The thermal diffusivity of cellular glass

logo_smallWe had a request of a customer about the thermal diffusivity of cellular glass. Generally, he had three questions:

  • What is the meaning of thermal diffusivity besides thermal conductivity?
  • What about the different types of cellular glass and their respective thermal diffusivity?
  • Is it an important parameter for standard applications?

The thermal diffusivity is defined as thermal conductivity / (specific heat * density) which gives  0.48 mm²/s for GLAPOR cellular glass and 0.34 mm²/s for solid glass. Because all cellular glass types have about the same thermal conductivities for the same density, we can generally state that the thermal diffusivity ranges from 0.37 to 0.55 mm²/s for cellular glass. The following link gives this property for all kind of materials.

The thermal diffusivity give us a measure how fast a system goes to thermal equilibrium. If we heat copper with our finger, the new equilibrium is attained fast (111 m²/s) and we have a cold feeling. If we heat glass with our finger, it takes more time to reach equilibrium and the glass feels less cold. Once the equilibrium is reached, the thermal diffusivity does not play anymore.

Thermal diffusivity has a minor effect on the inner climate of buildings. If wood (0.08) is used, the building will need more time to come into equilibrium. On the other hand, this property is very important during the design of a factory. It is directly related to the length of a production line for cellular glass because a lower thermal diffusivity is harder to anneal, it involves a longer lehr.

CNUD EFCO

Dynamic thermal conductivity measuments are all measuring the thermal diffusivity and the thermal conductivity is determined from this value by multiplying with density and specific heat.

CRU02_2_LCD_datalogger_system_webv1601

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