TY - JOUR A1 - Lemouedda, A. A1 - Breuer, Michael A1 - Franz, E. A1 - Botsch, T. A1 - Delgado, A. T1 - Optimization of the angle of attack of delta-winglet vortex generators in a plate-fin-and-tube heat exchanger JF - International Journal of Heat and Mass Transfer N2 - Delta-winglet vortex generators (VGs) are known to enhance the heat transfer between the energy-carrying fluid and the heat transfer surfaces in plate-fin-and-tube banks. In this study optimal angles of attack of the delta-winglets are investigated based on the Pareto optimal strategy. The optimization process combines a CFD analysis, genetic algorithms and the response surface methodology. The angle of attack of a pair a delta-winglet-type VGs mounted behind each tube is varied between β = −90° and +90°. Three circular tube rows with inline and staggered tube arrangements are investigated for Reynolds numbers from 200 to 1200 (based on the inlet height and inlet velocity). The flow structure and heat transfer behavior is analyzed in detail for certain cases and the staggered and the inline tube arrangements are compared. Finally, for each of these arrangements the optimal sets of angles of attack for different Reynolds numbers are presented. Y1 - 2010 U6 - https://doi.org/10.1016/j.ijheatmasstransfer.2010.07.017 SN - 0017-9310 VL - 53 IS - 23/24 SP - 5386 EP - 5399 PB - Elsevier BV ER - TY - CHAP A1 - Lemouedda, A. A1 - Breuer, Michael A1 - Franz, E. T1 - Pareto optimization of heat transfer enhancement of finned-tube heat exchangers with delta-winglet vor-tex generators T2 - Turbulence, heat and mass transfer 6 : proceedings of the Sixth International Symposium on Turbulence, Heat and Mass Transfer Rome, Italy, 14 - 18 September, 2009 N2 - For circular finned tubes often used in heat exchangers, the wake regions behind the tubes are regions with low heat transfer coefficient. Delta-winglet vortex generators on the fin surfaces reduce the width of the wake regions and improve the overall heat transfer rate. The present work studies numerically the effect of enhancing the performance of the finned-tubes using delta-winglets. Simulations were carried out on a model of three circular tube rows with circular fins for Reynolds numbers of 500, 700, and 900 (based on the inlet velocity and the hydraulic diameter of unit cell). Eighteen basic configurations with different number and positions of delta-winglets were investigated. The flow and heat transfer behaviors are analyzed for certain configurations. Finally, the optimal configurations are presented based on the Pareto optimality strategy. Y1 - 2009 SN - 978–1–56700–262–1 U6 - https://doi.org/10.1615/ICHMT.2009.TurbulHeatMassTransf.1860 SN - 2377-2816 SP - 1015 EP - 1018 ER - TY - CHAP A1 - Raufeisen, A. A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - Time-Dependent Three-Dimensional Simulation of the Turbulent Flow and Heat Transfer in Czochralski Crystal Growth Including the Three-Phase Boundary Movement T2 - High Performance Computing in Science and Engineering 2010 - Transactions of the High Performance Computing Center, Stuttgart, HLRS 2010 N2 - In the literature, numerical computations of the Czochralski process for crystal growth are conducted using a quasi-steady state assumption for the crystallization neglecting time-dependent effects. In the present work, an algorithm is developed, which allows to calculate the transient behavior of the crystallization interface including the movement of the three-phase boundary and the free surface of the melt. Thus, in conjunction with the computation of the turbulent melt flow and heat transfer, more realistic predictions of the crystal growth can be achieved. Test cases show that with the algorithm, realistic phenomena like crystal diameter increase and decrease during the growth process could be reproduced. Y1 - 2011 SN - 9783642157479 U6 - https://doi.org/10.1007/978-3-642-15748-6_27 SP - 353 EP - 367 PB - Springer CY - Berlin, Heidelberg ER - TY - CHAP A1 - Raufeisen, A. A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - Time-Dependent Three-Dimensional Simulation of the Turbulent Flow and Heat Transfer in Czochralski Crystal Growth Including the Three-Phase Boundary Movement T2 - High Performance Computing in Science and Engineering '10 N2 - In the literature, numerical computations of the Czochralski process for crystal growth are conducted using a quasi-steady state assumption for the crystallization neglecting time-dependent effects. In the present work, an algorithm is developed, which allows to calculate the transient behavior of the crystallization interface including the movement of the three-phase boundary and the free surface of the melt. Thus, in conjunction with the computation of the turbulent melt flow and heat transfer, more realistic predictions of the crystal growth can be achieved. Test cases show that with the algorithm, realistic phenomena like crystal diameter increase and decrease during the growth process could be reproduced. Y1 - 2011 SN - 9783642157479 U6 - https://doi.org/10.1007/978-3-642-15748-6_27 SP - 