共查询到20条相似文献，搜索用时 31 毫秒
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Bert G. Heusinkveld Adrie F.G. Jacobs Albert A.M. Holtslag 《Agricultural and Forest Meteorology》2008,148(10):1563-1573
Open-path gas analyzers are popular in eddy covariance flux measurements of trace gasses (i.e. CO2). The quality of the data, however, may be influenced by several factors. Exposure in an outdoor environment invariably causes the instrument to become colder or warmer than the air temperature. Instruments with internal temperature regulation and/or from heat generated by active electrical components can also influence the sensor temperature. In addition, sensors can have condensation problems on their optical windows thus affecting the quality of the measurement. Unreasonable measurements have been widely discussed, especially in moist, high-latitude regions. As this is a very important research problem facing flux studies, we examined how wetness (dew and raindrops) on the surface of the focus lens of the popular LI-COR LI-7500 infrared gas analyzer may affect flux measurements from the open-path eddy-covariance system. Field experiments showed that additional sensor heating may inhibit dew formation yet greatly improve the quality of flux measurements. A detailed energy balance approach was used to model the gas analyzer window temperature under environmental conditions and dew effect through a pair of LI-COR LI-7500, with and without heat treatment, in a grassland ecosystem in the Netherlands. With the proposed model, existing datasets can be filtered for dew events. Data from three different flux measurement sites were then used to assess the magnitude of dew effects on longer time-scales; 2 years from the Netherlands and 3 weeks of data from an arid coastal desert. About 30% of the measurements were affected by dew in the grassland area versus 4% in the arid region during the dry season. Sensor heating suppresses dew formation but might lead to errors in trace gas fluxes evaluated over long periods, thus we analyzed how sensor heating or cooling affects trace gas flux measurements. Additions to a recent (2006) correction and application to a horizontally and vertically oriented LI-COR LI-7500 are presented as they deal with sensor heating problems in eddy-covariance systems. The sensor energy balance model, together with the proposed modified sensor heating corrections, were used to estimate sensor temperature effects on long-term scale CO2 flux measurements and showed that additional heating does affect the turbulent trace gas CO2 fluxes but is very minor, especially for a horizontally mounted LI-COR LI-7500 gas analyzer. Further efforts are urgently needed to improve the data quality and quality of flux measurements. 相似文献
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日光温室热压风压耦合自然通风流量的模拟 总被引：2，自引：0，他引：2
通风是温室环境调节的重要手段,通风流量计算涉及流量系数与风压体型系数,因此有必要定量分析不同通风模式下的通风流量及对应的系数,为通风调节提供理论依据。本文分析了热压风压耦合作用对通风流量的影响机理,构建了通风流量与热压风压作用关系的数理模型;采用CO2气体示踪法测试日光温室模型(按1:5的比例缩小)在不同通风口宽度条件下的通风流量,将试验测得的通风流量、空气温度、风速和通风口宽度等参数代入模型,对模拟值与实测值进行多元线性拟合,得出拟合度最高的流量系数与风压体型系数。结果表明：当温室模型通风口宽度为3、5和7cm（相当于实际温室通风口宽度为15、25、35cm）时,热压风压耦合作用的通风流量可按G=0.81S•（H•?T/T)0.5 +0.078S•u、G=0.63S•（H•?T/T)0.5 +0.067S•u 和G=0.46S•（H•?T/T)0.5 +0.058S•u分别计算,式中S、H、?T、T、u分别为通风口面积、宽度、室内外温差、室外温度和风速;相应的流量系数分别为0.78、0.60和0.44,风压体型系数分别为0.04、0.05和0.07;在总通风流量中,当室外风速高于1.5m·s-1时,风压通风流量所占总通风流量的比例均高于50%,风压通风占主导作用;当室外风速大于2.5m·s-1时,风压形成的通风流量所占比例均大于70%,说明此条件下可忽略温度即热压的影响。 相似文献
