| A direct numerical simulation based on a finite element method has been used to examine the nature of g-jitter induced connective flows during a typical protein crystal growth (PCG) experiment in a microgravity environment. A study has been conducted to elucidate the mechanisms and parameters that control particle and fluid motions induced by small vibrations for Re p < 300. The simulation has been validated against the analytical solution in Stokes limits, terminal velocity and some results obtained in the parabolic flight experiments.; Both the experimental and numerical investigations (parametric studies) identified six parameters of importance: frequency and amplitude of the applied vibration, particle diameter and density, fluid density and fluid viscosity. In the Stokes regime, the numerical results were found to be in good agreement with the analytical results of Coimbra and Rangel (2001). The comparisons showed that in a fixed frame of reference, the particle-to-fluid motion amplitude ratio is a function of the fluid-to-particle density ratio (alpha = rho f/rhop) and parameter S which is dependent on the vibration frequency, particle radius and fluid viscosity (S = f R2/9v). The numerical results obtained beyond the Stokes regime, over a wide range of Reynolds numbers (Rep < 300), showed that the particle motion amplitude approaches the cell vibration amplitude within 1% when the ratio alpha 2/S becomes greater than about 20.; The numerically predicted fluid streamlines clearly showed that the flow past a moving particle consists of a vortex ring and occurrence of a flow separation when the particle oscillated in the proximity of one of the cell walls, during the deceleration phase of the fluid motion at Rep = 19. The numerical results also revealed the importance of wall confinement. The general observation from the numerical experiments is that the smaller cells suppress both the particle motion amplitude and velocity.; Most importantly, this research confirmed that the g-jitter induced convective flows are likely to occur during the microgravity crystal growth. In a typical protein crystal growth process (rhop = 1.2 g/cm3, D = 10∼500 mum, water-based PCG), convection was predicted to occur even at accelerations as low as 1 mug. |
