Simulation Study On The Uniformity Of Atmospheric Pressure Plasma Jet Arrays

Atmospheric pressure plasma jets(APPJs)can product rich active species in atmosphere and become a novel low temperature plasma discharge technology in recent years.APPJs containing plentiful active species show well application potential in traditional material processing and surface modification.APPJs also have wide potential in biomedicine with their feature of temperature of room temperature which could directly touch living body.In practical applications,a large treatment area to improve efficiency is needed while it is small in a single APPJ.Compared with a single APPJ with a long radius,the APPJ array consisting of packed APPJ units can achieve much better stability and flexibility.In general,the spatial plasma distribution downstream is in mottling patterns with bad uniformity,while the uniformity of plasma directly influences the treatment effect and efficiency.In many applications,the operation results vary with the plasma doses.For example,the outcomes in biomedicine can be varied from bacteria killing to mutation breeding or wound healing according to the plasma dose.Thus,the APPJ array uniformity improvement is of great important meaning in enlarging application range and increasing efficiency.Focusing on the improvement of APPJ array,combining simulation and artificial neutral network(ANN)methods,the following work is done in this paper:(1)The multi-physical field coupling model for APPJ array establish: using USim simulation software as platform,the multi-physical field coupling model of the APPJ array is established,and the self-consistent spatio-temporal evolution of the APPJ array is realized based on the directly coupling of flow field,electric field,temperature field as well as chemical reactions and synchronous iteration of flow and electric fields.By comparing the typical results in the experiment,the accuracy of the model is verified from three aspects: propagation velocity,electron density and plasma distribution characteristics.(2)For free plasma jets without a substrate downstream,through modulating flow and electric fields parameters(working gas flow rate,distance between adjacent jets,He rate between adjacent jets,voltage intensity,voltage polarity,and voltage rise time),analyzing the APPJ array development,the relationship between the plasma range and the flow and electric fields is gained.Moreover,the merge condition of adjacent plasma jet units is confirmed.Orthogonal experiment method is used to study the influence of coupling control flow field and electric field parameters on the uniformity,and the influence degree of each parameter on the uniformity is analyzed.(3)For plasma jets with a substrate downstream,the influence of a parallel/sloped substrate is studied at first.Then,taking the sloped metal substrate as an example,how to use flow and electric field modulations as well as coupling modulations to improve the plasma uniformity of the substrate surface with a non-uniform substrate is studied.The results show that a parallel substrate downstream helps form a uniform flow field and improve plasma homogeneity.While inhomogeneous electric field happens at the surface of a sloped substrate leading to the decrease of plasma uniformity.Flow field modulations(the working gas inflow speed in each unit and the He rate between adjacent jets)can slightly improve the plasma homogeneity;electric field modulations(the voltage intensity and rise time in each unit)could realize the simultaneous breakdown of the plasma jets with a better plasma homogeneity.With electric field modulations,there is always a region with low plasma density due to flow field distribution.Taking advantage of the flow and electric field modulations,a large area of uniform discharge forms.(4)To make further advances,a basic strategy of uniformity improvement is thus acquired by the ANN method.The ANN method could make fully use of the flexibility of APPJ array and modulate flow and electric field parameters according to the practical demands.Based on the above study with/without a substrate downstream,the ANNs with reasonable accuracy is trained.After training,the computing time for getting results by a group of given flow and electric field parameters falls substantially.Taking advantage of the quick calculation,it is possible to scan a large range of parameters to find the suitable parameters for further optimizing.During the process of scanning,the target parameters could be diverse to find the parameters which can meet various needs of different applications.Through this process,the strategy is formulated and preliminarily validated for the possibility and feasibility that using the predictive ability of the ANN method to improve the plasma homogeneity.