Numerical Simulation on Impact Velocity of Ceramic Particles Propelled by Supersonic Nitrogen Gas Flow in Vacuum Chamber

Abstract

A low-pressure cold spray, which is conducted in a vacuum chamber, is under development in Japan. In this paper, the gas flow-field as well as the particle velocity of the low-pressure cold spray is numerically solved. A special attention is paid to the effect of the pressure in the vacuum chamber (back pressure) on the particle velocity. The working gas is nitrogen, and its stagnation temperature upstream of the nozzle is set at 573 K. The back pressure is set at constant values ranging from 3×102 to 1×105 Pa. The stagnation pressure upstream of the nozzle is kept constant at 30 times as much as the back pressure. The numerical results show that the decrease in the back pressure causes the decrease in the particle velocity in front of the normal shock wave. On the contrary, the decrease in the back pressure eases the particle deceleration through the normal shock wave. As a whole, due to the balance of the effects of the back pressure and the normal shock wave, the optimum value of the back pressure to obtain the maximum impact velocity varies depending on the particle diameter.