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Thermodynamics Performance Evaluation of a Two-Shaft Gas Turbine Power Plant Robert Poku Department of Mech/Marine Engineering,Niger Delta University, Wilberforce Island, Bayelsa State.Nigeria. Abstract In this work, the performance of a two-shaft Gas Turbine power plant was evaluated based on the efficiencies of the plant from the year 2002 to 2007.The parameters used in the evaluation are the ambient conditions, thermal efficiencies, and the inlet and outlet temperatures of the power turbine. The results showed that the highest thermal efficiency of the turbine was obtained in the year 2006 when the average compressor inlet temperature of the turbine and the power turbine outlet (exhaust) temperature are the least. With the increase in thermal efficiency of 42.62%, rise in value of compressor pressure ratio of 7.78 and least compressor inlet temperature of 25.080C as seen in table 2. The research shows that gas turbine plants perform better in temperate regions than tropical. Therefore, to increase the efficiency of an existing gas turbine plants in high temperature climates, retrofitting an air cooler that will always reduce the temperature back or close to the design temperature before compression is necessary. Keywords: Power Turbine, Gas Generator, Thermal Efficiency, Thermodynamics Performance Evaluation, Two-Shaft Gas Turbine Plant Nomenclature Cp = Specific Heat Capacity (KJ/KgK) thermal=Thermal Efficiency W12= Compressor Power (KJ/Kg) PR = Pressure ratio Wout= Specific Work Output (KJ/kg) y = Isentropic index W12= Compressor Power(KJ/Kg) p = Pressure (bar) Wt = Isentropic TurbineWork(KJ/Kg) T = Temperature (0C) Cpg= Specific Capacity of the Gas(KJ/KgK) Q23= Heat Input (KJ/Kg) ma= Mass of the air (Kg/s) mg= Mass of the gas (Kg/s) pt = Isentropic Efficiency of the Power Turbine Ppt = Power Turbine Power (KJ/Kg) Cpa= Specific Capacity of the air(KJ/KgK) Δp = Pressure drop in the combustion chamber m=Mechanical Transmission Efficiency1.Introduction Gas turbine plants which started from its simplest form that operates on Brayton’s cycle have undergone tremendous modifications. These different metamorphoses in gas turbine plants were made possible as a result of researches that were carried out on plant performance and subsequently proffering the outputs of these researches that has led to the improvement of gas turbines. One of the products of such researches is the two-shaft gas turbine. The two-shaft gas turbine unlike the simple gas turbine that operates on Brayton’s cycle has two turbines , the compressor turbine that drives the compressor and the power turbine that produces the power. However, in spite of the improvements and modifications of gas turbine plants, their performance to a very large extent depends on the operational environments. This in effect means that the power outputs and efficiencies of gas turbine plant depend on the ambient temperatures of the operating environment.