Evacuated powder insulation for district heating applications

摘要

The possibility to design a pipe system with a new CFC-free insulation is being investigated. The objective is to describe a pipe insulation which is as effective as the CFC-blown polyurethane foam (PUR) insulation, at comparable cost and which, at the same time, meets any environmental requirements that may be made in the foreseeable future. The thermal conductivity of vacuum-packed powder has been measured in district heating applications and a specification for a suitable packaging material has been proposed. Of the powders tested, fine-grained kieselguhr and opacified aerogel have been found to have the lowest thermal conductivities, i e 0.004 - 0.005 W/(m K) at pressures up to about 0.01 kPa, which is about a factor of 8 less than PUR. Opacified aerogel has better insulation properties than kieselguhr at pressures over about 1 kPa. A five-component plastic/aluminium laminated foil has been investigated as packaging material. An integrated insulation technique where the insulation packages are immobilized in CFC-free PUR is estimated to have considerably higher insulation capabilities than CFC-blown PUR. 9 refs. 11 figs