Formulation and Validation of an Efficient Computational Model for a Dilute, Settling Suspension Undergoing Rotational Mixing
Abstract
Designing processing equipment for the mixing of settling suspensions is a challenging problem. Achieving lowcost mixing is especially difficult for the application of slowly reacting suspended solids because the cost of impeller power consumption becomes quite high due to the long reaction times (batch mode) or due to largevolume reactors (continuous mode). Further, the usual scaleup metrics for mixing, e.g., constant tip speed and constant power per volume, do not apply well for mixing of suspensions. As an alternative, computational fluid dynamics (CFD) can be useful for analyzing mixing at multiple scales and determining appropriate mixer designs and operating parameters. We developed a mixture model to describe the hydrodynamics of a settling cellulose suspension. The suspension motion is represented as a single velocity field in a computationally efficient Eulerian framework. The solids are represented by a scalar volumefraction field that undergoes transport due to particle diffusion, settling, fluid advection, and shear stress. A settling model and a viscosity model, both functions of volume fraction, were selected to fit experimental settling and viscosity data, respectively. Simulations were performed with the opensource Nek5000 CFD program, which is based on the highorder spectralfiniteelement method. Simulations were performed for the cellulose suspension undergoing mixingmore »
 Authors:
 Publication Date:
 Research Org.:
 National Renewable Energy Lab. (NREL), Golden, CO (United States)
 Sponsoring Org.:
 USDOE Office of Energy Efficiency and Renewable Energy (EERE), Bioenergy Technologies Office (EE3B)
 OSTI Identifier:
 1352135
 Report Number(s):
 NREL/PO510067519
 DOE Contract Number:
 AC3608GO28308
 Resource Type:
 Conference
 Resource Relation:
 Conference: Presented at the 88th Annual Meeting of The Society of Rheology, 1216 February 2017, Tampa, Florida
 Country of Publication:
 United States
 Language:
 English
 Subject:
 09 BIOMASS FUELS; settling suspensions; rotational mixing; largevolume reactors; computation fluid dynamics; CFD; cellulose suspension
Citation Formats
Sprague, Michael A., Stickel, Jonathan J., Sitaraman, Hariswaran, Crawford, Nathan C., and Fischer, Paul F. Formulation and Validation of an Efficient Computational Model for a Dilute, Settling Suspension Undergoing Rotational Mixing. United States: N. p., 2017.
Web.
Sprague, Michael A., Stickel, Jonathan J., Sitaraman, Hariswaran, Crawford, Nathan C., & Fischer, Paul F. Formulation and Validation of an Efficient Computational Model for a Dilute, Settling Suspension Undergoing Rotational Mixing. United States.
Sprague, Michael A., Stickel, Jonathan J., Sitaraman, Hariswaran, Crawford, Nathan C., and Fischer, Paul F. Tue .
"Formulation and Validation of an Efficient Computational Model for a Dilute, Settling Suspension Undergoing Rotational Mixing". United States.
doi:. https://www.osti.gov/servlets/purl/1352135.
@article{osti_1352135,
title = {Formulation and Validation of an Efficient Computational Model for a Dilute, Settling Suspension Undergoing Rotational Mixing},
author = {Sprague, Michael A. and Stickel, Jonathan J. and Sitaraman, Hariswaran and Crawford, Nathan C. and Fischer, Paul F.},
abstractNote = {Designing processing equipment for the mixing of settling suspensions is a challenging problem. Achieving lowcost mixing is especially difficult for the application of slowly reacting suspended solids because the cost of impeller power consumption becomes quite high due to the long reaction times (batch mode) or due to largevolume reactors (continuous mode). Further, the usual scaleup metrics for mixing, e.g., constant tip speed and constant power per volume, do not apply well for mixing of suspensions. As an alternative, computational fluid dynamics (CFD) can be useful for analyzing mixing at multiple scales and determining appropriate mixer designs and operating parameters. We developed a mixture model to describe the hydrodynamics of a settling cellulose suspension. The suspension motion is represented as a single velocity field in a computationally efficient Eulerian framework. The solids are represented by a scalar volumefraction field that undergoes transport due to particle diffusion, settling, fluid advection, and shear stress. A settling model and a viscosity model, both functions of volume fraction, were selected to fit experimental settling and viscosity data, respectively. Simulations were performed with the opensource Nek5000 CFD program, which is based on the highorder spectralfiniteelement method. Simulations were performed for the cellulose suspension undergoing mixing in a laboratoryscale vane mixer. The settledbed heights predicted by the simulations were in semiquantitative agreement with experimental observations. Further, the simulation results were in quantitative agreement with experimentally obtained torque and mixingrate data, including a characteristic torque bifurcation. In future work, we plan to couple this CFD model with a reactionkinetics model for the enzymatic digestion of cellulose, allowing us to predict enzymatic digestion performance for various mixing intensities and novel reactor designs.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Apr 11 00:00:00 EDT 2017},
month = {Tue Apr 11 00:00:00 EDT 2017}
}

In this paper we develop a computational model for the mixing and transport of a dilute biomass slurry. The objective was to create a sufficiently simple and efficient model for biomass transport that can be coupled with reaction models for the study of conversion of cellulosic biomass into fermentable sugars. Our target system is 5%bymass ..alpha..cellulose, which is our proxy for more complex lignocellulosic biomass. In the authors' previous work, an experimental investigation with ..alpha..cellulose under two vanemixer configurations showed a bifurcation between a settling regime, for which settling effects dominate, and a suspended regime, for which solids are mostlymore »

Formulation, Implementation and Validation of a TwoFluid model in a Fuel Cell CFD Code
Water management is one of the main challenges in PEM Fuel Cells. While water is essential for membrane electrical conductivity, excess liquid water leads to flooding of catalyst layers. Despite the fact that accurate prediction of twophase transport is key for optimal water management, understanding of the twophase transport in fuel cells is relatively poor. Wang et. al. have studied the twophase transport in the channel and diffusion layer separately using a multiphase mixture model. The model fails to accurately predict saturation values for high humidity inlet streams. Nguyen et. al. developed a twodimensional, twophase, isothermal, isobaric, steady state modelmore » 
EM experiments for computational model validation for AH1S Cobra Helicopter
The effort described here describes a set of outdoor experiments performed on the AH1S Cobra helicopter in order to validate and compare to the computational electromagnetic models of the bulk structure of the airframe in the frequency bands up to 4 GHz. Also included in this were coupling measurements to wires and cables inside of the airframe and various cavity to HPM pulse in this frequency range as part of other activities. Additionally, the low power modeling compression will be completed in this time frame. 
Validation of CFDBWR, a new twophase computational fluid dynamics model for boiling water reactor analysis.
To allow the detailed analysis of the twophase coolant flow and heat transfer phenomena in a boiling water reactor fuel bundle the CFDBWR model is being developed for use with the commercial code STARCD which provides general twophase flow modeling capabilities. The paper reviews the key boiling phenomenological models, describes the overall strategy adopted for the combined CFDBWR and STARCD boiling models validation and presents results of a set of experiment analyses focused on the validation of specific models implemented in the code. The location of vapor generation onset, axial temperature profile and axial and radial void distributions were calculatedmore » 
Overview of Computational Model Validation and its Relationship to Inverse Problems.
Abstract not provided.