Thermo-Fluid-Dynamics using OpenFOAM - Heat transfer and vortex structures in plate-heatexchangers

Transcription

1 Thermo-Fluid-Dynamics using OpenFOAM - Heat transfer and vortex structures in plate-heatexchangers Johann Turnow University of Rostock Faculty of Mechanical Engineering and Shipbuilding Chair of Modeling and Simulation Albert-Einstein-Str Rostock Germany

2 Institute of Modeling and Simulation (LEMOS) founded in October 2010 start with 3 scientists, today: 10 PhD students and 2 PostDocs main fields of research: Shiphydrodynamics Thermo-Fluid- Dynamics Mixing with chem. Reactions Hardware: HPC Neptun 2700 cores HPC Titan 3800 cores (2015)

3 Focus of research Dimples using dimples to reduce resistance and enhance heat transfer in heat exchangers, turbine blades, numerical and experimental investigations including surface optimization on flow structures and heat transfer

4 Focus of research Dimples Proper Orthogonal Decomposition (POD) Analysis shows energetic relevant structures is LES flow fields Transport of fluid out of the dimple characterized by tornado-like structures UNIVERSITÄT ROSTOCK Fakultät für Maschinenbau und Schiffstechnik 5

5 Focus of research Dimples genetic algorithm to find optimal surface structure for best thermohydraulic performance mutation of heat transfer surface using simple mesh diffusion equation in OpenFOAM using mesh motion algorithm (tetfemsolver) no time consuming remeshing is required for each mutant simple handling/automatization using pyhton

6 Dimples convergence optimized structure convergence of optimization process reduction of recirculation zones enhancement of thermo-hydraulic performance up to 16%

7 Focus of research Fouling in heat exchangers coupling of Lagrange Particle Tracking (LPT) and Euler method using extra fouling phase (conversion of particles) calculating heat transfer and pressure drop through fouling on different structured surfaces e.g. ribs, dimples detailed analysis of fouling probability on structured surfaces

8 Focus of research Thermal comfort in a car cabin in summary using shear stresses, sector integrated heat fluxes and humidity local comfort index

9 Heat transfer and vortex structures in plate-heat-exchangers 1. Motivation / Introduction 2. Numerical / Experimental methods 3. Heat transfer / pressure loss 4. Vortex structures and variation of corrugation profile 5. Summary / Outlook

10 1. Introduction Plate-and-Shell heat exchanger (PHE) )* Standard: rectangular shape simple, robust homogeneity of flow Defined surface patterns enhance mixing processes to increase heat transfer rates )* UNIVERSITY OF ROSTOCK Chair of Modeling and Simulation Dr. J. Turnow

11 1. Introduction Plate-and-Shell heat exchanger (PHE) object of interest: circular PHE properties: robust, simple no sealing needed due laser welding ensures an uniform pressure distribution at the outer walls flow homogeneity can not be ensured UNIVERSITY OF ROSTOCK Chair of Modeling and Simulation Dr. J. Turnow

12 2. Numerical methods Numercial setup RANS in line with low-reynolds formulation of k ω-sst model LES dynamic mixed model (Vreman et al., 1994) for subgrid contribution of momentum and scalar variable turbulent viscosity ν t and turbulent Prandtl number Pr t are dynamically determined in space and time UNIVERSITY OF ROSTOCK Chair of Modeling and Simulation Dr. J. Turnow

13 3. Heat transfer / pressure loss Validation Detailed grid convergence studies careful mesh generation especially the contact points UNIVERSITY OF ROSTOCK Chair of Modeling and Simulation Dr. J. Turnow

14 3. Heat transfer / pressure loss Validation Variation of turbulence models k ω SST model show best performance UNIVERSITY OF ROSTOCK Chair of Modeling and Simulation Dr. J. Turnow

15 3. Heat transfer / Pressure loss Circular PHE pressure distribution: good comparison to experiments nearly constant pressure gradient in streamwise direction Symmetric pressure distribution in lateral direction UNIVERSITY OF ROSTOCK Chair of Modeling and Simulation Dr. J. Turnow

16 3. Heat transfer / Pressure loss Results PHE Flow structures Flow distribution homogeneous Flow channels evolving through contact points Recirculation zone behind contact points

17 3. Heat transfer / Pressure loss Conjugate heat transfer (CHT) Conjugate Heat Transfer (CHT) Direct Coupling of hot and cold fluid side

18 4. Vortex structures and variatiation of corrugation profile Vortex structures Analysis of vortex structures using LES Testcase: simplified cut-out channel including 15 sinusoidal waves both channels are energetically coupled using CHT gives the opportunity for design modifications, e.g. corrugation radius

19 4. Vortex structures and variatiation of corrugation profile Modification of corrugation profiles Flow structures characterized by Stable recirculation zones Evolving shear layer structures Streamlines λ 2 - surfaces

20 4. Vortex structures and variation of corrugation profile Modifaction of corrugation profile Increase of thermo-hydraulic performance up to 10% Comparison of vortex structures original dimples

21 Summary / Outlook Homogeneous flow field within the circular PHE from experiment and simulation Constant friction factor and small Nusselt number enhancement for increasing Reynolds numbers determined LES show complex vortex structures including shear layer structures stable recirculation zones behind contact points decrease thermohydraulic performance Variation of corrugation profile to reduce recirculation zones and heat transfer enhancement

22 Thank you! Johann Turnow University of Rostock Faculty of Mechanical Engineering and Naval Architecture Chair of Modeling and Simulation Albert Einstein Str Rostock Germany johann.turnow@uni-rostock.de