A review of slurry aeration 2. Mixing and foam control

Aerators for animal waste slurries are usually required to mix and to control foam production as well as to oxygenate the slurry. The research to date shows that most animal waste slurries can be adequately mixed by a specific power input of between 10 and 30 W/m³ and that prior separation of coarse solids (e.g. over 500 μm), can reduce this by up to 23%. However, there is evidence that specific power inputs between 0·9 and 2·3 W/m³ are typical on farms, and so most on-farm mixing is probably inadequate.The problems arising from excess foaming are discussed, and the reasons for it are explored. Methods of foam control are reviewed and it is concluded that chemical techniques are generally inferior to mechanical methods due to the detrimental effects they have on aerator efficiency. Power requirements for mechanical foam control are found to vary between 30 and 200 W/m³.     

A review of slurry aeration 1. Factors affecting oxygen transfer

The energy costs of aerobic odour control for pig slurry using present aerators are estimated to be about 14% of the average gross margin per pig produced. Therefore improved aeration efficiency is economically desirable. Reported aerator performance and other experimental data are reviewed to identify the major factors influencing efficiency. Mostly, these show that aeration is less efficient in animal waste slurries than in water. However, a significant minority suggest the reverse, indicating that improvements can be made by increasing specific power dissipation, reducing the dry matter of the slurry by separation and aerating at warmer temperatures by insulating to reduce thermal losses. These factors and others are discussed in detail using specific examples.     

Centrifugation for separating piggery slurry 2. Economic effects on slurry storage

Using the data from previous work on a decanting centrifuge and the performance data of brushed screen/roller press (BSRP) type separators, the costs and benefits of including these machines in slurry storage installations are calculated. When considering the reduction in storage costs only, separation using a brushed screen/roller press can be justified for units exceeding 8000 pig places. A decanting centrifuge cannot be justified at all on this basis. If, however, the separated solids from the process can be sold for £25/tonne of dry solids, then this can offset the costs of even a decanting centrifuge installation costing £38 000.     

Centrifugation for separating piggery slurry 3. Economic effects on aerobic methods of odour control

The costs of reducing the odours from piggery slurries to an inoffensive level and storing that slurry in an inoffensive state are discussed. Five different combinations of aerobic treatment and separation for slurries containing initially between 1·5 and 8% d.m., from 2000 and 8000 pigs, and with storage for five days or 30 days are considered. The five combinations are aeration of raw slurry; separation then aeration; centrifugation then aeration; aeration of raw slurry then centrifugation; and separation then aeration then removal of more solids by centrifugation. The costs of storing the effluents from these processes are also included.For slurry from the smaller herd and for a short storage period, the cost of aerobic treatment of raw slurry is lower than other treatments when the slurry is less than 4·5% d.m. Using a brushed screen/roller press separator to remove solids before aeration produces the cheapest control of odours for slurries above 4·5% d.m.When 30 days' storage or more is required, separation before aeration is cheaper for slurries with more than 3% d.m. and the costs of using a decanting centrifuge (costing £38 000) before aeration is similar to aerating raw slurry at 6% d.m.With a large (8000 pig) herd, using the centrifuge before aeration to produce slurry that is inoffensive for 30 days is the cheapest method at all dry matter contents. When storage is required for only five days, separation or centrifugation before aeration have similar costs, these costs are similar to the cost of aerating raw slurry when it contains less than 3% dry matter, but as dry matter content of the raw slurry increases the cost rises steeply. Removing solids from slurry by centrifugation after aeration increases the overall costs compared to aerating raw slurry.     

Performance of CERES-Rice and CERES-Wheat models in rice–wheat systems: A review

Rice–wheat (RW) systems are critical to food security and livelihoods of rural and urban poor in south Asia and China, and to regional economies in southeast Australia. The sustainability of RW systems in south Asia is, however, threatened by yield stagnation or decline, and declining partial factor productivity, soil organic C and water availability. Crop models potentially offer a means to readily explore management options to increase yield, and to determine trade-off between yield, resource-use efficiency and environmental outcomes. This paper reviews the performance of CERES-Rice and CERES-Wheat in Asia and Australia in relation to their potential application towards increasing resource use efficiency and yield of RW systems.

The performance of the models was evaluated using simulated and observed data on anthesis and maturity dates, in-season LAI and growth, final grain yield and its components, and soil water and N balances from published studies across Asia and Australia, and then by computing the statistical parameters for the major characters. Over the four data sets examined for anthesis and six for maturity dates, CERES-Rice predicted those dates fairly well (normalised RMSE = 4–5%; D-index = 0.94–0.95), but over the 11 sets for grain and 4 for biomass yield, the predictions were more variable (normalised RMSE = 23% for both; D-index 0.90 and 0.76, for grain and biomass, respectively). Model performance was poorer under conditions of low N, water deficit, and low temperatures during the reproductive stages. Over the three data sets examined, CERES-Wheat predicted the anthesis and maturity dates quite well (normalised RMSE = 4–5%; D-index = 0.94–0.99), and over eight sets for grain and two sets for biomass yield the model predicted them also reasonably well (RMSE = 13–16%; D-index = 0.86–0.97). Only one study evaluated the DSSAT RW sequence model with fairly satisfactory predictions of rice and wheat yields over 20 years with adequate N, but not the long-term change in soil organic C and N. Predictions of in-season LAI and crop growth, and soil and water processes were quite limited to investigate the robustness of model processes.

