Entropic efficiency of energy systems

Abstract

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 where the second term in brackets denotes the lost (dissipated) work into heat.The dimensions number [Pi]s describing the local entropy production s[tripe prime] in a quenched flame is related to [pi]s ~ (PeDO)-2 where [Pi]s = s[triple prime]l2/k,l = [alpha]/Su0 a characteristic length, k thermal conductivity, [alpha] thermal diffusivity, Su0 the adiabatic laminar flame speed at the unburned gas temperature, PeD0 = Su0D/[alpha] the flame Peclet number, D the quench distance. The tangency condition [varpi]PeD0/[varpi][theta]b = 0, where [theta]b = Tb/Tb0, Tb and Tb0 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 ~ [pi]s1/2In view of this relation, the heat transfer from a pulse combustor becomes a measure for the entropic (thermal) efficiency of pulse combustion systems.