Research On Hydraulic Performance Improvement And Jet Breakup Characteristics Of Impact Sprinkler With Dispersion Device

Sprinkler irrigation is an irrigation method that saves water,labour and has a good application efficiency.However,the energy requirement is larger when compared with other methods of irrigation.This is particularly true in the case of impact sprinklers for their pressure requirements are higher than for instance,rotating plates and pivot sprinklers.Operating the impact sprinkler under a low working pressure make the water to concentrate around the end of jet,giving less water applied in the forepart and middle sections of the spray range.With the development of agricultural production,an imbalance between the demand and supply of global energy are increasingly gaining momentum.As a consequence,a major challenge that arises amongst many researches in the field of sprinkler irrigation is how to reduce the energy consumption of sprinkler irrigation systems.In this research,a new type of nozzle-dispersion devices was developed to improve the performance characteristics of impact sprinklers under low pressure conditions.Extensive experiments were conducted under the manufacturer's standard and nonstandard conditions of dispersion-nozzle devices and working pressures,and then compared with the commercial LP R33 sprinkler.The main objective were to(1)study the optimal combination of the dispersion and nozzle devices to improve the hydraulic performance of the impact sprinkler under low pressure conditions;(2)evaluate the effect of sprinkler rotation with the optimal combination of nozzle and water dispersion device on water distribution uniformity;(3)analyze the jet characteristics of the optimal sprinkler,and establish an empirical spray range formula based on the dispersion angle(?)and nozzle diameter(D2)for the optimal impact sprinkler;(4)To analyze the jetbreaking characteristics of the original and modified impact sprinklers,and find out why the hydraulic performance of new sprinkler is better through the jet breakup analysis;(5)conduct a comparative analysis of the hydraulic performance of the optimal impact sprinkler and the commercial LP R33 model of rotary plate sprinkler from Nelson Irrigation.(1)In the first part of this study,a several new types of fixed dispersion devices were designed and manufactured.It includes a holder and spring dispersion device that protrudes into the jet.An orthogonal analysis of the spray range and water distribution analyses was used to select six types of the dispersion devices.The shortest spray range(R)was chosen as the index of the effect on a sprinkler's hydraulic performance caused by a fixed dispersion device,and a method to calculate the shortest range was established.The important influencing factors were in the order of A(insertion depth d)> B(width D)> C(angle a)> shape of the tip(pointed or flat).The purpose of this new device was to obtain sufficient breakup of the jet that can improve the water distributions in the middle and near the sprinkler,while the spray range is maintained at the same time.The dispersion devices were first tested with a standard nozzle of size 8 mm in the laboratory to evaluate their effect on hydraulic performance characteristics to select the best dispersion device for further testing.Comparison of the dispersion devices revealed that using type C2 on the impact sprinkler and the 8 mm standard nozzle gives a much better water distribution and spray range under intermediate pressure of 200 k Pa.Simulated uniformity ranged from 71.22 to 80.77% % which surpassed 75% when the spacing was from 1 to 1.4R.The deviations in droplet diameter were found to range from 0.41~0.59 mm,with a mean value of 0.51 mm,and the CV varied from 76~114%,with a mean value of 96%.Further laboratory testing of the best dispersion device(type C2)were carried out by using five principal nozzle sizes of 4,5,6,8,10 mm.It was found that the combined effect of the 6 mm nozzle had the advantage of a larger discharge coefficient and spray range under a low pressure of 150 k Pa.The water distributions from the sprinkler was considerably improved near and in the middle section of the range,and the design parameters of a circular nozzle should satisfy the principle that d + C(D2),which should not be larger than 6 mm for the test sprinkler.Simulated uniformity was greatly improved with an average value of 83.33%.Droplet diameter at the end of the jet decreased as the disperse spacing increased.Mean droplet size from impact sprinkler with type C nozzle was 0.36 mm.The regression analysis of the effect of disperse spacing and working pressure on droplet diameter at the end of the jet in mm(Dr)fits quite well.The combined effect of a 6 mm nozzle and the pointed dispersion device with an insertion depth of 4.5 mm seems to offer some advantages under low-pressure conditions for impact sprinklers.The differences in the rotation completion times between the quadrants were insignificant differences between the quadrants of the rotation cycle