2. Insulation performance and environmental factors

2.1 Influence of humidity

Environmental moisture in gaseous form (water vapour) or liquid form (condensation water or accidental infiltration) can penetrate insulating materials in service, reducing their nominal thermal resistance in the dry state. Determining the thermal performance of wet insulation is a complex problem. While it is indeed possible to define the apparent thermal conductivity of a wet medium, measuring this conductivity is extremely tricky, due to mass flows and phase change phenomena in addition to simple heat transfer. Two approaches are a priori possible:

• or solve the complete heat and mass transfer equations and accurately assess the effects of humidity on heat transfer under the given application conditions;...