Investigating the effect of inserting longitudinal fins on the overall thermal performance of spirally coiled tubes

摘要

Flow in curved pipes have been considered as a well-known technique of passive enhancement of heat transfer rate. However, there exists a lack of research considering the impact of geometrical modifications on heat transfer properties of spiral coils. In the present study, thermal and hydrodynamic behavior of the flow in spirally coiled tubes equipped with longitudinal internal fins are numerically studied. Steady three dimensional flow of water is simulated. The geometrical parameters in the present study include fin number, fin height, and fin width. Results reveal that for the spirals with a pair of horizontal fins, the increase in fin protrusion leads to PEC as high as 2.99. However, inappropriate orientation of longitudinal fins severely deteriorates the heat absorption capability of the spiral while imposing excessive pressure drop. This inefficiency is attributed to the disruption in formation of Dean vortices due to the presence of radial bumps. Thus, four-fin and three-fin configurations are generally inefficient. Changing the fin orientation in the two-fin geometries from horizontal to vertical lead to a similar inefficiency with the PEC falling as low as 0.24. Finally, the effect of local curvature on the thermal behavior of the spiral tube is investigated.