Print Email Facebook Twitter Heat transfer in finite sized particles suspensions Title Heat transfer in finite sized particles suspensions Author Hageman, Tim (TU Delft Mechanical, Maritime and Materials Engineering) Contributor Breugem, Wim-Paul (mentor) Degree granting institution Delft University of Technology Date 2017-10-06 Abstract Heat transfer is important in many applications. For instance, due to the decrease in size of electronics, itbecomes more necessary to have efficient and smaller cooling systems. In order to increase the effect of thecooling liquids used, it might be interesting to add extra solid particles with a high conductivity, to possiblyincrease the effective heat transfer fromthe wall to the liquid. These particles can be separated in 2 categories:point particles, with a very small size compared to the flow phenomena, and finite sized particles, which dueto their larger size are able to significantly influence the fluid flow. In this thesis, the finite sized particlesand their effect on the effective conductivity have been analyzed by using a CFD code. The main focus hasbeen on the effect of the mechanical and thermal Stokes numbers, which give an indication about the timerequired for the particles to react to changes in surrounding flow and temperature compared to the relevantflow time scale.To investigate the effect of large particles on the effective conductivity of a fluid a numerical method tosolve heat transfer inside a fluid and between fluid and particles has been implemented. This method, basedon an immersed boundary method combined with DNS, is able to solve both isolated particles and extremelyhigh conductivity particles. To solve the heat transfer for finite conductivities, a volume of fluid method hasalso been implemented. These methods have been verified by comparing the simulation results to knownresults for single sphere heat transfer and conservation of energy.With this code, the influence of the thermal and mechanical Stokes numbers have been analyzed forlaminar Couette flow. In order to gain a better understanding of the underlying heat transfer mechanics, ithas been assumed that the natural convection is negligible and the density ratio between the particle and thefluid is taken to be equal to one (no effects of gravity). From this it appeared that the effective conductivityof a suspension can be split in 3 components: the non-moving conductivity, an enhancement due to fluidconvection induced by the particles and an increase in heat transfer due to particle convective heat transfer.The non-moving conductivity is only dependent on the conductivity of the particles and the fluid, andon the particle concentration. It stays close to constant independent of Stokes numbers. In contrast, thefluid convection appeared to scale significantly with the mechanical Stokes number and with the particleconcentration. This appeared to be due to the increase in particle inertia resulting in more movement inwall normal direction and as a result moving more fluid in wall normal direction. The particle convectionappeared to not only scale with the thermal Stokes number and the particle concentration, but also with themechanical Stokes number. This increase was caused by the particles being able to absorb and release morethermal energy for higher thermal Stokes numbers, and thus transport more heat from the hot wall to thecold wall.Finally, the resulting effective conductivity and effective viscosity of the suspension were compared andit was shown that it is possible to enhance the heat transfer more than the viscosity, but only by either introducinga small amount of highly conductive particles, or by introducing well-conducting particles with verylow mechanical Stokes numbers. It appeared to not be possible to increase the heat conductivity more thanthe viscosity for particles with equal or lower conductivity compared to the fluid. Subject Multiphase flowHeat transferSuspensionfinite-sized particlesImmersed boundary methodDNSVolume of fluid To reference this document use: http://resolver.tudelft.nl/uuid:127e6166-0974-4dc1-a9a7-7953fec3d510 Part of collection Student theses Document type master thesis Rights © 2017 Tim Hageman Files PDF Thesis_Tim_Hageman.pdf 5.83 MB Close viewer /islandora/object/uuid:127e6166-0974-4dc1-a9a7-7953fec3d510/datastream/OBJ/view