Study on composite heat transfer characteristics of semi-molten, wide-size-distributed dilute-phase particle groups around tubes

Centrifugal granulation and waste heat recovery technology represent a highly promising method for liquid slag treatment. However, the insufficient cooling of high-temperature slag particles results in the formation of semi-molten slag particles, which pose significant equipment damage risks to waste heat recovery equipment and limit the industrial application of centrifugal granulation technology. Therefore, investigating enhanced heat transfer measures and mechanisms for slag particle groups within confined granulation chambers is of substantial practical importance. This study establishes a three-dimensional physical model for heat transfer outside tubes in a dilute-phase slag particle system. FLUENT is employed to numerically simulate the phase-change-enhanced heat transfer behavior of semi-molten particle groups on surfaces. The composite heat transfer characteristics of the slag particle group under different operating conditions are analyzed. The results demonstrate that horizontal water-cooled tubes can effectively increase the turbulence of the slag particle-air flow field, thereby enhancing gas-solid heat transfer intensity and raising the air temperature around the tubes by 245 K. An increase in the initial particle temperature leads to a significant rise in the average liquid fraction of the particles at the outlet. Reducing particle size and increasing the Spread coefficient both enhance the cooling and phase-change rate of particles by increasing their surface area, with particle size having a more pronounced effect. Notably, while an increase in the Spread coefficient facilitates enhanced composite heat transfer of particles, it adversely affects gas-solid heat transfer, with radiation dominating the heat exchange behavior, accounting for over 70 %. The fin structure enhances both radiative and convective heat transfer capabilities, and when the fin radius is doubled, the liquid fraction of particles at the outlet decreases by 6.5 %. This research provides a theoretical foundation for the rapid cooling of dilute-phase particle groups in confined spaces and the utilization of waste heat from high-temperature particle groups. It holds significant implications for advancing the understanding of enhanced heat transfer mechanisms in high-temperature dilute-phase particle systems and improving industrial application technologies.