EP4300008A1 - Passive dual-phase space cooling system - Google Patents

Abstract

The present invention relates to a passive cooling system (1) for two-phase cooling of a room (100), with a closed passive two-phase cooling circuit (2) for a two-phase heat transfer fluid (3, 3a, 3b) circulating therein during operation, the two-phase cooling circuit ( 2) has at least one evaporator (10) for arrangement in the space to be cooled (100) and at least one condenser (20) for arrangement outside the space to be cooled (100), which has at least one feed line (30) and at least one return line ( 40) are connected to each other in the circuit (2). To adjust the boiling temperature of the heat transfer fluid (3, 3a, 3b) in the cooling system (1), the two-phase cooling circuit (2) further has at least one pressure adjustment container (50) in fluid communication with the at least one return line (40) for storing liquid heat transfer fluid (3a ), which is designed such that during operation the heat transfer fluid (3a) can be stored in the at least one pressure adjustment container (50) under a variably adjustable fluid pressure.

Description

FIELD OF THE INVENTION

The present invention relates to a passive cooling system for cooling a room, which has a closed passive two-phase cooling circuit for a two-phase heat transfer fluid circulating therein during operation.

BACKGROUND OF THE INVENTION

While the cooling of rooms with an external energy supply is usually technically manageable, the cooling of rooms in locations remote from the power grid or the emergency maintenance of room cooling in the event of a power failure, in particular the cooling of rooms with critical infrastructure and/or in a highly regulated environment , sometimes challenging. Examples of rooms with critical infrastructure or rooms in a highly regulated environment include server rooms or control and electrical engineering rooms in nuclear plants. The critical infrastructure itself is usually protected against power failures by an independent power supply. However, the power capacity of independent power supplies is limited and is often not sufficient to actively dissipate the heat load induced by the infrastructure. Cooling systems with passive cooling circuits are of particular interest for these applications. Passive cooling circuits are characterized by the fact that the transport of the heat transfer fluid within the circuit is effected exclusively by the prevailing temperature differences between the assigned heat source and heat sink, so that passive cooling systems without active means of influencing flow, such as electric pumps or the like, or only with minimally active ones resources.

Two-phase cooling systems, in which the heat transfer fluid (also called energy transfer fluid or refrigerant or coolant) carried in a circuit between an evaporator and a condenser undergoes a phase transition from liquid to gaseous and back again, are fundamentally from the Known from the prior art, for example DE 10 2014 205 086 B3 . Compared to single-phase circulation systems, they enable high heat transport rates with low driving temperature differences.

The effectiveness of two-phase systems, in particular passive two-phase systems, depends crucially on whether the heat transfer fluid's boiling temperature is suitably matched to the combination of temperature and pressure conditions in the cooling circuit, so that the desired temperatures are achieved in the evaporator and condenser Evaporation and condensation processes can actually take place. At the same time, the boiling temperature of the heat transfer fluid must also meet application-related specifications, such as specifying a temperature at which cooling should begin effectively. However, heat transfer fluids that have appropriate boiling temperatures for a specific application while meeting any technical safety and environmental requirements are not always available.

The invention is therefore based on the object of further developing a passive two-phase room cooling system of the type mentioned in such a way that the system can be better adapted to application-related specifications in terms of temperature with a simple and cost-effective structure.

This task is solved by the passive cooling system according to claim 1. Advantageous embodiments of the cooling system are the subject of the dependent claims.

SUMMARY OF THE INVENTION

According to the present invention, a passive cooling system for cooling a room, in particular a room with an electrically induced heat load, is proposed, which has a closed passive two-phase cooling circuit for a two-phase heat transfer fluid circulating therein during operation. On the one hand, the two-phase cooling circuit includes at least one evaporator Arrangement in the room to be cooled, which is designed to evaporate liquid heat transfer fluid from the room while absorbing thermal energy, and on the other hand at least one capacitor for arrangement outside the room to be cooled, which is designed to evaporate vaporous heat transfer fluid while releasing thermal energy a heat sink outside the room, in particular to the environment outside the room, to condense. The two-phase cooling circuit further comprises at least one flow line fluidly connecting the at least one evaporator to the at least one capacitor for transporting evaporated heat transfer fluid from the at least one evaporator to the at least one condenser, as well as at least one fluidly connecting the at least one capacitor to the at least one evaporator Return line for transporting condensed heat transfer fluid from the at least one condenser to the at least one evaporator. According to the invention, the two-phase cooling circuit further has at least one pressure adjustment container in fluid communication with the at least one return line for storing liquid heat transfer fluid, wherein the at least one pressure adjustment container for adjusting the boiling temperature of the heat transfer fluid in the cooling system is designed such that during operation the heat transfer fluid in the at least one pressure adjustment container can be stored under a variably adjustable fluid pressure.

According to the invention, it was recognized that passive two-phase room cooling systems can be technically very easily adapted to application-related specifications by variable adjustment of the fluid pressure within the cooling circuit with regard to the temperature at which cooling should begin effectively. Because of the variable adjustability of the fluid pressure within the cooling circuit, the operating point of the two-phase heat transfer fluid can be adjusted variably along its saturation vapor pressure curve, so that the heat transfer fluid evaporates or condenses either at higher or low temperatures. If it is desired for a specific application that the cooling effect of the cooling system should begin at a room temperature of 20 ° C, for example, the boiling point of a heat transfer fluid intended for the application is at a higher temperature under normal pressure (atmospheric pressure), for example at 26°C, the effective boiling temperature of the heat transfer fluid in the closed two-phase cooling circuit can be reduced to 20°C in the system by appropriately setting a negative pressure, ie a pressure below atmospheric pressure. Conversely, the effective boiling temperature of the heat transfer fluid in the closed two-phase cooling circuit can be increased by appropriately setting an overpressure, ie by increasing the fluid pressure, if it is desired for a specific application that cooling should only start at a temperature that is above the temperature the boiling point of the heat transfer fluid intended for the application is at normal pressure (atmospheric pressure). To adjust the fluid pressure, a pressure adjustment container is proposed according to the present invention, which is in fluid communication with the return line and which is designed such that liquid heat transfer fluid can be stored therein during operation under a variably adjustable fluid pressure.

