Nonsteady-state heat flow may be described by the following partial differential equation:

where D_T is the thermal diffusivity; this expression is the thermal equivalent of Fick’s second law of diffusion (Equation 5.4b). The thermal diffusivity is defined according to

In this expression, k, ρ, and c_p represent the thermal conductivity, the mass density, and the specific heat at constant pressure, respectively.

(a) What are the SI units for D_T?

(b) Determine values of D_T for aluminum, steel, aluminum oxide, soda–lime glass, polystyrene, and nylon 6, 6 using the data in Table 19.1. Density values are included in Table B.1, Appendix B.

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