The mass transfer of carbon dioxide through the outer polyethylene casing of district heating pipes, at room temperature, was evaluated, using different test methods. The mass transfer either through polyethylene casings on polyurethane preinsulated district heating pipes or through polyethylene casings alone was mea sured. Permeability coefficients of different polyethylene casings were about 20 · 10-18 kg·m-1·s-1·Pa-1. Permeability coefficients for carbon dioxide in polyurethane foam is about 100 times lower, which means that the mass transfer resistance to car bon dioxide of the polyurethane foam in a district heating pipe is negligible in com parison with the polyethylene casing.
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