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

where DT 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 cp represent the thermal conductivity, the mass density, and the specific heat at constant pressure, respectively.
(a) What are the SI units for DT?
(b) Determine values of DT 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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