一种低压低功耗高增益放大器的设计

提出了一种基于1.5μm BCD(Bipolar-CMOS-DMOS)工艺的低压低功耗高增益运算放大器。该放大器可在低至1.8 V的电源电压下正常工作。设计中采用多级差分级级联和共模反馈结构,通过双重嵌套式米勒补偿结构进行补偿。新颖的带有静态电流控制的甲乙类输出级使得在实现轨到轨输出的同时,有效地减小了放大器的交越失真。测试结果表明,提出的设计目标均已实现,放大器在5 V的电源电压下,开环增益达到96.3 dB,在10 V/V固定增益比应用时,增益误差为±0.06%,-3 dB带宽为45 kHz,静态工作电流在60μA以下。     

Regarding the influence of the Van der Hoven spectrum on wind energy applications in the meteorological mesoscale and microscale

We demonstrate the use of high frequency data (HFD) to reproduce the power spectrum shown by Van der Hoven in 1957. His work represents the basis of wind energy standards such as averaging and variability in the frequency domain. Our results unveil discrepancies with Van der Hoven's approach, which can be related to constraints in the computing capabilities in the 1950's. We show a major eddy-energy peak at a period of 2 days and a smaller eddy-energy peak contribution at frequencies higher than the region known as the spectrum gap. The variance calculated by the area under the curve indicated that the spectral energy is mainly due to the Power Spectral Density (PSD) values located in the microscale region. We calculated the economic value of this energy based on the turbulence kinetic energy of the wind data set. We also conclude that, given the results of the present study, HFD analysis in the frequency domain uncover eddy energy peaks that determine energy fluctuations in the short and long terms. This information is lost every time data are erased from current monitoring systems.     

燃煤飞灰伏安特性的实验研究

1前言国家最新颁布的《火电厂污染物排放标准》将火电厂烟尘的最低排放浓度从200 mg/m3提高到了50mg/m3,不仅使国内长期、普遍应用的电除尘器面临一次严峻的考验,也为电除尘技术的深入研究提供了机遇。电除尘器的长期运行实践表明,对于飞灰颗粒,尤其5μm以下的微细颗粒能否被收     

进气系统阻力对柴油机性能影响的试验研究

通过发动机台架试验,研究进气系统阻力对柴油机性能的影响。得到D9-220柴油机进气系统和空滤器的最大阻力限值,为进气管路的设计和空滤器的选择提供了依据。     

冷量计量仪表的选型

首先介绍了冷量计量方法,然后以盐水为例介绍了在冷量计量方面应该注意的问题,并对参与冷量计量的仪表在选择时应注意的事项作了详细说明。     

汽轮机热喷涂的研究与应用

采用超音速火焰喷涂方法,通过工艺试验研究,得到一套最佳喷涂工艺,涂层为Co基碳化钨时,明显提高了汽轮机高温部件的耐冲蚀能力。     

热管在油田加热炉上的应用研究

对热管元件应用于油田火筒式加热炉必须解决的技术关键问题进行了研究。根据传热学原理,给出了盈制热管工作温度的工程实用技术;针对油田加热炉改造问题,提出以热管流动阻力最小为目标函数的一种优化设计思想,用以限制烟气的流动阻力。通过40余台加热炉的改造实践证明,改造后加热炉的热效率平均提高8％左右,热管温度控制及烟气阻力控制是改造设计的关键。     

An experimentally validated thermo-mechanical model for the prediction of thermal contact conductance

A predictive model for estimating thermal contact conductance between two nominally flat metallic rough surfaces has been developed and experimentally validated. The predictive model consists of two complementary parts, the first of which is a surface deformation analysis to calculate the actual area of contact for each contact spot, while the second accounts for the effects of constriction resistance and gas gap conductance between the contacting surfaces. A surface characterization technique is developed which generates an equivalent 3-D surface profile from multiple 2-D profiles and determines the unique wavelengths of importance for the surface deformation and constriction resistance models. For given surface profiles and material properties of two contacting surfaces, and a specified contact pressure, the surface characterization technique filters out non-essential wavelengths on the surface, after which the surface deformation analysis calculates the deformation and contact area of each contacting asperity by considering three different modes of deformation, namely, elastic, elastic–plastic, and plastic. The constriction resistance model is then used to calculate the constriction resistance for each contacting asperity based on the area of contact and radius of curvature of the asperity. The constriction resistance values for all the contacting asperities are then used to calculate the total thermal contact conductance. An experimental facility has also been constructed to measure thermal contact conductance of interfaces to verify the results of the predictive model. Good agreement has been found between the model predictions and experimental measurements, validating the modeling approach.     

Freezing-induced splashing during impact of molten metal droplets with high Weber numbers

The impact of molten tin droplets (0.6 mm diameter) on solid surfaces was observed for a range of impact velocities (10–30 m/s), substrate temperatures (25–200 °C) and substrate materials (stainless steel, aluminum and glass). The substrate was mounted on the rim of a rotating flywheel and the collision of single droplets with the moving substrate was photographed. Droplet impact Reynolds number ranged from 2.2 × 10⁴ to 6.5 × 10⁴ and Weber number from 8.0 × 10² to 7.2 × 10³. On a hot surface there was no splashing and droplets spread to form disk-like splats with smooth edges. Solidification around the edges of droplets spreading on cold surfaces created a solid rim that obstructed flow and triggered splashing. An analytical model was developed to predict the transition temperature at which splashing disappeared by assuming that the thickness of the solid layer had to equal that of the splat in the time the droplet spread to its maximum extent in order to obstruct liquid flow. The model predicted the transition temperature for aluminum and stainless steel surfaces, assuming that thermal contact resistance between the droplet and substrate varied between 10⁻⁶ and 10⁻⁷ m² K/W. The model also predicted that tin droplets would not splash on glass surfaces maintained at or above room temperature, and this was confirmed by experiments.     

Diagnostic considerations for optical laser-extinction measurements of soot in high-pressure transient combustion environments

Laser-extinction diagnostics can provide spatially and temporally resolved measurements of attenuation from combustion-generated soot within the path of the beam. When laser-extinction techniques are utilized in high-pressure combustion environments, however, a number of complications may be encountered that are not present in low-pressure environments. Several of these experimental difficulties were investigated in diesel engine environments, and solutions that facilitated acquisition of reliable laser-extinction data were demonstrated. Beam steering due to refractive index gradients within the combusting gases was observed, and a full-angle beam divergence of over 100 mrad was measured. A spatial-filtering scheme was employed to reduce the collection of forward-scattered light and background combustion luminosity while ensuring full collection of the steered beam. To further reject combustion luminosity, a narrow-bandpass laser-line filter was employed, after diffusing the transmitted light sufficiently to avoid the effects of significant spatial non-uniformities of the filter. As the windows were subjected to thermal and mechanical stresses, dynamic etaloning effects due to the photoelastic properties of synthetic fused silica were observed. Dynamic changes in the polarization of the exit beam were also observed, as stress-induced birefringence in the windows caused dynamic phase retardation of the transmitted beam. Although these photoelastic effects could not be eliminated, they were mitigated by introducing curvature to the wavefronts in the laser-extinction beam and using polarization-insensitive elements in the detection optics. Soot deposits on window surfaces were removed ablatively using a coaxial, high-energy, pulsed Nd:YAG laser beam.