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A new type of passive sampler for the determination of NH3 emission from land surfaces and manure storages was tested in a micrometereological mass balance method. The sampler consists of 2 glass tubes, each with a length of 10 cm and an internal diameter of 0.7 cm. The two glass tubes are connected in series, with one end fitted with a thin stainless steel disc having a 1 mm hole in the center. The inner surface of each glass tube is coated with oxalic acid. The results show that the passive flux sampler can be used to give accurate determinations of NH3 emission. The passive flux sampler makes gas washing bottles, pumps, flow meters, anemometers, and electricity unnecessary and ammonia loss can be determined easily and cheaply without the requirement of a large labor force. 相似文献
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基于光伏光热的地下空间太阳能烟囱效应影响因素研究 总被引：3，自引：3，他引：0
提出了将太阳能烟囱效应与太阳能光伏光热(PV/T)技术相结合来强化地下空间通风的技术措施.为研究该通风模式的影响因素,基于质量和热量平衡理论,建立了风井通风性能的数学模型,分析了换热器管排数、风井高度、热水水温和流速对通风性能的影响.结果表明:风井内换热器存在最大有效管排,管间距为0.032、0.038、0.047 m时换热器的最大有效管排数分别为9、13、18,在有效管排数范围内,随着管排数的增加风井出口温度升高,通风量先增大后减小;空气质量流量随着风井高度增加、热水温度升高明显增大,随着热水流速增大而缓慢增大;风井出口空气温度随着风井高度增加而降低,随着热水温度升高、流速增大而升高.最后,通过拟合得到计算风井空气质量流量的经验公式. 相似文献
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Vents and seals in non-steady-state chambers used for measuring gas exchange between soil and the atmosphere 总被引：3，自引：0，他引：3
Despite decades of research to define optimal chamber design and deployment protocol for measuring gas exchange between the Earth's surface and the atmosphere, controversy still surrounds the procedures for applying this method. Using a numerical simulation model we demonstrated that (i) all non‐steady‐state chambers should include a properly sized and properly located vent tube; (ii) even seemingly trivial leakiness of the seals between elements of a multiple‐component chamber results in significant risk of measurement error; (iii) a leaking seal is a poor substitute for a properly designed vent tube, because the shorter path length through the seal supports much greater diffusive gas loss per unit of conductance to mass flow; (iv) the depth to which chamber walls must be inserted to minimize gas loss by lateral diffusion is smaller than is customary in fine‐textured, wet or compact soil, but much larger than is customary in highly porous soils, and (v) repetitive sampling at the same location is not a major source of error when using non‐steady‐state chambers. Finally, we discuss problems associated with computing the flux of a gas from the non‐linear increase in its concentration in the headspace of a non‐steady‐state chamber. 相似文献
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A new sampling technique for measuring the concentrations of trace gases (CH4, CO2 and N2O) in the soil atmosphere from well‐defined depths is described. Probes are constructed from silicone tubing closed with silicone septa on both ends, thereby dividing an inner air space from the outer soil atmosphere without a direct contact. The gas exchanges between the inner and outer atmosphere only by diffusion through the walls of the silicone tube. Tests revealed that the gases N2O, CO2 and CH4 in the enclosed space reached 95% equilibrium with the surrounding atmosphere at 20°C within 7 h or faster. The probe measurements are reproducible: the standard deviation of samples taken from 26 probes stored in the laboratory atmosphere equalled that of a standard gas. The probes can easily be constructed and installed at specified depths in the soil. The method has the