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Evacuation as a means of reducing the gas-conducted heat through a thermal insulation has been considered in the past mainly for low temperature and aerospace applications. The extension of this work to higher temperatures has shown that it is possible to use evacuated load-bearing fibrous insulation up to at least 750°C hot face. Load-bearing tests on thermal insulations showed that microporous silica insulation has very high compressive strength whereas rockwool and aluminosilicate fiber insulations compress by up to 50 percent under atmospheric pressure compressive load. A plane guarded hot plate apparatus to measure thermal conductivity of a load-bearing specimen has been used to obtain data for a range of typical fibrous and block thermal insulations. Of the materials tested, fibrous materials give the largest change in thermal conductance on evacuation, but evacuated opacified microporous silica has the lowest thermal conductivity. A practical device utilizing these data has been built and tested.
thermal insulation, heat transmission, thermal conductivity, high temperature tests, microporous materials
Research physicist, Electricity Council Research Centre, Capenhurst, Chester,