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CFD Modeling of Two-Phase Flows

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Dr. Anastasios Georgoulas

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Advanced Engineering Centre, School of Architecture Technology and Engineering, University of Brighton, Brighton BN2 4AT, UK
Interests: computational fluid dynamics (CFD) modeling of diabatic two-phase flows with phase change (pool boiling, flow boiling, cavitation); turbulent multiphase flows (water–sediment/turbidity currents, water–air/free-surface flows); heat and mass transfer; aerodynamics; HVAC
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Dear Colleagues,

The flow of two distinct, but interacting fluid phases (gas, liquid or solid) can be characterised as a two-phase flow. In such flows, the interface between the phases is directly influenced by their relative motion or by other potential mechanisms such as phase-change (e.g., boiling, condensation, cavitation). Fluid phase combinations include, solid-liquid (i.e., solid particles dispersed in a liquid flow), solid-gas (i.e., solid particles dispersed in a gas stream), liquid-gas (e.g., open-channel hydraulics, bubbly flows, sprays) and liquid-liquid (e.g., oil-water flows in pipes). Two-phase flows occur in a wide range of natural processes as well as industrial applications. Examples include, but are not limited to, sediment transport processes in rivers, impact of rain drops in the soil, irrigation systems, aeration tanks, drying processes for powder production, fuel injection, heat exchangers, refrigerators, nuclear reactors, medical sprays. The necessity for design optimisation, performance improvement as well as safety assessment of various industrial systems and products that utilise two-phase flows, create the need for detailed, quantitative information regarding such complex flows. This is possible to be achieved either utilising high resolution experimental measurements or by the application of two-phase numerical modelling techniques. In the last few decades, advancements in the development of robust numerical modelling techniques and methodologies as well as in the availability of computational resources, has rendered Computational Fluid Dynamics (CFD) a quite useful and robust tool for the prediction of two-phase flows.

The main goal of this Special Issue is to bring together users and developers of different CFD-based approaches and codes, in order to share their experience from the development, validation and/or application of two-phase flow CFD tools for the prediction of a variety of different types of two-phase flow, for fundamental as well as applied research purposes. Both interface capturing/tracking methods as well as Eulerian-Eulerian and Eulerian-Lagrangian approaches are welcome.

Dr. Anastasios Georgoulas
Guest Editor

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Keywords

Two-phase flow
Interface capturing/tracking techniques
Eulerian-Eulerian approach
Eulerian-Lagrangian approach

Published Papers (2 papers)

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Research

23 pages, 4819 KiB

Open AccessArticle

The Effect of Hydraulic Diameter on Flow Boiling within Single Rectangular Microchannels and Comparison of Heat Sink Configuration of a Single and Multiple Microchannels

by Konstantinos Vontas, Manolia Andredaki, Anastasios Georgoulas, Nicolas Miché and Marco Marengo

Energies 2021, 14(20), 6641; https://doi.org/10.3390/en14206641 - 14 Oct 2021

Cited by 6 | Viewed by 1689

Abstract

Phase change heat transfer within microchannels is considered one of the most promising cooling methods for the efficient cooling of high-performance electronic devices. However, there are still fundamental parameters, such as the effect of channel hydraulic diameter

D_{h}

whose effects on fluid [...] Read more.

D_{h}

whose effects on fluid flow and heat transfer characteristics are not clearly defined yet. The objective of the present work is to numerically investigate the first transient flow boiling characteristics from the bubble inception up to the first stages of the flow boiling regime development, in rectangular microchannels of varying hydraulic diameters, utilising an enhanced custom VOF-based solver. The solver accounts for conjugate heat transfer effects, implemented in OpenFOAM and validated in the literature through experimental results and analytical solutions. The numerical study was conducted through two different sets of simulations. In the first set, flow boiling characteristics in four single microchannels of

D_{h}

= 50, 100, 150, and 200

μ m

with constant channel aspect ratio of 0.5 and length of 2.4

mm

were examined. Due to the different

D_{h}

, the applied heat and mass flux values varied between 20 to 200

kW / m^{2}

and 150 to 2400

kg / m^{2} s

, respectively. The results of the two-phase simulations were compared with the corresponding initial single-phase stage of the simulations, and an increase of up to 37.4% on the global Nu number

N u_{g l o b}

was revealed. In the second set of simulations, the effectiveness of having microchannel evaporators of single versus multiple parallel microchannels was investigated by performing and comparing simulations of a single rectangular microchannel with

D_{h}

of 200

μ m

and four-parallel rectangular microchannels, each having a hydraulic diameter

D_{h}

of 50

μ m

. By comparing the local time-averaged thermal resistance along the channels, it is found that the parallel microchannels configuration resulted in a 23.3% decrease in the average thermal resistance

{\bar{R}}_{l}

compared to the corresponding single-phase simulation stage, while the flow boiling process reduced the

{\bar{R}}_{l}

by only 5.4% for the single microchannel case. As for the developed flow regimes, churn and slug flow dominated, whereas liquid film evaporation and, for some cases, contact line evaporation were the main contributing flow boiling mechanisms. Full article

(This article belongs to the Special Issue CFD Modeling of Two-Phase Flows)

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24 pages, 7258 KiB

Open AccessArticle

Numerical Study and Experimental Validation of Skim Milk Drying in a Process Intensified Counter Flow Spray Dryer

by Umair Jamil Ur Rahman and Artur K. Pozarlik

Energies 2021, 14(16), 4974; https://doi.org/10.3390/en14164974 - 13 Aug 2021

Cited by 4 | Viewed by 2028

Abstract

This research presents 3D steady-state simulations of a skim milk spray drying process in a counter-current configuration dryer. A two-phase flow involving gas and discrete phase is modeled using the Eulerian–Lagrangian model with two-way coupling between phases. The drying kinetics of skim milk is incorporated using the Reaction Engineering Approach. The model predictions are found to be in accordance with the experimental temperature measurements with a maximum average error of 5%. The validated computational model is employed further to study the effects of nozzle position, initial spray Sauter Mean Diameter (SMD), air inlet temperature, and feed rate on the temperature and moisture profiles, particle impact positions, drying histories, and product recovery at the outlet. The location of the nozzle upwards (≈23 cm) resulted in maximum product recovery and increased the mean particle residence time at the outlet. A similar trend was observed for the highest feed rate of 26 kg/h owing to the increased spray penetration upstream in the chamber. The maximum evaporation zone was detected close to the atomizer (0–10 cm) when the spray SMD is 38 µm, whereas it shifts upstream (40–50 cm) of the dryer for an SMD of 58 µm. The high air inlet temperature resulted in enhanced evaporation rates only in the initial 10–20 cm distance from the atomizer. The results obtained in this study are beneficial for the development of the novel vortex chamber-based reactors with a counter flow mechanism. Full article

(This article belongs to the Special Issue CFD Modeling of Two-Phase Flows)

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