k-values of Insulation Material
The following values can be used for the common insulation materials used:
k-value (W/m.K)
Closed cell elastomeric insulation 0.034 - 0.0374
Polyurethane 0.021 - 0.026
Fibre glass 0.03 - 0.033
Polystyrene 0.028 - 0.03
For other types of insulation material, refer to the manufacturer's catalogs and specifications for
the k-values.
If polyurethane is used with an external metal cladding (e.g. aluminium or galvanized), there will
be two k-values involved in the computation equation. However, since the cladding is a good
thermal conductor, it is possible to ignore this thin metal (usually 0.3 - 0.5 mm thick) in the
calculation of the polyurethane thickness required.
Nevertheless, if necessary, the following equation can be used:
r3[kb*ln(r1/r2) + ka*ln(r1/r2)] = (ka*kb) (T3 - T1)
h (T3 - Ta)
where ka and kb are the k-values for the two different material
r3 and T3 are the radius and surface temperature of the external cladding
The k-value for aluminium (kb) is 212 W/m.K
h-values
The following convective heat transfer coefficients can be used for different surface
conditions (assuming free convection):
h-value (W/m.K)
Matt surfaces, black or grey 9 - 10
Metallic surfaces, not polished 7 - 8
Metallic surfaces, polished 5 - 6
Section 7 Page 96
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