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

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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.