Transfer Irreversibilities in the Lenoir Cycle: FTT Design Criteria with ε-NTU.

This work extends the steady flow Lenoir cycle within finite-time thermodynamics (FTT) by incorporating heat transfer irreversibilities through the ε-NTU formalism and a non-isentropic expansion modeled via the expander isentropic efficiency ηE. The total conductance UT (sum for the two heat exchangers) is partitioned between hot and cold units using uL=UL/UT, with UT=UH+UL. For each triplet (τ=TH/TL, UL, UT), we closed the cycle by determining T1, the working fluid temperature at the cooler outlet and heater inlet, T2, the heater outlet and expander inlet, and T3, the expander outlet and cooler inlet. Using these states, we compute the heat rates Q˙12, Q˙31 and the net power P. In addition to the thermal efficiency η, the following extended objective functions are evaluated: the efficient power EF, the ecological efficiency ϕ, and the second law efficiency ηII. Parametric sweeps on uL for τ ϵ 3.25,3.75 and UT ϵ 2.5,5.0,7.5,10 kW show unimodal curves for P(uL) and maxima. A robust result places the optima of P, η, EF, ϕ, and ηII in a distribution band at uL~0.6. This guideline offers clear design guidance for allocating exchange area in heat recovery and microgeneration, maximizing power, high η, and exergetic utilization with contained entropic penalty.