Volume 77, Issue 2, February 2006
Index of content:
- THERMOMETRY; THERMAL DIFFUSIVITY; ACOUSTIC; PHOTOTHERMAL AND PHOTOACOUSTIC
Thermal contact conductance of ceramic AlN and oxygen-free high-conductivity copper interfaces under low temperature and vacuum for high-temperature superconducting cryocooler cooling77(2006); http://dx.doi.org/10.1063/1.2165567View Description Hide Description
In this article, a device for measuring thermal contact conductance under low temperature and vacuum for cryocooler cooling in high-temperaturesuperconducting(HTS) system is presented. Such device may be used to simulate the real running condition of HTS equipments cooled by cryocooler. It is also convenient for temperature controlling. The thermal conductivity of ceramicAlN and the thermal contact conductance (TCC) between AlN and oxygen-free high-conductivity copper for the temperature range of 45–140 K and the vacuum range of have been measured using axial steady heat-flow method on the Giffard-McMahon cryocooler with 5 W (20 K) capacity. Investigation shows that the TCC of the interface increases as the temperature and the pressure load of contact interface increase, and the conductivity of ceramicAlN increases as temperature rises. An analysis based on micro- and nanocryogenic concepts is made to explain the behaviors of thermal conductivity for AlN and thermal contact conductance for the interface.
Apparatus for in situ prediction of the thermal conductivity of fiberglass batts using acoustic propagation constant77(2006); http://dx.doi.org/10.1063/1.2167129View Description Hide Description
This article describes a novel technique for the measurement of the thermal conductivity of low-density fiberglass insulation and other related fibrous insulation materials using a noninvasive acoustic apparatus. The experimental method is an extension of earlier acoustic methods based upon the evaluation of the propagation constant from the acoustic pressure transfer function across the test material. To accomplish this, an analytical model is employed that describes the behavior of sound waves at the outlet of a baffled waveguide. The model accounts for the behavior of the mixed impedance interface introduced by the test material. Current results show that the technique is stable for a broad range of absorber thicknesses and densities. Experimental results obtained in the laboratory show excellent correlation between the thermal conductivity and both the real and imaginary components of the propagation constant. Correlation of calculated propagation constant magnitude versus measuredthermal conductivity gave an of 0.94 for the bulk density range typical for manufactured fiberglass batt materials. As an improvement to earlier acoustic techniques, measurement is now possible in noisy manufacturing environments with a moving test material. Given the promise of such highly correlated measurements in a robust method, the acoustic technique is well suited to continuously measure the thermal conductivity of the material during its production, replacing current expensive off-line methods. Test cycle time is reduced from hours to seconds.