Numerical simulation of jet-lifting under variable gravity field

We conducted a series of numerical simulations to investigate the efficiency of a pneumatic method to convey lunar soil under earth (9.8 ms ^-2) and lunar (1.62 ms^-2) gravity field. This numerical modeling was based on PFC2D with a fluid and particle coupling functions. During simulations, air jet at various pressures was injected into a 0.2 m diameter and 2m long tube that was filled with 8 mm diameter spherical particles. It was determined that the pressure of 5×10³ Pa was enough to loft particles at lunar gravity but not at earth gravity. Thus the jet-lifting method under reduced gravity conditions will be more efficient and will require the utilization of less injected gas than when used under Earth gravity conditions. Increasing the pressure to 10⁴ Pa was enough to loft particles at earth gravity. When the air injection pressure was decreased to 10³ Pa, the lofting under both gravitational fields ceased. We postulate that one of the important parameters in the fluidization of a bed of particles is the friction acting between neighboring particles. If the injected fluid cannot overcome such frictional forces, the sample would not be fluidized. As the more detailed observation suggest, this may be the major reason why at lower air pressures only the particles subjected to lunar gravity can successfully be jet-lifted.