共查询到20条相似文献，搜索用时 15 毫秒
1.
为了提高滴灌系统水力设计的准确性,基于有限元原理,提出一种计算薄壁内镶贴片式滴灌带能量损失和灌水均匀度的方法,局部水头损失根据贴片式滴头结构、管内压力和管道壁厚确定,沿程水头损失通过改进Darcy－Weisbach公式编写计算机程序,分析了不同滴灌带的水头损失及均匀度变化规律,并与《微灌工程技术规范》中推荐计算方法的结... 相似文献
2.
Ceres Duarte Guedes Cabral de Almeida Tarlei Arriel Botrel Rod J. Smith 《Irrigation Science》2009,27(3):209-214
The microtube is a simple and cheap emitter that was widely used throughout the world in the early days of drip irrigation.
Its length can be adjusted according to the pressure distribution along the lateral line and the discharge from the microtube
can be adjusted by its length. This not only counters the pressure loss due to pipe friction but also makes it suitable for
undulating and hilly conditions, where pressure in the lateral line varies considerably according to the differences in elevation.
This is the major problem facing the designer, i.e., emitter flow changes as the acting pressure head changes. In this study,
a novel micro-sprinkler system is proposed that uses microtube as the emitter and where the length of the microtube can be
varied in response to pressure changes along the lateral to give uniformity of emitter discharges. The objective of this work
is to develop and validate empirical and semi-theoretical equations for the emitter hydraulics. Laboratory testing of two
microtube emitters of different diameter over a range of pressures and discharges was used in the development of the equations
relating pressure and discharge, and pressure and length for these emitters. The equations proposed will be used in the design
of the micro-sprinkler system, to determine the length of microtube required to give the nominal discharge for any given pressure.
The semi-theoretical approach underlined the importance of accurate measurements of the microtube diameter and the uncertainty
in the estimation of the friction factor for these tubes. 相似文献
3.
通过试验研究了标准管径16 mm的5种内镶贴片式滴灌带的局部水头损失,分析了滴灌带局部水头损失占沿程水头损失的比值hjt/hf和局部水头损失系数α的变化规律.结果表明:相同工作压力下,滴灌带当量直径随壁厚的增大而减小,造成沿程水头损失和局部水头损失的增大,局部水头损失与壁厚、滴头断面面积和雷诺数有关.随着雷诺数的增大,滴灌带局部水头损失占沿程水头损失的比值hjt/hf减小,最小值可达到0. 67,但仍超过中国制定的微灌工程技术规范设计标准(0. 1~0. 2).通过对试验数据进行多元回归分析,提出了滴灌带局部水头损失系数与过水断面收缩比和雷诺数的关系式,相关系数为0. 96. 相似文献
4.
Pedro Vallesquino 《Irrigation Science》2008,26(6):475-486
A new method for simulating lateral hydraulics in laminar or turbulent flow has been developed. The outflow is considered
as a discrete variable and the friction head losses are calculated using the Darcy–Weisbach equation with an equivalent friction
factor. Local head losses are also computed by applying equivalent coefficients that can be dependent on Reynolds number.
Considering these premises, a compact expression that is valid for any type of regime has been deduced for calculating global
head losses along any lateral stretch. The proposed method is useful to workout the hydraulic computation of laterals with
the inlet segment at full or fractional outlet spacing, and complex laterals when a different pipeline diameter, slope, flow
regime or emitter gap have to be considered. 相似文献
5.
