| abstract |
1422535 Cryosurgical instrument SPEMBLY Ltd 12 June 1973 [16 June 1972] 28316/72 Heading A5R [Also in Division F4] A cryosurgical instrument comprises a hollow body including a passage 10 for introducing a primary gaseous refrigerant at substantially its critical pressure, a passage 9 for introducing a secondary refrigerant at a temperature below the critical temperature of the primary refrigerant and a passage 3A to lead the primary fluid which is condensed by heat exchange to a hollow working lip 1B for evaporation and cooling. The probe 1A leads via an orifice 3B, into the hollow tip 1B of the probe 1A which has an outlet duct 12, and the heat exchanger has a first passage 34 communicating with the source of primary refrigerant and with the duct 3A and a second passage 23 adapted to receive the secondary refrigerant. The passages 12, 23, 34 are defined by thin gauge stainless steel tubes 1-4 rigidly sealed to one another in spaced relationship by interposed rings 5-7 of rectangualr cross-section brazed in position. The primary refrigerant is methane which is led in through a tube 10 at about 4.62 x 10<SP>6</SP> N/m<SP>2</SP> and escapes through a hole 8 in the ring 5 to atmosphere where it is oxidised or to a compressor for recycling. The secondary refrigerant is liquid nitrous oxide. |