Some Studies of the Effects of Axial Conduction in a Tube Wall on the Steady-State Laminar Convective Heat Transfer

Abstract

Whenever a superheated fluid flowing inside a tube is cooled to its saturated state, there is a sudden and significant increase in the heat transfer coefficient at the solid-fluid interface. Since the temperature of the fluid remains almost constant, this causes a step change in heat flux at the tube wall. This increased heat flux will increase the temperature of the tube wall. Even for thin wetted tubes, this temperature increase can cause considerable heat flow along the axial direction of the tube. This axial conduction in the tube wall may have an influence on the rate of condensation of the fluid and the amount of heat removed from the fluid flowing inside the tube. There are other situations, such as in power plants, where a step increase in heat flux to the tube may occur. Therefore, a detailed study of this effect of a step increase in heat transfer at a given location was initiated. A careful examination of the literature reveals that a considerable amount of work has been done in the area of conjugate heat transfer in channel flows. The present investigation was prompted by the increase in heat transfer near the condensation point of a superheatedmore » vapor being cooled inside a circular pipe. The conjugate heat transfer with the added complexity of a two-phase flow prevented this exact problem from being solved. In order to reduce the complexity of the problems, the effects of axial tube wall conduction on the steady-state, laminar, convective heat transfer of a single-phase fluid with a step change in heat flux were studied.« less