DK2574408T3

DK2574408T3 - Process and apparatus for supplying a refrigerant stream

Info

Publication number: DK2574408T3
Application number: DK11183587.2T
Authority: DK
Inventors: Cerkez Kaya
Original assignee: Air Liquide
Priority date: 2011-09-30
Filing date: 2011-09-30
Publication date: 2018-06-06
Also published as: EP2574408B1; PL2574408T3; EP2574408A1; ES2670824T3

Description

The object of the present invention is a method and a device for supplying a coolant media flow. This coolant media flow is used during thermal coating to achieve effective cooling of the components to be coated and the spray materials.

Components are often thermally coated to alter the surface properties of the component with respect to corrosion, wear, or temperature resistance. The change of adhesive properties or static and/or sliding friction is also often in the foreground of the coating. Other functional surfaces can also be created in this manner. In thermal coating, two materials that regularly differ in terms of their physical properties at least are combined with each other. For instance, layers of plastics, metals, alloys, carbides, oxides, ceramics and mixtures of these materials are applied by thermal coating. In thermal coating, the components to be coated are coated in one or several passes, wherein flame spraying process, high velocity flame spraying process, electric arc spraying process and plasma spraying process are used to apply a spray material.

The coating or the spray material is formed from a material that is melted or fused and applied to the component surface. Thereby, the component surface should not be melted regularly. The bonding of the layer to the component surface takes place primarily by mechanical grouting, alternatively or additionally by diffusion.

In order to prevent thermal damage to the component or change of properties of the component, it is necessary to set the temperature as accurately as possible. This is also necessary in order to achieve good adhesion of the coating on the component surface, since excessive heating of the component, shear stresses can develop between the coating and component surface due to the resulting expansion and subsequent shrinkage during cooling, which can at least lead to partial detachment of the coating from the component surface.

So far, in the case of thermal coating, cooling takes place by means of carbon dioxide introduced into a stream of compressed air or else by atomised liquid carbon dioxide to form carbon dioxide snow. This coolant medium is then applied to the component surface.

For instance, WO 2008/027 900 A2 describes a method for cooling with a cryogenic liquid that is brought into contact with a throttling gas or with another cryogenic liquid by means of a nozzle.

For a variety of applications, it is known to discharge media by means of nozzles. For instance, DE 10 2009 052946 A1 discloses a process for producing a protective coating by means of a cold gas spraying nozzle. In US 3 703 991A a method for producing artificial snow for skiing is disclosed. In DE 101 21 590 A1 a method for cooling in machining processes is also disclosed. In US 5 520 331A a device for extinguishing fire is disclosed.

Flereby, the cooling effectiveness essentially depends on how much coolant medium and in which composition the same impinges on the component surface and, in particular, how much carbon dioxide snow impinges on the component surface, limes on the component surface and how far there is heat exchange between component and carbon dioxide or coolant medium: This is often unsatisfactory and, in particular, when the components move fast and/or have a rotating thermal mass, as is the case, for instance, when coating rollers, disks and spheres, it is difficult from the state of the art to achieve an effective and sufficient cooling of component surface.

Based on this, the present invention has the object to provide a method and a device for supplying a coolant medium in which the disadvantages known from the state of the art are partially at least overcome and in particular to provide a method and a device for supplying a coolant medium in which the coolant medium flow is adjustable with respect to flow rate and composition.

These tasks are solved by independent claims. The subordinate claims are directed at advantageous developments.

Advantageous developments are also specified by the features disclosed in the description, which can be combined in any technologically meaningful manner with each other and with features of the claims. The same applies to features disclosed in the figures.

