Optimizing Power and Thermal Efficiency of an Irreversible Variable-Temperature Heat Reservoir Lenoir Cycle

Ruibo Wang,Yanlin Ge,Huijun Feng,Lingen Chen

doi:10.3390/app11157171

Abstract

Applying finite-time thermodynamics theory, an irreversible steady flow Lenoir cycle model with variable-temperature heat reservoirs is established, the expressions of power (P) and efficiency (η) are derived. By numerical calculations, the characteristic relationships among P and η and the heat conductance distribution (uL) of the heat exchangers, as well as the thermal capacity rate matching (Cwf1/CH) between working fluid and heat source are studied. The results show that when the heat conductances of the hot- and cold-side heat exchangers (UH, UL) are constants, P-η is a certain “point”, with the increase of heat reservoir inlet temperature ratio (τ), UH, UL, and the irreversible expansion efficiency (ηe), P and η increase. When uL can be optimized, P and η versus uL characteristics are parabolic-like ones, there are optimal values of heat conductance distributions (uLP(opt), uLη(opt)) to make the cycle reach the maximum power and efficiency points (Pmax, ηmax). As Cwf1/CH increases, Pmax-Cwf1/CH shows a parabolic-like curve, that is, there is an optimal value of Cwf1/CH ((Cwf1/CH)opt) to make the cycle reach double-maximum power point ((Pmax)max); as CL/CH, UT, and ηe increase, (Pmax)max and (Cwf1/CH)opt increase; with the increase in τ, (Pmax)max increases, and (Cwf1/CH)opt is unchanged.

Highlights

As a further extension of traditional irreversible process thermodynamics, finite-time thermodynamics (FTT) [1,2,3,4,5,6,7,8,9,10,11] has been applied to analyze and optimize performances of actual thermodynamic cycles, and great progress has been made
FTT has been applied in micro- and nano-cycles [12,13,14,15], thermoelectric devices [16,17], thermionic devices [18,19], gas turbine cycles [20,21,22], internal combustion cycles [23,24], cogeneration plants [25,26], thermoradiative cell [27], chemical devices [28,29], and economics [30,31]
The Lenoir cycle (LC) model [54] was proposed by Lenoir in 1860

Summary

Introduction

As a further extension of traditional irreversible process thermodynamics, finite-time thermodynamics (FTT) [1,2,3,4,5,6,7,8,9,10,11] has been applied to analyze and optimize performances of actual thermodynamic cycles, and great progress has been made. It looks like a triangle in the cycle T-s diagram It is a typical atmosphere pressure compression HEG cycle, the compression process required by the HEG during operation is realized by atmosphere pressure and it can be used in aerospace, ships, vehicles, and power plants in engineering practice. Where NH1 and NL1 are the heat transfer unit number of the two HEXs, CHmax(CHmin) is the larger (smaller) of CH and Cw f 1, and CLmax(CLmin) is the larger (smaller) of CL and kCw f 1 Substituting CH = CL → ∞ into Equations (4), (5) and (13)–(15) yields the expressions of the effectiveness of the two HEXs, P, η, and T1 for an irreversible SFLC with constant temperature HR [62]: EH = 1 − exp(−NH).

Numerical Examples and Discussions

Cycle Performance Optimization When the HTC Distributions of the Two HEXs Can

TCR Matching Optimization

Findings

Conclusions