DEVICE FOR GENERATING A CO2 SNOW BEAM

Description

[0001] The invention relates to a device for generating a CO 2 snow jet, with an expansion channel extending in a flow direction for generating a CO 2 gas / CO 2 snow mixture starting from liquid CO 2 , wherein the expansion channel has an inlet opening for supplying liquid CO 2 and an outlet opening for discharging the CO 2 gas / CO 2 snow mixture, and with a nozzle for generating a jacket jet which surrounds the CO 2 gas / CO 2 snow mixture discharged from the outlet opening of the expansion channel and accelerates it, wherein the expansion channel has a plurality of channel sections arranged one behind the other in the flow direction,wherein the cross-section of the expansion channel, lying in a plane orthogonal to the flow direction, changes locally in a respective transition or transition region between the channel sections, and wherein the cross-section of the expansion channel at the upstream end of a respective channel section is larger than the cross-section of the expansion channel at the upstream end of the channel section arranged upstream of the respective channel section in the flow direction. Such devices have proven themselves in practice for the gentle cleaning of surfaces, e.g., workpiece surfaces, before painting or coating processes, or functional surfaces in the semiconductor industry and in medical technology. In particular, surface cleaning using a CO2 snow jet (so-called "CO2 snow jets") enables dry (water-free),Solvent-free and residue-free removal of filmy and / or particulate contaminants (e.g. dust, ablation residues, cutting emulsion residues, fingerprints, etc.).

[0002] To generate a CO2 snow jet, liquid CO2 (carbon dioxide) is fed into the expansion channel via the inlet opening at an initial pressure of typically around 60 bar or, when supplied from low-pressure tanks, around 20 bar. Over the length of the expansion channel, the pressure drops from the initial pressure at the inlet opening to ambient pressure (usually 1 bar) at the outlet opening. As the pressure drops, a gradual phase transition from liquid CO2 to gaseous CO2 occurs, with simultaneous cooling of the mixture. When the pressure falls below the triple point of CO2 (5,185 bar), the remaining liquid phase is at least partially converted into solid CO2 in the form of snow crystals, so-called CO2 snow. CO2 "snow" is therefore CO2 in a solid state and not "snow" in the sense of frozen water.The resulting CO2 snow crystals are entrained by the CO2 gas, which has been accelerated as a result of the expansion, and are expelled from the outlet together with the CO2 gas as a CO2 gas / CO2 snow mixture. The CO2 gas / CO2 snow mixture is then concentrated by the sheath jet formed by the nozzle and further accelerated into a CO2 snow jet.

[0003] The cleaning effect of a CO 2 snow jet when it hits a surface is essentially based on four mechanisms: 1. Embrittlement of contaminants through rapid cooling (sublimation point of CO 2 snow at atmospheric pressure: -78.5 °C); 2. Abrasion through momentum transfer (accelerated CO 2 snow crystals transfer pressure and shear forces when they hit the surface); 3. Chemical dissolution of contaminants, e.g. adsorption compounds (when CO 2 snow crystals hit a surface, CO 2 can be converted into a supercritical state; in this state, CO 2 is a good chemical solvent); 4. Expulsion of contaminants through an approximately 500-fold increase in volume when CO 2 sublimates from the solid phase into the gas phase.

[0004] WO 02 / 075799 A1 and US Pat. No. 7,762,869 B2 disclose non-generic devices for generating a CO2 snow jet, in which the phase transformation from liquid CO2 to CO2 snow occurs only in a mixing chamber, into which liquid CO2 is expanded into a carrier gas that is also supplied. This CO2 snow / carrier gas mixture is further conveyed through successive Venturi nozzles and physically treated, whereby the snow content in the mixture increases. DE 10 2016 123 816 A1 also discloses such a device. WO 2004 / 033154 A1 likewise discloses a non-generic device for generating a CO2 snow jet, in which liquid CO2 is expanded in a large-volume expansion chamber and then combined with a carrier gas stream, which is then fed to a Laval nozzle.The expansion space can be considered as an expansion channel with two channel sections and a transition area between them, with the cross-section increasing in the transition area to the downstream channel section.

