Thermal Conductivity of Vermiculite

The thermal conductivity of expanded vermiculite is mainly determined by its grain composition loose bulk density. Characteristically, the grain composition has a greater influence on the thermal conductivity than the loose bulk density.

Large vermiculite easily orients perpendicularly to the heat flux and "λ" is much better than unoriented. Grains less than 1.2 mm almost do not orient.

To find the approximate thermal conductivity of vermiculite in dry condition at normal temperature, you can use the following formula:

λ = (0,039 + 0,00011 gH) * 0.01 * kcal / m * h * ° С

where "gH" - volumetric density of exfoliated vermiculite in kg/m3.

Exfoliated Vermiculite

gH kg/m3, max

λ, kcal / m * h * ° С
(t = 25 oС)

λ, kcal / m * h * ° С
( t > 100 oС)

Micron

130

0,0534 ± 0,01

0,062 + 0,00016t

Superfine

120

0,0522 ± 0,01

0,059 + 0,00017t

Fine

110

0,0511 ± 0,01

0,057 + 0,00020t

Medium

95

0,0483 ± 0,01

0,054 + 0,00025t

Large

65

0,0461 ± 0,01

0,052 + 0,00028t

 

As the table shows the coefficient "λ" increases, when temperature increases. Increase in "λ" (when temperature increases) in small fractions is not as intense as in large ones.

 

Therefore, when using vermiculite for high temperature (t > 100 ° C) insulation, grain sizes not exceeding 2.5 mm should be used.

 

An important advantage of exfoliated vermiculite is its low emissivity value, 0.60 kcal. / M2 * h * (K/100)4.

This fact favorably influences the ability of vermiculite insulation at temperatures above 500 ° C, when the percentage of the total heat emission in the heat transfer increases sharply.

 

FACTS:

As world experience shows, vermiculite is very successfully used in construction, as fireproof bulk insulation. Flowability properties of vermiculite allows to fill the void of irregular shape. Thermal conductivity of 20 cm vermiculite layer equals to 1.5 m thick brick wall or 2 m thick concrete wall.

Owing to this feature, the use of vermiculite in attics insulation allows to reduce heat losses by:

  • 75% - if the layer is 5 cm thick,
  • 85% - if the layer is 7.5 cm thick,
  • 95% - if the layer is 10 cm thick.

 

Thermal conductivity of some construction materials, W / mK

 Exfoliated Vermiculite

0,04 - 0,062 

 Basalt Canvas

0,04 - 0,062 

 Keramzite Gravel

0,12 

 Asbestos slab

0,13 

 Concrete foam

0,14 - 0,18 

 Cavity Brick

< 0,56 

 Solid Brick

> 0,6 

 Brickwork

0,8 

 Concrete

1,45 

 Ferroconcrete

1,6 

19.10.2017   12:01

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