Chen Lingen, Feng Huijun, Ge Yanlin
Institute of Thermal Science and Power Engineering, Wuhan Institute of Technology, Wuhan 430205, China.
School of Mechanical & Electrical Engineering, Wuhan Institute of Technology, Wuhan 430205, China.
Entropy (Basel). 2020 Jun 17;22(6):677. doi: 10.3390/e22060677.
A theoretical model of an open combined cycle is researched in this paper. In this combined cycle, an inverse Brayton cycle is introduced into regenerative Brayton cycle by resorting to finite-time thermodynamics. The constraints of flow pressure drop and plant size are taken into account. Thirteen kinds of flow resistances in the cycle are calculated. On the one hand, four isentropic efficiencies are used to evaluate the friction losses in the blades and vanes. On the other hand, nine kinds of flow resistances are caused by the cross-section variances of flowing channels, which exist at the entrance of top cycle compressor (TCC), the entrance and exit of regenerator, the entrance and exit of combustion chamber, the exit of top cycle turbine, the exit of bottom cycle turbine, the entrance of heat exchanger, as well as the entrance of bottom cycle compressor (BCC). To analyze the thermodynamic indexes of power output, efficiency along with other coefficients, the analytical formulae of these indexes related to thirteen kinds of pressure drop losses are yielded. The thermodynamic performances are optimized by varying the cycle parameters. The numerical results reveal that the power output presents a maximal value when the air flow rate and entrance pressure of BCC change. In addition, the power output gets its double maximal value when the pressure ratio of TCC further changes. In the premise of constant flow rate of working fuel and invariant power plant size, the thermodynamic indexes can be optimized further when the flow areas of the components change. The effect of regenerator on thermal efficiency is further analyzed in detail. It is reported that better thermal efficiency can be procured by introducing the regenerator into the combined cycle in contrast with the counterpart without the regenerator as the cycle parameters change in the critical ranges.
本文研究了一种开放式联合循环的理论模型。在该联合循环中，借助有限时间热力学将逆布雷顿循环引入回热布雷顿循环。考虑了流动压降和设备尺寸的限制。计算了循环中的13种流动阻力。一方面，用四种等熵效率来评估叶片和导叶中的摩擦损失。另一方面，九种流动阻力是由流动通道的横截面变化引起的，这些变化存在于顶部循环压缩机（TCC）入口、回热器入口和出口、燃烧室入口和出口、顶部循环涡轮机出口、底部循环涡轮机出口、热交换器入口以及底部循环压缩机（BCC）入口处。为了分析功率输出、效率以及其他系数的热力学指标，得出了这些指标与13种压降损失相关的解析公式。通过改变循环参数对热力学性能进行优化。数值结果表明，当BCC的空气流量和入口压力变化时，功率输出呈现最大值。此外，当TCC的压力比进一步变化时，功率输出会出现双最大值。在工作燃料流量恒定和发电厂尺寸不变的前提下，当部件的流通面积变化时，热力学指标可进一步优化。详细分析了回热器对热效率的影响。结果表明，与无回热器的联合循环相比，当循环参数在临界范围内变化时，通过在联合循环中引入回热器可获得更好的热效率。
