Transient conjugated heat transfer in pipes involving two-dimensional wall and axial fluid conduction

This paper presents an analysis for an unsteady conjugated heat transfer problem in thermally developing laminar pipe flow, involving two-dimensional wall and fluid axial conduction. The problem is solved numerically by a finite-difference method for a thick-walled, infinitely long, two-regional pipe which is initially isothermal with a step change in the constant outside temperature of the heated downstream section. A parametric study is done to analyze the effects of four defining parameters, namely the Peclet number, wall-to-fluid thermal conductivity ratio, wall-to-fluid thermal diffusivity ratio and wall thickness to inner radius ratio. The predicted results indicate that, although the parameters affect the heat transfer characteristics at the early and intermediate periods, the time to reach the steady state does not change considerably. With the boundary conditions of the present problem, the thermal inertia of the system is mainly dependent on the flow conditions rather than on the wall characteristics.