太阳能平板集热器关键参数对其热性能的影响

为了提升太阳能在建筑能源供给体系中的比重,形式多样的太阳能集热设备及其系统在建筑领域得到了广泛应用。基于机理分析法,建立了具有单层玻璃盖板的管板式太阳能平板集热器的稳态传热模型。并且针对集热管间距、集热管内径、工质入口温度和工质质量流量等关键参数对集热器集热效率的影响特性进行了数值模拟与分析。结果表明,建立的该稳态传热模型是可行的;此外,在其余参数值保持不变的情况下,减小集热管间距或增加集热管内径均可使集热器瞬时效率增大;增大工质入口温度会导致集热器瞬时效率下降;而增大工质质量流量会提升集热器瞬时效率。这些结论对于太阳能平板集热器在太阳能建筑一体化的实际应用中,具有一定的参考作用。     

An automated and semi-continuous method for the analysis of water-soluble constituents in PM(2.5)

An automated and semi-continuous method for measuring water-soluble constituents in PM(2.5) was developed. The system consists of a multi-tube diffusion scrubber (MTDS), a low temperature particle impactor (LTPI), an inertial air/liquid separator, and two ion chromatography systems. The MTDS acts as an interfering gas removal system and also as a humidifier for growing particles. Since the MTDS operates at 40 degrees C, the loss of volatile compounds and hydrological conversion of nitrogen oxides to nitrite were not of significant concern. The condensation of water vapor, dissolution of soluble constituents, and capture of insoluble particles occurred in the LTPI. The condensed liquid containing the dissolved species and the insoluble particles was separated from the airflow using an inertial air/liquid separator. The analysis of cations and anions in the effluent liquid was performed using two ion chromatography systems. The collection efficiency, including the inlet loss, of the system was 96.6+/-7.1% at an air flow rate of 1.0 SLPM. The limits of detection ranged from 12 to 57 ng/m(3) for major ionic constituents without any pre-concentration procedure. This method was tested in the field and the average data capture was over 90%, demonstrating the reliability of the system.     

环缝内衬旋风器除尘理论与实践

为提高除尘器的耐磨性和减少二次扬尘、提出在旋风除尘器内壁设置环缝内衬的增效防磨新方法。建立了具有在紊流边界层中由于流速不等而导致粉尘上下侧面压力不同所产生的二次扬尘影响下的旋风除尘器分级效率理论计算式。理论分析、半工业试验和工业应用实践的结果表明：环缝内衬旋风除尘器的除尘效率优于无环缝内衬旋风除尘器的除尘效率。     

入口截面高宽比对旋风分离器内流场的影响

气相采用雷诺应力模型(RSM)模拟,颗粒相采用拉格朗日坐标系随机轨道模型,模拟具有不同高宽比的入口截面下的旋风分离器内气固两相流流动特性。采用适当的高宽比,能使旋风分离器近壁面保持较高的气流速度,强化外旋涡,能使颗粒更容易被壁面捕集而分离,对提高分离效率有重要作用。     

Strength of sandy and clayey soils cemented with single and double fluid jet grouting

Innovations in jet grouting technology have primarily focused on the cutting efficiency of the jets, with the aim of creating larger columns and increasing the productivity of construction sites. Relatively little attention has been paid to the consequences of the grouting system on the mechanical properties of the formed material. This paper investigates this aspect by analysing the results of two field trials carried out in both sandy and clayey soils, where single and double fluid jet grouting were simultaneously performed, with varied grout composition and injection parameters. Parallel uniaxial compressive tests on samples cored from the columns show that the material formed with the double system is systematically lower in strength than the material formed using the single fluid system. The mineralogical composition of samples cored from the columns was analysed by performing parallel Scanning Electron Microscopy (SEM), X-ray diffraction analysis (XRD), Differential Thermal Analysis (DTA) and Thermo-Gravimetric Analyses (TGA) to determine the reasons for this difference. A lower proportion of cementitious products, an accelerated carbonation of portlandite and a less homogeneous distribution of cement hydration products was found on the surface of the soil particles of the double samples than for the single fluid columns.     

