The degree of heat transfer of a material with a thickness of 1 m and the unit is W / mk or Kcal / mh ° C
Air 0.025
Water 0.6
Alcohol or oil 0.1 - 0.2
It is the heat conduction characteristic of a material with a certain thickness and is expressed as U value. The unit is W / ㎡K. The unit is W / ㎡K.
If the thickness is more than or equal to 1 mm in terms of thermal conductivity, it is expressed as a thermal transmittance rate. In other words, the thermal conductivity can be understood as a thermal property with respect to the unit thickness. When the thickness changes, the thermal conductivity is divided by the thickness and the result is the thermal transmittance rate.
That is, thermal conductivity / thickness (meter) = thermal transmittance rate. [Tip: Thermal Conductivity / thermal transmittance rate = Thickness (Meter)] If the thickness of a material is 1m, the thermal transmittance rate becomes equal to the thermal conductivity.
The thermal resistance is 1 / thermal transmittance rate. That is, the reciprocal of the thermal transmittance rate. Therefore, the calculation can be made as thickness / thermal conductivity. The unit is m2k / W, which is also referred to as R value.
The heat transmittance rate of the composite materials should not be the sum of the heat transmittance rates of each material. The sum of the thermal resistances should be obtained, and then the reciprocal should be calculated.
Thickness (m) / thermal conductivity = thermal resistance
The heat transmittance rate of the wall composed of concrete 20cm (1.73W / ㎡k) and 10cm (0.034 W / ㎡k) of Bead Method No.1 insulation is as follows.
Thermal resistance of concrete = 0.2/1.73 = 0.116
Thermal resistance of insulation = 0.1/0.034 = 2.94
Total Thermal Resistance = 0.116 + 2.94 = 3.056 ㎡k/W
Total heat transmittance rate = 1/3.056 = 0.327 W/㎡k