Multiphysics modeling with open source software

University of Latvia

November, 2018

In this project, an air-cooled parallel plate fin heat sink is modelled using the conjugate heat transfer (CHT) model and heat transfer problem is solved for solid and gas phases. Thermal resistance of the heatsink is estimated in three ways - via the CHT model, analytically and using a simplified FEM model that prescribes an empirical convective heat transfer coefficient on solid-fluid boundaries.

This project is part of the EOF-Library training course. EOF-Library is efficient, fully parallelized Elmer FEM and OpenFOAM coupler designed for coupled electromagnetic, fluid and heat transfer simulations.

Given

- A video tutorial for geometry and mesh generation in Salome-platform
- A video tutorial for setting up OpenFOAM and Elmer FEM
- Mesh in the OpenFOAM format
- An Elmer FEM simulation model that uses an empirical heat transfer coefficient

Problem definition

Gas properties | Air |

Heatsink properties | Aluminium |

Flow velocity | 2 m/s |

Air temperature | 300 K |

Dissipated power | 100 W (applied on hsBtm) |

Tasks

Basic

- Get simulation running and produce meaningful results.
- From simulation results calculate heatsink thermal resistance using Eq. (2) from https://www.electronics-cooling.com/2003/02/estimating-parallel-plate-fin-heat-sink-thermal-resistance/ and compare with analytically estimated value using Eq. (3).

Advanced

- Engineers often use empirical heat transfer coefficients on solid-fluid boundaries to avoid simulating convection and speed up simulations. Check the validity of such an approach using the provided Elmer FEM model. Take the heat transfer coefficient from www.engineeringtoolbox.com/convective-heat-transfer-d_430.html, but also check with other sources as well. Compare the results against OpenFOAM.
- Attempt to make your own improvements to numerical models - decrease computational time, while maintaining accuracy; modify geometry, mesh or parameters to further explore the problem and OpenFOAM functionality.

Hints

- A reference solution in Ansys CFX and access to computer with licensed software is available to students registered to the course. Ask tutors for more info.
- Study this tutorial https://cfd.direct/openfoam/user-guide/v6-cavity/
- Study chtMultiRegionFoam tutorials “/tutorials/heatTransfer/chtMultiRegionFoam/”, in particular, pay attention to “coolingSphere” and “heatedDuct”.
- It may take a long time for the simulation to reach a steady state solution. Use the PIMPLE algorithm by setting “nOuterCorrectors” coefficient >1. This will allow you to circumvent the Courant–Friedrichs–Lewy condition and use values Co>1000.

Useful links

OpenFOAM

- http://foam.sourceforge.net/docs/Guides-a4/OpenFOAMUserGuide-A4.pdf
- http://www.wolfdynamics.com/images/OF_intro_training/all.pdf

Other