Performance Analysis Of A Noyel LNG Vaporizer And Experimental Study On The Related Falling Film Heat Transfer

With the increasing hindering of the environmental issue and energy crisis on the world economy, more attention has been paid to the utilization of natural gas, a clean and high-efficient energy resource. The storage and vaporizing equipment of Liquefied Natural Gas (LNG) is also becoming the hotspot in both research and development aspects.Open-Rack Vaporizer (ORV) for LNG, a kind of heat exchanger heated by sea water, is widely used in the base-load case at the LNG terminals. However, the ice formation on the external surface of the heat transfer tubes hinders a further performance improvement of this facility. One of the ways to overcome the problem is the application of a high performance ORV (named as SuperORV), which is characterized by its heat transfer tube with a double-tube structure at the lower part, called the LNG vaporizing section. The research concerning the SuperORV is rarely reported in China, meanwhile, the method of utilizing water film for heating (typical mode in SuperORV) is also rarely investigated by thermal engineering researchers, due to the fact that this type of heat transfer is seldom applied in traditional heat exchangers. However, this heat transfer has been proven practically significant not only in academic aspect for film’s heat transfer investigation but also in industrial aspect for the process and equipment design in cryogenics and LNG industry.In order to provide reference for the design, type selection and operation management of the LNG facility, the simulation work aiming to investigate the performance of the heat transfer tube in the SuperORV and the experimental work aiming to investigate the heat transfer characteristics of the chilled falling film outside a vertical tube are conducted based on the approach of combining theory with practice. The main research contents include:1) After analyzing the heat exchange in the heat transfer tube of a SuperORV, the heat transfer region is divided into the single-phase liquid convection zone, the subcooled boiling zone, the saturated boiling zone and liquid deficient zone along the vaporizing section, and the single-phase vapor convection zone along the heating section in terms of diverse mechanisms about the different regimes of LNG evaporation. A steady state distributed parameter model is established and validated to simulate the LNG evaporating process in a SuperORV heat transfer tube. 2) Based on the distributed parameter model, numerical simulation is then conducted to present the heat transfer performance of the heat tube in SuperORV, considering the effects of the heat transfer enhancement techniques and the ice thicknesses. The distributions of some important parameters concerning heat transfer characteristics are presented. Effects of heat transfer enhancement techniques and different icing status are also discussed for the performance prediction of this type of vaporizer.3) Based on a review of the experiment schemes in the literatures and on a summary of the principles and objectives of our study, an experimental apparatus has been designed and built up. A series of experiments have been conducted to observe the heat transfer characteristics of the chilled downward film outside a vertical tube and their relation with the Reynolds number. The correlations for the non-dimensional average heat transfer coefficient of the cooled water film are then summarized by fitting the experimental results in three typical Reynolds number intervals.