Drop size distribution below different wet-cooling tower fills

Drop size distribution is measured photographically below three different counter-flow wet-cooling tower fills (cross-fluted film, trickle and fibre cement) and a number of splash grid configurations installed below a trickle fill. The air and water flow rates are varied to investigate their influence on drop size. The data for each test case is presented as a cumulative mass distribution curve, Sauter mean diameter, Rosin–Rammler distribution curve and Rosin–Rammler function. The main objectives are to describe the implemented experimental apparatus and measurement techniques and to determine the drop size distribution beneath different fills and ultimately the drop size reduction capability of grids installed below the fill. An important conclusion is that the Rosin–Rammler distribution curve generally does not fit the measured data adequately and thus should be avoided.     

A review of drop size measurement — the application of techniques to dense fuel sprays

The numerous experimental techniques that have been devised for measuring drop size distributions in sprays are reviewed. The techniques have been conveniently grouped into three categories for this purpose.

1. (i) Mechanical methods such as droplet capture, cascade impaction, frozen drop and wax methods and a sedimentation technique.

2. (ii) Electrically based methods comprising the Wicks-Dukler technique, the charged wire probe and the hot wire anemometer.

3. (iii) Optical methods consisting of photography, holography, laser diffraction, laser anemometry and various other techniques based on light scattering.

The limitations of each technique are identified in order to assess which are potentially useful in the high density sprays produced by large oil burner atomisers.     

高温条件下柴油机喷雾粒度的测量

为了了解柴油机燃烧室中燃油与空气的混合及后续燃烧过程，准确地描述燃油雾化和油洋蒸发过程是至关重要的。运用激光衍射法测量注体喷雾粒度具有对喷雾无干扰，设备简单数处理迅速等优点，但这种方法对加热环境中的蒸发液雾进行测量进，由于光路上存在的温度及浓度梯度，激光被折射而偏转，结果受到严重影响，以往对柴油机喷雾的测量大都在常温不蒸发条件下进行的，而本则是通过对粒子激光衍射测量原理的深入分析，对基于激光衍射     

Modeling drop size distributions

There is abundant literature discussing the prediction of a representative drop diameter in a spray. However, there are relatively few publications discussing prediction of a drop size distribution in sprays. In the present paper, we review the three available methods for modeling drop size distributions: the maximum entropy method, the discrete probability function method, and the empirical method.     

Continuous monitoring of back wall stress corrosion cracking growth in sensitized type 304 stainless steel weldment by means of potential drop techniques

Stress corrosion cracking (SCC) tests on welded specimens of sensitized type 304SS with a thickness of 20 mm were performed in sodium thiosulphate solution at room temperature, with continuous monitoring of the SCC growth, using the techniques of modified induced current potential drop (MICPD), alternating current potential drop (ACPD) and direct current potential drop (DCPD). The MICPD and DCPD techniques permit continuous monitoring of the back wall SCC, which initiates from a fatigue pre-crack at a depth of about 4 mm, from which it propagates through more than 80% of the specimen thickness. The MICPD technique can decrease the effect of the current flowing in the direction of the crack length by focusing the induced current into the local area of measurement using induction coils, so that the sensitivity of the continuous monitoring of the back wall SCC is higher than that of the ACPD and DCPD techniques.     

汽轮机内湿蒸汽实验测量技术现状

为了研究汽轮机内湿蒸汽两相流的湿度、水滴的粒径和分布,以及水滴的带电特性,近年来国内外发展了一些新的测量技术,包括光散射法、微波法、电容法、图像法等。本文对这些新的测量技术作了较为全面的概述和介绍,对不同的测量方法进行了比较和分析,并对测量技术的发展进行了展望。     

Microscale Contacting of Two Immiscible Liquid Droplets to Measure Interfacial Tension

In various microfluidic devices, surface tension and interfacial tension values are necessary to analyze the fluid behavior in microchannels, and evaluating the values of interfacial tension is especially important for gas–liquid and liquid–liquid flows. A pendant drop method is commonly used to measure the interfacial tension value; however, the pendant drop method requires strict accuracy in measuring the droplet size when the droplet has a nonspherical shape, as well as an accurate value of the density difference between the two liquids. In this work, a new measurement method called the “liquid bridge-inducing microscale contact method” has been developed in which the interfacial tension can be obtained from the bridging of two liquid droplets extruded from opposing ends of glass capillary tubes or formed on the ends of round metal rods. By measuring the radii of curvature of each liquid surface and interface, we calculate the Laplace pressure on the surface and interface, and derive the interfacial tension value using the Laplace equation. The results show that the values of interfacial tension obtained from the two methods are approximately the same and that the liquid bridge-inducing microscale contact method is capable of accurate interfacial tension measurements.     

