| Thermal batteries are also called molten salt batteries/thermal activated reserve batteries,which are disposable battery products with high reliability.Thermal batteries are widely used in various military and civilian “heavy weapons” due to their excellent long-term and highly reliable energy storage characteristics.In recent years,with the higher demands for the functions,performances and reliability requirements of equipment,the application of thermal batteries becomes more and more extensive.From the initial use as a power supply for the fuze of artillery shells,thermal batteries have gradually expanded to mines,torpedoes,bombs,rockets,nuclear weapons and other modern weapons and equipment.And then,they have developed into the main power supply for the ground-to-air missiles,air-to-ground missiles,air-to-air missiles,ship-to-ship missiles,aircraft emergency and so on,such as the AIM-120,rattlesnake of American,the P-73 of Russian and the long-range missiles of China.In recent years,with the higher demands for the function and performance requirements of aerospace and weapons equipment,thermal batteries are developing towards miniaturization,integration,large capacity long life,long-term storage and high reliability in harsh environment.There have new challenges to the safety design of thermal batteries.On the one hand,the accurate analysis and reliable prediction of thermal battery performance are related to the performance of missiles and other equipment,and the improvement of thermal battery performance depends on the optimization of thermal battery design parameters.On the other hand,thermal runaway problem of thermal battery threatens the safety and reliability of equipment,so it is necessary to conduct in-depth research on the thermal runaway problem.Therefore,this dissertation has done a lot of exploratory work in thermal battery performance simulation and failure control.The main innovative achievements are as follows:(1)The thermal battery performance in the activation stage is simulated and analyzed.A simulation model of heat source and a numerical method of activation performance considering the ignition time interval of heat pellets are proposed,and a more accurate activation time results of thermal battery is obtained.An activation experimental platform of thermal battery is built to verify the accuracy of calculated results.Some useful conclusions are obtained by simulation and experiment results,including: when the ignition time interval of the heat pellets is considered in the heat source model,the closer the electrolyte is to the bottom,the longer the time for its temperature to rise to the melting point.The activation time of thermal batteries is determined by the time when the bottom electrolyte reaches the melting point.Adding an electrical match to the bottom of the thermal battery can significantly shorten the activation time of thermal batteries.Compared with only one electrical match at the top of the cell stack,the activation time can be reduced by 5.2 %.The higher the ambient temperature,the shorter the activation time.The activation time can be decreased by 18.8 % when the ambient temperature raises from 233 K to 333 K.With the total thickness and number of pellets unchanged,the activation time can be shortened by6.2 % compared to uniform thickness of pellets when the thickness of the bottom pellets is10.5 mm and that of the middle pellets is 7.5 mm.(2)The performance of thermal battery in working(discharging)stage is simulated and analyzed.A simulation method of the thermal battery performance in discharge stage is proposed.The effects of thickness distribution of heat pellets and insulators,and ambient temperature on the discharge performance are simulated and analyzed.The following useful conclusions are obtained: the discharge time is determined by the solidification time of bottom electrolyte;The discharge time is related to the thickness of heat pellets and insulators.Properly adjusting the thickness of each component can prolong the discharge time.The higher the ambient temperature is,the longer the discharge time is.When the ambient temperature increases from 233 K to 333 K,the discharge time increases by about2.5 times.The discharge time can be increased by reducing the thickness of the upper and middle heat pellets to increase the thickness of the bottom insulator.(3)The design parameters of the thermal battery are optimized.Taking the thickness of heat pellets and insulators as optimization variables and the activation time and discharge time as objective functions,the multi-objective optimization of structure parameters is carried out by Genetic Algorithm(GA).The results show that after multi-objective optimization,the discharge time can be extended by 3.19 %,while the activation time only increases by 1.13 %.When the activation time satisfies the given interval,the discharge time can be prolonged by changing the thickness of heat pellets and insulators.(4)The self-controlled parameterization simulation for thermal battery is developed.The automatic simulation of the thermal battery performance is realized,specifically,parameterized modeling,automatic grid division,automatic addition of boundary conditions,automatic calculation of solver,automatic extraction of simulation results and automatic generation of simulation reports.The design efficiency of thermal battery is significantly improved,which meets the practical application requirements of engineering simulation in the author’s unit.(5)The thermal runaway problem of the thermal battery is studied.The heat generation mechanism of thermal battery under high temperature no-load condition is analyzed,and a heat source model considering the uneven heat generation of different unit cells in the thermal battery is proposed.The thermal runaway simulation model is established,and the thermal runaway simulation analysis is carried out.A high temperature no-load experiment is carried out to verify the effectiveness of the simulation analysis.Through simulation and analysis,the following useful conclusions are obtained: the increase of the chemical reaction rate of positive and negative active substances leads to the increase of thermal runaway possibility;The shell temperature cannot be used as the criterion to evaluate the thermal runaway.Ambient temperature has little influence on thermal runaway phenomenon of thermal battery.According to the thermal simulation results,the reaction rate of the active substance is deduced when the battery is out of control,which has certain reference value for the thermal design of the thermal battery stack.To sum up,this dissertation takes the key problems in the development of thermal battery urgently needed by the author’s unit as the breakthrough point,conducts in-depth research on the performance simulation and thermal runaway problems in the activation and working stages of thermal batteries,and obtains certain beneficial conclusions. |
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