Study On Pattern Of Mainline Looped Pipe Networks For Microirrigation

Micro-irrigation is a kind of irrigation method which is based on the demand of the plant , transports the water and nutrition well-distributed and accurately with little flow to the root zone through the piping system and emitters on the last pipe, including drip irrigation, micro sprinkler irrigation, bubble irrigation and seeping irrigation, etc. Micro-irrigation system is made up of water resource project, head control, transport and distribution pipe networks, emitters. Micro-irrigation belongs to partial irrigation and the small flow under low pressure is its major feature. With duration of one irrigation long , designed irrigation cycle short, controlling water quantity and wetted scope accurately, and transporting directly the water and nutrition to the root zone, micro irrigation can save water, land, energy and be easy to carry out autocontrol management.With the development and utilization rate of water resource rising and the area applying the micro irrigation technology increasing, the optimizing design theory and method emerged in endlessly. But there are some problems deserving of study. For example, the optimizing designs based on established pipe network layout are difficult to be realized overall optimization; The pipe network layout hangs chiefly on experiences of designers; The pipe network form is single, the common pipe network is tree pipe network and widely applied especially in micro irrigation project among the tree pipe network, the looped pipe network and the mixed pipe network. Because of the problems mentioned above, hydraulic analysis and optimal design and operating characteristic of looped pipe network applied in micro irrigation were researched in this paper, as well as the condition on which the invests of looped pipe network is lower than those of tree pipe network applied in micro irrigation project. And through the exemplification and analysis, the principal conclusions were obtained as follows:1. Hydraulic Analysis of Looped Pipe Network Applied in Micro-irrigation EngineeringHydraulic analysis of single outlet of single-loop or double-loop pipe network is simple, the pipe water flows and water head losses can be calculated through the mathematical calculation when the flows of system and pipe network layout established, then the pipe diameter can be calculated. Hydraulic analysis of double-outlet or multi-outlet are more complicated and can be determined by tentative calculation. 2. Optimal Water Head Design of Looped Pipe Networks in Mirco-irrigation EngineeringDesign water head of mirco-irrigation system determines pressure class of selection pipe and is basically in direct proportion to investment of water distribution networks. Selecting 0.3MPa pipe can save the investment of main pipeline of more than 25%, compared with 0.4MPa pipe; Design water head of mirco-irrigation system is direct proportion to operating electricity charges ; When investment of pipe networks is same or similar,selecting larger diameter pipe and lower pressure pearing rate can reduce energy consumption. For emission exponent of emmiter higher than 0.571, decreasing working head is favor of prolonging lateral laying length or raising irrigation uniformity,reducing Rotation Irrigation times and improving using efficiency of pipeline.3. Technical and Economic Index of Looped Pipe Networks in Mirco-irrigation EngineeringFor single-looped pipe network , when LB:LA of pipeline net layout is greater than 0.8, adopting looped pipe network layout is more economical and can save the investment of main pipeline of less than 40% ,compared with tree pipe network layout; For double-looped pipe network , when LB:LA of pipeline net layout is greater than 1, adopting looped pipe network layout is more economical and can save the investment of main pipeline of less than 55.5%,compared with tree pipe network layout;As water transportation capacity is same, Pipe Diameter 0f using tree pipe network layout can be larger one to two grade than looped pipe network layout, utilizing efficiency of looped pipe network is precent 100 and higher one than tree pipe network;When distance between water outlet to node of pipe network is close to half of cycle length ,total water head loss of looped pipe netwotk is the largest; As maximum lifting height is same(maxium water head loss) ,lift height changing range of looped pipe network is less than tree pipe net,that pressure difference between outlets is less, centralization of pump working extents in system operation is propitious to stability of system running.