Default Material Values KOPI
Thermal Resistivity
Section titled “Thermal Resistivity”Below are values obtained from CIGRE, Sintef and NMBU, which should be viewed as a guide only. We always recommend that a measure thermal resistivity on the masses as local conditions affect the value.
| Mass | Wet [mK/W] | Dry [mK/W] | Source |
|---|---|---|---|
| Gravel (coarse-fine) | 0.5 | 2.5 | Cigre TB 714 (2017)12 |
| Sand (coarse-fine) | 0.5 | 2.0 | Cigre TB 714 (2017)12 |
| Sand (sorted) | 0.6 | 3.5 | Cigre TB 714 (2017)12 |
| Silt | 0.7 | 2.5 | Cigre TB 714 (2017)12 |
| Topsoil | 0.7 | 2.0 | NMBU measurement10 |
| Turf | 2 | 17 | SINTEF measurement10 |
| Clay | 0.25 | 17 | SINTEF measurement10 |
| Mass | Thermal Resistivity [mK/W] | Source |
|---|---|---|
| Bentonite | 0.4- 0.6 | SINTEF measurement10 |
| Tarmac | 0.5-1.0 | SINTEF measurement10 |
| Concrete for duct banks | 1.0 | IEC 60287-2-1:20239 |
| Concrete for duct banks | 0.613 | SINTEF measurement13 |
IEC 60287
Section titled “IEC 60287”IEC 60287 has a more general approach to masses based on moisture content presented in the table below:
| Thermal resistivity [mK/W] | Mass description | Weather conditions |
|---|---|---|
| 0.7 | Very moist | Persistently moist |
| 1.0 | Moist | Regular rain |
| 2.0 | Dry | Rare rain |
| 3.0 | Very dry | Little to zero rain |
Metals:
Section titled “Metals:”| Thermal resistivity [mK/W] | Electrical resistivity at 20°C [μΩ*m] | Temperature coefficient [1/K] | Relative permability | |
|---|---|---|---|---|
| Steel | 0.019 1 4 | 0.138 2 3 1 4 9 | 0.0040 3 9 | 250 ≈ 215.67-126.43j 2 5 9 |
| Stainless steel | 0.69 8 | 0.7 6 7 8 | 0.00094 | 1 6 7 8 |
| Magnetic stainless steel | 0.69 8 | 0.7 6 7 8 | 0.00094 | 1000 ≈ 862.7-505.72j 6 7 8 |
Cables in Water Filled Pipes
Section titled “Cables in Water Filled Pipes”ρ = (2 * π * U)/(1+ 0.1 * De * ((V+(Y * θ) * ln(Dd/De))))
ρ = thermal resistivity applied to the pipe filling.
θ = the average temperature of water.
Dd = inner diameter of the pipe
De = diameter of the cable or an equivalent diameter of the group of the group of cable calculated according to IEC.
U = 0.1 (for water)
V = 0.03 (for water)
Y = 0.001 (for water)
| Source | |
|---|---|
| U = 0.1 (for water) | IEC 60287-2-1 |
| V = 0.03 (for water) | IEC 60287-2-1 |
| Y = 0.001 (for water) | IEC 60287-2-1 |
Empty water filled pipes
Section titled “Empty water filled pipes”For empty water filled pipes and water filled pipes without a heat source, a fixed thermal resistivity of 1.6 mK/W is applied.
“The Engineering Handbook” and “The Engineering ToolBox” sets the thermal conductivity for water at 0.609 W/mK, at 26.8°C. This is recalculated to approximately 1.6 mK/W for the temperature expectet to occur in a trench.
Footnotes
Section titled “Footnotes”-
American Society for Metals, Metals Handbook, Ninth Edition, Volume 1, Properties and Selection: Iron and Steels, Beijing, China: China Machine Press, 1988. ↩ ↩2
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L. Meyerhoff, “A-C Resistance of Pipe-Cable Systems with Segmental Conductors,” AIEE. Trans., vol. 71, no. III, pp. 393-414, 1952 ↩ ↩2
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Y. Sun, D. Niu and J. Sun, “Temperature and carbon content dependence of electrical resistivity of carbon steel,” in 2009 4th IEEE Conference on Industrial Electronics and Applications, Xi’an, China, 25-27 May 2009. ↩ ↩2