EP3318825B1

EP3318825B1 - Method and apparatus for cooling objects with a cryogenic liquid using fluidic oscillating nozzles

Info

Publication number: EP3318825B1
Application number: EP16020427.7A
Authority: EP
Inventors: Ernst Miklos; Rudolf Berghoff; Alexander Alekseev; Andreas Rupieper
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2016-11-02
Filing date: 2016-11-02
Publication date: 2021-12-29
Anticipated expiration: 2036-11-02
Also published as: EP3318825A1

Description

The invention relates to a method and an apparatus for cooling objects with a cryogenic liquid.
Today, nozzles are being used for quickly and gently cooling various objects such as food, metals, plastics, agricultural products etc. by means of cryogenic liquids such as liquid Nitrogen (LIN) oder liquid air (LAIR) or other cryogenic temperature fluids such as CO₂, O₂, CH₄ etc. Such nozzles can be flat jet nozzles, single hole or multi hole nozzles, full cone nozzles, hollow cone nozzles, angled or wide angle nozzles etc.
Also in chemistry or metallurgy and other areas cryogenic nozzles are used.
Particularly, objects to be cooled are more or less homogeneously and evenly sprayed with the respective cryogenic liquid. For example, the document EP 2 884 206 A1 discloses cryogenic liquid cooling of objects.
A specific characteristic of such a spraying process is the fact that the temperature difference between the cooling fluid (LIN, LAIR etc) and the object to be cooled is in the range of about 200°C which is extremely large (due to the fact that the boiling temperature of such cryogenic fluids is often lower than -180°C while the temperature of the objects to be cooled usually corresponds to the ambient (e.g. room) temperature).
This extremely high temperature difference causes the so-called Leidenfrost effect, wherein a vapor layer is formed between the cryogenic liquid and the surface of the object or substance to be cooled (can be liquid or solid).
This vapor layer has a heat-insulating effect and reduces a heat transfer between the cryogenic liquid and the object to be cooled. The Leidenfrost phenomenon for instance explains why a water drop moves on a hot plate instead of evaporating instantly.
The reduced heat transfer caused by the Leidenfrost effect is bad for cooling and causes long cooling times and a less efficient use of cooling fluids.
Based on the above, the problem to be solved by the present invention is to provide a method and an apparatus for cooling an object by means of a cryogenic liquid that allow an efficient and easy cooling of substances with a cryogenic fluid.
This problem is solved by a method having the features of claim 1 and an apparatus having the features of claim 9. Preferred embodiments of the respective aspect of the present invention are stated in the corresponding sub claims and are described in detail below.
According to claim 1, the method for cooling at least one object, comprises the steps of: providing at least one object to be cooled, and spatially distributing a cryogenic cooling liquid using at least one nozzle onto said at least one object so that the at least one object is cooled, particularly frozen, wherein said at least one nozzle is a fluidic oscillating nozzle, and wherein said at least one fluidic oscillating nozzle is configured to generate a spatially oscillating jet of said cryogenic cooling liquid while maintaining a constant flow rate of the cryogenic cooling liquid through the nozzle.
Particularly, the spatial distribution of the cryogenic cooling liquid by means of the fluidic oscillating nozzle helps to reduce the negative impact of the Leidenfrost effect, since the insulating vapor barrier can be disrupted by the oscillating flow. Furthermore, using a fluidic oscillating nozzle is less difficult than generating a pulsating jet or flow of a cooling agent using a cryogenic nozzle which may alternatively be used in order to reduce the Leidenfrost effect. However, generating such pulsating jets is a relatively difficult task, since a corresponding device/mechanism is needed (e.g. a rotating nozzle rim or an ultrasound generator) which complicates the design and increases maintenance and costs.
Preferably, the method according to the invention uses a plurality of such fluidic oscillating nozzles. Particularly, the nozzles can be equidistantly spaced with respect to one another.
Particularly, the spatially oscillating jet of the cryogenic cooling liquid disturbs or even removes a vapor layer on the surface of the at least one object to be cooled so that the heat transfer away from the at least one object is increased.
Of course, a plurality of objects can be cooled with the present method according to the invention, wherein objects may be cooled successively (e.g. in a tunnel freezer, see below) or all at the same time (e.g. in a cabinet freezer, see below).
Particularly, the at least one fluidic oscillating nozzle comprises no moving parts and is configured to generate said oscillating jet by means of its geometric design, i.e., the geometric design of the involved flow paths of the nozzle. Particularly, such a fluidic nozzle is described in detail in US4955547 A (cf. e.g. Fig. 3).
Particularly, the heat distribution in a space around the at least one object (this space can be an internal space of an enclosure such as a chamber of a cabinet freezer or a tunnel of a tunnel freezer) takes place due to evaporation of the cryogenic cooling liquid in the oscillating jet.
Furthermore, according to an embodiment of the method according to the invention, said cryogenic cooling fluid is one of or comprises one of: liquid nitrogen (LIN), liquid air (LAIR), liquid carbon dioxide (LIC), or any other suitable cryogenic cooling liquid.
