Investigation On Heat Transfer And Magnetic Characteristics Of Fe₃O₄/Paraffin Phase Change Composite

Phase change material is a functional material that can absorb or release energy at a constant temperature,enabling heat storage and temperature regulation.With its large latent heat and stable performance,paraffin wax has been widely used in solar heat storage,energy conservation and thermal management of electronic devices.However,it still has some shortages such as poor thermal conductivity and leakage.Considering the requirements of heat storage system,it is necessary to improve the thermal conductivity,strengthen its thermal response efficiency and enhance its stability,which will be important for further application of phase change materials.Based on current researches about preparation and performance control of nanoparticles/paraffin composite,composite phase change materials are prepared using magnetic Fe₃O₄ nanoparticles and paraffin wax in this thesis.Measurements on heat transfer and heat storage characteristics are also carried out.Simulation results based on lattice Boltzmann method are compared with and experimental results to validate the model.Simulations and experiments are designed to analyze the heat transfer characteristics and magnetron characteristics of the materials during the phase transition process.Besides,the heat transfer and temperature changes during the phase change process under external magnetic field forces are tested in the work.The magnetic Fe₃O₄ nanoparticles and the paraffin-based composite phase change materials with different mass fractions of nanoparticles are prepared,and the heat transfer and heat storage properties such as specific heat capacity and latent heat of phase change are measured with differential scanning calorimetry method.Effects of different nanoparticle mass fraction on thermal properties are explored,and the trends of thermal physical properties under different conditions are analyzed.It is discovered that composite phase change materials have good heat transfer and storage characteristics along with good stability.Lattice Boltzmann method is used to simulate the heat transfer characteristics of the phase change process.Effects of nanoparticle quality,Rayleigh number and heat source conditions on heat transfer in phase change process are investigated.At the same time,an experimental bench of heat transfer characteristics of phase change process are designed.Simulation and experimental results are used to investigate the changes of temperature field and flow field during phase transition.It is found that the composite phase change material of magnetic Fe₃O₄nanoparticles and paraffin showed better heat transfer performance than pure paraffin phase.Based on the lattice Boltzmann method,the magnetic field force model is added to carry out the numerical simulation of the phase change process under a magnetic field force.Meanwhile,the series of experiments on the heat transfer characteristics under the magnetic field force are designed.The influence of magnetic field force is studied by means of simulation and experiment.Factors like loads,directions and mass fraction of nanoparticels are all taken into consideration.It is found that the addition of different magnetic field forces can promote or inhibit the heat transfer and flow process of the phase cha nge process.