[0005] CO2 snow blasting must be distinguished from CO2 dry ice blasting, which is usually more abrasive. In this process, dry ice pellets (pellets made of solid CO2, i.e., not CO2 snow crystals) are accelerated in a blasting system and blasted onto a workpiece to be cleaned. While dry ice pellets are typically produced in a pelletizer separate from the blasting system and then fed to the blasting system in batches, CO2 snow blasting enables continuous operation and is therefore particularly suitable for automation. US 2010 / 0170965 A1 and WO 2015 / 109101 A1 relate to and disclose pellet blasting devices in which dry ice pellets guided in a jet are further crushed by a grid-like aperture.

[0006] US 2006 / 0124156 A1 discloses a device having the features of the preamble of claims 1 and 5.

[0007] The object of the present invention is to further improve a generic device such that a higher cleaning effect is achieved with CO2 snow blasting. The device should be able to be operated economically.

[0008] This object is achieved by a device having the features of independent claims 1 and 5.

[0009] Such a design makes it possible to increase the momentum of the CO2 snow jet, particularly of the CO2 snow particles, and thus enhance the abrasiveness when the CO2 snow jet impacts a surface to be cleaned. This allows even strongly adhering contaminants on the surface to be reliably removed. In particular, a design of the device according to the invention makes it possible to increase the momentum of the CO2 snow particles already in the expansion channel, which promotes economical operation of the device.

[0010] According to the invention, it was discovered that during the phase transformation from liquid CO2 to gaseous CO2 in the expansion channel, a two-phase flow develops, with the liquid phase flowing annularly around the edge of the expansion channel (fluid flow) and the gas phase flowing in a central region of the expansion channel (gas flow). It has also been found that the gas flow has a flow velocity approximately 10 to 100 times higher than the fluid flow. The gas phase cannot be used for CO2 snow production; it is lost.

[0011] It is understood that for the operation of a device according to the invention, liquid CO 2 can be supplied to the expansion channel at different outlet pressures, in particular at an outlet pressure in a range of approximately 5 to 70 bar.

[0012] Because the cross-section of the expansion channel in a device according to the invention changes as claimed in a respective transition or transition region between the channel sections, a pressure jump occurs at each of these transitions or transition regions, which causes turbulence in the fluid and gas flow and thus mixing of the gas and liquid phases. As the gas and liquid phases mix, the liquid phase is accelerated by the faster-flowing gas phase. Snow particles, which arise from the accelerated liquid phase upon further expansion, thus emerge from the outlet opening of the expansion channel at increased speed. The increase in momentum of the snow particles associated with the increase in speed leads to greater abrasiveness when the snow particles hit a surface and consequently to an improved cleaning effect.

[0013] Furthermore, because the snow particles already have a comparatively high velocity upon exiting the expansion channel, less acceleration of the snow particles by the sheath jet is required to achieve a predetermined target velocity compared to prior art devices. This allows the gas flow through the nozzle required to generate the sheath jet to be reduced, thus lowering the operating costs of the device.

[0014] The mixing of the liquid and gas phases caused by the cross-sectional change in the respective transition or transition region further promotes the conversion of liquid CO2 into CO2 snow. This allows the proportion of CO2 snow in the CO2 snow jet to be increased, which further increases the abrasiveness when the CO2 snow jet impacts a surface to be cleaned.

[0015] Furthermore, the pressure jump and the resulting turbulence of the flow at the respective transition or transition area can promote the formation of larger liquid droplets and, subsequently, the formation of larger snow crystals, thereby increasing momentum transfer upon impact with a surface to be treated. This can further improve the cleaning effect of CO2 snow blasting.

[0016] In a preferred embodiment, a cross-sectional change in the respective transition can occur abruptly, meaning that the transition, in particular, does not extend in the direction of flow. The mixing of the gas phase and the liquid phase is then particularly effective, since the abrupt cross-sectional changes cause particularly strong pressure jumps and turbulence in the two-phase flow.

