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The modeling of air supply devices has been identified from the International Energy Agency (IEA) Annex 20 project as one of the most important problems in applying computational fluid dynamics (CFD) to predict air flow pattern and air distribution in buildings, and the complicated HESCO nozzle diffuser used in the IEA Annex 20 test room has been proved to be particularly difficult to model. In a previous study, a simplified model for this diffuser was developed and validated against experimental data. It has been shown that this model can yield good prediction for the wall jet flow issued from the diffuser, but whether this model is capable of correctly predicting the global flow pattern in the whole test room was not known. In this paper, the benchmark data of the IEA Annex 20 Test Cases B2 and B3 were used to evaluate the performance of the model for the prediction of the global air flow pattern in the test room. It was demonstrated that this model can predict the air flow pattern in the whole test room for both the Test Cases B2 and B3 with reasonable accuracy. The significance of a velocity correction when comparing the numerical prediction with experimental data obtained using omni-directional anemometers was also discussed. 相似文献
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Tetsuhiko Maeda Tetsuya Suekane Yoshihiro Okuno Sigeharu Kabashima 《Electrical Engineering in Japan》2000,133(2):11-19
The effects of diffuser shape and back pressure on the performance of closed‐cycle disk MHD generators are investigated with two‐dimensional numerical simulations taking account of the boundary layer. The enthalpy extraction ratio decreases and fluctuates periodically with increase in the back pressure. The amplitude of power output fluctuation and the period depend on the volume of the inverse flow region. For the reduced height diffuser, the inverse flow region is suppressed and the fluctuation becomes smaller than that for the constant height diffuser. When operated with a back pressure lower than an optimum value, the diffuser does not work because of reacceleration in the diffuser. For the higher back pressure, on the contrary, the inverse flow region propagates into the MHD channel, then the enthalpy extraction ratio is reduced and the Mach number at the exit of the MHD channel becomes lower than unity. For the optimum back pressure, high enthalpy extraction ratio is achieved and the adiabatic efficiency at the diffuser exit is decreased by several percent from that evaluated at the MHD channel exit. © 2000 Scripta Technica, Electr Eng Jpn, 133(2): 11–19, 2000 相似文献
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Hsiao-Kuo HsuenKen-Ming Yin 《International Journal of Hydrogen Energy》2011,36(9):5487-5499
The cathode compartment of membrane electrode assembly (MEA) of the proton-exchange-membrane fuel cell (PEMFC) is studied theoretically. A pseudo-phase-equilibrium approach adopting an approximate phase-equilibrium equation, incorporated with the associated equations of gaseous multi-component diffusion, liquid water capillary transport, and surface electrochemical kinetics, well characterizes the performance of cathode electrode under unsaturated feed. The pseudo-phase-equilibrium approach avoids the need of explicit liquid water front tracking so that only a single domain formulation, without consideration of the interior boundary, is required for the simulation. In order to illustrate the capability of the proposed approach, a mathematical model of the cathode compartment of MEA in one-dimension is formulated, in which gas species concentration profiles, liquid water distribution, and liquid water front are calculated. The validity of the pseudo-phase-equilibrium approach is then evaluated over an extensive polarization range under specified operating temperature, pressure, and inlet humidity. The solutions obtained using the pseudo-phase-equilibrium approach and the exact phase-equilibrium equation are compared over a wide range of parameter values. In addition, the influences of important transport parameters such as water transport coefficient, gas diffuser porosity, and absolute liquid permeability are evaluated and discussed. 相似文献
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光学传感器星上定标漫射板的特性测量 总被引:6,自引:5,他引:1
为了考察星上定标漫射板的光学特性及其在航天环境下的稳定性,对其进行了方向半球反射比(DHR)、双向反射比因子(BRF)、双向反射分布函数(BRDF)等反射特性的测量;同时,进行了系列环境模拟试验.结果显示:星上定标漫射板反射率在可见近红外波段可达0.99,光谱差异<0.01,在短波红外波段达0.95以上;10~60°BRF变化低于0.1, 0~60°BRDF变化<0.045,其方向特性与光谱、紫外辐照关系不大;漫射板350 nm反射率在120 h等效紫外辐照下的衰变<3%,其光学特性受原子氧、质子轰击影响甚微,并通过了航天级力学环境试验.试验研究表明:漫射板具备高反射率、光谱平坦性、朗伯性及其在航天环境下的稳定性,能够满足航天应用要求. 相似文献
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紫外-真空紫外遥感仪器采用铝制漫反射板,传统光学研磨的漫反射板不均匀、半球反射率低、漫反射特性很差,这会影响仪器定标精度。本文提出光学研磨+化学磨砂的新工艺与检测方法,并搭建主要测试装置。测试结果表明,新工艺的朗伯余弦辐射特性得到明显改善,在0°与45°入射时归一化曲线接近标准余弦曲线;300nm处半球反射率均匀度从0.77提到到0.98;200-400nm半球反射率平均提高33%;将其应用于紫外-真空紫外遥感仪器上进行了角度响应测试,漫反射特性明显优于美国02年发射的同类仪器SBUV/2。 相似文献