In the method according to the invention for supplying a coolant medium flow, a coolant medium flow is introduced through a coolant medium nozzle into a carrier gas flow, wherein the coolant medium is liquid and/or gaseous. The method is characterised in that the carrier gas flow is passed through a Laval nozzle, wherein the Laval nozzle has a longitudinal axis and the coolant medium flow is inlet such that the exit of the coolant medium flow takes place in the carrier gas flow within or downstream of the Laval nozzle. A Laval nozzle is understood to be a nozzle in which the cross-section of the nozzle initially narrows in the flow direction and then widens again until the gas emerges. A carrier gas flow is understood to mean a flow of a carrier gas. The carrier gas is present in gaseous form. A coolant medium flow is understood to mean a flow of a coolant medium. The coolant medium is present in liquid and/or gaseous. It can change its state of aggregation upon exit from the coolant medium nozzle, such that a liquid coolant medium is at least partially gaseous and/or solid after emerging from the coolant medium nozzle. The coolant medium nozzle may be an arbitrary nozzle; in particular, it may also be the exit of a tube.

The Laval nozzle initially accelerates the carrier gas flow. At the same time, when the outlet of the coolant medium flow in the carrier gas flow takes place within the Laval nozzle, carrier gas flow and coolant medium flow are mixed together. Distribution of the coolant medium in the carrier gas flow takes place. If the coolant medium nozzle is positioned in such a manner that the outlet of the coolant medium flow takes place downstream of the Laval nozzle, the mixing of coolant medium and carrier gas takes place in the carrier gas flow generated by the Laval nozzle. Due to the acceleration experienced by the carrier gas in the Laval nozzle, basically turbulent or quasi-turbulent flow is generated into which the coolant medium is introduced. Thus, good mixing of coolant medium and carrier gas takes place.

According to an advantageous embodiment of the method, the coolant medium nozzle can be displaced in the longitudinal-axis direction of the Laval nozzle relative to the Laval nozzle.

Alternatively or additionally, the coolant medium nozzle is replaceable in design. Consequently, coolant medium nozzles of different flow-through cross-sections can be set interchangeably for different areas of application.

Due to the choice of the position of the coolant medium relative to the Laval nozzle according to the invention and in particular by the preferred displacement of the coolant medium nozzle relative to the Laval nozzle, the composition can be set or adjusted, in particular with regard to the distribution of aggregate states of the coolant medium, thus, which proportion of the coolant medium is present in liquid form, which proportion in solid form and which proportion in gas form, the spatial distribution of the coolant medium in the carrier gas flow and/or the particle size, in particular the droplet or grain size of the liquid or solid phase.

In particular, when carbon dioxide is used as coolant medium, an adjustment of the size distribution of the carbon dioxide snow on the one hand and the spatial distribution of the carbon dioxide snow particles in the carrier gas flow can be achieved. If a predominantly liquid coolant medium, for instance, liquid nitrogen or liquid argon is used as coolant medium, the droplet size distribution of the nitrogen or argon in the carrier gas flow can be adjusted.

Due to the efficient atomisation of the coolant medium in the carrier gas flow is possible by selecting the position of the coolant medium relative to the Laval nozzle or by the preferred displacement of the coolant medium nozzle relative to the Laval nozzle, the setting of a particle size distribution and/or a spatial distribution of the coolant medium in the carrier gas flow in adaptation to the respective requirements of cooling. Thus, when used in thermal coating or thermal spraying, the particle size and the distribution of the particles in the carrier gas flow to the nature of the component to be coated, in particular with regard to the reduction of thermal expansion and shrinkage, and of the spray materials are adjusted, in order to reduce or avoid defective layer formation or adhesion due to thermally induced shear stresses.

According to an advantageous embodiment of the method according to the invention, the coolant medium is in liquid state when flowing through the coolant medium nozzle.

In particular, when carbon dioxide in liquid form is supplied to the coolant medium nozzle as a coolant medium, it may come at least partially to the formation of coolant medium in solid state after exiting the coolant medium nozzle, for instance as carbon dioxide snow and partial evaporation of carbon dioxide. When using liquid nitrogen and/or argon, there is regularly at least partial evaporation of the nitrogen and/or argon.

The use of a fundamentally liquid coolant medium has proved to be advantageous, since the evaporation enthalpy can thus be used for cooling. The same applies optionally at least partially to the formed carbon dioxide snow, in which the sublimation coldness can be used for cooling the component surface.

According to a further advantageous embodiment of the method according to the invention, the coolant medium comprises at least one of the following substances: - Carbon-dioxide (C02); - Nitrogen (N2); and - Argon (Ar).

