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991.
建立了包含蓄热层的太阳能烟囱发电系统非稳态传热数学模型,研究了集热系统特性和蓄热层的增温效应,结果表明:蓄热层表面温度、气流温度、集热棚板温度相互影响,随时间有较大波动;气流温升主要发生在气流入口至集热棚半径1/3处,蓄热层表面温度沿径向逐渐升高,在集热棚出口段有明显下降;集热棚板、蓄热层底部及四周是系统热量损失的主要地方;系统运行非稳定期,在没有太阳辐射时,深层蓄热层不参与向气流放热过程,而是继续从浅层蓄热层吸热,浅层蓄热层贮存的热量并不全向气流传递。系统运行平稳期,蓄热层底层的温度趋于定值;理论发电功率的变化趋势与气流温度随时间变化趋势一致。 相似文献
992.
993.
柴油机颗粒捕集器内颗粒沉积结构的实验研究 总被引:1,自引:0,他引:1
基于可视化单通道实验系统,采用激光位移测量方法,对柴油机颗粒在陶瓷捕集器内的沉积过程进行了在线测量.研究结果发现,颗粒沉积过程分为4个阶段:深床期、长树期、搭桥期和颗粒层期;颗粒层厚度的增加在长树期迅速增长,而后在颗粒层期呈缓慢增加的趋势.颗粒层过滤期颗粒层的孔隙结构受过滤速度的影响,过滤速度增大,颗粒层的渗透系数和孔隙率减小,形成的颗粒层致密.实验结果证实了当Pe<1时,渗透系数和孔隙率随Pe的增大而减小,且变化显著;当Pe>1时,渗透系数和孔隙率随Pe数的变化趋于平坦. 相似文献
994.
Yiqun HUANG Yiran LI Man ZHANG Boyu DENG Hao KONG Junfeng WANG Junfu LYU Hairui YANG Lingmei WANG 《Frontiers in Energy》2021,15(2):320
Diffusion of oxygen in the ash layer usually dominated the combustion of oil shale semicoke particles due to the high ash content. Thus, effective diffusivity of oxygen in the ash layer was a crucial parameter worthy of careful investigation. In this paper, the effective diffusivity of oxygen in the ash layer of Huadian oil shale semicoke was measured directly using an improved Wicke-Kallenbach diffusion apparatus. The experimental results showed that higher temperature would lead to a higher effective diffusivity and a thicker ash layer had the negative effect. Especially, the effective diffusivity along the direction perpendicular to bedding planes was much lower than that along the direction parallel to bedding planes. In addition, an effective diffusivity model was developed, which could be used to describe the mass transfer of oxygen in the ash layer of oil shale semicoke. 相似文献
995.
996.
A detailed numerical three-dimensional (3D) model for a planar solid oxide fuel cell (SOFC) is developed in this paper. The 3D model takes into account detailed processes including transport, chemical and electrochemical processes taking place in the cell. Moreover, effects of the composite electrodes are taken into account by considering an electrochemically active layer of finite thickness in each of the electrodes. The developed model is applied to a repeating unit of an anode-supported SOFC working under direct internal reforming conditions. Detailed results for chemical species, temperature, current density and electric potential distribution are presented and discussed. It was found that the temperature distribution across the cell is more uniform in the interconnects than in the inner part of the cell. However, only small differences in the electric potential between the electrode and the corresponding interconnect are found. The current density in the electrodes is found to be high near the electrolyte and low deep into the electrochemically active layer. The current density is also low under the ribs of the interconnects. 相似文献
997.
998.
The heat transfer of pool boiling in bead packed porous layers was experimentally investigated to analyze the effects of the bead material, bead diameter and the layer number of the porous bed on the transport of flux and the heat transfer coefficients. The glass and copper bead, the bead sizes of 4 mm and 6 mm as well as the bead packed porous structures ranging from one to three layers were chosen in the experiments. The pool boiling heat transfer in the bead packed porous structures and that on the plain surface were compared to analyze the enhancement of pool boiling heat transfer while the bead packed porous layers were employed. The maximum relative error between the collected experimental data of the pure water on a plain surface and the theoretical prediction of pool boiling using the Rohsenow correlation was less than 12%. Besides, the boiling bubble generation, integration and departure have a great effect on the pool boiling and were recorded with a camera in the bead stacked porous structures of the different layers and materials at different heat flux. All these results should be taken into account for the promotion and application of bead packed porous structures in pool boiling to enhance the heat transfer. 相似文献
999.
We study the influence of boundary layer stability on the near‐surface wind speed, especially for high‐wind conditions. An analysis of the wind speed ratio between two vertical levels observed at tall masts in the North Sea and The Netherlands demonstrates that over sea non‐neutral conditions commonly occur, even when the 10 m wind speed is 7 Bft or higher (at least 13.9 ms?1). Over land, stability conditions are always close to neutral for these strong wind conditions. This is because over land, large vertical temperature differences are rare in these conditions. An analysis of 30 years of station data shows that even in storm conditions the ratio of the 10 m wind speed between sea and land depends systematically on the difference between the air temperature and the sea surface temperature. The observational results are reproduced by HARMONIE, a state‐of‐the‐art Numerical Weather Prediction model, although the impact of stability is smaller than in the observations. A model sensitivity analysis for a severe storm shows that the near‐surface wind speed over sea can vary by 10% depending on the difference between the air temperature and the sea surface temperature. The results presented in this study indicate that even in conditions that are usually classified as ‘(near) neutral’, small variations in stability may have a significant impact on the wind profile. They also indicate that for high wind speeds, the sea‐to‐land wind speed ratio is dominated by the stability over sea as in these conditions the stability over land is close to neutral. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
1000.
In this study, we consider the frictional sliding contact problem between a functionally graded magnetoelectroelastic (MEE) layer resting on a perfectly insulated rigid half plane and a perfectly conducting rigid flat punch with frictional heat generation. The punch is subjected to magnetoelectromechanical loads. The graded layer is modeled as a nonhomogeneous medium with a transversely isotropic stress–strain law and an exponential variation of the magnetoelectrothermoelastic properties along the thickness direction. Neglecting inertia effects and assuming a constant friction coefficient, the solution is obtained within the framework of steady-state plane magnetoelectrothermoelasticity under plane strain conditions. The heat equation is first solved using Fourier transform to yield the temperature field in the layer which is then substituted in the MEE governing equations. These equations are solved analytically using the same transform leading to three coupled Cauchy-type singular integral equations in which the main unknowns are the normal contact stress, the electric displacement, and the magnetic induction. These equations are then solved numerically to obtain the distributions of the normal contact stress, electric displacement, and magnetic induction at the surface of the graded medium. The main objective of this paper is to study the effect of the nonhomogeneity parameter; the friction coefficient; and the elastic, electric, and magnetic coefficients on the surface contact pressure, electric displacement, and magnetic induction distributions for the case of flat punch profile. 相似文献