By variable adjustment of the fluid pressure, the amount of heat transfer fluid in the evaporator, the condenser, the flow line and the return line can also be adjusted. Thus, by increasing the pressure on the heat transfer fluid in the pressure adjustment container, heat transfer fluid can be discharged from the pressure adjustment container and introduced into the remaining parts of the closed two-phase cooling circuit. Conversely, by reducing the pressure on the heat transfer fluid in the pressure adjustment container, heat transfer fluid can be removed from the remaining parts of the closed two-phase cooling circuit and received in the pressure adjustment container. In this way - as discussed further below - in particular the filling level of the liquid heat transfer fluid in the evaporator can be variably adjusted, in particular variably fine-adjusted.

In principle, various configurations of the pressure adjustment container according to the invention are conceivable in order to adjust the boiling temperature of the heat transfer fluid in the cooling system.

According to a first advantageous embodiment of the invention, the pressure adjustment container can be designed as a membrane storage container. Included the membrane storage container has a flexible pressure membrane which divides an interior of the pressure adjustment container into a first chamber and a second chamber, the first chamber being designed to store liquid heat transfer fluid and being in fluid communication with the return line, while in the second chamber a working fluid, in particular a gas, which can be stored or stored with a variably adjustable pressure. For this purpose, the pressure adjustment container can have a filling valve for filling or emptying the second chamber with working fluid. As a result, the pressure of the working fluid in the second chamber can be variably adjusted by varying the filling quantity of the second chamber with the working fluid. The pressure of the working fluid in the second chamber is in turn transferred via the pressure membrane to the fluid pressure of the heat transfer fluid in the cooling circuit, so that as a result the fluid pressure of the heat transfer fluid in the cooling system and thus the boiling temperature of the heat transfer fluid are variable via the variably adjustable pressure of the working fluid in the second chamber are adjustable.

The flexible pressure membrane preferably consists of a flexible, elastic plastic or rubber. The pressure membrane is designed in such a way that the working fluid and the heat transfer fluid are separated from one another in a fluid-tight manner.

In order to be able to set the pressure of the working fluid in the second chamber to a desired value, the pressure adjustment container can further have a pressure measuring device, in particular a pressure gauge, for determining the pressure of the working fluid in the second chamber. In particular, it can be provided that the pressure measuring device is operatively connected to the filling valve via feedback in order to set the boiling temperature of the heat transfer fluid in a controlled manner in a control circuit. For this purpose, the filling valve can be operated remotely.

According to a second advantageous embodiment of the invention, the pressure adjustment container can be designed as a bladder storage container which has a container housing and a storage bladder accommodated in the container housing. According to a first embodiment of the bladder storage container, in In an interior of the storage bladder, a working fluid, in particular a gas, can be stored or stored with a variably adjustable pressure, whereas liquid heat transfer fluid can be stored in a gap between an outside of the storage bubble and an inside of the container housing, the gap being in fluid communication with the return line. According to an alternative second embodiment of the bladder storage container, liquid heat transfer fluid can be stored in an interior of the storage bladder, the interior of the storage bladder being in fluid communication with the return line, while in a space between an outside of the storage bladder and an inside of the container housing a working fluid, in particular a gas , can be stored or stored with variably adjustable pressure.

Analogous to the pressure adjustment container, the bladder storage container can also have a filling valve, in particular a remotely operated filling valve for filling or emptying the interior of the storage bladder or alternatively for filling or emptying the gap with the working fluid, in order to thus use the fluid stored in the interior or in the gap Amount of working fluid to variably adjust the fluid pressure of the heat transfer fluid in the cooling system and thus the boiling temperature of the heat transfer fluid. Similar to the pressure membrane, the storage bladder can be made of a flexible, elastic plastic or rubber. The storage bladder is designed in such a way that the working fluid and the heat transfer fluid are separated from one another in a fluid-tight manner.

According to a third advantageous embodiment of the invention, the pressure adjustment container can be designed as a piston storage container, the piston storage container having a cylinder container housing and a piston mounted in a sealing manner relative to an inner wall of the cylinder container housing. The piston is slidably mounted in the cylinder container housing along a cylinder longitudinal axis of the cylinder container housing and divides an interior of the cylinder container housing into a first chamber for storing liquid heat transfer fluid, which is in fluid communication with the return line, and a second chamber in which a working fluid, in particular a gas, can be stored or stored with a variably adjustable pressure. This is where the piston is sealed in the cylinder container housing so that the working fluid and the heat transfer fluid are separated from each other in a fluid-tight manner. The piston storage container can also have a filling valve, in particular a remotely operated filling valve for filling or emptying the second chamber with working fluid, in order to variably adjust the pressure of the working fluid in the second chamber by varying the filling quantity of the second chamber, which in turn is mediated via the piston allows variable adjustment of the fluid pressure in the cooling system and thus the boiling temperature of the heat transfer fluid.

As with the first embodiment variant of the pressure adjustment container, a pressure measuring device, in particular a pressure gauge, for determining the pressure of the working fluid can also be provided in the second and third embodiment variants of the pressure adjustment container. It can also be provided that the pressure measuring device is operatively connected via feedback to the corresponding, remotely operated filling valve in order to adjust the boiling temperature of the heat transfer fluid in a controlled manner.

