(BQ) Part 2 book "Fundamentals of Heat and Mass transfer" has contents: Internal flow, free convection, boiling and condensation, heat exchangers, radiation - processes and properties, radiation exchange between surfaces, diffusion mass transfer. | 2/21/11 5:09 PM Page 517 C H A P T E R Internal Flow 8 2/21/11 518 5:09 PM Page 518 Chapter 8 Internal Flow H aving acquired the means to compute convection transfer rates for external flow, we now consider the convection transfer problem for internal flow Recall that an external flow is one for which boundary layer development on a surface is allowed to continue without external constraints, as for the flat plate of Figure . In contrast, an internal flow, such as flow in a pipe, is one for which the fluid is confine by a surface. Hence the boundary layer is unable to develop without eventually being constrained. The internal flow configuration represents a convenient geometry for heating and cooling fluids used in chemical processing, environmental control, and energy conversion technologies. Our objectives are to develop an appreciation for the physical phenomena associated with internal flow and to obtain convection coefficients for flow conditions of practical importance. As in Chapter 7, we will restrict attention to problems of low-speed, forced convection with no phase change occurring in the fluid. We begin by considering velocity (hydrodynamic) effects pertinent to internal flows, focusing on certain unique features of boundary layer development. Thermal boundary layer effects are considered next, and an overall energy balance is applied to determine fluid temperature variations in the flow direction. Finally, correlations for estimating the convection heat transfer coefficient are presented for a variety of internal flow conditions. Hydrodynamic Considerations When considering external flow, it is necessary to ask only whether the flow is laminar or turbulent. However, for an internal flow we must also be concerned with the existence of entrance and fully developed regions. Flow Conditions Consider laminar flow in a circular tube of radius ro (Figure ), where fluid enters the tube with a uniform velocity. We know that
