Study On Bubble Characteristics Of Air-liquid In External Loop Airlift Reactor By Improved Dual-tip Electrical Conductivity Probe

External loop airlift reactor (EL-ALR) is a type of the modified bubble column reactor for air-liquid or air-liquid-solid system and has the advantages with simple structure low expense, easy to scale up and without moving part as both classical bubble column and stirred tank have. All the advantage make it popular used in chemical engineering, petrochemical engineering, biochemical processes and waste water treatment processes. Although much work has been done on study of hydrodynamics in EL-ALRs, most of the reseach were focused on the global parameters in EL-ALR. The detailed information on local hydrodynamics in EL-ALRs is still lackage, especially for bubble behaviors. Hydrodynamics in multiphase flow was considered as the most complicated in the chemical enginerring processes due to bubble deformation and many factors affect the bubble behavior, which include physical property of gas and liquid, operation conditions, reactors structure and scales. On the other hand, the measurement technology on bubble behavior is limited. It is necessary to develop more effective and reliable technics. The parameters of bubble in multiphase system are very important for the control of industrial processed and for design and scale-up of reactors especially the interfacial area which determined the mass transfer between the phases. 1. Therefore, further investigation on bubble behavior in external loop airlift reactor has great meanful in theory development and applications in the industrial processes.The aim of this work is to experimentally determination of the bubble behavior in the external loop airlift reactor. A measurement technics of dual-tip conductivity probe was modified. The problem of signal sensitivity and stability of probe has been improved with a new structure of the measurement system. Several bubble parameters such as gas holdup, bubble size and bubble size distribution, bubble rise velocity and their profile in radial and axial was experimentally investigated with the improved dual-tip conductivity probe in an external loop airlift reactor. The effect of liquid properties such as liquid viscosity, surface tension and electrolytes on the bubble behavior was studied. The new results obtained in this work are summarized as follows:1. The measurement technics on bubble behavior in multiphase flow system with dual-tip conductivity probe was improved. The single quality and stability of the measurement system has been improved so that the better results was obtained and can be used for the bubble parameter measurement for for air-liquid and high solid concentration system. The reliability and stability of improved dual-tip conductivity probe were confirmed by investigating the signal quality and comparing the test results between original and improved probes. It is a useful contributions in gas behavior mensurement in multi-phase flow system. 2. The radial and axial profile of bubble parameters such as gas holdup, bubble size and size distributions, bubble rise velocity at different superficial gas velocity were investigated in external loop airlift reactor with the improved dual-tip conductivity probe . The Core-peaking and Wall-peaking of gas holdup were observed in distributor area and developed flow area respectively. The experimental results give detailed information on the bubble behavior which provide a basic data for the design and scale-up of reactor.3. The effect of liquid viscosity, surface tension, electrolytes on bubble behaviors went further invastigated. The results shows:a. When surface tension is decreased, the gas holdup increases, but bubble size and bubble velocity decreases at lower superfical gas velocity. The probability number density distribution of bubble size is narrow. The effect of surface tension on the bubble parameter was not evident as the superficial gas velocity is high.b. Gas holdup was firstly increased and then decreased with the liquid viscosity was increased. The variation of viscosity in the small value range has little effect on bubble size but reduces the bubble rise velocity when liquid viscosity is decreased. When the liquid viscosity is large value range, the bubble size was decreased and bubble rising velocity was increaded with the viscosity increased.c. The model to correlating gas holdup with surface tension and superficail gas velocity was developed based on the experimental data. The relative error is less than 10%.