In principle, it is also conceivable that the pressure adjustment container has no piston, no storage bladder, no pressure membrane or the like. Instead, it can be provided that the heat transfer fluid in the pressure adjustment container is directly overlaid with a pressurized working gas, for example nitrogen, as a pressure cushion. In this case there is direct contact between the heat transfer fluid and the working gas, i.e. the working gas and the heat transfer fluid are not separated from each other in a fluid-tight manner. In this embodiment, the pressure adjustment container can preferably have a working gas make-up device, in particular in order to variably adjust the pressure of the working gas pressure cushion, which in turn allows a variable adjustment of the fluid pressure in the cooling system and thus the boiling temperature of the heat transfer fluid. In this configuration, the working gas is preferably selected so that the working gas and the heat transfer fluid do not react chemically with one another.

The working fluid that is used for pressure adjustment in the previously described variants of the pressure adjustment container can, for example Be air or nitrogen. Nitrogen offers the advantage over air that it does not promote corrosion and does not contribute to the aging and brittleness of the pressure membrane in the membrane storage container or the storage bladder in the bladder storage container.

In principle, the present scope of protection can refer to the cooling system according to the invention in the unfilled state, i.e. without heat transfer fluid, or in the filled state, i.e. with heat transfer fluid. Accordingly, according to an advantageous embodiment of the invention, it can be provided that the two-phase cooling circuit is filled with a two-phase heat transfer fluid.

The two-phase heat transfer fluid preferably has a boiling temperature in a range between 22 °C and 35 °C, in particular between 24 °C and 30 °C or between 25 °C and 27 °C, at a pressure of 1013 mbar (normal conditions). The two-phase heat transfer fluid is therefore preferably a low-boiling heat transfer fluid which, under normal conditions, boils at moderate temperatures in the range of normal room temperatures or slightly above. However, it is also conceivable that the two-phase heat transfer fluid at a pressure of 1013 mbar (normal conditions) has a boiling temperature, for example in a range between -18 ° C and 15 ° C, in particular between 0 ° C and 10 ° C. If cooling of such a heat transfer fluid is only to begin at temperatures in the range of around 20 ° C, the boiling temperature of the heat transfer fluid would have to be increased accordingly by increasing the fluid pressure in the cooling system using the pressure adjustment container.

For example, a heat transfer fluid sold by 3M ^™ under the trade name Novec ^™ 5110 can be used as a two-phase heat transfer fluid. Novec ^™ 5110 is an insulating gas with good environmental properties (very low global warming potential [GWP<1 (Global Warming Potential)], no ozone depletion potential), which represents a sustainable alternative to sulfur hexafluoride (SF ₆ ). Novec ^™ 5110 has a boiling point of 26.9 °C under normal conditions (atmospheric pressure), is non-flammable, non-flammable, electrically non-conductive, has a low viscosity and is an inert substance very good compatibility with other materials, also has no corrosive effect and therefore offers a high level of operational safety in use.

Since the setting of the operating point of the heat transfer fluid should advantageously be possible with a moderate pressure adjustment, the two-phase heat transfer fluid is preferably designed in such a way that at a pressure of 800 mbar it has a boiling temperature in a range between 18 ° C and 24 ° C, in particular between 19 °C and 22 °C. The Novec ^™ 5110 heat transfer fluid mentioned above as an example has a boiling temperature of around 20 °C at a pressure of 800 mbar.

Accordingly, according to a preferred embodiment of the invention, the cooling system, in particular the pressure adjustment container, is configured so that the fluid pressure is in a range between 1 mbar and 6000 mbar, in particular between 30 mbar and 4000 mbar, preferably between 100 mbar and 1500 mbar, particularly preferably between 500 mbar and atmospheric pressure or between 700 mbar and atmospheric pressure, can be variably adjusted.

According to a further advantageous embodiment of the invention, the evaporator and/or the condenser are designed as heat exchangers.

In particular, the evaporator can have one or more evaporation channels that rise obliquely relative to the horizontal, in which liquid heat transfer fluid can evaporate from the room during operation while absorbing thermal energy. On the one hand, the diagonally ascending arrangement of the evaporation channels ensures that evaporated heat transfer fluid can rise and leave the evaporator unhindered. On the other hand, the sloping, particularly non-vertical arrangement of the evaporation channels achieves a good cross section between the warm air rising in the room and the evaporator. It has proven to be advantageous with regard to both aspects if the one or more evaporation channels have an angle relative to the horizontal in a range between 1° and 45°, in particular between 10° and 25°, preferably between 15° and have 20°. Depending on the surface tension properties of the heat transfer fluid, very shallow angles relative to the horizontal in the range of just a few degrees can be considered, which advantageously allow the evaporator to be arranged flat under the ceiling of the room to be cooled. If several evaporators are provided, the evaporators or their one or more evaporation channels can also be arranged at different angles.

According to a further advantageous embodiment of the invention, the two-phase cooling circuit is preferably filled with a two-phase heat transfer fluid to such an extent that during operation a maximum fill level of the liquid heat transfer fluid in the one or more evaporation channels is in a range between 50% and 99%, in particular between 60%. and 90% of a vertical extent of the one or more evaporation channels. In the present case, the vertical extent of the one or more evaporation channels means the dimension of the one or more evaporation channels in the vertical direction, i.e. that dimension which is the length of the one or more evaporation channels times the sine function value of the included angle between the one or more evaporation channels corresponds to the several evaporation channels and the horizontal. By having a maximum fill level in this area, disadvantageous eruption processes in the one or more evaporation channels - similar to the eruption processes in a geyser - and thus undesirable pressure surges in the cooling circuit can be avoided in an advantageous manner.

