Evaluation of SUNPACK Tube Vacuum Quality. Final Report, 1 September 1978-31 May 1980

摘要

The viability of all glass, selectively coated, evacuated tubular solar collectors has been demonstrated in many field installations now in operation. Some questions remain concerning the cost of the collector tubes and the long-term durability of the hermetically-sealed vacuum jacket. The work performed under this contract addresses parts of both these questions. A major and critical process step in collector tube manufacture is the bake-out process. Contract work was aimed at: first, investigating the possible elimination of this step, and second, the shortening of the process time required and the reduction of capital equipment required to produce good quality collector tubes. The long term durability of the vacuum jacket, direct breakage aside, depends on the permeation rate of atmospheric gases into the jacket through the glass. From prior scientific investigation, the most likely atmospheric constituent gas to cause this problem is Helium. Helium is a minor constituent of air having a partial pressure of 4 x 10 exp -3 Torr. If, however, this equilibrium pressure could be reached in the vacuum jacket, heat conduction losses would take place from the tube in operation, causing a degradation of collector performance. Various aspects and tests concerning this phenomenon are investigated under the contract. (ERA citation 08:012177)