Entropy production in flames

Abstract

Thermodynamic foundations of the thermal entropy production are rested on the concept of lost heat , ( Q T ) δT. The thermomechanical entropy production is shown to be in terms of the lost heat and the lost work as δS 8= 1 T Q T δT+δW l where the second term in brackets denotes the lost (dissipated) work into heat. The dimensionless number Π s describing the local entropy production s‴ in a quenched flame is found to be Π s ∼(Pe d 0) −2, where Π s = s‴l 2 k , l = α S u 0 (a characteristic length), k thermal conductivity, α thermal diffusivity, S u 0 the adiabatic laminar flame speed at the unburned gas temperature, Pe d 0 = S u 0D α the flame Peclet number, and D the quench distance. The tangency condition ∂ Pe d 0 ∂θ p = 0 , where θ b = T b T b 0 , T b and T b 0 denoting, respectively, the burned gas (nonadiabatic) and adiabatic flame temperatures, is related to an extremum in entropy production . The distribution of entropy production between the flame and burner is shown in terms of the burned gas temperature and the distance from the burner.