In particular, when used in thermal coating or spraying, the carbon dioxide has proven to be advantageous as a coolant medium, since the formation of carbon dioxide snow can be good for the distribution of the coolant medium on the component surface and thus effective cooling can be achieved and the sublimation cooling effect used for cooling the component surface. When using liquid nitrogen or argon, the enthalpy of evaporation can advantageously be used for further cooling of component surface. Nitrogen and argon are inert gases that can be used to suppress reactions with the component surface during coating and cooling, in particular to suppress oxidation reactions. According to a further advantageous embodiment of the method according to the invention, the carrier gas comprises at least one of the following gases: - Air; - Argon; - Nitrogen; and - Carbon dioxide

In order to allow the simplest possible process control, it is preferred to use an identical gas as carrier gas and coolant medium, wherein the gas is used preferably as coolant medium at least partially in another state of aggregation. The use of air as a carrier gas has proven to be particularly cost effective.

In particular, in the case of air as carrier gas, and generally, when the carrier gas has a certain humidity, ice formation may occur at the coolant medium nozzle. This can preferably be counteracted, in that the coolant medium nozzle is provided with a thermal insulation, for instance, in which a coating of a plastic, in particular of polytetrafluoroethylene, is provided.

According to a further advantageous embodiment of the method according to the invention, the carrier gas flow is passed through a porous body before the coolant medium flow is introduced.

Particularly preferred here is the use of a sintered material, such as a sintered metal or a sintered ceramic, to form the porous body. The routing of the carrier gas flow through a porous body results in a flow equalisation downstream of the porous body. At the same time, the porous body can be used advantageously for mechanical holding and/or centring of the coolant medium nozzle in the Laval nozzle.

According to a further advantageous embodiment of the method according to the invention, the coolant medium nozzle is formed centred relative to the Laval nozzle. In particular, when the Laval nozzle has an axis of symmetry in the form of the longitudinal axis, that is rotationally symmetrical about the longitudinal axis, it is advantageous to centre the coolant medium relative to the Laval nozzle, thus to form it on the longitudinal axis of the Laval nozzle. In this manner, it can be achieved that the coolant medium flow is added in the region of the highest flow velocity of the carrier gas flow, which leads to a particularly good distribution of the coolant medium in the carrier gas.

According to a further advantageous embodiment of the method according to the invention, the coolant medium flow is introduced in the direction of the longitudinal axis of the Laval nozzle.

It has been found that addition of the coolant medium in the direction of the longitudinal axis leads to a particularly uniform distribution of the coolant medium in the carrier gas. In certain cases, it may also be advantageous instead to introduce the coolant medium flow at an angle to the longitudinal axis, in particular when strongly asymmetric applications have to be acted upon by a coolant medium flow. This can be achieved, for instance, by supplying the coolant medium nozzle with coolant medium through a coolant medium feed line formed in the direction of the longitudinal axis of the nozzle, but the coolant medium nozzle has an outlet opening, which activates a coolant medium flow in a direction that differs from the longitudinal axis.

According to a further aspect of the present invention, a device for supplying a coolant medium flow is proposed that comprises: - a Laval nozzle with an inlet side and an outlet side; - a carrier gas connection attached to the inlet side of the Laval nozzle; and according to the invention, the coolant medium nozzle is designed such that an outlet opening of the coolant medium nozzle lies within the Laval nozzle or the outlet opening of the coolant medium nozzle is located behind the outlet side of the Laval nozzle.

Hereby, the outlet side is the limiting plane of the Laval nozzle, which is formed opposite the inlet side. The carrier gas connection is understood as meaning a connection through which a carrier gas can flow into the Laval nozzle. Thus, in the case where the supply opening of the coolant medium nozzle is located behind the outlet side of the Laval nozzle, the outlet side of the Laval nozzle lies between the supply connection of the coolant medium nozzle and the inlet side of the Laval nozzle.

The device according to the invention can preferably be used for the method according to the invention.

The coolant medium nozzle is slide-able along a longitudinal axis of the Laval nozzle.

