Essential to estimating the potential exposure from dusts of toxic, hazardous or irritant powders is the evaluation of the dustiness of the powders being handled. Dustiness is the tendency of a ...powder to aerosolize with a given input of energy. Evaluating dustiness of a manufactured powder can alert to a potential exposure to workers. It can also aid in the selection of manufacturing processes/operations which generate less dust for a particular substance and can provide vital information to guide selecting/creating powders which generate less dust. A widely used (but marginally understood) instrument to evaluate powder dustiness is the Rotating Drum. Using computational fluid dynamics, we have numerically investigated the flow inside the Rotating Drum dustiness tester during its operation. A complete description of the flow aerodynamics associated with operation of this instrument will assist in the interpretation of dustiness measurements conducted with this instrument.
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•CFD simulations are used to characterize the Rotating Drum Dustiness test.•The Rotating Drum preferentially measures 8 μm < d < 24 μm aerosolized dust.•Low experimental dustiness values result from powder agglomeration.•The Rotating Drum has an internal spatial loading bias.•Experiment confirms the internal spatial loading bias of the Drum.
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•Computational fluid dynamics simulations are used to characterize Heubach dustiness drum.•Efficiency of drum (“instrument function”) depends on orientation of internal ...vanes.•90°-oriented vanes generate strong swirl that destabilizes the axial jet.•A destabilized axial jet (90° vane orientation) efficiently entrains small (d < 1 μm) dust particles.
Potential exposure from hazardous dust may be assessed by evaluating the dustiness of the powders being handled. Dustiness is the tendency of a powder to aerosolize with a given input of energy. Previously we used computational fluid dynamics (CFD) to numerically investigate the flow inside the European Standard (EN15051) rotating drum dustiness tester during its operation. The present work extends those CFD studies to the widely used Heubach rotating drum. Air flow characteristics are investigated within the Abe-Kondoh-Nagano k-epsilon turbulence model; the aerosol is incorporated via a Euler-Lagrangian multiphase approach. The air flow inside these drums consists of a well-defined axial jet penetrating relatively quiescent air. The spreading of the Heubach jet results in a fraction of the jet recirculating as back-flow along the drum walls; at high rotation rates, the axial jet becomes unstable. This flow behavior qualitatively differs from the stable EN15051 flow pattern. The aerodynamic instability promotes efficient mixing within the Heubach drum, resulting in higher particle capture efficiencies for particle sizes d < 80 μm.
The effect of surfactant molecular mass transport on the normal impact and spreading of a droplet of its aqueous solution on dry horizontal substrates is investigated experimentally for a range of ...Weber numbers (20−100). The postimpact dynamics of film spreading and its recoil behavior are captured using high-speed real-time digital imaging. Hydrophilic (glass) and hydrophobic (Teflon) substrates were used with water and aqueous solutions of three different surfactants of varying diffusion rates and ionic characteristics: SDS (anionic), CTAB (cationic), and Triton X-100 (nonionic). Their solutions facilitate larger spread and weaker surface oscillations compared to a pure water drop colliding at the same Weber number. On a hydrophobic surface, the drop rebound and column fracture are inhibited by the presence of the surface-active agent. Besides reagent bulk properties, dynamic surface tension, surface wettability, and droplet Weber number govern the transient impact−spreading−recoil phenomena. The role of dynamic surface tension is evident in comparisons of impact dynamics of droplets of different surfactant solutions with identical equilibrium surface tension and same Weber number. It was observed that higher diffusion and interfacial adsorption rate (low molecular weight) surfactants promote higher drop spreading factors and weaker oscillations compared to low diffusion/adsorption rate (high molecular weight) surfactants.
Instability and breakup of a viscous annular liquid sheet that is exposed to co-flowing inner and outer gas streams have been investigated using a nonlinear spatial stability analysis. A perturbation ...expansion method is used with the initial amplitude of the disturbance as the perturbation parameter. The evolution of the two gas–liquid interfaces is tracked until the sheet breaks up and the breakup length is determined. The model is validated by comparison with available experimental data. The effects of liquid swirl strength, gas-to-liquid density ratio, radius of curvature ratio, and liquid viscosity on the sheet instability and breakup have been studied. The results show that at very low values of liquid swirl, it has a stabilizing effect on sheet breakup, but as the swirl strength increases, it strongly destabilizes the sheet. Also, with increasing swirl strength, the occurrence of the large surface deformations moves from the inner interface to the outer interface. The sheet breakup length increases slightly and then decreases rapidly with an increase in liquid swirl strength. Without liquid swirl, the axisymmetric mode is the dominant instability mode. However, with increasing liquid swirl strength, the higher helical modes become dominant and the breakup becomes increasingly asymmetric. When the undisturbed liquid sheet has a purely axial motion, the inner gas stream is more effective in sheet breakup than the outer gas stream. In the presence of liquid swirl, the outer gas stream is more disruptive than the inner gas stream. The breakup length becomes shorter as gas-to-liquid density ratio and the radius of curvature ratio increases. Increase in liquid viscosity tends to slow the disturbance growth and increases the sheet breakup length.
Experimental results for phase transition during extended thermal cycling of the salt hydrate LiNO3·3H2O in both heterogeneous nucleation and self-seeding as well as material compatibility are ...presented. Controlled samples of this phase-change material (PCM) are heated and cooled between 20 and 40 °C. This was carried out for 1000 thermal cycles to ascertain the long-term suppression of subcooling without degradation in latent heat (h sf). In heterogeneous nucleation, two additives were considered, Zn3OH4(NO3)2, and Zn(NO3)2·6H2O, whereas the self-seeding was induced by less than complete (90%) melting. The two nucleating agents were selected by the minimal lattice-mismatch method for salt crystals. Self-seeding was found to completely suppress subcooling without any loss in the latent heat of fusion, whereas heterogeneous nucleation with additives resulted in a subcooling of ΔT s > 3 °C and an up to 8–52% loss in latent heat after 1000 thermal cycles. Additionally, the material compatibility test was conducted with Al 3003, Al 1100, and SS 304 for 4000 heating−cooling cycles. The corrosion rates observed without nucleating agents were insignificant and less than typically observed in similar metals exposed to marine conditions.
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