A jet mixing study in two phase gas–liquid systems (original) (raw)
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Experimental Study of the Mixing Time in a Jet-Mixed Gas-Liquid System
Chemical Engineering & Technology, 2010
In the present work, the impeller in the conventional gas-liquid mixed vessels was replaced by a fluid jet as the mixer. Using an experimental setup, the effect of several parameters on the mixing time as a measure of the liquid-phase mixing intensity, which is one of the required transport characteristics for designing gasliquid mixed systems, was studied. The results show that gas injection decreases the mixing time in comparison with the ungassed condition, but the mixing time is not necessarily decreased by increasing the gassing rate. On the basis of the amount of the jet Reynolds number and gassing rate, and thus the created circulation pattern, the mixing time may be decreased or increased. Also, the location of the probe for cases in which there are more dead zones in the vessel have a considerable effect on the measured mixing time. With increasing uniformity of the velocity domain, the influence of the probe location was reduced. Also, by increasing the jet flow rate and decreasing the nozzle diameter, the length of the jet, the amount of entrained bulk fluid, and the intensity of recirculation flow increased, and thus the mixing time decreased.
Experimental and CFD Studies on the Effect of the Jet Position on Mixing Performance
2009
The effect of jet positions on the homogenization progress of a dye in a rectangular tank equipped with a jet was studied. Water entered the tank laterally from the top and left the tank from the opposite wall at the same height. The suction position was fixed at one of the tank corners and seven positions were considered for the jet nozzle. A predefined volume of the dark Nigrosine was injected to the tank input as the tracer during 4s in all experiments. During the dye injection and mixing progress, the front and bottom views of the tank were recorded by a digital camera. The experimental results showed that as the jet nozzle was installed in the opposite wall from the tank input, the worst performance was obtained in comparison with the other jet positions. However, the jet nozzle position of 90° with respect to the tank input had the best performance. All of the experiments were modeled by Computational Fluid Dynamics (CFD). Finally, the CFD predicted dye spreading was verified ...
Studies on Mixing Time of Non-Newtonian Fluids in Jet Mixer
Mixing is one of the common unit operation employed in chemical industries. Conventional mixers are equipped with impellers but are expensive for mixing in large storage tanks and underground tanks. Jet mixers have become an alternative to impellers for over 50 years in the process industry. For the design of jet mixers, the detailed hydrodynamics of the mixing process is not properly understood. In the present paper, hydrodynamic techniques are used to simulate jet mixing in a cylindrical tank. The flow circulation patterns with in the tank and their effect on mixing of a soluble salt are studied. An experiment was carried out to study the effects of various parameters such as nozzle diameter, jet position and jet velocity on mixing time. Results show that, for a given geometric arrangement, jet dia is significantly more important in determining mixing time of jet mixer for non Newtonian fluids. The optimum jet was found to be the jet dia of 15 mm for jet located at various positions at the top of the tank which gave the shortest mixing time for non Newtonian fluids. An increase in the nozzle diameter was found to reduce the mixing time at a given level of power consumption and in turn in the energy efficiency can be improved. The results obtained shows a good understanding of hydrodynamic aspects of mixing process in jet mixed tanks
Experimental Investigation of the Use of Synthetic Jets for Mixing in Vessels
Journal of Fluids Engineering, 2011
Mixing is an important process in various industries. Different designs have been suggested in order to reduce the local shear rates in mechanically stirred mixing vessels, also known as continuously stirred tank reactors, in order to account for the mixing requirements for sensitive materials such as biological materials and biofluids where the high shear rate may damage the sensitive materials. This paper reports on the development of a continuously stirred tank reactor that can be used to achieve a variety of mixing assignments. This mixing is achieved using synthetic jets. The mixing performance was assessed using flow visualization techniques. The effects of fluid viscosity on mixing time were investigated. The results are very encouraging and are suggestive that the use of synthetic jets in mixing is a viable alternative to the conventional methods of mixing in vessels.
