Abstract Flow analysis in sphere-packed pipes (SPP) for different pipe to sphere diameter ratios was experimentally performed in order to clarify a relationship between the heat transfer and pressure drop characteristics. The experiments, using water as a working fluid, were carried out with Re D = 2000–33,000 and Pr = 5.0–6.0. Experimental results of the pressure drop characteristics were compared with the Ergun’s and Drag model correlations. Empirical correlations for the averaged Nusselt number are proposed, and SPP heat transfer performance is compared with that of the swirl flow. Furthermore, the applicability of the SPP system to the first wall cooling is also discussed from the temperature distribution aspect of the heating wall.