Preliminary evaluation of the applicability of sand transport formulae for use in Kuwait

Field experiments were conducted to measure sand transport rate using eight vertical sand traps and the speed of wind-blown sand in a natural setting. A Leatherman sand trap with an inlet width of 0.01 m and a height of 1.5 m was selected to measure sand flux in the field. The trap was assessed for its efficiency by comparing its collection of sand particles concurrently with the collection by a fence of 50% porosity and 2 m height, erected near the trap. It was found that such a trap design tends to under-collect material under variable winds by about 40% compared with the fence. The wind direction and speed were measured at five fixed heights: 2, 4, 6, 8 and 10 m and at 5-s intervals. Based on the available records, the wind shear velocity in eight directions was determined for the dates of collection in the sand traps. The sand transport rates were then predicted using four well-known sand transport equations. Setting the actual coefficients of these equations to a unity, the flux for each run was calculated and then compared with the calibrated flux derived from the trap collections. Empirical coefficients of these selected equations were evaluated and found to have higher values than those cited in the literature: C_B=3.5, C_Z=3.4, C_K=4.4 and C_L=6.1 for the equations proposed by Bagnold (1941), Zingg (1953), Kawamura (1951) and Lettau and Lettau (1978) respectively. Electronic Publication     

Effect of temperature on carbon nanoparticle collection efficiency using photoelectric ESP

The electrostatic precipitator (ESP) technique is a promising method for enhancing the particulate matter (PM) emission reduction efficiency of diesel engines, and is much better than the diesel particulate filter (DPF) technique. However, the ESP's low efficiency in collecting PM with diameters less than several tens of nanometers remains a problem because the particle charging efficiency decreases as the size of the nanoparticles decreases. To improve the collection efficiency of nanosized PM, we used a photoelectric charger to increase the charging efficiency of nanoparticles ahead of the ESP system. Carbon nanoparticles produced using a spark discharge generator were used to evaluate the collection efficiency of the combined photoelectric charger and ESP system. The particle sizes were measured using a scanning mobility particle sizer system at various experimental temperatures similar to the temperature of DPF systems commonly used in diesel engines. We succeeded in obtaining improved collection efficiencies at increased inner temperatures of the photoelectric charging chamber. As the temperature increased from 694 °C to 839 °C at the inlet of the photoelectric chamber, the efficiency of PM collection improved significantly to 28.5% for a particle diameter of 18.4 nm.     

地埋管换热器形式、管径及岩土温度对其换热性能的影响

建立了单U形与双U形地埋管换热器的三维数学模型。对外径25mm与32mm的单U形与双U形地埋管换热器换热性能的模拟研究表明,相同管径双U形地埋管换热器比单U形地埋管换热器换热量提高20%左右,但外径25mm的单U形地埋管换热器可以获得更大的进出口温差;对于双U形地埋管换热器,外径32mm与25mm相比,换热性能无明显优势;工程应用中,在地埋管用地面积充足时,建议选用外径25mm的单U形地埋管换热器,否则应选用外径25mm的双U形地埋管换热器;岩土温度每升高1℃,出口水温升高0.23℃,换热量下降5%左右。     

Experimental campaign to determine grated inlet clogging factors in an urban catchment of Barcelona

Urban drainage systems have two different drainage layers, one superficial and another underground, that are connected through drain inlets and manholes. Specifically, a collection system is formed by inlets distributed throughout a basin, with the function of collecting and directing the surface runoff into sewers. Generally, the hydraulic characterisation of the inlet system considers the grates in an ideal state, free of dirt and debris obstructions, although often this is not the case. In these cases, clogging effects should be considered as a reduction in terms of hydraulic efficiency. The aim of this paper is to present a methodology to determine, quantitatively, the hydraulic efficiency reduction of partially clogged grated inlets. With this aim, clogging patterns for the most common grated inlets operating in Barcelona (Spain) were defined and experimental tests at real scale were carried out in order to determine the hydraulic efficiency reduction due to clogging phenomena.     

