Limiting Isothermal Flow in Pipes

An explicit formulation is given for the limiting isothermal flow of a gas in a horizontal pipe. For isothermal flow, the ratio of critical pressure to initial pressure equals the initial Mach number times the square root of the ratio of specific heats. The critical-pressure ratio for isothermal flow is higher than that for adiabatic flow. Some comparisons are drawn between isothermal, adiabatic, and incompressible flow.