DE102021129205A1 - Pressure equalization and volume equalization in a fluid circuit - Google Patents

Abstract

A fluid arrangement (8) with a fluid circuit (10) with incompressible fluid (12) with a varying total volume (VF) contains a compensating arrangement (18) with a compensating tank (16) with a tank volume (VB) which, during operation, has a compensating volume (VA ) of the fluid (12) and a compressible preload element (32) with preload volume (VV) with preload pressure (pV), with a discharge line (20) with discharge valve (26) from a discharge opening (22) to the expansion tank (16), and with a supply line (26) with a supply valve (30) from the expansion tank (16) to a supply opening (28), the fluid (12) having a discharge pressure (pA) at the discharge opening (22) and a supply pressure (pA) at the supply opening (28) pZ) is smaller than the discharge pressure (pA), the compensation arrangement (18) being closed off in terms of pressure, and a pressure range of the preload pressure (pV) being selected such that the current preload pressure (pV) is always between the supply pressure (pZ) and the discharge pressure ( pA).An object arrangement (6) contains the fluid arrangement (8) and an object (4) through which the fluid (12) flows in the fluid circuit (10).An aircraft (2) contains the object arrangement (6) as a cooling arrangement for fuel cells (5 ) as an object (4) for driving the aircraft (2). When operating the fluid arrangement (8) or the object arrangement (6) or the aircraft (2), the discharge valve (24) and / or the supply valve (30) is opened to To lead fluid (12) from or into the fluid circuit (10) in order to reduce or increase the pressure p in the fluid (12).

Description

The invention relates to a fluid assembly, such as a cooling assembly. The fluid arrangement contains a fluid circuit, for example a cooling circuit for cooling an object present in the cooling circuit, through which an incompressible fluid, e.g. a coolant, circulates during operation. With a change in its temperature level, the fluid is subject to a change in volume in relation to a certain pressure, i.e. at atmospheric pressure, for example. It therefore has a total volume that varies in this sense. However, if there is no space for the fluid to change volume, the fluid reacts with a pressure change in the fluid circuit. This applies in particular to incompressible fluids.

From the DE 10 2017 001 447 A1 an expansion tank for a coolant circuit of an internal combustion engine of a motor vehicle is known, with an expansion opening through which coolant of the coolant circuit can flow into and out of an interior space of the expansion tank, with a membrane being arranged in the interior space of the expansion tank, which divides the interior space into a fluidic the compensating opening connected compensating volume and divided into a separate from this bias volume, which can be filled with a medium via a filling opening of the equalizing tank.

The object of the present invention is to propose improvements in relation to a fluid arrangement.

The object is achieved by a fluid arrangement according to patent claim 1. Preferred or advantageous embodiments of the invention and other categories of the invention result from the further claims, the following description and the attached figures.

The fluid assembly includes a fluid circuit. When the fluid arrangement is operated as intended, an incompressible fluid circulates through the fluid circuit. The volume of fluid in the fluid circuit varies over time. This is because the fluid undergoes thermal expansion as the temperature changes. The thermal expansion of the fluid discussed here affects the fluid as a whole. What is meant here is not the temperature fluctuation of the fluid during circulation in the fluid circuit, e.g. a cooling circuit, which usually naturally has sections with different fluid temperatures, but the change in the temperature level in the fluid circuit as a whole. In particular, the fluid arrangement serves or is set up to set a predeterminable pressure level in the fluid during operation, which circulates in the fluid circuit. For this purpose, the fluid circuit is equipped in particular with a pump or feed pump for the fluid.

The fluid assembly is, for example, a cooling assembly; this serves or is then set up for cooling an object which is in the fluid circuit--which is then a cooling circuit--is located. In other words, the fluid circulates through or along the cooling circuit, absorbing heat from the object and releasing it to another point in the cooling circuit, e.g. to a cooler.

The changing "volume" of the fluid refers to the volume that the fluid would assume without external constraint, i.e. e.g. at atmospheric pressure, if it has the appropriate temperature and can actually carry out a volume change. In fact, however, only the (constant) volume/internal space of the fluid circuit is available to the fluid in the fluid circuit. A "volume increase" mentioned above cannot take place in the fluid circuit (due to the constraints of the given volume of the fluid circuit). Instead, the fluid reacts - precisely because of its incompressibility - with a strong increase in pressure in the fluid circuit. Therefore, as explained below, a compensating tank is provided on the fluid circuit in order to drain or supply "additional" or "missing" fluid volume caused by temperature changes in the fluid circuit and thus to avoid the forced increase / decrease in pressure in the fluid circuit.

"Incompressible" is to be understood here in the sense of the usual incompressibility of liquids such as water or oil. In fact, these liquids are compressible to a certain, but very small degree, and therefore react with a significantly greater increase in pressure in a closed volume - compared to e.g. compressible media, e.g. gases such as air or nitrogen - with otherwise the same conditions (volume, temperature change, . ..).

The fluid assembly contains the fluid. In the above sense, the fluid has a total volume that varies with its temperature level.

The fluid assembly also includes a balancing assembly. This contains the expansion tank mentioned above (also "pressure expansion tank"). The expansion tank has a constant tank volume. The expansion tank is “connected” to the fluid circuit, ie connected to it in fluid communication via a discharge/supply opening or discharge/supply line (see below). Fluid can therefore between mechanical fluid circuit and expansion tank flow back and forth via the openings / lines.

When the fluid arrangement is operated as intended, the equalizing tank is completely filled as follows: On the one hand, the equalizing tank is filled with fluid in the amount or size of an equalizing volume. On the other hand, it is filled with a compressible prestressing element; this occupies a preload volume in the expansion tank and in each case has a current preload pressure. Both components together fill the container completely. The more fluid (compensation volume) that is present in the compensation tank or tank volume, the more the preload element is compressed onto the remaining tank volume, namely the preload volume. The sum of the compensating volume and the preload volume is therefore always constant and equal to the container volume.

Strictly speaking, the term "compensation" or "pressure compensation" tank means the following: the compensation tank is actually more of a volume compensation tank than a pressure compensation tank. Because if the volume of the fluid changes due to a temperature change, excess (at the same or . similar fluid pressure no longer in the fluid circuit "suitable") fluid / volume in the expansion tank as compensation volume (proportion) transferred. On the other hand, fluid is routed from the expansion tank back into the fluid circuit in order to fill the latter with more fluid when the volume of the fluid decreases in order to create a In other words, more or less (partial) volume of the fluid is “outsourced” from the fluid circuit to the expansion tank as an equalization volume.

The corresponding compressibility of the prestressing element allows fluid to flow into or out of the expansion tank and thereby adjust the pressure of the fluid in the fluid circuit. A corresponding preload pressure in the preload volume is then established - depending on the currently available compensation volume. The hypothetical volume of the fluid that it would occupy at atmospheric pressure and the cavity that is actually available for the fluid volume, which it can fill, are decisive for the fluid pressure in the fluid circuit. In other words, the evacuation of a specific amount/compensation volume of fluid from the fluid circuit allows the pressure in the fluid in the fluid circuit to be influenced. In this respect it is possible according to the invention to adjust or control the fluid with regard to its pressure in the fluid circuit without having to expose the fluid to contact with oxygen if the prestressing element does not contain oxygen (at least at the boundary with the fluid).

