垃圾焚烧炉炉排风量测量方法的比较研究

自动燃烧控制(ACC)系统是垃圾焚烧自动控制的核心技术。基于ACC系统原理,并结合垃圾焚烧炉在不同场景下的风量测量特点,分析了均速管流量计、双文丘里流量计、热式质量流量计等主流流量计的测量原理和优缺点,为垃圾焚烧发电厂流量计选型提供依据。     

Imaging and radiation of laminar jet diffusion flames with low coflow air velocity in microgravity

We present imaging results and radiation measurements from laminar jet diffusion flames burning in coflowing air conditions. Color and pseudocolor flames are obtained and used to analyze flame brightness and shape, which show that flames under normal gravity are brighter than in microgravity. The longer residence times for microgravity flames result in increased radiative loss, which leads to local extinction and low temperature at the flame tip. Flame radiation fractions for microgravity flames are larger than those in normal gravity for C₂H ₄ and CH ₄. The velocity of coflowing air has a much more pronounced effect on radiation from microgravity flames compared to those in normal gravity. The radiation fractions from ethylene‐fueled flames in microgravity are large, leading to local extinction at the flame tip. We also analyzed the flame radiation fraction.     

Experimental study of convective heat transfer during cooling with low air velocity in a stack of objects

During cooling with low air velocity (u0.2 m·s⁻¹) of a stack of foodstuffs (a few centimeters dimension), the radiation and conduction between products can be of the same order of magnitude as convection. A method was developed to quantify these various transfer modes. The experiment was carried out using an in-line spherical arrangement; however, the same methodology can be applied to other product shapes. The results confirm that the heat transfers by radiation and conduction cannot be neglected. In addition, the convective heat transfer coefficient varies not only with air velocity but also with the product position in the stack.     

计算机技术在流速仪法测流中的应用

流速仪法测流理论成熟,测试工艺完善,精度较高,测量容易控制,具有重复性好、成果非常可靠等优点,但同时存在着计算任务繁重的缺点,因此大大地限制了该方法在生产中的应用.本文介绍了如何运用现代计算机软、硬件技术改进流速仪法测流,使这种流量测量方法能更好地为生产、科研服务.     

Laminar burning velocity with oxygen-enriched air of syngas produced from biomass gasification

Several studies on the laminar burning velocity of syngas mixtures have been conducted by various researchers. However, in most of these studies, dry air was used as the oxidizer, whereas very few studies have been conducted on syngas combustion in oxygen – enriched air. In this work, a numerical and experimental study on the laminar burning velocity of a mixture of H₂, CO and N₂ (20:20:60 vol%) was performed using air enriched with oxygen as the oxidizer, varying the oxygen content from 21% up to 35% for different equivalence ratios. Numerical calculations were conducted using three detailed reaction mechanisms and transport properties. Flames were generated using contoured slot-type nozzle burners, and Schlieren images were used to determine the laminar burning velocity with the angle method. The experiments were performed under the conditions of Medellin (1550 m.a.s.l.), 0.838 atm and 298 K. The laminar burning velocity increases with the concentration of the oxygen in the mixture due to the increase of the reaction rate; for a stoichiometric mixture, the laminar burning velocity increases by almost 25% with an increment of 4% of oxygen in the oxidant. However, the flammability limits also increase, allowing stable flames to exist in a wider range of equivalence ratios.     

Pressure drop of the film-enlarged tube bundles in air-water two-phase cross flow in evaporative air cooler

An experiment was carried out to investigate the relation of the maximum velocity of air passing through narrowest passage, mass flux of spray water in one square meter in one hour and the pressure drop of tube bundles. Twelve equations were obtained for the relation. The results show that the pressure drop of the tube bundles increases with increase of the maximum velocity of air and the mass flux of spray water. Comparing the pressure drop of the bare tube bundles with that of the film-enhanced tube bundles, it is found that the pressure drop of the film-enhanced tube bundles is lower about 11% and the surface roughness of the film-enhanced plates is a main factor that influences the pressure drop. The data and method obtained in the paper can be used to compute the pressure drop of the film-enhanced tube bundles and is helpful for selection of fan.     

Correlation analysis on the SGS velocity between phases in an isotropic gas-particle two-phase flow with FDF model

Correlation of the SGS (sub-grid scale) velocity between the two phases in an isotropic gas-particle two-phase flow was numerically investigated with FDF model. The results show the SGS gas velocity seen by the particles varies with the relative velocities between particle phase and gas phase. The relative velocity between the two phases produces the effect of the anisotropic turbulence on the particles. The variation of Stokes number influences the magnitude of the interaction between the two phases.     

