Abstract
Flow resistance and bubble transport in a helical static mixer were studied experimentally and numerically. The inline mixer increases the volume fraction of gas in liquids by breaking bubbles into smaller sizes with a micrometer size in the flow experiments. The gas–liquid flow was simulated by a combination of computational fluid dynamics and Taylor expansion methods of moments. The friction factor of the helical static mixer is much smaller than that of the Kenics static mixers. The pressure drop increases with the Reynolds number, and the increment is larger when the Reynolds number is higher. The equidistant pressure drop increases with the argument of Reynolds number, and increases when the pitch decreases from upstream to downstream. The energy expenditure increases significantly when the variable-pitch coefficient is too small. The bubble geometric mean diameter decreases and the geometric standard deviation increases when the gas–liquid fluid flows through the mixer. The variable pitch structure enhances the bubble breakup effectively. The change of the bubble size decreases with the argument of the Reynolds number. The effect of the mixer has a limitation on breaking the bubbles.
Highlights
Mixing is one of the core unit operations performed to enhance heat and mass transfer or chemical reactions for multiphase or multicomponent dispersions in modern industrial processes.In recent decades, developments have been made on the design principles and methods of different kinds of mixing equipment for various process objectives, such as fine chemicals, agrochemicals, pharmaceuticals, cosmetics, food, drinking water and wastewater treatment [1]
The results showed that showed that the friction factors of flow decreased by 8% to 15.1%, while the heat transfer was the friction factors of flow decreased by 8% to 15.1%, while the heat transfer was enhanced by 34.1% to enhanced by 34.1% to 46.8%
Edgefold-twisted tape (ETT) was inserted in the tube and tested the tube and tested by Cui and Tian [13], the results showed that both of the Nusselt number and the by Cui and Tian [13], the results showed that both of the Nusselt number and the friction factor are friction factor are larger than those of the TTT [14]
Summary
Mixing is one of the core unit operations performed to enhance heat and mass transfer or chemical reactions for multiphase or multicomponent dispersions in modern industrial processes. Lei et al [11] numerically studied the fluid flow and heat transfer of pipe flow in a modified helical helical static mixer with perforated holes on the staggered twisted tapes (Figure 1b). The hydrodynamic air dispersing method refers to breaking up bubbles using a high-speed shear into microbubbles (d < 50 μm), which can be dispersed into liquid phase stably [18] This method has the advantage of low energy-consumption, high efficiency for mixing and mass transfer, and is environmentally friendly compared to other methods such as ultrasonic cavitation [19], chemical reaction or electrolysis [20,21]. The swirling flow induced by the helical mixer elements can cause phase separation and the gas can concentrate in the center of the tube This effect is unbeneficial to the gas–liquid contacting and mixing. Simulations of a 3D model were performed to analyze the flow characteristics and BSD and find out the effects of Reynolds number and variable-pitch coefficient
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