  The temperature fluctuations generated by viscous dissipation in an isotropic
turbulent flow are studied using direct numerical simulation. It is shown that
their scaling with Reynolds number is at odds with predictions from recent
investigations. The origin of the discrepancy is traced back to the anomalous
scaling of the dissipation rate fluctuations. Phenomenological arguments are
presented which explain the observed results. The study shows that previously
proposed models underpredict the variance of frictional temperature
fluctuations by a factor proportional to the square of the Taylor-scale
Reynolds number.