Increasing gas-liquid contacting using a confined plunging liquid jet
Journal of Chemical Technology & Biotechnology, 2003
The plunging liquid jet bubble column is an effective device for gas-liquid contacting. Small bubbles are formed in a high-shear region surrounding the plunging jet, leading to high interfacial area per unit volume of gas. At the same time, the counter-current flow downstream of the jet leads to regions of high gas holdup, producing high interfacial area per unit volume of reactor. This paper presents a study of the void fraction in the pipe-flow zone of the downcomer in a plunging jet reactor. It was found that the Ergun equation, using the standard constants derived from data for pressure drop in packed beds of solids, successfully predicted the gas void fraction for both bubbly and churnturbulent flow conditions provided the increase in bubble size, with increasing gas input, was taken into consideration. Drift-flux analysis was also applied to the pipe-flow zone, and highlighted the transition from bubbly to churn-turbulent flow and a maximum gas void fraction operating condition of approximately 0.55. From the analysis the distribution coeffient for the downflowing system was found to be in the range 0.99-1.04, which was consistent with the measured radial void fraction profile and developed pipe flow for the two-phase mixture. Figure 7. Gas void fraction and total volumetric flux radial profiles. *, gas void fraction ----, eqn (11) for a = 26 --, eqn (12) for X = 0.26 and Y = 27.
Scientific Research and Essays
In the present work, the effect of nozzle angle (22.5º, 45º and 67.5º) on mixing time for jet mixing tanks with the various ratios of liquid height (H) to tank diameter (D), including 0.5, 1, and 1.5, are studied by using computational fluid dynamics (CFD). The results revealed that CFD model with standard k-epsilon is successfully employed to predict the concentration profiles and mixing time by using the fine mesh and second order upwind scheme. The simulated results showed that the different jet nozzle angles result in different flow patterns. The results also indicate that the mixing time is mainly a function of the jet potential core length. Moreover, the jet path length or jet centerline velocity (jet kinetic energy) is considered as the secondary effect on mixing time, which depends on the tank geometry.
Study of Jet Mixing in Flocculation Process
International Journal of Innovative Research in Engineering & Multidisciplinary Physical Sciences, 2018
Jet- mixing is widely used in various processing units for purposes as homogenization of physical properties of liquids in tanks, to ensure proper heat and mass transfer in various operations, prevention of stratification, and prevention of deposition of suspended particles. As Flocculation process is an important part of surface water treatment, use of jet in flocculation is an effective solution so as to remove turbidity in an efficient way. Most of the researchers have focused on experimental estimation and developed various mixing correlations, considering the effect of parameters like jet velocity, jet configuration, tank geometry. Recently, use of CFD simulation to predict parameters as well as flow patterns precisely that validates the experiments is on the rise. This review focuses on the study of various parameters used in experimental and CFD work on jet mixing and general conclusions have been drawn concerning the various parameters.
Influence of Issued Jet Conditions on Mixing of Confined Flows
The development of the velocity and scalar fields in a coaxial jet mixer has been experimentally investigated applying simultaneously Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) methods. Mixing of a turbulent jet (water solution of Rhodamin 6G) issued from a long round nozzle (l/d = 60) with co-flow (water) was studied. Because of the nozzle length the boundary layers of the inner flow already merged upstream of the jet exit. The issued jet conditions were changed installing vortex generators (tabs) at the nozzle exit. The tabs of rectangular and triangular forms with heights of 13 15 % the inner nozzle diameter accelerated mixing significantly but the scalar field developed to the homogeneous state faster than the velocity one. Turbulent characteristics measured downstream of the jet exit gave evidence the mixing specific behind the rectangular and triangular tabs.
Experimental and CFD investigation on mixing by a jet in a semi-industrial stirred tank
Chemical Engineering Journal, 2005
This paper reports the results of a study on the flow generated and mixing time in a semi-industrial tank equipped with a side entry jet mixer. For this purpose, a three dimensional modeling is carried out using an in-house Computational Fluid Dynamics (CFD) code. In this study, the theoretical mixing curves predicted by the CFD were validated by experiments. The