The temperature of a lumped system varies with time according to:
$$\frac{T(t) - T_{\infty}}{T_i - T_{\infty}} = e^{-bt}$$
where $b = \frac{hA}{\rho V c_p}$ is the time constant, $h$ is the heat transfer coefficient, $A$ is the surface area, $\rho$ is the density,
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