磁力泵冷却循环回路的设计及数值模拟

为避免磁力泵温升过高导致永磁体退磁及隔离套损坏,该文对磁力泵冷却循环回路的设计方法进行了探讨,采用ANSYS-APDL软件计算出了隔离套的涡流发热,根据热平衡确定冷却循环流量并设计了冷却循环回路。基于SIMPLEC算法和标准k-ε湍流模型,通过求解三维N-S方程及能量方程,对冷却循环回路内部流场及温度场进行了数值分析。从数值模拟可以看出,冷却循环回路内部流动为圆周运动和直线运动合成的螺旋运动。对比内循环、外循环2种方式表明,内循环方式隔离套底部温升最高、压力较低;外循环方式温度场分布较均匀,最高温升小于10 K,满足设计要求。在冷却循环流量相同的情况下,轴孔孔径在设计尺寸一定范围内波动对外循环方式的冷却效果影响不大,轴孔分别为3、4、5 mm,其最高温升分别为9.2、9.3、9.4 K并且分布基本相同。通过分析不同转速下冷却循环回路的流场、温度场,发现当内磁转子不转动时,流场最高温度达到了386 K,而随着转速的增加最高温度逐步降低,表明增加泵的转速能够促进不同流体层间的热量交换,改善冷却循环回路的冷却效果。该研究可为磁力泵冷却循环回路的设计提供参考。     

Effect of moving mean covariance adjustments on error and genetic variance estimates and selection of superior lines in peanuts (Arachis hypogaeal L.)

Summary Effects of moving mean covariance adjustments on error control, genetic variance component estimates and selection were examined in nine trails in peanut breeding nurseries. Neighbourhood sizes of two to fourteen adjacent plots were used in two types of moving mean covariates: one based on adjacent plot yields and a second based on adjacent plot residuals after removal of replicate and treatment effects. Both covariate types reduced error variance, in one trial by up to 57%, although the covariate type giving the most error reduction varied among trials. Generally most error variance reduction occurred when six to eight adjacent plots were used.In some trials genetic variance component estimates following covariance adjustment were higher than those from unadjusted analyses and in other trials they were lower. As the neighbourhood size included in the moving mean increased from two to fourteen plots the genetic variance component estimate changed considerably in some trials. However, large rank changes did not appear to be associated with these genetic variance component changes as neighbourhood size had little influence on the selection of progenies. Also, genetic effects included in the yield covariate had little influence on selection of elite lines as essentially the same lines were chosen or rejected when residual covariates lacking these genetic effects wre used.     

Polymorphisms of α-amylase activity in barley landraces and cultivars from China

Summary -Amylase activity was assayed by measuring reducing power equivalent for 80 accessions of cultivated barley, Hordeum vulgare L., representing major barley growing areas of China. Replications were applied at two different levels of the experiment and enzyme activity was assayed on four consecutive days starting on the 6th day after germination. The area under the curve formed by connecting the four data points was integrated as the measurement of -amylase activity. The results established that there was extensive variation in -amylase activity in cultivated barley; about three-fold difference existed among accessions assayed. Comparisons were also made between six- and two-rowed, and between covered and naked barleys. The results showed that high -amylase activity was not necessarily associated with six-rowed type, and that covered barleys were slightly higher in -amylase activity than naked ones.     

淡水养殖塘甲烷通量观测时段的选取对年排放量的影响研究

淡水养殖塘是甲烷（CH₄）排放的热点区域。准确观测CH₄年排放量还存在较大挑战,尤其是采用低频的观测方法。因此,本研究以亚热带长江三角洲区域典型淡水养殖塘为研究对象,基于涡度相关方法（Eddy covariance,EC）测定的2016—2020年养殖塘水-气界面高频连续CH₄通量数据,探讨了对淡水养殖塘CH₄通量进行箱式法等低频观测时,在一日内的最佳观测时间以及一年内的最佳观测日数,从而实现对CH₄年排放量的准确估算。结果表明：一日当中最佳的观测时间春季为14：30—16：30、夏季和秋季为6：30—8：30、冬季为11：30—13：30,与EC连续观测获取的各季节日均值比较,以上选取方案估算的日均值不确定性最小,变化范围为0.1%~4%;在准确估算日均值的基础上,对于一年内的最佳观测天数,建议至少需要在全年均匀选取80 d,即观测频率为每月6~7 d,且均匀分布在每月的上中下三旬,才能够达到一年内连续观测获取的年均值±20%之内的高精度估算。当全年观测日数少于20 d时,CH₄通量年均值估算的不确定性可高达50%。该研究结果可在无高频连续CH₄通量观测前提下,为养殖水体CH₄通量观测时段方案设计以及降低内陆水体碳收支估算不确定性等提供科学依据和参考。     