Effect of face velocity and the nature of aerosol on the collection of submicrometer particles by electrostatic precipitator

Despite the electrostatic collection of aerosol particles as one of the most widely used air cleaning methods, there has not been sufficient amount of effort devoted to investigate its performance in the full range of operating conditions. This paper reports results of the tests of a two-stage electrostatic precipitator (ESP) conducted in the particle size range of 0.018-1.2 microns over a range of flow rates using NaCl and Environmental Tobacco Smoke (ETS) test aerosols. The total collection efficiency of the precipitator was found to increase with an increase in the count median diameter (CMD) of the particles, to have polynomial dependence on flow rate and no significant dependence on the type of test aerosol. The fractional efficiency of the precipitator was found to be dependent on flow rate. However, the 'critical' particle size of about 1.2 microns was found to exist when the fractional collection efficiency becomes independent of flow rate. For submicrometer particles, the collection efficiency was found to be independent of particle size at flow rates below 560 l/s. A minimum in the efficiency was observed in the 0.1-0.45 micron particle size range and for particles smaller than about 0.02 micron.     

单U形和双U形地埋管换热器传热模拟

以单U形和双U形地埋管换热器为研究对象,应用FLUENT软件对其传热性能进行了数值模拟。将计算结果与实验测试结果进行比较,验证了该模拟模型的准确性。结果表明,在排热工况下,单U形管换热器的单位井深换热量约为86 W/m,而双U形管换热器的单位井深换热量达到120W/m。在打井费用较高的场合,可以考虑使用双U形管。研究了进口水温、流速以及埋管深度等因素对U形管传热量的影响。     

高层住宅单、双层玻璃窗经济性比较

从使用、节能、投资等方面分析了武汉地区某高层住宅采用单、双层玻璃窗的经济性;认为在该地区,高层住宅采用双层玻璃窗比采用单层玻璃窗经济,单框双玻铝合金窗比双层钢窗经济。     

溴化锂吸收式热泵变设计工况分析

以单效溴化锂吸收式热泵为例,对系统进行热力计算。通过改变设计工况下某单一变量(驱动热源温度,热水进口温度,低温热源温度),分别分析了机组效率变化情况,得出热水出口温度与低温热源温度、驱动热源温度相互制约关系,即:不同低温热源下热水进、出口温度有最大值。不同驱动热源温度下热水出口温度有最大值。     

MATLAB modelling and examination of the effect of heat capacity of basin and glass cover on performance of solar still by thermal models

There are numerous researcher-developed mathematical models for single slope passive solar stills which considered the effect of heat capacities of basin and glass cover as negligible. The negligence parameter also plays a vital role in the prediction of the thermal performance of the system. In this paper, an effort has been made to evaluate the cumulative yield, energy efficiency and exergy efficiency of a single slope passive solar still with and without considering the heat capacities of basin and glass cover by using various thermal models such as Dunkle’s model, Zheng Hongfei et al.’s model and Tsilingiris model. These models were studied and compared with and without considering the heat capacity of solar components such as basin and glass cover. The thermodynamic model of this system is developed, and executed in a MATLAB code. By comparing the theoretical values of the cumulative yield, energy efficiency and exergy efficiency, it was found that consideration of the heat capacities of glass cover and basin gives a higher output in all the thermal models.     

Numerical study on PM10 collection efficiency in a wire-cylinder electrostatic precipitator under multi-field coupling

The PM10 collection efficiency of a wire-cylinder electrostatic precipitator (ESP) was studied by means of a developed mathematical model, including the multi-field coupling between the gas flow field, the particle dynamic field and the electric field, and applying the Deutsch–Anderson Equation. The diffusion charging mechanism was considered due to the diameter range of PM10. The investigated variables were the applied potential, the gas velocity and the particle distribution. Numerical results indicate that the diffusion charging has significant influence on PM10 removal performance and the effect is more obvious with the decreasing diameter, and that the PM10 collection efficiency increases with the increasing applied potential and the increment of collection efficiency is more significant at lower voltage. Moreover, as the gas velocity at inlet decreases, collection efficiency of PM10 will increase. Finally, the overall efficiency increases with increasing the mean diameter of particle distribution. The research results can provide theoretical and technical references for the design of novel ESP aiming at economy and environment protection.     

