Manufacture And Performance Study Of Porous Copper Fibers Skeleton Compositie Phase Change Material

Phase change materials(PCMs) have huge latent heat and their temperatures can keep almost constant during phase change. These characteristics make them have an incredible potential of being applied in thermal management of large power electronic device and lithium battery, utilization of solar energy, optimization of energy system and heat storage materials. Promoting the application of PCMs in the above fields will make a contribution on the energy conservation, emission reduction and sustainable development. However, the intrinsic poor thermal conductivity extremely weakens the phase change heat transfer efficiency so limits the application range and efficiency of PCMs. Furthermore, those existing methods to enhance the thermal conductivity of PCMs respectively have their defects. To solve above problems, this thesis embedded paraffin in a porous copper fibers skeleton(PFCS) to enhance its thermal conductivity and achieve high the impregnation ratio, for the purpose of improve the phase change heat transfer performance. The main contents in this thesis were as follows:(1) A process to manufacture the porous copper fibers skeleton composite phase change material(MF-PCM) was developed. Paraffin was chosen as phase change material, and copper fibers with different diameters were manufactured using multi-tooth cutting tool. Then PCFS was made with different porosities by sintering process and paraffin was impregnated into it by the assistance of vacuum. MF-PCMs with impregnation larger than 98.3% were manufactured. The result of differential scanning calorimetry showed that the latent heat of MF-PCM was smaller than pure paraffin, but their melting temperatures were slightly higher than pure paraffin.(2) Through setting up the visual temperature measuring system, the quasi one-dimensional phase change heat transfer performance of MF-PCM was studied. The differences of phase change heat transfer behaviors between MF-PCM and pure paraffin was compared by visual investigating the evolution of their melting interfaces. It was found that the existence of PCFS suppressed the natural convection of liquid paraffin, resulting the inclination of melting interface of MF-PCM was much smaller than pure paraffin.But the enhancement in heat conduction outweighted its suppression in natural convection, therefore a significant enhancement on heat transfer performance of paraffin by the addition of PCFS was found.Also, the effects of porosity and diameter of fiber on the quasi one-dimensional phase change heat transfer performance of MF-PCM were explored.It was found that decreasing the porosity could improve the phase change heat transfer performance of MF-PCM, and the effect of diameter of fiber on the phase change heat transfer performance was slight.(3) A heat sink with MF-PCM used for thermal management of large power LED was designed and its temperature control performance was investigated experimentally. Other two filling modes of heat sink(with pure paraffin,empty) were introduced as control cases. The transient temperature control performance of heat sinks with MF-PCM were tested successively in four input powers, three cycle working mode, three environmental temperature and with/without a DC fan. Also, the effects of porosity and diameter of fiber on the transient temperature control performance were explored. During its temperature control region,the temperature control performance of the heat sinks with MF-PCM were superior to that of the heat sink with pure paraffin.As the input power increased, the performance improvement of the heat sink with MF-PCM compared with that with pure paraffin became more obvious.(4) A numerical model of the heat sink with MF-PCM was established based on the sensible heat capacity method.For offering an accurate input for the numerical model, sapphire method was employed to measure the function of the equivalent heat capacity of paraffin with temperature. ANSYS? Icepak was used to build and solve the finite element numerical model, then the simulation results were compared with the experimental results to verify the accuracy of the model.While the porosity of MF-PCM was 75%, the simulation results matched accurately with the experimental results. Finally, in order to providing references for further study, the effects of phase change temperature, the material of metal fiber and the shape of MF-PCM on the thermal performance of the heat sink were investigated simulatively based on the number model by fixing the porosity at 75%.