Convective flows in TEXSTAN are considered an internal flow when the pressure gradient is considered an unknown variable, and therefore within the numerical procedure it is guessed and often iteratively adjusted to satisfy integral conservation of mass. The internal flow geometries that can be analyzed by TEXSTAN include

• circular pipes
• planar ducts
• annular ducts

This section describes how internal flows are modeled, and the section pipe flow presents the details of how an internal flow dataset is formulated and constructed.

In Reynolds number the concepts of hydraulic diameter and its associated hydraulic-diameter Reynolds number are presented. In friction are descriptions of how the surface friction and friction coefficient for each solid surface are formulated. In heat transfer are descriptions of how the surface heat transfer, heat transfer coefficient, and the Nusselt number for each solid surface are formulated.

The integration control subsection describes how the physical and computational domains for an internal flow geometry are formulated and how the integration stepsize is formulated and controlled.

In initial profiles is a discussion of how TEXSTAN auto-generates laminar and turbulent initial (starting) profiles for the various internal flow geometries. In output files is a presentation of the various output options for printing the results of the integration and a description of the files that are formatted to permit easy plotting using an external user-supplied plotting package.