Warning: Trying to access array offset on value of type bool in /var/www/foxof.com/wp-content/plugins/all-in-one-schemaorg-rich-snippets/functions.php on line 914
Warning: Trying to access array offset on value of type bool in /var/www/foxof.com/wp-content/plugins/all-in-one-schemaorg-rich-snippets/functions.php on line 914
Warning: Trying to access array offset on value of type bool in /var/www/foxof.com/wp-content/plugins/all-in-one-schemaorg-rich-snippets/functions.php on line 914
Warning: Trying to access array offset on value of type bool in /var/www/foxof.com/wp-content/plugins/all-in-one-schemaorg-rich-snippets/functions.php on line 916
Warning: Trying to access array offset on value of type bool in /var/www/foxof.com/wp-content/plugins/all-in-one-schemaorg-rich-snippets/functions.php on line 916
Warning: Trying to access array offset on value of type bool in /var/www/foxof.com/wp-content/plugins/all-in-one-schemaorg-rich-snippets/functions.php on line 916
Home / Heating / Infrared heating and radiation / Emissivity (français – español)
Thermal emissivity of materials in the framework of heating and construction
Share this page
Principle of thermal emissivity
The emissivity of a material (ε) is its capacity to absorb and reemit energy by radiation. This physical value indicates how much a surface emits thermal infrared radiation compared to an ideal body called “black body”. The “black body” is the most efficient in terms of heat emission by radiation, ε=1=maximum.
Emissivity of materials for emitting radiation
Difference in emissivity between 2 materials (sleek-reflective white IR / rough-absorbent black IR)
Thermal emissivity in the context of radiation heating
Contribution of emissivity in the radiant power
The emissivity of a surface varies according to several parameters (which makes it difficult to measure):
- the nature of the material.
- surface condition. The rougher (as opposed to sleek) the surface of the emitting material, the better the emissivity.
- the colour. A black pan will have a better emissivity than a silver pan.
- the temperature of the material. The higher the temperature, the better the emissivity.
A few indicative values of emissivity of materials used to transmit heat in the context of heating:
- ε (anodised aluminium) =0.77
- ε (polished aluminium) =0.05 (the surface being therefore a significant non-negligible part)
- ε (glass) =0.93
- ε (smooth metal) =0.25
- ε (metal coated with specific emissive powder to maximise the emissivity) =0.96 – sources www.degxel.co.uk
In clear terms, when we talk about the diffusion efficiency of radiation by a heater, the knowledge of the material is not sufficient to draw a conclusion. Other factors described above are essential.
Infrared thermography of an infrared heater with an emissivity ε of 0.96 (max = 1) – Source www.degxel.co.uk
Thermal emissivity in the context of construction
Thermo-detector of emissivity of the measured material (wall)
- ε (stone)=0.93
- ε (frosted glass)=0.93
- ε (frosted tiles)=0.92
- ε (non-smooth wood)=0.90
- ε (red brick)=0.90
- ε (plaster)=0.90
The surface emissivity is taken into account when measuring the surface temperature of a wall using an infrared thermo-detector. The gun captures the surface temperature of the material without contact. We can thus deduce thermal bridges and the risk of mould.
Other topics that may be of interest to you
To know more about The best insulators for construction
To know more about The best heaters
To know more about Identifying thermal bridges and preventing mould
FOX48
