The Study Of Carbon Dioxide Dilution And Supercritical Binary Fluid On Heat And Mass Transfer Phenomenon And Mechanism

Along with the rapid economic development of human society,the extensive use of fossil fuels has led to escalating levels of carbon dioxide in the atmosphere,which brought a very serious environmental problems,such as the recent concern of the "greenhouse effect" problem.For this reason the world have raised the practical energy saving program and is actively working to develop new applications technology.However,if the direct limit carbon dioxide emissions will be an impediment to some extent,on a country's economic development.So the study of efficient carbon dioxide capture technology can bring both good economic and social effects,but also be able to protect the natural environment,alleviate or even suppress the greenhouse effect made a positive contribution.In addition,there are a lot of gas-liquid mass transfer phenomenon in the chemical,oil refining,metallurgy,biochemistry and other industrial processes,due to the complexity of the actual process,the reality of the production of the lack of effective means of testing.Therefore it is very necessary to establish a precise and efficient test system.Liquid mass transfer behavior mainly in the form of bubbles in the actual production activities,often related to the collapse of bubble,polyethylene and complex deformation behavior of bubbles in the existing experimental conditions there is still no theory can predict bubbles accurately transfer mass behavior.Mass transfer process is the basis of a single bubble bubbles research behavior,so the complete system study about the behavior of bubbles in the liquid phase mass transfer fluid does an importantsignificance and practical value.This paper designed a visualization experiment system to study the carbon dioxide bubbles dilution mass transfer process at different temperature and pressure conditions,and the images of different initial bubble size were real-time collected,after data analysis finishing,we got some conclusions:1.The mass transfer process in bubble diameter variations obey zoning laws,including fast zone,transition zone,slow zone.Rapid changes in cell diameter area very quickly,slow changes in the slowest zone,a transition zone is from fast to slow and gradual process of change.Under normal circumstances the duration of the fast zone around 200 s,the duration of the transition zone is about 100 s,while the duration of the slow zone is more than up to 2000 s.2.Transition time relates about pressure and temperature.The greater the pressure,the greater the turning radius,the shorter the transition period,the lower the temperature,the longer the transition time,but overall,the gap is not very big.3.The different regions within the mass transfer rate difference is very large,the same conditions,rapid and slow the rate of mass transfer zone area mass transfer rates differ at three to four orders of magnitude,the same pressure conditions,the mass transfer rate is lower than the temperature.4.The effects of surface tension and contact angle of buoyancy of the bubbles,the results show that when the bubble size is large,the buoyancy dominant role,the contact angle is small,when the bubble radius is less than the surface tension of about 0.7mm dominant role.5.Change of dynamic contact angle bubble with bubble size variation is closely related to the region quickly bubble dynamic contact angle increases rapidly slow the bubble equilibrium contact angle of the region remained stable.Equilibrium contact angle of the size of the state and the pressure was linear within the range of experimental studies equilibrium contact angle of less than 90°.6.We numerically investigate the change process of bubble at a fixedinterface and free surface conditions,numerical results show the change process of bubble affected by the temperature and pressure.In addition,there are lots of heat and mass transfer phenomena about super-critical fluids in the industry,and it is important for many special and occasions,such as cryogenics,air separation,energy and other fields.We numerically investigate the natural convection of super-critical nitrogen/argon(0.9/0.1 in molar fraction)binary fluid in a three-dimensional rectangular cavity in the present study.The influences of the Piston effect,Soret effect and Dufour effect on the development of the natural convection are investigated with the bottom-heated and top-isothermal conditions.The complete set of the equations describing the flow and heat transfer characteristics of the super-critical binary fluid are solved by the SIMPLE algorithm combined with multigrid acceleration.The results show that the stable thermal boundary layer forms at the bottom of the cavity during the initial heating phase,and the Piston effect as the dominant role accelerates the energy transport in this period.After the thermal plume breaks the boundary layer and moves upward,the natural convection occurs with the appearance of a cold boundary layer near the top.The Soret effect caused by the temperature gradient drives the component migration,resulting in the Dufour effect which promotes the energy transport.The results indicate that the Soret effect and Dufour effect promote heat and mass transfer in the natural convection of super-critical binary fluids.