Studies On Mass Transfer In A Helical Tube Reactor And Its Application

Helical Tube Reactor(HTR)has the advantages of simple structure,no innternal component,ease of temperature control,high pressure resistance and so on.The secondary flow generating by the helical structure can strengthen the heat transfer,mass transfer,and mixing process.Currently,the basic researches of HTR are mainly focused on fluid flow,heat transfer,mixing,and reactor structure optimazation,whereas little attention was paid to the mass transfer.Since gas-liquid fluid flow has a significant influence on mass transfer,the gas-liquid flow pattern in the HTR is systematically studied under different operating,structural,and physical parameters firstly.According to the above results,the empirical correlations for flow pattern transition were proposed.Then,effect of flow pattern on the mass transfer was investigated.Further the influences of different parameters on the mass transfer were also studied.Finally,the HTR was applied to the preparation of nano-materials.The main research contents are as follows:1.The flow pattern of water-nitrogen system in the HTR is systematically studied via a visual method.In this work,the HTR is composed of two parts:a feeding component and a helical tube.Results show that there are four main flow patterns in the HTR:plug flow,bubble flow,slug flow,and annular flow.For the bubble flow,the phenomenon of bubble reunion deformation was occurred along the radial direction,leading to a bubble stability area.Then,effects of reactor placement way,reactor structure,liquid viscosity,and surface tension on the flow pattern distribution maps are investigated.In addition,the theoretical empirical correlation of flow pattern transformation were obtained,which is defined as follows:jG/jL=0.84×10-4 HeL-0.082 We1.52(bubble flow to plug flow)jG/jL=31×HeL-0.26 WeL0.06(annular flow to plug flow)2.In this section,the mass transfer of HTR was investigated by using a calcium hydroxide-carbon dioxide system.Effects of flow pattern transition on the mass transfer was investigated,and then the influence of reactor placement,reactor structure,solid content,and CO2 concentration on the carbonation curve and total liquid volume mass transfer coefficient were studied when the flow pattern was fixed.The best mass transfer condition was determined.Furthermore,the total liquid volume mass transfer coefficient of HTR can be improved by 5.2 times when compared with the traditional stirred tank reactor.3.The calcium carbonate-carbon dioxide system was applied to prepare nanometer calcium carbonate in the optimal mass transfer conditions,and the product size,crystal form,were analyzed.Compared with the traditional stirred tank reactor,the particle size distribution of nano-CaC03 produced by HTR is more uniform and the average particle size can improve up to44 nm.