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Advanced Gas Turbine Cycles phần 2

Việc chuyển đổi năng lượng nhiệt đến một cơ khí có thể chỉ bằng phương tiện của một chu kỳ nhiệt động lực học. Nó có thể được định nghĩa là một chuỗi các quá trình nhiệt động lực học trong đó chất lỏng làm việc trải qua một loạt các thay đổi trạng thái và cuối cùng trở về trạng thái ban đầu của nó. | Description of the LMS100 and its features 4 2.1 Description of the thermodynamic process The conversion of thermal energy to a mechanical one is possible only by means of a thermodynamic cycle. It can be defined as a succession of thermodynamic processes in which the working fluid undergoes a series of state changes and finally returns to its initial state. The character of the thermodynamic cycle together with its details influences significantly the design of the engine and its parameters. That is why the relations of the cycle parameters need to be precisely analyzed 3 . 2.1.1 The simple gas turbine cycle The thermodynamic cycle of a simple gas turbine is described by the Brayton-Joule cycle. It consists in the ideal case of four processes two isentropic and two isobaric ones. In this cycle depicted in figure 1 the working fluid undergoes an isentropic compression from the state 1 to the state 2. Then it is heated isobarically in the combustion chamber to the state 3. An isentropic expansion leads to the state 4 and an isobaric cooling to the initial state 1. In figure 1 the heat supplied to the cycle in the combustion chamber is denoted as Q2-3 and the heat carried away during the process 14 as Q4-1. a b Figure 1 a the ideal simple cycle depicted in the T s diagram b scheme of the open simple cycle 4 . 5 Description of the LMS100 and its features The basic indicator which describes the cycle and which is a measure of its thermodynamic perfection is the thermal efficiency nth . It is the ratio of the amount of energy changed into mechanical energy to the thermal energy supplied to the system n g2 g- 4-1 2.1 With the assumption that the processes 1-2 and 3-4 are isentropes between two isobars the thermal efficiency can be stated as dth 1 _ Cp T4 - T1 CpT - T2 1 K-1 2.2 1 - n K where the pressure ratio is _ n P1 In reality as a result of different type of losses the thermodynamic cycle looks differently. It can be observed in figure 2. In compression and .