| The technology of water-saving irrigation has developed rapidly due to the high efficiency of water saving in recent years,the micro irrigation technology with low-pressure which can be effectively reduced the costs is popular.Using the experimental method,the hydraulic properties of the film-bag irrigation with low-pressure can be studied combined with the knowledge of hydraulics and hydrodynamics theory.Based on the experiment,the flow characteristic,the distribution law of the pressure,the head loss and the uniformity of the film-bag irrigation under the condition of a low-pressure were studied and analyzed;finally,the maximum length of the film-bag was calculated and the film-bag was improved.The main conclusions are as follows:(1)Effects of the inlet pressure,the diameter and the laying length on the outflow of the film-bag irrigationBy the influence of inlet pressure,the pore diameter and the length of the bag,the orifice flow was not same,while,the outflow curve showed a total of a single peak type.The outflow of the film-bag decreased with the length of the bag laying,and the position of the maximum flow rate would move forward the first end of the film-bag as the laying length increased;the orifice flow increased with the increase of the diameter and pitch of the film-bag,the position of the maximum value of the flow rate is also moved forward.(2)Effects of the laying length,the hole distance and the aperture on the pressure head and the loss of the head of the film-bagWith the different film-bag laying length,the hole distance and the aperture,the pressure head curve along the path was always reduced.With the increase of inlet pressure,the measured pressure of the same film-bag increased with the different section,however,as the observation section moves towards the end of the film bag,the amplitude of the increase was reduced.With the inlet head,the hole distance andthe aperture increasing,the head loss of the film-bag irrigation showed a decreasing trend;and with the laying of the length increasing,the head loss increased;moreover for a longer film-bag,the larger hole aperture and the pore distance could be used to obtain the smaller head loss and improve the uniformity of the film-bag irrigation.We analyzed the relations between the ratio of measured head loss to standard values calculated by recommend code and the inlet pressure,the pitch and the aperture,and finally we got the result that the head loss correction and the inlet pressure was a significant quadratic function.(3)The influence factors of irrigation uniformity and the calculation of the maximum laying length of the film-bagAll specifications of the film-bags have reached the requirements of the production efficiency of the emitter,which could be used for testing,moreover,the smaller the deviation coefficient,the higher the accuracy of the emitter.Keeping the flow hole distance unchanged,with the increase of the inlet pressure head,the flow deviation rate decreased.As the hole distance and the aperture increase,the flow deviation rate was also decreasing,furthermore,under the same inlet pressure head,with the increase of the laying length of the film-bag,the flow deviation rate increased.When the slope is i=0,the formula of the maximum allowable length of the film-bag was given,in addition the maximum allowable laying length of the film-bag is respectively calculated when the inlet pressure is 0.2m,0.3m,0.4m and 0.5m,as well as the hole spacing is 30 cm,40cm.(4)The improvement of the film-bagThe poor filed flatness and reverse slope terrain,which will reduce the advance speed of the flow in the film-bag,and even arise the phenomenon of Yong-water,it may cause the film-bag to roll,the phenomenon that have greatly reduced the efficiency irrigation of the porous film-bag.In view of the above problems,a film-bag irrigation with a function of water storage and an improved film-bag for improving the uniformity of the film-bag irrigation are put forward. |
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