Device for generating a CO2 snow jet

A 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, said 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), the device (2) comprising a nozzle (26) for generating an outer jet (28) which surrounds and accelerates the CO2 gas/CO2 snow mixture (8) discharged from the outlet opening (22) of the expansion channel (6), wherein

• the expansion channel (6) has multiple channel sections (36a, 36b, 36c, 36d, 36e, 36f, 36g) arranged one in front of the other in the flow direction (14), which widen continuously over an extension of each said channel section (36a, 36b, 36c, 36d, 36e, 36f, 36g) in the flow direction (14),
• an expansion channel (6) cross section (40) that lies on a plane orthogonal to the flow direction (14) tapers suddenly radially inwardly in transition between each said adjacent channel sections (36a, 36b, 36c, 36d, 36e, 36f, 36g) in the flow direction (14), to form an annular screen surface (50) to serve as a collision surface for snow particles that have already been formed, such that the snow particles, when they hit the screen surface are compacted and grow together to form larger snow agglomerates,
• the expansion channel cross section at an upstream end of each said channel section is smaller than the expansion channel cross section at a downstream end of a channel section arranged immediately upstream of each said channel section in the flow direction (14), and
• the expansion channel (6) cross section (46d) at the upstream end (48d) of each said channel section (36d) is larger than the expansion channel (6) cross section (46c) at the upstream end (48c) of the channel section (36c) arranged immediately upstream of each said channel section (36d) in the flow direction (14),
• the expansion channel (6) is formed by at least one cavity of a workpiece, said workpiece having a wall delimiting the expansion channel (6), the transition tapers suddenly radially inwardly with respect to that wall, the expansion channel is configured such that a two-phase flow arises in the course of the phase conversion of liquid CO2 into gaseous CO2 that takes place in the expansion channel, said CO2 liquid phase flowing annularly at the edge of the expansion channel and the CO2 gas phase flowing in a central region of the expansion channel, the change in cross-section in the transition (38a, 38b, 38c, 38d, 38e, 38f) brings about a pressure jump, as a result of which turbulences are generated in the flow within the expansion channel, which mixes up the CO2 liquid phase and the CO2 gas phase such that in the course of the intermixing of the gas and liquid phases, the liquid phase is accelerated by the faster flowing gas phase such that snow particles resulting from the accelerated liquid phase emerge from the outlet opening of the expansion channel at increased velocity.