A periodic method of determining thermal diffusivity

Renew, W. D. (1966). A periodic method of determining thermal diffusivity Master's Thesis, School of Engineering, The University of Queensland.

       
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Author Renew, W. D.
Thesis Title A periodic method of determining thermal diffusivity
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 1966
Thesis type Master's Thesis
Supervisor Dr- K.J. Bullock
Total pages 147
Language eng
Subjects 09 Engineering
Formatted abstract

In heat transfer calculations, two of the more important properties of a material are thermal conductivity (K) and thermal diffusivity (α). They are connected by the relation, α = K/pCp where p is the density of the material and Cp its specific heat. Thus if α, p and Cp are known, K may be determined.

One class of method (the static type) consists in measuring  directly, whereas the dynamic type of experiment yields a value of . This thesis describes such a dynamic method, in which one end of a long metal bar is subjected to periodic heating. Corresponding temperature oscillations are produced at points along the bar, with a gradual decay in amplitude. The value of diffusivity is calculated from measurements of the temperature attenuation between two points, and the phase lag between the temperature oscillations.

This procedure was followed for the case of a mild steel bar 3/4 in. diameter x 2'-6” long. Both square-wave and sine-wave heat supplies were used, but only the former proved satisfactory. Two types of heater were designed, a resistance coil type and one employing an element of silicon-carbide. Tests were carried out at low frequencies ranging from 0.002 to 0.005 c.p.s.

A value of 0.51 ft2 hr-1 was obtained for the thermal diffusivity of a bar of commercial mild steel. The estimated error of the determination is ±5%. This result was compared with values given in previous papers. Though the accuracy is not high, it is sufficient for some engineering purposes. Further experiments are expected to yield an accuracy of ±2%.

Keyword Torsion -- Electromechanical analogies
Elasticity
Calculus of tensors
Thermal diffusivity

 
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