Gas-flow rate and reynolds number in a tube of plasma jet device

Summary form only given. For flow in a pipe or tube, the Reynolds number (Re) is generally defined with fluid velocity, tube diameter, and kinematic viscosity. With a certain value of Re, the flow will become unstable and turbulent. This instability occurs with different fluids, usually when Re is over 2000. The laminar flow is stable if Re is less than 2000. In the interval between 2000 and 4000, laminar and turbulent flows are possible and are called "transition" flows, depending on other factors, such as pipe roughness and flow uniformity. In an atmospheric plasma jet of pencil type, a glass tube is used to insert the discharge gas. The property of plasma jet depends on the gas flow velocity which is given by the tube diameter and the volumetric gas flow rate. However, there exists an optimal flow velocity to obtain a stable plasma jet. The dependence of flow velocity on the instability of discharge plasma can be analyzed with Reynolds number which defines the stability of flow such as the stable laminar flow and the turbulent flow in hydro-kinetics. In this report the optimum flow velocity in a glass tube of plasma jet is investigated according to the stability of discharge plasma with the variation of Reynolds number. In the range of stable discharge where the laminar flow is sustained, the length of plasma jet column and plume is increased and the operational discharge voltage is decreased as the flow velocity is increased in the glass tube. However, if the gas flow velocity is increased to be over the critical value of turbulent flow, the length of plasma jet column as well as the plasma current varies unstably. In the conclusion the flow velocity has the limited value to keep the laminar flow inside the glass tube for the stable discharge of plasma jet.