when the 6 mm nozzle was tested with the sprinkler.It was found that the rotation speed decreased approximately linearly as the value of d + C was increased.All of the nozzles with diameters smaller than 6 mm gave a reaction force from the jet flow that was much stronger,and the deflector was pushed back quickly to reorient.When the nozzle diameter is too large,the deflector tends to strike the jet flow with a weaker force which is not enough to efficiently rotate the sprinkler.It can therefore be concluded that the value of d + C should not exceed 6 mm in order to avoid low sprinkler rotation speed.An empirical equation of the variation trend of rotation speed and the value of D2 and the working pressure was established for the test sprinkler.However,slight differences in water distributions from 0 to 1.7 mm/h were found for the nozzle,suggesting a better water distribution uniformity for the test sprinkler.For overlapped CUs,the impact sprinkler with F2 gave small differences of 2.81% at Q1/2 and Q3/4 at 40% spacing,and the lowest was 0.36% at Q1/2 and Q3/4 at 20% spacing.Hence,the test sprinkler could have the advantage to be placed in fewer rows to give better uniformity in large sprinkler irrigated fields.(2)The second study is related to the spray performance which is of immense importance in the design of sprinklers with respect to the nozzle and the dispersion device.Type C2 appears to cause more breakup and the spray angle was larger than other types of dispersion devices tested.The new formula for spray range based on the spray angle was established and tested with other formulas showed a high accuracy of the spray ranges computed by this formula,and the average relative error was less than 2.8%.Additional experiments on the spray performance were carried out by using nozzle of different sizes demonstrates that the 6 mm nozzle gives a better breakup and dispersion of the jet from the test sprinkler.The new formula based on the nozzle diameter for calculating spray range had a high accuracy attested by other formulas and with an average relative error less than 4%.The relationship between the angle of dispersion and the initial breakup length of the jet and the nozzle diameter gave formulas that were accurate with errors less than 10%.Since these formulas are based on the angle of dispersion,it could be useful to estimate water distribution uniformity for irrigation sprinklers.(3)In the third study,a comparison of the spray distribution pattern uniformity for the original sprinkler and the modified sprinkler was conducted.The spray characteristics for the modified sprinkler were better than those produced by the original sprinkler and the number of droplets increased with increasing spray angle due to early breakup which is beneficial for greater uniformity.Combination of the nozzle-dispersion device had a strong effect on minimizing the degree of spray non-uniformity for the impact sprinkler,and the CV values were less than 10%.This result may suggest that the modified sprinkler was working efficiently and was better than the original sprinkler by providing a higher spray distribution pattern uniformity.(4)Comparative research on hydraulic performance between the modified sprinkler and the commercial LP R33 sprinkler was carried out in the fourth study.Under the same conditions of working pressure,the impact sprinkler produced a larger spray range and the water distributions were improved in the middle and near positions of the spray range.The best simulated uniformity was the combined spacing factor of 1.4R for the modified sprinkler and the CUs was increased by 4% compared with the LP R33.The droplet diameters from the modified sprinkler were much larger than the LP R33 at the middle position of jet,and the sizes of the droplets were also larger than that of the LP R33.Additionally,in the end position of spray range,the droplet diameters from the modified sprinkler were quite smaller than the LP R33.Droplet velocities from the LP R33 sprinkler ranged between 0.2 and 6.4 m/s,while that from modified sprinkler were slightly larger ranging from 0.15 to 7.7 m/s under low pressure.The introduction of the dispersion device with pointed tip in combination with nozzles for the modified sprinkler offers some advantages over the LP R33 sprinkler under low-pressure conditions.Key innovations in this research include a new type of nozzle and dispersion device for an impact sprinkler which runs quite better than the well-known commercial LP R33 sprinkler from Nelson Irrigation.The introduction of the modified impact sprinkler could be of immense benefit for saving water in the recent times of limited water resources and rising energy costs in sprinkler irrigated fields.The development of a simulation model to characterize the breakup and dispersion of jet from the perspectives of a dispersion device.Establishment of formulas such as droplet diameter equation,and the equation for the rotation speed based on the value of D2;spray range formulas which are based on the angle of dispersion.