A corresponding pretensioning element is therefore used to apply pressure to the fluid in the expansion tank. The prestressing element contains or forms the prestressing volume mentioned above. Here, "compressible" is related to "incompressible" and means that the biasing element is significantly more compressible than the fluid.

A separator in the surge tank between the fluid and the biasing element may be present but is optional. A membrane would be conceivable, for example, which separates the fluid from the remaining volume of the reservoir (preload volume, e.g. gas space/air space) of the expansion tank. The preload volume is not connected to the environment of the expansion tank, but is blocked from it.

The compensation arrangement contains a discharge line. The discharge line leads from a discharge opening of the fluid circuit to the expansion tank or connects both elements of the fluid circuit and expansion tank to exchange fluid. The discharge line contains a discharge valve which is closed regularly or in a basic state (no fluid flow through the discharge line possible), but which can be opened to release the discharge line (fluid flow possible). In the fluid circuit, the fluid has a current discharge pressure at the discharge opening when the fluid arrangement is in operation. The drain line can also be a "zero line", i.e. there is only the drain valve between the fluid circuit and the expansion tank. The discharge line serves or is set up to (when the discharge valve is open) allow fluid to be discharged from the fluid circuit into the expansion tank, provided there is a corresponding pressure drop from the fluid circuit to the expansion tank, see below. When the drain valve is closed, the fluid circuit is shut off from the equalizing tank, i.e. the volume / interior space of the fluid circuit (including the drain line up to the drain valve) and the equalizing tank (including the drain line up to the drain valve) are constant and mutually blocked volumes.

The compensating arrangement contains a supply line which basically corresponds to the discharge line. The supply line leads from the expansion tank to a supply opening of the fluid circuit or also connects both elements for the exchange of fluid. The supply line also contains a supply valve which is closed regularly or in a basic state and which can be opened to release the supply line (fluid flow is possible). In the fluid circuit during operation of the fluid arrangement, the fluid has a current at the supply opening supply pressure up. The supply line can also be a "zero line", ie there is only the supply valve between the fluid circuit and the expansion tank. The supply line serves or is set up to allow fluid to be supplied from the equalizing tank into the fluid circuit (when the supply valve is open), provided there is a corresponding pressure drop from the equalizing tank to the fluid circuit, see below. When the supply valve is closed, the fluid circuit is shut off from the equalizing tank, ie the volume / interior space of the fluid circuit (including the supply line up to the supply valve) and the equalizing tank (including the supply line up to the supply valve) are each constant and mutually blocked volumes.

The supply valve and/or discharge valve can be designed either as a purely binary controllable valve (open/closed) or as a steplessly controllable valve.

The supply pressure in the fluid circuit is always lower than the discharge pressure when it is operated as intended. The latter is a property of the fluid circuit that is inherent in normal operation, e.g. due to flow-dynamic conditions in the fluid circuit. The relevant property of the fluid circuit is assumed for the present invention.

In particular, the expansion tank contains two openings through which the above-explained volume exchange/compensation of fluid between the fluid circuit and the expansion tank takes place. The openings are therefore equalization openings or ends of the discharge/supply lines or valves.

Like the fluid circuit, the compensating arrangement is designed to be closed in terms of pressure. It is therefore a passive compensation arrangement in this sense: only the supply/discharge valves can be opened or closed, no (partial) volume of the compensation arrangement and also of the entire fluid arrangement can be changed. The preload pressure cannot be changed externally, but, as explained above, is only set by the amount of the compensation volume and the temperature level of the fluid/preload element. No fluid can leave or be added to the fluid assembly. Only the exchange of fluid between the fluid circuit and the expansion tank is possible. The biasing element is passive, constant, consistent. No parts can be added to or removed from this (at least in regular operation, e.g. during the adjustment of the fluid pressure in the fluid circuit by exchanging fluid with the expansion tank). Not considered here are special operating states of the fluid arrangement, such as its commissioning/maintenance/repair of the fluid arrangement (initial introduction/replacement of fluid/preloading element e.g. due to aging/diffusion losses/...).

In the fluid arrangement, a pressure range of the preload pressure is selected such that the current preload pressure for all intended operating states of the fluid arrangement is always between the current supply pressure and the current discharge pressure. "Pressure range" here is the possible pressure of the prestressing element at any time in all possible intended operating states of the fluid arrangement, since the actual current prestressing pressure - as explained above - fluctuates or varies in regular operation of the fluid arrangement.

In particular, the pressure level of the fluid in the fluid circuit must be kept in a predeterminable level range (to be understood in the corresponding sense of “pressure range”) or at a specific level. This takes place with the selective and required opening of the discharge valve or the supply valve. In this way - as explained above - a volume fraction of fluid can be removed from or added to the fluid circuit in order to provide a corresponding quantity of the fluid in the fluid circuit for a given current volume / temperature expansion state, so that a desired pressure / pressure level is set there. By opening the valves as required, fluid is always discharged or supplied from/into the fluid circuit.

Due to the fact that the pressure range of the preload pressure is selected accordingly, the current preload pressure is always between the current supply pressure and the current discharge pressure. This results in a respective pressure drop between the discharge opening and the equalizing tank or between the equalizing tank and the supply opening, in order to always ensure fluid is discharged from the fluid circuit at the discharge opening and fluid is supplied into the fluid circuit at the supply opening in the above-mentioned directions. This is then done simply by opening the relevant valves without the additional use of pumps or other aids.

The entire constant volume / interior space of the fluid arrangement is therefore made up of the parts: constant volumes of fluid circuit, discharge line, supply line and expansion tank. This volume is therefore constant overall. All balancing processes etc. take place within this constant, closed volume.

A passive buffer element can optionally be connected to the fluid circuit, for example as a further, but customary, expansion tank in the form or comparable to one from the above-mentioned DE 10 2017 001 447 A1 , which communicates firmly and permanently (without the interposition of valves or a valve that is permanently open in regular operation) with the fluid in the fluid circuit. In this way, smaller pressure fluctuations in the fluid circuit can be compensated for without having to open one of the drain/supply valves. In other words, another passive reservoir is implemented to reduce possible pressure pulsations. In particular, the valves can be protected in this way, in that they are relieved of correspondingly small corrective movements and the pressure in the fluid in the fluid circuit nevertheless remains within desired limits.

Optionally, check valves can be implemented in the fluid circuit in order to ensure a specific flow direction for the fluid, e.g. if it contains branches and parallel sub-lines.