Furthermore, the evaporator can have a steam collection chamber located downstream, into which the evaporation channels open and which is fluidly connected to an upstream end of the feed line. Advantageously, evaporated heat transfer fluid can collect and relax in the steam collection chamber before it is passed through the flow line to the condenser.

In order to keep the flow resistance for evaporated heat transfer fluid as low as possible, the lines should be dimensioned accordingly. This is how it can be done In a further advantageous embodiment of the invention, it can be provided that the feed line has a line diameter in a range between 50 mm and 200 mm, in particular in a range between 100 mm and 150 mm. The low flow resistance prevents the passive transport of the heat transfer fluid within the circuit from breaking down, in particular that the mass flow of the heat transfer fluid is as high as possible, which increases the amount of heat dissipated.

In contrast, the diameter of the return line for returning the condensed heat transfer fluid can be smaller due to the low density of the heat transfer fluid in the liquid state. According to a further advantageous embodiment of the invention, it can be provided that the return line has a line diameter in a range between 25 mm and 100 mm, in particular in a range between 50 mm and 75 mm. Due to the smaller diameter of the return line, the total amount of heat transfer fluid for filling the system can also be kept lower than when using larger line diameters for the return line, which is always filled with liquid heat transfer fluid during operation.

The flow line and/or the return line can also be thermally insulated or have thermal insulation.

Analogous to the evaporator, the condenser can also have one or more condensation channels that are inclined at an angle to the horizontal, in which vaporous heat transfer fluid can condense during operation, releasing thermal energy to the heat sink, for example to the ambient air outside the room. Here too, the obliquely inclined arrangement ensures, on the one hand, a safe outflow of the condensed heat transfer fluid and, on the other hand, a good cross section between the condensation channels and the heat sink, such as the ambient air (heat sink) which absorbs the heat and consequently rises in the area of the condensation channels. It has proven to be advantageous with regard to both aspects if the one or more condensation channels have an angle in one area relative to the vertical between 5° and 70°, in particular between 15° and 30°, preferably between 20° and 25°. If several capacitors are provided, the capacitors or their one or more condensation channels can also be arranged at different angles.

Both the evaporation channels of the evaporator and the condensation channels of the condenser can be formed by evaporator tubes or condenser tubes. I.e. the evaporator may include one or more evaporator tubes that form the one or more evaporation channels. Analogously, the condenser can have one or more condenser tubes that form the one or more condensation channels. The evaporator tubes or the condenser tubes can, for example, be arranged in a single, double or multi-row arrangement of tubes running next to one another, in particular parallel to one another, and in particular extend between the respective distributor and the steam collection chamber or condensate collection chamber.

The evaporator tubes and the condenser tubes are preferably designed as finned tubes. Finned tubes are tubular components that have fins made of highly heat-conducting material to improve the heat transfer. The ribs serve to enlarge the pipe surface and can be produced on the outside, for example by rolling (similar to thread rolling), by soldering or welding, by pressing or grooving into the pipe wall.

Alternatively or additionally, the evaporator tubes and the condenser tubes can also have ribs or channels inside the tubes in order to increase the tube surface and optimize the evaporation/condensation surface.

The nature of the pipe surfaces (inside and outside) can also be designed through suitable surface design in such a way that a higher heat transfer can be achieved compared to a smooth pipe. Suitable structures are, for example, coatings that increase the roughness of the surface, or turbulators and/or ribs that convert the laminar boundary layer into a turbulent flow and thereby increase heat transfer.

For example, longitudinal grooves or rectangular rods distributed over the circumference of the inside can also be incorporated or attached within the one or more evaporator tubes or the one or more condenser tubes. Advantageously, these serve for better heat transfer from the respective pipe to the heat transfer fluid or for better heat transfer from the heat transfer fluid to the respective pipe. In addition, this also makes it possible to achieve better flow control of the evaporating heat transfer fluid.

Plate heat exchangers with straight or shaped plates can also be used instead of finned tubes. Generally speaking, many structures designed as so-called cooling ceiling panels or radiators can be adapted or modified for two-phase room cooling by suitable arrangement.

In addition, latent heat storage plates - as described below - can also form cooling fins of the evaporator, in particular can be arranged in series one behind the other as cooling fins on pipes of the evaporator.

In order to increase the heat exchange between the condenser and the ambient air, the cooling system can, according to a further advantageous embodiment of the invention, also have a convection shaft for arrangement outside the room to be cooled in which the condenser is arranged. On the one hand, when ambient air is used as a heat sink, the convection shaft ensures that the heat-absorbing ambient air is well dissipated through natural convection. On the other hand, the convection shaft can provide protection from solar radiation or shading of the condenser and the air surrounding it, whereby the heat sink can be kept at a low temperature level even in strong sunlight. The convection shaft also serves to protect the capacitor from environmental influences, for example from wind and weather influences, especially hail.

Air, in particular the ambient air, outside the room to be cooled is preferably considered as a heat sink. But it is also conceivable that as An ice storage or a water reservoir can be used as a heat sink. In principle, the ice storage or the water reservoir can be used alone as a heat sink or in addition to an air heat sink. A water trickle system, which is operated, for example, with water from a higher reservoir or a river or lake, can also be used to realize the heat sink on the condenser or to reinforce another heat sink.

For safety reasons, it can also be provided that the two-phase cooling circuit has an overpressure protection, in particular an overpressure valve, which opens automatically at a predefined, preferably adjustable fluid pressure in the two-phase cooling circuit in order to avoid damage caused by excessive pressures in the system. Advantageously, the overpressure protection, in particular the overpressure valve, is arranged in the area of a highest point of the two-phase cooling circuit, in particular in the area of a highest point of the flow line.

