Heat transfer in two-zone thick-walled pipes with axial varying periodic temperature boundary condition

The combined heat transfer in thick-walled pipes is investigated by also considering axial heat conduction. The problem considers a two-zone infinite pipe. There is a constant outer wall temperature boundary condition in the upstream region of the pipe. In the downstream region, the outer wall temperature is assumed to vary periodically in the axial direction spatially. This problem, where the flow is assumed to be laminar, is solved numerically by the finite difference method. The effects of the basic parameters of wall thickness ratio, Peclet number, wall-fluid thermal conductivity coefficient ratio and wall-fluid thermal diffusivity coefficient ratio on the interface heat flux are investigated. The effects of the axial dimensionless frequency on the results are also taken into account in the studies. The results obtained are highly dependent on the parametric values. It is observed that the wall thickness ratio is more effective than the other parametric values. In addition, it can be said that the pipe wall and fluid axial conduction cause heat transfer to the upper flow region at a non-negligible scale.