A compact photopyroelectric set up for the determination of temperature variation of thermal conductivity and heat capacity of solids

摘要

A compact photopyroelectric cell has been designed and fabricated. Using this cell the thermal transport parameters, thermal diffusivity (α). thermal effusivity (e), thermal conductivity (K), and specific heat capacity (c{sub}p), for any solid material can be measured. It mainly consists of a thermally thick copper-backing on which a PVDF film of thickness 28mm,which is the pyroelectric detector, is attached. The PVDF film is Nickel-Chromium coated, which converts thermal waves into electrical signals. Connections are taken from the 'rout and back of the film. The sample whose thermal properties are to be determined is kept on the film and irradiated with a modulated light beam. The light is guided to the sample through an optical fiber. When modulated light falls on the sample, the sample gets heated periodically and thermal waves are generated. The pyroelectric detector converts the thermal waves into corresponding electrical signals and is measured using a Lock-in amplifier. Thermal properties are determined by measuring the amplitude and phase of the pyroelectric output signal. The system can be immersed into a liquid nitrogen chamber so that the sample temperature can be varied and controlled. The cell enables one to measure thermal transport properties down to 77K. Calibration of the cell has been done by making measurements on a sample of known thermal properties. The cell is found to work well and is found to be very convenient for making measurements.