[0017] According to the claim, the cross-section of the expansion channel at the upstream end, i.e. at the rear end in the direction of flow, of a respective channel section is larger than the cross-section of the expansion channel at the upstream end of the channel section arranged upstream of the respective channel section in the direction of flow. The cross-section of the expansion channel at the upstream end of a respective channel section therefore becomes larger from channel section to channel section, viewed in the direction of flow. In this respect, the expansion channel widens over its entire extent, viewed in the direction of flow. Preferably, the cross-section of the expansion channel at its outlet opening is larger than the cross-section of the expansion channel at its inlet opening. In this way, the risk of the expansion channel becoming blocked by CO2 snow crystals that form, in particular by larger CO2 snow agglomerates, can be reduced.This promotes reliable function of the device.

[0018] Within the scope of a preferred embodiment, the respective transition can extend in the direction of flow. The respective transition is then designed as a transition region that connects the respective channel sections to one another. In this case, the cross-section of the expansion channel can change, in particular continuously, along the extent of the respective transition region in the direction of flow. For example, it can be provided that the expansion channel tapers or widens conically in the respective transition region.

[0019] To generate a stable sheath jet and effectively accelerate the CO2 gas / CO2 snow mixture, it is also advantageous if the nozzle for generating the sheath jet is designed as an annular nozzle, in particular one that concentrically encloses the expansion channel. It is particularly advantageous if the nozzle is designed as a supersonic nozzle (Laval nozzle). In this way, the speed of the snow particles and thus the momentum that can be transferred to a surface can be further increased. Dry gases, for example air or nitrogen, in particular ultrapure air or ultrapure nitrogen, have proven particularly advantageous as carrier gases for the sheath jet.

[0020] According to the invention, the cross-section of the expansion channel decreases in the flow direction at least at some transitions or transition regions, preferably at every transition or transition region. It proves to be advantageous if the cross-section decreases in a respective transition or transition region by 25% to 75%, more preferably by 40% to 60%. In this respect, a minimum cross-sectional area of ​​a respective transition or transition region lying in a plane orthogonal to the flow direction can be between 75% and 25%, preferably between 60% and 40%, of the cross-sectional area at the downstream end, i.e. at the front end in the flow direction, of the channel section arranged upstream of the respective transition or transition region in the flow direction.A larger change in cross-sectional area leads to a larger pressure jump, which is beneficial for effective mixing of the gas and liquid phases. A smaller change in cross-sectional area, on the other hand, is beneficial for a higher flow rate of the CO2 gas / CO2 snow mixture.

[0021] It proves particularly advantageous if the expansion channel tapers radially inward in the respective transition or transition region (claim 2). This makes it possible to guide the liquid phase, which flows particularly annularly at the edge of the expansion channel, particularly effectively in the direction of the gas flow, which promotes the mixing of the gas and liquid phases.

[0022] Furthermore, it proves particularly advantageous if the respective transition or transition region forms a circular orifice, i.e., the expansion channel tapers radially inward evenly over the circumference of the expansion channel (claim 3). The mixing of the annularly flowing liquid phase with the gas phase is then particularly effective. A orifice surface of a respective orifice can serve as a collision surface for already formed snow particles. Upon impact with an orifice surface, the snow particles can be compacted and coalesce into larger snow agglomerates, thereby increasing the abrasiveness when the compacted snow particles or snow agglomerates impact a surface.

[0023] In a preferred embodiment, the aperture surface can be oriented orthogonally to the flow direction. In this case, the expansion channel tapers abruptly. In other preferred embodiments, the aperture surface can be oriented at an angle to the flow direction. In this case, the respective transition can be formed as a transition region extending in the flow direction. Preferably, the expansion channel can taper conically in the respective transition region.