Dimensional analysis approach to estimate local head losses in microirrigation connectors 总被引：1，自引：0，他引：1
Danieli Bariviera Zitterell Jose Antonio Frizzone Osvaldo Rettore Neto 《Irrigation Science》2014,32(3):169-179
Local losses, which affect the uniformity of water application, are often ignored in the design of irrigation systems. Some accessories have no simple, efficient equations to estimate these losses. The main objective of this work was to develop an equation to estimate the local head loss in lateral passage connectors. Fifteen connector/pipe combinations were tested. The connectors were characterized by their internal diameters and dimensions. The local head loss was determined by subtracting the head loss on the connector and pipe from the head loss on the pipe. The parameters affecting the local head loss were defined as dimensionless terms using Buckingham’s theorem. A mathematical model was developed that presented a determination coefficient of 93.31 %. Elements such as the inner diameter of the connector, pipe length, connector, water flow velocity, Reynolds number and Froude number influenced the local head loss in the connectors. The model was compared with the observed data and presented excellent performance. It can be used to calculate the local head loss in lateral passage connectors. 相似文献
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我国温室产业近年来发展迅猛,由于面积、种植结构与密度等与大田差异较大,沿用大田滴灌系统的设计方法已不适宜,需要根据温室的具体条件确定设计方法。根据我国普通单栋温室情况,通过室内试验研究分析了入口压力、支管长度、毛管间距3个因素对滴灌系统中支管沿程压力分布的影响。结果表明:支管沿程压力分布的均匀性随支管长度的增加、毛管间距和首部压力的减小而降低。结合滴头的水力特性参数得出支管上的最大允许压力偏差为30.85%。毛管间距0.6、0.9和1.2m条件下,满足水力偏差要求的单栋温室支管最大铺设长度分别为20、40和60m。运用量纲分析方法将影响支管水头损失的基本量导出为3个无量纲量υd/ν、υ2/(g d)和L d/s2,通过多元回归建立支管水头损失的经验预测模型(R2=92.4%)。分析了支管能坡曲线的函数形式,回归得到了支管水头损失比和沿程压力分布模型。以上模型预测值与实测数据拟合效果良好,可用于温室滴灌系统水力计算及规划设计。 相似文献
8.
Summary Experiments were carried out to evaluate the performance of various types of drip irrigation emitters, widely used in Israel, using waste water from a storage reservoir. Fine particulate matter agglomerated by microbial by-products and in-line developed biomass were the principal clogging agents. Clogging fluctuated, increased as water quality deteriorated and decreased when it improved. There were definable differences between emitters of various types as to their clogging susceptibility which were not directly correlated with differences in emitter flow-rate, although, for any particular type, the emitter with smaller discharge was always more sensitive to clogging. The clogging process generally started with emitters located at the far end of the lateral and partial emitter clogging was more common than complete plugging. Overflow was also found in most emitter types and was more common in regulated emitters. Reliable long term operation of most emitter types was achieved with filtration at 80 mesh (180 m opening) combined with daily chlorination and bimonthly lateral flushing. Regular lateral discharge monitoring was found to be a convenient way to detect the initiation of the clogging process. Chlorination was most efficient when applied before the emitters became massively clogged. 相似文献
9.
滴头锯齿型迷宫流道消能特性的流体动力学分析 总被引：3，自引：0，他引：3
在对所选取的3种代表性锯齿型迷宫式滴头流道参数进行精确测定的基础上,利用圆管紊流理论和CFD流场模拟软件对锯齿形迷宫流道的消能机理进行了研究。结果表明：光滑圆管紊流理论不足以解释锯齿型迷宫流道的消能机理;压力沿流道长度方向呈线性递减,各消能尖角单元压力损失相等,符合线性叠加规律;摩阻系数随着压力增加而降低,并很快稳定在一定数值上;在中、高压区滴头流道内部流动为紊流,在低压区可能存在从层流到紊流或者光滑紊流到全紊流的流态转捩行为。 相似文献
10.
