Measurements of Pipe Insulation Thermal Conductivity at Below Ambient Temperatures Part I: Experimental Methodology and Dry Tests

摘要

Mechanical pipe insulation systems are installed around cold cylindrical surfaces, such as chilled pipes, which often work at below ambient temperatures in industrial and commercial building applications. The thermal performance of pipe insulation systems is affected by local ambient conditions and might vary gradually with time. Most published data are extrapolated from flat slab configurations of the insulation materials, but the measured thermal conductivity from flat slabs might over or under estimate the actual thermal conductivity of cylindrical shaped pipe insulation systems due to radial configuration and longitudinal split joints. A methodology for measuring thermal conductivity of cylindrical shaped pipe insulation systems exists in the ASTM standards but it is based on a heated pipe approach with outward heat flow. If the average temperature of the pipe insulation system is below ambient temperature then a more accurate prediction of the pipe insulation actual thermal conductivity is needed for the design of insulation systems in chiller pipe applications.In this paper, a novel experimental apparatus to measure the thermal conductivity of mechanical pipe insulation systems at below ambient temperatures, is presented. The new apparatus was validated with two pipe insulation systems, cellular glass and Polyisocyanurate (PIR), used to benchmark our measurements against data available in the public domain. The thermal conductivity of additional three pipe insulation materials, that is, fiberglass, flexible elastomeric and phenolic, was also measured at several insulation temperatures at below ambient and in dry non-condensing ambient conditions. Correlations of the pipe insulation thermal conductivity were developed based on insulation specimen average temperature and wall thicknesses. Corresponding uncertainties of the measurements and the edge effects of the longitudinal butt joints are also critically analyzed in this paper. This paper is the first part of the pipe insulation measurements under dry non-condensing conditions and the measurements under wet condensing conditions will be presented in a following paper.