| Fertilizer application device is one of the important components in the first part of water-fertilizer integration system.As a more frequently used fertilizer application device in recent years,the jet type fertilizer applicator has been popularized and applied in a large area in China’s intelligent water-fertilizer integrated machine.Compared with other traditional fertilizer applicators,the jet type has good fertilizer absorption performance,wide working range and high mixing degree,while it has higher stability in water and fertilizer mixing and control.The jet fertilizer applicator is a miniaturized application of the liquid-liquid mixing center jet pump,which mainly uses the roll suction effect of the high-speed jet from the nozzle to generate negative pressure inside the fertilizer suction chamber,and then sucks the fertilizer from the mother liquor bucket and mixes with the water flow in the main channel,and finally enters the drip irrigation system and delivers it to the crop roots.According to previous research,the structure of the suction chamber,which is the key part of water-fertilizer mixing,has a direct impact on the suction performance of the jet fertilizer applicator.Therefore,it is the focus of the research of the jet fertilizer applicator to understand the internal hydraulic characteristics of the jet fertilizer applicator under different working conditions and to propose optimization and improvement plans for the structure of the key parts of the jet fertilizer applicator on this basis,so as to better perform the working performance of the jet fertilizer applicator.Research on jet fertilizer applicators has focused on performance testing,derivation of efficiency equations,and optimization of fertilizer suction chamber dimensions.Few studies have been conducted on the cavitation flow characteristics and nozzle structure inside the suction chamber that affect the suction performance of the jet fertilizer applicator.To address this research status,this paper firstly investigates the difference of fertilizer suction volume of SSQ jet fertilizer sample under different inlet and outlet pressure difference based on experiments,and uses a high-speed camera to observe the cavitation flow phenomenon inside the jet fertilizer under corresponding working conditions,analyzes the mechanism of cavitation on the suction performance of the jet fertilizer,and explores the periodic characteristics of vacuole cloud shedding associated with the vibration noise of the jet fertilizer;Secondly,based on the numerical fluid calculation method,the internal flow characteristics of jet fertilizer applicators with different nozzle lengths were numerically simulated to investigate the differences in various fertilizer absorption performance indexes,internal flow fields and cavitation characteristics of jet fertilizer applicators,and the 3D printed jet fertilizer applicator model with improved nozzles was experimentally verified;finally,the jet fertilizer applicator model with dual-suction nozzle pipes was constructed,and numerical calculations were performed to obtain Finally,we constructed a jet fertilizer model with double suction port pipe and obtained the optimized fertilizer suction performance of the double suction port jet fertilizer applicator by numerical calculation,and analyzed the effect of different nozzle lengths on the performance of the double suction port fertilizer applicator and the difference of its internal flow characteristics.The main findings of this paper were obtained as follows:(1)In the test of fertilizer suction performance and cavitation characteristics of SSQ jet fertilizer applicator,it was found that in the normal working stage of 0～0.15 MPa,the size of fertilizer suction flow of jet fertilizer sample parts showed a significant linear positive correlation with the size of differential pressure between import and export,and in the range of differential pressure between import and export of 0.15MPa～0.31 MPa,cavitation phenomenon could be observed to occur first near the nozzle outlet.At this time,the growth rate of fertilizer absorption began to slow down,and with the increase of the differential pressure between the import and export,the bubbles from the beginning of the sporadic bubbles became ring-shaped bubbles and continued to develop into a cloud of bubbles extending to the diffusion section,and when the cloud-shaped bubbles appeared,the trend of increasing fertilizer absorption dropped significantly,which was analyzed to be due to the clogging of the flow channel after the cavitation cloud fell off,resulting in the restricted fertilizer absorption performance.The lengths of the vacuole clouds under different working conditions showed periodic fluctuations,with constant elongation and shortening along the axis of the fertilizer applicator main tube in the fertilizer absorption chamber as well as in the diffusion section,and the process of vacuole shedding inside the jet fertilizer applicator also showed obvious periodic changes.(2)In the numerical calculation study of the jet fertilizer applicator with different nozzle lengths,it was concluded that the nozzle length had a significant effect on the fertilizer absorption performance of the jet fertilizer applicator.Under the condition of differential pressure between inlet and outlet greater than 0.5 MPa,the fertilizer applicator with nozzle length L has the lowest performance indexes in terms of fertilizer suction concentration,inlet flow ratio and fertilizer suction efficiency;compared with the condition of nozzle length L,the maximum fertilizer suction capacity of other fertilizer applicators with smaller nozzle length is increased by more than 10%.The longer the nozzle,the negative pressure distribution inside the fertilizer applicator,the corresponding cavitation phenomenon and its proportion,are the main reasons affecting the fertilizer suction performance of the jet type fertilizer applicator.(3)By studying the fertilizer suction performance and internal flow characteristics of the double-suction jet fertilizer applicator,the results show that the fertilizer suction performance of single-and double-suction jet fertilizer applicators varies with the differential pressure between import and export in the same way,but under the same working conditions,all the fertilizer suction performance indexes of the double-suction fertilizer applicator are better than those of the single-suction fertilizer applicator with the corresponding nozzle length.Different nozzle lengths also have significant effects on the fertilizer suction performance of the double-port fertilizer applicator,and different nozzle lengths also have significant effects on the double-port jet fertilizer applicator,and the best double-port fertilizer applicators optimized under different operating conditions with the differential pressure of 0.1 MPa,0.3MPa and 0.6 MPa are nozzle length L,L/2 and nozzle length 0,respectively,which are higher than the corresponding nozzle lengths of the The fertilizer suction capacity of the single-port fertilizer applicator increased by 23.1%,10.2% and 11.1%,respectively.By studying the pressure distribution inside the dual-port fertilizer applicator,it was found that the addition of a fertilizer suction pipe could effectively expand the negative pressure distribution area inside the suction chamber,thus improving the suction capacity of the dual-port fertilizer applicator for fertilizer injection and coiling. |
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