Numerical analysis of local flow heat transfer of supercritical LNG across the pseudophase transition in different airfoil channels

Abstract

As the core equipment of floating storage and regasification unit (FRSU), the function of liquefied natural gas(LNG)vaporizer is to heat the LNG from -162 °C to normal temperature under supercritical pressure, which is a pseudophase transition process. This paper numerically investigates the local flow and heat transfer of supercritical LNG during the pseudophase transition process of three airfoil channels with different structures and shapes under transcritical temperature condition. The secondary flow generated by the shape and structure of the airfoil has an important influence on the local flow heat transfer performance. Especially in the liquid-like region, the three airfoil fins not only generate mixed disturbance of the velocity vector in the y-direction, but also generate secondary vortices in the z-direction, which can more effectively interfere with the boundary layer and enhance the heat transfer performance. As the temperature increases, the density and the viscosity of the supercritical LNG in the pseudo-critical and gas-like regions decrease, the vortexes formed in the three airfoil fins appear above or below the tail of the airfoil. The research shows that under the selected conditions, Fin-2 has the best hydraulic performance, especially in the gas-like region, and its f-factor can be lower than 0.02. Because Fin-2 changes the curvature of the leading edge and minimizes the impact surface, it is conducive to the rapid discharge of local fluid, thus reducing the flow resistance and generating secondary flow at the tail of the airfoil. Fin-3 has the best heat transfer performance, and its j-factor is 5–10% higher than that of other airfoil fins. This is the tail shape of the airfoil is concave, and the secondary vortices are located in the concave area, which disturbance the boundary layer and improve the heat transfer process.