Recent Advances in Single and Multiphase Flows in Microchannels

A special issue of Fluids (ISSN 2311-5521).

Deadline for manuscript submissions: closed (31 October 2020) | Viewed by 39787

Special Issue Editors


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Guest Editor
Department of Industrial Engineering, University of Bologna, viale Risorgimento, 2, 40136 Bologna, Italy
Interests: numerical methods; heat transfer; turbulent flows; two-phase flow; microchannels; micro-junctions
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Guest Editor
Department of Mechanical, Materials and Manufacturing Engineering, University of Nottingham, Nottingham NG7 2RD, UK
Interests: capillary flow; phase-change; heat transfer; numerical simulation; two-phase flow; lubrication theory

Special Issue Information

Dear Colleagues,

Heat and mass transport in microchannels is key to diverse applications that span many disciplines in science and engineering, from mechanical, chemical, energy, and environmental engineering, to biological and medical science.

Notable examples range from thermal management of power electronics, to mobilisation of pollutants in unsaturated soil, capillary-cleaning of fouling and biofilms, microencapsulation for drug delivery, medical treatment of diseased tissues, deformability of cells in biofluids, and (bio)chemical microreactor technology, to name a few.

Within microchannels, unlike large-scale flows, phenomena such as viscous heating, surface tension, interfacial resistance to heat and mass transfer, van der Waals interactions, diffusiophoresis, and diffusioosmosis can have dominant effects on the transport mechanisms.

Although recent advances in microfabrication techniques such as micromilling, embossing technology, additive manufacturing, and photolithography have allowed substantial reduction to microchannel size and manufacturing cost, the understanding of the underlying flow physics is still plagued with significant uncertainty.

Therefore, the new insight into the governing flow/heat transfer mechanisms in the microscale, required for the optimal development, design, and operation of the next-generation microfluidic devices, is the driving motivation of this Special Issue.

This Special Issue welcomes contributions that focus on recent developments in single and multiphase flows in microchannels, including (but not restricted to) gas–liquid, liquid–liquid, particle-laden and colloidal-suspension flows, the impact of channel geometry on fluid dynamics and heat transfer, fundamental aspects of thin-film dynamics and evaporation, flow boiling heat transfer and critical heat flux, flow boiling instabilities in multimicrochannel evaporators, the enhancement of single-phase cooling, microstructured surfaces, thermally- and surfactant-driven Marangoni flows, electrokinetics, diffusiophoresis, diffusioosmosis, and theoretical approaches such as lubrication theory and asymptotics.

We invite contributions in all areas of experimental and computational methods, multiscale models, and theoretical approaches that focus on the aforementioned mechanisms dominated by the microscale.

Dr. Beatrice Pulvirenti
Dr. Mirco Magnini
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Fluids is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • microfluidics
  • single-phase flow
  • multiphase flow
  • flow boiling
  • thin-films
  • computational fluid mechanics
  • multiscale modelling

Published Papers (14 papers)