In a preferred embodiment, the pressure range of the biasing pressure is selected through a choice of container volume and the amount and type of biasing element. The background to this is that the volume / interior of the fluid circuit (which is available for the fluid) and the supply and discharge lines are given or are assumed to be unchangeable according to design specifications / geometric / thermal / fluidic boundary conditions etc. Furthermore, it is assumed that the quantity of fluid in the fluid arrangement as well as its thermal expansion properties and the temperature range to which the fluid can be exposed are also given in this sense. The choice of container volume then determines how much space is available for the pretensioning element, in view of the required compensation volume for the fluid. In this way, a suitable prestressing element can be selected, which then has the desired pressure range in terms of the resulting prestressing pressure in operation under the given framework conditions. Alternatively or additionally, the pretensioning element (material, quantity, size) can also be selected and the container volume can be selected appropriately with regard to its then known properties.

In a preferred embodiment, the pressure range of the preload pressure is selected such that the current preload pressure for all intended operating states of the fluid arrangement is always above the current supply pressure plus a lower reserve pressure. Alternatively or additionally, the pressure level is selected such that the current preload pressure for all intended operating states of the fluid arrangement is always below the current discharge pressure minus an upper reserve pressure. This ensures that there is always at least a pressure gradient between the fluid circuit and the expansion tank at the level of the lower (supply line) or upper (discharge line) reserve pressure in order to be able to safely drain or supply fluid to or from the fluid circuit by opening the corresponding valve. Safe fluid transport through the corresponding line can also take place taking into account the pressure drops that are inevitably present, e.g. in the discharge/supply lines or valves.

In a preferred embodiment, the fluid circuit contains a pump that conveys the fluid through the fluid circuit during operation. The circuit also contains an object through which the fluid flows. The discharge opening is arranged downstream of the pump between the latter and the object. The supply port is located upstream of the pump, between the latter and the object. The supply and discharge openings are arranged in particular close to/directly on the pump. Particularly in the case of a single pump, these are those locations in a fluid circuit which—in the fluid circuit—have the lowest (upstream before or at the pump inlet) and greatest fluid pressure (downstream after or at the pump outlet). Thus, in relation to the equalizing tank, which is connected by the discharge and supply line in the manner of a series connection between the discharge and supply opening, a maximum pressure drop is available in order to pump fluid into or out of the equalizing tank.

In a preferred embodiment, the supply valve is an automatic valve which is set to a predeterminable automatic pressure in the direction of the supply opening. If it falls below this value, it opens automatically and if it is exceeded, it closes automatically. In particular, a customary hysteresis is provided here in order to avoid too frequent opening/closing etc. The automatic valve is in particular a pressure reducer whose (reduced) setting pressure corresponds to the automatic pressure. Thus, as soon as the supply pressure falls below the automatic pressure, the automatic valve opens and fluid is fed into the fluid circuit through the supply opening until the supply pressure is again reached at the level of the automatic pressure. Then the supply of further fluid stops. This ensures that the supply pressure does not fall below the automatic pressure; in particular, is kept constant on this (within limits, depending on the hysteresis). No further (active) valve control implemented externally, for example by a control device, is required for a corresponding valve. This leads to easy pressure control in the fluid cycle. However, a valve instead of a pressure regulator provides a reduced pressure drop across the valve instead of the pressure regulator. This allows for a smaller expansion tank. The pressure reducer, on the other hand, is advantageously self-regulating, but has the disadvantage of a higher pressure loss across the pressure reducer, which necessitates a larger expansion tank.

Alternatively, this solution is also possible for the discharge valve; the automatic pressure then corresponds to a desired discharge pressure, which is automatically adjusted.

In a preferred embodiment, the fluid assembly includes a controller. This has an input for a current measurement pressure. The measuring pressure is the (currently) detected fluid pressure at a measuring point in the fluid circuit. The control device is connected to the discharge valve and/or the supply valve. The control device is also set up, as required and optionally: to open the discharge valve and/or the supply valve in order to bring or maintain at least one of the current measured pressures in a respective permissible range by discharging and/or supplying fluid into the fluid circuit. “As required and optionally” is to be understood in such a way that it is initially decisive which of the valves is actually connected to the control device, because only connected valves can be controlled. Depending on whether the pressure is then to be lowered or raised in order to bring the measuring pressure into the desired pressure range or to keep it in this range, the discharge valve or the supply valve is then opened in order to supply or discharge the pressure/pressure level in the fluid circuit of fluid to lower or raise.

In this case, the pressure can be recorded/measured directly at that location in the fluid circuit as a measuring point at which a specific pressure is of interest or is to be set. Alternatively, however, the pressure can also be measured at another measuring point in the fluid circuit and - e.g. empirically or through tests or theoretical considerations - the pressure at another location in the fluid circuit at which a specific pressure is of interest/is to be set can be deduced from this. Possible points of interest for fluid pressure in the fluid circuit are, for example, a maximum pressure at the entrance of an object, e.g. at a fuel cell entrance, possibly plus an estimated pressure difference between the fuel cell entrance and the measuring point. The reason for this is, for example, that the object must not be subjected to a higher fluid pressure. A minimum pressure at a pump inlet would also be conceivable as a point of interest in order to avoid cavitation in the pump, possibly plus an estimated pressure drop between the pump inlet and the measuring point. The control of the supply/discharge valve is omitted, for example, in the above-mentioned embodiment as an automatic valve.

In particular, the fluid arrangement contains at least one pressure sensor/recorder for detecting a current measured pressure of the fluid at a specific point/area of the fluid circuit as a measuring point. The controller can then operate in response to pressure-correlated data collected from the sensor. In particular, a specific pressure in the fluid at the measuring point can be set (controlled or regulated). In particular, the control takes place on the basis of a pressure-correlated variable provided by the pressure sensor. In particular, the pressure value of the fluid in the fluid circuit can be kept between a lower and an upper threshold value at the measuring point, for example by regulation. Estimated values of pressure drops between the location of interest and the measuring point can also be used to set pressures at locations of interest other than the measuring point

In a preferred variant of this embodiment, the fluid arrangement contains an object and/or a pump which is arranged in the fluid circuit. The object or the pump has the fluid flowing through it and therefore has a corresponding inlet for fluid. At least one of the current gauge pressures is correlated to the pressure of the fluid at the upstream inlet of the object/pump. As explained above, the measuring point can be directly at the inlet (correlation is then identity) or at another location in the fluid circuit whose fluid pressure is correlated with the fluid pressure at the inlet via an assumed/known pressure difference. In particular, the object/the pump can thus be protected from excess pressure or fluid pressure that is too low.

