A model for heating and evaporation of a droplet cloud and its implementation into ANSYS Fluent

© 2018 Elsevier Ltd A model for heating and evaporation of a cloud of monocomponent droplets in air, taking into account the evolution of droplet number densities, is developed and implemented into ANSYS Fluent. Functionality testing of the new customised version of ANSYS Fluent is based on its application to the analysis of a droplet cloud in a two-phase back-step flow. It is shown that the effect of the droplet cloud needs to be taken into account when estimating the heat and mass transfer rates from the carrier phase to the droplets

Numerical study of nanoparticle formation in a free turbulent jet

© Published under licence by IOP Publishing Ltd.Di-ethyl-hexyl-sebacate (DEHS) aerosol nanoparticle formation in a free turbulent jet as a result of nucleation, condensation and coagulation is studied using fluid flow simulation and the method of moments under the assumption of lognormal particle size distribution. The case of high nucleation rates and the coagulation-controlled growth of particles is considered. The formed aerosol performance is jet is numerically investigated for the various nozzle diameters and two approximations of the saturation pressure dependence on the temperature. It is demonstrated that a higher polydispersity of the aerosol is obtained for smaller nozzle diameters

A model for multi-component droplet heating and evaporation and its implementation into ANSYS Fluent

The main ideas of the model for multi-component droplet heating and evaporation, based on the analytical solutions to the heat conduction and species diffusion equations in the liquid phase, and its implementation into ANSYS Fluent CFD software are described. The model is implemented into this software via User-Defined Functions (UDF). The predictions of ANSYS Fluent with the newly implemented model are verified against the results predicted by the previously developed in-house research code for droplets comprising of a mixture of ethanol and acetone evaporating and cooled down in ambient air.Publisher Statement: NOTICE: this is the author’s version of a work that was accepted for publication in International Communications in Heat and Mass Transfer. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in International Communications in Heat and Mass Transfer, [90, (2017)] DOI: 10.1016/j.icheatmasstransfer.2017.10.018© 2017, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/<br/

Modelling of the evolution of a droplet cloud in a turbulent flow

The effects of droplet inertia and turbulent mixing on the droplet number density distribution in a turbulent flow field are studied. A formulation of the turbulent convective diffusion equation for the droplet number density, based on the modified Fully Lagrangian Approach, is proposed. The Fully Lagrangian Approach for the dispersed phase is extended to account for the Hessian of transformation from Eulerian to Lagrangian variables. Droplets with moderate inertia are assumed to be transported and dispersed by large scale structures of a filtered field in the Large Eddy Simulation (LES) framework. Turbulent fluctuations, not visible in the filtered solution for the droplet velocity field, induce an additional diffusion mass flux and hence additional dispersion of the droplets. The Lagrangian formulation of the transport equation for the droplet number density and the modified Fully Lagrangian Approach (FLA) make it possible to resolve the flow regions with intersecting droplet trajectories in the filtered flow field. Thus, we can cope successfully with the problems of multivalued filtered droplet velocity regions and caustic formation. The spatial derivatives for the droplet number density are calculated by projecting the FLA solution on the Eulerian mesh, resulting in a hybrid Lagrangian–Eulerian approach to the problem. The main approximations for the method are supported by the calculation of droplet mixing in an unsteady one-dimensional flow field formed by large-scale oscillations with an imposed small-scale modulation. The results of the calculations for droplet mixing in decaying homogeneous and isotropic turbulence are validated by the results of Direct Numerical Simulations (DNS) for several values of the Stokes number

The fully Lagrangian approach to the analysis of particle/droplet dynamics: Implementation into ansys fluent and application to gasoline sprays

The fully Lagrangian approach (FLA) to the calculation of teh number density of inertial partucles in dilute gas-particles flows was incorporated into teh CFD code ANSYS Flunet. The new verion of ANSYS Fluent was applied to moedling dilute gas-particle flow around a cylinder and liquid droplets in a gasoline fuel spray. In a steady-state case, thre predictions of the FLA for the flow around a cylinder and those based on teh equilibrium Eulerian method (EE) are almost the same for small Stokes number (Stk) and small Reynolds number (Re). FLA predicts higher values of the gradients of particle number densities in front of the cylinder compared with the ones predicted by the EE for larger values of Stk and Re. Application of FLA to a direct injection gasoline fuel spray has concentrated on the computation of the number densities of droplets. Results revelaed good agreement between the numerical simulation and exeperimental data