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Research

15 pages, 1445 KiB  
Article
Numerical Study of Bloodstream Diffusion of the New Generation of Drug-Eluting Stents in Coronary Arteries
by Leandro Marques and Gustavo R. Anjos
Fluids 2021, 6(2), 71; https://doi.org/10.3390/fluids6020071 - 5 Feb 2021
Cited by 1 | Viewed by 2622
Abstract
The present work aims at developing a numerical study on the drug diffusion in the bloodstream in a coronary artery with drug-eluting stent implanted. The blood was modeled as a single-phase, incompressible and Newtonian fluid and the Navier–Stokes equation was approximated according to [...] Read more.
The present work aims at developing a numerical study on the drug diffusion in the bloodstream in a coronary artery with drug-eluting stent implanted. The blood was modeled as a single-phase, incompressible and Newtonian fluid and the Navier–Stokes equation was approximated according to the Finite Element Method (FEM). The dynamics of drug-eluting concentration in bloodstream was investigated using four drug-eluting stents with different mass diffusivities in microchannels with variable cross sections, including a real coronary artery geometry with atherosclerosis. The results reveal complex drug concentration patterns and accumulation in the vicinity of the fat buildup. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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20 pages, 4720 KiB  
Article
Efficiency Improvement of Miniaturized Heat Exchangers
by Iris Gerken, Thomas Wetzel and Jürgen J. Brandner
Fluids 2021, 6(1), 25; https://doi.org/10.3390/fluids6010025 - 6 Jan 2021
Cited by 3 | Viewed by 2685
Abstract
Micro heat exchangers have been revealed to be efficient devices for improved heat transfer due to short heat transfer distances and increased surface-to-volume ratios. Further augmentation of the heat transfer behaviour within microstructured devices can be achieved with heat transfer enhancement techniques, and [...] Read more.
Micro heat exchangers have been revealed to be efficient devices for improved heat transfer due to short heat transfer distances and increased surface-to-volume ratios. Further augmentation of the heat transfer behaviour within microstructured devices can be achieved with heat transfer enhancement techniques, and more precisely for this study, with passive enhancement techniques. Pin fin geometries influence the flow path and, therefore, were chosen as the option for further improvement of the heat transfer performance. The augmentation of heat transfer with micro heat exchangers was performed with the consideration of an improved heat transfer behaviour, and with additional pressure losses due to the change of flow path (pin fin geometries). To capture the impact of the heat transfer, as well as the impact of additional pressure losses, an assessment method should be considered. The overall exergy loss method can be applied to micro heat exchangers, and serves as a simple assessment for characterization. Experimental investigations with micro heat exchanger structures were performed to evaluate the assessment method and its importance. The heat transfer enhancement was experimentally investigated with microstructured pin fin geometries to understand the impact on pressure loss behaviour with air. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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21 pages, 3488 KiB  
Article
Numerical Investigation of Thermally Developing and Fully Developed Electro-Osmotic Flow in Channels with Rounded Corners
by Nicola Suzzi and Marco Lorenzini
Fluids 2021, 6(1), 22; https://doi.org/10.3390/fluids6010022 - 4 Jan 2021
Cited by 3 | Viewed by 2436
Abstract
Electro-osmotic flow, that is, the motion of a polar fluid in microducts induced by an external electric field, is one micro-effect which allows fluid circulation without the use of mechanical pumping. This is of interest in the thermal management of electronic devices, as [...] Read more.
Electro-osmotic flow, that is, the motion of a polar fluid in microducts induced by an external electric field, is one micro-effect which allows fluid circulation without the use of mechanical pumping. This is of interest in the thermal management of electronic devices, as microchannels with cross sections of almost arbitrary shape can easily be integrated on the chips. It is therefore important to assess how the geometry of the channel influences the heat transfer performance. In this paper, the thermal entry region and the fully developed electro-osmotic flow in a microchannel of rectangular cross section with smoothed corners is investigated for uniform wall temperature. For the fully developed region, correlations for the Poiseuille and Nusselt numbers considering the aspect ratio and nondimensional smoothing radius are given, which can be used for practical design purposes. For thermally developing flow, it is highlighted how smoothing the corners increases the value of the local Nusselt number, with increases up to 18% over sharp corners, but that it also shortens the thermal entry length. It is also found that Joule heating in the fluid may cause a reversal of the heat flux, and that the thermal entry length has a linear dependence on the Reynolds number and the hydraulic diameter and on the logarithm of the nondimensional Joule heating. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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16 pages, 3118 KiB  
Article
Numerical Investigation of Two-Phase Flows in Corrugated Channel with Single and Multiples Drops
by Gustavo R. Anjos
Fluids 2021, 6(1), 13; https://doi.org/10.3390/fluids6010013 - 31 Dec 2020
Cited by 2 | Viewed by 1912
Abstract
This work aims at investigating numerically the effects of channel corrugation in two-phase flows with single and multiples drops subject to buoyancy-driven motion. A state-of-the-art model is employed to accurately compute the dynamics of the drop’s interface deformation using a modern moving frame/moving [...] Read more.
This work aims at investigating numerically the effects of channel corrugation in two-phase flows with single and multiples drops subject to buoyancy-driven motion. A state-of-the-art model is employed to accurately compute the dynamics of the drop’s interface deformation using a modern moving frame/moving mesh technique within the arbitrary Lagrangian–Eulerian framework, which allows one to simulate very large domains. The results reveal a complex and interesting dynamics when more than one drop is present in the system, leading eventually in coalescence due to the amplitude of the corrugated sinusoidal channel and distance between drops. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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15 pages, 7810 KiB  
