DE3008355A1 - Refrigerator for aircraft galleys - using dry ice vapours passed through capillary nozzle and venturi tubes - Google Patents

Abstract

A refrigerator evaporates the solid or liquid refrigerant in a separate container at a pressure above the working pressure and at a temp. below the working temp. The refrigerant vapour is discharged at a high flow velocity from the container, is evaporated in two Venturi tubes, and directed into the refrigeration space after its velocity has been reduced. Such a refrigerator combines a low weight with small overall dimensions and does not coat the food packages with a layer of ice and water.

Description

description

The invention relates to a method for operating a cooling unit, a coolant continuously in its pressure-equalized cooling space is initiated.

Cooling units are generally because of their energy supply part, of coolant pumps, motors and the like.

voluminous and heavy. The use of such cooling units is therefore disadvantageous in those cases in which the lowest possible weight and volume of the cooling unit is important. This applies, for example, to cooling units that are required for cooling food and beverages in commercial aircraft. These Cooling units also only need to be replaced for a limited period of time of the coolant, e.g. for the duration of a long-haul flight.

There are cooling units for commercial aircraft of the type mentioned above known that are charged with dry ice (solid carbon dioxide). That continuously evaporating cold carbon dioxide enters the upper part of a cold room the cooling unit, sinks down due to its density and cools the in the cold room storing dishes. Such a cooling unit has several disadvantages. On the one hand the evaporating dry ice is covered with a heat-insulating layer Water ice, which affects the evaporation process of the dry ice. Furthermore, the formation of a water ice layer on the food or its packaging annoying. After all, the flow rate of the cold CO2 is in many cases too low to provide reliable cooling over the entire area of the refrigerator compartment to ensure.

Accordingly, the invention is primarily to a method of operation directed a cooling unit, which has a low weight and volume and in which the disadvantages of the prior art for commercial aircraft are known become avoided cooling device.

This object is achieved in that the solid or liquid coolant under pressure in a container separate from the cooling space above the operating pressure and at a temperature below the operating temperature of the cooling space is evaporated, and that the gaseous coolant thus obtained with high flow rate from the container to the operating pressure the cold room relaxed and after reducing its flow velocity is introduced into the refrigerator.

The inventive solution prevents water in the Container condenses and forms a heat-insulating layer on the coolant. Furthermore, by regulating the flow rate of the from the container gaseous coolant escaping in the cold room achieves effective cooling will. The flow rate of the entering preferably at the bottom of the cooling space gaseous coolant therefore depends on the dimensioning of the cooling space, the type of the goods to be cooled and the desired cooling temperature and can be in the order of magnitude from a few cm / sec to a few m / sec. The speed of the container leaving gas should, however, be as high as possible. If the gaseous coolant should move in a laminar flow after leaving the container, what is desirable in most cases is its flow velocity at Do not leave the container greater than the speed of sound.

In order to prevent the gaseous coolant immediately after the Condensed out of the container, it is advantageously before the expansion warmed up. The extent of the warming depends on the thermodynamic data of the Coolant, in particular the enthalpy of vaporization, the pressure gradient between the Gas inside and outside the container and other factors that are known to those skilled in the art are common.

According to an advantageous embodiment of the invention, the coolant is a gas that is liquid or solid at the temperature of the cold room. As particularly beneficial for the cooling of food, not least because of its easy handling, Dry ice proved. However, since the invention does not apply to the refrigeration of food is limited, all other known coolant systems can also be used in the Processes of the invention can be used by evaporation, or sublimation also through adiabatic cooling a gaseous coolant in the form of a cold one Gas, e.g. hydrogen, nitrogen, air, noble gases such as helium, neon, Argon and krypton, fluorine, fluorine-chlorine hydrocarbons (freons) and the like.

