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Mean wind force coefficients of nacelles are investigated by a wind tunnel test and are compared with those in current codes, such as the Germanischer Lloyd Guideline 2010 (GL2010) and Eurocode, in order to clarify the effects of the ground, presence of a hub, turbulence in the incident flow and nacelle length on these coefficients. Formulas for the mean wind force coefficients are proposed as a function of yaw angles. It is found that mean wind force coefficients of wind turbine nacelles specified in GL2010 are underestimated in comparison with those obtained by wind tunnel tests. Pressure measurements of a nacelle are also conducted. Notably, the mean pressure coefficients for design load case 6.2 (DLC6.2) are significantly larger than those for design load case 6.1 (DLC6.1) in IEC61400‐1. Maximum and minimum mean pressure coefficients are proposed for the DLC6.1 and DLC6.2 by the wind tunnel test, which are similar to those in Eurocode and are larger than those proposed in GL2010. Copyright © 2012 John Wiley & Sons, Ltd.     

First-principles GGA + U calculation investigating the hydriding and diffusion properties of hydrogen in PuH2+x, 0 ≤x≤ 1

The hydrogen (H) diffusion process is a crucial issue related to storage of plutonium safely. In this work, first-principles GGA + U calculation is performed to elucidate the hydriding and diffusion behaviors of an additional H atom (H_i) in “perfect” PuH_2+x (0 $\le x\le$ 1) matrixes. It finds the value of incorporation energy increases with increasing x. The interaction energies show that an extra H_i atom interacts much further with surrounding host atoms in PuH₃ than in other Pu hydride matrixes. The minimum migration paths of a H_i atom in PuH_2+x are characterized by the image nudged elastic band (CINEB) method. The H_i atom diffuses in PuH₂, PuH_2.25, and PuH₅ matrixes through directly migrating from an octahedral interstice to its nearest octahedral site with energy barriers of 1.36 eV, 1.15 eV, and 1.59 eV, respectively. Oppositely, the metastable I_H-site plays a dominant role for the H_i migration into the O-site in PuH_2.75. The diffusion path of the H_i atom in PuH₃ is I_Pu $\to$ I_H0160 $\to$ I_PU path with the lowest migration energy of 0.72 eV, which concludes the H_i has relatively higher mobility in PuH₃. These findings provide detailed insight into how the H atom corrodes the Pu metal by connecting H atom diffusion in PuH₂, PuH₃, and intermediate compositions, which can be great interest for assisting the development of the new nuclear fuel for next generation reactors.     

Effect of calcination conditions on time on-stream performance of Ni/La2O3–ZrO2 in low-temperature dry reforming of methane

A series of catalysts based on Ni supported on mesoporous La₂O₃–ZrO₂ was prepared and tested in low-temperature (400 °C) dry reforming of methane for 100 h on stream. The catalysts were obtained from the same precursor by calcining in either flowing air or Ar at different temperatures. Both the temperature and the atmosphere had an effect on the catalytic activity and on-stream stability. With increasing calcination temperature, the dispersion of Ni decreased. Surprisingly, this resulted not in the lower, but in the higher intrinsic activity of Ni species. This increase can be rationalized by assuming that the rate-determining step is not CH₄ decomposition, but the removal of carbon deposits from Ni particle by reaction with CO₂. The catalysts calcined at 800 °C in Ar and air showed the strongest and the second strongest deactivation, respectively, caused by the formation of crystalline carbon coatings due to a lower number of CO₂ adsorption sites. The size of Ni particles favoring the formation of layered carbon species was found to be the main origin of the catalysts deactivation in the low-temperature dry reforming of methane.