| With the continuous progress of society and economy, energy and environmental problems have become increasingly prominent. Energy saving and emission reduction has become increasingly urgent. The storage and use of thermal energy and the development of new energy vehicles are two promising directions. Thermal energy storage and utilization can further improve energy efficiency, the development of new energy vehicles can reduce fossil energy use and promote the development of new energy, thereby reducing pollutant emissions. Being one of the four core technologies in electric vehicle, battery thermal management become the focus and hotspot in recent years. The potential of phase change materials(PCM) used in thermal management and thermal energy storage is tremendous. As a kind of good heat transfer media, oscillation heat pipe(OHP) can compensate the disadvantage of low thermal conductivity for PCM and can also connect PCM with the outside. In this paper, numercial simulation on the battery thermal management based on different heat transfer medium and experimental investigation on the thermal performance of PCM/OHP coupling modules are carried out in this paper. The main research contents and conclusions are as follows:(1) Comprehensively parametric investigation on the thermal management system of several cylindrical battery packs based on air, mini-channel liquid cooled cylinder and PCM were performed numerically. The variation laws of maximum temperature rising and local temperature difference at the condition of different ventilation types, gap spacing, cell diameters, mass flow rate of cooling water, flow direction, conductivity of PCM and latent heat of PCM were studied and analyzed. The results showed that the local temperature difference increased firstly and then decreased with the increase of wind speed. Reversing the air flow direction between adjacent rows is not necessarily appropriate and the gap spacing should not be too small and too large. It is prone to thermal runaway when the ambient temperature is too high, and the most suitable value of S/D(the ratio of spacing distance between neighbor cells and cell diameter) is gradually reduced along with the increase of cell diameter. Considering both the maximum temperature and local temperature difference, the cooling style by liquid cooled cylinder can demonstrate advantages compared to natural convection cooling only when the channel number is larger than eight. The capability of reducing the maximum temperature is limited through increasing the mass flow rate. The capacity of heat dissipation is enhanced first and then weakened along with the rising of entrance size, when the inlet mass flow rate is constant. Compared that without PCM, the maximum temperature of battery pack filled with PCM rose significantly at first and then slowly over time. At the end of the discharge, the maximum temperature decreased evidently, but with the increase of thermal conductivity of PCM, the reduce is not obvious. In the case of large temperature difference within battery monomer and that the positive and negative electrodes arranged on the same side respectively, it is hard to control the temperature uniformity of the battery module through reducing the phase change temperature and increasing the thermal conductivity of PCM. The style II or style III is necessary for the aging battery pack with uneven heat generation occurring in the positive and negative electrodes.(2) Closed loop OHPs(CLOHP) with different turns were designed, manufactured and tested. The effects of different turn number, cooling conditions and different installation angles on the starting temperature, thermal resistance and thermal load range of CLOHP were studied. The results showed that the start-up temperature of the three-turn CLOHP, four-turn CLOHP and five-turn CLOHP were about 51?°C, 72?°C and 95?°C, respectively. The start-up temperature of CLOHPs showed positive correlation with the amount of turn. when the whole width was constant, difficult or unstable oscillation tended to occur in the CLOHP with less turns. Increasing the heating power and reducing the amount of turn were beneficial in reducing the thermal resistance of the CLOHP, which was in agreement with the conclusions of previous studies. When the heating power was constant, difficult or unstable oscillation tended to occur in the CLOHP with less turns. With the increase of installation angle, the thermal resistance of OHP decreases rapidly first and then almost remains unchanged. The angle range where thermal resistance is obviously affected by the installation angle decreases with the increase of heating power.(3) Two performance test experimental platforms for PCM/OHP coupling modules were constructed and a comprehensive investigation on the thermal performance of PCM/OHP coupling modules under different supplied heating power and operating conditions was performed experimentally. The results showed that the starting temperature of the OHP should be lower than the phase transition temperature of the PCM. The paraffin wax/CLOHP system showed much better dynamic thermal performance in the heating process and much better static thermal performance in the cooling process than those of the paraffin wax system. The section of the OHP in the energy storage tank served as condensation section and evaporation section in charge process and discharge process, respectively. Raising the heating power could increase the number of instantaneous oscillation. The trend of the temperature difference between the OHP and EG/paraffin composite before the PCM melting was similar to those filled with water under the same condition, but the difference value was larger, which were much smaller than those between the CLOHP and the paraffin. The thermal response time of the PCM was quite short, and the oscillation and the temperature variation had good synchronization. The installation angle has little influence on the heat transfer efficiency and the PCM/OHP coupling module for thermal energy storage has good cycle performance. |
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