[0024] Within the scope of an alternative embodiment according to the independent claim 5, the cross-section of the expansion channel can increase in the direction of flow at least at some transitions or transition regions, preferably at every transition or transition region, wherein each transition region is designed as a bulge of any desired shape, in particular oval or bubble-shaped or spherical segment-shaped. In this way, particularly strong turbulence is created in the flow and thus good mixing of the liquid and gas phases. The increase in cross-section creates turbulence in the two-phase flow, which brings about particularly effective mixing of the liquid and gas phases. Furthermore, a local widening of the expansion channel can cause the liquid CO 2 to expand further, which promotes the conversion of the liquid CO 2 into CO 2 snow.

[0025] It is furthermore advantageous if the respective transition or transition region extends in the flow direction over a length of 0 to 5.0 mm, more preferably over a length of 0 to 4.0 mm, more preferably over a length of 0 to 3.0 mm, more preferably over a length of 0 to 2.0 mm, in particular over a length of 1.0 to 2.0 mm (claim 6).

[0026] In particular, such a design allows the expansion channel to be relatively long, allowing a relatively large proportion of the liquid CO2 to be converted into CO2 snow, and allowing the resulting CO2 snow crystals to grow into larger crystals without blocking flow through the expansion channel. This allows the proportion of CO2 snow in the CO2 snow jet, particularly the proportion of larger snow agglomerates, to be increased, which increases the momentum of the CO2 snow jet and thus improves the cleaning effect.

[0027] With regard to simple production, it proves to be advantageous, regardless of any widening of the expansion channel along its extension in the flow direction, if at least some channel sections, in particular all channel sections, have a constant cross-section over their respective extension in the flow direction (claim 7).

[0028] According to another embodiment, it may prove advantageous if at least some channel sections, in particular all channel sections, possibly with the exception of a feed section that may be provided, widen over their respective extent in the flow direction, i.e. the cross-section at the downstream end of a respective channel section is larger than the cross-section at the upstream end of this channel section (claim 8). It is assumed that such a widening of the channel sections causes a further acceleration of the flow according to the principle of the Laval nozzle, whereby the speed and thus the momentum of the snow crystals can be further increased. Furthermore, the widening of the channel sections further reduces the risk of the expansion channel becoming blocked by CO2 snow that is formed. It is particularly preferred if the respective channel sections widen continuously, in particular conically.

[0029] For an efficient conversion of liquid CO 2 into CO 2 snow, it is further advantageous if the expansion channel has a maximum cross-sectional area of ​​less than 5.0 mm 2<, preferably less than 3.0 mm 2<, more preferably less than 1.0 mm 2<, more preferably less than 0.5 mm 2< in a plane orthogonal to the flow direction (claim 9).

[0030] Furthermore, it proves to be advantageous if the expansion channel is formed by at least one cavity of a workpiece, in particular a cylindrical tubular body (claim 10). It is possible for the workpiece defining the expansion channel to be monolithic. For example, it is possible for a workpiece with a cavity to be produced using an additive manufacturing process (e.g. 3D printing). It is also possible for the workpiece to be composed of two or more workpiece halves which, when assembled, define a cavity. For example, it is possible for the workpiece halves to be produced using a vacuum casting process and subsequently joined together. Furthermore, it proves to be advantageous if the workpiece is made of a plastic.

[0031] Further features, details and advantages of the invention emerge from the appended patent claims and the drawings and subsequent description of preferred embodiments of the device according to the invention.

[0032] The drawing shows: Figure 1 is a schematic representation of an embodiment of a device for generating a CO 2 snow jet in a partially sectioned view; Figure 2a is a side view of a tubular body half of a tubular body surrounding an expansion channel of the device according to Fig. 1 in a first embodiment; Figure 2b in Figure 2a Section marked IIb in an enlarged view; Figure 2c a sectional view of the section according to Figure 2b along the Figure 2b drawn section line IIc - IIc; Figure 2a perspective view of the tubular body half of the tubular body according to Figure 2a; Figure 3a a side view of a tubular body half of a tubular body surrounding an expansion channel of the device according to Fig. 1 in a further embodiment; Figure 3b in Figure 3a section marked IIIb in an enlarged view; Figure 3c a perspective view of the tubular body half of the tubular body according to Figure 3a ; Figure 4a a side view of a tubular body half of a tubular body surrounding an expansion channel of the device according to Fig. 1 in a further embodiment; Figure 4b in Figure 4a section marked IVb in an enlarged view; Figure 4c a perspective view of the tubular body half of the tubular body according to Figure 4a .