1. 1.) Wenn das Zusatzvolumen an Fluid vollständig im Ausgleichsbehälter einliegt bzw. einliegen würde, gilt: Das Vorspannelement ist dann maximal komprimiert und weist dann als Vorspanndruck höchstens einen bestimmungsgemäßen Mindestwert des Abfuhrdruckes auf. Dieser Fall gilt insbesondere, wenn das Fluid sein maximal zulässiges Temperaturniveau erreicht hat, das Fluid also maximal ausgedehnt ist und somit eine Maximalmenge von Fluid in den Ausgleichsbehälter ausgelagert ist.
2. 2.) Wenn kein Zusatzvolumen an Fluid im Ausgleichsbehälter einliegt bzw. einliegen würde, gilt: Das Vorspannelement ist dann maximal ausgedehnt und weist dann als Vorspanndruck wenigstens einen bestimmungsgemäßen Höchstwert des Zufuhrdruckes auf. Dieser Fall gilt insbesondere, wenn das Fluid sein minimal zulässiges Temperaturniveau erreicht hat, das Fluid also minimal ausgedehnt ist und somit überhaupt kein Fluid in den Ausgleichsbehälter ausgelagert ist. Dann ist allenfalls eine Mindestreserve / Sicherheitsreserve (damit der Ausgleichsbehälter nicht leerläuft) an Fluid noch im Ausgleichsbehälter vorhanden.

A preferred embodiment of the invention assumes that in a specified temperature range, the varying total volume of the fluid is always between a minimum volume and a maximum volume that is larger by a known additional volume. The temperature range is assumed to be known. This corresponds, for example, to the permissible operating conditions for the fluid arrangement according to design specifications. The total volume of the fluid is then also assumed to be known due to the knowledge of its properties with regard to temperature expansion and the known quantity of the fluid in the fluid arrangement. According to this embodiment, the container volume is dimensioned as follows (both of the following conditions must be met):

1. 1.) When the additional volume of fluid is completely in the reservoir or is included The following applies: The prestressing element is then maximally compressed and then has at most a specified minimum value of the discharge pressure as prestressing pressure. This case applies in particular when the fluid has reached its maximum permissible temperature level, ie the fluid has expanded to the maximum and a maximum amount of fluid has therefore been transferred to the expansion tank.
2. 2.) If there is or would be no additional volume of fluid in the expansion tank, the following applies: The prestressing element is then maximally expanded and then has at least one specified maximum value of the supply pressure as the prestressing pressure. This case applies in particular when the fluid has reached its minimum permissible temperature level, ie the fluid has expanded to a minimum and therefore no fluid at all has been transferred to the expansion tank. Then there is at most a minimum reserve / safety reserve (so that the expansion tank does not run empty) of fluid in the expansion tank.

The material and quantity of the pretensioning element and its pressure properties are also assumed to be given or already selected. In combination with the quantity and properties of the preload element, the appropriate reservoir volume is selected: In such a way that when the fluid quantity in the reservoir is increased by the additional volume, the preload element is compressed and the pressure in the preload pressure increases, at least at the specified maximum value of the supply pressure starts and ends at the latest at the specified minimum value of the discharge pressure.

As a result, it is ensured that the preload pressure is kept below the lowest possible discharge pressure, and fluid can therefore always be discharged from the cooling circuit at the discharge opening. Furthermore, the preload pressure is always kept above the highest possible supply pressure; it is also always possible to supply fluid to the cooling circuit at the supply opening.

In a preferred variant of this embodiment, the preload pressures are each increased by a lower reserve pressure and/or lowered by an upper reserve pressure, so that the pressure differences that occur between the expansion tank and the fluid circuit do not drop below corresponding minimum values (reserve pressures).

In a preferred embodiment, the biasing element is a compressible loose gas or a compressible elastic object. In particular, the loose gas contains no oxygen. It is present in particular as a loose gas bubble in the expansion tank, ie as a gas space or gas volume, ie a gas-filled partial space of the expansion tank in which no fluid is present. "Elastic" is to be understood here in the sense of compressible but "solid / not gaseous". However, the object can in particular be gas-filled, for example, in which case the compressibility/elasticity is then essentially achieved by the gas/the gas filling. In particular, the object is a gas-filled stretchable cushion or a foam body made of closed-cell foam. The individual closed foam cells then roughly correspond to a large number of gas-filled elastic bodies/partial objects.

In a preferred embodiment, the fluid arrangement is a cooling arrangement for cooling an object. The fluid circuit is then a cooling circuit for the object to be cooled, which in particular contains the object to be cooled. The fluid is a fluid effecting the cooling of the object. The invention is particularly suitable for such cooling circuits.

The object of the invention is also achieved by an object arrangement according to claim 12. This contains the fluid arrangement according to the invention and an object which is contained in the fluid circuit and through which fluid flows during operation.

The object arrangement and at least some of its possible embodiments as well as the respective advantages have already been explained in connection with the fluid arrangement according to the invention.

In a preferred embodiment, the object assembly is a cooling assembly and the object is a fuel cell assembly. The fuel cell arrangement contains at least one fuel cell that is to be cooled by the cooling arrangement, i.e. that the fluid flows through/around. The fuel cell is, in particular, one in an electrically powered aircraft. "Powered" is understood to refer to the aircraft's main engine for flight. So the aircraft is not powered by internal combustion engines / turbines / engines, but by electric motors, e.g. with propellers. The electrical energy for the electric motors and thus the flight / propulsion of the aircraft is generated by the fuel cells. The electrically powered aircraft thus contains a fuel cell arrangement with fuel cells, which in turn are cooled by the cooling arrangement. In this application in particular, the cooling system according to the invention is particularly advantageous because of its pressure control/regulating properties.

The object of the invention is also achieved by an aircraft according to patent claim 14. This contains the object arrangement described above in the form of the cooling arrangement with the fuel cell arrangement as the object. As described above, the aircraft is powered in flight by the electrical energy obtained from the fuel cells.

The aircraft and at least some of its possible embodiments and the respective advantages have already been explained in connection with the fluid arrangement according to the invention and the object arrangement according to the invention.

The object of the invention is also achieved by a method according to patent claim 15. This is used to operate the fluid arrangement according to the invention or the object arrangement according to the invention or the aircraft according to the invention. In the method, the discharge valve is opened in order to conduct fluid via the discharge line from the discharge opening from the fluid circuit to the equalizing tank in order to lower the current discharge pressure, and/or the supply valve is opened in order to convey fluid via the supply line from the equalizing tank to the supply opening and into the fluid circuit to increase the current supply pressure.

The method and at least some of its possible embodiments and the respective advantages have already been explained in connection with the fluid arrangement according to the invention, the object arrangement according to the invention and the aircraft according to the invention.

The invention is based on the following findings, observations and considerations and also has the following embodiments. The embodiments are sometimes also referred to as “the invention” for the sake of simplicity. The embodiments can also contain parts or combinations of the above-mentioned embodiments or correspond to them and/or optionally also include embodiments that have not been mentioned before.

