Centrifugal turbines have recently regained interest of the engineering community as they could serve as cost-effective alternatives in diverse energy applications. In this device, the energized flow undergoes expansion in the radial outward direction while being entrained by a circular arrangement of airfoil-shaped blades. Yet, their primary and advanced performance estimations have dubiously relied on axial turbine loss correlations as part of their current design paradigm. To the authors knowledge, any convincing and reliable assessment of such practice has still not been reported. Thereupon, this paper conducts an inferential comparative study in which losses of several twin centrifugal and axial cascades are predicted by means of empirical axial loss correlations backed with credible 3D CFD simulations. Ultimately, the significant results disparity and inconsistency points out the inadequacy of the identified practice and the need of a proper and practical centrifugal turbine loss model.

The application of proton-exchange membrane fuel cells (PEMFCs) in maritime transportation is currently in the spotlight due to stringent emissions regulations and the establishment of a carbon trading system. However, salt in the marine environment can accelerate the degradation of proton-exchange membranes (PEM), which are the core component of PEMFCs. In this study, the effect of the NaCl concentration and temperature on the degradation of Nafion, the benchmark PEMFC membrane, was analyzed ex situ by accelerated degradation using Fenton’s test. The membrane properties were studied by mass change, fluoride ion emission, FTIR spectroscopy, and tensile test. The results showed that the degradation of Nafion membranes increased with the increase in temperature and NaCl concentration. Further studies revealed that Nafion produces C=O bonds during the degradation process. Additionally, it was found that sodium ions replace hydrogen ions in degraded Nafion fragments based on analysis of the weight change, and the rate of substitution increases with increasing temperature. A better understanding of the degradation behavior of Nafion in salty environments will lead to the advanced manufacturing of PEM for applications of PEMFCs in maritime transportation.

The power plant and drive systems in a conventional helicopter cause high development and operating costs, compromise safety, and introduce performance limitations. Even though much effort is devoted to mechanical transmission systems, the use of electric components promises a higher reliability. Magnetic gearboxes address many of the problems in mechanical transmissions, but proved to be too heavy at this time. However, since this technology has not achieved its full potential, improvements are imminent and could allow its implementation in the near future. Several combinations with energy sources, amongst which liquid hydrogen (LH2), showed a turboshaft with kerosene to offer the lightest configuration. For the lower required power range, Avgas piston engines should at least be replaced with more efficient diesel engines. The possibility of using electric motors, such as the switched reluctance motor, to drive the tail rotor is possible at the expense of weight. The use of LH2, which has a threefold higher energy density than kerosene, in a helicopter seems feasible; though heavier due to an increased helicopter volume and tank weight, it offers a free cold source for high-performing high-temperature superconductive devices.

No abstract

Rock salt has excellent properties for its use as underground leak‐proof containers for the storage of renewable energy. Salt solution mining has long been used for salt mining, and can now be employed in the construction of underground salt caverns for the storage of hydrogen gas. This paper presents a wide range of methods to study the mineralogy, geochemistry, microstructure and geomechanical characteristics of rock salt, which are important in the engineering of safe underground storage rock salt caverns. The mineralogical composition of rock salt varies and is linked to its depositional environment and diagenetic alterations. The microstructure in rock salt is related to cataclastic deformation, diffusive mass transfer and intracrystalline plastic deformation, which can then be associated with the macrostructural geomechanical behavior. Compared to other types of rock, rock salt exhibits creep at lower temperatures. This behavior can be divided into three phases based on the changes in strain with time. However, at very low effective confining pressure and high deviatoric stress, rock salt can exhibit dilatant behavior, where brittle deformation could compromise the safety of underground gas storage in rock salt caverns. The proposed review presents the impact of purity, geochemistry and water content of rock salt on its geomechanical behavior, and thus, on the safety of the caverns.

No abstract

No abstract

No abstract