The formation of a device in which a coolant medium nozzle is designed to be slide-able within a Laval nozzle allows the adjustment of the properties of the coolant medium flow during supply from the device, in particular with regard to the particle size distribution and the distribution of the particles in the carrier gas flow.

According to an advantageous embodiment of the device according to the invention, the coolant medium nozzle is formed coaxially to the Laval nozzle.

By coaxial it is meant that an axis of the coolant medium nozzle is identical to a corresponding axis of the Laval nozzle. In particular, the coolant medium nozzle is formed so that it has an outlet opening that faces in the direction of the outlet side and is formed symmetrically about the longitudinal axis of the Laval nozzle.

Through the coaxial design of the Laval nozzle and the coolant medium nozzle, the slide-ability in the direction of the longitudinal axis can be achieved in a simple design manner. By an outlet opening symmetrical to the longitudinal axis, a substantially symmetrical spatial distribution of coolant medium in the carrier gas flow can be achieved.

According to a further advantageous embodiment, the coolant medium nozzle comprises a tube, preferably with an inner diameter of less than 1.5 mm, preferably less than 1.0 mm, particularly preferably less than 0.5 mm.

Preferably, a capillary is used as a coolant medium nozzle or for supplying the coolant medium to the coolant medium nozzle, which makes it possible to supply the coolant medium in sufficiently small economically reasonable volume flows. The inner diameter of the capillary and/or of the tube can be adjusted depending on the necessary cooling and other conditions such as the applied coolant medium pressure in order to achieve the most efficient cooling possible.

In principle, the present invention allows particle or droplet size distributions that are adjustable with a slide-able coolant medium nozzle, for instance particle diameters or droplet diameters of 20 to 40 pm [micrometre] up to 0.2 to 0.3 mm [millimetre].

According to a further advantageous embodiment of the device according to the invention, the coolant medium nozzle comprises at least one of the following nozzles: - a Laval nozzle, - a constricted tube; and - a tube A constricted tube is understood to mean a tube whose flow-through cross-section is reduced at least in a subsection. With a tube as coolant medium nozzle, this has a substantially constant cross-section through which fluid flows. Under a tube, also a capillary with an inner diameter of 1.5 mm and less is advantageously understood. A Laval nozzle is preferably used when it is necessary, due to the circumstances, to increase the outlet velocity of the coolant medium flow. A tube, in particular a capillary, as a nozzle is preferably used when only a fairly short coolant medium nozzle is necessary, that is, the coolant medium flow is to be introduced in the upstream direction of the Laval nozzle. In the constricted tube, the inner diameter allowing flow-through is preferably reduced by more than 30%, for instance, from an inner diameter of about 0.8 mm to 0.4 mm or 0.5 mm. If the coolant medium nozzle is designed as a Laval nozzle, then the flow-through diameter from upstream of this Laval nozzle to the central part of the Laval nozzle can be reduced by at least 50%, for instance, from 0.8 mm to 0.3 mm. Even with a constricted tube as the coolant medium nozzle, the reduced flowthrough cross-section leads to an acceleration of the coolant medium flow.

The production of a Laval nozzle or a constricted tube as a coolant medium nozzle is preferably and independently of the present invention is carried out by heating a metal capillary and pulling it apart.

According to a further advantageous embodiment of the device according to the invention, a porous body is formed between the carrier gas connection and the Laval nozzle.

This porous body is exposed to flow through of the carrier gas during operation. It preferably involves a sintered body, in particular a sintered metal body or a sintered ceramic body. Due to the flow through the porous body, the carrier gas flow is made uniform, so that when the carrier gas flows into the Laval nozzle, defined conditions prevail, so that smaller pressure fluctuations and the like in the carrier gas supply before the porous body are compensated.

According to a further advantageous embodiment of the device according to the invention, the coolant medium nozzle is centred by a porous body relative to the Laval nozzle.

Thereby, an embodiment is selected in which the coolant medium nozzle is still slide-able. At the same time, the porous body can also be used to streamline the carrier gas flow.