Application of models to evaluate options to increase water and N use efficiency requires the ability to perform well at the margin where deficit stress begins. While both models generally perform satisfactorily under water and N non-limiting conditions, the little evidence available suggests that they do not perform well under resource-limiting situations. We recommend that the models’ key processes under the water and N limiting conditions be further evaluated urgently. The DSSAT sequence model also needs to be further evaluated against observations for a range of locations and management using data from long-term experiments in RW systems.     

叶片式渣浆泵叶轮中浆体浓度分布数值模拟

离心式渣浆泵叶轮中固液两相流动，对于不同颗粒粒径有不同的运动规律和渣浆浓度分布。采用FLUENT软件，并以颗粒碰撞理论为基础的颗粒动力学双流体模型，来对颗粒渣浆泵叶轮内部流动进行数值模拟，揭示其固体相的颗粒分布和运动规律，就能够比较精确地了解叶轮磨损的主要区域和磨损规律，这样有助于改善离心式渣浆泵叶轮的水力设计，减少磨损，提高使用寿命。对颗粒直径分别为0．5，1，2min时颗粒浓度分布进行了数值模拟，对颗粒相体积分布图的分析表明，模拟结果与实验结论基本相同。     

离心泵作透平性能预测研究综述及展望

在化工、石油、矿山等高耗能产业中,存在大量高压流体通过减压阀进行直接排放的现象,造成了大量的能源浪费.采用离心泵反作透平对这部分能量进行回收利用是一种经济且实用的方法,但对离心泵在透平工况下的性能预测是其应用的关键技术及难点之一.文中系统总结了近年来国内外对离心泵作透平在性能预测方面的研究进展,并对未来的研究方向进行了...     

Centrifugation for separating piggery slurry 1. The performance of a decanting centrifuge

Odour nuisance arising from piggery slurry can be prevented by aeration. The stability of aerobically treated slurry, which is free of offensive odours, increases as the dry matter of the slurry decreases. This paper investigates the performance of a decanting centrifuge as one means of achieving a lower dry matter in piggery slurry.Slurry was centrifuged to show the effects of various operating conditions; 61% of the total solids were removed from slurry of 8% dry matter content wet basis (d.m.) in the form of fibrous solids of 27% d.m. and 43% of the total solids were removed from slurry of 2% d.m. as fibrous solids of 30% d.m. When the raw slurry had 8% d.m., centrifuging reduced the volume needed for liquid storage by 17%. A particle size analysis of the solids which remained in the centrifuged liquid showed that 98% were less than 0·020 mm diameter. This agrees with the predicted maximum size of particle left in the centrifuged liquid. Centrifuged liquid from the dilute slurry contained only 4% of particles greater than the predicted maximum diameter of 0·012 mm.     

微孔曝气增氧技术在湖北地区的应用研究

介绍目前湖北地区几种常用的增氧方式.通过试验比较,使用微孔曝气增氧的技术相比一般增氧机,能提高增氧效率值10％,节能88％以上,具有静音、节能、高效、安全等巨大优势.探讨微孔曝气增氧设备在湖北地区的推广应用前景.     

国内三维GIS发展综述

根据国内外的文献资料,指出了地理信息系统技术(GIS)已经被大量应用于资源管理、环境监测、城市规划、土地管理及交通、水利、林业等领域,但GIS技术的发展还远没有止境。人们已经不满足于传统的二维(2D)GIS软件平台,取而代之的是空间的、立体的三维GIS。三维GIS已成为新的科学研究的热点,已发展为新的信息产业。并对3DGIS的发展趋势做了科学的预测。     

Heat from aerobic treatment of piggery slurry

The proportion of chemical energy released as heat energy by microbial degradation of piggery slurry is estimated from the oxygen demand during continuous culture aerobic treatment at controlled reaction temperatures between 15 and 50°C and mean microbial residence times between 0·5 and 8 days. The net energy production and the potentially recoverable heat, after allowing for unavoidable losses, are also discussed.     

沼液对番茄果实品质的影响

本文以L402番茄为供试品种，用L9（3^4)正交表安排试验，以等氮、等磷、等钾为前提条件，将沼液与普遍施用的化肥、化肥－沼液混施（各占50％）进行对比试验，辅以根外追施沼液，研究不同施肥量、施肥各类及叶面喷施沼液浓度的不同水平组合对番茄品质指标的影响，用方差分析法分析试验结果。试验表明，施用沼液或植株叶面喷施沼液对改善番茄果实的品质有很好的作用。     

A review of rainwater harvesting

This article reviews recent literature on rainwater harvesting and its potential application for crop production. Some 170 articles published between 1970 and 1980 were found, all of them revealing an awareness of the increasing need for rainwater harvesting and a recognition of its potential.A definition of rainwater harvesting is presented on the basis of three characteristics common to it: arid to semi-arid climate, local water, and small-scale operation. The following elements are considered:runoff inducement — vegetation management, surface treatment, chemical treatment;runoff collection — Micro-Catchment Water Harvesting (MCWH) and Runoff Farming Water Harvesting (RFWH);storage and conservation.Design aspects of MCWH are reviewed: MC size, ratio of contributing area to collecting area, and layout. MCWH is especially suitable to non-irrigated areas. The Kinematic Wave Equation and Dynamic Equations have been used in modelling MCWH.RFWH can be useful in improving irrigation water availability in surface reservoirs. For modelling RFWH, the Unit Hydrograph Method is suitable. More research is required to determine the potential of runoff farming without surface reservoirs.     

