G9
Process Simulation 2

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17:35
conference time (CEST, Berlin)
Modeling of the Aluminium Electrolysis Process: Feeding and Dissolution of Alumina Particles
26/10/2021 17:35 conference time (CEST, Berlin)
Room: G
H. Gesell, R. Gutt, N. Janssen, U. Janoske (Bergische Universität Wuppertal, DEU)
H. Gesell, R. Gutt, N. Janssen, U. Janoske (Bergische Universität Wuppertal, DEU)
The main objective of the Hall-Héroult process, which is applied to produce primary aluminium, is the electrolytic reduction of alumina (Al2O3) dissolved in an electrolyte. The electrolyte mainly consists of cryolite (Na3AlF6) and is present in a molten condition at around 960°C. Alumina, as the raw material of the process, is permanently fed to the bath. After the injection, alumina particles have to reach the temperature of the surrounding bath, before they start to dissolve. The dissolution rate is controlled by thermal and chemical conditions as well as the transport and mixing of particles and electrolyte. The present model describes the feeding and dissolution of alumina particles to the bath. It is implemented in the OpenFOAM® framework using the Lagrangian approach for the coupling of continuous (electrolyte and liquid aluminium) and dispersed phase (alumina). The model solves the mass transfer from dispersed to continuous phase, the energy equation, and the transport of dissolved concentration. Moreover, the influence of thermal conditions and turbulent mixing because of gas bubbles arising under the anodes, is considered by the model. The velocity field is adopted from previously executed MHD simulations (described in part II). With the help of the developed model, various studies are carried out. The focus corresponding to the increased flexibility of electric power consumption is on the thermal behaviour during cold operating conditions of the electrolysis cell. It has to be ensured, that the full amount of fed alumina is dissolved. The sinking of undissolved alumina to the bottom of the cell has to be prevented as it has a negative impact on cell efficiency. The results show a dependency of dissolution rate and total dissolution time on the bath temperature. Even more important is the bath superheat defined by the difference of bath temperature and liquidus temperature of the bath. Furthermore, the influence of process parameters like grain size, chemical conditions of the bath, velocity distribution, and turbulent mixing are studied in detail.
aluminium electrolysis, Hall-Héroult process, dissolution, mass transfer, alumina feeding, Lagrangian particle tracking, turbulent mixing, OpenFOAM®
17:55
conference time (CEST, Berlin)
Bottle Sanitization Modeling
26/10/2021 17:55 conference time (CEST, Berlin)
Room: G
C. Shiau, L. Zhao, M. Ciciora, A. Huchthausen, Y. Lou, S. Qu (PepsiCo, USA)
C. Shiau, L. Zhao, M. Ciciora, A. Huchthausen, Y. Lou, S. Qu (PepsiCo, USA)
In the food and beverage industry, one of the effective aseptic measures to eliminate microorganisms enter the product from the package is by spray rinsing, which refers to flushing the package using liquid. New packages and processing lines typically undergo exhaustive bio-validations to meet residual targets and decide if a rinsing setting for a specific package is effective. Due to the physical limitations and insufficient understanding for identifying the exact cold spots, bio-validation's effectiveness is dependent on estimating the worst spot for testing as only a few locations in a package can be tested. A tool that can pinpoint the cold spots before physical validation can guide the rinsing setting to maximize cleaning effectiveness while minimizing water usage. This study developed an aseptic model to enhance the understanding of the spray rinsing process, including the package (bottle) and spray nozzle using the Computational Fluid Dynamics (CFD) tool. This model's target application is to provide better insights for improved package and equipment designs and eventually contribute to the optimization of the entire packaging sanitization process. An unsteady three-dimensional two-phase (liquid/gas) turbulent flow model is developed. The Volume of Fluid (VOF) method is applied to capture the interphase physics. CFD results from the model allow the instantaneous tracking of the liquid coverage on the package surface by various rinsing settings. Qualitatively, flow shielding and/or channeling due to specific package feature designs can be visualized. These designs induce special flow patterns on the bottle surface during the rinsing process and affect the cold spots. The mechanical and chemical aspects of this spray rinsing can be approximately quantified by extracting the wall shear stress and the cumulative volume fraction of liquid during the rinsing process, respectively. The time-dependent liquid volume in the package can also be monitored to track the draining process after rinsing. Accompanied with measurement data from the physical spray rinsing process, this study lays the foundation for an end-to-end simulation-driven process optimization.
