# Modelling of a Non-Transferred Plasma Torch Used for Nano-Silica Powders Production
To synthesize nanosilica particles, a non-transferred arc system is run on nitrogen plasma gas, followed by a short mixing section of silicon tetrachloride (SiCI4) and carrier mixing gas (nitrogen and hydrogen) heated to about 1373.15 K and injected in the plasma tail flame. The process starts with vaporization of precursor materials owing to the high enthalpy of the plasma, and then the temperature of the material vapor transported by the nitrogen tail flame decreases drastically; the vapor is highly supersaturated due to this quenching, which results in a rapid production of numerous nanoparticles via homogeneous nucleation, heterogeneous condensation, and coagulation between nanoparticles themselves. Nowadays, the manufacturing processes of nanoparticles by a thermal plasma process is experimentally achieved. However, the understanding of the growth mechanism of the nanoparticles and the control of the size and the composition of the particle remains insufficient. In most cases, it is impossible to measure different aspects of the process, and only the characteristics of the final products are evaluated because there is a complex interaction between the thermo-fluid field, the induced electromagnetic field, and the particle concentration field [19]. Numerical modelling can be a powerful approach, allowing a better understanding of the growth mechanism of nanoparticles and improving torch designs and plasma processes at relatively low prices. Several research efforts have been dedicated to modelling the plasma flow and heat transfer coupled with the electromagnetic field inside and outside the plasma torch. Simulation of the arc inside a DC torch was first developed by [PERSON] and [PERSON] [20] and [PERSON] [21]. In these models, the arc breakdown and reattachment operations in the plasma torch are accurately evaluated. A transient simulation of a DC plasma torch has been performed later by [PERSON] [22] to evaluate the substrate temperature with heating time and to estimate different precursor effects on the thermal flux to the substrate. Subsequently, [PERSON] [23] and [PERSON] [24] employed new models with the large eddy simulation technique to simulate the turbulent plasma flow inside a DC non-transferred arc plasma torch and the effect of particle injection. For nanopowder production, the nanoparticles are generated not in the high-temperature plasma core but in the interfacial regions between the plasma and the cold gas at low to intermediate temperature. Lower-temperature regions tend to be more turbulent with multiscale eddies. These eddies strongly affect the transport processes of nanoparticles. Moreover, a combined plasma torch including a plasma jet of the DC arc plasma torch fed to the inlet of the RF-ICP plasma torch and used for nano-powder production has been presented by [PERSON] [25] in order to reduce the power of the RF discharge in the plasma torch. Recently, a numerical model applied to a triple DC plasma torch used to synthesize nanoparticles was performed by [PERSON] [26]. The results of the simulation presented an analysis of the thermal environment inside the reactor to control the condensation process of the nanoparticles. In the present study, a two-dimensional axisymmetric turbulent model of a DC non-transferred plasma torch used for the synthesis of nano-silica was developed. Moreover, the effect of different plasma parameters such as the current and the gas flow rate were investigated, and discussion about the efficiency of the torch for different cases was realized. Furthermore, in this work, a DC non-transferred plasma torch was used to synthesis silica nanoparticles. In this study, the principal objective was the optimization of the circumstances of this process in terms of the production rate and the primary particle size. Numerical results were compared with the experimental measurements.