[0033] Figure 1 shows a schematic representation of an embodiment of a partially illustrated device for generating a CO 2 snow jet 4, designated overall by the reference numeral 2.

[0034] The device 2 has an expansion channel 6, which serves to generate a CO2 gas / CO2 snow mixture 8 starting from liquid CO2. In the exemplary case, the expansion channel 6 is formed by a cavity of a cylindrical tubular body 10. The tubular body 10 and the expansion channel 6 extend along a central axis 12 in a flow direction 14.

[0035] The expansion channel 6 has an inlet opening 18 for supplying liquid CO 2 at its upstream end 16, i.e., at its rear end in the flow direction 14. The expansion channel 6 further has an outlet opening 22 for discharging the CO 2 gas / CO 2 snow mixture 8 formed in the expansion channel 6 at its downstream end 20, i.e., at its front end in the flow direction 14.

[0036] To produce the CO2 gas / CO2 snow mixture 8, liquid CO2 is fed, for example and preferably at an initial pressure of approximately 60 bar or, when supplied from low-pressure tanks, approximately 20 bar, through device components not shown via the inlet opening 18 to the expansion channel 6 in the flow direction 14. Over the extent of the expansion channel 6 in the flow direction 14, the pressure drops from the initial pressure at the inlet opening 18 to ambient pressure (approximately 1 bar) at the outlet opening 22. As the pressure drops, a gradual phase transformation from liquid CO2 to gaseous CO2 takes place with simultaneous cooling of the mixture. During the phase transformation, a two-phase flow forms, with the liquid phase flowing annularly at the edge of the expansion channel 6 and the gas phase flowing in a central region of the expansion channel 6.When the pressure drops below the triple point of CO2 (5.185 bar), the remaining liquid phase gradually transforms into solid CO2 in the form of CO2 snow crystals 22, so-called CO2 snow. Three phases are then present. The resulting CO2 snow crystals 24 are entrained by the gas flow, accelerated, and discharged from the outlet opening 22 together with the CO2 gas as a CO2 gas / CO2 snow mixture 8. As explained above, the cross-sectional changes and the resulting pressure jumps result in the formation of larger snow crystals, in particular a larger proportion of snow.

[0037] The device 2 further comprises a nozzle 26 for generating a sheath jet 28 from a carrier gas, for example and preferably from ultrapure air or ultrapure nitrogen. In the example shown, the nozzle 26 is designed as an annular nozzle, which preferably concentrically surrounds the tubular body 10. For example and preferably, the nozzle 26 can be designed as a Laval nozzle in a conventional manner. The sheath jet 28 surrounds the CO2 gas / CO2 snow mixture 8 discharged from the outlet opening 22 of the expansion channel 6 and accelerates it into a CO2 snow jet 4.

[0038] The CO 2 snow jet 4 can be used as explained above and in a manner known per se to remove filmy and / or particulate contaminants 30 from a workpiece surface 32.

[0039] In the Figures 2a to 4cVarious configurations of the expansion channel 6 are shown in detail. In each of the configurations shown, the tubular body 10 surrounding the expansion channel 6 is formed, by way of example and preferably, from preferably two, preferably identical, tubular body halves 34. Figures 2a to 5b each show such a tubular body half 34 in different views. The tubular body halves 34 are, by way of example and preferably, made of plastic, for example, using a vacuum casting process. The tubular body halves 54 can be joined together, for example, by means of ultrasonic welding, laser welding, gluing, crimping, or by pressing the tubular body halves 54 into a casing pipe.