Furthermore, according to an embodiment of the method according to the invention, said at least one object is one of: food, a plant (or a part therof), meat, seafood, fish, a beverage, an object formed out of a metal or comprising a metal, an object formed out of a synthetic material or comprising a synthetic material.
Furthermore, according to an embodiment of the method according to the invention, the step of providing said at least one object corresponds to transporting the at least one object with a transport velocity on a conveyor through a tunnel of a tunnel freezer, which tunnel freezer comprises said at least one nozzle (or said plurality of nozzles).
Particularly, said nozzle(s) is/are configured to discharge the cryogenic cooling liquid downwards onto the at least one object or the plurality of objects to be cooled.
Further, according to an embodiment of the method according to the present invention, the cryogenic cooling liquid is provided upstream said at least one nozzle with an inlet pressure, wherein said inlet pressure is controlled depending on said transport velocity.
Further, according to an embodiment of the method according to the present invention, the cryogenic cooling liquid is discharged through the at least one nozzle with a flow rate, wherein said flow rate is controlled depending on said transport velocity, particularly said flow rate is a volumetric flow rate having the SI-unit m³/s.
In other words, having e.g. an even spatial distribution of objects on the conveyor, said inlet pressure or flow rate can be controlled depending on the throughput of the objects to be cooled through the tunnel freezer.
Further, according to an alternative embodiment of the method according to the present invention, the step of providing said at least one object corresponds to placing the at least on object (or a plurality of objects) in a chamber, particularly a chamber of a cabinet freezer, wherein said at least one nozzle is configured to discharge the cryogenic cooling liquid into said chamber.
When cooling objects or their surfaces in enclosures or tunnels, also the convection in the internal space defined by said enclosure or tunnel matters regarding cooling efficiency. Particularly, the better the swirling in said space, or the flow through said space (particularly circulation), the easier heat can be transported from the object to be cooled to the cold gas phase.
Therefore, according to an embodiment of the method according to the present invention, evaporated cryogenic cooling liquid is distributed in a space adjacent said at least one object (e.g. an internal space of a tunnel freezer or of a chamber of a cabinet freezer) by means of at least one fan or a plurality of fans.
According to yet another aspect of the present invention, an apparatus for cooling, particularly freezing, an object by means of a cryogenic cooling liquid is disclosed, which apparatus is preferably used in the method according to the present invention, and which apparatus comprises: an internal space for receiving said at least one object to be cooled, at least one nozzle that is configured to discharge said cryogenic cooling liquid into the internal space and onto the object to be cooled when the latter is arranged in said internal space, wherein according to the invention, the at least one nozzle is a fluidic oscillating nozzle (e.g. as described above).
Particularly, the apparatus may comprise a plurality of such nozzles arranged in said internal space. Particularly, the at least one nozzle or said plurality of nozzles are arranged such in said internal space that the cryogenic cooling liquid is discharged downwards onto the at least one object or the objects to be cooled.
According to the invention, said at least one fluidic oscillating nozzle is configured to generate a spatially oscillating jet of said cryogenic cooling liquid while maintaining a constant flow rate of the cryogenic cooling liquid through the nozzle.
Further, particularly, the at least one nozzle is configured to provide said spatially oscillating jet of said cryogenic cooling liquid such that the heat distribution in said internal space takes place due to evaporation of the cryogenic cooling liquid in the oscillating jet.
Particularly, according to an embodiment of the apparatus according to the present invention, said internal space is formed by a tunnel, particularly having an inlet for arranging objects to be cooled into the internal space of the tunnel and an outlet for taking cooled objects out of the internal space of the tunnel, wherein the apparatus further comprises a conveyor for transporting objects to be cooled through said internal space formed by the tunnel with a defined transport velocity (i.e. the velocity of the conveyor).
Further, according to an embodiment of the apparatus according to the present invention, the apparatus comprises a control unit that is configured to control an inlet pressure of the cryogenic cooling liquid upstream said at least one nozzle or a flow rate of the cryogenic cooling liquid through the at least one nozzle, wherein said inlet pressure or flow rate is preferably controlled depending on said transport velocity.
According to yet another embodiment of the apparatus, said internal space is formed by a closable chamber, e.g., here said apparatus forms a cabinet freezer.
According to a further embodiment of the apparatus (e.g. tunnel freezer or cabinet freezer), the apparatus comprises at least one fan (or a plurality of fans) for distributing evaporated cryogenic liquid inside the internal space of the apparatus (see also above).
Further features, advantages and embodiments of the present invention shall be described with reference to the Figure below, wherein