Methods for measuring the effective thermal conductivity of metal hydride beds: A review

The effective thermal conductivity of metal hydride beds is a crucial parameter for metal hydride reactor design. In this review, methods and principles for the measurement of the effective thermal conductivity of metal hydride beds are discussed, including steady-state techniques (the radial heat flow, comparative cut bar, guarded heat flow meter, and guarded hot plate methods) and transient techniques (the hot-wire, thermal probe, transient plane source, and laser flash methods). Reports of effective thermal conductivity measurements for characterizing metal hydride beds have been reviewed, including the measurement methods, material composition, measurement results, temperature, and gas pressure. The advantages, disadvantages, and applications of each measurement method have been presented, and an assessment regarding different techniques of measurement has been conducted. Laser flash and transient plane source are found to be the most frequently used methods, and have been increasingly applied in recent years. Finally, a brief discussion of recommended future development of effective thermal conductivity measurement is presented.     

坝后背管承载性能研究进展

以理论分析法、模型试验与原型观测法、有限单元法为线索总结了近年来坝后背管承载性能的研究成果。重点评析了管道外包混凝土开裂前后应力状态的计算方法、外包混凝土裂缝宽度的计算方法、提高管道耐久性的措施、有限单元法在坝后背管中的应用。提出了需要进一步深入研究的问题,包括合理的钢材配置计算方法、钢衬外包混凝土裂缝控制研究、非线性承载性能和破坏机理研究、动力承载性能研究、温度控制和温度应力分析、新型材料和新型结构型式研究等。     

Experimental study on 75 kWth downdraft (biomass) gasifier system

Experimental study on 75 kW_th, downdraft (biomass) gasifier system has been carried out to obtain temperature profile, gas composition, calorific value and trends for pressure drop across the porous gasifier bed, cooling–cleaning train and across the system as a whole in both firing as well as non-firing mode. Some issues related to re-fabrication of damaged components/parts have been discussed in order to avoid any kind of leakage. In firing mode, the pressure drop across the porous bed, cooling–cleaning train, bed temperature profile, gas composition and gas calorific value are found to be sensitive to the gas flow rate. The rise in the bed temperature due to chemical reactions strongly influences the pressure drop through the porous gasifier bed. In non-firing mode, the extinguished gasifier bed arrangement (progressively decreasing particle size distribution) gives much higher resistance to flow as compared to a freshly charged gasifier bed (uniformly distributed particle size). The influence of ash deposition in fired-gasifier bed and tar deposition in sand filters is also examined on the pressure drop through them. The experimental data generated in this article may be useful for validation of any simulation codes for gasifiers and the pressure drop characteristics may be useful towards the coupling of a gasifier to the gas engine for motive power generation or decentralized electrification applications.     

Experimental study of evaporating water-ethanol mixture sessile drop: influence of concentration

In this paper we study the evaporation of a drop on a rough polytetrafluoroethylene substrate. A water-ethanol binary drop of few millimetres size is evaporating in a controlled pressure environment. An experimental set up is built to investigate the influence of ethanol concentration and drop profile on the evaporation rate. The measurements were performed using an optical technique. This latter allows measurements of the dynamic contact angle, the drop volume and the base width as function of time. For pure substances (water, ethanol) the evaporation rate and the drop profile are found to have a monotonous evolution with time. For binary water-ethanol mixtures, three stages corresponding to different wetting behaviours are identified. The evaporation rate measurement indicates that the more volatile component evaporates entirely in the first stage while in the last stage the less volatile component is dominantly evaporating. The behaviour of the wetting angle is correlated with the volume of the drop and the ethanol concentration. It was clearly demonstrated that at high ethanol concentration (75%) the wetting contact angle of the drop matches the behaviour of pure ethanol during the first stage and tends to follow the behaviour of pure water during the third stage. This suggests that, as the ethanol evaporates in the first stage it diffuses to the interface where it dictates the surface tension properties and hence the wetting contact angle. Towards the end of the droplet lifetime, the wetting contact angle jumps to join the behaviour of pure water.     

Recent advances in the measurement of strongly radiating, turbulent reacting flows

Recent advances in diagnostic methods are providing new capacity for detailed measurement of turbulent, reacting flows that are strongly radiating. Radiation becomes increasingly significant in flames containing soot and/or fine particles, and also increases with physical size. Therefore many flames of practical significance are strongly radiating. Under these conditions, the coupling between the turbulence, chemistry and radiative heat transfer processes is significant, making it necessary to obtain simultaneous measurement of controlling parameters. These environments are also particularly challenging for laser-based measurements, since soot and other particles increase the interferences to the signal and the attenuation of the beam. The paper reviews the influence of physical scale and of the properties of the medium on approaches to perform measurements in such strongly radiating flows. It then reviews the recent advances in techniques to measure temperature, mixture fraction, soot volume fraction, velocity, particle number density and the scattered, absorbed and transmitted components of radiation propagation through particle laden systems. Finally it also considers remaining challenges to diagnostic techniques under such conditions.     

数字化检测技术在模具修复中的研究与应用

随着模具在制造业应用领域的发展,模具修复工作也显得极为重要.首先简要介绍了数字化检测技术的重要思想,进而详细阐述了数字化检测技术在模具修复中的检测方法和检测步骤,最后利用一实例验证了数字化检测技术在模具应用中的可行性.     

