This work predicts the hydrodynamics and heat transfer modes in gravity-driven dilute particle flow with application to thermochemical energy storage system by implementing one-dimensional force and energy equations. The relative contribution of conduction, convection, and radiation heat transfer into a sCO₂ loop was explored at different operating conditions of counterflow gas velocity, solid mass ratio, particle size, and temperature along the reactor's height at a steady state. The results show that larger particle size allows higher counterflow gas velocity with a lower risk of particle entrainment. However, the effect is counterbalanced by attenuation in the convective heat transfer between particle and wall. Radiation heat transfer is more prominent at higher temperatures, contributing about 50% to the overall heat transfer. For small solid mass ratio (< 0.04), the conduction is negligible. The predicted overall heat transfer coefficient of 400 W/m²K is considered to be significant for the relatively dilute flow conditions. Finally, the temperature distribution profiles are presented at different particle sizes and gas inlet temperatures.