following advantages compared with other methods that use spaces with holes in them for gas exchange: (i) the silicone probe enables trace gases to be sampled in wet soils, including ones that are waterlogged or temporarily saturated; (ii) the sampling itself does not create low pressure and hence does not create mass flow in the soil matrix from undefined depths; and (iii) the probe can be made to take samples of gas of any required size. The silicone probes did not show ageing effects during 18 months of use in the field in a mineral soil under grass. The probes yielded comparable results: three probes inserted at 5 cm depth in a uniformly treated 100‐m2 plot provided nearly identical average trace gas concentrations within the measurement period. 相似文献
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A new procedure (HMR) for soil‐atmosphere trace‐gas flux estimation with static chambers is presented. It classifies data series into three categories according to criteria based on the application of a particular non‐linear model and provides statistical data analyses for all categories. The two main categories are non‐linear and linear concentration data, for which data are analysed by, respectively, the non‐linear model and linear regression. The third category is represented by concentration data within the range of experimental error, or noise, from sites with no significant flux. Data in this category may be analysed by linear regression or simply classified as no flux. The particular non‐linear model has been selected among alternatives because its exponential curvature generally fits non‐linear static chamber concentration data well, and because it can be proven, mathematically, to be robust against horizontal gas transport through the soil or leaks in the chamber. The application of the HMR procedure is demonstrated on 244 data series of nitrous oxide accumulation over time. On average, 47% of these data were non‐linear, with an average flux increase over linear regression of 52%. The classification and analysis of data with a small signal‐to‐noise ratio requires special attention, and it is demonstrated how diagnostic graphical plots may be used to select the appropriate data analysis. The HMR procedure has been implemented as a free add‐on package for the free software R and is available for download through CRAN ( http://www.r‐project.org ). 相似文献
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A re-examination of closed flux chamber methods for the measurement of trace gas emissions from soils to the atmosphere 总被引：2，自引：0，他引：2
The most widely used method for measuring the emission of a trace gas such as N2O from soil to the atmosphere involves the accumulation of the gas under closed chambers followed by sampling and analysis (by gas chromatography or infrared methods). These chambers can affect the gas exchange, and so improved designs have been proposed. We have tested their performance. One design includes a vent tube to allow ambient pressure fluctuations to occur also inside the chamber. We tested it against a sealed version on two different grassland sites during N2O peak emissions in spring 1997. On a welldrained soil with a fairly large air permeability vented chambers yielded fluxes as much as five times those of sealed chambers, depending on wind speed. By contrast, on a heavier and wetter soil with smaller air permeability vented chambers averaged only 88% of the fluxes observed with sealed chambers. The effects of venting cannot be explained solely on the basis of mean pressure differences inside and outside the chamber. It seems more likely that wind blowing over the vent depressurizes the chamber (Venturi effect), resulting in significant gas flow from the more permeable soil into the interior of the chamber. The opposite trend for the less permeable soil suggests that diffusion losses through the vent tube are greater than the increase in concentration due to soil gas flow. Venting can create larger errors than the ones it is supposed to overcome. 相似文献