[0040] In each of the illustrated embodiments, the expansion channel 6 has a plurality of channel sections 36a, 36b, 36c, 36d, 36e, 36f, 36g arranged one behind the other in the flow direction 14. The expansion channel 6 further has transitions or transition regions 38a, 38b, 38c, 38d, 38e, 38f arranged between the respective channel sections 36a, 36b, 36c, 36d, 36e, 36f, 36g. In the transitions or transition regions 38a, 38b, 38c, 38d, 38e, 38f, the cross-section 40 of the expansion channel 6, which lies in a plane orthogonal to the flow direction 14, changes locally. The change in cross-section in the respective transition or transition region 38a, 38b, 38c, 38d, 38e, 38f leads in each case to a pressure jump, whereby turbulences are generated in the flow within the expansion channel 6, which cause a mixing of the phases present in the expansion channel 6, in particular the CO 2 liquid phase and the CO 2 gas phase.

[0041] First, a respective channel section is considered: When designing according to the Figures 2a to 2d The channel sections 36a, 36b, 36c, 36d, 36e expand conically over their respective extent in the flow direction 14. A feed section with a constant cross-section is provided in front of these channel sections 36a, 36b, 36c, 36d, 36e. By way of example and preferably, the channel sections 36a, 36b, 36c, 36d, 36e are designed as truncated cone-shaped, i.e., conically expanding, cavities within the tubular body 10. As shown in Figure 2b As shown by way of example for the channel section 36c, the cross section 42c of the expansion channel 6 at the downstream end 44c of a respective channel section 36c is therefore larger than the cross section 46c at the upstream end 48c of this channel section 36c.

[0042] As in Figure 2bAs shown by way of example for the channel sections 36c and 36d, in the present embodiment the cross section 46d of the expansion channel 6 at the upstream end 48d of a respective channel section 36d is larger than the cross section 46c of the expansion channel 6 at the upstream end 48c of the channel section 36d in the flow direction 14 before the respective channel section 36d arranged channel section 36c. The cross-section 46c,d of the expansion channel 6 at the upstream end 48c,d of a respective channel section 36c, 36d thus becomes larger from channel section 36c to channel section 36d, as seen in the flow direction 14.

[0043] Now the transitions between the channel sections are considered: In a respective transition 38a, 38b, 38c, 38d between the channel sections 36a, 36b, 36c, 36d, 36e according to the design Figures 2a to 2d the expansion channel 6 tapers abruptly radially inwards. As in Figure 2bAs shown by way of example for the channel sections 36c and 36d, the cross section 46d of the expansion channel 6 at the upstream end 48d of a respective channel section 36d is smaller than the cross section 42c of the expansion channel 6 at the downstream end 44c of the channel section 36d in the flow direction 14 before channel section 36c arranged in this channel section 36d.

[0044] By way of example and preferably, the respective transition 38a, 38b, 38c, 38d in the present case each forms a circular ring-shaped aperture 50, wherein an aperture surface 52 is oriented orthogonally to the flow direction 14 (cf. Figures 2b and 2c ).

[0045] The Figures 3a to 3cshow a further different embodiment of the expansion channel 6, in which the channel sections 36a, 36b, 36c, 36d, 36e, 36f and an exemplary supply section have a constant cross section orthogonal to the flow direction 14 over their respective extent in the flow direction 14. As in Figure 3b As shown by way of example for the channel sections 36c and 36d, the cross section 54d of a channel section 36d arranged downstream in the flow direction 14 is larger than the cross section 54c of the channel section 36c arranged upstream of this channel section 36d in the flow direction 14. The respective channel sections 36a, 36b, 36c, 36d, 36e, 36f are, by way of example and preferably, formed as circular-cylindrical cavities in the tubular body 10.

