Simulation And Optimation Of Fluid Distribution Characteristics In The Header Of FLNG Plate-fin Heat Exchanger

Plate-fin heat exchanger is the core equipment of floating liquefied natural gas(FLNG)production,storage and unloading device,with characteristics of high efficiency and compactness,small heat transfer temperature difference,as well as strong design flexibility.In order to improve the fluid distribution uniformity and work efficiency of FLNG plate-fin heat exchanger in actual operation,three-dimensional numerical models with different inlet parameters and working conditions are established.Based on the simulation results,a set of simulation software is developed for plate-fin heat exchanger,which could reflect the distribution characteristics in header.Finally,an optimized parametric designing method is developed for header.The research achievements are described as follows:(1)Numerical model of fluid distribution in the header are developed.Based on ANSYS platform,three-dimensional numerical model is established under stable and sloshing working conditions,with a set of parameter index evaluating the uniformity of fluid distribution in the header.Compared with experimental data allocation for headers in literature,the results show that more than 95% of the data errors are within ±10%.(2)Fluid distribution of the header under steady and sloshing working conditions are simulated.According to the actual working conditions,the numerical simulation is carried out with mass flow density,inlet quality,rolling and swaying parameters as variables.At the meantime,inlet and outlet parameters of header are calculated including fluid distribution,mass flow rate,flow velocity and pressure drop.Finally,the outlet distribution curve of mass flow rate is fitted by least square method,and a computational model for fluid distribution under different working conditions is developed.(3)Aimulation model and software for the header of heat exchanger are developed reflecting the distribution characteristics.A flow correction method for the outlet mass flow rate of heat exchanger is proposed with the correction factors of mass flow rate,inlet distribution and sloshing working conditions introduced.Finally,simulation software for FLNG plate-fin heat exchanger is developed reflecting the distribution characteristics of the header,embedding the general performance calculation model based on layer distribution.(4)Optimum structure of diversion header is designed for offshore operation.In this paper,the outlet parameters of the optimized header are compared and analyzed horizontally under different punched rows and angles,based on optimized structural header with diversion baffle.At the same time,the simulation software of FLNG plate-fin heat exchanger is used to verify the performance before and after the improvement.The results show that the effective improvement range of heat transfer performance for the optimized header is 11.0%～17.1%,and the effective reduction range of flow pressure loss is 54.6%～72.6%.For the working conditions studied in this paper,the optimum punched number is 12,and the angle is 40 degrees according to the parameter index proposed.