Residence time distribution in thermal insulation materials

This paper presents residence time distribution (RTD)-based characterization of thermal insulation materials, constructed upon a boiling water heat source-based testing system. Different types of metals, glasses, and polymeric materials are tested and analyzed. Every test plate material is subjected to a boiling water-based heating at one of its sides (waterside), while the other side (airside) is open to the ambience. The temperature data at these two sides of the test plate are then used to construct the relevant RTD curves. The properties of the RTD curves and the associated RTD parameters are found to be dependent on the thermal insulation capability of the test material. Specifically, the RTD curves unveil maximum heating frequency that the test plate is subjected to, and the stabilization time required by the test plate to achieve equilibrium under heating conditions. Accordingly, new metrics are defined for characterizing thermal insulations: (i) thermal shielding efficiency based on the maximum heating frequency, and (ii) thermal stabilization efficiency based on the stabilization time. Subsequently, the tested materials are characterized using the proposed metrics, along with the conventional thermal resistance-based metric. The proposed metrics are found to bring out the proper thermal shielding abilities of different types of materials that are hitherto remaining obscured by the limited capability of the conventional thermal resistance-based characterization.