According to a further advantageous embodiment of the invention, can the gaseous coolant after exiting the container in a coolant circuit be introduced, in which it is flowing through the cooling chamber after it has been passed through mixed with warmer coolant and the coolant mixture fed back to the cooling chamber will. This development of the invention represents an essentially closed one Is a coolant system in which the coolant circulation without external energy, e.g.

electrical energy to operate pumps, evaporators * underneath the operating temperature or the like takes place. The only source of energy which is required is the kinetic energy of the gas flowing out of the container Coolant s.

According to a further advantageous embodiment of the invention there is a local pressure gradient in the circuit with the gas flowing out of the container generated. The pressure gradient is determined by at least one of the from the container Generated leaked gaseous coolant flowed through Venturi nozzle. The gaseous one When passing through the Venturi nozzle, coolant creates suction, which already causes it coolant in the circuit in the direction of flow of the coolant flowing out of the container Gas is sucked in and circulated in the cooling system. Other methods can be used applied. be, wu by the kinetic energy of the outflowing gaseous To bring about coolant in the cooling system a circulation, So you can for example drive pumps, turbines or the like with the escaping gaseous cooling medium, which in turn allow the coolant in the circuit to circulate. Such However, embodiments of the invention are structurally more complex than when used a venturi that has no moving parts.

The gaseous coolant flowing out of the cooling space is preferred pre-cooled on the surface of the container before mixing with the colder coolant. If the gaseous coolant is heated before exiting the container should, this can preferably be done by means of heat exchangers through the from the cooling room escaping warmer coolant happens.

According to a further advantageous embodiment (isfcornl of the invention the gaseous coolant can be introduced at the bottom of the cooling space and at the same ge (lenüberlikfcn (1 can be derived from the upper end Flow through the cooling chamber can be achieved from bottom to top.

The invention is further directed to apparatus for practicing of the method of the invention.

The invention is not limited to the use of the device for Operation of a cooling unit for cooling food in commercial aircraft is limited. Rather, the device can also be used anywhere where a stream of cold gaseous cooling medium is required, e.g. when cooling electronic Components. Furthermore, the device (J of the invention can advantageously be used as a portable refrigerator can be used, e.g. in the form of a picnic suitcase. In the end the device of the invention can be used not only as a cooling unit; she can can be used wherever a constant flow of a liquefied or solid gases is required, e.g.

if the corresponding gases are not compressed in steel cylinders To be available. In this type of application, the device of the invention provides a device for the evaporation of liquefied or solid gases.

The device of the invention consists essentially of a container for receiving the solid or liquid coolant, a cold room for receiving of the goods to be cooled, a tubular extension attached to the container with a narrow opening or capillary at its end facing away from the container as well a first pipe connection between the pressure vessel or the Approach and the cooling space, the diameter of the first tube connection being larger than that of the tubular extension, as well as a Druckausgleleh to the outlet of the excess coolant after crossing the cooling room.

The roiir-shaped approach is preferably in the form of a lallial trained heat exchanger provided.

According to a further advantageous embodiment of the invention is the cooling space with the container-side end of the first pipe connection via a second Pipe connection connected, with the gaseous coolant leaving the cooling space when traversing the second pipe connection with the surface of the container and possibly brought into contact with the heat exchanger.

For this purpose, the container is preferably provided with cooling fins. He can, for example, have a surface shaped like a corrugated sheet, through which at the same time a higher stability of the container compared to the internal pressure of the container is achieved.

The second pipe connection preferably encloses the container and the tubular extension with the formation of an annular gap. This creates a particularly good cooling of the circulating coolant or heating of the Reached the container and the gas flowing through the tubular extension.

According to a further advantageous embodiment of the device of the invention is between the first and the second pipe connection at least arranged a Venturi nozzle into which the tip of the tubular extension protrudes. One can see the performance of the device also increase by that one arranges two or more Venturi nozzles one inside the other, with the tip of the tubular extension protrudes into the innermost, smallest Venturi nozzle.

