| abstract |
A cryogenic device and a method for selectively dispensing a jet of gas or a mixture of gas and liquid cryogen particles, that is, single phase or two phase fluid, at the user's option, from a nozzle selected from a range of nozzle sizes. Pressurized liquid cryogen is supplied through an orifice to a nozzle-equipped expansion chamber also connected to a pressure regulated source of gas. A valve-controlled passage venting to the atmosphere from the expansion chamber is normally closed but, when open, is effective to reduce the chamber pressure by a major fraction of 1 psig provided the gas flow from the pressurized gas source is interrupted. The single phase gas jet dispensed in the non-venting mode substantially instantly converts to a stable two phase jet of gas and liquid particles irrespective of which one of the nozzle sizes is then in use. If the liquid cryogen pressure falls during the use of a larger nozzle, the pressure is quickly re-established by briefly admitting gas from the pressure regulated source via the expansion chamber and back flow into the liquid supply. |