Numerical simulation of hydrodynamics and heat transfer in a bubbling fluidized bed with horizontally immersed tubes and Geldart B particles

In particle-based sCO₂ Brayton cycle CSP systems, fluidized beds equipped with horizontally immersed tubes function as heat exchangers between solid particles and supercritical CO₂, enabling high heat transfer efficiency and superior particle mixing. However, systematic guidance regarding the effects of tube bundle configurations and operating conditions on the overall heat transfer coefficient (HTC) remains scarce. The Eulerian-Eulerian method was used to study the effects of tube arrangement, gas velocity, tube spacing, and particle size on flow and heat transfer performance. The results revealed that staggered configurations outperformed in-line arrangements at low velocities (∼2U_mf), while the in-line configuration excelled at higher velocities. Nevertheless, the overall difference in HTC between the two configurations remained within 3 %. In contrast, the effect of velocity on HTC was much more significant; as the velocity increased, the HTC of the in-line and staggered configurations increased by 11.87 % and 6.25 %, respectively. Reduction in vertical tube spacing produced a characteristic nonlinear response in HTC, exhibiting an initial decline followed by recovery across all experimental conditions, with peak variations constrained to 3.98 %.When the horizontal spacing was decreased from 60 mm to 40 mm, the HTC of the in-line and staggered configurations decreased by 4.32 % and 3.53 %, respectively. When the particle diameter increased from 250 μm to 500 μm, the HTC of in-line arrangements decreased by 5.76 %, whereas the staggered configuration showed a slight increase of 0.58 %. Moreover, it was found that the staggered arrangement regained its heat transfer performance advantage at a particle size of 500 μm. These results provide valuable theoretical support for the design of industrial fluidized bed systems.