改进型INTER-MIG桨尾涡结构的PIV试验与模拟

采用粒子图像测速(PIV)技术和计算流体力学(CFD)对改进型INTER-MIG桨釜内尾涡结构进行研究,将数值模拟结果与PIV试验进行了比较,分析了几种湍流模型的差异;利用2D-PIV对尾涡结构进行涡量分析,并探讨桨叶直径对尾涡的影响,以及尾涡与湍动能之间的关系.结果表明:LES对尾涡的预测优于Reynolds平均法;改进型INTER-MIG桨在运动过程中产生运动轨迹不对称的上下尾涡,桨叶下尾涡先于上尾涡形成,下尾涡最大涡量高于上尾涡;在尾涡形成到发展至最大的过程中,桨叶直径对下尾涡的径向位移影响较大,在桨叶直径D/T=0.57时,桨叶下尾涡沿径向方向运动最快,湍动能最大;当尾涡开始衰减后,桨叶直径越大,尾涡耗散的速度越快;湍动能最大值介于两尾涡之间,且伴随着尾涡的发展而增大,随其衰弱而减小.研究结果表明改进型INTER-MIG桨釜内的搅拌机理,可以为该桨叶釜内的工程和优化设计提供参考.     

小兴安岭天然阔叶混交林生长季CO_2通量特征分析

森林生态系统CO2通量的研究已成为全球变化研究的热点之一。本文采用开路式涡度相关系统对小兴安岭天然阔叶混交林CO2通量进行为期1a的连续观测（2008年）,分析了生长季（5-9月）CO2通量的变化特征。结果表明,在生长季,天然阔叶混交林系统的CO2通量变化范围为-0.46～0.42mg.m-2.s-1;最大吸收量出现在6月份的9：00,最大释放量出现在7月份的5：00。白天气温低于26.63℃时,碳吸收量随气温的升高而加大;但气温超过26.63℃后,则呈相反趋势。夜晚气温在13.50℃时的碳释放量最大。2008年整个生长季呈现白天碳吸收,夜晚碳释放的现象,总体表现为碳吸收,吸收总量为212.32g.m-2。     

Cross-evaluation of measurements of peatland methane emissions on microform and ecosystem scales using high-resolution landcover classification and source weight modelling

The methane exchange in an oligotrophic mire complex was measured on the ecosystem and microform scale with the eddy covariance (EC) and the closed chamber technique, respectively. Information about the distribution of three distinct microform types in the area of interest and in each 30 min EC flux source area was derived from a high-resolution (1 m²) landcover map in combination with an analytical source weight model (Kormann and Meixner, 2001). The mean weighted coverage of flark, lawn and hummock microforms in the EC source area (0.3% : 57% : 43%) closely mirrors the overall distribution in the area of interest (0.5% : 50.1% : 49.4%), despite great differences in microform coverage between individual 30 min EC source areas. The measured ecosystem flux was fitted to the sum of three microform flux models based on environmental variables and weighted by their fractional coverage in the EC source area. This method resulted in a better representation of the ecosystem flux compared to an approach based on only one flux model for the whole ecosystem (R² = 0.87, RMSE = 0.44 vs. R² = 0.74, RMSE = 0.61, n = 5181) and thus constitutes a successful down-scaling of measured ecosystem scale flux to the microform scale. A comparison of down-scaled and measured microform fluxes reveals a good agreement for lawn microforms and systematic differences for flark and hummock microforms. Reasons for the differences are thought to be the limited resolution of the landcover classification and the systematic underestimation of hummock fluxes by the closed chamber technique. As a result, hummock fluxes derived by down-scaling of EC fluxes are considered to be more dependable than closed chamber fluxes. The seasonal ecosystem methane budget from gap-filled EC measurements was 9.4 ± 0.2 g CH₄ m⁻²; the budget derived from up-scaled microform measurements was 8.0 ± 0.8 g CH₄ m⁻². The lower value of the latter budget is attributed to the underestimation of flark and hummock fluxes by closed chamber measurements and to the microform gap-filling procedure. Generally, estimates from up-scaled microform measurements are found to be less certain than estimates from EC measurements.     