[0046] When designing according to the Figures 3a to 3cthe respective transitions 38a, 38b, 38c, 38d, 38e between the channel sections 36a, 36b, 36c, 36d, 36e, 36f are designed as transition regions 38a, 38b, 38c, 38d, 38e, thus each extending in the flow direction 14. By way of example and preferably, each transition region 38a, 38b, 38c, 38d, 38e has a first section 56 tapering conically radially inward and a second cylindrical section 58 adjoining the conical section 56 in the flow direction 14 (in Figure 3b shown as an example for the transition region 38c). The respective transition regions 38a, 38b, 38c, 38d, 38e connect the channel sections 36a, 36b, 36c, 36d, 36e, 36f with one another in terms of flow.

[0047] When designing according to the Figures 3a to 3c the respective transition region 38a, 38b, 38c, 38d, 38e also forms a circular aperture 50, wherein an aperture surface 52 is oriented inclined to the flow direction 14 (cf. Figure 3b ).

[0048] The Figures 4a to 4c show a further different embodiment of the expansion channel 6, in which the cross section of the expansion channel initially increases in the flow direction 14 in the respective transition region 38a, 38b, 38c, 38d, 38e, 38f. By way of example and preferably, the respective transition region 38a, 38b, 38c, 38d, 38e, 38f is formed as an oval-like bulge (cf. Figure 4b ). Viewed in the flow direction 14, in the case illustrated as an example, the respective extension of the transition regions 38a, 38b, 38c, 38d, 38e, 38f in the flow direction decreases from transition region to transition region (cf. Figure 4a ).

[0049] The channel sections 36a, 36b, 36c, 36d, 36e, 36f, 36g have the Figures 4a to 4cshown embodiment each have a constant cross-section over their respective extension in the flow direction 14, wherein the cross-section 54d of a channel section 36d arranged downstream in the flow direction 14 is larger than the cross-section 54c of the channel section 36c arranged upstream of this channel section 36d in the flow direction 14 (in Figure 4b shown as an example for the channel sections 36c and 36c). of the transition areas 38a, 38b, 38c, 38d, 38e, 38f in the flow direction from transition area to transition area (cf. Figure 4a ).

[0050] The channel sections 36a, 36b, 36c, 36d, 36e, 36f, 36g have the Figures 4a to 4cshown embodiment each have a constant cross-section over their respective extension in the flow direction 14, wherein the cross-section 54d of a channel section 36d arranged downstream in the flow direction 14 is larger than the cross-section 54c of the channel section 36c arranged upstream of this channel section 36d in the flow direction 14 (in Figure 4b shown as an example for the channel sections 36c and 36c).

Claims

1. Device (2) for generating a CO2 snow jet (4), comprising an expansion channel (6) which extends in a flow direction (14) for generating a CO2 gas / CO2 snow mixture (8) based on liquid CO2, the expansion channel (6) having an inlet opening (18) for supplying liquid CO2 and an outlet opening (22) for discharging the CO2 gas / CO2 snow mixture (8), and the device also comprising a nozzle (26) for generating a jacketed jet (28) which surrounds and accelerates the CO2 gas / CO2 snow mixture (8) discharged from the outlet opening (22) of the expansion channel (6), the expansion channel (6) having a plurality of channel portions (36a, 36b, 36c, 36d, 36e, 36f, 36g) arranged one behind the other in the flow direction (14), the cross section (40) of the expansion channel (6), which cross section lies in a plane orthogonal to the flow direction (14), varying locally in a relevant transition or transition region (38a, 38b, 38c, 38d, 38e, 38f) between the channel portions (36a, 36b, 36c, 36d, 36e, 36f, 36g), and that the cross section (46d) of the expansion channel (6) at the upstream end (48d) of a relevant channel portion (36d) is larger than the cross section (46c) of the expansion channel (6) at the upstream end (48c) of the channel portion (36c) arranged upstream of the relevant channel portion (36d) in the flow direction (14), characterized in that the cross section (40) of the expansion channel (6) reduces in the flow direction (14) at least at some of the transitions or transition regions (38a, 38b, 38c, 38d, 38e, 38f).

