Theoretical and experimental study on heat transfer behaviour in gun tubes using aerosil additive for surface erosion protection

Abstract

The action of additive particles on reducing heat transfer from the hot, compressed propellant gas flow into the barrel of a powder gun has been investigated by both theoret~cal considerations and experiments performed at the 20 mm calibre erosion gun of ISL. For this purpose a boundary layer model was developed and its theoretical results were compared with bore temperature measurements carried out at two measuring stations which are placed near the forcing cone inside the gun tube. For theoretical description, Prandtl's boundary layer equations were applied to solve the unsteady, compressible and turbulent boundary layer development for determination of the heat flux q(x) from propellant gas to barrel wall. A solution of the heat conduction equation was used to get the entire tube temperature development during firing. We assumed that the additive particles used (aerosil: SiOJ in this study form a thin deposit layer acting as a barrel coating on the barrel's inner surface. The thickness of this layer is determined by matching the calculated temperature distribution to that obtained by thermocouple measurements. It was found that the SiOz layer thickness is of the order of 1.5 pm k 0.5 pm per firing which is in accordance with metallographic investigations of surface sensors at ISL.