Analysis of LNG flow and enhanced heat transfer characteristics within tubes with structural enhancements

Natural gas is widely used as a clean energy source and because of its convenient transportation, high calorific value, and large reserves. It is therefore of great importance to study its liquefaction characteristics to improve its utilization rate and reduce energy consumption. In this paper, the liquid flow and heat transfer characteristics of natural gas in spiral tubes (both smooth tubes and those with internal structural enhancements such as grooves and ribs) are studied by numerical simulations. The results indicate that the structural enhancements have a notable impact on the fluid pressure drop, but no significant influence on the heat transfer coefficient. When a structural enhancement is aligns closely with the corresponding location of high-speed fluid flow, both the pressure drop and heat transfer tend to increase. However, the overall heat transfer coefficient does not reach a high level, despite these structural enhancements. Increasing the number of ribs increases the heat transfer capacity, while smaller ribs with enhanced surfaces are particularly beneficial for improving the overall heat transfer efficiency. An additional analysis is conducted on the temperature and velocity distributions of natural gas flow in the tubes, and the relationships between pressure drop, heat transfer coefficient, gas inlet velocity, and volume fraction during natural gas liquefaction are compared. Furthermore, the impact of the number, position, and size of the structural enhancements on condensation in the tubes is discussed, and a comprehensive evaluation factor is introduced.