Meshless methods for ‘gas ‐ evaporating droplet’ flow modelling

The main ideas of simulation of two-phase flows, based on a combination of the conventional Lagrangian method or fully Lagrangian method (FLM) for the dispersed phase and the mesh-free vortex and thermal blob methods for the carrier phase, are summarised. A meshless method for modelling of 2D transient, non-isothermal, gasdroplet flows with phase transitions, based on a combination of the viscous-vortex and thermal-blob methods for the carrier phase with the Lagrangian approach for the dispersed phase, is described. The one-way coupled, two-fluid approach is used in the analysis. The method makes it possible to avoid the `remeshing' procedure (recalculation of flow parameters from Eulerian to Lagrangian grids) and reduces the problem to the solution of three systems of ordinary differential equations, describing the motion of viscous-vortex blobs, thermal blobs, and evaporating droplets. The gas velocity field is restored using the Biot-Savart integral. The numerical algorithm is verified against the analytical solution for a non-isothermal Lamb vortex. The method is applied to modelling of an impulse two-phase cold jet injected into a quiescent hot gas, taking into account droplet evaporation. Various flow patterns are obtained in the calculations, depending on the initial droplet size: (i) low-inertia droplets, evaporating at a higher rate, form ring-like structures and are accumulated only behind the vortex pair; (ii) large droplets move closer to the jet axis, with their sizes remaining almost unchanged; and (iii) intermediate-size droplets are accumulated in a curved band whose ends trail in the periphery behind the head of the cloud, with larger droplets being collected at the front of the two-phase region

Mathematical modelling of heating and evaporation of a spheroidal droplet

Objective: Dialysis patients frequently report a change of taste that is reversible after renal transplantation, suggesting that uremic toxins may negatively influence taste. Currently, frequent nocturnal home hemodialysis (NHHD) is the most effective method of hemodialysis, and is associated with the lowest levels of uremic toxins. We studied preferences for various foods as an indicator of taste perception. We questioned whether food preference differs between NHHD patients and those on conventional hemodialysis. Design and Patients: In this transverse, cross-sectional pilot study, we assessed food preference by means of a questionnaire for patients on NHHD (n=6; 8 hours of dialysis per night, for 5 or 6 nights a week) and 3 age-matched and sex-matched control groups: chronic home hemodialysis patients (HHD; n=9; 4 to 5 hours of dialysis per day, 3 days a week), chronic in-center hemodialysis patients (CHD; n=18; 4 to 5 hours of dialysis per day, 3 days a week), and healthy control subjects (HC; n=23). Results: Mean scores for food preference did not differ between groups (P=.32). Similarly, the preference for product groups did not differ between groups. On an individual product level, we found only minor differences. The NHHD patients had a preference for savory snacks, as did the HC and CHD groups, whereas the HHD group had a preference for sweet snacks (P <.05). Hemodialysis patients reported dry mouth more often than did the HC patients (P <.05). Conclusions: Frequent NHHD has no major impact on food preference. The change in taste reported by NHHD patients is not related to their particular food preferences. (C) 2010 by the National Kidney Foundation, Inc. All rights reserved

Robust interpolation for dispersed gas-droplet flows using statistical learning with the Fully Lagrangian Approach

A novel methodology is presented for reconstructing the Eulerian number density field of dispersed gas-droplet flows modelled using the Fully Lagrangian Approach (FLA). In this work, the nonparametric framework of kernel regression is used to accumulate the FLA number density contributions of individual droplets in accordance with the spatial structure of the dispersed phase. The high variation which is observed in the droplet number density field for unsteady flows is accounted for by using the Eulerian-Lagrangian transformation tensor, which is central to the FLA, to specify the size and shape of the kernel associated with each droplet. This procedure enables a high level of structural detail to be retained, and it is demonstrated that far fewer droplets have to be tracked in order to reconstruct a faithful Eulerian representation of the dispersed phase. Furthermore, the kernel regression procedure is easily extended to higher dimensions, and inclusion of the droplet radius within the phase space description additionally enables the droplet size distribution and its statistics, such as average and variance, to be determined for polydisperse flows. The developed methodology is applied to a range of 1D and 2D steady-state and transient flows, for both monodisperse and polydisperse droplets, and it is shown that kernel regression performs well across this variety of cases. A comparison is made against conventional direct trajectory methods to determine the saving in computational expense which can be gained, and it is found that $10^3$ times fewer droplet realisations are needed to reconstruct a qualitatively similar representation of the number density field in which the absolute error is generally below $10^{-1}$

A model for heating and evaporation of a droplet cloud and its implementation into ANSYS Fluent

© 2018 Elsevier Ltd A model for heating and evaporation of a cloud of monocomponent droplets in air, taking into account the evolution of droplet number densities, is developed and implemented into ANSYS Fluent. Functionality testing of the new customised version of ANSYS Fluent is based on its application to the analysis of a droplet cloud in a two-phase back-step flow. It is shown that the effect of the droplet cloud needs to be taken into account when estimating the heat and mass transfer rates from the carrier phase to the droplets