According to a further advantageous embodiment of the invention are the cooling space and the second pipe connection surrounding the container directly next to one another arranged, a single door closing the cooling unit being provided and between the door and the door-side wall of the cooling space and the second pipe connection a gap is formed for the gaseous coolant to pass through. Through this a particularly compact design of the cooling unit is obtained.

All essential parts of the device of the invention exist made of steel or sheet steel. Depending on the nature of the coolant, the operating pressures and the application, however, other materials can also be used. For example, a portable cooling unit like the picnic suitcase mentioned above consist essentially of plastic, possibly with the exception of those parts where a heat exchange should take place and accordingly metals with better thermal conductivity, e.g. steel, copper or the like are more appropriate.

Further preferred features and advantages of the invention result from the following description, reference being made to the drawings. It show: Figure 1 is a schematic view of a cooling unit of the invention, the is intended for the cooling of food in commercial aircraft; figure 2 shows a schematic longitudinal section through a cartridge containing the coolant for use in the device of the invention; Figure 3 is a schematic longitudinal section through the evaporator part of another embodiment of the device of the invention.

According to Figure 1 is in a container 1, which with a closure 2 Can be closed gas-tight and on its side wall cooling ribs 3, which the wall at the same time give a greater compressive strength, has, go to dry ice.

The container 1 is provided at one end with a tubular extension 4, the one at its end remote from the container with a capillary-like design Tip 5 is equipped. To prevent the evaporating in the container Carbon dioxide condenses when leaving the tip 5, the approach 4 is with heat exchanger fins 6 equipped, through which the carbon dioxide flowing through the approach is heated. The carbon dioxide exiting at almost the speed of sound traverses the tip 5 then two nested Venturi nozzles, a first, larger one 7 and a second, smaller Venturi nozzle 8. The tip 5 protrudes into the smaller one Venturi nozzle 8, which in turn protrudes into the larger Venturi nozzle 7. In the arrangement of the Venturi nozzles 7, 8 is the carbon dioxide flowing out of the tip 5 first accelerated and then slowed down and arrives at a moderate flow rate via a first pipe connection 9 to one Refrigerator (10) it flowed through along its entire length from bottom to top. Then will the gaseous coolant via a second pipe connection 11 to the venturi nozzles 7, 8 supplied. It leaves the refrigerator via a gap 12 between the Partition between the cooling space 10 and pipe connection 11 and one of the cooling unit covering door 13, through which both the refrigerator 10 and the shutter 2 of the Container 1 are accessible, is formed. In the upper area of the cooling unit, i.e., near the door 13, an opening 14 is provided through which excess gaseous coolant can escape, so that there is no overpressure in the cooling system builds up. After crossing the gap 12, the now warmer gaseous stream flows Coolant past the cooling fins of the container 3 and is cooled down somewhat there. However, its temperature is still sufficient to flow past the heat exchanger fins 6 the carbon dioxide in the tubular extension 4 to prevent a To sufficiently heat condensation during relaxation.

The cold carbon dioxide emerging from the tip 5 at high speed generates a pressure gradient when flowing through the Venturi nozzle arrangement 7, 8 which sucks in the gaseous cooling medium circulating in the circuit 9, 10, 11 or is accelerated. The circulating gaseous coolant is constantly mixed with colder gas flowing out of the container.

The cooling unit according to Figure 1 can be outwardly through not shown Thermal insulation materials must be covered. When loaded with a suitable Amount of dry ice, it ensures a cooling effect of, for example, 6-10 hours.

The following additional descriptions are some thermodynamic Data to be taken: In the container 1 is carbon dioxide at -80 "C and a pressure introduced by 1 bar. Its specific enthalpy is 70 kJ / kg according to the Mollier diagram. By absorbing heat in container 1, a change in state to -70 "is obtained C and 2 bar, corresponding to a specific enthalpy of 82 kJ / kg. That evaporated CO2 is heated to -100 C in the approach 4 by means of the heat exchange fins 6; its specific enthalpy at -100 C and 2 bar is 698 kJ / kg. This will prevents the carbon dioxide after exiting the nozzle by adiabatic Cooling condenses. After relaxation, the carbon dioxide shows -55 ° C and 1 bar corresponding to a specific enthalpy of 665 kJ / kg.

