| Latent functional fluid (LFF) is a novel multiphase fluid which consists of microencapsulated phase change material (MEPCM) particles and conventional single phase fluid. In the phase change temperature range, the phase change materials (PCM) absorb or release latent heat during their melting or crystallization process which results in LFF having an ability of heat storage. Magnetic fluid is another type of functional fluid which has both the dynamic characteristic of liquid and the magnetic properties of the bulk magnetic material and has an ability to respond to an external magnetic field. Some of its thermal parameters (such as density, viscosity, thermal conductivity, etc.) will change with the external magnetic field changes. Thus magnetic fluid is a controllable heat transfer fluid and its flow and energy transport process could be controlled by the external magnetic field. To combine the heat storage of LFF and the controllable energy transport process of magnetic fluid, magnetic latent functional fluid (MLFF), an innovative multiphase fluid, which consists of magnetic phase change microcapsule (MPCMC) particles and carrier fluid, has been proposed. Due to the magnetism and heat storage of the MPCMC particles, MLFF is a controllable, heat storange and enhanced heat transport fluid. The following aspects of MLFF will be studied in this thesis.(1) Preparation of MPCMCMagnetic microcapsules containing paraffin cores within urea-formaldehyde and melamine-urea-formaldehyde shells were fabricated utilizing in situ polymerization, with iron nano-particles as magnetic particles. The thermal properties, surface morphologies, magnetic properties and iron nano-particles content of the magnetic phase-change microcapsules were investigated by scanning electronic microscopy (SEM), differential scanning calorimetry (DSC), vibrating sample magnetometry (VSM) and inductively coupled plasma quantometry (ICP). The influence of iron nano-particles on morphologies and specific saturation magnetization was also considered. The morphologies and intensity of MPCMC with two kind shells were compared.(2) Measurement of apparent specific heat capacity and thermal conductivity of MLFFThe apparent specific heat capacity and thermal conductivity of MLFF were experimentally investigated by DSC technique and transient short-hot-wire method, respectively. The effects of the MPCMC volume fractions and components in the MPCMC on the apparent specific heat capacity and thermal conductivity of MLFF were discussed. A dramatic variation of the thermal conductivity was observed in the presence of an applied magnetic field.(3) Experimental investigation on convective heat transfer of MLFFTo investigation on convective heat transfer of MLFF in the presence of magnetic field, a convection loop using MLFF as work fluid was made, and the magnetic field was produce by a cylindrical Nd-Fe-B permanent magnet in the loop. Through the measurement on bulk mean temperature and wall temperature, the influence of magnet location, volume fraction of MPCMC, mass flow rate, and heat flux on convective heat transfer of MLFF was experimentally analyzed.(4) Numerical simulation on convective heat transfer of MLFFBased on fluid dynamics and electromagnetics, a mathematical model for describing convective heat transfer characteristic of MLFF flow in circular tube under an external magnetic field was established. The influence of magnetic field strength, volume fraction of MPCMC, mass flow rate, and heat flux on convective heat transfer of MLFF was analyzed. The mechanism of magnetic field influence on MLFF convective heat transfer was revealed. The convective heat transfer of MLFF was enchanced by magnetic field, and the enhancement reason was that the distributions of MPCMC volume fraction and slurries temperature were changed due to magnetic force on MPCMC. For verify the reasonableness of mathematical model and experiment system, the experimental and simulated values of wall temperature were compared. |
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