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21.
22.
An equation of state for 1,1-difluoroethane (HFC 152a, CH3CHF2) has been developed on the basis of reliable experimental data including PVT, liquid Cp, and saturated-liquid-density data measured by our group. It is a non-dimensionalized virial equation whose functional form is the same as that originally developed for 1,1,1,2-tetrafluoroethane (HFC 134a) in our group. The effective range is for pressures up to 15 MPa, temperatures from 230 to 450 K, and densities to 1000 kg m−3. The equation represents reliable PVT measurements within ± 1% in pressure for the superheated vapour and supercritical fluid, while within ±0.5% in density for the compressed liquid. In addition, it should be noted that the equation represents the other essential thermodynamic properties including vapour pressures, saturated-liquid/ vapour densities, isobaric/isochoric specific heats and sound velocity in both the liquid and gaseous phase of HFC 152a. 相似文献
23.
Sensitivity analysis is used to show how uncertainties in basic factors, such as heat transfer, pressure drop, compressor efficiency, and thermophysical properties, influence the result of heat pump cycle performance estimations. By comparing the results of this analysis with uncertainty levels of estimations and experimental determinations, it is established to what extent improvements in accuracy are needed. The investigation was carried out for several different applications and, as working fluids, both pure substances and non-azeotropic mixtures were examined. It was found that evaporation heat transfer and compressor efficiency are two areas where improvements are needed. It is also shown that estimates using very accurate, substance-specific, equations of state differ from those using more general types by up to 1 % for COP and 2% for capacity. 相似文献
24.
Quasi-static and dynamic crushing behaviors of aluminum and steel tubes with a cutout 总被引:3,自引:0,他引:3
Tubular members are commonly used as an energy absorber in engineering structures and many such members have a cutout. In this study, the crushing behaviors of tubes with a cutout are characterized and the effects of cutout on the energy absorption capabilities of these tubes are quantified. Systematic parametric studies were carried out to study the effect of material properties, including yield and ultimate strength of material, strain rate effect, location of cutout, tube length and impact speed on the crushing behaviors and energy absorption capacity of aluminum and steel tubes. First, a numerical model was constructed with a commercial explicit finite element code. It will be first proven that the numerical simulation can produce sufficiently accurate results in an economic manner. Subsequently, the crushing behavior of aluminum and steel tubes with a cutout was experimentally characterized and their energy absorption capacity was evaluated in terms of mean crushing force, peak crushing force and specific energy absorption (SEA). Tubes of various lengths with a cutout located at different locations, subject to both quasi-static and dynamic impact loadings were considered. For steel tubes, the numerical simulation investigated the influence of the strain rate effect and variation in strain hardening ratio of the material. Empirical equations describing the mean and peak crushing forces of aluminum and steel tubes with a cutout were developed using linear and nonlinear regression methods applied to the results obtained from the numerical and experimental studies. 相似文献
25.
保序回归的大样本性质 总被引:1,自引:0,他引:1
邢务强 《西安邮电学院学报》2004,9(4):110-112
利用保序回归与极大似然估计之间的关系,从极大似然估计解的大样本性质出发,得到了保序回归解的两个大样本性质。 相似文献
26.
It is necessary to determine the accurate reflectance of painted surfaces for the review of paint finishes by computer graphics (CG) before actual painting of the exterior color of automobiles, and for quality control during production and inspection processes. We have optimized a method for measuring reflectance by using a statistical technique. We have found that the reflectance of a painted surface is best measured at an incident angle of 60° and at five aspecular angles of 10°, 18°, 28°, 40°, and 90°. Our method makes it possible to accurately reproduce reflection characteristics of paint finishes containing special flake pigments, such as pearl mica. Also it was proved that our method can apply not only to solid and metallic coatings but to all painted surfaces. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 275–282, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20125 相似文献
27.
动态规划模型在生产存贮中的应用 总被引:1,自引:0,他引:1
吴明鑫 《陕西科技大学学报》2003,21(5):29-31
利用动态规划模型研究了生产管理中生产存贮问题的数学模型,给出了动态规划的最优性原理和动态规划基本方程,并给出了该数学模型求解的一个实例。 相似文献
28.
Ideal-gas thermodynamic properties for natural-gas applications 总被引:2,自引:0,他引:2
Calculating caloric properties from a thermal equation of state requires information such as isobaric heat capacities in the ideal-gas state as a function of temperature. In this work, values for the parameters of thec
p
0
correlation proposed by Aly and Lee were newly determined for 21 pure gases which are compounds of natural gas mixtures. The values of the parameters were adjusted to selectedc
p
0
data calculated from spectroscopic data for temperatures ranging from 10 to 1000 K. The data sources used are discussed and compared with literature data deduced from theoretic models and caloric measurements. The parameters presented will be applied in a current GERG project for evaluating equations of state (e.g., the AGA 8 equation) for their suitability for calculating caloric properties. 相似文献
29.
一、引言从束流动力学的观点出发,对于粒子束在直线加速器中的运动,有两种主要的分析方法,也即粒子轨迹跟踪法及考察束流包络运动的方法。前者是通过解单粒子运动方程,跟踪大量的单粒子运动轨迹而后进行分析;后者则是通过解束流的包络线方程,根据束流包络的变化来进 相似文献
30.
用数值方法对泊松方程求解时,往往要对迭代的中间结果作适当的压缩处理,以加快收敛速度和避免溢出。本文提出一种单一指数因子的非线性压缩法。一维数值模拟结果表明,平衡态时不必进行压缩处理。而在非平衡态时,最佳指数压缩因子的大小与杂质浓度有关。参考本文给出的数值计算结果,根据给定器件的杂质浓度分布,选定一最佳指数压缩因子,可以使泊松方程的数值求解过程具有最快的收敛速度。 相似文献