The kinetic energy released when the carbon dioxide flows out (33 kJ / kg = 91.4 Wh / kg) is used in the double Venturi nozzle 7.8 for acceleration of the circulating cold room gas mixture is used. This is both a gas movement for the heat transfer at the container 1 and for the distribution of the cooling gas in the cooling room 10 generated.

The amount of heat consumed for the kinetic energy of 33 kJ / kg the overall cooling performance also benefits.

This increases the cooling capacity when the state changes by 1 bar, -80 "C, 70 kJ / kg to 1 bar, + 10 ° C, 790 kJ / kg from 646 kJ / kg to 679 kJ / kg.

The exit velocity of the carbon dioxide at the tip is 5 approx. 310 m / sec. The flow velocity is after leaving the second Venturi nozzle approx. 26 m / sec and after reaching the first pipe connection 9 approximately 2 m / sec at a temperature of -20 C, which is extended until reaching the refrigerator compartment 10 increases to about 0 ° C. The temperature of the coolant leaving the cold room is approx. + 100C at the gap 12, it sinks when passing the cooling fins 3 and the heat exchanger 6 to +20 C. The coolant is released from the Venturi nozzles at a temperature of around -10 C 7, 8 sucked in.

It can be just when using the device of the invention in Aircraft be advantageous to the coolant - to a certain extent in a loose state - Do not fill directly into the built-in cooling unit, but rather to fill the coolant into cartridges outside the aircraft, which are then placed in the appropriately shaped containers introduced or exchanged for "used" cartridges can be. Preferred designs for such coolant cartridges or the Containers can be seen from FIGS. 2 and 3.

According to Figure 2, there is a cartridge (15) for receiving the coolant (here: dry ice) essentially consists of a tube with a circular cross-section, which is closed at one end - and at its other end with a lid (16) of a cold-resistant, elastic material, e.g.

Silicone rubber, lockable. The shell of the cartridge is peripheral with a plurality of bores (17) for the vaporized coolant to pass through equipped in the container (1).

The container (1) is in turn with a conventional clamping device (18) position-wise fixable lid (19) closable, which at the same time also the Cover (16) secures.

The container has at its end opposite the lid (19) a pipe socket (20) for the passage of the evaporated coolant and introduction same in the coolant circuit.

In Figure 3, the evaporator part of a device is schematically Invention shown, in the 3 cartridges according to Figure 2 are einführbr. Functionally gloich-like Parts are given the same reference numerals as in FIGS. 1 and 2 The coolant (dry ice) evaporating in the cartridges (15) does not pass through shown bores (17) of the cartridge wall and the pipe socket (20) in a collecting tube (21), which merges into the tubular extension (4). The slats (6) are in the manner shown in Figure 3 so arranged that from the not shown Warmer coolant coming from the cold room washes around the cooling fins (&) as closely as possible, the coolant being as tortuous as possible due to the arrangement of the cooling fins Takes away.

In the embodiment shown here, there is only a single Venturi nozzle (8) required because here from a larger one, evaporating in the cartridges (15) Amount of coolant is assumed. A conventional one serves as a backup for the cover (19) Latch mechanism (18).

