A pseudo-homogeneous multi-component equilibrium model is developed to study fluid flow behavior and heat transfer during decompression of a buried natural gas pipeline. The model includes non-isentropic effects of heat transfer and viscous dissipation. The heat transfer involves transient heat conduction through the pipe wall and the soil. A numerical scheme is developed to efficiently solve the resulting conservation equations simultaneously with the heat transfer equation. The study shows that the inclusion of transient heat transfer is necessary for accurate modeling the decompression of natural gas pipelines. The temperature reduction on the pipe wall due to fluid expansion can be crucial for the proper design of pipelines to prevent brittle behavior of the pipe steel.

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