Since the transport of the heat transfer fluid within the circuit should be passive, i.e. preferably without active means for influencing the flow, such as electric pumps or the like, or only with minimally active means, it is in the nature of things that the inlet of the condenser is preferably vertically higher than the outlet of the evaporator is arranged so that rising evaporated heat transfer fluid can reach the condenser. Conversely, the outlet of the condenser is preferably located above the inlet of the evaporator so that liquid heat transfer fluid can flow into the evaporator (exclusively) under the force of gravity. The condenser is preferably arranged higher overall in the vertical direction than the evaporator.

According to a further advantageous embodiment of the invention, the cooling system can also have a latent heat storage in order to provide a buffer function when thermal overloads or peak loads occur. For this purpose, the latent heat storage can have a phase change material (PCM = Phase Change Material). Phase change materials use the melting process from solid to liquid to store large amounts of heat at an almost constant temperature and if necessary, for example overnight, released again through the reverse process from liquid to solid. In this way, temporal fluctuations in the room air temperature can be reduced by an average temperature.

The phase change material preferably has a melting point that is above or in the range around the boiling point of the heat transfer fluid in the two-phase cooling circuit. For example, the melting temperature of the phase change material is in a range between 30 °C and 35 °C or in a range between 24 °C and 30 °C or between 25 °C and 27 °C.

Even if the cooling circuit fails or other (additional) thermal overloads occur or if transients are too high, the latent heat storage can absorb peak loads. The latent heat storage is preferably designed in such a way that it alone is able to absorb the thermal power generated in the room in such a way that the room air temperature does not exceed a temperature of 40 ° C or 50 ° C over several hours, for example over 10 hours, or that if the cooling circuit fails, the room air temperature does not exceed 40 °C or 50 °C over 0.5 or 1 hour, for example.

According to an advantageous embodiment of the invention, it can be provided that the latent heat storage is part of the evaporator. In particular, the latent heat storage can form cooling fins of the evaporator. For example, a phase change material may be included in cooling fins of the evaporator, such as in the fins of finned tubes that form the evaporation channels of the evaporator.

According to a further advantageous embodiment of the invention, the latent heat storage can have one or more latent heat storage plates in which a phase change material is enclosed. For example, such plates can be formed by a metal shell, in particular an aluminum shell, which is filled with a phase change material. The metal shell, in particular the aluminum shell, can be formed by joining two formed metal plates, in particular aluminum plates, together, optionally connected at two points in the middle, and connected at the converted edge, in particular be glued. Aluminum, as one of several possible materials for the metal shell, ensures high heat transfer and has an inherently low tendency to corrode. Such plates are available, for example, as so-called CSM plates (compact storage modules) from Rubitherm Technologies GmbH, Berlin.

According to a particularly advantageous embodiment of the invention, it can be provided that the latent heat storage plates filled with phase change material form cooling fins of the evaporator, in particular are arranged in series one behind the other as cooling fins on pipes of the evaporator. In this way, the latent heat storage plates have, in addition to the buffer function, an additional function as cooling fins for the evaporator of the two-phase cooling circuit.

DESCRIPTION OF DRAWINGS

Fig. 1

eine perspektivische Ansicht einer beispielhaften Ausführungsform des erfindungsgemässen passiven Kühlsystems zur Kühlung eines Raums in einer schematischen Darstellung;

Fig. 2

eine Seitenansicht des beispielhaften Kühlsystems gemäss Fig. 1;

Fig. 3

eine Draufsicht des beispielhaften Kühlsystems gemäss Fig. 1;

Fig. 4

Siedelinie des Wärmeträgerfluids Novec^™ 5110; und

Fig. 5

eine schematische Schnittdarstellung eines Verdampferrohrabschnitts mit integriertem Latentwärmespeicher zur Verwendung im Kühlsystem gemäss Fig. 1.

Further advantageous aspects of the invention result from the following description of an exemplary embodiment of the invention with reference to the figures; these show:

Fig. 1

a perspective view of an exemplary embodiment of the passive cooling system according to the invention for cooling a room in a schematic representation;

Fig. 2

a side view of the exemplary cooling system according to Fig. 1 ;

Fig. 3

a top view of the exemplary cooling system according to Fig. 1 ;

Fig. 4

Boiling line of the heat transfer fluid Novec ^™ 5110; and

Fig. 5

a schematic sectional view of an evaporator tube section with integrated latent heat storage for use in the cooling system according to Fig. 1 .

DETAILED EXAMPLE

Fig. 1 , Fig. 2 and Fig. 3 show a possible exemplary embodiment of a passive cooling system 1 according to the invention, which is used to cool a room 100, in particular a room with an electrically induced heat load, such as a control and electrical engineering room in a nuclear plant.

The core of the cooling system 1 is a closed passive two-phase cooling circuit 2, in which a two-phase heat transfer fluid 3 circulates during operation. The two-phase cooling circuit 2 comprises, on the one hand, an evaporator 10, which in the present exemplary embodiment is arranged in the ceiling area of the room 100 to be cooled, and, on the other hand, a condenser 20, which is arranged outside the room 100 to be cooled. By definition, the evaporator 10 is designed to evaporate liquid heat transfer fluid 3a from the space 100 into the gaseous/vaporous phase while absorbing thermal energy, whereas the condenser 20 is designed, according to definition, to evaporate vaporous heat transfer fluid 3b while releasing thermal energy to the environment outside Room 100 to condense back into the liquid phase.

