The Structural Design And Optimization Of The Cold Spraying Nozzle

In order to study the cold spray technology on Mg alloy surface,the designed supersonic nozzle is optimized according to the theory of hydrodynamics and aerodynamics.The FLUENT software is used to simulate the gas flow.The velocity, temperature and pressure of gas particles are analyzed in the Laval Nozzle.According to the simulation results,the nozzle structure is improved to make the velocity of gas and particle best.The key of Cold Spray technology is accelerating the velocity of materials to supersonic in the Laval nozzle,then the powder of materials is deposited on the surface effectively.The velocity of outlet was impacted by inlet parameters.At the same Laval nozzle structure,the velocity of inlet less impact on outlet speed,particularly inlet velocity blow 50m/s.And increasing air pressure of inlet deeply is difficult realization.The main method of raising the speed of outlet is getting up the gas temperature of inlet with suitable pressure.Through analysis the data of simulation,appropriately extending the length of expanding nozzle's zone can obtain both lower temperature and higher speed at outlet.A k-ε(RNG) model was used in the simulation in order to understand the character of the flows in Laval-Nozzle.According to the shape variation of the Laval-Nozzle,a structured non-uniform grid system has been used to divide the computation domain.The second-order difference style was selected for the discrimination of the convection in the differential equation,and the SIMPLE method is used to solve the gas phase flow. According to the application of this principle,the pressure,temperature and velocity's distribution are analyzed with FLUENT software.Optimal designing structure of the nozzle is:Inlet diameter:D1=15.2mm;outlet diameter:D2=13mm;throat radius:Rcr= 3.5mm;Diverging angle:α=30°;L1=20.9mm;expanding angle:β=10°;L2=50mm; Total length:L=70.9mm.Then,the optimized nozzle properties were simulated and get a reasonable result.It proved that the velocity of outlet had been improved effectively.So, The nozzle had been designed and manufactured.The optimization effective had been proved by the spraying experiment.