Conventional torches used for vacuum plasma spraying are equipped with a conically diverging nozzle, through which supersonic conditions are achieved. The use of the conical nozzles does not prevent expansion waves from forming at the nozzle outlet. For this reason, specially designed Laval nozzles are used. This paper describes the design work from the design of a Laval nozzle for use under negative pressure conditions to its experimental verification. First, a methodology for designing the Laval nozzle and some numerical results are presented. A prototype nozzle is then compared experimentally with a commercially available conical nozzle. The test results show that the use of the specially designed Laval nozzle delivers a longer core jet and reduces turbulent scattering. These features are expected to improve the injection molding process under vacuum conditions. Paper includes a German-language abstract.

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