Solar-heat collection tube

Abstract

A solar-heat collection tube includes: a central metal tube through which a heat medium flows; a glass tube, which covers the outer periphery of the central metal tube such that an annular vacuum space is defined between the glass tube and the central metal tube; and a metal thermal-expansion-difference absorption portion, which absorbs the thermal expansion difference between the central metal tube and the glass tube. The glass tube includes an end portion having an end surface. The thermal-expansion-difference absorption portion is formed from metal, and includes a connecting end connected to the end portion of the glass tube. The connecting end is formed to be gradually reduced in thickness. The connecting end is connected to the glass tube in a state in which the connecting end enters the end portion of the glass tube through the end surface of the glass tube.

1 . A solar-heat collection tube comprising:
 a central metal tube through which a heat medium flows;
 a glass tube, which covers an outer periphery of the central metal tube such that an annular space is defined between the glass tube and the central metal tube, wherein the glass tube includes an end portion having an end surface; and 
 a thermal-expansion-difference absorption portion, which absorbs a thermal expansion difference between the central metal tube and the glass tube, wherein 
 the thermal-expansion-difference absorption portion is formed of metal in an annular shape and includes a connecting end, which is connected to the end portion of the glass tube, 
 the connecting end is formed to be gradually reduced in thickness, 
 the connecting end is connected to the glass tube in a state in which the connecting end is inserted in the end portion of the glass tube through the end surface of the glass tube, 
 the glass tube includes a portion that is connected to the connecting end of the thermal-expansion-difference absorption portion and a remainder portion formed of a material that is different from a material of the connected portion, and 
 as a material of the connected portion, a glass is used that has a coefficient of thermal expansion that is closer to the coefficient of thermal expansion of the metal of the connecting end than the coefficient of thermal expansion of a glass forming the remainder portion is. 
   
     
     
         2 . The solar-heat collection tube according to  claim 1 , wherein a material of the thermal-expansion-difference absorption portion has a coefficient of linear expansion from 5.0×10 −6  (K −1 ) to 5.2×10 −6  (K −1 ). 
     
     
         3 . The solar-heat collection tube according to  claim 1 , wherein the thermal-expansion-difference absorption portion is a metal bellows. 
     
     
         4 . The solar-heat collection tube according to  claim 3 , wherein
 the metal bellows includes an accordion portion with two ends, which each have a cylindrical portion, and   an inner diameter of the accordion portion is formed to be equal to an inner diameter of the cylindrical portion.   
     
     
         5 . The solar-heat collection tube according to  claim 1 , wherein the central metal tube is formed of stainless steel. 
     
     
         6 . The solar-heat collection tube according to  claim 3 , wherein the metal bellows is connected, by welding, to a flange portion formed on the central metal tube. 
     
     
         7 . (canceled)