| 摘要 |
PURPOSE: To assure an operating state which is always kept in its most suitable condi tion in response to a circumstance of cooling load and to make a positive prevention of over-rotation of an expansion turbine by a method wherein a variable volume type low temperature expansion turbine is arranged at a more downstream side of a return bypass passage and there is provided a control device for adjusting a nozzle opening degree. CONSTITUTION: A device 1 for liquefying herium is constructed such that a main compressor 4 is arranged in a herium circulating passage L passing reciprocatably through a heat exchanger 2 and having a cooling load 3 as its flowing-out point and flowing-in point. A main turbine (a main expansion turbine) 5 is arranged in series with the bypass passage L3. In addition, a herium drawing passage L4 arranged at a downstream side of a high pressure supplying passage L2 is provided with a super critical herium turbine 6 of which nozzle opening degree can be changed. In turn, there are provided a thermometer 74 for sensing a herium temperature in the bypass passage L3 at the downstream side of a second main turbine 52 and a nozzle opening degree setting device 8 to which this temperature sensing signal is inputted. Then, a nozzle opening degree of a SHE turbine 6 is set in response to a temperature of herium detected by the thermometer 74.
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