The invention is based on the following observation: the operation of fuel cells for the electrified propulsion of aircraft requires the fuel cells to be cooled. An incompressible fluid / thermal fluid is used for cooling. Due to temperature fluctuations, there are thermally induced pressure fluctuations in the system, i.e. within the cooling system / cooling circuit. These have to be compensated in a targeted manner in order not to exceed a maximum pressure at the inlet of the fuel cells in the present case. The pressure at the inlet of fuel cell stacks, for example, must not exceed 2.5 bar in this case. The cooled stacks are only designed for this maximum pressure. At the same time, it should be prevented that the pressure drops so far that cavitation occurs in the pumps. The pressure at the inlet of the pumps that are used to cool the fuel cell stacks must not fall below a pressure of around 1.5 bar, for example, in order to avoid cavitation. As a result, pressure control within a defined range is required. The pressure must therefore be kept within a specified range

One possibility would be to use an expansion tank that communicates permanently with the cooling circuit, comparable to the one from DE 10 2017 001 447 A1 to use, ie to use, which is charged with an inert gas (e.g. nitrogen) as a preload volume at a corresponding pressure level in order to raise the pressure in the system. For example, air cannot be used due to incompatibility with the coolant (fluid). For this purpose, the preload volume could be realized with nitrogen and a nitrogen bottle connected to the preload volume with a pressure reducer could be used. A reservoir / pressure tank / gas bottle for nitrogen is available for pressurizing the pressure equalization tank, for example using a pressure reducer. The pressure reducer would be set to the desired setpoint of a preload pressure in the preload volume. If the pressure in the system (pressure in the cooling circuit and thus preload pressure in the preload volume) increases and the nitrogen reacts with an excessive pressure increase, the nitrogen would be released from the preload volume via a valve, e.g. overpressure valve, if necessary. If, on the other hand, the pressure in the system decreases, the less nitrogen could no longer provide the required pressure, the nitrogen in the preload volume would be refilled from the nitrogen bottle via the pressure reducer. Nitrogen from the nitrogen bottle is therefore consumed by constant pressure changes in the cooling circuit due to fluctuations in the temperature level of the fluid. It is therefore necessary to carry an additional pressure vessel to provide an inert gas (nitrogen). The pressure tank / nitrogen bottle must therefore be replaced or refilled after a certain period of time or at regular intervals.

The basic idea of the invention is to shift the mass of the thermal fluid for pressure control from the cooling system to an adjacent system (compensating arrangement or compensating tank) and vice versa. This adjacent system represents a closed system when the valves (discharge / supply valve) to the cooling system (cooling circuit) are not open. A valve (supply valve) can be opened to selectively increase the pressure at the inlet to the combustion engine to raise fabric cell stacks. Another valve (discharge valve) can be opened to specifically reduce the pressure at the inlet of the fuel cell stack. The mass transfer (fluid from the cooling circuit to the expansion tank and vice versa) takes place in the open valve positions due to the pressure differences (discharge pressure / preload pressure / supply pressure) with reference to the adjacent system.

The coolant (fluid) is shifted as required from the cooling system (cooling circuit) to an adjacent area that is closed off from the cooling system (expansion tank) and into the cooling system from an adjacent area that is closed off from the cooling system for pressure control (measurement pressure) of the system at selected points of the Systems (measuring points or known pressure-correlated points, e.g. inlet of the fuel cells / pump inlet) exclusively using the existing system pressures and using shut-off devices (shut-off / supply valve) or throttle devices (automatic valve). As a result, no additional rotating or moving parts are required to generate pressure.

The idea of the invention is also the use of different pressures at different points in the fluid circuit, placement of the discharge and supply opening there, and the combination with the use of separate supply and discharge lines, i.e. use of the pressure drop between discharge and supply opening and the series connection from discharge line - expansion tank - supply line.

The (main) pressure control takes place without a permanently communicating pressure vessel, which would have to be refilled or replaced at regular intervals. The (main) pressure control takes place without additional components for increasing the pressure, such as a nitrogen bottle.

The invention is generally suitable for all corresponding fluid circuits, not just for cooling circuits, and is at best explained here on the basis of cooling circuits as representative.

According to the invention, the pressure is regulated within a fluid circuit, in particular a cooling system for hydrogen-powered aircraft, exclusively by using the existing system pressures via the targeted switching of valves. In particular, a method for pressure control within a cooling system for hydrogen-powered aircraft results. In particular, the system pressure of a cooling system for hydrogen-powered aircraft is regulated by targeted thermal fluid mass displacement using the existing system pressures.

According to the invention, there is a comparatively small reservoir; no additional rotating / moving parts for pressurization, recourse to existing sub-components (valves), simple design, low costs, small, light components (no compressed gas cylinder) and long service lives, since e.g. solenoid valves with switching cycles > 100,000,000 are available.

The result is the cooling of hydrogen-electric systems for air traffic and a method for pressure control within a cooling system for fuel cell-powered aircraft without additional pressure vessels that have to be replaced / refilled at regular intervals.

• 1 ein Flugzeug mit Brennstoffzellen, die von einer Fluidanordnung gekühlt werden,
• 2 eine zu 1 alternative Fluidanordnung mit Automatikventil,
• 3 eine zu 1 alternative Fluidanordnung mit alternativer Zufuhröffnung,
• 4 eine zu 1 alternative Fluidanordnung mit zwei Messstellen für Messdrücke,
• 5 Druckverhältnisse in der Fluidanordnung.

Further features, effects and advantages of the invention result from the following description of a preferred exemplary embodiment of the invention and the attached figures. Show, each in a schematic principle sketch:

• 1 an aircraft with fuel cells cooled by a fluid assembly,
• 2 one to 1 alternative fluid arrangement with automatic valve,
• 3 one to 1 alternative fluid arrangement with alternative feed opening,
• 4 one to 1 alternative fluid arrangement with two measuring points for measuring pressures,
• 5 Pressure conditions in the fluid arrangement.

1 shows a detail of an aircraft 2, not shown. This has an electric drive, not shown, so it is powered by electric energy instead of fossil fuels for flying. The electrical energy is obtained from an object 4 in the form of a fuel cell arrangement, which contains three fuel cells 5 here. During operation, the fuel cells have to be cooled.

The aircraft 2 therefore contains an object arrangement 6; This includes the object 4 and a fluid arrangement 8 in the form of a cooling arrangement for cooling the object 4, here the fuel cells 5 shown.

The fluid arrangement 8 contains a fluid circuit 10, here a cooling circuit for the actual cooling of the object 4. During operation, the cooling circuit 10 has an incompressible fluid 12 (medium) flowing through it, which is 1 only indicated and only within an expansion tank 16 is explicitly shown. Otherwise, a flow of the fluid 12 in the fluid circuit 10 is indicated by arrows 14 . The fluid 12 is part of the fluid arrangement 8. The fluid 12 causes the actual cooling of the object 4 in that it absorbs heat from this or the fuel cells 5 as it flows through/past and within the fluid circuit 10 on a cooler 11 in the form of a cooling system returns. Three pumps 15 in the fluid circuit 10 are used to maintain the circulatory flow of the fluid 12 in the direction of the arrows 14.

Since there are a total of three fuel cells 5 in the object arrangement 6 , the fluid circuit 10 is divided into three parallel branches at a filter mixer 17 , each of which contains one of the three fuel cells 5 and pumps 15 . The three branches reunite between pumps 15 and cooler 11 . In the following, the invention is explained as an example using only one of the three branches. Non-return valves 38, which are not explained in detail here, ensure, among other things, that the direction of flow of the fluid 12 is maintained in the direction of the arrows 14.

