共查询到20条相似文献,搜索用时 46 毫秒
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针对两种不同时序位置热斑在大冷气量燃气涡轮通道内的迁移对涡轮气动性能、叶片表面热负荷和气动激振力的影响开展了数值模拟研究,对比分析了涡轮效率、叶片表面温度分布、出口总温分布、非定常激振力时域/频域特征等,对进口热斑时序位置的选取方式进行了讨论。结果表明对于气冷燃气涡轮,与热斑正对通道中心相比,热斑正对导叶前缘可以有效降低动叶热负荷、改善第二级导叶温度分布均匀性、抑制效率下降、降低非定常激振力水平,有利于改善燃气涡轮气动热力性能。研究结果为大冷气量双级燃气涡轮热斑时序位置选取提供了依据。 相似文献
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用有限时间热力学方法分析存在传热损失时,热声制冷机微热力学循环模型的火用经济性能,导出循环利润率与工质振荡温度,以及利润率与制冷系数的特性关系,并数值分析了价格比、横向温度梯度等参数对火用经济性能的影响。 相似文献
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本文分别对单级氨水吸收式制冷循环和GAX循环进行了计算机模拟,在热源温度TH为120℃、TM为25℃、TL为5℃的情况下,两个循环的制冷系数分别为0.589和0.776,GAX循环高出31.8%。(火用)效率分别为15.4%和27.4%,GAX循环高出77.9%。在α-h图上别对两个循环的热力学结构进行了比较分析,认为循环的改进取决于热机子循环的热力学完善程度,GAX循环与单级循环内部的热泵子循环的(火用)需求是相同的,只是由于GAX循环改善了热机子循环的过程耦合结构,减少了(火用)的消耗而获得了整个循环的增益。 相似文献
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基于两级节流、中间完全冷却的R410a双级制冷循环,建立了热力学模型并进行了性能分析。结果表明,随着双级循环中间压力的升高,系统制冷量和耗功均降低,系统COP先升高后降低,系统存在最优中间压力,并且对应最优中间压力存在最优中间温度。与单级循环相比,双级循环的高压级压缩机排气温度低于单级循环的排气温度,约低35.47℃,双级循环系统COP提高了约7.41%。■分析表明,蒸发器■损失最大,约占总■损失的42.78%,其次,冷凝器■损失占32.50%;压缩机■损失最小,约为16.70%,其中,低压级压缩机■损失比高压级压缩机高约28.60%。由双级循环中膨胀机代替节流阀循环的分析得出,膨胀机循环性能COP比节流阀提高了约42.24%,■损失降低约23.74%,膨胀机循环无论在参数优化还是性能改善方面,均比节流阀循环具有一定优势。 相似文献
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针对矩形肋片热沉, 分别以最大热阻最小化和基于(火积)耗散定义的当量热阻最小化为优化目标, 采用二维传热模型并结合有限元数值仿真对其进行构形优化, 比较了两种目标下的热沉最优构形, 并分析了全局参数(综合了对流换热系数、肋片占据的总面积及其热导率的函数)和材料占比对两种目标(最大热阻、当量热阻)及其对应最优构形的影响. 结果表明: 热沉外形固定时, 两种目标下均不存在最优的肋片厚度; 热沉外形自由变化时, 两种目标下的最优构形存在一定的差异. 此外, 全局参数对两种目标下的最优构形均没有影响, 而材料占比对两种目标下的最优构形均有较大影响. 提高全局参数和材料占比均可以减小最大热阻最小值和当量热阻最小值, 但对两种目标的减小程度不同. 总体上, 调节热沉结构参数使当量热阻最小, 可以同时获得很好的局部极限性能; 而调节热沉结构参数使最大热阻最小, 获得的整体平均散热性能却较差. 因此, 对本文热沉模型进行优化时, 以当量热阻最小化为优化目标更合理. 相似文献
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《Heat Recovery Systems and CHP》1992,12(2):143-158
Power generation with low temperature geothermal resources is not economically viable due to the poor thermal efficiency of organic Rankine cycles (ORC). A novel idea is proposed where a vapour absorption chiller (VAC) can be employed to lower the ORC condensing temperature, thus increasing its power output. This paper presents detailed analysis of a VAC that operates with water-lithium bromide to extract heat from the geothermal brine leaving the ORC vaporizer. The evaporator of the VAC serves as the ORC condenser. A computer program is coded to simulate the combined ORC-VAC performance and compare it with that of the conventional ORC. The results indicate that the ORC-VAC option would render power generation more economical. The organic fluid flow rate in the ORC per unit power output is cut by at least 50% in this case, thus reducing the ORC size and turbine cost. Moreover, even though the ORC-VAC includes more components, the total heat exchange area requirement per unit power output remains practically unchanged. 相似文献
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A statistical model of homopolymer DNA, coupling internal base-pair states (unbroken or broken) and external thermal chain fluctuations, is exactly solved using transfer kernel techniques. The dependence on temperature and DNA length of the fraction of denaturation bubbles and their correlation length is deduced. The thermal denaturation transition emerges naturally when the chain fluctuations are integrated out and is driven by the difference in bending (entropy dominated) free energy between broken and unbroken segments. Conformational properties of DNA, such as persistence length and mean-square-radius, are also explicitly calculated, leading, e.g., to a coherent explanation for the experimentally observed thermal viscosity transition. 相似文献
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This study presents a new design that uses a combination of a graded hole transport layer (GH) structure and a gradually doped emissive layer (GE) structure as a double graded (DG) structure to improve the electrical and optical performance of white organic light-emitting diodes (WOLEDs). The proposed structure is ITO/m-MTDATA (15 nm)/NPB (15 nm)/NPB: 25% BAlq (15 nm)/NPB: 50% BAlq (15 nm)/BAlq: 0.5% Rubrene (10 nm)/BAlq: 1% Rubrene (10 nm)/BAlq: 1.5% Rubrene (10 nm)/Alq3 (20 nm)/LiF (0.5 nm)/Al (200 nm). (m-MTDATA: 4,4′,4″ -tris(3-methylphenylphenylamino)triphenylamine; NPB: N,N′-diphenyl-N,N′-bis(1-naphthyl-phenyl)-(1,1′-biphenyl)-4,4′-diamine; BAlq: aluminum (III) bis(2-methyl-8-quinolinato) 4-phenylphenolate; Rubrene: 5,6,11,12-tetraphenylnaphthacene; Alq3: tris-(8-hydroxyquinoline) aluminum). By using this structure, the best performance of the WOLED is obtained at a luminous efficiency at 11.8 cd/A and the turn-on voltage of 100 cd/m2 at 4.6 V. The DG structure can eliminate the discrete interface, and degrade surplus holes, the electron-hole pairs are efficiently injected and balanced recombination in the emissive layer, thus the spectra are unchanged under various drive currents and quenching effects can be significantly suppressed. Those advantages can enhance efficiency and are immune to drive current density variations. 相似文献
