Hydrodynamics And Mass Transfer Characteristics Of Falling Film Under Offshore Floating Conditions

As a highly efficient mass and heat transfer technology,liquid falling film flow was widely used in many fields such as petrochemical,aerospace,food processing,energy,refrigeration and nuclear industries.China is now moving toward the ambitious goal of becoming a maritime power,and more and more efforts are being invested in offshore industrial production,making the design of equipment and process optimization under marine conditions an increasing research hotspot for researchers.The falling film flow process is expected to play an important role in practical applications such as offshore oil and gas exploration,waste gas treatment,and ship refrigeration,but the unit operations and processes under marine conditions need to withstand various swaying and vibration effects caused by wave motion,so it is necessary to explore and study the characteristics of falling film in marine floating conditions for further applications.In this work,a combination of experiments and CFD simulations was used to study the hydrodynamics and mass transfer characteristics of the falling film flow under marine floating conditions.The experiments were carried out by visualization method to obtain the liquid film flow pattern;and the effective interfacial area a_eand the liquid side mass transfer coefficient k _Lwere determined by chemical absorption method.Based on the experimental results,CFD simulations were used to further reveal the influence of the oceanic conditions on the hydrodynamics and mass transfer characteristics of the falling film.The main conclusions of the study are as follows:1.In the visualization experiments of the hydrodynamics of the falling film under marine floating conditions,the liquid film presented different flow modes under the different forms of platform motion.Among them,non-titling oscillations including Tx,Tz,and Rz motion had less influence on the liquid film flow modes,and all the liquid film presented complete liquid film flow compared with stationary conditions;titling oscillations such as Ry motion and inclined states caused significant transformation of liquid film flow mode,and the liquid film presented falling film flow with dry patches and corner rivulet flow.2.In the experiments of mass transfer characteristics of falling film under marine floating conditions,the effective interfacial area a_eand the liquid side mass transfer coefficient k _Lin a vertical falling film tube was investigated by using the CO₂chemisorption method with Na OH solution.The results indicated that the values of a_eand k _Lunder non-titling oscillations were basically the same compared with stationary states;the value of a_edecreased significantly while the value of k _Lincreased sharply under titling oscillations,and the falling film characteristics were significantly deteriorated.The increase of liquid rate could improve the mass transfer performance to a certain extent.In addition,the relative fluctuation magnitude of a_eand k _Lincreased with the increase of motion amplitudes and periods,the relative change rate of a_edecreased while the relative change rate of k _Lincreased with the increase of inclined degree.3.The VOF method and three-dimensional transient model were adopted to simulate the falling film flow process in marine conditions,and the reliability of the simulation method was verified by comparing the simulated average liquid film thickness values with the theoretical empirical calculations.The liquid film pattern under different motions was obtained by numerical simulation,and the influence of motion forms on the liquid film patterns was analyzed qualitatively.The quantitative data of liquid holdup and liquid film turbulence kinetic energy are obtained,and the Ry motion has the most significant effect on liquid holdup and turbulence kinetic energy compared with other motions.The effects of the oceanic conditions on the a_eand k _Lare further explained in the context of the numerical simulation results.