers <NUM> are arranged in the longitudinal direction (LD) of the pipe <NUM>. However, other folding directions are possible.

Further plies <NUM> may be added by filament winding in order to build the laminate <NUM>.

The end portions <NUM> of some of the carbon fibers <NUM> may then be electrically connected into a bundle <NUM>.

The ply <NUM> is then electrically connected to the power supply <NUM> via the electric cable <NUM>.

To regulate the heating, a temperature measuring means <NUM> may be placed on the pipe <NUM>. The electric current through the carbon fibers <NUM> may be regulated by means of electrical elements <NUM>, e.g., a resistor, inserted into the circuit.

Automated electric current regulation can be achieved by connecting the temperature measuring means <NUM> with a micro controller.

Claim 1:
A pipe (<NUM>) having a peripheral wall (<NUM>) including a ply (<NUM>) of one or more electrically conductive carbon fibers (<NUM>), the ply (<NUM>) being configured and electrically connectable to a power supply (<NUM>) in such a way that the one or more carbon fibers (<NUM>) are heated when power is supplied to the ply (<NUM>), characterized in that the pipe (<NUM>) is for heating a cryogenic liquefied gas (<NUM>).