Southern Research has developed a facility to measure the effective thermal conductivity of porous materials at varying atmospheric pressures and constituent gases. The pressure radial inflow apparatus (PRIA) combines the technology of both Southern Research's comparative rod apparatus (CRA) and traditional radial inflow apparatus (RIA). The outer surface of a two-inch diameter cylindrical specimen is heated with a resistance heater tube capable of 1200°F. Radial heat flow is measured in a water calorimeter with a three-inch gage length. The entire specimen/heater assembly is operated in a pressure vessel rated for 5000 psi. Digital acquisition of the temperatures throughout the stack and within the calorimeter allows for the calculation of steady state and quasi-steady state effective thermal conductivity of solid fluid systems. Southern Research has used the PRIA to evaluate effective thermal conductivity of a commercially available insulation in the temperature range from 70°F to 800°F and in pressures of 0 psig to 1300 psig carbon dioxide. Surface temperatures were measured on 1/4 inch thick silica-based material. The maximum operating temperature was limited by the wall temperature of the PRIA pressure vessel; data could not be collected beyond 800°F for carbon dioxide. The isobars at pressures above the critical pressure (1070 psi) of carbon dioxide clearly show the fluid phase changes as the effective thermal conductivity of the system rises sharply near the fluid's critical temperature (87.9°F), and then falls as the density of the supercritical fluid phase becomes more gas-like.
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