A numerical study on flow and heat transfer characteristics of the LNG storage tank feed pipeline

As a low-carbon fuel, liquefied natural gas (LNG) requires strict temperature control during transportation. Direct injection into pipelines at ambient temperature induces significant thermal stress, potentially causing permanent damage.This study employs numerical simulation to investigate the flow and heat transfer characteristics of LNG feed pipeline during pre-cooling, cold holding, and unloading stages. Significant flow maldistribution and temperature stratification occur during pre-cooling and cold holding, with maximum circumferential and wall-thickness temperature differences reaching 40 K and 23 K, respectively, and a maximum temperature drop rate of 27 K/h. During unloading, the flow reaches full-pipe conditions. While circumferential temperature differences become minimal, the wall-thickness gradient reaches 53 K, with a maximum drop rate of 30 K/min. Cold holding temperature critically affects structural safety, as an excessively rapid temperature drop during unloading may induce thermal stress beyond the material yield limit.To mitigate this risk, a minimum of 23 hours of pre-cooling and cold holding is recommended, accompanied by real-time temperature monitoring to ensure thermal stability. Flow rate and fluid temperature are key parameters affecting heat transfer. Inlet temperature exerts a stronger influence on wall temperature than flow rate, suggesting that increasing flow or lowering inlet temperature can improve cooling efficiency. Although unloading rate affects heat transfer, its impact on wall temperature fluctuations is limited.Moreover, complex pipeline structures, such as elbows and T-junctions, induce secondary vortices and flow disturbances, enhancing turbulence and thermal mixing. These effects improve local convective heat transfer and highlight the importance of geometric design in cryogenic pipeline systems.