  Using direct numerical simulations of turbulent thermal convection for
Rayleigh number ($\mathrm{Ra}$) between $10^6$ and $10^8$ and unit Prandtl
number, we derive scaling relations for viscous dissipation in the bulk and in
the boundary layers. We show that contrary to the general belief, the total
viscous dissipation in the bulk is larger, albeit marginally, than that in the
boundary layers. The bulk dissipation rate is similar to that in hydrodynamic
turbulence with log-normal distribution, but it differs from $(U^3/d)$ by a
factor of $\mathrm{Ra}^{-0.18}$. Viscous dissipation in the boundary layers are
rarer but more intense with a stretched-exponential distribution.
