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排序方式: 共有8033条查询结果,搜索用时 15 毫秒
1.
Khaled Al-Farhany Mohammed A. Alomari Ahmed Al-Saadi Ali Chamkha Hakan F. Öztop Wael Al-Kouz 《亚洲传热研究》2022,51(2):1691-1710
In the current work, numerical simulations are achieved to study the properties and the characteristics of fluid flow and heat transfer of (Cu–water) nanofluid under the magnetohydrodynamic effects in a horizontal rectangular canal with an open trapezoidal enclosure and an elliptical obstacle. The cavity lower wall is grooved and represents the heat source while the obstacle represents a stationary cold wall. On the other hand, the rest of the walls are considered adiabatic. The governing equations for this investigation are formulated, nondimensionalized, and then solved by Galerkin finite element approach. The numerical findings were examined across a wide range of Richardson number (0.1 ≤ Ri ≤ 10), Reynolds number (1 ≤ Re ≤ 125), Hartmann number (0 ≤ Ha ≤ 100), and volume fraction of nanofluid (0 ≤ φ ≤ 0.05). The current study's findings demonstrate that the flow strength increases inversely as the Reynolds number rises, which pushes the isotherms down to the lower part of the trapezoidal cavity. The Nuavg rises as the Ri rise, the maximum Nuavg = 10.345 at Ri = 10, Re = 50, ϕ = 0.05, and Ha = 0; however, it reduces with increasing Hartmann number. Also, it increase by increasing ϕ, at Ri = 10, the Nuavg increased by 8.44% when the volume fraction of nanofluid increased from (ϕ = 0–0.05). 相似文献
2.
In this work, an experimental study of melting heat transfer of nano-enhanced phase change materials(NePCM) in a differentially-heated rectangular cavity was performed. Two height-to-width aspect ratios of the cavity, i.e., 0.9 and 1.5, were investigated. The model Ne PCM samples were prepared by dispersing graphene nanoplatelets(GNP) into 1-tetradecanol, having a nominal melting point of 37℃, at loadings up to 3 wt.%. The viscosity was found to have a more than 10-fold increase at the highest loading of GNP. During the melting experiments, the wall superheat at the heating boundary was set to be 10℃ or 30℃. It was shown that with increasing the loading of GNP, both the heat storage and heat transfer rates during melting decelerate to some extent, at all geometrical and thermal configurations. This suggested that the use of NePCM in such cavity may not be able to enhance the heat storage rate due to the dramatic growth in viscosity, which deteriorates significantly natural convective heat transfer during melting to overweigh the enhanced heat conduction by only a decent increase in thermal conductivity. This also suggested that the numerically predicted melting accelerations and heat transfer enhancements, as a result of the increased thermal conductivity, in the literature are likely overestimated because the negative effects due to viscosity growth are underestimated. 相似文献
3.
为了实现太赫兹信号的可调谐滤波,设计了一种基于柔性材料的太赫兹可调谐滤波器。通过扭曲特氟龙(Teflon)波导形成环型谐振器,实现了160~200 GHz频段的带阻滤波功能。改变谐振腔长可实现自由频谱范围(FSR)和滤波频点的调谐,实验测试了自由频谱范围在1.9 GHz和2.8 GHz间切换以及相应的滤波特性。研究表明,谐振腔长一定时,改变弯曲半径可实现滤波阻带抑制度的调节,柔性材料太赫兹环型谐振器可用于可调谐滤波,且具有较高的自由度。 相似文献
4.
The present research work deals with the numerical simulation of double cavity scramjet combustor by using two equation standard k- turbulence model and finite-rate/eddy-dissipation reaction models which is again coupled with Reynolds-Averaged Navier-Stokes (RANS) equations to investigate the influence of variation of inlet boundary condition of air as well as H2 fuel on the combustion flow-field of scramjet engine subsequently. At the same time, the validations of the current computational approach have been completed against a standard experimental data which is available in the literature. An acceptable similarity is observed between present numerical approach with the experimentally attained schlieren photograph and the pressure distribution curve. In the present work, 8 different cases are studied. Among them, first four cases are investigated for the variation of inlet boundary condition of air and the remaining four cases are studied for the variation of inlet boundary condition of H2 fuel. The obtained results show that the formation of high-pressure region around the cavities for case 3 and case 4 actually helps to push the greater amount of air to the cavity region where it is mixed with adequate amount of H2 for proper and stable combustion whereas for case 6, it is observed that most of the combustion phenomena closely fitted into a small space of the combustor and mainly occurs near the cavity region. 相似文献
5.
