Numerical study on dense-phase powder conveying in the feeding system of powder fueled ramjets

A better understanding of gas-solid flow in the pneumatic conveying of dense powders is an essential prerequisite for effective design and operation of conveying systems in powder fueled ramjets. This paper presents a resistance modified model applicable to the dense-phase powder conveying in gas-driven piston powder feeding system based on Two-Fluid Model (TFM), and the dynamic grid techniques related to the output powder mass flow rate has been applied on gas-driven piston boundary. The validity of the modified model is confirmed by comparing the predicted powder mass flow rate with data obtained from the experiment. The resistance modified model, which incorporates a comprehensive consideration of gas momentum loss by accounting for local solid fraction, interphase slip velocity, and powder diameter, is proved to significantly improve the accuracy of predicting dense powder conveyance. The features of gas-solid flow evolution in gas-driven piston powder feeding systems are numerical explored. The formation of the fluidizing gas cavity and its radial diffusion characters are studied and the influences of the total pressure of fluidizing gas on mass flow rate of powders are obtained. And choked occurs in gas-powder two-phase conveying to realize a stable propellant feeding under specific pressure ratio conditions. Moreover, pressure ratio determines pressure distribution in nozzle pipe revealing the transition of the flow pattern from core flow to annular flow corresponds directly to the pressure ratio.