CFD, CPG, Beverage, VOF, Multi-phase
18:15
conference time (CEST, Berlin)
Predicting Solder Shape Evolution During Solder Reflow in Packaging Assembly Processes
26/10/2021 18:15 conference time (CEST, Berlin)
Room: G
A. Sengupta, X. Pan, S. Medikonda, A. Srivastava, A. Shejwal, K. Morgan (Ansys Inc., USA)
A. Sengupta, X. Pan, S. Medikonda, A. Srivastava, A. Shejwal, K. Morgan (Ansys Inc., USA)
Solder reflow is performed in flip-chip packaging and Surface-Mount Technology (SMT) assembly processes for Ball-Grid Array (BGA) packages. In this process, the two parts (chip-substrate or package-PCB) are heated to a temperature of 200-260C, where the solder melts and forms an interconnection. The solder joints can form different shapes due to both the incoming warpage of the parts and additional CTE mismatch-induced warpage during the attach process. The highly distorted solder shapes result in defects such as solder bridging and non-wet opens. Owing to the large probability for such defects in new package technologies, costly design-of-experiments have to be conducted to establish the process window for maximum assembly yields. Currently, the prevalent techniques for modeling solder reflow, like Surface Evolver or Fluid-Structure Interaction methods, cannot fully capture the interactions between the solid parts and fluid-like molten solder balls, while being efficient enough to render full package simulations computationally feasible. We demonstrate that the novel fully implicit Incompressible Smoothed Particle Galerkin (ISPG) technique implemented in LS-Dyna is very efficient in capturing all relevant physics of solder reflow process. It employs a Lagrangian particle-based solution of the Navier-Stokes equation for molten solder and can be easily coupled with structural physics within one (LS-Dyna) solver. In this technique, the solder shape evolution is governed by the surface tension of solder material and structural boundary conditions, while the contact angle controls the interfacial behavior. We show that ISPG technique can accurately predict solder joint shapes, while interacting with the Copper pad and Solder Mask layer on the substrate and PCB sides. We also demonstrate the capability to simulate large-scale reflow involving hundreds of solder joints where the package and PCB warpage are modeled. This shows great potential in fine-tuning packaging assembly process parameters through guidance from simulation.
solder reflow, SMT, BGA, ISPG, surface tension, solder bridging, non-wet opens
18:35
conference time (CEST, Berlin)
Investigation of Flow Field and Heat Transfer with an Array of Slot Jet Reattachment Nozzle Over Stationary and Moving Surfaces
26/10/2021 18:35 conference time (CEST, Berlin)
Room: G
M. Farzad, C. Koh, S. Ramsay, L. Zhao (PepsiCo, USA); S. Tibos, PepsiCo, GBR)
M. Farzad, C. Koh, S. Ramsay, L. Zhao (PepsiCo, USA); S. Tibos, PepsiCo, GBR)
Drying is an inevitable industrial operation, which exists in a broad spectrum of applications such as food and agriculture, forestry products, chemicals, and pharmaceuticals. Convective hot air drying using traditional impinging jet nozzles is widely utilized as the main technique in dehydration of moist porous materials. However, conventional nozzles such as slot jet and in-line jet nozzles are generally inefficient in drying of fragile and thin materials as a low air mass flow rate is needed to avoid potential damage to the products due to the high exerted force by impinging jet nozzles. Since drying is an energy extensive process, improvement in the drying efficiency and enhancing the quality of products are essential. Therefore, slot jet reattachment (SJR) nozzle has been developed as an alternative technology to the common in-line jet (ILJ) nozzle, slot jet (SJ) nozzle, and perforated plate. SJR nozzle provides higher heat transfer rates and better product quality at the same time compared to the slot jet nozzle. Furthermore, SJR nozzle allows for controlling the exerted impingement pressure and flow direction by simply changing its exit angle. This study numerically investigates the convective air-drying characteristics of an array of SJR nozzles and compares it to those of a common SJ nozzle. First, an k-ϵ turbulence model is developed to predict the heat transfer coefficients generated by a single SJR and SJ nozzles adjacent to the impingement surface. Then, heat transfer coefficients are calculated based on the different operating conditions (nozzle outlet air temperature and flow rate) and various SJR nozzle’s geometrical parameters (nozzle angle and nozzle exit opening) over both stationary and non-stationary impingement surfaces. Second, another nozzle is added next to the first nozzle to investigate the effect of arrays of SJR and SJ nozzles on the flow field issuing from the nozzles and the heat transfer rates. The comparisons are made based on the identical air mass flow rate criterion (same Re number). The results are presented for both stationary and moving surfaces for SJ and SJR nozzles. Utilizing these numerical models enable one to investigate the drying characteristics of SJ and SJR nozzles with various operating conditions and different geometrical SJR nozzle parameters. Moreover, based on the numerical results, SJR nozzle always resulted in higher local heat transfer coefficients, which show the superiority of an SJR nozzle in providing higher drying rates compared to those of SJ nozzle.
Slot Jet Reattachment, Slot Jet, Nozzle, Heat Transfer, Array of Nozzles, Moving Surface, Numerical Study
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