Şefik Bilir

Laminar flow heat transfer in pipes including two-dimensional wall and fluid axial conduction

Abstract An analysis is made for a conjugate heat transfer problem with thermally developing laminar pipe flow, involving two-dimensional wall and axial fluid conduction. The problem is solved numerically by a finite-difference method for a thick walled, two-regional pipe which has constant outside surface temperatures interfaced by a step change. An exact profile is used to discretize the differential equation in the fluid region, and the method exhibited a simple and fast tool to solve this highly complicated problem. The effects of the three defining parameters, the Peclet number, thickness ratio and wall-to-fluid conductivity ratio, are investigated, and it is observed that the most significant of these parameters is the Peclet number, in its effective range (Pe ⩽ 20).

NUMERICAL SOLUTION OF GRAETZ PROBLEM WITH AXIAL CONDUCTION

Heat transfer in the thermal entrance region of pipes is analyzed by the finite-difference method including the effect of axial fluid conduction. A hydrodynamically developed flow through a two-region pipe is investigated for constant surface temperatures by a step change and for insulated upstream and uniform wall heat flux in the downstream region. The rate of convergence is enhanced by discretizing the governing differential equation by an exact profile obtained from the analytical solution of the one-dimensional conduction-convection problem.

Transient conjugated heat transfer in thick walled pipes with convective boundary conditions

Abstract Transient conjugated heat transfer for laminar flow in the thermal entrance region of pipes is investigated by considering two dimensional wall and axial fluid conduction. The problem is handled for an initially isothermal, infinitely long, thick-walled and two-regional pipe for which the upstream region is insulated and solved numerically by a finite difference method for hydrodynamically developed flow with a step change in the ambient fluid temperature in the heated downstream region. A parametric study is done to analyse the effects of five defining parameters namely, wall thickness ratio, wall-to-fluid conductivity ratio, wall-to-fluid thermal diffusivity ratio, the Peclet number and the Biot number.

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

Abstract 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.