Study On Swirling Jet Mixer For Applying Fat-soluble Pesticides And Its Mixing Uniformity

The pesticide solutions include both fat soluble and water soluble.The permeability of fat soluble pesticides is greater than that of water soluble pesticides,so its control effect is better than that of water soluble pesticides.It is necessary to break up the oil into a fine oil bead by the intense mechanical agitation when fat soluble pesticide mixed with water.However,the emulsion oil droplet dispersion degree is not high.During the storage period,it is very easy to produce oil beads and break the emulsion,and it's hard to recover.Inline mixed pesticides can reduce the harm of pesticides to operators,environment and non-target organisms.At present,the mixed pesticide is mainly mixed with water soluble pesticides.It is difficult to study the inline mixing of fat soluble pesticides due to their insolubility.To characterize jet mixing profiles for in-line injection of pesticides,two-phase flow fields in conventional mixing chambers were investigated under various test conditions.The two-phase flow was formed with water mixed with either a water-soluble liquid or a fat-soluble liquid?silicon oil?.Test results illustrated that there were limitations for the conventional mixers to obtain uniform mixtures with the fat-soluble pesticide.To overcome these limitations,a new mixing device based on the swirling jet mechanism was conceived and developed to improve the mixture uniformity of water and the fat-soluble pesticide.The swirl jet mixer consisted of a spiral curved shrink tube,a diffuser and a spiral flow generator,and could accelerate the two-phase flow's spiral movement and blend the 2 kinds of liquids.In order to increase the swirling efficiency of swirling jet mixer,the spiral flow generator had 3 guide vanes?height was 6.5 mm,wrap angle was 15o?;the diffuser had also 3 guide vanes,but its height was from 0 to 6.5 mm;the pitch of the spiral curved shrink tube was 128 mm,and its converging angle was 16°.The in-line pesticide mixing is a process with higher productivity and safer operating conditions,which can reduce pesticide wastes and pollution.A computational fluid dynamics program?FLUENT?was used to simulate the flow field inside the swirling jet mixer to optimize its design.The boundary conditions of the water and the rapeseed oil were defined to a pressure input.The boundary condition of mixer outlet was defined to a pressure output.The total gauge pressure,the initial gauge pressure and the turbulence intensity were defined.The solid wall was supposed to be a non-slip,impervious and adiabatic boundary.The segregated and implicit modeling was identified by incompressible fluid.The steady flow and the k-e modeling of turbulent flow were identified.The mixture uniformity was evaluated by introducing the uniformity index ?a,representing that the two liquids were blended homogenously as ?a was 1.Simulated results can be briefly described as follows:?The ?a was 0.9989 across the entire cross sections inside the mixer,confirming uniform mixture profiles with the new mixer design.Therefore,the new swirling jet mixer would solve the non-uniform mixture problem associated with conventional mixers and could significantly improve the in-line injection technology to reduce pesticide waste.?The mixture uniformity for the mixer with a spiral curved shrink tube and shunt in the middle is the best among the six types of mixer.The mixture uniformity for the mixer with a spiral curved shrink tube is better than the mixer with a straight wall tube.The spiral curved shrink can improve the mixture uniformity of mixer,but it is not obvious.To verify the simulation results,the experiments were conducted in which the fluorescent tracers were mixed with the pesticides to enable the camera to track the mixing process in the transparent chamber.According to different physical and chemical properties of pesticides,Rapeseed oil and silicone oil are used as substitutes for fat soluble pesticides,they were added with oily fluorescent agent LUYOR-6100.Results are as follows:?1?Following the mixer F162009 with two diffusers?After the first diffuser,the fat soluble pesticide substitute rapeseed oil and silicone oil can be mixed with water evenly.?After the second diffuser,the fat soluble pesticide substitute rapeseed oil and silicone oil can also be mixed with water evenly.?From the first to the second,the mixing apparatus increased by 80 mm,but the mixture uniformity was not obvious.?2?Single factor analysis on mixing uniformity of swirling jet mixerThe purpose of the study is to determine the effective length of the mixer under the condition of uniform mixing of fat soluble pesticide?rapeseed oil?.A comparative analysis was made for the different diffusion angle,different injection methods,different contraction angle and different mixing tube length.Conclusions are as follows:?The mixture uniformity for the mixer with a diffuser is better than the mixer without diffuser.The value of RMSE for the mixer F162009 with diffuser is 4.7827,The value of RMSE for the mixer F192010 without diffuser is 5.6586,the mixing uniformity of mixer F162009 is better.?With the increase of the diffusion angle,the effective length of the mixer is reduced,the value of RMSE is increased,and the uniformity of mixing is changed.In addition to the diffusion angle,the other parameters are the same,the values of mixers for F192010?F19214 and F192018 are 5.6586,7.4037 and 9.1911.?The tangential direction of the shunt can significantly improve the mixing uniformity of the mixer.The value of mixer Q192014?tangential pesticide?is 5.9511,but the value of mixer F192014?normal pesticide?is 7.4037.?With the increase of the contraction angle,the value of RMSE is reduced and the mixing uniformity is improved,but the improvement is not obvious.In addition to the contraction angle,the other parameters are the same,the values of mixers for Q222014 and Q192014 is 5.7012 and 5.9511.?The mixing tube length has a significant effect on the mixing uniformity of the mixer.Reduce the mixing tube length,reduce the mixing uniformity.the values of mixers for Q222014 and Q221214 is 5.7012 and 10.9415.?3?An multivariate analysis on mixing uniformity of swirling jet mixerStructure parameters of the mixer were optimized by orthogonal experiments with 3-factors and 3-levels,which included that the contraction angle was 19°?22° and 25°,the mixing tube length was 20 mm?12 mm and 8 mm,and the diffusion angle was 10°?14° and 18°.The orthogonal experiment results are as follows:?The mixing tube length of swirling jet mixer for mixing uniformity is the most significant,followed by diffusion tube diffusion angle,no significant effect is the contraction angle shrink tube.?The order of the 3 levels of the contraction angle of the contraction tube on mixing uniformity is 25°?19° and 22°;The order of the 3 levels of the mixing tube length on mixing uniformity is 20 mm?12 mm and 8 mm;The order of the 3 levels of the diffusion tube diffusion angle on mixing uniformity is 18°?14° and 10°??On the premise of fat soluble pesticide mixing,the effective length of the swirling jet mixer Q252018 is the shortest.To sum up,through the finite element simulation analysis and orthogonal experimental verification,the mixer Q252018 is the best because its effective length is the smallest in the realization of fat soluble pesticide?rapeseed oil?uniform mixing.Its effective length is 69 mm,?₂ = 18°,?₁ = 25°,L₀ = 20 mm.