The Influence Of The Ejector Outlet Structure On The Mixing Performance In The Jet Reactor

Mixing process is an important unit operation in chemical engineering and other process industry.As a new type of high-intensity-mixing reactor,the jet-reactor has many advantages,such as simple structure,easy-to maintenance,no leakage,high efficiency and safety performance.It has already been widely used in process engineering,like absorption,oxidation,hydrogenation,hydration and etc.In many industrial cases,it is very likely to replace the general stirred tank reactor and become a dominant reactive device because of its comprehensive advantages.Many investigations on the hydrodynamic features and the mass transfer characteristics for jet-reactor have been reported in literature.However,the research related to the effect of the ejector outlet structure on the hydrodynamic features and the mixing performance of the jet-reactor has been rarely reported so far.Experiment shows that the ejector outlet structure directly affects these parameters of the jet-reactor such as the distribution of gas and liquid,the residence time,the average diameter of the bubbles and droplets,and so on,but the specific impact and the degree of the influence are not yet fully understood.Particle image velocimetry(PIV)is a new velocity measuring technique,transient and full field measurement with no interference.It can not only show fluid flow field,the physical form of the flow,but also provide quantitative information on the instantaneous flow field.Digital image analysis(DIA)is a non-intrusive technique,which can identify and quantify the unmixed zones,measure the end point and the mixing time of intimate mixing in the liquid-liquid mixing apparatus.Moreover,DIA can easily recognize and accurately measure individual bubble,irregular-shaped bubbles in a wide range of bubble sizes,achieve the information of the bubbles in the whole gas-liquid system.For investigating the two-phase mixing performance with different ejectors in the jet reactor,five different ejectors with different outlet structures were designed and tested in a transparent jet reactor using particle image velocimetry(PIV).And a new image analysis technique was used to analyse the liquid mixing information of n-hexane-water system and the air-water system.The gradation curves of the liquid-liquid mixing system were obtained for different injectors and different cyclic flow rates.The Sauter bubble diameter and the interfacial area of the gas-liquid system were also quantitatively determined based on the above experiments.The study showed that the mixing time,the degree of the mixing,the fluid distribution and the position of the stagnation point are closely related to the structural parameters of the ejectors outlet for the n-hexane-water system.The mixing time for the four-side hole ejector is about 50%shorter than that of the two-side one.The double-row hole ejector can result in a bigger vorticity,being conducive to the mixing of the liquid system than that of single-row hole one.In addition,the experiment also demonstrated that the liquid flow rate has little effect on the mixing performance of the jet reactor when it is bigger than a certain value.In the gas-liquid system,the Sauter diameter of bubbles decreases with the increase of the liquid flow rate.The rectangular hole ejector can provide the minimum value of the Sauter diameter and the biggest interfacial area for the tested five ejectors.