Fig. 1: shows an embodiment of an apparatus according to the present invention in the form of a tunnel freezer;
Fig. 2: shows a further embodiment of an apparatus according to the present invention in the form of a cabinet freezer;

Figures 1 and 2 show embodiments of an apparatus 1 according to the present invention that is configured to cool, particularly freeze, objects O. Particularly, Fig. 1 shows an apparatus in form of a tunnel freezer 1, while Fig. 2 shows an embodiment where the apparatus 1 is formed as a cabinet freezer 1. However, the present invention is in principle applicable to all kinds of apparatus that use discharging of a cryogenic cooling liquid L for cooling or freezing objects O.
According to Fig. 1 the apparatus 1 comprises an internal space I for receiving the objects O to be cooled, particularly to be frozen, as well as at least one nozzle 100 or a plurality of such nozzles 100, wherein the at least one nozzle 100 is a fluidic oscillating nozzle 100 that is configured to generate a spatially oscillating jet F of said cryogenic cooling liquid L while maintaining a constant flow rate of the cryogenic cooling liquid L through the nozzle 100.
The spatially oscillating jet F of the cryogenic cooling liquid L is made to disturb or even remove a vapor layer V that normally forms on the surface of the at least one object O to be cooled so that the heat transfer away from the at least one object O is increased.
As shown in the detail (dashed circle) of Fig. 1 and already mentioned above, the fluidic oscillating nozzle 100 preferably comprises no moving parts, but can be configured to generate said oscillating jet F by means of its geometric design. For instance, the fluidic oscillating nozzle 100 may let a central flow L of the cryogenic cooling liquid interact with two other flows L', L" so that said oscillating jet F is achieved. Alternative fluidic oscillating nozzle techniques may also be applied instead.
Due to the oscillating jet F (or a plurality of such jets F), the heat distribution in the internal space I takes place due to evaporation of the cryogenic cooling liquid in the oscillating jet(s) F.
As indicated in Fig. 1 the internal space I is formed by a tunnel 2 of the apparatus 1 which is designed as a tunnel freezer 1. The tunnel 2 comprises an inlet 2a for introducing objects to be cooled into the internal space I of the tunnel 2 and an outlet 2b for taking cooled objects O out of the internal space I of the tunnel 2.
The apparatus 1 further comprises a conveyor 5 for transporting objects O to be cooled through said internal space I formed by the tunnel 2 with a transport velocity u.
The direction D of the oscillations of the jet(s) F as indicated in the detail of Fig. 1 can be perpendicular to the direction of the velocity u, but may also be oriented parallel to said velocity u or may form some other angle with the velocity u.
Particularly, the at least one nozzle 100 or said plurality of nozzles 100 are arranged such in said internal space I of the apparatus 1 that the cryogenic cooling liquid L is discharged downwards onto the at least one object O or the objects O to be cooled.
Further, cryogenic cooling liquid L may be provided to the nozzle(s) 100 by a supply 8, e.g. a tank 8 that stores cryogenic cooling liquid L, which supply 8 may be connected to the nozzle(s) 100 via a valve 9.
Further, the apparatus 1 can comprise a control unit 6 that is configured to control an inlet pressure of the cryogenic cooling liquid L upstream said nozzle(s) 100 or a flow rate of the cryogenic cooling liquid L through the nozzle(s) 100, wherein said inlet pressure or flow rate is preferably controlled depending on said transport velocity u. For this, the control unit 6 may receive said velocity u from a suitable sensor of the conveyor 5 and may cooperate with an actuator that actuates the valve 9. Alternatively, as shown in Fig. 2, the apparatus 1 may also be formed as a cabinet freezer that comprises a closable chamber 7 which forms the internal space I of the apparatus 1. Here, the objects O to be cooled are placed into the internal space I and the chamber is closed. Also here, at least one fluidic oscillating nozzle 100 or several such nozzles 100 which may be formed as shown in the detail of Fig. 1 are used to generate an oscillating jet F (or several such jets) of the cryogenic cooling liquid L that particularly disturbs or removes the vapor layer V forming around the objects O upon cooling as described before.
Also here, the inlet pressure or flow rate of the cryogenic cooling liquid may be controlled depending on one or several parameters such as the temperature inside the internal space I etc.
In the embodiments of Figs. 1 and 2, the cryogenic cooling liquid L may be one of liquid nitrogen (LIN), liquid air (LAIR), or liquid carbon dioxide (LIC).