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苜蓿气体射流冲击联合常温通风干燥装备设计及试验 总被引：2，自引：2，他引：0
针对苜蓿干燥存在的处理量小、耗能高、叶片损失率高的问题,该文将紫花苜蓿的干燥过程分为高温和常温两个干燥段,设计了气体射流冲击联合常温通风干燥装备,包括基于狭缝型气体射流冲击管的气体射流冲带式干燥机和基于环境条件自动控制的常温通风箱式干燥机。利用计算流体动力学软件Fluent对狭缝型气流冲击管内部的流场进行数值模拟。结果显示增设扰流板可以改善狭缝型气体射流冲击管喷嘴出口气流速度分布的均匀性,速度变异系数由不设扰流板情况下的51.1%降为7.7%;利用单片机控制系统进行信息采集并控制通风的进行,解决夜间物料吸湿回潮、发热的问题。以紫花苜蓿作为原料对干燥装备的性能进行试验验证,结果表明:气体射流冲击联合常温通风干燥的苜蓿具有批次处理量大(150 kg/h)、叶片损失率小(干草的叶片损失率为1.5%)、能耗低(单位去水能耗3 408 k J/kg)的优点。研究结果为低能耗、低叶片损失率的苜蓿干燥技术与装备提供参考。 相似文献
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农户用机械通风钢网式小麦干燥储藏仓的气流场分析 总被引：1，自引：1，他引：0
为保障农户收获后高水分粮食不落地安全储藏,针对一种仓壁透气中心带通风立筒的圆形钢网式农户储粮干燥仓,应用CFD法对收获后高水分小麦在进行机械通风时的气流场进行仿真分析,将仓内小麦堆等效为多孔介质,分析静压、动压、流量等空间分布规律。结果表明:仓内静压和动压值随半径(横向)增加呈指数衰减;柱面流量随半径呈幂函数衰减;横截面流量随高度呈指数衰减;粮堆区竖向通风均匀度显著优于横向(径向);流量分布为仓底上粮面仓壁,仓壁气流流量只占总流量的24.6%;实仓风速测试结果与仿真分析结果规律一致,平均相对误差为16.35%,表明基于多孔介质模型和CFD法分析钢网式储粮干燥仓的流场分析具有较好的准确性,研究结果为此类钢网式储粮仓流场分析和优化提供了方法和依据。 相似文献
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Jae-Cheol Nam Deb J. Fish Alan J. Thorpe Soon-Ung Park 《Water, air, and soil pollution》2001,130(1-4):361-366
A quantitative study of the amount of air transported between the boundary layer and the free atmosphere is important for understanding air quality and upper tropospheric ozone, which is a greenhouse gas. Frontal systems are known to be an effective mechanism for the vertical transport of pollutants. Numerical experiments have been performed with a simple two-dimensional front model to simulate vertical transport of trace gases within developing cold fronts. Three different trace gases experiments have been done numerically according to the different initial fields of trace gases such as aerosol, ozone and H2O2. Trace gas field tilts to the east while the front tilts to the west. Aerosol simulation shows that pollutants can be transported out of the boundary to altitudes of about 10 km. The stratospheric ozone is brought downwards in a tropopause fold behind of the frontal surface. The meridional gradient in trace gas (H2O2) can cause a complicate structure in the trace field by the meridional advection. 相似文献
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开发大功率气体燃料发动机,利用沼气等绿色能源发电已经成为当前内燃机行业发展的重要课题之一。气体发动机对各缸进气均匀性的要求较高,气体发动机经常出现各缸进气不均匀的现象,从而影响发动机的动力性、排放性和可靠性。该研究利用数值分析方法求解,模拟CW6200型气体发动机进气系统内的流动情况,通过分析流动区域的压力场、速度场等参数对各缸进气均匀性进行了评价,同时分析了进气系统的流动阻力,优化设计了发动机的进气系统结构参数。数值分析及发动机性能试验表明：采用两级谐振系统后各缸流动不均匀性绝对值小于3%,各缸排温不均匀性绝对值小于2.5%,发动机动力性较好。因此,两级谐振系统可以有效改善进气总管预混式气体发动机的进气均匀性,提高发动机性能。 相似文献
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基于土体裂隙迹线方程和土体扰动模型的气爆松土参数优化 总被引：2，自引：2，他引：0
为明晰气爆技术对土壤的深松效果,采用剖面法观测土体裂隙及扰动情况,设计正交试验分析气爆参数对土体裂隙扩展的影响,建立了气爆土体裂隙迹线方程及土体扰动模型,讨论了土体破坏形式对松土效果的影响,结果表明:气爆深度小于25 cm时,土体以张拉破坏为主,气爆起劈力为0.17 MPa,土面易抬升,裂隙中心为气爆中心,裂隙扩展随气压增大而增大,土体扰动系数为50%;气爆深度大于25 cm时,土体以剪切破坏为主,气爆起劈力为0.39 MPa,土面抬升不明显,土体裂隙中心下移,且下移量随气压增大而增大,土体扰动系数大于50%,松土效果优于张拉破坏;气爆深度为30 cm、气爆压力为1 MPa左右较适宜。该研究可为气爆松土参数优化提供参考。 相似文献