The circuit 2 between evaporator 10 and condenser 20 is closed via a feed line 30 and a return line 40. The flow line 30 fluidly connects the evaporator 10 to the condenser 20 in the downstream direction, so that evaporated heat transfer fluid 3b can flow from the evaporator 10 to the condenser 20. Conversely, the return line 40 fluidly connects the condenser 20 to the evaporator 10 in the downstream direction, so that condensed heat transfer fluid 3a can flow back in liquid form from the condenser 20 to the evaporator 10.

As mentioned at the beginning, the two-phase cooling circuit 2 is a passive cooling circuit in which the heat transfer fluid 3 is transported exclusively due to the temperature difference between the air inside the room 100 (heat source) and the air in the environment outside the room 100 (heat sink). , ie without active means of influencing the flow, such as electric pumps or the like, or only with minimally active means. In particular, with this passive cooling system 1 it is possible to cool the air inside the room 100 without having to rely on electrical energy supply. The passive cooling circuit 2 thus ensures continuous cooling of the room 100 under appropriate boundary conditions.

The evaporator 10 and the condenser 20 are designed as heat exchangers, the evaporator 10 being in heat exchange with the warmer air inside the room 100 and the condenser 20 with a heat sink, in this case the cooler air in the environment outside the room 100. In the present exemplary embodiment, both the evaporator 10 and the condenser 20 consist of a two-row arrangement of several evaporator or condenser tubes 11, 21 arranged next to one another. These form several evaporation or condensation channels 12, 22 running parallel to one another, in which the evaporation or condensation processes can take place. Upstream, the evaporator or condenser tubes 11, 21 are connected to a respective distributor bar 13, 23, into which the respective downstream end of the feed line 30 or the return line 40 opens. Liquid heat transfer fluid 3a is distributed into the evaporator tubes 11 or the evaporation channels 12 of the evaporator 10 via the distributor bar 13 of the evaporator 10. In the same way, evaporated heat transfer fluid 3b is distributed via the distributor bar 23 of the condenser 20 into the condenser tubes 21 or the condensation channels 22 of the condenser 20. Furthermore, the evaporator 10 has a steam collection chamber 14 located downstream, into which the evaporator tubes 11 or the evaporation channels 12 open and which is fluidly connected to an upstream end of the flow line 30. In the same way, the condenser 20 also includes a downstream condensate collecting chamber 24, into which the condenser tubes 21 or the condensation channels 22 open and which is fluidly connected to an upstream end of the return line 40. Preferably the evaporator tubes 11 and the condenser tubes 21 are as in Fig. 5 shown as an example, designed as finned tubes, ie as tubes with cooling fins 17 arranged on the circumference in order to improve the transferred heat output.

Both the evaporator tubes 11 or the evaporation channels 12 and the condenser tubes 21 or the condensation channels 22 are arranged obliquely rising or inclined relative to the horizontal. On the one hand, this ensures that evaporated heat transfer fluid 3b can rise unhindered in the evaporator 10 and that condensed heat transfer fluid in the condenser 20 can flow downwards purely gravitationally. On the other hand, the obliquely rising or obliquely inclined, in particular non-vertical arrangement achieves a good cross section between the evaporator 10 or condenser 20 and the room or ambient air interacting with them. While in the present exemplary embodiment the condenser tubes 21 or the condensation channels 22 are inclined with respect to the vertical by an angle β of approximately 22.5 °, the evaporator tubes 11 or the evaporation channels 12 run obliquely upwards with an angle α of approximately 17.5 relative to the horizontal (see Fig. 2 ). The flat angle α relative to the horizontal in the evaporator tubes 11 allows a flat arrangement of the evaporator 10 under the ceiling of the room 100. In contrast, the steeply sloping arrangement of the condenser tubes 21 enables a space-saving arrangement of the condenser 20 in a convection shaft 60 outside the room 100, as in the Fig. 1-3 shown.

The chimney-like convection shaft 60 serves, on the one hand, to increase the removal of the ambient air interacting with the condenser 20 and the heat absorbed therein in the vertical direction due to natural convection - similar to a chimney. On the other hand, the convection shaft 60 can be used to shade the capacitor 20 and the ambient air surrounding it, whereby the heat sink (ambient air in the convection shaft 60) can be kept at a low temperature level even in strong sunlight.

In order to keep the flow resistance for evaporated heat transfer fluid 3b as low as possible, the line diameter of the flow line 30 in the present exemplary embodiment is 100 mm. By dimensioning the feed line 30 to a corresponding size, a high mass flow can be achieved, whereby the The amount of heat dissipated is increased. In contrast, the diameter of the return line 40 for returning the condensed heat transfer fluid 3a can be smaller due to the low density of the heat transfer fluid 3a in the liquid state. In the present exemplary embodiment, the diameter of the return line 40 is only 50 mm. Due to the smaller diameter of the return line 40, the total amount of heat transfer fluid for filling the system can also be kept lower.

Depending on the application, various two-phase heat transfer fluids can be used. However, a heat transfer fluid with a suitable boiling temperature is not available for every application, in particular temperature range. In the present exemplary embodiment, the cooling of the room 100 should start at around 20 ° C, with a heat transfer fluid sold by 3M ^™ under the trade name Novec ^™ 5110 preferably being used as the heat transfer fluid, as it has very good environmental compatibility and high compatibility with other materials having. Like from the in Fig. 4 As can be seen from the boiling line shown, Novec ^™ 5110 boils under normal conditions, ie at approximately 1 bar atmospheric pressure, but only at a boiling temperature of 26.9 ° C, ie only above the desired temperature at which the cooling of the room 100 should already begin.

