We derive scaling relations for the thermal dissipation rate in the bulk and
in the boundary layers for moderate and large Prandtl number (Pr) convection.
Using direct numerical simulations of Rayleigh-B\'{e}nard convection, we show
that the thermal dissipation in the bulk is suppressed compared to passive
scalar dissipation. The suppression is stronger for large Pr. We further show
that the dissipation in the boundary layers dominates that in the bulk for both
moderate and large Pr. The probability distribution functions of thermal
dissipation rate, both in the bulk and in the boundary layers, are stretched
exponential, similar to passive scalar dissipation.Comment: 13 pages, 6 figure