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Optical absorption in asymmetric double quantum wells driven by two intense terahertz fields
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Optical absorption is investigated for asymmetric double quantum wells driven by a resonant terahertz field and a varied terahertz field both polarized along the growth direction. Rich nonlinear dynamics of the replica peak and the Autler-Townes splitting of various dressed states are systematically studied in undoped asymmetric double quantum wells by taking account of multiple factors, such as the frequency of the varied terahertz field and the strength of the resonant terahertz field. Each electron subband splits into two dressed states when the resonant terahertz field is applied in the absence of the varied terahertz field, the optical absorption spectrum shows the first order Autler-Townes splitting of the electron subbands. When a varied terahertz field is added into the resonant system, the replica peak and the second order Autler-Townes splitting of the dressed states near the band edge respectively emerge when the varied terahertz field is non-resonant and resonant with these dressed states. When the strength of the resonant terahertz field is increased, the first order Autler-Townes double peaks and the replica peak in the optical absorption spectrum shift with the shifts of the dressed states. The presented results have potential applications in electro-optical devices. 相似文献
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Xinghua Liu Wenhao Yuan Jingsong Zhang Jiuzhong Yang Zhongyue Zhou 《Proceedings of the Combustion Institute》2021,38(1):651-659
Thermal decomposition of 1-hexene at temperatures 295-1410 K was conducted using a flash pyrolysis micro-reactor coupled to laser-based vacuum ultraviolet photoionization time-of-flight mass spectrometer (VUV-PI-TOFMS). The decomposition mechanism of 1-hexene was developed with the help of theoretical calculation performed at the MRCI/cc-pvtz//CASSCF/6–31+G(d,p) level. The γ-scission and diradical retro-ene reactions were determined as the main initial decomposition reactions in the temperature range 990-1240 K. Two diradical retro-ene reaction channels, 1,5-diradical and 1,6-diradical reactions, were proposed in order to interpret the appearance of the C4H8 species. The 1,5-diradical retro-ene reaction involved a 1,5-diradical intermediate that subsequently decomposed via CC β-scissions to the C2, C3 and C4 products. The 1,6-diradical retro-ene reaction proceeded via a 1,6-diradical intermediate and CC β-scissions to produce the C2 and C4 species. The proposed diradical retro-ene mechanism was evidenced indirectly by the early product distribution of 1-hexene pyrolysis in a flow reactor at 1173 K determined by synchrotron radiation VUV-PI-TOFMS. It was verified in the flash pyrolysis of 1-heptene as well. 相似文献
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单色仪在实际光谱测量前需要进行波长校准。文中分析了波长驱动原理,并推导了Czerny-Turner双光栅单色仪出射波长与步进电机脉冲数的关系式。在此基础上进行了波长校准实验。使用低压汞灯作为校准光源,在紫外波段和可见波段蓝端,扫描多条低压汞灯特征谱线,得到单色仪的指示波长与信号强度的关系数据。计算出单色仪出射这些谱线时使用的波长修正量。最后使用曲线拟合方法得到250 nm~450 nm光谱范围内单色仪出射任意波长时对应修正量的计算式。波长校准保证了单色仪的波长准确性。 相似文献
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Internal collision double ionization of molecules driven by co-rotating two-color circularly polarized laser pulses
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The double ionization process of molecules driven by co-rotating two-color circularly polarized fields is investigated with a three-dimensional classical ensemble model. Numerical results indicate that a considerable part of the sequential double ionization(DI) events of molecules occur through internal collision double ionization(ICD), and the ICD recollision mechanism is significantly different from that in non-sequential double ionization(NSDI). By analyzing the results of internuclear distan... 相似文献
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《Heat Recovery Systems and CHP》1990,10(2):161-175
This paper discusses a configuration of a Rankine cycle engine-driven heat pump, and includes a theoretical investigation of its performance characteristics. The system employs a Rankine power cycle, using R-113 as the working fluid, coupled to a vapour compression cycle heat pump using R-22. A novel feature of the concept is the use of hydraulically connected rolling diaphragm piston-cylinder devices as motor, compressor and pump.Heating and cooling COPs of 2.01 and 1.06 respectively are predicted, making the system potentially attractive where both heating and cooling are required. 相似文献