Session W17: General Fluid Dynamics: Multi-Physics Phenomena (10:00am - 10:45am CST)

Mass transfer from a core-shell cylindrical reservoir in cross flow

Mass transfer from a core-shell cylindrical reservoir subjected to a channel cross flow is numerically studied using lattice-Boltzmann simulations. The contribution of both the flow and the solute shell permeability to mass transfer is quantified by the Sherwood number, which is the dimensionless mass transfer coefficient. The transition from steady laminar flow to unsteady flow impacts the mass transfer, and thus, the release efficiency. Mass transfer is also considerably altered by the presence of a coating shell, which slows down the solute release. An empirical correlation, highlighting the contribution of the solute shell permeability, has been extracted from the obtained numerical data. The proposed correlation is useful for applications in controlled mass transfer from cylindrical reservoirs endowed with a coating semi-permeable shell.   

Augmented Brownian motion in micro-nanoscale multi-phase dynamics

Mesoscopic hydrodynamics and Langevin dynamics may be applied to a variety of problems concerning active colloids, nanoscale phase change, and bubble/droplet transport, providing a powerful compliment to experimental methods as well as materials and device design. This presentation focuses on two theoretical-numerical studies concerning mesoscale Brownian dynamics of colloidal and bubble-droplet transport. First, the problem of a Brownian particle being driven through a 1D periodic ``tilted washboard'' potential is revisited, and a novel negative differential mobility is observed prior to the onset of the well-known giant diffusion enhancement effect. The second problem concerns the calculation of the effective friction for a model of a heated nanoparticle undergoing a kind of ballistic-Brownian motion in its own vapor bubble formed via plasmonic super-cavitation. Both molecular dynamics simulations and a simplified hydrodynamics model are employed. The resulting motion is shown to be distinct from the hot Brownian motion observed elsewhere and relies on the (nearly) discontinuous change in properties between the vapor bubble and surrounding liquid. Applications and extensions of the theoretical framework of these models are discussed.   

Flux-Based Modeling of Coupled Momentum, Mass and Heat Transfer and Chemical Reactions in Multicomponent Systems

Since the pioneering work of Bird, Stewart and Lightfoot, ``Transport Phenomena'' (1960), momentum, heat and mass transfer have been unified under the same title. However, the unification has never been completed. Whereas an evolution equation in time is provided for the momentum flux, the mass and heat fluxes are determined through a direct assignment by constitutive equations. In the present work we establish the full unification of transport phenomena by developing appropriate evolution equations for all fluxes through the inclusion of inertial effects. This is achieved by using the nonequilibrium thermodynamics single generator bracket formulation developed in Beris {\&} Edwards ``Thermodynamics of Flowing Systems'' (1994). The derived equations are shown to be fully consistent with the Stefan-Maxwell/Soret-Dufour equations as derived from kinetic theory, which in turn, can be used for dilute gases to obtain all transport coefficients. The evolution equations result to the traditional Fourier and Fick laws in the long time limit. We also show how chemical reactions can be consistently incorporated in a way that can also accommodate flow-induced effects. In addition to inertia, those can include extra stresses when macromolecular components are involved.   

Capturing the internal dynamics of flow discontinuities

We extend Gibbs' concept of dividing surface to model flow discontinuities beyond that of just the phase interface. This is done by providing an alternative derivation for the dividing surface. Here, this extended definition of a dividing surface is referred to as the hypersurface. This hypersurface is a continuum approximation of a diffused region with fluid properties and flow parameters varying sharply, but continuously, across it. Here we show that the properties and equations describing a hypersurface can be derived from the equations describing the diffused region by integrating it, in the directions normal to the hypersurface. This is equivalent to collapsing the diffused region in the normal direction. Hence, ensuring that the hypersurface is both kinematically and dynamically equivalent to that of the diffused region, in a constrained zero thickness limit. The ability of our approach to model different forms of discontinuities and hypersurfaces is demonstrated by looking at various canonical problems such as material interface, vortex sheet, shock front, and expansion wave.   

Aerosols in Performance

The COVID pandemic has created a great deal of fear and uncertainty around whether aerosols from singers, actors and brass and woodwind instruments can transmit the virus. Measurements of aerosol emissions, hot wire anemometry plus schlieren and laser sheet visualizations are being made of flow from a variety of performers, with and without mitigation devices such as masks and bags. Preliminary results indicate that more aerosols are emitted from these performers compared to a person speaking quietly. A wide range of jet behaviors are observed, ranging from laminar vortex dominated flows to coherent turbulent jets with significant penetration into the environment. Masks/covers on both humans and instruments are effective at reducing jet momentum, although aerosol mitigation is highly dependent on fit and filter material.   

Vibrational excitation for Argon-Nitrogen mixed gaseous thermal plasma

The main objective of the present work is to investigate the vibrational excitation for Argon-Nitrogen mixed gaseous thermal plasma using Direct Simulation Monte Carlo (DSMC) simulations. Here, the harmonic oscillator model is applied to the vibrational mode with the characteristic vibrational temperature $\theta_{v\thinspace }= $3371 \quad K corresponding to Nitrogen molecules, and vibrational excitation is integrated with the rotational excitation. It is assumed that there is only one vibrational mode associated with each diatomic Nitrogen molecule. The DSMC simulations are carried out for temperature dependent vibrational relaxation collision number $Z_{v} = (C_{1}/T^{?}$\textit{) exp (C}$_{2} T^{-1/3}) $with the constants $C_{1\thinspace }=$ 9.1 \quad and$_{\mathrm{\thinspace }}C_{2\thinspace }=$\textit{ 220, }and \quad for rotational relaxation collision number $Z_{r} =$\textit{ 7.5} associated with the Nitrogen molecule with viscosity temperature index $? =$\textit{ 0.75} (VHS model), $? =$\textit{ 1.0} (Maxwell model), and $? =$\textit{ 0.5} (HS model). An important finding is that the rotational mode \quad comes to the equilibrium value with the translational mode very quickly. However, the vibrational relaxation slows as the temperature decreases The DSMC simulation result ensures that the collisiontemperaturedependent vibration rate is consistent with the principle of detailed balance. The vibrational distribution function sampled in the DSMC simulations is in excellent agreement (error within 2{\%}) with the Boltzmann distribution.