Claims (22)

A method for operating a cooling unit, in which A coolant is continuously introduced into the cooling chamber provided with a pressure equalization is, characterized in that the solid or liquid coolant in one of the container (1) separated from the cold room at a pressure above the operating pressure and evaporated at a temperature below the operating temperature of the cooling space (10) and that the gaseous refrigerant thus obtained has a high flow rate passed out of the container (10), relaxed to the operating pressure of the cooling chamber (1) and introduced into the cooling space (10) after reducing its flow rate will. 2. The method according to claim 1, characterized in that the gaseous Coolant is warmed up before decompression to prevent condensation. 3. The method according to claim 1 or 2, characterized in that the Coolant on at temperatures below the operating temperature of the cold room (10) is liquid or solid gas. 4. The method according to claim 1 or 2, characterized in that the The coolant is carbon dioxide. 5. The method according to claim 1 or 2, characterized in that one as a coolant nitrogen, air, noble gases, hydrogen or fluorinated or fluorinated / chlorinated Used hydrocarbons. 6. The method according to any one of claims 1-5, characterized in that that the gaseous coolant after exiting the container (1) in a coolant circuit (9, 10, 11) in which it is lzor passing through the cooling chamber (10) mixed with warmer coolant and the coolant mixture again the cooling space (10) is supplied. 7. The method according to any one of claims 1-6, characterized in that that the circulation of the gaseous coolant in the circuit (9, 10, 11) by the gaseous coolant flowing out of the container (1) takes place. 8. The method according to any one of claims 1-7, characterized in that that with the gas flowing from the container (f) in the circuit (9, 10, 11) locally a pressure gradient is generated. 9. The method according to any one of claims 1-8, characterized in that that the pressure gradient through at least one of the leaked from the container gaseous coolant flowing through Venturi nozzle (7, 8) is generated. 10. The method according to any one of claims 1-9, characterized in that that the gaseous coolant flowing out of the cooling space (10) before mixing is pre-cooled with the colder coolant on the surface of the container (1). 11. The method according to any one of claims 1-10, characterized in that that the gaseous coolant before exiting the container (1) by means of heat exchangers (6) is heated by the coolant emerging from the cooling space (10). 12. The method according to any one of claims 1-11, characterized in that that the gaseous coolant is introduced at the bottom of the cooling space (10) and at the same opposite upper end is derived. 13. Device for performing the method according to one of the claims 1-12, characterized by a container (1) for receiving the solid or liquid Coolant, a cooling space (10) for receiving the goods to be cooled, one on the Container (1) attached tubular extension (4) with a tip (5) with narrow opening at its end facing away from the container, a first pipe connection between the pressure vessel (1) or the extension (4) and the cooling space (10) and a pressure equalization (14) to allow excess coolant to escape after passing through the cooling space (10). 14. The device according to claim 13, characterized in that the tubular extension (4) with a lamellar heat exchanger (6) is provided. 15. Apparatus according to claim 13 or 14, characterized in that that the cooling space with the container-side end of the first pipe connection (9) over a second pipe connection (11) is connected, the one leaving the cooling space gaseous coolant when crossing the pipe connection (11) with the surface of the container (1) and possibly the heat exchanger (6) is brought into contact. 16. Device according to one of claims 13-15, characterized in that that the container (1) is provided with cooling and stabilizing ribs (3). 17. Device according to one of claims 13-16, characterized in that that the second pipe connection (11) the container (1) and the tubular extension (4) encloses forming an annular gap. 18. Device according to one of claims 13-17, characterized in that that between the first and the second pipe connection (11) at least one Venturi nozzle (7, 8) is arranged, into which the tip (5) of the tubular extension (4) protrudes. 19. Device according to one of claims 13-18, characterized by a second Venturi nozzle (8) protruding into the first Venturi nozzle (7), into which in turn the tip (5) of the tubular extension (4) protrudes. 20. Device according to one of claims 13-19, characterized in that that the cooling space (10) and the second pipe connection (11) surrounding the container (1) are arranged directly next to each other, with one closing the cooling unit Door (13) is provided and between the door (13) and the door-side wall of the Cold room (10) or the second pipe connection (11) a gap (12) for the passage of the Coolant is formed. 21. Device according to one of claims 13-19, characterized in that that the container (1) for receiving a cartridge (15) charged with the coolant or more is formed. 22. The apparatus according to claim 21, characterized in that the Container (1) for the introduction of the cartridge (15) one or more closable openings which are accessible without opening the door (13).