AbstractThe object of this work is to look into the long term viability of a partially evacuated, high performance, hot water, solar collector proposed by Roberts (1979). The collector involves an absorber plate inside an evacuated domed glass tube, sealed by a polymer seal onto a metal endcap. The proposed collector contains 15 torr of low thermal conductivity gas to suppress conduction losses from spurious gases arising in the collector.
A study was undertaken, and is shown, to predict the loss of vacuum in the polymer sealed collectors; for various vacuum sealing polymers. It is shown that viton is the most suitable polymer, and a design of a suitable seal is shown, with the design of a completed unit. An upper limit of loss of vacuum in the collectors is demonstrated to be 0.5 torr/year. This is due in main to permeation of water vapour, oxygen, and nitrogen through the seals.
An experimental study and theoretical comparison to, find a suitable low thermal conductivity gas, to infill into the collectors and to predict the thermal conductivity of this gas mixed with relevant quantities of the inleaking gases is shown. The thermal conductivity cell and electronic unit to do this study is presented It was found that Halocarbon 11 would be a suitable gas to inflow into the collectors, having a thermal conductivity of 8• 07X1- 0j-3 .W M-l K--1•.
Theoretical equations for binary, and multi-component gas mixtures are shown compared with our experimental results. These equations do not compare favourably; however it is shown that by using a combination of these equations the thermal conductivity of gases arising in the proposed collectors may be predicted to within 5%. The efficiency test of a completed unit is shown. This shows the efficiency of the partially evacuated collector to be similar to a high vacuum collector. The efficiency of the collector is shown not to deteriorate significantly within a period of ten years.
|Date of Award||1986|