In order to be able to adjust the boiling temperature of the heat transfer fluid 3 in the cooling system 1, it is provided according to the present invention that the cooling circuit 2 has a pressure adjustment container 50 for storing liquid heat transfer fluid 3a, which is in fluid connection with the return line via a riser or siphon-like line 42 40 stands. In accordance with the invention, the pressure adjustment container 50 is designed such that, during operation, the heat transfer fluid 3a is stored in the pressure adjustment container 50 under a variably adjustable fluid pressure.

In the present exemplary embodiment, the pressure adjustment container 50 is designed as a membrane storage container which has a flexible pressure membrane 53 made of an elastic material. The pressure membrane 53 divides the interior of the pressure adjustment container 50 into a first chamber 51 and a second chamber 52 so that the first chamber 51 and the second chamber 52 are separated from one another in a fluid-tight manner. While the first chamber 51 is designed to store liquid heat transfer fluid 3a and is in fluid communication with the return line 40, a working fluid 7, in particular a gas, can be stored in the second chamber 52 with a variably adjustable pressure. For this purpose, the pressure adjustment container 50 can have a filling valve 54 for filling or emptying the second chamber 52 with working fluid 7, so that the pressure of the working fluid 7 in the second chamber 52 can be variably adjusted by varying the filling quantity of the second chamber 52 with the working fluid 7. The pressure of the working fluid 7 in the second chamber 52 is in turn transmitted via the pressure membrane 53 to the fluid pressure of the heat transfer fluid 3 in the cooling circuit 2, so that as a result the fluid pressure of the heat transfer fluid 3 in the second chamber 52 is via the variably adjustable pressure of the working fluid 7 Cooling system 2 and thus the boiling temperature of the heat transfer fluid 3 can be variably adjusted. In the present exemplary embodiment, nitrogen is used as the working fluid 7 to adjust the pressure in the second chamber 52. Nitrogen offers the advantage over air that it does not promote corrosion and does not contribute to the aging and brittleness of the pressure membrane 53.

As shown by the boiling line in Fig. 4 As can be seen, it is sufficient for the Novec ^™ 5110 heat transfer fluid used here if the fluid pressure in the cooling circuit 2 is reduced by about 200 mbar below the atmospheric pressure of 1000 mbar, ie to about 800 mbar, to the boiling temperature of the heat transfer fluid 3 of 26.9 ° C to the desired value of 20 °C.

Like in particular Fig. 1 and Fig. 2 As can be seen, the condenser 20 is arranged at a higher level than the evaporator 10. In particular, the inlet of the condenser 20 is arranged vertically higher than the outlet of the evaporator 10 so that rising evaporated heat transfer fluid 3b can independently reach the condenser 20. Conversely, the outlet of the condenser 20 is located above the inlet of the evaporator 10 so that liquid heat transfer fluid 3a can flow into the evaporator 10 via the return line 40 exclusively under gravity.

This ensures that the transport of the heat transfer fluid within the circuit 2 can take place purely passively without active means for influencing the flow.

The pressure adjustment container 50 is also arranged at a level below the condenser 20, with the pressure membrane 53 preferably being arranged approximately at the desired fill level of the heat transfer fluid 3a in the evaporator 10. As already explained above, the evaporator 10 is not completely filled with liquid heat transfer fluid 3a. Preferably, the two-phase cooling circuit 2 is only filled with heat transfer fluid 3a to such an extent that, during operation, a maximum fill level of the liquid heat transfer fluid 3a in the evaporator tubes 11 or evaporation channels 12 is in a range between 50% and 99%, in particular between 60% and 90% vertical extension VH of the evaporator tubes 11 or the evaporation channels 12, i.e. H. in a range between 50% and 99%, in particular between 60% and 90%, of the dimension VH, which is the length VL of the evaporator tubes 11 or the evaporation channels 12 times the sine function value of the included angle α between the evaporator tubes 11 or the evaporation channels 12 and the horizontal corresponds. This advantageously avoids any eruption processes in the evaporator 10 and thus any pressure surges in the cooling circuit 2.

As already explained above, the cooling system 2 preferably additionally has a latent heat storage 80 with a phase change material 81 in order to provide a buffer function when thermal overloads or peak loads occur. Phase change materials 81 use the melting process from solid to liquid to store large amounts of heat at an almost constant temperature and, if necessary, to release them again through the reverse process from liquid to solid, for example overnight. In this way, temporal fluctuations in the room air temperature can be reduced by an average temperature.

It is preferably provided that the latent heat storage 80 is part of the evaporator 10. In particular, the latent heat storage 80 can form cooling fins 17 of the evaporator 10; or in cooling fins 17 of the evaporator 10, a phase change material 81 can be integrated. In particular, the Latent heat storage 80 - as in Fig. 5 - Shown have several latent heat storage plates 82, in which a phase change material 81 is enclosed and which are arranged threaded one behind the other on the evaporator tubes 11 of the evaporator 10 and thereby simultaneously form the cooling fins 17 of the evaporator tubes 11. In this way, the latent heat storage plates 82 have, in addition to the buffer function, an additional function as cooling fins 17 for the evaporator 10 of the two-phase cooling circuit 2.