The details and advantages disclosed for the method according to the invention can be transferred and applied to the device according to the invention and vice versa. In the following, the invention is explained in more detail with reference to the accompanying drawing, without being limited to the embodiments depicted therein. Shown in exemplary and schematic manner:

Fig. 1 a first embodiment of a device according to the invention; and Fig. 2 a second embodiment of a device according to the invention.

Fig. 1 schematically depicts a first embodiment according to the invention of a device 1 for supplying a coolant medium flow. The device 1 comprises a nozzle body 2 with a Laval nozzle 3. The Laval nozzle 3 comprises a first section 4, in which the flow-through cross-section decreases, a second section 5, in which the flow-through cross-section is constant, and a third section 6, in which the flow-through cross-section increases. The Laval nozzle 3 is formed rotationally symmetrical around a longitudinal axis 7. The Laval nozzle 3 has an inlet side 8 and an outlet side 9. In operation, the Laval nozzle 3 is exposed to flow-through from the inlet side 8 to the outlet side 9.

Connected to the inlet side 8 of the Laval nozzle 3 is a carrier gas connection 10, through which the device 1 can be supplied with a carrier gas during operation. Furthermore, the device 1 comprises a coolant medium nozzle 11 with an outlet opening 12 for introducing coolant medium into the carrier gas flow. The coolant medium nozzle 12 is connected to a coolant medium supply line 13. In operation, the coolant medium nozzle 11 is supplied via the coolant medium supply line 13 with coolant medium that is introduced through the outlet opening 12 in the carrier gas flow. Thereby, the coolant medium nozzle 11 is disposed in slide-able manner along the longitudinal axis 7 of the Laval nozzle 3, so that the coolant medium flow is introduced either within the Laval nozzle 3 into the carrier gas flow or is introduced downstream of the Laval nozzle 3 into the carrier gas flow. This means that the coolant medium nozzle 11 is designed to be longitudinally slide-able so that the outlet opening 12 is either positioned within the Laval nozzle 3 or positioned behind the outlet side 9 of the Laval nozzle 3. The latter case means that the outlet side 9 of the Laval nozzle 3 is located between the outlet opening 12 of the coolant medium nozzle 11 and the inlet side 8 of the Laval nozzle 3.

Fig. 1 shows a case where the coolant medium nozzle 11 is a Laval nozzle that lies within the Laval nozzle 3. In operation, a carrier gas is introduced through the carrier gas connection 10 into the Laval nozzle 3, whereby the resulting carrier gas flow in the Laval nozzle 3 is accelerated. In the resulting carrier, gas flow the coolant medium is then added as the coolant medium flow through the coolant medium nozzle 11. Due to the addition into the carrier gas flow whose flow properties change through the Laval nozzle 3, a distribution of the coolant medium and an atomisation of the coolant medium in the carrier gas flow take place. Depending on the position of the outlet-opening 12 of the coolant medium nozzle 11 in the Laval nozzle 3 or downstream of the Laval nozzle 3, other particle size distributions of the coolant medium in the carrier gas flow are achieved and other spatial distributions of the coolant medium in the carrier gas flow.

The reference numeral 14 indicates the displacement range in which the outlet opening 12 of the coolant medium nozzle 11 can move. Preferred is an embodiment in which the section around which the coolant medium nozzle 11 can protrude from the Laval nozzle 3 is less than one fifth of the length of the displacement section 14 in the direction of the longitudinal axis 7, preferably even less than one tenth.

Furthermore, the first exemplary embodiment of the device 1 according to the invention comprises a porous body 15. This is formed as a sintered metal disc and centres the coolant medium nozzle 11, and/or, the coolant medium supply line 13 inside the Laval nozzle 3. In operation, the carrier gas is forced through the porous body 15, this leads to homogenisation of the carrier gas flow. Thus, pressure and velocity fluctuations of the carrier gas can be damped before inlet into the Laval nozzle 3, so that uniform conditions always prevail during operation.

