tailieunhanh - Advanced Gas Turbine Cycles phần 4

Các chu kỳ nhiệt động lực học của một tuabin khí đơn giản được mô tả bởi các chu trình Brayton-Joule. Nó bao gồm trường hợp lý tưởng của bốn quá trình: hai đẳng entropy và hai isobaric. Trong chu kỳ này, được mô tả trong hình 1, các chất lỏng làm việc phải trải qua một nén đẳng entropy từ trạng thái 1 đến trạng thái 2. | Analytical study of the thermodynamic cycle 24 I K-1 HPC cpT2 I nHPC K - 1 I 1 1 T cpT4 1 . . í nT k J From the energy balance in the combustion chamber m 0 c pT3 mfHU mfcpfTf I m 0 mf cpT4 QL . results the equation for the ratio f . K-1 f mf _e - n HPC K m 0 HU-e cpT0 . where m f is the fuel mass flow. Having described all the components of the cycle its specific work can be stated GT T HPC LPC . . For the ideal case it is valid that nT nLPC nHPC . . For the sake of further investigations the final equation is represented in its dimensionless form and in dependence of two parameters nT and nLPC. Taking also into account that T2 T0 it can be stated GT cpT0 I e .1 - 1 A K-1 nT K J í n 1 V nLPC J K-1 K K-1 -nLPC K 2 . . Analytical study of the thermodynamic cycle 25 Next the formula for the thermal efficiency of the cycle follows also presented in terms of nT and nLPC Í 9- 1 - nth 1 nT K J K-1 nT K nLPC K-1 - nLPC K 2 . K-1 cpT0 HU 1 -9- GT f H In order to represent the efficiencies in a more readable way a new parameter n is introduced. It is defined as n e 0 1 _ 1-n nHPC nT . __ __ n n LPC nT This results in n 1 nLPC 1 nHPC nT n 0 n LPC n T n HPC 1 In the end the formula for nth versus nT n 9 is stated Í 1 i 9- 1 K 1 K 1 _ n 1-n --- 7Tt k n T K 2 l nT K J nth - n _ - 1-n 9 nT K 1 -9-cpTL Hu . The further parametric study of the formulae and can be found in the chapter . With losses included Analytical study of the thermodynamic cycle 26 Based on the assumptions made in the previous chapters we develop the formulae describing the components of the thermodynamic cycle including pressure losses in form of polytropic efficiencies and pressure drop coefficients Ị K-1 1 LPC cpT0 I n LPC K nPc - 1 HPC Ị K-1 1 c pT2 I nHPC K nPc d T I 1 k-1 nfT . . . Ị T4 1 V 1 From the properties of the combustion chamber results f k-1 e - nHPC k Hy -e cpT0 . In the end using the assumed pressure losses it can be .