Evolution of ash deposition and heat transfer degradation in honeycomb tube bundles for industrial waste heat recovery

Ash deposition-induced heat transfer deterioration is a critical bottleneck for the long-term efficient operation of gas-solid heat exchangers in waste heat recovery. This work experimentally investigates the effects of tube bundle arrangement, relative oblique tube pitch (1.75–2.75), flue gas velocity (5–9 m/s), and fly ash concentration (2.31–9.33 g/m 3 ) on ash deposition and heat transfer characteristics. All tests are performed at a 70 °C flue gas inlet temperature with 60 min continuous ash feeding per condition. Results show that at identical Reynolds numbers, the honeycomb tube bundle enhances wall shear stress via optimized flow channel geometry, effectively suppressing ash accumulation. Its clean-state Nusselt number is 14.3%–16.6% higher than that of the aligned tube bundle, while its ash-induced heat transfer degradation (12.34%–13.52%) is lower than the aligned bundle (14.02%–15.76%). Increasing tube pitch causes a 17.5% monotonic drop in clean-state Nu, whereas heat transfer degradation first rises then falls. Increasing the inlet flue gas velocity from 5 to 6 m/s reduces the heat transfer degradation from 14.12% to 8.57%; with a further increase to 9 m/s the degradation remains within 8.57%–9.42%. As fly ash concentration increases from 2.31 to 9.33 g/m 3 , degradation grows nonlinearly from 10.93% to 20.80%. It is concluded that a relatively small tube pitch, moderate flue gas velocity and controlled inlet ash concentration can effectively inhibit ash-related thermal resistance in honeycomb bundles, providing theoretical guidance for engineering optimization of anti-deposition heat transfer surfaces.