Thermal energy storage has become an integral part of Concentrated Solar Power (CSP) plants to guarantee continuous supply of power demand. For cost-effective solar power generation, the size and operating temperatures of CSP plants should be increased. Thermochemical energy storage (TCES) is the only available solution to meet energy density and high-temperature requirements. Air is mostly used as Heat Transfer Fluid (HTF) for high-temperature CSP plants. For the air-based system, metal redox reactions are good candidates as storage reactant. Application of metal oxide gas-solid redox reaction in storage systems requires an efficient reactor design. Cost-effectiveness and simplicity have made packed bed reactors a viable candidate for high-temperature applications. The high-pressure drop along the bed is the main drawback of such reactors preventing them from widespread applications. Split flow design modification could aid in reducing pressure drop while providing more flexibility in reactor performance control. A cylindrical split-flow packed bed reactor with an annulus for HTF flow is considered as a modified reactor design. The transient two-dimensional axisymmetric numerical model is developed for solving mass, momentum, and energy equations for both gas and solid phases using suitable reaction kinetics for the cobalt oxide redox reaction. A parametric study is performed on cylindrical-shaped split-flow reactor design as a basis for future optimization for complete storage cycle. The effect of split flow ratio and side-channel width on reactor performance are considered. It is shown that both parameters could be used effectively to design and optimize the reactor.