Constructal design for dual-pressure axial-flow turbine in organic Rankine cycle

Abstract

Dual-pressure organic Rankine cycle (ORC) has great advantages in low-temperature waste heat utilization systems. There are few studies on optimizing the performance and structure of the dual-pressure turbine, which is a key part of the dual-pressure ORC. The constructal design is performed for a dual-pressure axial-flow turbine (AFT) in a dual-pressure ORC to improve the turbine and cycle performances. Total power is taken as optimization objective function, volume ratio of the high-pressure turbine (HPT) and inlet pressure of the low-pressure turbine (LPT) are chosen as optimization variables, and total volume is employed as a constraint. After obtaining the optimization results, the impacts of some flow and structure parameters are analyzed. Furthermore, performances of the dual- and single-pressure AFTs are contrasted. The results demonstrate that the total powers of the dual-pressure AFT after the primary and twice optimizations are increased by 0.97% and 1.69% compared with the initial value, respectively. After the twice optimization, the optimal construct of the dual-pressure AFT is that the volume ratio of the HPT and inlet pressure of the LPT are 0.072 and 695 kPa, respectively. The nozzle inlet hub to tip radius ratios of the two turbines and the working-fluid mass flow rate ratio positively impact the total power, while the total volume hurts it. Besides, the dual-pressure AFT has a better performance advantage than the single-pressure AFT, and the total power of the former is 16.59% higher than that of the latter. The results confirm that the dual pressure is more suitable for low-temperature waste heat utilization systems than the single pressure and provide strategies for improving the turbine performance.