As shown in Figs. 1 and 2, the gaseous phase G of the coolant that is generated upon evaporation of the used cryogenic cooling liquid L is preferably distributed in the internal spaces I by means of at least one or a plurality of fans 4 that may be arranged in the respective internal space I.

Reference Numerals

1	Apparatus (e.g. tunnel freezer or cabinet freezer)
2	Tunnel
2a	Inlet
2b	Outlet

4	Fan
5	Conveyor
6	Control unit
7	Chamber
8	Cryogenic cooling liquid supply (e.g. tank)
9	Valve
100	Fluidic oscillating nozzle
D	Direction
F	Jet
G	Gaseous phase
L, L', L"	Cryogenic cooling liquid
O	Object
V	Vapor layer
U	Transport velocity

Claims

A method for cooling an object (O), comprising the steps of:
- providing at least one object (O) to be cooled,

- spatially distributing a cryogenic cooling liquid (L) using at least one nozzle (100) onto said at least one object (O) so that the at least one object (O) is cooled,
characterized in that
said at least one nozzle (100) is a fluidic oscillating nozzle (100),

which is configured to generate a spatially oscillating flow (F) of said cryogenic cooling liquid (L) while maintaining a constant flow rate of the cryogenic cooling liquid (L) through the nozzle (100).
The method according to claim 1, wherein said cryogenic cooling liquid (L) is one of or comprises one of:
- liquid nitrogen (LIN),

- liquid air (LAIR),

- liquid carbon dioxide (LIC).
The method according to one of the preceding claims, wherein said at least one object (O) is one of or comprises one of:
- food,

- a plant,

- meat,

- a beverage,

- an object formed out of a metal or comprising a metal,

- an object formed out of a synthetic material or comprising a synthetic material.
The method according to one of the preceding claims, wherein the step of providing said at least one object (O) corresponds to transporting the at least one object (O) with a transport velocity (u) on a conveyor (5) through a tunnel (2) of a tunnel freezer (1), which tunnel freezer (1) comprises said at least one nozzle (100).
The method according to claim 4, wherein the cryogenic cooling liquid (L) is provided upstream said at least one nozzle (100) with an inlet pressure, wherein said inlet pressure is controlled depending on said transport velocity (u).
The method according to claim 4, wherein the cryogenic cooling liquid (L) is discharged through the at least one nozzle (100) with a flow rate, wherein said flow rate is controlled depending on said transport velocity (u).
The method according to one of the claims 1 to 3, wherein the step of providing said at least one object (O) corresponds to placing the at least on object (O) in an internal space (I) of a closable chamber (7), particularly a chamber (7) of a cabinet freezer (1), wherein said at least one nozzle (100) is configured to discharge the cryogenic cooling liquid (L) into said internal space (I).
The method according to one of the preceding claims, wherein evaporated cryogenic cooling liquid (G) is distributed in a space adjacent said at least one object (O) by means of at least one fan (4).
An apparatus for cooling an object (O) by means of a cryogenic cooling liquid (L), the apparatus comprising:
- an internal space (I) for receiving said object (O) to be cooled,

- at least one nozzle (100) that is configured to discharge said cryogenic cooling liquid (L) into said internal space (I) and onto the object (O) to be cooled when the latter is arranged in said internal space (I),
characterized in that
the at least one nozzle (100) is a fluidic oscillating nozzle (100), which is configured to generate a spatially oscillating flow (F) of said cryogenic cooling liquid (L) while maintaining a constant flow rate of the cryogenic cooling liquid (L) through the nozzle.
The apparatus according to claim 9, characterized in that said internal space (I) is formed by a tunnel (2), wherein the apparatus (1) further comprises a conveyor (5) for transporting an object (O) to be cooled through said internal space (I) with a transport velocity (u).
The apparatus according to claim 10, characterized in that the apparatus (1) comprises a control unit (6) that is configured to control an inlet pressure of the cryogenic cooling liquid (L) upstream said at least one nozzle (100) or a flow rate of the cryogenic cooling liquid (L) through the at least one nozzle (100), wherein said inlet pressure or flow rate is controlled depending on said transport velocity (u).
The apparatus according to claim 9, characterized in that said internal space (I) is formed by a closable chamber (7).
The apparatus according to one of the claims 9 to 12, characterized in that the apparatus (1) comprises at least one fan (4) for distributing evaporated cryogenic liquid (G) inside the internal space (I).