| The vanadium redox flow battery is considered to be one of the most promising technologies for large-scale energy storage,with advantages of flexible design,high reversibility,and no cross-contamination,due to the same electrolytes in both half-cells.In spite of above advantages,the precipitation of active reactants at temperatures below 10 ? or above 40 ? has become a major barrier for the wide adoption of the vanadium redox flow battery.In addition to the safety issue,the operating temperature,which is determined by the heat generation during the charge and discharge process,the heat exchange between the battery system and the ambience,and the ambient temperature,may also affect the overall energy efficiency of the battery system.Therefore,this thesis focuses on the thermal of the vanadium redox battery,and aims to investigate the practical thermal management strategy and dynamic flow rate control strategy for the battery system,particularly under extreme temperature conditions.This study is conducted through the modelling and experimental approaches.First,a transient model of the vanadium redox flow battery is developed to derive the temperature rise as well as total power losses as a function of the applied current,active reactant concentration,and applied electrolyte flow-rate.Then,corresponding experimental studies are conducted to verify the effectiveness of the developed model.Main findings of the thesis include:(i)The real-time temperature of the battery system is largely affected by the applied current density and electrolyte flow-rate in comparison to other factors such as xxx.With increasing current density,the average temperature of the battery stack increases continuously.While with increasing flow rate of the electrolytes,the stack temperature first decreases to a small extent,and then rises when the increased heat generation resulting from the higher pressure drop exceeds the effect of the enhanced heat exchange.(ii)The temperature fluctuation of the battery stack is primarily determined by the depth of charge and discharge.Especially under stable ambient temperatures,the amplitude of the temperature fluctuation varies proportionally with varying depth of charge and discharge.(iii)The operating temperature has significant effects on the viscosity and conductivity of the electrolyte,leading the decreased pump losses decrease while the increased shunt losses at rising temperature of the battery system.In general,relatively low ambient temperatures would lead to higher heat generation compared to that generated at relatively high ambient temperatures.Based on the abovementioned findings,the temperature variation of the battery system under varying battery charge and discharge power is also investigated through the proposed model.And a dynamic flow-rate control strategy is developed for optimizing the flow rate of the electrolytes by incorporating the influences of the flow rate on the mass transfer,pump power losses,and temperature rise of the electrolytes.In addition to the flow-rate control strategy,other thermal management strategies of the vanadium redox flow battery are summarized as follows:(i)at relatively high ambient temperatures(above 30?),the non-stop,continuous charge-discharge cycles under relatively high current density should be avoided(such as current density larger than 50mA/cm~2.(ii)Extra attention should be paid to the condition at relatively low SOC during the discharge process.The discharge process should be immediately terminated if the stack temperature exceeds 40 ?.(iii)Excessive discharge process under relatively high ambient temperatures should be avoided while the temporary discharge behaviors would still be safe for the whole battery system.Note that all the studies performed in this thesis are based on the condition that no passive cooling is utilized to maintain the proper operating temperature range of the vanadium redox flow battery. |
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