Heat transfer in nano/micro multi-component and complex fluids with applications to heat transfer enhancement.

摘要

Suspension fluids are a class of complex fluids which are extensively used in industrial and biological systems. Examples of such fluids are nano/micro fluids, fiber suspensions in a paper making machine, particle filled thermal interface materials, food products, fluidized beds, chemical products and biological systems. The thermo-physical properties of these fluids are different from the pure fluids. Due to the various applications of such mixtures, it is important to determine the properties of the resultant complex fluid. In this research, thermal properties of complex suspension flows are investigated using numerical computations.;The objective of this research is to develop an efficient and accurate computational method to investigate heat transport in suspension flows. The method presented here is based on solving the lattice Boltzmann equation for the fluid phase, as it is coupled to the Newtonian dynamics equations to model the movement of particles and the energy equation to find the thermal properties. This is a direct numerical simulation that models the free movement of the solid particles suspended in the flow and its effect on the temperature distribution. This is a robust and efficient computational method for the analysis of solid particles suspended in fluid. An advantage of the lattice Boltzmann method is that the code can be easily implemented on parallel processors because of the local nature of the time evolution operator. Here, parallel implementations are done using MPI (message passing interface) method. Teragrid super computing resources have been used for large domain simulations.;In this study, convective heat transfer in internal suspension flow (low solid volume fraction, &phis;10%), heat transfer in hot pressing of fiber suspensions and thermal performance of particle filled thermal interface materials (high solid volume fraction, &phis;>40%) are investigated. The effect of different parameters such as particle size or thermal conductivity on thermal performance is discussed. The results have been compared to previous experimental, analytical or numerical studies. Large domain simulations show that the flow disturbance due to movement of suspended particles is the main reason for local and overall thermal enhancements in convective heat transfer of internal suspension flows. The results show that the heat transfer rate is enhanced about 10% at 5% particle volume fraction.;Hot pressing of wood fiber suspensions is studied numerically. It is shown that effective pre-heating of fiber suspensions can lead to considerable energy savings in paper making process. The results show that the thermal properties are highly dependent on the wood fiber type. The effective thermal conductivity changes about 45% for suspensions of different softwood and hardwoods at 20-40% of solid fiber contents.;Detail study of particle laden thermal interface materials (a dense suspension) in squeeze flow, shows that the microstructure changes in assembly process. This affects the thermal properties and needs to be considered for realistic thermal predictions. The results show that effective thermal conductivity is enhanced 2-7 times at &phis;=55% depending on particle size and conductivity. It is also shown that using ellipsoidal particles with aspect ratio=4 enhances the thermal conductivity 2.5 times compared to a mixture with spherical particles at &phis;=60%.