Analytical model of heat transfer in porous insulation around cold pipes.

A system is analysed that consists of a cold tube insulated with a porous material faced with a vapour retarding foil. Water vapour will diffuse through the vapour retarding foil and flaws in the foil and condense on the cold tube. To avoid build up of water in the insulation a hydrophilic wick cloth is wrapped around the cold tube and extended through a slot in the tubular insulation and the facing to the ambient so the condensed water can evaporate into the air. Some of the moisture in that part of the wick cloth situated in the slit in the insulation will diffuse back to the cold pipe and hence contribute to the heat uptake of the cold tube. This part is calculated for the stationary case and compared with the heat transfer through the tube shaped insulation material. In addition it is compared with the amount of heat absorbed from condensation on the cold tube of water vapour diffusing through the vapour retarding foil and possible flaws.