Numerical study on falling film flow outside the refrigerant tube.

The liquefied natural gas (LNG) floating production storage and offloading (FPSO) unit is a new type of floating production device developed for the exploitation, pretreatment, liquefaction, and storage of offshore natural gas. In this study, the shell side structure of the spiral-wound heat exchanger is analyzed, and the effects of varying the Reynolds number (Re), tube outer diameter, and number of distributors on the thickness of the shell-side liquid film are investigated. The results show that as the fluid flows down from the distributor, it hits the upper wall of the pipeline and diffuses evenly to both sides, before converging in between the two distributors. In the axial direction, the thickness of the liquid film increases first, reaches the highest at the peak, then decreases, reaches the lowest at the trough, and then increases again, forming a secondary peak at the drop. The thickness of the liquid film changes periodically, and the period is the distance between the two distributors. The thickness of the circumferential liquid film is negatively correlated with the circumferential angle, α. Moreover, the liquid film is thinnest at α = 120°, and is positively correlated with both the liquid mass flow rate and the outer diameter of the tube. The most uniform liquid film thickness is obtained when Re = 1500, the tube outer diameter is 12 mm, and the number of distributors is 6. The results from this study can guide the design of spiral-wound heat exchangers and facilitate their safe and efficient operation in natural gas liquefaction processes.