A helically coiled tube, a common heat transfer conduit, is widely used in chemical engineering, refrigeration, aerospace, and other fields, where heat transfer is enhanced by secondary flows. Under two thermal boundary conditions—uniform wall temperature and uniform heat flux—the heat transfer inside a helically coiled tube exhibits distinct behaviors. In this work, the convective heat-flux transport equation is employed to investigate how thermal boundary conditions influence heat transfer in helically coiled tubes. The results indicate that heat transfer is weakened on the inner side of the tube and strengthened on the outer side. Compared with the uniform wall-temperature boundary, the uniform heat-flux boundary yields a larger heat flux over a broader portion of the cross-section. The reason the uniform heat-flux boundary condition provides stronger heat-transfer capability than the uniform wall-temperature boundary is that the contribution vectors of the velocity and velocity gradients, in the wall-normal direction, to the heat flux are larger. The area-weighted average of the contribution of the velocity and its gradients to the heat flux correlates well with the local Nusselt number.

helically coiled tube, convective heat transfer, heat transfer enhancement