| 摘要 |
An adjustable Joule-Thomson cryogenic cooler with a downstream thermal compensation mechanism is taught. The cryogenic cooler includes a cryogen source coupled to a manifold input port, the manifold input port connected to a heat exchanger, the heat exchanger coupled to an orifice block, and the orifice block connected to an expansion chamber. A thin cylindrical tube is attached to the manifold to support the heat exchanger. The expansion chamber is defined by the orifice block, the exterior surface of the cylindrical tube, a portion of the interior of the cylindrical tube in communication with the exterior surface of the cylindrical tube through passages, a dewar stem, and a portion of the manifold. The dewar stem encloses the cylindrical tube and sealingly engages the manifold. The thermal compensation mechanism includes a bimetal cantilever in the expansion chamber portion of the cylindrical tube, an adjustment mechanism for adjusting the effective bimetal cantilever, and a needle valve mechanism. The needle valve mechanism includes a needle valve for the orifice of the orifice block. In operation cryogen passes from the source through the manifold input port and heat exchanger to the orifice. The pressure of the cryogen opens the needle valve and cryogen enters the expansion chamber. The cryogen expands as it leaves the orifice to form a cold end for the expansion chamber, and a thermal gradient as it moves downstream over the heat exchanger to the hot end of the expansion chamber. As the cryogen moves downstream a portion enters and leaves the cylindrical tube through its passages to cool the bimetal cantilever which bends as it cools to engage and end of a bell crank mounted in the orifice block. The other end of the bell crank engages the needle valve carriage to seat the needle valve in the orifice to stop the flow of cryogen into the expansion chamber. From the hot end of the expansion chamber, the cryogen vents through a manifold output port and vent tube. As the temperature of the expansion chamber rises, the bimetal strip returns to its original position permitting the cryogen under pressure to unseat the needle valve to enter the expansion chamber.
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