353 EP - 367 PB - Springer CY - Berlin, Heidelberg ER - TY - CHAP A1 - Raufeisen, A. A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - Analysis of Turbulent Structures in a Czochralski System Using DNS and LES Predictions T2 - High Performance Computing in Science and Engineering `07 N2 - A DNS of the turbulent flow and heat transfer in an idealized Czochralski configuration was conducted using a very fine grid. The results show the irregular forming of buoyant thermal plumes as well as the occurrence of a large, stable vortical structure in the bulk of the melt. In the averaged flow field a B´enard-cell-like pattern can be recognized. The DNS data served also as a reference for the validation of the LES method. The LES computations were conducted using different grid sizes, SGS models, and discretization methods. For relatively fine grids and central differences, the results agree very well with the DNS. Using an upwind discretization introduces numerical errors. In combination with coarser grids, this leads to large deviations and even qualitative differences. However, overall the computational effort could be reduced significantly by LES. Thus a compromise between accuracy achieved and effort required has to be found. Y1 - 2007 SN - 9783540747383 U6 - https://doi.org/10.1007/978-3-540-74739-0_25 SP - 371 EP - 386 PB - Springer CY - Berlin, Heidelberg ER - TY - JOUR A1 - Raufeisen, A. A1 - Jana, S. A1 - Breuer, Michael A1 - Botsch, T. A1 - Durst, F. T1 - 3D computation of oxygen transport in Czochralski crystal growth of silicon considering evaporation JF - Journal of Crystal Growth N2 - For Czochralski (Cz) growth of silicon single crystals, 3D unsteady simulations of the oxygen transport in the turbulent melt flow were conducted using a new formulation for the evaporation at the free surface found by Sakai et al. [Electrochem. Solid-State Lett. 5 (8) (2002) G72]. Compared with 2D results from literature, the computed oxygen concentration now fits the experimental data better, showing lower values in the critical region beneath the crystal than in previous simulations, which mostly arises from the more accurate prediction of the flow field. Further computations of Cz configurations show how the oxygen distribution can be influenced by rotation of the crucible and crystal. Y1 - 2007 U6 - https://doi.org/10.1016/j.jcrysgro.2006.11.349 SN - 0022-0248 VL - 303 IS - 1 SP - 146 EP - 149 PB - Elsevier BV ER - TY - JOUR A1 - Raufeisen, A. A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - Prediction of the three-phase boundary movement in Czochralski crystal growth JF - Journal of Crystal Growth N2 - A numerical algorithm is presented which allows three-dimensional time-dependent simulations of Czochralski and other crystal growth processes. Besides the computation of turbulent flow and heat transfer in the melt, it includes the movement of the crystallization interface between melt and crystal, the dynamics of the melt free surface with the meniscus and the variation of the three-phase boundary. Thus, there is the potential that crystal diameter variations, which occur during growth of the start and the end cone can be predicted. This is illustrated by results of sample computations. Y1 - 2010 U6 - https://doi.org/10.1016/j.jcrysgro.2010.05.009 SN - 0022-0248 VL - 312 IS - 16/17 SP - 2297 EP - 2299 PB - Elsevier BV ER - TY - JOUR A1 - Raufeisen, Alexander A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - LES validation of turbulent rotating buoyancy- and surface tension-driven flow against DNS JF - Computers & Fluids Y1 - 2009 U6 - https://doi.org/10.1016/j.compfluid.2009.01.002 SN - 0045-7930 VL - 38 IS - 8 SP - 1549 EP - 1565 PB - Elsevier BV ER - TY - JOUR A1 - Raufeisen, A. A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - DNS of rotating buoyancy– and surface tension–driven flow JF - International Journal of Heat and Mass Transfer Y1 - 2008 U6 - https://doi.org/10.1016/j.ijheatmasstransfer.2008.01.041 SN - 0017-9310 VL - 51 IS - 25/26 SP - 6219 EP - 6234 PB - Elsevier BV ER - TY - JOUR A1 - Raufeisen, A. A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - Transient 3D simulation of Czochralski crystal growth considering diameter variations JF - Journal of Crystal Growth N2 - For numerical simulations of the Czochralski crystal growth process, in the literature the quasi-steady state approach is used, i.e. the diameter of the crystal is kept constant. However, this leads to errors in the computation of the phase interface. In the present work, for the first time in 3D, the three-phase junction between melt, crystal and atmo-sphere is allowed to move in horizontal direction. Thus, diameter changes during the crystal growth process could be simulated accordingly. In the future, the vertical movement will be allowed as well, considering the free surface stresses. This will enable realistic predictions of the transient behavior of the crystallization front. Y1 - 2009 U6 - https://doi.org/10.1016/j.jcrysgro.2008.09.073 SN - 0022-0248 VL - 311 IS - 3 SP - 695 EP - 697 PB - Elsevier BV ER -