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.


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.


Microsoft Windows follows BELGLAS advice;-)

logo_smallBELGLAS uses the open source UBUNTU Linux operating system for his own purposes but with bigger customers, we work on their PC, which is always a Windows operating system. Updates are always irritating but this time, we were very happy.

imagesIt was announced that WINDOWS should have integrated the Ubuntu BASH shell, which is a typical LINUX operating system. This BASH shell works well within the WINDOWS system besides the POWERSHELL and should allow to run every program which runs under Ubuntu Linux. We tested already the GNU FORTRAN compiler and it seems to work well.

DownloadBELGLAS is now able to deliver programs which can be run on a WINDOWS computer although they were developed with GNU FORTRAN under LINUX. All the programs, written by BELGLASCZ will be available on a Dropbox server after simple request for known users.

FORTRANThe programs will not be open source because the FORTRAN source will not be shared. The programs are free to use without any responsibility for BELGLAS. The following programs will be shortly free of charge available:

  • calculation of the thermal stress during annealing
  • determination of the thermal conductivity with the low cost BELGLAS thermal conductivity measurement system.
  • calculation of the thermal stress on a cold and hot pipe
  • simulation of glass foaming
  • calculation of a budget price for a cellular production environment (CAPEX)
  • calculation of cellular glass production cost (OPEX)

For all these programs, BELGLAS will perform installation and consultancy if needed at an acceptable fee.

win-lin marriage