| 1. |
- Kumar, Vimal, et al.
(författare)
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Multiphase fluid flow and heat transfer characteristics in microchannels
- 2017
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 169, s. 34-66
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Tidskriftsartikel (refereegranskat)abstract
- The boiling flow or condensation is widely encountered in many industrial applications for both cooling as well as heating processes. Compact heat transfer devices, such as micro-heat exchangers and evaporators, are extensively used for both cooling as well as heating processes over conventional heat exchangers, such as microelectronic circuits, automobile and aerospace industries, due to high surface area to volume ratio and heat transfer rates, compactness and easy thermal control. For better design of micro- or mini-heat exchangers, a detailed specific knowledge of the multiphase flow and its properties such as the flow pattern during flow boiling, critical heat flux (CHF) and stable operation are very important. This paper provides a state of art review on boiling flow in microchannels since year 2000 till date. Flow patterns formed and the parameters influencing flow pattern transitions, during multiphase heat transfer in micro- or mini-channels, have been reviewed in detail. The flow regimes and flow pattern maps, and modeling approaches considered for boiling flow in micro-channels/devices with various challenges have been discussed. A lot of contradiction between the experimental data has been observed for the analysis of flow regimes and flow pattern maps. Further, the effect of hydrodynamics during flow boiling and CHF on heat transfer coefficient has been discussed in detail. Recently, with the advancement in measurement techniques, the heat transfer measurement technologies have been synchronized with the visualization techniques, which helped in understanding the boiling flow physics in micro- and mini-channels. Therefore, an in-depth understanding of flow patterns and regimes under boiling flow conditions in mini- and micro-channels can be used to predict the boiling heat transfer mechanism, which can be further used for developing better heat transfer models for boiling flow. Further, enhancement in heat transfer coefficient for boiling flow in microchannels, either by using complex microchannel configurations or nanocoating on the microchannel surface, have received attention recently, which have been discussed and analyzed in the present review. Both micro- and mini-channels have number of applications in aerospace, refrigeration and computational systems; therefore further attention is needed for more robust and precise design.
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| 2. |
- Kushwaha, Naveen, et al.
(författare)
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Impact of mixed convective and radiative heat transfer in spiral-coiled tubes
- 2019
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Ingår i: Transactions - ASME : Journal of Heat Transfer. - : ASME International. - 0022-1481 .- 1528-8943. ; 141:8
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Tidskriftsartikel (refereegranskat)abstract
- Spiral-coiled tube heat exchangers (SCTHE) have higher heat transfer as compared to the conventional heat transfer devices and are extensively used to extract heat from exhaust gases in the chemical processing industries and also from sunlight for domestic applications. However, no attention has been made to predict heat transfer characteristics considering combined convective and radiative heat transfer in spiral-coiled tubes. In the present study, numerical analysis has been performed to predict fluid flow and heat transfer characteristics by combined forced convection and thermal radiation in spiralcoiled tubes. The P-1 radiation and the renormalized group (RNG) k–e turbulence models have been used to study the effect of thermal radiation and turbulent convection heat transfer in the spiral-coiled tube, respectively, over a wide range of Reynolds numbers (10,000–100,000) and curvature ratios (0.02–0.05). The emissivity and optical thickness have been varied from 0.0 to 1.0 and 0.0 to 8.0, respectively, to investigate the effect of thermal radiation on heat transfer characteristics in spiral-coiled tubes. For the considered Reynolds number range, it is found that the heat transfer is enhanced by approximately 10% when radiation is taken into account. It is found that the heat capacity increased with an increase in optical thickness and wall emissivity. Further, the effect of optical thickness on fully developed flow is observed weak and the average heat transfer coefficient is influenced by the wall emissivity over the entire flow.
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| 3. |
- Vikash, Vikash, 1987, et al.
(författare)
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Design and development of high shear mixers: Fundamentals, applications and recent progress
- 2021
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 232
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Tidskriftsartikel (refereegranskat)abstract
- Dispersion of liquids/particles is a key important requirement in a variety of applications including coatings and paints, cosmetics, healthcare, food, and pharmaceutical processes. In all these industrial processes high intensity of energy is required to overcome the adhesion forces or increasing interfacial surface area per unit volume, which is achieved by high-pressure homogenizers, ultrasonic-assisted devices, and high shear mixers (HSMs). In this paper, HSMs are critically reviewed based on their design and development, and applications (such as dispersion of nanoparticles, emulsification, and mixing) in recent years. HSMs are comprised of rotational (rotor) and stationary (stator) parts with a small gap in between. It is found that there is a significant influence of stator geometry on the uniform size distribution as well as energy dissipation. Though there is extensive work on hydrodynamics and mixing in HSMs are available however, still there is no specific scale-up/down criterion is available for HSMs.
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| 4. |
- Vikash, Vikash, 1987, et al.
(författare)
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Effect of stator geometries on flow fields and mixing performance for viscous fluids
- 2022
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Ingår i: Chemical Engineering and Processing: Process Intensification. - : Elsevier BV. - 0255-2701. ; 180
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Tidskriftsartikel (refereegranskat)abstract
- High shear mixers (HSMs) find wide applications in industrial processes where intense mixing and dispersion of fluids play a vital role. In this work, the flow fields and mixing performance is analyzed in different batch HSMs with varying stator heads, such as disintegrated, slotted, and mesh. Further, the effect of viscosity, flow behavior and rotor speed on hydrodynamics and mixing performance is assessed through numerical investigations. The turbulent flow fields and mixing enhancement are characterized using standard k-ε turbulence model with multiple reference frames approach for various HSMs. The turbulent statistics like turbulent kinetic energy are found to be maximum in the stator hole region and varied with flow behavior. The energy dissipation within the rotor vicinity is found higher for mesh head geometry followed by disintegrated and slotted heads. The effect of tracer injection locations is evaluated to gain comprehensive information on the mixing performance inside the mixing tank. Mixing time (t95) was evaluated and correlated with the existing results. For viscous fluids, complete mixing is hard to achieve due to the presence of cavern effect in smaller stator holes HSM. Moreover, the results provided guidance for further selection, design and development of HSMs for process industries.
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| 9. |
- Vikash, Vikash, 1987, et al.
(författare)
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Mixing characterization in batch rotor-stator mixer
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Mixing characterization of existing batch rotor-stator mixer (RSM) is studied at different rotor speeds (2000, 4000 and 6000 rpm) for two different geometries with different stator heads, such as circular and square. Flow parameters such as mass flow rate, Power number and energy dissipation rate have been investigated in both geometries.
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| 10. |
- Vikash, Vikash, 1987, et al.
(författare)
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Nanoparticle de-agglomeration in viscous fluids using different high shear mixer geometries
- 2022
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 248:Part A
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, the effect of batch high shear mixer (HSM) geometries is studied on nanoparticles deagglomeration and power draw in water and aqueous glycerol solutions. The kinetics and mechanism of cluster break-up are investigated for disintegrated (less number of larger stator holes), and mesh (higher number of smaller stator holes) heads at different rotor speeds. Mesh head geometry is found to be more efficient for fines generation than disintegrated head. A bi-modal particle size distribution and erosion as dominant break-up mechanism is found. The size of the smallest fines is found to be ≈30 nm for mesh head and ≈50 nm for the disintegrated head. Z-average ranges from 180 to 310 nm for given operating and process conditions. The power draw is more in mesh head and increased with an increase in viscosity. Further, power draw increased with an increase in viscosity of continuous media and rotor speed.
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