Eshel Bresler 《Irrigation Science》1978,1(1):3-17
Summary Designing trickle irrigation systems involves the selection of a proper combination of trickle discharge rate, spacing between emitters, diameter and length of the lateral system for any given set of soil, crop and climatic conditions. Trickle irrigation is treated as transient and steady axisymmetric infiltration processes. An existing numerical solution to nonsteady state infiltration is used to quantify the effect of soil hydraulic properties and trickle discharge rates on emitter spacing (Fig. 2). The results of the analysis suggest the possibility of controlling the wetted volume of a soil by regulating the emitter discharge according to soil properties (Figs. 3 and 4). The surface distribution of a transformed soil water content (or pressure) function (Fig. 5) is derived from a linearized solution to steady infiltration. The analysis of steady and non-steady infiltration is employed to estimate the spacing between emitters as a function of discharge and water pressure conditions between emitters using hydraulic soil data (Fig. 6). Hydraulic conductivity parameters are given for 17 different soils (Table 1) to be used for design purposes. Theoretical analysis of soil water is combined with hydraulic principles to derive lateral diameter and length for engineering design requirements.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. 1977 Series, No. 134-E 相似文献
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为了阐明滴头制造偏差系数、灌水均匀度、毛管直径及毛管造价的内在联系,降低滴灌系统造价、提高灌水均匀度,通过理论推导结合实证计算的方法,系统分析了不同均匀度条件下滴头制造偏差系数极限值,以及滴头制造偏差系数、毛管直径、允许均匀度等三者的关系,并推导出毛管造价计算公式.结果表明:对于长度为100 m的毛管,当Keller均匀系数( EEU)为0.80时,制造偏差系数从0.05增大到0.07和0.11时,毛管造价分别增大8.7％和37.1％;当滴头制造偏差系数为0.03, EEU由0.80增大到0.85,0.90和0.95时,毛管直径分别增大20％,23.5％和56.5％,毛管造价也相应增大20％,53.8％和207.7％;当滴头制造偏差系数为0.05, EEU由0.80增大到0.85和0.90时,毛管直径则分别增大19.3％和32.8％,毛管造价也分别增大17.1％和71.4％;对于 EEU为0.95时,毛管允许最小流量大于平均流量,管径计算无解.在限定值范围内,滴头制造偏差系数和Keller均匀系数的微小增大将直接导致毛管直径和造价急剧增大;滴灌系统设计应选择制造偏差系数小的滴头及合理的灌水均匀度,以达到降低工程造价的目的. 相似文献
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A new method for calculating total friction head loss in center-pivots with an operational end-gun was developed. The proposed methodology is based on adjusting the previous friction correction factors for center-pivots with end-guns in order to correct their paradoxes and shortcomings. Equations presented in the current work are developed for center-pivots with a finite number of outlets along the lateral and constant outlet spacing and discharge as well as constant discharge and variable spacing. The proposed formulas depend on the number of outlets along the supply pipeline, the exponent of velocity term in the friction formula used and the distance that water is jetted by the end-gun. All equations reduce to the well-established equations for the friction correction factor when the end-gun is turned off. The equations presented here compare well to the stepwise friction calculation method, yet correct slight errors in the way that these friction correction factors were calculated in the past. 相似文献
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《Agricultural Water Management》1997,32(3):275-284
The hydraulic design of micro-irrigation systems to achieve high system uniformity has led design engineers to over-design irrigation systems arbitrarily. Commonly used emitter flow variations of 10–20% are equivalent to a uniformity coefficient of about 98-95%, or a coefficient of variation of emitter flow of only 3–7%. The uniformity of a micro-irrigation system is affected by not only hydraulic design but also manufacturer's variation, grouping of emitters, plugging, soil hydraulic characteristics and emitter spacings. Among all the factors affecting the uniformity, the hydraulic design, with an emitter flow variation of 10–20%, produces only a few percent change in uniformity. The manufacturer's variation of micro-irrigation emitters ranges from 2% to 20%. The hydraulic variation will be less significant when an emitter with 10% or more manufacturer's variation is selected. The grouping effect will reduce the coefficient of variation to half or more if four or more emitters can be grouped together. The effect of hydraulic design is also less significant with plugging situations. When there is no plugging, the emitter flow variation from 10% to 20% in hydraulic design will reduce spatial uniformity only about 8% from 93% to 85% when the emitter spacing is designed as half of the wetting diameter in the field. The hydraulic design criterion can be relaxed to 30%v of emitter flow variation, qvar(H), which can still achieve less than 20%v in coefficient of variation, or over 80% of uniformity coefficient in spatial uniformity of a micro-irrigation system 相似文献
17.
A computer model, SPRINKMOD, was tested with field data collected from a simple sprinkler irrigation system in operation.
