Comparison of isothermal and non-isothermal pipeline gas flow models

The transient flow of gas in pipes can be adequately described by a one-dim ensional approach. Basic equations describing the transient flow of gas in pipes are derived from an equation of motion (or momentum), an equation of continuity, equation of energy and state equation. In much of the literature, either an isothermal or an adiabatic approach is adopted. For the case of slow transients caused by fluctuations in demand, it is assumed that the gas in the pipe has sufficient time to reach therma l equilibrium with its constant-temperature surroundings. Similarly, when r apid transients were under consideration, it was assumed that the pressure changes occurred instantaneously, allowing no time for heat transfer to tak e place between the gas in the pipe and the surroundings. For many dynamic gas applications, this assumption of a process having a co nstant temperature or is adiabatic is not valid. In this case, the temperat ure of the gas is a function of distance and is calculated using a mathemat ical model, which includes the energy equation. In the paper, a comparison of different (isothermal and non-isothermal) mod els is presented. Practical examples have been used to emphasize difference s between models. (C) 2001 Elsevier Science B.V. All rights reserved.