Thermal Transport in Porous Superinsulations

Abstract

The improvement of thermal insulation systems promises large savings in primary energy consumption. “Superinsulations” with extremely low thermal conductivities can be implemented with evacuated highly porous powder, fiber or gel spacers. As these materials are load bearing, the thick pressure supporting steel or aluminum walls, generally employed in cryogenic storage tanks, can be substituted by thin and flat steel and plastic envelopes. For gel systems, even transparent glass panes can be used as protective covers. Thermal superinsulations can be used in many technical systems:

• hot water storage is possible with dwelling times of 1500 h compared to only 100 h for conventionally insulated tanks;

• electric house heating/storage systems can be built smaller and will have smaller losses if superinsulated;

• district steam heating systems up to now are economical only over distances of a few kilometers; superinsulated steam pipes have smaller diameters and smaller losses and can even be installed without expansion compensators;

• new high-temperature batteries (like the NaS-battery) for electro-automobiles depend on load-bearing superinsulations to keep the reactants liquid during parking periods;

• superinsulated refrigerators and freezers could be built with less cooling power and with larger useful volumina for a given outer geometry than conventional systems;