ENTROPIC EFFICIENCY OF ENERGY-SYSTEMS

Thermodynamic foundations of the thermal entropy production are rested on the concept of lost heat, (Q/T)delta-T. The thermomechanical entropy production is shown to be in terms of the lost heat and the lost work as delta-PI = 1/T[(Q/T) delta-T + delta-W(L) where the second term in brackets denotes the lost (dissipated) work into heat. The dimensionless number PI(s) describing the local entropy production s''' in a quenched flame is related to PI(s) approximately (Pe(D)0)-2 where PI(s) = s''' l2/k,l = alpha/S(u)0 a characteristic length, k thermal conductivity, of thermal diffusivity, S(u)0 the adiabatic laminar flame speed at the unburned gas temperature, Pe(D)0 = S(u)0D/alpha the flame Peclet number, D the quench distance. The tangency condition partial derivative Pe(D)0/partial derivative theta(b) = 0, where theta(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 burner. A fundamental relation between the Nusselt number describing heat transfer in any (laminar, transition, turbulent) forced or buoyancy driven flow and the entropy production is shown to be Nu approximately PI(s)1/2. In view of this relation, the heat transfer from a pulse combustor becomes a measure for the entropic (thermal) efficiency of pulse combustion systems.