Numerical Investgation Of Phase Change Heat Transfer For Super Open-frame Vaporizer

With the energy crisis and the increasingly serious environmental problems, LNG(Liquefied Natural Gas) has attracted increasing attention as a clean, and high calorific energy. The development of natural gas industry has become an important force improving the energy structure and promoting the development of low carbon economy. In practical application, LNG need to be gasificated and be heated to ambient temperature. Therefore, the LNG vaporizers have become indispensable equipments in natural gas industry. At present, the ORV(Open Rack Vaporizer) is used for basic load type LNG in receiving station in china, which is mainly dependent on foreign imports. With the contradictions between the rapid development of LNG industry and the limited gasification technology increasing, localization of LNG super ORV is imperative.This study analyzed previous research status about super ORV, designed a type of inner gasification pipe to support a new Open-Frame Vaporizer with inner spiral tubes and researched its performance of heat and mass transfer.Firstly, in this study, according to different mixing rules, physical property(such as density, specific heat capacity, thermal conductivity and dynamic viscosity) of LNG and NG(gaseous Natural Gas) was calculated. Secondly, the heat transfer process including preheating process, gasification process, the heating process of super ORV was analyzed based on its structure and working principle,and the calculation methods of heat transfer in each process had been summarized. Then the physical model and numerical model such as mixture multiphase model, turbulence model and phase change model included UDF were built. Thirdly, the performance such as the distribution of velocity field, temperature field, and the void fraction of heat and mass transfer in two type of tube(smooth tube and spiral tube) was researched by using software FLUENT. The results show that the secondary flow perpendicular to the direction of the mainstream comes into been in the spiral vaporizing tube, gasification rate at outlet of the spiral vaporizing tube was higher 6.1% than of that the smooth tube at the inlet velocity of 0.91m/s, and heat transfer enhancement of comprehensive performance evaluation factor η is greater than 1 in the inlet velocity range from 0.91 m/s to1.63 m/s. Fourthly, the structure parameters of spiral tube was optimized by carring out a orthogonal experiment. The results show that the optimal structure parameters of spiral tube is the narrow path of 8 mm, the thread rib width of 55 ° and the pitch of 120 mm. Finally, the numerical simulation result was verified, and it is shown that the errors between the simulation values and the experimental values are in a reasonable range.This research not only provides the theoretical basis for the development of super ORV, but provides reasonable research methods and ideas for the research and optimization as well.