Modeling flow, heat and mass transfer in a porous biomass plug - when used in an electrically heated tobacco system

Heating porous biomass samples is utilized in many industries for drying or extracting Volatile Organic Compounds (VOC) from the biomass. The heating may trigger physical and chemical processes within the material, such as release of VOC, thermal degradation and evaporation. Most of the processes triggered by the increased temperature are occurring simultaneously and are strongly interdependent. For most practical applications, it is important to have control of the complex processes occurring during heating to generate stable and controllable release of VOC. This is the case for products delivering the released VOC to consumers by inhalation, as is the case of an Electrically Heated Tobacco System (EHTS). Please download the full abstract below

Eulerian modeling of inertial and diffusional aerosol deposition in bent pipes

This paper presents a sectional Eulerian aerosol model for size-dependent droplet deposition at walls of the domain, driven by both diffusion and inertia. The model is based on the internally mixed assumption and employs the formulation for compressible aerosols. It is validated in a bent pipe geometry against models and experimental and numerical data from literature. Good agreement is found in both the diffusion and inertial deposition regimes. To improve the overprediction of inertial deposition by a boundary treatment that adopts zero-gradient droplet wall velocity, we use a corrected wall velocity, based on an analytical solution of the droplet motion near the wall. In the bent pipe setting the corrected wall velocity is found to reduce the overprediction of deposition and is less sensitive to grid refinement. We also show that refining the computational mesh near the pipe wall improves the predicted deposition efficiency, significantly. Finally, we present a parameter study varying the Reynolds number and the bend curvature. The deposition efficiency curve is recorded for droplet diameters ranging from the nanometer scale to beyond the micrometer scale, which is a unique contribution of this paper. The complete size range is simulated in only one simulation, due to the sectional approach. In the diffusion-dominated regime an increase in Reynolds number leads to a gradual enhancement of deposition. In the inertial regime, where droplet drift dominates deposition, a much stronger dependence on the Reynolds number is found. The dependence of the deposition on the bend curvature is less pronounced. The results shown in this paper establish the role of Eulerian simulation in predicting deposition of aerosol droplets and are useful for understanding size-dependent aerosol deposition in other more complex confined geometries

Non-local modulation of the energy cascade in broad-band forced turbulence

Classically, large-scale forced turbulence is characterized by a transfer of energy from large to small scales via nonlinear interactions. We have investigated the changes in this energy transfer process in broad-band forced turbulence where an additional perturbation of flow at smaller scales is introduced. The modulation of the energy dynamics via the introduction of forcing at smaller scales occurs not only in the forced region but also in a broad range of length-scales outside the forced bands due to non-local triad interactions. Broad-band forcing changes the energy distribution and energy transfer function in a characteristic manner leading to a significant modulation of the turbulence. We studied the changes in this transfer of energy when changing the strength and location of the small-scale forcing support. The energy content in the larger scales was observed to decrease, while the energy transport power for scales in between the large and small scale forcing regions was enhanced. This was investigated further in terms of the detailed transfer function between the triad contributions and observing the long-time statistics of the flow. The energy is transferred toward smaller scales not only by wavenumbers of similar size as in the case of large-scale forced turbulence, but by a much wider extent of scales that can be externally controlled.Comment: submitted to Phys. Rev. E, 15 pages, 18 figures, uses revtex4.cl

Comparison of experimentally measured and computational fluid dynamic predicted deposition and deposition uniformity of monodisperse solid particles in the Vitrocell® AMES 48 air-liquid-interface in-vitro exposure system

Accurately determining the delivered dose is critical to understanding biological response due to cell exposure to chemical constituents in aerosols. Deposition efficiency and uniformity of deposition was measured experimentally using monodisperse solid fluorescent particles with mass median aerodynamic diameters (MMAD) of 0.51, 1.1, 2.2 and 3.3 μm in the Vitrocell® AMES 48 air-liquid-interface (ALI) in vitro exposure system. Experimental results were compared with computational fluid dynamic, (CFD; using both Lagrangian and Eulerian approaches) predicted deposition efficiency and uniformity for a single row (N = 6) of petri dishes in the Vitrocell® AMES 48 system. The average experimentally measured deposition efficiency ranged from 0.007% to 0.43% for 0.51–3.3 μm MMAD particles, respectively. There was good agreement between average experimentally measured and the CFD predicted particle deposition efficiency, regardless of approach. Experimentally measured and CFD predicted average uniformity of deposition was greater than 45% of the mean for all particle diameters. During this work a new design was introduced by the manufacturer and evaluated using Lagragian CFD. Lagragian CFD predictions showed better uniformity of deposition, but reduced deposition efficiency with the new design. Deposition efficiency and variability in particle deposition across petri dishes for solid particles should be considered when designing exposure regimens using the Vitrocell® AMES 48 ALI in vitro exposure system

Wake-vortex decay in external turbulence

Wake vortices that form behind a moving aircraft represent 11 safety COil cern for other aircraft.s that follow. These tornado-like wake structures may persist for several minutes, extending for many kilometers across the sky. This safety issue is particularly important close to major airports where successive aircrafts follow approximately the same approach or departure paths at relatively high frequency. For this reason, safety regulations require aircrafts to be well separated in flight. This obviously limits the airport's throughput capacity, even to the point of leading to congestion and delays