6.
When we speak about capacitance moisture meters for bulk materials we have to face with different values of dielectric permittivity for different bulk materials in dehydrated state, what causes a method error that can be named ‘type uncertainty’. Besides, different varieties of the same material have different values of dielectric permittivity, which depend from geographical origin, processing conditions etc. It can be hardly predicted automatically and type uncertainty can be compensated only in separate situations with the help of preliminary calibration. Main tasks of the research are to develop new comparison principle of moisture measurement with better accuracy due to effective compensation of physical, chemical and granulometric composition influence on the result of moisture measurement, develop new primary and secondary instrument transducers. Moisture sensor consists of four measuring capacitors. Two of them should be filled with a sample, which moisture content should be determined, and other pair of measuring capacitors should be filled with a same substance, but previously dehydrated. Mathematical models, developed to take into account granulometric composition of a bulk material were used to carry out a comparison analysis for three types of instrument measuring transducers. Obtained results proved that suggested principle of moisture measurement provides effective compensation of granulometric composition influence. Developed measuring principle had been experimentally tested what helped to confirm that it provides two times better compensation of different physical and chemical composition for different materials in comparison with the direct comparison method. 相似文献
7.
8.
Alaa El‐Din H. Sayed Usama M. Mahmoud Fatma Essa 《Microscopy research and technique》2019,82(4):443-451
The microstructure of the oral cavity and alimentary canal of herbivorous fish Siganus rivulatus collected from the Red Sea were investigated by using scanning electron microscope (SEM). The results showed that S. rivulatus has three types of teeth, tri‐cusped, bi‐cusped, and papilliform. A taste bud (Type I) was recorded in the oropharyngeal cavity. Characteristic styles of microridges on the cell's surface inside the buccal cavity were recorded. Also, the distribution of the mucous cells in the lining of the mouth cavity, alimentary canal was observed. Mucosal folds along the distinct parts of alimentary canal, showed characteristic pattern which was complex in the intestinal mucosa. The results concluded that there are characteristic microstructures according to feeding habitat compared with other bony fishes. 相似文献
9.
柔性件装配偏差有限元分析方法中的敏感度矩阵来源于产品的理论数学模型,而理论数学模型与实际模型之间存在一定的外形差异,会产生很大的分析误差。针对该问题,提出了一种装配偏差分析的改进方法,即根据产品理论外形和误差源数据,运用网格曲面变形方法获取逼近零件实际形状的数学模型,代替理论数学模型进行装配偏差分析。开展了金属薄板的装配回弹试验以及飞机壁板件的装配偏差分析计算,使用仿真、试验及测量等手段获取了各类偏差分析结果,并进行比较。数据表明,装配偏差分析误差可减小到5%以内。 相似文献
10.
Limin Jin Xiaoli Yang Siufung Yu Puran Zheng Xian Chen Shumin Xiao Qinghai Song 《Journal of the American Ceramic Society》2022,105(9):5764-5773
Ultraviolet (UV) lasers with dynamic wavelength-tunability and high monochromaticity are crucial in a multitude of practical applications yet still remarkable challenges. Here, we show wide wavelength-tuning of single-mode UV lasing based on lanthanide-doped upconversion nanoparticles (UCNPs). The rationally designed Yb3+/Er3+/Tm3+/Gd3+/Ce3+ co-doped multilayer UCNPs, which exhibits a broad gain spectrum with the full width of half maximum of around 57 nm in the UV regime, are developed. More importantly, by taking advantages of a diffraction grating as the tuning component, stable single-mode emission can be achieved in the UCNPs-based external-cavity-extended Fabry–Pérot laser at room temperature. Specifically, the lasing threshold is around 137 µJ cm–2, which is two orders of magnitude lower than that in the previously reported articles. Precise wavelength-tuning from 310 to 363 nm can be realized by adjusting the Littrow angle. This achievement highlights a portable alternative to continuously wideband-tunable UV lasers and opens up new opportunities for constructing compact solid-state UV photon sources. 相似文献