2. Device (2) according to claim 1, characterized in that the cross section (40) of the expansion channel (6) reduces in the flow direction (14) at every transition or transition region (38a, 38b, 38c, 38d, 38e, 38f).

3. Device (2) according to claim 1 or claim 2, characterized in that the expansion channel (6) tapers radially inward in the relevant transition or transition region (38a, 38b, 38c, 38d, 38e, 38f).

4. Device (2) according to any of claims 1, 2 or 3, characterized in that the transition or transition region (38a, 38b, 38c, 38d, 38e, 38f) forms an annular screen (50), preferably a screen surface (52) being oriented orthogonal to the flow direction (14) or being oriented inclined to the flow direction (14).

5. Device (2) for generating a CO2 snow jet (4), comprising an expansion channel (6) which extends in a flow direction (14) for generating a CO2 gas / CO2 snow mixture (8) based on liquid CO2, the expansion channel (6) having an inlet opening (18) for supplying liquid CO2 and an outlet opening (22) for discharging the CO2 gas / CO2 snow mixture (8), and the device also comprising a nozzle (26) for generating a jacketed jet (28) which surrounds and accelerates the CO2 gas / CO2 snow mixture (8) discharged from the outlet opening (22) of the expansion channel (6), the expansion channel (6) having a plurality of channel portions (36a, 36b, 36c, 36d, 36e, 36f, 36g) arranged one behind the other in the flow direction (14), the cross section (40) of the expansion channel (6), which cross section lies in a plane orthogonal to the flow direction (14), varying locally in a relevant transition or transition region (38a, 38b, 38c, 38d, 38e, 38f) between the channel portions (36a, 36b, 36c, 36d, 36e, 36f, 36g), and that the cross section (46d) of the expansion channel (6) at the upstream end (48d) of a relevant channel portion (36d) is larger than the cross section (46c) of the expansion channel (6) at the upstream end (48c) of the channel portion (36c) arranged upstream of the relevant channel portion (36d) in the flow direction (14),the cross section (40) of the expansion channel (6) enlarging in the flow direction (14) at least at some of the transitions or transition regions (38a, 38b, 38c, 38d, 38e, 38f), preferably at every transition or transition region (38a, 38b, 38c, 38d, 38e, 38f), characterized in that a relevant transition region (38a, 38b, 38c, 38d, 38e, 38f) is formed as a protrusion, in particular an ovalshaped, bubble-shaped or spherical-portion-shaped protrusion.

6. Device (2) according to any of the preceding claims, characterized in that the relevant transition or transition region (38a, 38b, 38c, 38d, 38e, 38f) extends in the flow direction (14) over a length of 0 mm to 5 mm, preferably 0 mm to 4 mm, more preferably 0 mm to 3 mm, more preferably 0 mm to 2 mm, in particular 1 mm to 2 mm.

7. Device (2) according to any of the preceding claims, characterized in that at least some of the channel portions (36a, 36b, 36c, 36d, 36e, 36f, 36g), in particular all of the channel portions (36a, 36b, 36c, 36d, 36e, 36f, 36g), have a constant cross section (40) over their particular extension in the flow direction (14).

8. Device (2) according to any of the preceding claims, characterized in that at least some of the channel portions (36a, 36b, 36c, 36d, 36e, 36f, 36g), in particular all of the channel portions (36a, 36b, 36c, 36d, 36e, 36f, 36g), widen, preferably continuously, in particular conically, over their particular extension in the flow direction (14).

9. Device (2) according to any of the preceding claims, characterized in that the expansion channel (6) has a maximum cross-sectional surface of less than 5.0 mm2, preferably less than 3.0 mm2, more preferably less than 1.0 mm2, more preferably less than 0.5 mm2, in a plane orthogonal to the flow direction (14).

10. Device (2) according to any of the preceding claims, characterized in that the expansion channel (6) is formed by at least one cavity of a workpiece, in particular a cylindrical tubular body (10).