| 摘要 |
<p>PROBLEM TO BE SOLVED: To improve thermal insulation characteristics and increase ultimate vacuum by providing a radiation shield layer made of metal foil on outer periphery of a refrigerant pipe and winding a pipelike spacer made of synthetic resin spirally between an external pipe and the outside of the radiation shield layer. SOLUTION: A radiation shield layer 2 made of metal foil having small radiation coefficient such as copper foil, silver foil, aluminum foil, etc., is provided on outer periphery of a refrigerant pipe 1, and a pipelike spacer 4 having circular cross section is wound spirally between an external pipe 3 on the outside of the radiation shield layer 2 and it to constitute an extremely low temperature thermal insulation pipe. Synthetic resin having low heat transfer rate such as Teflon, polyester, etc., is used as a material of the spacer 4. The spacer 4 comes into point-contact with the radiation shield layer 2 and the external pipe 3 to reduce heat transfer rate and protect the radiation shield layer 2 by winding it spirally. Moreover, the spacer 4 is hollow and has small cross sectional area to reduce heat invasion from the spacer 4. Furthermore, when a hole 4a is provided on a pipe wall of the spacer 4 and a vacuum is formed from both ends of the spacer 4 as well as both ends of internal and external pipes 1, 3 simultaneously, ultimate vacuum is improved.</p> |