Due to changes in the overall temperature level of the fluid 12, it expands when heated and contracts when cooled, i.e. the total volume VF of the fluid 12 varies. The total volume VF of the fluid 12 refers to the volume that the fluid 12 would assume without being forced, i.e. for example at atmospheric pressure or a specific pressure p (pressure distribution/pressure level). In fact, however, only the total volume of the cooling circuit 10 (this is always assumed to be constant in the present case) is available for the fluid 12 . The expansion (“desired” by the fluid) leads (if this cannot take place due to the external restriction/constraint) to a pressure increase of the pressure p of the fluid 12 in the fluid circuit 10.

In order to compensate for this change in volume in the fluid 12 , a compensation arrangement 18 (framed in dashed lines) is connected to the cooling circuit 10 . This contains the equalizing tank 16 and a discharge line 20 which leads from a discharge opening 22 of the fluid circuit 10 to the equalizing tank 16 . The discharge line 20 contains an electrically controllable discharge valve 24 for releasing the discharge line 20 so that fluid 12 can flow through it. During operation, the fluid 12 has a current discharge pressure pA at the discharge opening 22 .

The equalization assembly 18 further includes a supply line 26 leading from the equalization tank 16 to three supply ports 28 of the fluid circuit 10, the supply line 26 including an electrically controllable supply valve 30 for releasing the supply line 26 to allow fluid 12 to flow therethrough. During operation, the fluid 12 has a current supply pressure pZ at the supply opening 28 which is lower than the discharge pressure pA.

The expansion tank 16 can alternatively be connected directly to the fluid circuit 10, i.e. the supply line 26 and/or the discharge line 20 degenerate into zero lines and between the fluid circuit 10 and the expansion tank 16 only the discharge valve 24 and/or the supply valve 30 are arranged.

The expansion tank 16 has a constant tank volume VB. When the fluid arrangement 8 is in operation, the compensating tank 16 is partially filled with a current compensating volume VA of the fluid 12 . Otherwise it is filled with a compressible preload element 32, which has a current preload volume VV and a current preload pressure pV.

The sum of the compensation volume VA and the preload volume VV is always constant and equal to the container volume VB. That is, fluid 12 and biasing element 32 fill the reservoir 16 completely. A part of the filling of the expansion tank 16 consists of a variable amount (current compensation volume VA) of fluid 12, the remaining part of the filling consists of the compressible prestressing element 32. The prestressing element 32 is here a gas bubble made of loose gas 34, alternatively a compressible elastic object 36, here an elastic bladder filled with gas. The pretensioning element 32 is also part of the compensating arrangement 18.

The compensating arrangement 18 (like the fluid circuit 10) is designed to be closed in terms of pressure. A print area 35 (see 5 ) of the preload pressure pV (all preload pressures pV that the preload element 32 can assume in all conceivable regular operating states of the fluid arrangement 8) is selected in such a way that the current preload pressure pV for all intended operating states of the fluid arrangement 8 is always between the current (lower) supply pressure pZ and the current (higher) discharge pressure pA.

In the event of an increase in the total volume VF (if this could expand unhindered) of the fluid 12 in the fluid circuit 10 due to an increase in temperature (total temperature level of all parts of the fluid 12), an additional volume proportion of the fluid 12 that arises in this way is discharged via the discharge line 20 into the expansion tank 16 . This is done by opening the discharge valve 24. The compensating volume VA in the compensating tank 16 increases, the preload element 32 is compressed, and the preload pressure pV increases. The Fluid 12 flows in the direction of arrow 37 because of the pressure drop between the preload pressure pV and the higher discharge pressure pA. After a sufficient quantity of fluid 12 has been removed from the fluid circuit 10, so that the pressure p and the discharge pressure pA of the fluid 12 in the fluid circuit 10 again has dropped as desired, the discharge valve 24 is closed again.

On the other hand, when the temperature decreases and the volume in the fluid 12 decreases, the supply valve 30 is opened. A corresponding quantity of fluid 12 thus flows back from the expansion tank 16 through the supply line 26 into the cooling circuit 10 . The compensating volume VA in the compensating tank 16 decreases, the prestressing element 32 expands, and the prestressing pressure pV falls. The fluid 12 flows in the direction of the arrow 39 because of the pressure drop between the preload pressure pV and the lower supply pressure pZ. After a sufficient quantity of fluid 12 has been introduced into the fluid circuit 10, so that the pressure p and supply pressure pZ of the fluid 12 in the fluid circuit 10 has risen again as desired, the supply valve 30 is closed again.

The pressure p is controlled as follows using a control device 40, which is only indicated symbolically here: The setpoint variable/value for the pressure p is the (upstream) inlet pressure of the fluid 12 at the fuel cell 5. This should be a maximum of 2.5 bar. The pressure p is therefore determined at a measuring point 42 in the fluid circuit 10 as the current measured pressure pM, here at the filter mixer 17 since the pressure p of the fluid 12 there corresponds to the pressure at the inlet of the fuel cell 5 . The control device 40 contains an input 44 for the measured pressure pM. The control device 40 is connected to the discharge valve 24 and the feed valve 30 in order to electrically actuate them. If the measured pressure pM rises above 2.5 bar, the control device 40 opens the discharge valve 24 until the measured pressure pM is again below 2.5 bar.

In other words: If the pressure in the filter-mixer 17, which ideally corresponds to the pressure at the inlet of the fuel cells 5, is greater than 2.5 bar, the discharge valve 24 between the outlet of the pumps 15 and the inlet of the expansion tank 16 (also " active reservoir") is opened. If necessary, an offset (upper reserve pressure pRO, see below) can also be implemented, e.g. to reduce safety against overshooting. Fluid 12 or liquid is then transferred from the fluid circuit 10 into the expansion tank 16 as an active reservoir, which is separated from the rest of the system (fluid circuit 10) after the drain and supply valves 24, 30 have been closed.

Another target value for the pressure p is the upstream inlet pressure at the pumps 15, which must not fall below 1.5 bar in order to avoid cavitation in the pumps 15. This pressure is equal to the supply pressure pZ at the supply opening 28. However, this pressure is not determined directly by measuring at the corresponding location.

Instead, it is known from the system design of the fluid arrangement 8 that the pressure at the inlet of the pumps 15 is about 0.5 bar lower than at the filter-mixer 17. This pressure difference of 0.5 bar was calculated taking into account the pressure drops from the inlet to the fuel cells 5 determined empirically up to the inlet of the pumps 15 (depending on the NPSH (Net Positive Suction Head) of the pumps 15, taking into account the operating parameters such as speeds, density/viscosity of the fluid 12 etc.). This results in a minimum value of 2.0 bar for the measured pressure pM at the measuring point 42. If the measured pressure pM falls below 2.0 bar, the control device 40 opens the supply valve 30 until the measured pressure pM of the fluid 12 has risen accordingly. The inlet pressure at the pumps can then be assumed to be 1.5 bar.

