XY热传导系数测试方法.docVIP

In-Plane Thermal Conductivity of Composite Materials ?Charles E. Powers NASA Goddard Space Flight Center (301) 286-8061 cpowers@ millerpowell@163.com ? The Materials Engineering Branch (MEB) has developed a technique to calculate the thermal conductivity of a material from thermal diffusivity (?), specific heat (Cp) and density (d) measurements using the following equation: q = ? Cpd. Thermal diffusivity is measured using the Angstrom’s temperature wave method. A peltier junction is used to generate a periodic heat wave along a specimen. Two thermocouples are used to measure the decay in amplitude and phase shift of the heat wave as it travels along the sample. These two parameters are used to calculate thermal diffusivity using the following equation: ? = (? fL2)/(?2) = (? fL2)/[(ln(a0/a1)] 2 where f is the frequency of the heat wave, L is the distance between the thermocouples, ? is the phase shift between the thermocouples, a0 is the amplitude of the temperature oscillation at the thermocouple closer to the peltier junction and a1 is the amplitude of the temperature oscillation at the other thermocouple. Typical thermal diffusivity specimens are cylindrical (or rectangular) in shape and have a length of 10 cm and a diameter around 1 cm. Specific heat measurements are made using a TA Instruments DSC 910 Differential Scanning Calorimeter. Typical specimens needed for this measurement are 20-50 mg in weight. The test is conducted by heating the samples at a rate of 20 °C/minute in a helium environment and measuring the heat flow vs. temperature of the sample. Using this information along with data collected from a reference sample of sapphire, specific heat calculations are then made for the specimen at every temperature of interest. This approach has become necessary to determine the thermal conductivity of composite materials. Standard techniques to measure thermal conductivity can not be used to measure the in-plane thermal conductivity of composites because