Knowledge of variation of thermophysical properties with temperature and composition is inevitable for construction of engines, mathematical modeling and calculations of thermophysical processes. Thermal expansion causes mechanical stress and as the result cracks or mechanical deformations appear. The described device is suitable for measurement of thermal expansion and derived thermophysical properties of metals and alloys (dilatometric analysis of alloys, transformation temperatures). The method using direct resistance heating by electric current is appropriate in temperature range from ambient up to melting point of the material under test. Sample in shape of rod is attached between two water-cooled terminal connectors. Electrical current from programmable power supply passes through the sample (electrical conductor) and electric energy changes directly into heat in the sample volume (internal volume heat source). Temperature of the sample is sensed by thermocouple to 1 000°C, optical pyrometer has to be used at higher temperature. The temperature sensed by thermocouple or optical pyrometer is used as feedback of a time - proportioning controller with integral and derivative function (PID controller). Heating or cooling rate is programmable. Thermal expansion is measured optically. Central part of the sample is projected by lens to optical sensor and dimension of its image is changed into electrical signal. Optical measurement eliminates thermal expansion of sensing points used for contact methods. Vacuum or argon atmosphere prevents the sample from oxidation during measurement. Losses by radiation are confined by cylindrical mirror to decrease dissipated heat and power supply demands.
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