**5. Conclusions**

In the present paper, by adopting the CFD-DEM coupling method, the effects of radial distribution on particle size and distribution thickness on heat transfer are studied, the utilization of the heat transfer ability and the equivalent thermal resistance in the packed bed is analyzed. The main findings are as follows.


The configurations in this work has improved the heat transfer in the packed bed, and increased the outlet temperature, it is important for energy saving, emission, and industrial applications.

**Author Contributions:** Conceptuallization: Z.L. and W.L.; methodology: S.W.; software: S.W.; validation: S.W.; resources: S.W.; formal analysis: S.W.; investigation: S.W.; datacuration: S.W.; writing: S.W.; review and editing: Z.L.; visualization: S.W.; supervision: S.W.; project administration: S.W.; funding acquisition: C.X.

**Funding:** The financial supporting was provided by National Key R&D Program of China (No. 2017YFB0603501).

**Acknowledgments:** We would like to acknowledge financial supports for this work provided by National Key R&D Program of China (No. 2017YFB0603501).

**Conflicts of Interest:** The authors declare no conflict of interest.
