Analysis of pressure drop, energy requirements, and entropy generation in natural gas pipelines at dense and pseudo-dense phases: a CFD study

Abstract Reducing pressure drop and energy requirements in the natural gas transmission is crucial for enhancing the performance of pipelines and reducing the greenhouse emission effect. In this study, a steady-state CFD modeling was conducted to examine the pressure drop, energy-specific toll (EST), and entropy generation rate (ER) of natural gas pipelines in the dense phase (DP), pseudo-dense phase (PDP), and vapor phase (VP). Three natural gas cases with varying compositions were utilized. The findings revealed that at all three cases, the pressure drop, EST, and ER in the DP were lower compared to those in the PDP and VP phases. For instance, in case 1, the EST in DP was 15 % and 67 % lower than in the PDP and VP, respectively. Similarly, the pressure drop in DP for case 1 was 7.5 % and 42.8 % lower than in the PDP and VP, respectively. Additionally, the ER in DP for case 1 was 12 % and 60 % lower than in the PDP and VP, respectively. The effect of mass flow rate on the pipeline performance indicated that as the mass flow rate increased from 30 to 50 kg/s, the pressure drop, EST, and ER for all cases and phases increased almost 2.7 times. Additionally, when the pipeline diameter increased from 0.3 to 0.6 m, the pressure drop, EST, and ER decreased almost 38, 38, and 16 times, respectively. The results of surface roughness revealed that for all cases and phases, the pressure drop, EST, and ER increased by almost 2.39, 2.39, and 2.2 times, respectively, as the surface roughness increased from 5 μm to 260 μm. Finally, this study developed mathematical models to investigate the pressure drop for pipelines in DP and PDP. The diameter of the pipeline had a greater effect on presser drop compared to the inlet mass flow rate and surface roughness.