The conditions of the HCSt are defined by four nondimensional parameters: the initial thermal Reynolds number, $ReT0=\rho fdpT0/\mu f$ where *T*_{0} = *T*(*t* = 0), the density ratio, *ρ** = *ρ*_{p}/*ρ*_{f}, the restitution coefficient, *e*, and the solids volume fraction, *ϕ*. Here, we use the conditions: Re_{T}_{0} = 50, *ρ** = 1 × 10^{+3}, *e* = 0.85, and *ϕ* = 0.15. For completeness, we note that these conditions are obtained from dimensional properties: *d*_{p} = 1 cm, *ρ*_{p} = 1 g/cm^{3}, *ρ*_{f} = 1 × 10^{−3} g/cm^{3}, *μ*_{f} = 2 × 10^{−3} g/cms^{−2}, *T*_{0} = 1 × 10^{+4} cm^{2}/s^{2}. The exact solution of the HCSt, Eq. (11), with the preceding conditions, is plotted in Fig. 1 for the time period of 38 s nondimensionalized by $T0/dp$. There are two stages of decay, the first dominated by inelastic dissipation (from particle collisions) and the second dominated by viscous dissipation (from the fluid). The transition between the two stages occurs at approximately *t** = 300 in Fig. 1.