A nozzle for a carbon dioxide snow cyclone separator shapes the swirling discharge from the separator to form a unidirectional downwardly directed flow. The nozzle passage is defined by an annular series of transversely concave, juxtaposed, elongate surfaces formed in the body of the nozzle, whereby the passage is scalloped in transverse cross-section. In preferred forms, there are four identical, laterally contiguous, surfaces in the annular series defining the nozzle passage, each of which extends through an arc of .pi. radians.