Parametric analysis of blade configurations for a small-scale nitrogen axial expander with hybrid open-Rankine cycle

• Published in: Energy conversion and management 2017-06, Vol.142, p.82-94
• Main Authors: Khalil, Khalil M., Mahmoud, S., Al- Dadah, R.K., AL-Mousawi, Fadhel
• Format: Article
• Language: English
• Subjects: Blade configurations; Carbon dioxide; Carbon dioxide emissions; CFD; Computational fluid dynamics; Computer applications; Computer simulation; Configuration management; Configurations; Emissions; Energy sources; Energy storage; Expansion; Fluid dynamics; Heat sources; Hybrid open-Rankine cycle; Liquid nitrogen LN2; Mathematical models; Mean-line design; Nitrogen; Parametric analysis; Parametric statistics; Pollution sources; Rankine cycle; Renewable energy technologies; Small-scale axial expander; Solar energy; Thermal power; Thermodynamic efficiency; Topping cycle; Wind power
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2017.03.018

•Develop cryogenic energy storage and efficient recovery technologies.•Integrate small scale closed and cryogenic open-Rankine cycles.•Investigate blade configuration on small-scale axial expander performance.•Use mean line and 3D CFD simulation for expander robust design procedure.•Predict effects of expander efficiency on hybrid open-Rankine cycle efficiency. During the last few decades, low-grade energy sources such as solar energy and wind energy have enhanced the efficiency of the advanced renewable technologies such as the combined Rankine. Furthermore, these heat sources have contributed to a reduction in CO2 emissions. To address the problem of the intermittent nature of such renewable sources, energy storage technologies have been used to balance the power demand and smooth out energy production. In this study, the direct expansion cycle (open Rankine cycle) is combined with a closed loop Rankine cycle to generate power more efficiently and address the problem of discontinuous renewable sources. The topping cycle of this system is a closed looped Rankine cycle and propane is used as a hydrocarbon fluid, while the direct expansion cycle is considered to be the bottoming cycle utilizing nitrogen as cryogen fluid. Small-scale expanders are the most important parts in many thermal power cycles, such as the Rankine cycle, due to the significant impact on the overall cycle’s efficiency. This work investigated the effect of using a number of blade configurations on the cycle’s performance using a small-scale axial expander. A three-dimensional Computational Fluid Dynamic (CFD) simulation was used to examine four proposed blade configurations (lean, sweep, twist, bowl) with three hub- tip ratios (0.83, 0.75, 0.66). In addition, a numerical simulation model of the hybrid open expansion- Rankine cycle was designed and modeled in order to estimate the cycle’s performance. The results show that when the expander’s efficiency increases, the hybrid open Rankine cycle’s thermal efficiency increases, where each 10% improvement in the expander efficiency will increase the cycle’s efficiency by 5.0%. The blade sweep configuration achieved the optimum expander efficiency of up to 75.5% using a hub to tip ratio of 0.83 and an expansion ratio of 1.5 with stator sweep −20° and a rotor sweep of 20°.