| 摘要 |
<p>1,194,621. Thermal switches; refrigerating. CRYOGENIC TECHNOLOGY Inc. 19 Feb., 1968 [17 April, 1967], No. 8067/68. Headings F4H and F4U. A thermal switch comprises first and second heat conducting members which are in contact above a predetermined temperature and are secured to members of different coefficients of thermal expansion so that they move apart at lower temperatures, an enclosure formed in part by one of said heat conducting members and a fluid in said enclosure, the fluid providing a heat flow path between the spaced members and being condensable at a second predetermined temperature to prevent further heat flow. As shown, the first and second heat conducting members 11, 13 are respectively secured to cylinders 19, 14 which are jointly mounted on a sealing ring 16. The latter is connected to a heat exchange plate 15 and the device is arranged between the cold end 12 of a multistage refrigerator and a load 17. A gas, e.g. neon or nitrogen is provided in space 20, members 11, 13, 14 and 15 are copper and cylinder 19 is an iron-nickel alloy of low thermal conductivity and coefficient of expansion. In operation, members 11, 13 are initially in contact and heat is conducted from 17 to 12 via members 15, 16, 14, 13 and 11. At a predetermined temperature members 11 and 13 separate and heat conduction proceeds at a lower rate since the heat path now includes the gas in the gap 24 between members 11 and 13. Eventually the gas condenses through cryopumping and heat conduction ceases. Load 17 may then be cooled to a lower temperature by a helium coil 18. In one modification (Figs. 5 and 6, not shown) ring 16 is omitted and cylinder 14 replaced by a plurality of spaced rods; in another (Fig. 7, not shown), ring 16, cylinder 14 and member 13 are formed integrally and plate 15 is omitted. The switch may be rectangular in crosssection and may be connected between successive stages of a cold-gas refrigerator (Figs. 9 and 10, not shown) so that the larger capacity warmer stage assists in cooling down the colder stage until a predetermined temperature is reached.</p> |