Claims (15)

Passive cooling system (1) for cooling a room (100), which comprises a closed passive two-phase cooling circuit (2) for a two-phase heat transfer fluid (3, 3a, 3b) circulating therein during operation, the two-phase cooling circuit (2) having the following : - at least one evaporator (10) for arrangement in the room (100) to be cooled, which is designed to evaporate liquid heat transfer fluid (3a) from the room (100) while absorbing thermal energy, - at least one condenser (20) for arrangement outside the room (100) to be cooled, which is designed to condense vaporous heat transfer fluid (3b) while releasing thermal energy to a heat sink outside the room (100), - at least one flow line (30) fluidly connecting the at least one evaporator (10) to the at least one condenser (20) for transporting evaporated heat transfer fluid (3b) from the at least one evaporator (10) to the at least one condenser (20); - at least one return line (40) fluidly connecting the at least one condenser (20) to the at least one evaporator (10) for transporting condensed heat transfer fluid (3a) from the at least one capacitor (20) to the at least one evaporator (10); - at least one pressure adjustment container (50) in fluid communication with the at least one return line (40) for storing liquid heat transfer fluid (3a), the at least one pressure adjustment container (50) being designed in this way for adjusting the boiling temperature of the heat transfer fluid (3) in the cooling system (1). is that during operation the heat transfer fluid (3a) can be stored in the at least one pressure adjustment container (50) under a variably adjustable fluid pressure. Cooling system (1) according to claim 1, wherein the pressure adjustment container (50) is designed as a membrane storage container which has a flexible pressure membrane (53) which divides an interior of the pressure adjustment container (50) into a first chamber (51) for storing liquid heat transfer fluid (3a ), in the There is fluid connection with the return line (40), and a second chamber (52), in which a working fluid (7), in particular a gas, can be stored or stored with a variably adjustable pressure, is divided. Cooling system (1) according to claim 1, wherein the pressure adjustment container (50) is designed as a bladder storage container which has a container housing and a storage bladder accommodated in the container housing, wherein - a working fluid, in particular a gas, with a variably adjustable pressure can be stored or stored in an interior of the storage bladder, and liquid heat transfer fluid (3a) can be stored in a space between an outside of the storage bladder and an inside of the container housing, the space being in fluid communication with the return line (40); or - liquid heat transfer fluid (3a) can be stored in an interior of the storage bladder, the interior of the storage bladder being in fluid communication with the return line (40), and a working fluid, in particular a gas, in a space between an outside of the storage bladder and an inside of the container housing, can be stored or stored with variably adjustable pressure. Cooling system (1) according to claim 1, wherein the pressure adjustment container (50) is designed as a piston storage container which has a cylinder container housing and a piston which is sealingly mounted relative to an inner wall of the cylinder container housing, the piston in the cylinder container housing along a cylinder longitudinal axis of the Cylinder container housing is slidably mounted and an interior of the cylinder container housing in a first chamber for storing liquid heat transfer fluid (3a), which is in fluid communication with the return line (40), and a second chamber in which a working fluid, in particular a gas , can be stored or stored with variably adjustable pressure. Cooling system (1) according to one of the preceding claims, wherein the two-phase cooling circuit (2) is filled with a two-phase heat transfer fluid (3, 3a, 3b). Cooling system (1) according to one of the preceding claims, wherein the two-phase heat transfer fluid (3, 3a, 3b) has a boiling temperature in a range between 22 °C and 35 °C, in particular between 24 °C and 30 °C, at a pressure of 1013 mbar or between 25 °C and 27 °C, and/or wherein the two-phase heat transfer fluid (3, 3a, 3b) has a boiling temperature in a range between 18 °C and 24 °C at a pressure of 800 mbar; or wherein the two-phase heat transfer fluid (3, 3a, 3b) has a boiling temperature in a range between -18 °C and 15 °C, in particular between 0 °C and 10 °C, at a pressure of 1013 mbar. Cooling system (1) according to one of the preceding claims, wherein the pressure adjustment container (50) is designed such that the fluid pressure is in a range between 1 mbar and 6000 mbar, in particular between 30 mbar and 4000 mbar, preferably between 100 mbar and 1500 mbar, in particular preferably between 500 mbar and atmospheric pressure or between 700 mbar and atmospheric pressure, is variably adjustable. Cooling system (1) according to one of the preceding claims, wherein the evaporator (10) has one or more evaporation channels (12) which rise obliquely with respect to the horizontal, in which, during operation, liquid heat transfer fluid (3a) absorbs thermal energy from the room (100 ) can evaporate. Cooling system (1) according to one of claims 8, wherein the two-phase cooling circuit (2) is filled with a two-phase heat transfer fluid (3, 3a, 3b), so that during operation a maximum fill level (FL) of the liquid heat transfer fluid (3a) in the one or more evaporation channels (12) is in a range between 50% and 99%, in particular between 60% and 90% of a vertical extent (VH) of the one or more evaporation channels (12). Cooling system (1) according to one of the preceding claims, wherein the condenser (20) has one or more condensation channels (22) which are inclined at an angle with respect to the horizontal, in which, during operation, vaporous heat transfer fluid (3b) releases thermal energy to the heat sink outside the Room (100) can condense. Cooling system (1) according to one of the preceding claims, further comprising a convection shaft (60) for arrangement outside the space (100) to be cooled, in which the condenser (20) is arranged. Cooling system (1) according to one of the preceding claims, further comprising a latent heat storage (80) with a phase change material (81), the phase change material (81) preferably having a melting point which is above the boiling point of the heat transfer fluid (3, 3a, 3b) in the two-phase -Cooling circuit (2). Cooling system (1) according to claim 12, wherein the phase change material (81) has a melting temperature in a range between 30 °C and 35 °C or in a range between 24 °C and 30 °C or between 25 °C and 27 °C. Cooling system (1) according to claim 12 or 13, wherein the latent heat storage (80) is part of the evaporator (10), in particular forming cooling fins (17) of the evaporator (10). Cooling system (1) according to one of claims 12 to 14, wherein the latent heat storage (80) has one or more latent heat storage plates (82) in which the phase change material (81) is enclosed, preferably the latent heat storage filled with the phase change material (81). -Plates (80) form cooling fins (17) of the evaporator (10), in particular as cooling fins (17) are arranged in series one behind the other on one or more evaporator tubes (11) of the evaporator (10).

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