Accurate Thermal Property Measurement of Fine Fibers by the 3-omega Technique

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Applied Thermal Engineering





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In a previous work, a complete model has been presented for the thermal property characterization of suspended wires using the 3ω technique. As validation of the model and comparison of the effects of measurement configuration, several samples are measured in a vacuum chamber (<0.001 Pa) using voltage and current sources for sample excitation. In particular, the characteristics of each excitation type are shown along with the effect of cancellation of the first harmonic (1ω) signal. Without cancellation, large uncertainties occur in thermal conductivity and thermal diffusivity measurement while volumetric heat capacity cannot be directly measured with acceptable accuracy. Using methods to cancel the 1ω voltage greatly improves measurement precision with the ability to independently measure the three aforementioned thermal properties. Voltage source excitation results in the most precise measurements. However, for samples with resistance (<∼0.5 kΩ), susceptible to the influence of other components of the circuit, an extrapolation procedure using measurements of varied Wheatstone bridge resistances is necessary to obtain thermal conductivity and heat capacity. Detailed uncertainty analysis of each measurement configuration shows that the voltage source provides the best overall measurement uncertainties (∼8.5% and ∼3.9% for thermal conductivity and diffusivity respectively).

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