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131.
根据城市居民对供水的可靠性、稳定性、经济节能性的需求,课题组提出了一种基于"双储"模式的供水系统,并按照本市德胜住宅小区的供水要求,设计了一套由储水池、气压罐、变频器、多台水泵机组等主要设备构成的全自动变频恒压供水系统.经过近半年的运行测试,系统有效地解决了传统供水方式中存在的问题,增强了系统的总体性能,有明显的节能效果. 相似文献
132.
城市供水系统具有时滞和非线性特性等特点,仅利用常规PID控制不能使供水系统的各项性能指标很好的满足要求.针对这一实际情况,在双储供水系统中设计了一种模糊技术与常规PID控制算法相结合的模糊PID复合控制系统,该系统能够减少能量浪费,提高水压稳定性.实践运行表明,该系统运行状况良好,性能优越,验证了其有效性和可靠性. 相似文献
133.
CH4、CO2、稀有气体的溶解度模型在地球科学领域应用广泛。它们的溶解度模型在研究流体包裹体的均一化压力、古气温变化、天然气运移与聚集规律、富氦天然气成藏、储层中气—水体积比等方面发挥着重要作用。主要综述了纯水与NaCl水溶液中CH4、CO2、稀有气体溶解度研究的新进展。重点介绍了精度高且适用性广的模型的建立过程及其适用范围,并给出了部分模型的计算结果。包括:①0~250 °C、0.1~200 MPa、0~6.0 mol/kg NaCl溶液中CH4的溶解度模型;②0~450 °C、0.1~150 MPa、0~4.5 mol/kg NaCl溶液中CO2的溶解度模型;③0~80 °C范围内大气稀有气体溶解度与亨利常数的计算模型;④纯水中稀有气体亨利常数计算模型;⑤0.1 MPa、0~65 °C、0~5.8 mol/kg NaCl溶液中稀有气体的溶解度模型。CH4与CO2的溶解度模型复杂,但精度高,适用范围广。稀有气体溶解度模型的精度相对较低,适用范围相对较小,有待进一步提高与改进。CO2—稀有气体—水体系中,低密度的CO2对稀有气体溶解度的影响较小,而高密度的CO2对稀有气体的溶解度有较大的影响。目前还无法判断CH4—CO2—稀有气体共存时对彼此溶解度的影响程度,其混合气的溶解度模型需要加强研究。 相似文献
134.
K. Natesan 《Oxidation of Metals》1988,30(1-2):53-83
Oxidation-sulfidation studies were conducted on sheet samples of nickel aluminide, containing 23.5 at. % Al, 0.5 at. % Hf, and 0.2 at. % B in an annealed condition and after preoxidation treatments. Continuous weight-change measurements were made by a thermogravimetric technique in exposure atmospheres of air, a low-
gas mixture, and low-
gas mixtures with several levels of sulfur. Detailed scanning electron microscopy (SEM), X-ray, and electron microprobe analyses of the corrosion product scale layers were performed. The air-exposed specimens developed predominantly nickel oxide; the specimen exposed to a low-
. 相似文献
135.
A novel approach was undertaken in producing porous AlN microelectronics tapes with high thermal conductivity and low dielectric constant. This method essentially utilised polymer micro-spherical powders that were used as a sacrificial mould to introduce controlled porosity into the green tapes during pyrolysis. The Al2O3-rich porous green tapes were then reaction sintered at 1680 °C for 12 h to achieve porous AlN tapes. This work builds upon the previously developed novel reaction sintering process that densified and converted Al2O3-rich tapes (Al2O3–20 wt.% AlN–5 wt.% Y2O3) to AlN tapes at a relatively low sintering temperature of 1680 °C. The sintering behaviour of the porous tapes was investigated, and the effects of the microspheres particle size and volume addition were studied. The microspheres successfully contributed to the significant reduction of tape density by porosity, and this contributed to lowering its dielectric constant. Dielectric constant of the AlN tapes were reduced to about 6.8–7.7 whilst thermal conductivity values were reasonable at about 46–60 W/m K. Coefficient of thermal expansion (CTE) values showed a linear trend according to phase composition, with the porous AlN tapes exhibiting CTE values of (4.4–4.8)×10−6 °C−1, showing good CTE compatibility with silicon, at 4.0×10−6 °C−1. The added porosity did not significantly affect the CTE values. 相似文献
136.
