تجزیه و تحلیل عملکرد برای یک متغیر مخزن حرارتی با دمای غیرقابل برگشت بسته شده با چرخه برایتون بازسازی میانی

In this paper, the theory of finite time thermodynamics is used in the performance analysis of an irreversible closed intercooled regenerated Brayton cycle coupled to variable temperature heat reservoirs. The analytical formulae for dimensionless power and efficiency, as functions of the total pressure ratio, the intercooling pressure ratio, the component (regenerator, intercooler, hot and cold side heat exchangers) effectivenesses, the compressor and turbine efficiencies and the thermal capacity rates of the working fluid and the heat reservoirs, the pressure recovery coefficients, the heat reservoir inlet temperature ratio, and the cooling fluid in the intercooler and the cold side heat reservoir inlet temperature ratio, are derived. The intercooling pressure ratio is optimized for optimal power and optimal efficiency, respectively. The effects of component (regenerator, intercooler and hot and cold side heat exchangers) effectivenesses, the compressor and turbine efficiencies, the pressure recovery coefficients, the heat reservoir inlet temperature ratio and the cooling fluid in the intercooler and the cold side heat reservoir inlet temperature ratio on optimal power and its corresponding intercooling pressure ratio, as well as optimal efficiency and its corresponding intercooling pressure ratio are analyzed by detailed numerical examples. When the heat transfers between the working fluid and the heat reservoirs are executed ideally, the pressure drop losses are small enough to be neglected and the thermal capacity rates of the heat reservoirs are infinite, the results of this paper replicate those obtained in recent literature.

Since the theory of finite time thermodynamics (FTT) or entropy generation minimization (EGM) was advanced [1], [2] and [3], much work has been performed for the performance analysis and optimization of finite time processes and finite size devices [4], [5], [6], [7], [8], [9] and [10]. Many achievements have been acquired on the performance analysis of Brayton cycles using FTT [11]. Leff [12] found the simple reversible Brayton cycle’s efficiency at maximum work output was . Bejan [13] took the entropy generation rate as the optimization objective and analyzed the performance of an endoreversible simple Brayton cycle and proved the power output reaches its maximum when the entropy generation rate of the cycle is minimum. Chen and co-workers [14], [15], [16], [17], [18], [19], [20], [21] and [22] analyzed and optimized the power, the power density and the efficiency for simple and regenerated, endoreversible and irreversible Brayton cycles coupled to constant and variable temperature heat reservoirs, deduced the general analytical formulae of the cycle power, the power density and the efficiency and analyzed the effects of the internal and the external irreversibilities on the cycle characteristics. Ibrahim et al. [23] examined the optimal power output of an endoreversible simple Brayton cycle coupled to constant and variable temperature heat reservoirs. Roco et al. [24] analyzed the maximum power and its corresponding efficiency as well as the maximum efficiency and its corresponding power of a regenerated Brayton cycle based on Ref. [16]. Feidt [25] analyzed the performance of an irreversible closed regenerated Brayton cycle by taking account of heat resistance and heat leak. Cheng and Chen [26] built a model for an endoreversible intercooled Brayton cycle, evaluated the maximum power and its corresponding efficiency and investigated the effects of the intercooled process on the power output and efficiency of the cycle. A further step of this paper is to study the performance of an irreversible closed intercooled and regenerated Brayton cycle coupled to variable temperature heat reservoirs using FTT. Analytical formulae about dimensionless power and efficiency are derived. The effects of component (regenerator, intercooler and hot and cold side heat exchangers) effectivenesses, compressor and turbine efficiencies, pressure recovery coefficients, heat reservoir inlet temperature ratio and cooling fluid in the intercooler and cold side heat reservoir inlet temperature ratio on optimal power and its corresponding intercooling pressure ratio, as well as optimal efficiency and its corresponding intercooling pressure ratio are analyzed by detailed numerical examples. Especially, the intercooling pressure ratio is optimized for optimal power and optimal efficiency, respectively.

In this paper, FTT is applied to study the effects of component (regenerator, intercooler, and hot and cold side heat exchangers) effectivenesses, the compressor and turbine efficiencies, the pressure recovery coefficients, the heat reservoir inlet temperature ratio and the cooling fluid in the intercooler and the cold side heat reservoir inlet temperature ratio on the optimal power and the corresponding intercooling pressure ratio, as well as the optimal efficiency and the corresponding intercooling pressure ratio of an irreversible closed Brayton cycle coupled to variable temperature heat reservoirs. The analytical formulae of the dimensionless power and efficiency of the cycle, as functions of component (regenerator, intercooler and hot and cold side heat exchangers) effectivenesses, the compressor and turbine efficiencies, the pressure recovery coefficients, the heat reservoir inlet temperature ratio and the cooling fluid in the intercooler and the cold side heat reservoir inlet temperature ratio, are derived. The intercooling pressure ratio is optimized for the optimal dimensionless power and the optimal efficiency, respectively. The method and the results are different from those in the classical analyses [32] and [33] in which the intercooling pressure ratios are generally determined according to the minimum specific work the compressors consumed.