What do we know about long laminar plasma jets?

Abstract

Silent and stable long laminar plasma jets can be generated in a rather wide range of working parameters. The laminar flow state can be maintained even if considerable parameter fluctuations exist in the laminar plasma jet or if there is an impact of laterally injected particulate matter and its carrier gas. The attractive special features of laminar plasma jets include extremely low noise level, less entrainment of ambient air, much longer and adjustable high-temperature region length, and smaller axial gradient of plasma parameters. Modeling results show that the laminar plasma jet length increases with increasing jet inlet velocity or temperature and the effect of natural convection on laminar plasma jet characteristics can be ignored, consistent with experimental observations. The large difference between laminar and turbulent plasma jet characteristics is revealed to be due to their different laws of surrounding gas entrainment. Besides the promising applications of the laminar plasma jet to remelting and cladding strengthening of the metallic surface and to thermal barrier coating preparation, it is expected that the laminar plasma jet can become a rather ideal object for the basic studies of thermal plasma science owing to the nonexistence of the complexity caused by turbulence.

A Simple Approach to Surface Modification Using Polytetrafluoroethylene (PTFE) with Laminar and Turbulent Flows of Micro Plasma Jets at Atmospheric Pressure

“…Because of the big inertial force in helium gas at high flow rate, the gas mixes much more rapidly and completely with ambient air. As the collision frequency increases between electrons and heavy particles in the turbulent jet, the energy transfer from electrons to heavy particles also becomes very active 31…”

The shift in the laminar‐to‐turbulent transition flow mode in atmospheric pressure plasma jet

“…The concentration of air in the plasma jet begins to saturate after the plasma jet becomes totally turbulent. [ 12–14 ]…”

“…The concentration of air in the plasma jet begins to saturate after the plasma jet becomes totally turbulent. [12][13][14] The transition from the laminar-to-the turbulent mode is closely related to the apparent decrease of plasma jet length. To check the mode transition, Reynolds numbers (R e ) are calculated.…”

Production of long, laminar plasma jets at atmospheric pressure with multiple cathodes

“…One of the methods for tackling such issues is the production of a long, quasi‐laminar plasma jet. A laminar plasma jet has such properties as a long and stable plasma jet, reduced entrainment of the atmosphere, reduced temperature gradient in the axial direction, and negligible noise emission . Several experiments have established that a laminar plasma jet has better performance in plasma spraying, remelting/cladding processing, hardening of a cast iron surface, and thermal barrier/hydroxyapatite coatings preparation compared with a short, turbulent plasma jet.…”