Characterisation of n-type GaAs, etched in a 5:1:1 mixture of H2SO4:H2O2:H2O, was performed using X-ray photoelectron spectroscopy (XPS) and electrochemical AC impedance. Quantitative XPS analysis of GaAs indicated that the as-received wafers had a gallium-rich native oxide which was not affected by solvent degreasing treatments. Subsequent, oxidative etching formed a thinner arsenic-rich oxide. It is suggested that etching causes initial thinning of the native oxide; subsequently, transport of Ga and As ions occurs through the film by high-field ionic conduction. Arsenic enrichment in the resultant oxide film arises from the greater mobility of Ga3+ ions compared with As3+ ions as well as the relative solubility of Ga2O3 compared with As2O3. The as-received oxide film thickness, determined from the ratio of the oxide to substrate XPS peaks, was approximately 1.1 nm. After etching this was reduced to about 0.7 nm. This thickness is consistent with the driving voltage for oxide formation being provided by the electrochemical potential difference between hydrogen peroxide and the GaAs wafer (i.e. between 0.4 V, for As, and 1.2 V, for Ga, at a nm V−1 ratio of 2). Capacitance measurements, derived from electrochemical impedance data, combined with film thickness data, gave a value of about 5 for the dielectric constant of As2O3. 相似文献
137.
138.
Na2O-PbO-Nb2O5-SiO2 glass-ceramic were synthesized by melt-quench process.The crystallization processing of the dielectric phases were carried out at temperature range from 750 to 900 ℃.The effects of Na2O content on crystallization and dielectric properties of Na2O-PbO-Nb2O5-SiO2 glass-ceramic were investigated by means of differential thermal analysis(DTA), X-ray diffraction (XRD) and dielectric constant measurements.The results show that Pb2Nb2O7, NaNbO3 and PbNb2O6 are the crystallization phases which would be formed from the Na2O-PbO-Nb2O5-SiO2 glass at the temperature range from 750 to 900 ℃.For a definite Na2O content, the dielectric constant increases with crystallization temperature.The initial crystallization temperature of NaNbO3 phase decreases with the increase of Na2O content, leading to the increase of dielectric constant of the glass-ceramic.Formation of PbNb2O6 phase at 850 and 900 ℃ would greatly increase the dielectric constant of Na2O-PbO-Nb2O5-SiO2 glass-ceramics, but the increase of Na2O content will inhibit the crystallization of PbNb2O6 phase. 相似文献
139.
挤压温度对Mg-9Gd-4Y-0.6Zr合金组织与力学性能的影响 总被引:8,自引:0,他引:8
为提高Mg-9Gd-4Y-0.6Zr合金的强度,研究了不同温度下的挤压组织对合金力学性能的影响。结果表明,随着挤压温度从500℃降低到400℃,其晶粒度也从126μm细化到7.4μm,抗拉强度和延伸率分别从200.1MPa和2.93%提高到312.4 MPa和5.6%。通过力学性能和晶粒尺寸之间的关系计算出该合金的Hall-Petch常数Ky为327.6 MPa.μm1/2,明显高于纯镁及常规镁合金的Ky。大量稀土元素的固溶及其第二相粒子对晶界和位错运动的阻碍作用是合金Ky值较高的主要原因。 相似文献
140.
Tae-Sik Kim Young-Je An Kwang Ho Kim Won-Sub Chung Young-Rae Cho 《Metals and Materials International》2006,12(4):339-343
The effect of the dielectric constant (k) of bonding materials in a screen-printed carbon nanotube (CNT) cathode on the field
enhancement factor was investigated for high-efficiency CNT cathodes using the ANSYS software. The values obtained by a simulation
study were compared to the experimental results obtained for screen-printed CNT cathodes. The field enhancement factor increased
as the dielectric constant decreased, reaching a maximum value at a dielectric constant of 1, the value for a vacuum. The
findings indicate that the larger sheet resistance of the bonding materials, after the firing process, can be attributed to
the larger emission current of the CNT cathode. From these results, it was concluded that the best bonding materials for screen-printed
CNT cathodes should have a low dielectric constant and a high sheet resistance. This finding can be used as criteria for selecting
bonding materials for use in CNT pastes for highly efficient CNT cathodes. 相似文献