In other words: If the pressure in the filter-mixer 17, which ideally corresponds to the pressure at the inlet of the fuel cells 5, falls below 2.0 bar, the supply valve 30 between the expansion tank 16 (active reservoir) and the suction gas lines of the pumps 15 ( there are the feed openings 28) open. If necessary, an offset (lower reserve pressure pRU, see below) can also be implemented, e.g. to reduce safety against overshooting. Fluid 12 or liquid is then shifted from the expansion tank 16 in the form of the active reservoir into the fluid circuit 10 .

The control device 40 thus brings or maintains the current measurement pressure pM by draining and/or supplying fluid 12 into the fluid circuit 10 in a permissible range of here 2.0 to 2.5 bar. The current measurement pressure pM is correlated with the pressure p of the fluid 12 at the upstream inlet of the object 4 or is this pressure. It is also correlated with the pressure at the upstream inlet of the pump 15, here over an estimated pressure difference of 0.5 bar.

In the compensating arrangement 18 there are thus two actively controlled valves (discharge/supply valve 24, 30) with their valve positions as manipulated variables (open/closed, optionally infinitely variable).

The prerequisite for the procedure explained above is the following: the pressure at the pump outlet and thus at the discharge opening 22 (discharge pressure pA) is always greater than the pressure in the active reservoir, So the expansion tank 16, namely the preload pressure pV. In addition, this pressure in the expansion tank 16 is always greater than the pressure at the pump inlet, namely the supply pressure pZ at the supply opening 28 while avoiding cavitation.

The following boundary conditions apply here: for all specified operating conditions of the pumps 15, it applies that their outlet pressure is never less than 6.5 bar, so the discharge pressure pA is never less than 6.5 bar. The pump inlet pressure is always kept constant at 1.5 bar, so the supply pressure pZ is always a maximum of 1.5 bar.

In the present case, the pressure difference between the discharge pressure pA and the preload pressure pV and between this and the supply pressure pZ should always not drop below 0.5 bar. This is guaranteed with an upper and lower reserve pressure pRU and pRO of 0.5 bar. Therefore, the preload pressure pV must always be kept above the current or constant and thus above a maximum value of the supply pressure pZ of 1.5 bar plus a lower reserve pressure pRU of 0.5 bar, i.e. above 2.0 bar. In addition, the preload pressure pV must always be kept below the current and thus below a minimum value of the discharge pressure pA of 6.5 bar minus an upper reserve pressure pRO of also 0.5 bar, i.e. below 6.0 bar.

The active reservoir in the form of the expansion tank 16 must therefore be designed in such a way that it keeps this pressure range 35 between 2.0 bar and 6.0 bar under the given thermal boundary conditions (−55° C. to 120° C. for the fluid 12). In the present case, this results in a container volume VB of the compensating container 16 of 45 l in total, i.e. for fluid 12 (compensating volume VA) and preload element 32 (preload volume VV). It was taken into account that in the stated temperature range the fluid 12 increases from its minimum volume (at -55° C.) by at most an additional volume VZ of 22 liters to its maximum volume Vmax (at 120° C.). The compensating volume VA must therefore be at least 22 liters plus a minimum reserve of e.g. 1-3, here 2 liters of fluid 12, which should always remain in the compensating tank 16. Proceeding from this, the container volume VB is selected such that with the given material/gas 34 of the prestressing element 32, this generates the desired prestressing pressures pV when compressed to the respectively remaining prestressing volume VV. In this respect, the pressure level of the preload pressure pV is or is selected by selecting the container volume VB and the quantity and type of the preload element 32 .

In this respect, the following applies: The tank volume VB is dimensioned as follows: If the additional volume VZ of fluid 12 is completely contained in the equalizing tank 16, the preload element 32 has at most a specified minimum value of 6.5 bar of the discharge pressure pA minus the upper reserve pressure pRO of 0 as the preload pressure pV. 5 bar, but if there is no additional volume VZ of fluid 12 in the equalizing tank 16 (but only the minimum reserve of 2 liters), the preload element 32 has at least an intended maximum value of 1.5 bar of the supply pressure pZ plus the lower reserve pressure pRU as the preload pressure pV 0.5 bar.

5 shows the pressure conditions just illustrated.

On the fluid circuit 10 in 1 In addition, another passive reservoir 46 in the form of a customary compensation tank is permanently connected in fluidic communication. This ensures a weakening of possible pressure pulse actions of the pressure p in the fluid 12.

2 shows an alternative embodiment of the fluid assembly 8 to 1 . Here the discharge valve 30 is an automatic valve 48, here in the form of a pressure reducer. This is set to an automatic pressure pT of 1.5 bar. As soon as the supply pressure pZ at the supply opening 28 falls below 1.5 bar, the automatic valve 48 opens so that the fluid 12 flows out of the expansion tank 16 through the supply line 26 and the supply opening 28 in the direction of the arrow 39 into the fluid circuit 10; The pressure p in the fluid 12 increases due to the increase in volume or mass of fluid 12 in the fluid circuit 10. As soon as the supply pressure pZ at the supply opening 28 exceeds 1.5 bar, the automatic valve 48 closes the controller 40. Due to the greater pressure drop across the automatic valve 48 compared to 1 However, a larger lower reserve pressure pRU of 1.0 bar must be provided for the preload pressure pV. The preload pressure must therefore always be kept above 2.5 bar. According to the considerations above, this leads to a larger reservoir volume VB of the equalizing reservoir 16. 5 shows the value in round brackets.

3 shows a further alternative embodiment of the fluid arrangement 8 to 1 . The supply opening 28 is here on or in the area of the filter mixer 17. This results in a slightly shorter dead time for controlling or regulating the pressure p in the fluid 12, since the "correction point", ie the inlet point for fluid 12 in the Fluid circuit 10 in the form of the supply opening 28 is located at the measuring point 42 . The pressure level at the supply port However, calculation 28 is higher than in 1 , since, viewed from the pump inlet, the pressure drop across the fuel cells 5 of an estimated 0.5 bar is added. The supply pressure pZ to be set is not 1.5 bar, but 2 bar. According to the explanations 2 this leads to an inevitably higher lower limit value of the preload pressure pV and thus again to an increased tank volume VB. 5 shows the value in square brackets.

4 finally another alternative embodiment of the fluid arrangement 8 is shown in FIG 1 . Here, in addition to the measuring point 42 on the filter mixer 17 for a measured pressure pM1, there is a further measuring point 42 for a measured pressure pM2 on the supply line 26, which in this sense corresponds to the supply opening 28. Two linked setpoint values (both measured pressures pM1,2 at both measuring points 42) are therefore processed in the control device 40, namely the actual pump inlet pressure (measured pressure pM2) and the inlet pressure (measured pressure pM1) at the fuel cell 5. This enables direct regulation of the Pump inlet pressure, the inlet pressure at the fuel cell 5 is dominant. However, this results in a higher complexity of the control device 40.

