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162. Two-phase flow structures in a helically coiled microchannel: An experimental investigation.

Author

Saisorn, Sira, Benjawun, Phakkhanan, Suriyawong, Adirek, Asirvatham, Lazarus Godson, Mondal, Pranab Kumar, and Wongwises, Somchai

Subjects
TWO-phase flow, MICROCHANNEL flow, ANNULAR flow, PRESSURE drop (Fluid dynamics), POROSITY, CENTRIFUGAL force, CHANNEL flow
Abstract

At the microfluidic scale, the utilization of helically coiled channels (HCCs), also known as a spiral channel, for two-phase flow offers numerous advantages in various applications. Existing articles mainly focus on the macro-scale transport, examining secondary flows induced in curved channels. The increasing demand, however, for innovative miniature equipment for thermal energy management emphasizes the importance of comprehending gas–liquid micro-scale flow in curved channels. Unfortunately, despite a vast body of literature on this paradigm, there is still a lack of systematic investigations into the underlying facets of two-phase micro-scale transport in HCCs. To address this gap, our study conducted experiments on adiabatic two-phase air–water flow inside an up-flow helical micro-scale tube. The tube had a hydraulic diameter of 0.87 mm, a coil diameter of 50 mm, and a helical pitch of 20 mm. The primary aim was to explore the impact of centrifugal force on flow pattern, void fraction, and frictional pressure drop characteristics. Additionally, we carefully examined the phase separation phenomenon influenced by the secondary flows induced by the curved channel. In particular, we compared the gas-core flow pattern (either throat-annular flow or annular flow), void fraction, and frictional pressure drop obtained from our experiments on the helical tube with corresponding results based on straight micro-scale channel configurations for an Eötvös number of approximately 0.01. In summary, this study delves deep into the crucial aspects of two-phase micro-scale transport in HCCs, contributing to a better understanding of these systems for future advancements in micro-channel applications. [ABSTRACT FROM AUTHOR]

Published
2023
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163. Reaction characteristics of non-Newtonian species in a microreactor: The role of electroosmotic vortices.

Author

Mehta, Sumit Kumar, Kakati, Rahul, Rahman, Ayaz, Mondal, Pranab Kumar, and Wongwises, Somchai

Subjects
ELECTRO-osmosis, TRANSPORT equation, SPECIES, CHEMICAL reactions, MICROBUBBLES, ELECTRORHEOLOGY, BIOCHEMICAL substrates
Abstract

With a focus on biochemical applications and utilizing relevant physical properties, the current study numerically analyzes the impact of electroosmotic vortex and fluid rheology on the chemical reaction characteristics of species. This is achieved by installing integrated positively charged patches on the extended region of the microreactor with three inlets for injecting the reactants and generating the electroosmotic vortex. In order to produce species "C" in the extended region of the microreactor, it is presumed that reactant species "A" is injected through the upper and lower inlets and reactant species "B" is injected via the intermediate inlet. To solve the associated transport equations with appropriate boundary conditions, a thorough theoretical framework is developed. The results show that the ability of the reactant species to react is boosted when vortices form in the microreactor, increasing the convective mixing strength for reactant species. Furthermore, the fluid rheology significantly affects the reaction characteristics, which is a noteworthy finding. For fluids exhibiting a higher shear-thinning nature, the average concentration of the produced species follows an increasing–decreasing trend with the Carreau number. Additionally, it becomes apparent that the influence of the Damkohler number on the average generated species concentration is negligible at lower Carreau numbers, but it increases with the Damkohler number at higher Carreau numbers. The study also reveals that both rheological and chemical parameters have a substantial impact on the flow rate of product species. Overall, the findings of this investigation provide valuable insights for the development of technologically advanced electroosmotic microreactor capable of effectively generating the intended product species. [ABSTRACT FROM AUTHOR]

Published
2023
Full Text
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