Simulation Study On Condensation Flow And Heat Transfer Characteristics On The Tube Side Of LNG Spiral Wound Heat Exchanger

Natural gas plays a crucial role in achieving carbon peak and carbon neutrality goals as a clean energy source.Among them,as one of the main equipment in the natural gas liquefaction process,the spiral-wound heat exchanger(SWHE)is widely used due to its compact structure and high heat transfer efficiency.In the natural gas liquefaction process,both the natural gas and mixed refrigerants in the SWHE undergo multi-component condensation phase change,making the heat and mass transfer process extremely complex.The relevant research on SWHE in natural gas liquefaction has started relatively late and is insufficient.Therefore,this article conducts further simulation research on the condensation process of hydrocarbon mixed media in the tube side of SWHE in the natural gas liquefaction process,aiming to address the shortcomings of existing research.Firstly,simulation research is conducted on the single-phase flow and heat transfer conditions on the tube side.A three-stage structure is used in the physical model to balance the calculation accuracy and workload.The grid is verified for independence based on the heat transfer coefficient and frictional pressure drop.The Realizable k-ε model is selected as the turbulence model,which has been validated to be the best fit with experimental data.The accuracy of the model is validated through a comparison of experimental data and y+ values.The simulation results show that the heat transfer coefficient and frictional pressure drop of the single-phase fluid on the SWHE tube side increase with the mass flow rate and decrease with the pipe diameter.Secondly,a calculation model is built for two-phase condensation flow and heat transfer of mixed media on the tube side.Based on the research results of literature and the accumulated experience of the project team,the multiphase flow model considers the VOF model for condensation interface capturing,the RSM model for turbulence modeling with interface turbulence anisotropy,and the classical Lee model for phase transition modeling.The limitations of the VOF model and the characteristics of the condensation film are analyzed,and corrections are made for droplet entrainment,condensation film turbulence Pr number,and gas-liquid interface velocity gradient.The physical model also uses a three-stage structure,and the grid independence verification is carried out separately for the boundary layer grid and the main flow grid due to the influence of the condensation film.The impact of multi-component condensation on heat transfer is calculated using the extensively validated Modified Silver method.The calculation model is widely validated from three aspects: vapor quality,heat transfer coefficient,and frictional pressure drop,using classical correlations and literature experimental data.The deviation is within ±15%,proving the accuracy and reliability of the calculation.Finally,based on the above models,numerical simulations were carried out for hydrocarbon mixed working fluids on the tube side of SWHE,and the heat transfer characteristics of the mixed working fluids under different operating and structural parameters were analyzed.The results showed that the flow regime transition on the tube side of SWHE was mainly affected by gravity and shear force,and as the mass flow rate increased,the dryness fraction corresponding to the flow regime transition decreased,while the saturation pressure had little effect on the flow regime transition.A significant secondary flow appeared at the outlet section,but the velocity of the secondary flow was relatively small compared to the main flow velocity.After considering the effect of mixing,the overall change in heat transfer coefficient was small,and there was a decreasing trend at high dryness fractions.The cross-sectional void fraction increased with the increase of dryness fraction and mass flow rate,and decreased with the increase of saturation pressure,while the effect of helix angle and helix diameter was small.The deviation between the simulated results of heat transfer coefficient and friction pressure drop and the recommended correlation by Neeraas was within ±15%,indicating that the correlation was accurate and reliable within the simulation range.This study laid a theoretical foundation for further understanding the flow and heat transfer characteristics of multi-component condensation on the tube side of LNGSWHE and the design of related heat exchangers.