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为提高秸秆热解气的净化率,防止装置堵塞,该研究设计了旋风分离器与回转指杆轮相结合的两级净化装置,I级旋风分离器主要分离热解气中大粒径杂质,II级指杆轮使小粒径灰尘、焦油等杂质与锥形指杆碰撞、聚集、并在高速回转作用下离心分离,实现热解气高效净化。研究确定了I级净化装置的结构参数,设计了II级净化装置,确定了指杆轮与锥形指杆的参数及排列方式。以指杆轮转速、热解气的进口速度和芯筒入筒体深度为影响因素,以热解气的净化率和压力损失为指标,进行了二次通用旋转组合样机性能试验。利用Design-Expert8.0.6软件对试验数据进行方差和响应面分析,建立了影响因素与指标之间的数学模型,采用多指标优化法确定最优组合并进行了试验验证。试验得到最优组合参数:指杆轮转速为3 030 r/min,进口速度为19.5 m/s,芯筒入筒体深度为210 mm,此时的压力损失为1 971.73 Pa,热解气总净化率为84.2%,达到了净化要求。研究结果可为秸秆热解气净化装置研究提供理论依据。 相似文献
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J.J. Finnigan 《Agricultural and Forest Meteorology》2009,149(3-4):725-729
Kowalski correctly points out that the analysis in [Finnigan, J.J., 2006. The storage term in eddy flux calculations. Agric. Forest Meteorol., 136, 108–113] ignores the interplay between the storage terms and the WPL corrections. In this note we develop an expression for the vertical convective velocity that accounts for the effect of both the ‘steady state’ and unsteady ‘storage’ WPL terms on the flux of a trace gas like CO2 measured with an open path sensor and sonic anemometer. The expression is derived using the mass density rather than the mixing ratio so that the eddy fluxes take the conventional covariance form that is commonly used in turbulence textbooks. 相似文献
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基于CFD的养殖污水净化内循环流化床反应器结构优化 总被引：2，自引：2，他引：0
针对水产养殖污水净化对内循环流化床反应器的相关要求及流化状态下反应器结构、操作参数与相流体力学行为的密切关系,该文利用构建的描述不同结构、操作参数反应器气液两相流动的计算流体力学数学模型,分析了不同结构、操作参数下反应器液体流场、液体循环流量、气含率的变化规律,得到了对于内径200 mm、底部采用均孔布气盘的反应器,在表观气速为0.5~2.5 cm/s时,导流筒与反应器的内径比0.5,导流筒高度与反应器内径比6,导流筒下端到反应器底部距离50 mm,导流筒上端到液面距离100 mm为最优值;针对液体循环流量,使用相关数学模型求解理论值并与试验值进行比对,通过偏差分析探究了数学模型应用的局限性;使用MATLAB最小二乘法拟合了反应器在最优结构参数下表观气速与液体循环流量、气含率的关系,验证了拟合公式的精确性。该研究为内循环流化床反应器在水产养殖污水处理中的设计应用提供理论和技术参考。 相似文献
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硅胶管气样原位采集技术研究土壤N_2O浓度及通量变化 总被引：3，自引：1，他引：2
箱法被广泛用于监测土壤N_2O排放通量,但在原位采集高浓度土壤N_2O、全天候监测N_2O通量变化、动态研究土壤剖面N_2O的行为等方面存在弊端.本研究通过室内模拟硅胶管对N_2O的通透性,探索硅胶管用于原位采集土壤气样的理论可行性.田间试验设施用铵态氮肥(NH_4~+)、施用硝态氮肥(NO_3~-)及施用硝态氮肥加葡萄糖(NO_3~-+C)等3个处理,同时安置硅胶管和采样箱,验证硅胶管法在原位采集高浓度土壤N_2O气样、监测土壤N_2O浓度以及排放通量的实际效果,并与箱法进行比较.结果表明,硅胶管内外的N_2O气体经2.9 h达到95%的平衡,完伞能满足大田采样要求;用硅胶管法原位采集高浓度土壤N_2O气样的效果显著优于箱法采样.其浓度变化表现出明显的时间规律,浓度梯度法计算的N_2O排放通量与箱法测定结果呈显著正相关,但数值偏低;偏低的程度取决于采样位置和土壤中N_2O产生位置的匹配程度.建议采用埋于土壤表层的硅胶管计算地面N_2O排放通量,或在不同土层埋人硅胶管研究土壤剖面N_2O行为的时空变异. 相似文献
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A method based on disposable pipet extraction (DPX) sample cleanup and gas chromatography with mass spectrometric detection by selected ion monitoring (GC/MS-SIM) was established for 58 targeted pesticide residues in soybean, mung bean, adzuki bean and black bean. Samples were extracted with acetonitrile and concentrated (nitrogen gas flow) prior to being aspirated into DPX tubes. Cleanup procedure was achieved in a simple DPX-Qg tube. Matrix-matched calibrations were analyzed, and the limits of quantification (LOQ) of this method ranged from 0.01 mg kg(-1) to 0.1 mg kg(-1) for all target compounds. Coefficients of determination of the linear ranges were between 0.9919 and 0.9998. Recoveries of fortified level 0.02 mg kg(-1) on soybean, mung bean, adzuki bean and black bean were 70.2-109.6%, 69.1-119.0%, 69.1-119.8%, and 69.0-120.8%, respectively, for all studied pesticides. Moreover, pesticide risk assessment for all the detected residues in 178 market samples at Beijing market area was conducted. A maximum 0.958% of ADI (acceptable daily intake) for NESDI (national estimated daily intake) and 55.1% of ARfD (acute reference dose) for NESTI (national estimated short-term intake) indicated low diet risk of these products. 相似文献