Multi-coupled mass transfer mechanisms during solvent removal of nitrocellulose-based propellant

Abstract

This work has designed and developed an industrial-scale experiment system for studying the multi-coupled mass transfer mechanisms included in the solvent removal of the propellant grains. In this respect, the propellant grains were subjected to hot air convection for two hours at a temperature of 40.0°C and relative humidity of 85.0%, of which the mass flow rate was 595.0 kg·h−1 (or 720.0 kg·h−1). The measured data of the transient solvent content were analyzed based on the nonlinear least-squares regression. A slop method was used to predict the effective diffusivity of the solvents held in the propellant grains. In addition, the adsorption kinetics behavior and the mechanism of the propellant grains to the water vapor were studied in detail. As a result, both the vaporization of the solvents as well as the adsorption of the water vapor appeared on the surface of the propellant grains at the same time. The ethanol inside the propellant grains has a greater effective diffusivity compared to ether. The mass transfer in the solvent removal of the propellant grains was controlled by both the internal and external resistances. Moreover, the adsorption of the propellant grains to the water vapor was dominated by physical adsorption.