Calibration parameters for the integrated silver method for mercury in air. II

The analytical parameters for the measurement of mercury in air have been investigated for the integrated silver method. The ultimate sensitivity of the method and the reproducibility of the standard curve are discussed. The proper storage of the activated silver absorber is described, as well as the storage of a mercury-air sample on the silver element.The collection efficiency for mercury has been found to be quantitatively reversible, with respect to both capture and release. The collection process on silver is highly specific for mercury. Benzene, for example, is not retained on silver, though it can give a spurious response when sampled directly by a “continuous” ultraviolet photometer. Most commonly encountered organic vapors, which give a response at mercury absorption wavelengths, are not retained by the silver element and do not, therefore, interfere with subsequent ultraviolet measurement of the desorbed mercury vapor.For ambient air sampling, the optimum flow-rate was found to be 1.51/min. This also proved to be a suitable flow-rate for desorption and assay. Pure air, as carrier, has been found to be satisfactory, since no differences have been noticed when comparative measurements have been made using inert gases.Instrumental measurement by means of a digital integrator has been found to be superior to a recorder output using peak height. Peak area measurement, by integrator, is not affected by the rate of diffusion of the mercury vapor within the sampling system and optical train.     

《中山市污水工程专项规划》编制中的三个问题

<中山市污水工程专项规划>编制中存在污水量指标、污水处理率、污水收集系统布置等方面的问题,建议在多专业、多学科的配合下,在充分调查研究的基础上得出接近实际情况的用水量预测结果,且不宜采用过高的指标;政府可将根据管网收集污水量计算的污水处理率作为考核指标,提高污水处理设施的效益,保证城镇污水处理厂投入运行后的实际处理负荷能力;优化污水收集系统的布置,落实污水泵站的用地,并在设计文件中体现.     

Oil removal from water in parallel plate gravity-type separators

Aspects of oil removal by gravity separation in parallel plate separators have been investigated both theoretically and experimentally. Attention has been paid to the possible influence of retention time distribution, co- or countercurrent flow (in tilted plate separators) and to the effect of perforation of the plates. Perforation enables an easy removal of separated oil in horizontal plate separators. It appears that the overflow rate-related to the horizontal projection of the real plate area-determines the performance of a plate separator in all these cases. A residence time distribution will lower the separation efficiency only when it is caused by a velocity profile over the width of the tank or by an extremely unequal distribution of the influent over the plates. A tilted full plate separator and a horizontal perforated plate separator with the same overflow rate perform equally well as to separation efficiency; only secondary, practical reasons will determine the choice between either construction.     

含硫气田水微正压气提过程分析优化

针对含硫气田水正压气提效率低、负压气提设备投资较高且工艺流程较为复杂的问题,开展了微正压气提除硫实验。同时采用Aspen Plus软件进行微正压气提过程模拟分析,以气提效率和水处理成本作为评价指标,分析了气水比、塔压、进水pH、进水流量和进水硫化物含量对气提效果的影响。结果表明,微正压气提在进水pH为4.5~5.5、塔压30 kPa以下、气水比为6~10条件下,气提效果较好。现场应用表明,优化后微正压气提平均效率为93.15%,相比优化前气提效率提高了13.86%,年可节约水处理成本约46.11万元,为同类含硫气田水处理技术提供了一定的参考。     

Wind tunnel-based testing of a photoelectrochemical oxidative filter-based air purification unit in coronavirus and influenza aerosol removal and inactivation

Recirculating air purification technologies are employed as potential means of reducing exposure to aerosol particles and airborne viruses. Toward improved testing of recirculating air purification units, we developed and applied a medium-scale single-pass wind tunnel test to examine the size-dependent collection of particles and the collection and inactivation of viable bovine coronavirus (BCoV, a betacoronavirus), porcine respiratory coronavirus (PRCV, an alphacoronavirus), and influenza A virus (IAV), by a commercial air purification unit. The tested unit, the Molekule Air Mini, incorporates a MERV 16 filter as well as a photoelectrochemical oxidating layer. It was found to have a collection efficiency above 95.8% for all tested particle diameters and flow rates, with collection efficiencies above 99% for supermicrometer particles with the minimum collection efficiency for particles smaller than 100 nm. For all three tested viruses, the physical tracer-based log reduction was near 2.0 (99% removal). Conversely, the viable virus log reductions were found to be near 4.0 for IAV, 3.0 for BCoV, and 2.5 for PRCV, suggesting additional inactivation in a virus family- and genus-specific manner. In total, this work describes a suite of test methods which can be used to rigorously evaluate the efficacy of recirculating air purification technologies.