How to determine if a material is heat-insulating?
Thermal conductivity——The key to material insulation performance
Thermal conductivity (usually denoted by k, λ or κ) refers to the inherent ability of a material to transfer or conduct heat. It is the third method of heat transfer apart from convection and radiation. The process of heat conduction can be quantified using appropriate rate equations. The rate equation in this mode of heat conduction is based on Fourier's law of heat conduction.
The thermal conductivity is generated through the continuous collisions of molecules and does not cause the overall movement of the solid itself. Heat moves along the temperature gradient, that is, from the regions with high temperature and high molecular energy to the regions with lower temperature and lower molecular energy. This transfer will continue until thermal equilibrium is reached. The rate of heat transfer depends on the size of the temperature gradient and the thermal properties of the material.
It is defined as the amount of heat that passes through a unit area (1 m²) of a material per unit thickness (1 m) within a unit of time, with the unit being W/m·K. [ W. Watt, m: meter, K: Kelvin ]
The thermal conductivity of specific materials is highly dependent on several factors. These factors include temperature gradients, the properties of the material, and the length of the path along which the heat travels.
Materials with amorphous structure and low density have lower thermal conductivity. When the moisture content and temperature of the material are lower, the thermal conductivity is also lower.
The thermal conductivity of materials determines how we use them. For instance, materials with low thermal conductivity perform exceptionally well in housing and industrial insulation, while high thermal conductivity materials are highly suitable for applications in kitchenware and cooling equipment.Generally, materials with a thermal conductivity greater than 200 W/(m·K) are referred to as high thermal conductivity materials, while materials with a thermal conductivity of no more than 0.12 W/m·K are called insulation materials.
The thermal conductivity is a key component of the relationship between materials. The ability to understand thermal conductivity enables us to utilize the materials in various aspects of life to achieve the best performance. Effective thermal rate testing and measurement are of vital importance for this task.
The following are the thermal conductivities of common materials :
|
Material
|
Thermal Conductivity (W/m·K)
|
|
ABS-Plastic
|
0.25
|
|
Acetals
|
0.3
|
|
Acrylic
|
0.06
|
|
Alkyds
|
0.85
|
|
Alumina, Pure
|
30~40
|
|
Aluminum, Pure
|
237
|
|
Aluminum, Cast
|
100~180
|
|
Asphalt
|
0.75
|
|
Brick, Building brick
|
0.69
|
|
Brick, Diatomaceous earth
|
0.24
|
|
Brick, Fireclay
|
1.04
|
|
Cardboard, Celotex
|
0.048
|
|
Cardboard, Corrugated
|
0.064
|
|
Calcium Silicate Board
|
0.05~0.07
|
|
Cement, Mortar
|
1.16
|
|
Cement, Portland
|
0.29
|
|
Ceramic Fiber
|
0.09~0.2
|
|
Concrete, Ceramsite
|
0.77
|
|
Concrete, Foamed
|
0.21
|
|
Concrete, Stone 1-2-4 mix
|
1.37
|
|
Copper, Pure
|
401
|
|
Corkboard,10lb/ft 3
|
0.043
|
|
Diamond
|
2300
|
|
Diatomaceous earth
|
0.061
|
|
Epoxy
|
0.2~2.2
|
|
Epoxy Glass
|
0.3~0.5
|
|
EPS
|
0.033~0.036
|
|
Glass
|
0.12
|
|
Glass, Foamed
|
0.044~0.058
|
|
Glass, Silica
|
1.38
|
|
Glass Wool
|
0.032~0.040
|
|
Phenolic Resin Foam
|
0.023~0.025
|
|
Plaster
|
0.48
|
|
Plexiglass
|
0.19
|
|
Polyethylene Foam
|
0.047
|
|
Polyurethane Foam
|
0.025
|
|
Rock Wool
|
0.04
|
|
Rubber, Butyl
|
0.26
|
|
Rubber, Hard
|
0.19
|
|
Rubber, Silicone
|
0.19
|
|
Rubber Foam
|
0.034
|
|
Silica aerogel
|
0.016
|
|
Silicon, 99.9%
|
150
|
|
Stone, Granite
|
2.8
|
|
Stone, Limestone
|
1.3
|
|
Stone, Marble
|
2.5
|
|
Stone, Sandstone
|
1.83
|
|
Wood
|
0.17
|
|
Wood Shavings
|
0.059
|
Data source from the internet. For reference only.
