Heat and Mass Transfer in Polyurethane Insulated District Cooling and Heating Pipes

Abstract

The heat and mass transfer in PUR insulated pipes used for dis trict cooling and district heating is studied. During the aging of the pipes, the blowing agent, in this study CO2 for the PUR foam will diffuse out through the casing and air components will diffuse into the foam. This diffusion will deterio rate the thermal properties of the insulation foam. For district cooling pipes, in ward diffusion and condensation of water vapor may occur which may increase the risk for corrosion, change the thermal properties, and affect leakage alarms. Theo retical models for mass and heat transfer are developed and solved numerically. The importance of the quality of the casing, the insulation thickness, the wall thickness of the casing, and the surrounding temperature is studied. Results for the diffusion process, thermal conductivity, and amount of condensed water are presented. The quality of the casing has a vital importance on the diffusion process. With a higher density of the casing, the diffusion process will be slower and the deterioration of the thermal properties become slower. The surrounding temperature, the insula tion thickness, and wall thickness of the casing are also of great importance. The amount of condensed water in the PUR foam is found to be very small during a pe riod of thirty years and will hardly affect the thermal performance or the leakage alarms.