低温环境中空冷器的设计

针对低温环境中空冷器使用所遇到的问题，提出了解决防止流体在管内凝固和冻结的方法，并对防冻防凝的几种方法进行了比较。     

An assembled annular stepwise diverging tube for the measurement of laminar burning velocity and quenching distance

Laminar burning velocities of premixed flames provide essential data in combustion studies. To facilitate an in situ monitoring in the field, a method using the annular diverging tube (ADT) and its improved version of the annular stepwise diverging tube (ASDT) were introduced in previous studies. Although the reliability and applicability of these methods has been verified, additional improvements are necessary for the field application. In this study, an assembled annular stepwise diverging tube (A-ASDT) was introduced. Each step-unit was fabricated separately to have higher dimensional precision and to selectively assemble suitable step-units. Thus, the burner configuration could be easily adjusted, and the experimental resolution could be controlled. Heat transfer through the burner was suppressed to extend the duration of the experiment. The characteristics of the critical flame-propagation-velocity (FPV) that are less affected by the channel gap scale were investigated in more detail. The critical FPVs were comparable to the laminar burning velocities for methane, propane, and DME. The quenching distances could be measured easily, and the quenching Peclet number was directly evaluated. In conclusion, in our knowledge, this A-ASDT may be one of the fastest, easiest, and approvable methods for the prediction of the laminar burning velocity and the quenching distance. Therefore, it can be adopted in the fuel-consuming field to monitor the characteristics of flammable mixtures.     

Burning velocity measurement of fluorinated compounds by the spherical-vessel method

Burning velocity has been measured using the spherical-vessel (SV) method for four hydrofluorocarbons (HFCs), i.e., difluoromethane (HFC-32), 1,1,2-trifluoroethane (HFC-143), 1,1,1-trifluoroethane (HFC-143a), and 1,1-difluoroethane (HFC-152a). Experiments were conducted for initial pressures in the range 78-108 kPa and initial temperatures in the range 280-330 K, over wide ranges of HFC-air equivalence ratios. The burning velocities were determined from the rate of pressure increase by applying a spherical-flame propagation model. Flame propagation behavior was observed in a cylindrical vessel equipped with optical windows by employing schlieren photography. It was found that the values of burning velocity derived from the spherical-vessel method are in good agreement with the ones obtained with schlieren method. It is found that the SV method is adequate for determining the burning velocity for weakly flammable HFCs as well as for moderately flammable compounds. The burning velocity of each HFC was obtained as a function of temperature, pressure, and equivalence ratio. The maximum burning velocities of HFC-32, HFC-143, HFC-143a, and HFC-152a were determined to be 6.7, 13.1, 7.1, and 23.6 cm s⁻¹, respectively. The maximum burning velocity occurred for slightly fuel-rich concentrations. The magnitude of the burning velocity is strongly dependent on the ratio of H atoms to F atoms in the HFC molecules.     

Experimental estimate of the laminar burning velocity of iso-octane in oxygen-enriched and CO2-diluted air

Oxygen-enriched combustion is of great interest for industrial applications, since membrane separation technology can be used. The objective of this work is to provide unique data on laminar burning velocity, a key parameter in real combustion development, for the oxygen-enriched combustion of an iso-octane/air mixture for various dilution (by air or CO₂) cases. Experiments were carried out in a stainless steel combustion chamber at atmospheric pressure and 373 K. The iso-octane was mixed with a mixture of O₂, CO_2, and N₂. The volume fraction of O₂ was varied from 21% to 29% and CO₂ was varied from 0% to 28%. The classical shadowgraphy technique was used to detect the reaction zone in order to deduce the un-stretched burning velocity, using a nonlinear methodology. All the experimental data were compared with the numerical results obtained with chemical kinetic schemes available in the literature. For further experimental investigations, a correlation is proposed to predict laminar burning velocity as a function of the quantity of O₂ and CO₂ in the gas mixture. Finally, analytical and experimental data concerning Markstein length are discussed.     

汽车空调暖风系统平行流换热器换热性能研究

平行流换热器以其结构紧凑、换热效率高的特点已广泛应用于汽车空调中.简要介绍了汽车空调暖风系统平行流换热器结构,采用计算流体力学(CFD)数值模拟方法对平行流换热器的换热性能进行了分析,比较了空气侧风速和水流量对其换热量和流动阻力的影响.模拟结果表明:在增加相同百分比的情况下,增加空气侧风速比增加水流量对换热器换热量的影响大16%左右,但增加空气侧风速和水流量对换热器换热能力的影响均有限;随着风速的提高,换热量增加率逐渐减小,而空气侧阻力增加率越来越大;随着水流量增加,水侧压降增大非常明显;但两者增加对空气侧出口温度影响均不明显.     