The original data for laterals and the amount and way leakage is considered were modified to evaluate the model sensitivity.
The model predicted the pump station flow rate within 2% and the pump station pressure head within 5% with the original data
collected. For this irrigation system, no practical effect was observed in the system operating point by changing the lateral
pipe characteristics, lateral leakage amount and distribution, lateral pipe roughness and lateral local loss coefficient for
flow past a riser outlet. The amount of leakage had more effect on the model simulation of pressure heads than the way leakage
was considered, localized or distributed along the laterals. The use of a variable local loss coefficient, K
r, along the 350-m hand-move laterals had a negligible effect on both system operating point and distribution of pressure heads
along the laterals.
Received: 14 February 1998 相似文献
18.
The effect on emitter clogging of four filtration systems (sand, screen, disc and a combination of screen and disc filters) and six emitter types placed in laterals 87 m long, using two different effluents with low suspended solid levels from a wastewater treatment plant, was studied for 1000 h. Four of the emitters were molded and welded into dripline wall, two of them being pressure-compensated and the other two non-pressure-compensated. The other two emitters, both pressure-compensated, were inserted into thick wall. Emitter clogging was affected mainly by emitter type, location along the lateral and the interaction between these two factors. Differences among emitters with larger clogging were only observed at the end of dripline. Two molded and welded emitters showed the worst performance: one non-pressure-compensated with the lowest passage section, and the other pressure-compensated that, after 800 h working at higher dripline flow and particle load, experienced an important decrease in flow rate. Only with the effluent that had a higher number of particles, did the filter and the interaction of filter and emitter location have a significant effect. Emitters placed after screen and sand filters showed the largest flow rates at the lateral ending, even though only sand filtration significantly reduced turbidity and suspended solids. Emitters protected by a disc filter experienced the largest flow rate reductions. 相似文献
19.
为了研究配置参数对轻小型喷灌机组能耗的影响,在基于遗传算法的喷灌机组能耗计算模型基础上,以机组4.4CP-45为例,采用四因素三水平考虑交互作用的正交设计,就管道管径、喷头间距、喷头数、喷头工作压力及其交互作用对机组单位能耗的影响进行了对比分析,在此基础上建立了机组能耗的多元回归模型.研究结果表明,喷头工作压力对能耗的影响最显著,其次为管道管径,喷头数的影响也很明显,喷头间距对能耗的影响体现在与其他参数的交互作用中.4组主要的交互作用因素中,喷头间距与喷头数的作用最敏感,其后依次为管径与喷头数、喷头间距与管径、喷头间距与喷头工作压力,因而在机组配置参数的选择中,参数间交互作用不可忽略.经综合比较,机组配置参数最优组合方式为喷头间距为15 m、管径为80 mm、喷头数9个、管道末端喷头工作压力为0.25 MPa,此时机组单位能耗为4.53 kW·h/(mm·hm2),比优化前降低了22.6%,比只考虑单因素作用得到的最优组合方式降低了1.0%,且配置参数的选择更能为用户所接受.机组能耗多元回归模型复相关系数达0.88,确定性系数为0.774,比较可靠,能为喷灌工程设计及性能评价提供一定的借鉴作用. 相似文献
20.
自压滴灌支管灌水单元设计方法 总被引：2，自引：0，他引：2
为了解决山地自压滴灌支管灌水单元水力设计问题,以滴头制造偏差、水力偏差和微地形偏差产生的综合流量偏差率作为灌水均匀度衡量标准,计算出支管灌水单元不同压力区允许水压力偏差和最大水压力,根据不同压力区支管水压力递推关系,确定出支管压力偏差分配系数,将支管单元设计转变为支管设计和毛管设计;支管设计采用两阶段设计法,计算出支管各节点水压力,根据该水压力和不同压力区允许最大水压力,对支管进行压力单元的划分,在不同压力区选择不同类型的滴头,使滴头额定工作压力与地形高差提供的工作压力相匹配．研究结果可直接用于山地支管灌水单元设计,计算可在Excel表格中完成,设计方法简单实用． 相似文献