Power and efficiency optimizations for an open cycle two-shaft gas turbine power plant

In finite-time thermodynamic analyses for various gas turbine cycles,there are two common models:one is closed-cycle model with thermal conductance optimization of heat exchangers,and another is open-cycle model with optimization of pressure drop(PD)distributions.Both of optimization also with searching optimal compressor pressure ratio(PR).This paper focuses on an open-cycle model.A two-shaft open-cycle gas turbine power plant(OCGTPP)is modeled in this paper.Expressions of power output(PP)and thermal conversion efficiency(TCE)are deduced,and these performances are optimized by varying the relative PD and compressor PR.The results show that there exist the optimal values(0.32 and 14.0)of PD and PR which lead to double maximum dimensionless PP(1.75).There also exists an optimal value(0.38)of area allocation ratio which leads to maximum TCE(0.37).Moreover,the performances of three types of gas turbine cycles,such as one-shaft and two-shaft ones,are compared.When the relative pressure drop at the compressor inlet is small,the TCE of third cycle is the biggest one;when this pressure drop is large,the PP of second cycle is the biggest one.The results herein can be applied to guide the preliminary designs of OCGTPPs.

Optimization of the power, efficiency and ecological function for an air-standard irreversible Dual-Miller cycle

This paper establishes an irreversible DualMiller cycle (DMC) model with the heat transfer (HT) loss, friction loss (FL) and other internal irreversible losses. To analyze the effects of the cut-off ratio (ρ) and Miller cycle ratio (rM) on the power output (P), thermal efficiency (η) and ecological function (E), obtain the optimal popt and optimal rMopt, and compare the performance characteristics of DMC with its simplified cycles and with different optimization objective functions, the P,η and E of irreversible DMC are analyzed and optimized by applying the finite time thermodynamic (FTT) theory. Expressions of P,η and E are derived. The relationships among P,η, E and compression ratio (ε) are obtained by numerical examples. The effects of ρ and rM on P,η, E, maximum power output (MP), maximum efficiency (MEF) and maximum ecological function (ME) are analyzed. Performance differences among the DMC, the Otto cycle (OC), the Dual cycle (DDC), and the Otto-Miller cycle (OMC) are compared for fixed design parameters. Performance characteristics of irreversible DMC with the choice of P,η and E as optimization objective functions are analyzed and compared. The results show that the irreversible DMC engine can reach a twice-maximum power, a twicemaximum efficiency, and a twice-maximum ecological fiinction, respectively. Moreover, when choosing E as the optimization objective, there is a 5.2% of improvement in η while there is a drop of only 2.7% in P compared to choosing P as the optimization objective. However, there is a 5.6% of improvement in P while there is a drop of only 1.3% in rj compared to choosing as the optimization objective.