机车牵引电机冷却风道空气流场的分析

利用ANSYS FLOTRAN对机车牵引电机冷却风道内流场进行三维计算分析,获得了管道进出口压差和流量,为新型机车冷却管道的设计提供了可靠的依据。建议改进风道进出口形状,避免或减少流动分离,提高设备冷效率。     

Experimental study of humid air reverse diffusion combustion in a turbulent flow field

Experiments were performed to investigate the differences between the propane/air turbulent diffusion reactive flows past bluff-body and the propane/humid air turbulent diffusion reactive flows in the same conditions. The velocity distributions of the non-humid reactive flow fields and the humid reactive flow fields were measured by particle image velocimetry (PIV) techniques. The temperature fields were measured by high temperature thermocouples, and NO_x distributions were obtained by using gas detection instruments. The results show that although humid air reactive flow fields are similar to non-humid flow fields in general, there are some differences in the humid air combustion flow field comparing with the non-humid combustion flow field: the center of the reversed-flow region goes forward; the dimension of the reversed-flow region is smaller; the peak temperature and NO_x formation are reduced. It is suggested that humid air combustion is helpful to shorten the axial length of combustors, and reduce the formation of pollutants. __________ Translated from Journal of Shanghai Jiaotong University, 2006, 40(8): 1 287–1 292 [译自: 上海交通大学学报]     

Some studies on the flow passage dimension for solar air heating collectors

The effect of the dimensions of rectangular ducts through which air flows in solar air heaters on the air heater performance has been studied for laminar, transitional and turbulent flows. The collector performance and required pumping power to maintain the flow are assessed from a simple mathematical model. The effective energy collected has been determined for different case studies, and the duct depth has been optimised with respect to this effective energy. That is, an optimum duct depth is determined for different flow rates for collecting maximum energy at minimum pumping cost.     

Electrostatic probe measurement in an industrial furnace for high-temperature air conditions

Electrostatic probe measurements are reported that identify flame location, displacement speeds of reaction region, and other flame properties within an industrial furnace that is operated with high-temperature preheated air. The electrostatic probe has advantages over other methods when a furnace is operated with high-temperature air. The probe consisted of a fine detection wire and a supporting tube that played a role of the reference electrode. The reaction regions were found to be widely dispersed and weakened as they moved downstream. However, the ion-current signals still included many sharp peaks, perhaps associated with the thin reaction thickness, contrary to the flame structure expected from the high-temperature air combustion. It was also possible to estimate the displacement speeds of reaction region by using the cross-correlation method between two ion current records detected by parallel detection components. The results demonstrate that the electrostatic probe is useful to detect the structure and state of the reaction mode in industrial furnaces even in the presence of high-temperature air combustion.     

Unsteady Flow at Low Flow-rate Region in a Semi-open Propeller Fan （Velocity Fluctuation outside of Blade Tip）

In order to clarify the unsteady flow fields at low flow-rate region with positive gradient on pressure-flow-rate curve,the experimental investigation was carried out at rotor inlet and outside of rotor blade tip without casing in a semi-opened propeller fan using a hot-wire anemometer.A single I-type hot-wire probe was used,and the data obtained were processed by the use of phase-locked averaging,ensemble averaging and FFT analyzing.The flow fields at rotor inlet and outside of rotor blade tip were discuss...     

Modeling of the optimum tilt of a solar chimney for maximum air flow

The aim of this work is to develop a mathematical model to determine the tilt that maximizes natural air flow inside a solar chimney using daily solar irradiance data on a horizontal plane at a site. The model starts by calculating the hourly solar irradiation components (direct, diffuse, ground-reflected) absorbed by the solar chimney of varying tilt and height for a given time (day of the year, hour) and place (latitude). In doing so it computes the transmittance and absorbance of the glazing for the various solar irradiation components and for various tilts. The model predicts the temperature and velocity of the air inside the chimney as well as the temperatures of the glazing and the black painted absorber. Comparisons of the model predictions with CFD calculations delineate the usefulness of the model. In addition, there is a good agreement between theoretical predictions and experiments performed with a 1 m long solar chimney at different tilt positions.     

某下送风多功能厅气流组织及节能性的实测与分析

实测了采用下送风空调方式的某多功能厅的温度场和速度场。获得了夏季三种工况下的温度、速度分布及其随时间的变化。评价了该空调房间的节能性以及舒适状况。结果表明,在一定送风量和送风参数下能够满足舒适性要求,且具有较明显的节能效果,通风效率为1.7~3.2。     

射流理论在空调中的应用

本文以气流组织为例阐述了射流在空调中的应用及重要性,并对射流在空间形成的速度场进行了数学描述。