CFD Study Of The Intensified Micro Mixing Performance In A Multi-channel Micro Impinging Stream Reactor

In chemical industries,reactors are the most important equipment.The intensification of reactors has got a lot attention during past few decades.The key factor of reactors' intensification is intensified micromixing,i.e.,mixing at molecular level,as it controls all other reaction parameters such as selectivity,yield,production of by-product,heat generation,etc.Many attempts have been made to decrease size of reactor but increase mixing.In those attempts different reactors e.g.,capillary channel or micro channel reactors,confined impinging jet reactor,spinning disk reactor,rotating reactor etc.,were developed.The designing of these reactors is based on the principle to improve mass transfer per unit time.The high amount of mass transfer in unit time can be achieved either by increasing the contact area among fluid streams or by increasing the velocity to create impinging.As compared to traditional chemical reactors,these novel reactors are showing a remarkable improvement in mixing efficiency and are used in the preparation of polymers,catalysts,nano-articles,extraction processes,absorption etc.However,there are some problems like limited fluid volumes,blocking of microchannels,difficulties in manufacturing and fabrication,expensive and inflexibility to scale up are attached to these reactors and limit their use in big chemical industries.A multi-channel micro impinging reactor has been fabricated with visible polyplex glass.The reactor has four inlet channels and a big reaction area.The outlet is kept large to ensure a smooth outflow of streams after reacting.The reactors has option to make one,two or four channels be operational as per choice.In MC-MISR mixing and mass transfer efficiency has been increased by intensifying the interaction among chemical species.The fluid streams from both inlets enter into reaction chamber at a high velocity and intensely impinging with each other.This allows the streams to break up into tiny fragments and increase the molecular interaction between chemical species.The micromixing performance of MC-MISR is appreciable and promising.There are more than one novel aspects of this study:(1)A multichannel micro impinging stream reactor has been developed.Micromixing efficiency in MC-MISR has been investigated by Villermaux-Dushman(iodate-iodide)competing parallel reaction scheme.The micromixing efficiency has been measured in terms of segregation index(Xs)and effects of increasing velocity or Re on micromixing have been drawn.As value of Re is increasing the segregation index Xs is decreasing.For Re>3000,the value of Xs falls in?10-5,which indicates a very good level of micromixing.(2)A multiphase computational fluid dynamics(CFD)study has completed.A k-?turbulence model,Eularian multiphase model and finite-rate species transport models are used in cooperation with transient state and gravity to investigate fluid behavior and micromixing in MC-MISR.The numerical results show a good agreement with the experimental results.And multiphase flow patterns give a good understanding of water-air phase and liquid-liquid interaction before and after impinging.(3)A scale up study also completed by operating two and four channels and effects of increasing number of channels and fluid volume have been investigated.A performance comparison has been made among one,two and four channels and results have been drawn.And it is evident from results that increasing the number of channels does not have any drastic effect on micromixing.At a high Re(>3000)the segregation index Xs for one,two and four channels are almost same.This is probably because of high impinging and a good interaction between streams at a high velocity.As compared to other microreactors,the MC-MISR offers advantages i.e.,handling of large fluid volumes,avoid blocking of outlet channels,high degree of mass transfer and mixing etc.This makes it applicable for polymerization reactions and formation of nano-materials in large amount.Scaling up of microreactors for industrial use always has been a challenge for engineers.This limits the use of microreactors only for research purposes.But with the development of MC-MISR a new path for researchers and engineers has been paved.