An Investigation of Thermal Processes in Insulation with a Thin-Film Coating on Heating Network Piping

Piping heat insulation consisting of mineral wool as the main layer and a fiberglass cover is deformed and suffers damages during day-to-day operation. This increases the heat losses through insulation when a heat carrier flows through the pipeline. This investigation is devoted to the use of a thin-film coating (TFC) in the arrangements of existing conventional heat insulation on heating networks to improve the insulation's effectiveness and reduce the heat losses. The effectiveness of a TFC was evaluated experimentally in a model section of a pipeline that enabled us to simulate actual operating conditions of the piping in a heat supply system. The experiment is based on the determination of heat fluxes flowing through the heat insulation of a pipeline using an infinite cylindrical layer method. To theoretically substantiate the energy-saving effect from the application of a TFC, a numerical investigation of thermal processes occurring within the insulation was performed. Since the considered type of insulation is air-permeable and the permeability depends on the state of the main and cover layers, the effect of convection on heat transfer in the porous insulation with a permeable cover on heating network piping was numerically studied. The effect of a TFC on thermal processes and effectiveness indices was analyzed for two methods of a heating network's installation: indoors or outdoors. The results demonstrate that it is advisable to use a TFC in the existing heat insulation to improve its effectiveness and reduce thermal energy losses due to a decrease in the heat fluxes by 17% after application of the TFC. The numerical predictions suggest that indoor pipelines should be provided with one TFC layer, while outdoor pipelines should be coated with at least two TFC layers.