AN670 – Heat capacity determination of low density insulation materials by calorimetry

INTRODUCTION

Maintaining acceptable temperatures in buildings (by heating and cooling) uses a large proportion of global energy consumption, leading to a high R&D in terest in more efficient insulation materials. Among others, aerogels are interesting low density, low conductivity materials in which the liquid component of the gel has been replaced with a gas. Cp of such an insulation material is a key parameter that describes its aptitude to accumulate heat. As large sample masses are preferred for accurate Cp determination, the C80 calorimeter is perfectly adapted for the measurement.AN-670

EXPERIMENTAL

Three materials are tested. Spaceloft® has a low density (150kg.m-3) and extremely low conductivity(14mW/m.K at 40°C). Deprom is a common thermal insul ator based on extruded polystyrene and with an extremely low density (40kg.m-3) and low conductivity (27mW/m.K). Expansed PVC is relatively dense. Sample masses range from 300mg to 4g. All samples are heated from 30°C to 45°C at 0.15 °C.min-1. A blank test with empty vessels is run using the same procedure.

RESULTS AND CONCLUSIONS

Heat Capacity is calculated from eq.1, where Ab and As are the HeatFlow signals for blank and sample tests respectively, and β is the instantaneous heating rate (see document TN149).

AN-670b

A polynomial regression can be obtained from the experimental data, in order to extrapolate to higher or lower temperatures. Here, the benefit of C80 vessels is that they allow testing large sample volumes, meaning that samples masses are significant even with low density materials. Heat capacity differences as high as 0.1 J.g-1.K-1 between Deprom, Spaceloft®, and expanded PVC samples are easily measured.