Reference List

2

Airplane

4

object

5

fuel cell

6

object arrangement

8th

fluid arrangement

10

fluid circuit

11

cooler

12

Fluid

14

Arrow

15

pump

16

surge tank

17

filter mixer

18

balancing arrangement

20

discharge line

22

discharge opening

24

discharge valve

26

supply line

28

feed opening

30

supply valve

32

biasing element

34

gas

35

print area

36

Object

37

Arrow

38

check valve

39

Arrow

40

control device

42

measuring point

44

Entry

46

reservoir (passive)

48

automatic valve

vf

total volume (fluid)

vb

container volume

v.a

Compensation Volume (Fluid)

vv

bias volume

vz

additional volume (fluid)

p

Print

pA

discharge pressure

pZ

supply pressure

pv

preload pressure

pM

measurement pressure

pT

automatic printing

pRU

reserve pressure below

Per

reserve pressure above

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102017001447 A1 [0002, 0026, 0052]

Claims (15)

fluid arrangement (8), - with a fluid circuit (10) through which an incompressible fluid (12) circulates during operation, - with the fluid (12), which has a total volume (VF) that varies with its temperature level, - with a compensation arrangement (18): - With an equalization tank (16) having a constant tank volume (VB), which during operation is partially filled with an equalization volume (VA) of the fluid (12) and otherwise with a preload volume (VV) of a compressible preload element (32) that has a current preload pressure (pV), - with a discharge line (20) which leads from a discharge opening (22) of the fluid circuit (10) to the expansion tank (16), the discharge line (20) containing a discharge valve (26) for releasing the discharge line (20), the fluid (12) has a current discharge pressure (pA) at the discharge opening (22) during operation, - With a supply line (26) which leads from the expansion tank (16) to a supply opening (28) of the fluid circuit (10), the supply line (26) containing a supply valve (30) for releasing the supply line (26), the fluid (12) has a current supply pressure (pZ) at the supply opening (28) during operation, which is lower than the discharge pressure (pA), - the compensating arrangement (18) being completed in terms of printing technology, - wherein a pressure range of the preload pressure (pV) is selected such that the current preload pressure (pV) for all intended operating states of the fluid arrangement (8) is always between the current supply pressure (pZ) and the current discharge pressure (pA). Fluid arrangement (8) after claim 1 , characterized in that the pressure range of the prestressing pressure (pV) is selected by selecting the container volume (VB) and the quantity and type of the prestressing element (32). Fluid arrangement (8) according to one of the preceding claims, characterized in that the pressure range of the preload pressure (pV) is selected such that the current preload pressure (pV) for all intended operating states of the fluid arrangement (8) is always above the current supply pressure (pZ) plus a lower reserve pressure (pRU) and/or below the current discharge pressure (pA) minus an upper reserve pressure (pRO). Fluid arrangement (8) according to one of the preceding claims, characterized in that the fluid circuit (10) has a pump (15) conveying the fluid (12) through the fluid circuit (10) during operation and an object (4 ) contains, and the discharge opening (22) is arranged downstream of the pump (15) between the latter and the object (4) and the supply opening (28) is arranged upstream of the pump (15) between the pump (15) and the object (4). Fluid arrangement (8) according to one of the preceding claims, characterized in that the supply valve (30) is an automatic valve (48) which is set in the direction of the supply opening (28) to a predeterminable automatic pressure (pT) below which it automatically opens and when it is exceeded it closes automatically. Fluid arrangement (8) according to one of the preceding claims, characterized in that - the fluid arrangement (8) contains a control device (40) which has an input (44) for a current measurement pressure (pM) at a measurement point (42) in the fluid circuit (10 ), - wherein the control device (40) is connected to the discharge valve (24) and/or the supply valve (30) and is set up to, if necessary and optionally: - close the discharge valve (24) and/or the supply valve (30). open in order to bring at least one of the current measurement pressures (pM) into a respective permissible range or to keep it in this range by removing and/or supplying fluid (12) into the fluid circuit (10). Fluid arrangement (8) after claim 6 , characterized in that the fluid arrangement (8) contains an object (4) arranged in the fluid circuit (10) and/or a pump (15), with at least one of the current measurement pressures (pM) being related to the pressure (p) of the fluid (12 ) at an upstream inlet of the object (4) or the pump (15). Fluid arrangement (8) according to one of the preceding claims, characterized in that - in a specified temperature range, the varying total volume (VF) of the fluid (12) lies between a minimum volume and a maximum volume which is larger by an additional volume (VZ), - the container volume (VB ) is dimensioned as follows: - if the additional volume (VZ) of fluid (12) is completely contained in the expansion tank (16), the preload element (32) has at most a specified minimum value of the discharge pressure (pA) as preload pressure (pV), - if If there is no additional volume (VZ) of fluid (12) in the expansion tank (16), the prestressing element (32) has little as the prestressing pressure (pV). tens an intended maximum value of the supply pressure (pZ). Fluid arrangement (8) after claim 8 , characterized in that the prestressing element (32) has at most one specified minimum value of the discharge pressure (pA) minus an upper reserve pressure (pRO) as the prestressing pressure (pV), and/or the prestressing element (32) has at least one specified maximum value as the prestressing pressure (pV). the supply pressure (pZ) plus a lower reserve pressure (pRU). Fluid arrangement (8) according to any one of the preceding claims, characterized in that the biasing element (32) is a compressible loose gas (34) or a compressible elastic object (36). Fluid arrangement (8) according to one of the preceding claims, characterized in that the fluid arrangement (8) is a cooling arrangement for cooling an object (4), the fluid circuit (10) being a cooling circuit for the object (4) to be cooled, and that Fluid (12) is a cooling of the object (4) causing fluid. Object arrangement (6), with the fluid arrangement (8) according to one of the preceding claims, and with an object (4) which is contained in the fluid circuit (10) and through which the fluid (12) flows during operation. Object arrangement (6) according to claim 12 combined with claim 11 , characterized in that the object arrangement (6) is a cooling arrangement and the object (4) is a fuel cell arrangement which contains at least one fuel cell (5) to be cooled by the cooling arrangement (). Aircraft (2), with the object arrangement (6) after Claim 13 , The aircraft (2) being powered in flight by the electrical energy obtained from the fuel cells (5). Method for operating a fluid arrangement (8) according to one of Claims 1 until 11 or an object arrangement (6) according to one of Claims 12 until 13 or an airplane (2) after Claim 14 , in which: - the discharge valve (24) is opened in order to conduct fluid (12) via the discharge line (20) from the discharge opening (22) out of the fluid circuit (10) to the expansion tank (16) in order to increase the current discharge pressure (pA ) and/or - the supply valve (30) is opened in order to lead fluid (12) via the supply line (26) from the expansion tank (16) to the supply opening (28) and into the fluid circuit (10) in order to to increase the current supply pressure (pZ).

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