石灰浆荷电雾化特性的试验

将静电效应引入石灰浆烟气脱硫中,是烟气脱硫技术发展的新途径.而对石灰浆荷电雾化特性的研究则是石灰浆荷电雾化脱硫技术的关键.首次应用三维粒子动态分析仪（3D- PDA） 建立石灰浆荷电雾化试验装置,测定了石灰浆荷电雾化后的速度和粒径分布特性.对不同的荷电电压和石灰浆流量进行了测试,并运用相关的数据处理方法,得到了荷电石灰浆滴的三维速度与粒径的相关和统计特性.结果表明静电效应的引入能很好地提高石灰浆雾化质量,同时提高了浆滴的速度以及改善了粒径分布的均匀性,在荷电电压为5～10 kV时效果尤为明显.     

A review of agricultural spray metering

The increasing use and cost of chemical pesticides in crop spraying demands the use of spray application monitors and controllers in order to reduce the serious distribution errors which can occur. In particular, with current trends towards low volume spraying, where higher concentrations of the active ingredient are used, the operation must be more closely controlled if optimum use of the chemical is to be achieved.In this paper the principles of spray metering are explained and research into application rate control by regulation of the total flow and active ingredient concentration are reviewed and compared. The principles involved are described and the weaknesses and strenths of each system identified. Commericial examples of both types of system are given. An appraisal of the flowmeters and ground speed transducers currently available is given and their operation and suitability for this application are described.     

高性能紧凑型水泵的三元设计方法

基于泵的三元设计理论与数值试验相结合的方法,采用轴流式水泵的外形结构对某高比转数混流泵进行了设计,提出了高性能紧凑型水泵设计方法。首先,基于雷诺时均方法对该高比转数混流泵的性能进行了数值计算和分析,并将计算结果和试验值进行了比较,最大误差在3%以内,验证了数值计算模型的准确性。其次,采用轴流式水泵的外形结构基于泵的三元设计理论对该泵进行了重新设计,运用全三维考虑流体粘性的雷诺时均方法对设计结果进行计算分析与验证,最终的设计结果表明：新设计紧凑型水泵满足所有设计指标,在设计流量下裸泵效率达到了0.927,并且在较宽的流量范围内具有良好的水力性能。对比原混流泵和新设计紧凑型水泵性能,可以发现：新设计紧凑型水泵裸泵效率比原混流泵提高了3%,并且其轴面最大直径比原混流泵减少了38%,说明新设计的水泵能够有效减小泵的尺寸、重量并具有优异的水力性能。     

水泵水轮机转轮三维反问题设计与特性研究

采用全三维反问题设计方法,按照水泵工况确定设计参数,从水轮机方向进行流场计算,完成某一中高水头水泵水轮机转轮的水力设计。针对设计开发的转轮,通过模型实验测试其在不同运行工况下的性能。结果表明,设计的水泵水轮机转轮在水泵工况下的最高机组效率达到91.34%,且机组运行平稳;水轮机工况的最高机组效率为88.5%。基于全流道粘性数值计算的转轮内部流动分析表明,水泵工况下,水流光顺地通过流道,转轮内部流动损失较小;水轮机工况下,转轮进口附近存在较严重冲击损失且叶片背面低压区面积较大,影响转轮的作功能力。     

施用沼液对桃树光合作用及生长量的影响

本文通过随机区组试验方法，研究了沼液作为肥料施用对桃树光合作用及生长量的影响。经数理分析得出结果，施用沼液对桃树净光合速率、水分利用率、单枝叶片数等都有很大的提高，而且在试验浓度内，浓度越高，影响越显著；但对桃树的蒸腾速率、CO2总传导度、气孔导度、桃树枝条长度及生长叶长宽等影响不明显。从试验结果初步可以看出，施用沼液对桃树光合作用和生长有较为明显的促进作用，沼液是一种值得推广的农用有机肥料。     

空间转动3-SPS-S并联机构运动学性能分析

提出了将空间三维转动3-SPS-S并联机构作为隧道管片安装机器人的微调机构,对该机构进行了运动学性能分析。在建立机构运动学模型,求解机构的位置逆解及其雅可比矩阵基础上,建立了局部刚度、局部灵活度和驱动性能3项性能评价指标。结合具体应用对该机构进行了运动性能评价。分析结果表明该机构具有良好的运动性能,能满足工程需要。