| Hilly and mountainous areas account for more than 2/3 of the total cultivated land in China,and mini-tiller are indispensable agricultural machinery at this stage.The electric mini-tiller has a wider application prospect than the internal combustion engine mini-tiller because of its advantages of flexible flexibility,small vibration,low noise and no exhaust emission.Li ion battery pack is the only energy source of the electric mini-tiller researched in this paper,and its endurance,life and safety are closely related to temperature.Lithium-ion battery generates heat during the field cultivation of the electric mini-tiller.The maximum temperature of the battery pack can reach 70°C,far exceeding the upper limit of 40°C suitable for the working temperature of lithium-ion batteries.If heat dissipation and temperature equilibrium are not in time,it is easy to cause the battery heat accumulation,monomer battery inconsistency between increasing thermal runaway,even lead to power system malfunction,battery capacity attenuation too fast and adverse conditions such as safety accident happened.But at present,the research on the heat dissipation system of the electric mini-tiller unit is very few,so it is necessary to develop the suitable,reasonable and effective heat dissipation system for the battery pack of the electric mini-tiller for the specific conditions of the battery box discharge,heat generation and environmental factors under the farming state of the electric mini-tiller.In this paper,a passive liquid heat dissipation system,which is based on the actual working conditions of an electric mini-tiller,is studied with the combination of experiment and simulation,and the passive liquid heat dissipation system is studied to meet the heat dissipation requirements of the lithium ion battery pack.Firstly,according to the principle of lithium ion battery reaction and the mechanism of heat production,the thermal characteristics of the battery are analyzed,and the numerical model of the thermal effect of lithium ion battery is set up,and the key parameters are calculated.The accuracy of the established numerical model and key parameter settings is verified through discharge test in battery pack.The results show that the simulation model is used to simulate the temperature field of the battery pack,and the simulation temperature error is less than 5.3%at the same test position and compared with the experimental data in the battery chamber.Then the effects of discharge ratio,battery clearance and ambient temperature on the distribution of temperature field were studied.The effect of discharge ratio and ambient temperature on the temperature distribution of the battery pack of the electric mini-tiller was significant.Secondly,in order to ensure that the battery pack of electric electric mini-tiller works in the suitable temperature range,the discharge current data of the battery pack in the actual tillage of the electric mini-tiller is measured in the field,and the distribution of the temperature field of the battery pack of the electric mini-tiller is analyzed.The results show that,under the condition of ambient temperature of 35℃,the maximum temperature of the battery can reach 55.223℃and the maximum temperature difference is 7.957℃,which is far higher than the upper limit of the suitable working temperature range of the lithium ion battery after the discharge of the electric mini-tiller.Thirdly,according to the actual farming environment of electric mini-tiller,combined with the heat dissipation requirements of electric mini-tiller,a single medium passive heat dissipation system with aluminum baffle and aluminum fins with heat dissipation is designed.The heat dissipation effect was studied,and the influence of the wall thickness on the heat dissipation of the passive heat dissipation system was analyzed.The results show that the designed single-medium passive heat dissipation system reduces the maximum temperature of the simplified battery pack from 54.615°C to 45.035°C when the natural convection heats up,and the maximum temperature difference decreases from 9.741°C to 2.757°C,which is much better than natural convection.Then,in order to further strengthen the heat dissipation effect and reduce the weight of the heat dissipation system,a solid-liquid dual-medium heat dissipation scheme with aluminum heat conduction cavity filled with heat conduction liquid is proposed.The heat dissipation performance of the two-medium heat dissipation scheme with 25%,50%,75%and 100%liquid filling ratio is studied by simulation.The results show that the heat dissipation performance of the system can not be further improved by the solid-liquid two-medium heat dissipation scheme without considering the vibration action.However,under the same heat dissipation performance,the weight of 0.5mm heat conduction chamber filled with 100%liquid is 333.08g,and the weight of the heat conduction plate is only 38.83%,which greatly reduces the weight of the heat dissipation system.Finally,based on the theory of fluid free liquid level sloshing under external excitation,the process of enhancing the heat exchange capacity of the system by liquid motion in the heat conduction chamber under the action of electric mini-tiller vibration is analyzed.After the vibration signals of the battery pack of the electric mini-tiller under field tillage were measured,the heat dissipation effect of the passive heat dissipation system under the action of vibration was studied by simulation.The results show that the maximum acceleration amplitude of the low frequency component in the battery pack of the electric mini-tiller is more than 10 m/s~2.The vibration has a large energy and can drive the liquid in the heat conduction plate of the designed passive liquid-cooling system to form a large amplitude of sloshing.The passive radiating system of the battery pack of the electric mini-tiller is designed to apply the principle of the free surface sloshing under the external excitation,using the vibration of the electric mini-tiller to drive the heat conduction fluid in the passive heat dissipation system,and strengthen the system heat dissipation capacity.The battery pack of the electric mini-tiller battery is at the end of the environment temperature of 35°C centigrade,after the discharge of the tillage current is finished.The highest temperature inside is 39.4°C,and the maximum temperature difference is 2.7°C,which meets the heat dissipation requirement of the electric mini-tiller. |
PDF Full Text Request