OPTIMIZATION RESEARCH ON THE COOLING OF LITHIUM BATTERY PACK FOR ELECTRIC MINI TILLER Dian Dong Wei Geng Ji Dian Chi Zu De San Re You Hua Yan Jiu
The electric mini tiller can produce extra heat during working, which leads to the problem that the span life of battery is shortened significantly. So, it is crucial to deduce the process of heat dissipation regarding batteries and show the simulations with Fluent. The data indicate that most of cells would generate the ideal temperature range under the natural condition, and thus the mode of forced cooling for batteries is imperative. In order to research the influence of different factors including the temperature, the velocity and the passage form of cooling liquid, an orthogonal experiment table has been designed and then the scheme of cooling is optimized. Compared with the control, the optimized outcomes imply that all cells are in the expected scope and the difference among cells is reduced obviously, extending the service life of batteries. Zhai Yao Dian Dong Wei Geng Ji Zai Zuo Ye Guo Cheng Zhong Hui Chan Sheng Ming Xian De Re Liang ,Jiang Zao Cheng Dian Chi Zu Shou Ming De Guo Zao Shuai Tui Tui Dao Liao Dian Chi Zu De San Re Guo Cheng ,Shi Yong Fluent Ruan Jian Fang Zhen Liao Dian Chi De Wen Du Bian Hua Shu Ju Biao Ming Zi Ran San Re Xia Da Duo Shu Dian Chi Dan Ti De Wen Du Jiang Pian Chi Qi Zui Jia Fan Wei ,Yin Ci Xu Yao Cai Qu Qiang Po Leng Que Wei Fen Xi Leng Que Ye Ti De Su Du Wen Du He Tong Dao Dui Dian Chi Zu San Re De Ying Xiang ,She Ji Liao Zheng Jiao Shi Yan Biao ,Dui Dian Chi Zu De San Re Fang Shi Jin Xing Liao You Hua Jie Guo Xian Shi Dian Chi Zu Dan Ti Wen Du Du Zai Zui You De Fan Wei Nei Qie Bu Yi Zhi Xing Ming Xian Jiang Di ,Zhe Jiang You Zhu Yu Yan Chang Dong Li Dian Chi Zu De Shou Ming INTRODUCTION The mini tiller is driven by a gasoline or diesel internal combustion engine of 2~7.5 kW, weighs 50~150 kg and has a tilling depth of 10~16 cm. Because of the advantages such as being multifunctional, small in size and light weight, it is one of the most popular agricultural machinery equipment in the hilly and mountainous regions. Recently, the disadvantages of the mini tiller have been noticed by the researchers. For example, intense vibration produced by the mini tiller may result in neurological disorder and organ damage (Li et al. 2016) In addition, these defects also cause severe injuries even death (Fabbri A. et al. 2017) Aiming at these shortcomings, some studies have been fulfilled. The majority of the vibration is from the engine and the vibration effect of different fuels must be considered (Heidary B. et al. 2013) Parts of the vibration are generated during the tilling process and the geometry of blade and the scoop angle characteristics of a handheld tiller's rotary blade has been explored (Zhang Y. H. et al. 2016) For cutting off transfer of vibration, pre stress means are adopted to analyse the vibration of the mini tiller, and the consistency between theoretical outcome and test data has been achieved (Wang Z. et al. 2018) Although such studies are beneficial to enhance the performance of mini tiller, it is tough to eliminate those deficiencies. Considering the structure characteristic of mini tiller all components have been installed under the rigid mode, replacing the gasoline internal combustion by an electric motor may be feasible to boost its operating properties (Liang X. C. et al. 2018) The electric mini tiller has several advantages such as light weight, low noise and zero emission, and thus it can meet the needs of modern agriculture development. Although the electric mini tiller has some advantages, yet unwanted performance of the apparatus is hard to be ignored. 1 Liang X.C. Ph.D. Eng. Huang S. Ms. Stud. Eng. Vol. 58, No. 2 2019 76 Specifically, when the electric mini tiller is working, extra heat will be generated by the batteries. It is well known that the energy system of electric mini tiller is made up by a number of cells; the difference among cells will be enlarged if the thermal energy fails to be dissipated rapidly, leading to add difficulty on managing their heat. It is crucial to keep the batteries under the ideal temperature range, which is constructive to extend the span life of cells. Relevant published papers have demonstrated how to control the temperature of battery. In order to improve the performance, the modelling method to battery thermal analysis is proposed and thermal characteristic and influence law have been confirmed (Li J. et al. 2016) In fact, cooling fluid is vital to the service life of battery, so a working medium is researched in both theoretical analysis and experimental research (An Z. et al. 2018) The working condition is associated with the thermal energy, so the typical situation may be more valuable to be explored regarding temperature rise (Guo Y. et al. 2018) The adaptable algorithm can strengthen the cooling effect and a greedy algorithm is simulated (Chen K. et al. 2018) In essence, heat produced appears from the chemical reaction during battery working and it is imperative to conduct some research on these settings (Zhu H. et al. 2018) The electric mini tiller is a new thing for the majority of operators, and inadequate experiments have been done. It is well known that lithium battery is main component of storing energy for most of agricultural apparatus, but few experiments focused on thermal analysis have been completed, which is related to the span life of lithium battery. In fact, the mini tiller's working conditions are distinctly different to the vehicles, so thermal analysis of the battery should be completed according to the operating condition of mini tiller, and thus the service life of batteries can be enhanced notably. MATERIALS AND METHODS For the sake of temperature issue solving satisfactorily, it is valuable to research the process of heat dissipating during electric mini tiller working. An elementary prototype shown in Figure 1 has been designed by the author and his students, and the concerned analysis is focused on the tiller. Fig. 1 Electric elementary prototype and battery box Compared with the traditional mini tiller, the manufacturing cost of the prototype is huge. In order to decrease the cost, the capacity of battery and the power of electric motor are both smaller than the computing outcome, verifying the feasibility of the prototype. The main parameters are listed as below. Table 1 Specification of the prototype Mini tiller item Parameter Motor type Direct current motor Electric motor power kW 0.75 Related rotation speed r min 1800 Battery type Li NiCoMn lithium ion battery Battery capacity A h 20 Cooling mode Air cooling When the cell is regarded as a whole, heat produced inside of cell is transferred from the inner to outer layer through conduction and it is calculated with the formula q gradT (1) Where: q is the vector of heat flux, [W/m] is the thermal conductivity coefficient, [W/(m.k) T is the temperature, [K] grad is the temperature gradient, 1 k m " " is minus which means that the gradient direction is the direction of temperature rising. Vol. 58, No. 2 2019 77 If the air passes the surface of battery, part of the heat is dissipated by convection means, and such heat exchange is calculated as follows: v m f Q hA T T (2)