Light scattering for particle characterization

Light scattering has proved to be one of the most powerful techniques for probing the properties of particulate systems. The purpose of this paper is to review the status of elastic light scattering. The emphasis is on recent developments, rather than being over-repetitive of earlier reviews, but considerable background is included with the aim of making the paper self-contained. There is an extensive summary of theoretical treatments, including both historical work and new. On the experimental side, while there is some discussion of well-tried methods, the emphasis is on recent techniques for measuring other properties as well as size. This includes, among others, the fractal treatment of agglomerates, determination of particle shape and measurement of refractive index. The discussion is broad rather than deep to provide a wide-ranging review of an extremely active field.     

Generalized Procedure for Improved Accuracy of Thermal Contact Resistance Measurements for Materials With Arbitrary Temperature-Dependent Thermal Conductivity

Thermal contact resistance (TCR) is most commonly measured using one-dimensional steady-state calorimetric techniques. In these experimental methods, a temperature gradient is applied across two contacting beams and the temperature drop at the interface is inferred from the temperature profiles of the rods that are measured at discrete points. During data analysis, thermal conductivity of the beams is typically taken to be an average value over the temperature range imposed during the experiment. Here, a generalized theory is presented that accounts for temperature-dependent changes in thermal conductivity. The procedure presented enables accurate measurement of TCR for contacting materials whose thermal conductivity is any arbitrary function of temperature. For example, it is shown that the standard technique yields TCR values that are about 15% below the actual value for two specific examples of copper and silicon contacts. On the other hand, the generalized technique predicts TCR values that are within 1% of the actual value. The method is exact when thermal conductivity is known exactly and no other errors are introduced to the system.     

Flame propagation in heterogeneous mixtures of fuel drops and air

An experimental study is conducted on the influence of fuel chemistry on the flame speeds of flowing mixtures of fuel drops in air at atmospheric pressure. Air is supplied at room temperature to a 10 cm² test section which is fitted with quartz windows to provide optical access to the flame. Sixty-four evenly spaced airblast atomizers ensure a uniform fuel distribution in the mixture entering the flame zone. Variation in mean fuel drop size is accomplished by varying the air flow rate to the airblast atomizers.Schlieren pictures of the flame provide the basic data for the measurement of flame speed, using the angle method. The fuels employed include a conventional No. 2 fuel oil, plus various blends of JP7 with stocks containing single-ring and multiring aromatics. For all fuels the measured flame speed is found to be inversely proportional to SMD above some critical size, indicating that in this range of large drop sizes evaporation rates are controlling to flame speed. The fuels exhibiting the highest flame speeds are those containing multiring aromatics. This is attributed to the higher radiative heat flux emanating from their soot-bearing flames, which enhances the rate of evaporation of the fuel drops approaching the flame front.     

SIZE EFFECT ON SURFACE TENSION AND CONTACT ANGLE BETWEEN PROTEIN SOLUTION AND SILICON COMPOUND,PC, AND PMMA SUBSTRATES

Detailed contact angle measurements are performed for protein drops on phenylcarbamide (PC), polymethyl methacrylate (PMMA), silicon nitride, and glass substrates by goniometer-sessile drop technique. Drop sizes are ranged from 0.1 to 6 w l with radius of curvature less than 1 mm. The bovine serum albumin (BSA) protein concentrations are 0.0, 0.1, 1.0, and 10 mg/ml. The results show weak dependence of the drop size for deionized water drops on all substrates and increased dependence of the drop size for protein drops with different protein concentrations. The significance of drop size effect varies from substrate to substrate; the effect is strongest for PC substrate, which is a nearly hydrophobic surface. The drop size dependence can be partly explained by the modified Young's equation.     

Operational characteristics of high-pressure, high-efficiency water-hydrogen-electrolysis

After more than 5000 h of operation of the 100-kW-Pilot-Electrolyzer developed by the Gesellschaft für Hochleistungselektrolyseure zur Wasserstofferzeugung mbH (GHW), the experience accumulated so far allows for the scale up to the Megawatt size of this high pressure electrolysis. Several operational concepts ranging from constant current long time tests over solar photovoltaic energy storage to subsecond compensation of power plant network fluctuations have been successfully simulated. The responses of the main system parameters during these simulations are described. For partial load operation, the normally increased hydrogen percentage in the produced oxygen has been stabilized by a special lye circulation control. The material problems, like corrosion under extreme conditions, are solved up to now. Some of the material aspects are discussed. As measurement and control techniques are the backbone of the safety system, sensors and signal processing are briefly mentioned. The single cell voltage measurement is explained. In total, the gained knowledge allows the design of this kind of electrolyzer for wherever its use is technically and economically attractive. The decreasing acceptance of air pollution improves the position of electrolysis. Beginning with an overview on high-pressure electrolyzers actually realized, an outlook on coming projects and future applications is given.     

基于能量损失的低压省煤器系统节能效果研究

基于热力学第一定律的基本理论,以火电厂能量损失为研究对象,分析低压省煤器投入运行后对电厂各项能量损失的影响,建立了定功率条件下计算低压省煤器节能量的数学模型。该计算模型根据局部参数的测量就能较准确的评价低压省煤器的节能效果,简化了试验过程。将该方法应用在某国产330 MW机组上,并与热平衡图法和等效焓降法的计算结果进行了比较,证明了该方法的准确性。