Metrology for Developing Highly Efficient Thermal Insulations or Super-Insulation Materials

Back

 

Rational energy usage plays an important role in industry these days. Furthermore, an increasing number of high-tech applications require perfected thermal protection systems. In these cases, implementing super-insulation materials enables specific solutions to be devised. In close co-operation with industrial partners, the Bavarian Center for Applied Energy Research (ZAE Bayern) in Würzburg, Germany, has been working on developing and optimising such systems for many years.

The key parameter for thermal insulation systems is thermal conductivity. Therefore exact and reliable measurements are necessary for optimizing existing materials and developing new materials. Super-insulation materials are distinguished by their extremely low thermal conductivity. In porous insulation materials, heat is conducted through the solid material structure, transported in the gaseous phase and radiated. In super-insulation materials, the heat conducted via the gas inside the pores is efficiently curbed by means of evacuation and by implementing microporous materials. By evacuating insulation systems with porous fillings, super evacuated insulation materials (VIPs, see Fig. 1) can be produced which have a thermal conductivity of less than 0.004 Wm-1K-1 at 20°C which is 10 times lower than the thermal conductivity of polystyrene (Fig. 2). As a means for comparison, air has a thermal conductivity of 0.026 Wm-1K-1. The insulation system's vacuum-tight casing comprises, for example, multi-layered compound film or thin stainless-steel sheeting.

Evacuated foil insulation has outstanding insulation properties at low temperatures, making it most suitable for cryo-applications (T < -180 °C). Effective thermal conductivity values of far less than 0.001 Wm-1K-1 are achieved here, using layered, highly-reflective metallic foils separated by spacers.

For high temperature applications, heat transport via the gas molecules is effectively reduced by employing microporous silicates which lead to restricted movement within the microporous structure. Thermal conductivity values of less than 0.06 Wm-1K-1 at 1000 °C can be realised here.

Super-insulation materials are employed in high-tech fields such as cryotechnology, space technology and fusion research, but also in domestic refrigerators and innovative buildings. In applications such as these, it is even more important that a maximum insulating effect is achieved for a given thickness.

 

Fig. 1: Vacuum insulation panel (VIP) which consists of a porous filling and a vacuum-tight casing. Here a multi-layered compound film serves as casing.

 

Fig. 2: Comparison between polystyrene and a vacuum insulation panel (VIP). A VIP with a thickness of 2 cm provides the same thermal insulation as polystyrene with a thickness of 20 cm.

 

For more information pleace contact:

Dr. Hans-Peter Ebert
Head of Division: Functional Materials for Energy Technology
Bavarian Center for Applied Energy Research (ZAE Bayern)
Am Hubland, 97074 Würzburg, Germany
Phone: +49 931/ 705 64-34
Fax:    +49 931/ 705 64-60
Email:
ebert@zae.uni-wuerzburg.de
http://www.zae-bayern.de


Back