Abstract
As suggested by much smaller microscopic Carnot efficiency of a transversely oscillating gas-parcel in a thermoacoustic engine than macroscopic Carnot efficiency of the whole stack, the Lagrangian microscopic energy efficiency of a gas parcel is different from the macroscopic energy efficiency of the whole stack. The relationship of the former to the latter is theoretically discussed. Furthermore, it is numerically shown that the microscopic energy efficiency in a wet stack is considerably lower than that in a dry stack due to both heat loss by latent heat of water evaporation and more heat influx associated with evaporation.
Highlights
A gas parcel moves forward and backward repeatedly with propagation of an acoustic wave.1 In addition, a gas parcel expands and contracts repeatedly due to pressure oscillation of an acoustic wave
The energy efficiency of a thermoacoustic engine is upper bounded by the Carnot efficiency, which is solely determined by the temperatures at hot (TH) and cold (TC) ends of a stack as the following equation
The present results enable a detailed analysis of local energy efficiency of a thermoacoustic engine with the Lagrangian point of view as well as its transformation into macroscopic one
Summary
A gas parcel moves forward and backward repeatedly with propagation of an acoustic wave. In addition, a gas parcel expands and contracts repeatedly due to pressure oscillation of an acoustic wave. In the idealized Stirling cycle, the change from state 4 to state 1 is isochoric with heat influx to a gas parcel from the wall with a temperature gradient. A gas parcel radiates a sound wave by absorbing net heat from the wall with a temperature gradient. In a real traveling-wave thermoacoustic engine, the thermodynamic cycle of a gas parcel considerably deviates from the Stirling cycle, as already shown in Ref. 8. The energy efficiency of a thermoacoustic engine is upper bounded by the Carnot efficiency (ηCarnot), which is solely determined by the temperatures at hot (TH) and cold (TC) ends of a stack as the following equation:
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