Numerical Simulation Of Fluid Flow And Heat Transfer In LNG Submerged-combustion Vaporizer

As a clean energy, liquefied natural gas has received much attention from public society in recent years. Research on equipment of LNG storage and vaporization has also become hotspot in research field. LNG submerged-combustion vaporizer is a kind of heat exchanger with high thermal efficiency. It mainly used for peak load system. Although the shell and tube heat exchanger with baffles has been further discussed, the sturcture and simulation of LNG submerged-combustion vaporizer which specializes for the vaporization of low temperature fluid is rarely reported. Study the flow and heat transfer condition and discuss more reasonable structures and parameters. These are of great practical value.A numerical simulation of flow and heat transfer process in LNG submerged-combustion vaporizer is done by CFD software FLUENT. A structure with inclined heat exchanger tube is suggested. Average velocity and turbulence kinetic energy of turbulent water in shell and heat transfer coefficient of vaporizer are also got. The main findings are as follows:A physical numerical model of LNG submerged-combustion vaporizer is built, with Standard k-εModel describing the turbulent flow, mixture model dealing with multiphase flow, discrete phase model describing the couple calculation between the gas phase and the water phase, UDF function to add source term expressing the process of vaporization.By the method of numerical simulation, flow field distribution, temperature distribution and pressure distribution of LNG submerged-combustion vaporizer are got to describe the flow and heat transfer process in the vaporizer; void fraction distribution alone the tube length is got to describe flow condition, gas phase distribution and liquid phase distribution; curve of the resistance loss is given.The numerical simulation results show that there will be vapor deposition in horizontal heat exchanger tube when the horizontal tube is used in LNG vaporizer. For this reason, the paper refers to use inclined tube fraction. Through the numerical simulation of flow and heat transfer process with horizontal tube, inclined tube of various tilt angles of 1, 1.5, 2, 3 respectively, the influence of tilt angle has been got. The results show that the larger tilt angle is, the more helpful to eliminate vapor deposition. On the other hand, increasing tilt angle will affect the structural stability of vaporizer. Considering the two facts mentioned above, the best tilt angle is 2. The influence of gas injected to turbulent water and total heat transfer factor in various Reynold number is investigated. When Reynold number is in the range of 10~4～5×10~5, average velocity and average turbulence kinetic energy of water and total heat transfer factor of vaporizer increase greatly; keeping increasing Reynold number, average velocity and average turbulence kinetic energy of water can still increase, while total heat transfer factor hasn't remarkable change any more because of the influence of heat transfer film coefficient inside the tube. The best Reynold number of gas injected is 5×10~4.