thermal properties

High resistance of products made of SIMAX glass against sudden changes in temperature - thermal stability - depends on the low coefficient of linear thermal expansivity, relatively low module tensile elasticity and relatively high thermal conductivity which result in a lower thermal gradient in the product wall. When cooling and heating the glass product, no undesireable inner tension is created. If a glass product is broken down as a result of changing temperature, it is caused by tensile stress on the product surface by linear expansivity of the glass at the time of quick cooling from the product surface.

Permissible thermal stress depends on temperature gradient in the glass part wall. Provided that there is no temperature shock, the glass can be used up to temperatures about 300 °C. Generally and with respect to packing and jointing material, it is recommended to use the glass piping and apparatus up to temperature about 200 °C.

The boundary of possibility of quickly changing temperatures depends on thermal stress evoked by process conditions, connection and fixing of parts, and is also influenced by different wall thickness of these parts. For these reasons, limiting value cannot be specified for all encountered technological and process
conditions.

A substantial condition of good resistance against temperature shock is absence of mechanical working and scoring of the uniform glass surface to coarse scratches or dull stains.

The temperature shock is a quick temperature change between the glass part and the environment. It depends on wall thickness of glass parts and way of heating. Resistance of glass parts against thermal heating according to PN 13 8900.

 

heat transfer

Orientation values of total coefficient of heat transfer through glass SIMAX walls:

  • When used as condenser (steam condensation around tubes, cooling water through tubes)
    k = 290–580 W/m2K (250–500 kcal/m2 h °C)
  • When used as evaporator (water evaporation around tubes, steam condensation in tubes)
    k = 465–814 W/m2K (400–700 kcal/m2 h °C)
  • When used as heat exchanger (heated liquid around tubes, heating liquid through tubes)
    k = 250–400 W/m2K (200–350 kcal/m2 h °C)

change in length depending on temperature

The glass SIMAX features a very low coefficient of thermal expansivity. Change in length of a piping line, length 100 m, depending on temperature is given in the following table:

In case of longer lines, the change in length of the piping due to change in temperature should be taken into consideration and the piping should be fixed in a way that allows for the length change. This is usually achieved by using various expansion joints.

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