Thermal conductivity of polyurethane foam cell gases: Improved transient hot wire cell – data of isopentane + n-pentane mixtures – Extended Wassiljewa-model

The thermal conductivity of pure components and binary mixtures of n-pentane, isopentane and nitrogen was measured at temperatures between 309 and 414 K and at pressures up to 1.0 MPa using an apparatus based on the transient hot wire method. These mixtures are important in the assessment of the progress of the thermal insulation capacity of closed cell polyurethane foams during the total life time of the respective applications. The experimental thermal conductivity data were correlated with the Wassiljewa mixing rules as modified by Mason and Saxena, and predicted using two new empirical models, with average deviations under 0.4% and 0.6%, respectively. Significant changes were performed in the apparatus, with the design of a new measuring cell and the simplification of the tubing system. A new experimental procedure was also developed leading to a considerable improvement in the precision of the results.