In the article Measurements of the Thermal Conductivity and Thermal Diffusivity of

Chapter 3, Problem 13

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In the article “Measurements of the Thermal Conductivity and Thermal Diffusivity of Polymer Melts with the Short-Hot-Wire Method” (X. Zhang, W. Hendro, et al., International Journal of Thermophysics, 2002:1077–1090), the thermal diffusivity of a liquid measured by the transient short-hot-wire method is given by

\(\lambda=\frac{V I A}{\pi l a}\)

where \(\lambda\) is the thermal diffusivity; V and I are the voltage and current applied to the hot wire, respectively; l is the length of the wire; and A and a are quantities involving temperature whose values are estimated separately. In this article, the relative uncertainties of these quantities are given as follows: \(V, 0.01 \% ; I, 0.01 \% ; I, 1 \% ; A, 0.1 \% ; a, 1 \%\)

a. Find the relative uncertainty in \(\lambda\)

b. Which would reduce the relative uncertainty more: reducing the relative uncertainty inl to \(0.5 \%\) or reducing the relative uncertainties in V, I, and A each to 0?

Equation Transcription:

Text Transcription:

\lambda=VIA over la

\lambda

V,0.01%; I, 0.01%; I, 1%; A, 0.1%;a, 1%

\lambda

0.5%

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