Fig. 2 schematically depicts a second embodiment of the present invention. Here, for the sake of clarity, only the differences from the first embodiment will be described. For the rest, reference is made to the description of the first embodiment. In the second embodiment of the device 1 according to the invention, another coolant medium nozzle 11 is formed. The coolant medium nozzle 11 is formed in this case as a capillary that also represents the coolant medium supply line 13. The coolant medium, such as carbon dioxide exits only from the coolant medium supply line 13 through the outlet opening 12 of the coolant medium nozzle 11 and is then atomised and distributed in the carrier gas flow.

The method according to the invention and the device 1 according to the invention can be used advantageously for applying a coolant medium flow into the section of a component surface that is to be thermally coated or sprayed. In particular, when carbon dioxide is used as coolant medium and optionally also as a carrier gas, an adaptable distribution of the particle sizes and effective cooling of the component surface occurs, through which thermally induced shear stresses between the coating and component surface can be effectively reduced or avoided.

List of reference numbers 1 device for supplying a coolant medium flow 2 nozzle body 3 Laval nozzle 4 first section 5 second section 6 third section 7 longitudinal axis 8 inlet side 9 outlet side 10 carrier gas connection 11 coolant medium nozzle 12 outlet opening 13 coolant medium supply line 14 slide-able section 15 porous body

Claims

A method of supplying a refrigerant stream for cooling a component in connection with thermal coating, wherein a refrigerant stream is passed through a refrigerant nozzle (11) into the carrier gas stream, said refrigerant being liquid or gaseous, characterized in that a carrier gas stream is fed. through a Laval nozzle (3), wherein the Laval nozzle (3) comprises a longitudinal axis (7) and the coolant stream is administered such that the outflow of the coolant stream into the carrier gas stream occurs within or downstream of the Laval nozzle (3).

The method of claim 1, wherein the refrigerant nozzle (11) in the direction of the longitudinal axis (7) of the Laval nozzle (3) can be displaced relative to the Laval nozzle (3).

The method of claim 1 or 2, wherein the coolant during flow of the coolant nozzle (11) is in liquid aggregate mode.

A process according to any one of the preceding claims, wherein the refrigerant comprises at least one of the following substances: - Carbon dioxide (CO2); - Nitrogen (N2); and - Argon (Ar).

A process according to any one of the preceding claims, wherein the carrier gas comprises at least one of the following gases: - Air; - Argon; - nitrogen; and - Carbon dioxide.

A method according to any one of the preceding claims, wherein the carrier gas stream is passed through a porous body (15) before the refrigerant stream is supplied.

A method according to any one of the preceding claims, wherein the refrigerant nozzle (11) is designed as centered relative to the Laval nozzle (3).

A method according to any one of the preceding claims, wherein the refrigerant stream is fed in the direction of the longitudinal axis (7) of the Laval nozzle (3).

Apparatus (1) for supplying a refrigerant stream comprising - a Laval nozzle (3) having an inlet side (8) and an outlet side (9); a carrier gas connection (10) connected to the input side (8) of the Laval nozzle (3); and - a refrigerant nozzle (11), wherein the refrigerant nozzle (11) is configured such that an outlet opening (12) for the refrigerant nozzle (11) lies within the Laval nozzle (3) or the exit opening (12) for the refrigerant nozzle (11) is behind at the exit side (9) of the Laval nozzle (3), characterized in that the refrigerant nozzle (11) can be displaced along a longitudinal axis (7) of the Laval nozzle (3).

Device (1) according to claim 9, wherein the refrigerant nozzle (11) is coaxial with the Laval nozzle (3).

Device (1) according to any one of claims 9 to 10, wherein the refrigerant nozzle (11) comprises a tube, preferably with an inner diameter less than 1.5 mm.

Device (1) according to any one of claims 9 to 11, wherein the refrigerant nozzle (11) comprises at least one of the following nozzles: - a Laval nozzle, - a constricted tube; and - a tube.

Device (1) according to any one of claims 9 to 12, wherein a porous body (15) is formed between the carrier gas connection (10) and the Laval nozzle (3).

Device (1) according to any one of claims 9 to 13, wherein the refrigerant nozzle (11) is centered relative to the Laval nozzle (3) by means of a porous body (15).