Patent GB-925343-A (GB)
Title: Process of regulating freeze-drying operations and apparatus for carrying out said process
IPC: A23C1/08
Filed: 1962-01-15
Abstract: 925,343. Freeze drying. SOC. D'UTILISATION SCIENTIFIQUE ET INDUSTRIELLE DU FROID USIFROID. Jan. 15, 1962 [Jan. 17, 1961], No. 1456/62. Class 34 (2). In an apparatus and process for regulating freeze-drying or lyophilization operations, frozen substance to be dried is placed in an evacuable enclosure and on a support, temperature of which can be varied, the steam leaving the frozen substance being eliminated by a trap located in the enclosure, the process being such that a continuous transfer of steam from the frozen substance to the trap is maintained and the total pressure in the enclosure is modified as a function of the variations in a given property of the substance, the pressure modification being achieved by introducing in the enclosure controlled amounts of incondensable gases. Water is removed from a frozen substance S, Fig. 1, in jars 5 in a chamber C, evacuable by a pump V, by heat supplied to a plate P upon which the jars are supported, the steam evolved being removed by condensing as ice on a trap G which is cooled by a refrigerator M. A continuous transfer of the steam from the substance to the trap G is automatically maintained by varying the temperature of the plate P by an electrical resistance R modified in accordance with the variations of the temperature on the substance. These temperature variations are noted by a thermometric device T comprising a thermometer T 1 , a galvanometer 28 and battery 35, which device automatically and simultaneously controls, via the main electricity supply; both the resistance R and also means for introducing controlled amounts of incondensable gases, e.g. air, into the chamber to adjust the total pressure therein. The means for introducing the gases into the chamber comprises electromagnetic valves 16, 17 separated by a chamber E having a volume which is variable by a piston 23, the valves being actuated to allow air to be supplied by a device comprising an electric motor 41 which drives a cam 51 to alternatively move contacts 47, 50 into fixed contacts 53, 54 in communication with the valves 16, 17 respectively. The motor 41 is supplied with current only when the temperature of the substance S as sensed by the device T is below a predetermined valve to which the galvanometer 28 is adjusted so as to move contacts 63, 64 thereon into contact, current also passing from the motor both to the valves 16, 17 and to a conductor of the resistance R. In a modification, Fig. 2 (not shown), the jars are mounted on three superposed plates, each having an electrical resistivity-measuring cell placed thereon which contain some substance S so that the continuous transfer of steam from the frozen substance and the total pressure in the chamber is automatically modified as a function of the variation in the electrical resistivity of the substance. In a further modification, the variation of electrical resistivity is again utilized and the chamber is formed of two portions permanently connected by a tubular neck portion, the plates and the condenser being positioned in the upper and lower portions respectively.