Increasing net CO2 uptake by a Danish beech forest during the period from 1996 to 2009

The exchange of CO₂ between the atmosphere and a beech forest near Sorø, Denmark, was measured continuously over 14 years (1996-2009). The simultaneous measurement of many parameters that influence CO₂ uptake makes it possible to relate the CO₂ exchange to recent changes in e.g. temperature and atmospheric CO₂ concentration. The net CO₂ exchange (NEE) was measured by the eddy covariance method. Ecosystem respiration (RE) was estimated from nighttime values and gross ecosystem exchange (GEE) was calculated as the sum of RE and NEE. Over the years the beech forest acted as a sink of on average of 157 g C m⁻² yr⁻¹. In one of the years only, the forest acted as a small source. During 1996-2009 a significant increase in annual NEE was observed. A significant increase in GEE and a smaller and not significant increase in RE was also found. Thus the increased NEE was mainly attributed to an increase in GEE. The overall trend in NEE was significant with an average increase in uptake of 23 g C m⁻² yr⁻². The carbon uptake period (i.e. the period with daily net CO₂ gain) increased by 1.9 days per year, whereas there was a non significant tendency of increase of the leafed period. This means that the leaves stayed active longer. The analysis of CO₂ uptake by the forest by use of light response curves, revealed that the maximum rate of photosynthetic assimilation increased by 15% during the 14-year period. We conclude that the increase in the overall CO₂ uptake of the forest is due to a combination of increased growing season length and increased uptake capacity. We also conclude that long time series of flux measurements are necessary to reveal trends in the data because of the substantial inter-annual variation in the flux.     

Carbon exchange in a freshwater marsh in the Sanjiang Plain, northeastern China

Northern wetlands are critically important to global change because of their role in modulating atmospheric concentrations of greenhouse gases, especially CO₂ and CH₄. At present, continuous observations for CO₂ and CH₄ fluxes from northern wetlands in Asia are still very limited. In this paper, two growing season measurements for CO₂ flux by eddy covariance technique and CH₄ flux by static chamber technique were conducted in 2004 and 2005, at a permanently inundated marsh in the Sanjiang Plain, northeastern China. The seasonal variations of CO₂ exchange and CH₄ flux and the environmental controls on them were investigated. During the growing seasons, large variations in net ecosystem CO₂ exchange (NEE) and gross ecosystem productivity (GEP) were observed with the range of −4.0 to 2.2 (where negative exchange is a gain of carbon from the atmosphere) and 0-7.6 g C m⁻² d⁻¹, respectively. Ecosystem respiration (RE) displayed relatively smooth seasonal pattern with the range of 0.8-4.2 g C m⁻² d⁻¹. More than 70% of the total GEP was consumed by respiration, which resulted in a net CO₂ uptake of 143 ± 9.8 and 100 ± 9.2 g C m⁻² for the marsh over the growing seasons of 2004 and 2005, respectively. A significant portion of the accumulated NEE-C was lost by CH₄ emission during the growing seasons, indicating the great potential of CH₄ emission from the inundated marsh. Air temperature and leaf area index jointly affected the seasonal variation of GEP and the seasonal dynamic of RE was mainly controlled by soil temperature and leaf area index. Soil temperature also exerted the dominant influence over variation of CH₄ flux while no significant relationship was found between CH₄ emission and water table level. The close relationships between carbon fluxes and temperature can provide insights into the response of marsh carbon exchange to a changing climate. Future long term flux measurements over the freshwater marsh ecosystems are undoubtedly necessary.     

煤粉炉内扩散火焰关于大尺度涡的“砂轮”效应初探

以110MW、四角切向喷射的煤粉动力锅炉为对象，借助CFX4.2软件，在α-250工作站对该型锅炉的燃烧过程开展了数据模拟研究，研究发现：在该型炉膛内存在某种由准强制涡和准自由涡所组成的涡结果，这些涡均属于大尺度涡（非亚格子涡）；在这些准强制涡和准自由涡即大尺度涡之间以及某些涡与固壁或涡与喷射气流之间因扩散燃烧及强剪切而导致局部火焰增强现象即所谓“砂轮”效应，从Zeldovich转换和广义Reynolds比拟及粘性耗散的角度，定性地分析了这一效应。