Article
Effect of Functional Surfaces with Gradient Mixed Wettability on Flow Boiling in a High Aspect Ratio Microchannel
by Vahid Ebrahimpour Ahmadi, Akam Aboubakri, Abdolali Khalili Sadaghiani, Khellil Sefiane and Ali Koşar
Fluids 2020, 5(4), 239; https://doi.org/10.3390/fluids5040239 - 10 Dec 2020
Cited by 20 | Viewed by 3331
Abstract
Flow boiling is one of the most effective phase-change heat transfer mechanisms and is strongly dependent on surface properties. The surface wettability is a crucial parameter, which has a considerable effect on the heat transfer performance, particularly in flow boiling. The contact angle [...] Read more.
Flow boiling is one of the most effective phase-change heat transfer mechanisms and is strongly dependent on surface properties. The surface wettability is a crucial parameter, which has a considerable effect on the heat transfer performance, particularly in flow boiling. The contact angle determines the number of nucleation sites as well as bubble dynamics and flow patterns. This study introduces three new generation mixed wettability surfaces and compares them with a wholly hydrophobic surface reference sample, in flow boiling in a high aspect ratio microchannel. The mixed wettability substrates have five regions as fully Al2O3, (hydrophobic zone) region, three different patterned configurations with various A* values, and fully SiO2 (hydrophilic zone) region, where A* is defined as A Al2O3/A total (hydrophobicity ratio). Boiling heat transfer results were obtained for each surface at various wall heat fluxes and three different mass fluxes. According to the obtained results, significant enhancements in heat transfer (by up to 56.7%) could be obtained with biphilic surfaces compared to the reference sample (hydrophobic surface). Performed flow visualization proves that the tested biphilic surfaces enhance heat transfer by reducing the bubbly flow regime and extending the slug regime. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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20 pages, 2575 KiB  
Article
A Qualitative Numerical Study on Catalytic Hydrogenation of Nitrobenzene in Gas-Liquid Taylor Flow with Detailed Reaction Mechanism
by Mino Woo, Lubow Maier, Steffen Tischer, Olaf Deutschmann and Martin Wörner
Fluids 2020, 5(4), 234; https://doi.org/10.3390/fluids5040234 - 8 Dec 2020
Cited by 3 | Viewed by 2652
Abstract
While the number of computational studies considering two-phase flows in microfluidic systems with or without mass transfer is increasing, numerical studies incorporating chemical reactions are still rare. This study aims to simulate the catalytic hydrogenation of nitrobenzene in gas-liquid Taylor flow by combining [...] Read more.
While the number of computational studies considering two-phase flows in microfluidic systems with or without mass transfer is increasing, numerical studies incorporating chemical reactions are still rare. This study aims to simulate the catalytic hydrogenation of nitrobenzene in gas-liquid Taylor flow by combining interface-resolving numerical simulations of two-phase flow and mass transfer by a volume-of-fluid method with detailed modeling of the heterogeneous chemical reaction by software package DETCHEMTM. Practically relevant physical properties are utilized for hydrodynamic and mass transfer simulations in combination with a preliminary reaction mechanism based on density functional theory. Simulations of mass transfer are conducted using a predetermined velocity field and Taylor bubble shape. At the beginning of the simulation when liquid nitrobenzene is not saturated by hydrogen, axial profiles of surface species concentrations and reaction rates show local variations. As hydrogen dissolves in nitrobenzene, the concentration profiles of surface species at the wall become uniform, eventually reaching an equilibrium state. Neglecting the local variation in a short initial period will allow further simplification of modeling surface reactions within a Taylor flow. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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14 pages, 3092 KiB  
Article
Validations of the Microchannel Flow Model for Characterizing Vascularized Tissues
by Sedigheh S. Poul, Juvenal Ormachea, Stefanie J. Hollenbach and Kevin J. Parker
Fluids 2020, 5(4), 228; https://doi.org/10.3390/fluids5040228 - 30 Nov 2020
Cited by 5 | Viewed by 2558
Abstract
The microchannel flow model postulates that stress-strain behavior in soft tissues is influenced by the time constants of fluid-filled vessels related to Poiseuille’s law. A consequence of this framework is that changes in fluid viscosity and changes in vessel diameter (through vasoconstriction) have [...] Read more.
The microchannel flow model postulates that stress-strain behavior in soft tissues is influenced by the time constants of fluid-filled vessels related to Poiseuille’s law. A consequence of this framework is that changes in fluid viscosity and changes in vessel diameter (through vasoconstriction) have a measurable effect on tissue stiffness. These influences are examined through the theory of the microchannel flow model. Then, the effects of viscosity and vasoconstriction are demonstrated in gelatin phantoms and in perfused tissues, respectively. We find good agreement between theory and experiments using both a simple model made from gelatin and from living, perfused, placental tissue in vitro. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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15 pages, 6097 KiB  
Article
Gas-Liquid Flow and Interphase Mass Transfer in LL Microreactors
by Brendon J. Doyle, Frederic Morin, Jan B. Haelssig, Dominique M. Roberge and Arturo Macchi
Fluids 2020, 5(4), 223; https://doi.org/10.3390/fluids5040223 - 28 Nov 2020
Cited by 3 | Viewed by 2939
Abstract
This work investigates the impact of fluid (CO2(g), water) flow rates, channel geometry, and the presence of a surfactant (ethanol) on the resulting gas–liquid flow regime (bubble, slug, annular), pressure drop, and interphase mass transfer coefficient (kla) [...] Read more.
This work investigates the impact of fluid (CO2(g), water) flow rates, channel geometry, and the presence of a surfactant (ethanol) on the resulting gas–liquid flow regime (bubble, slug, annular), pressure drop, and interphase mass transfer coefficient (kla) in the FlowPlateTM LL (liquid-liquid) microreactor, which was originally designed for immiscible liquid systems. The flow regime map generated by the complex mixer geometry is compared to that obtained in straight channels of a similar characteristic length, while the pressure drop is fitted to the separated flows model of Lockhart–Martinelli, and the kla in the bubble flow regime is fitted to a power dissipation model based on isotropic turbulent bubble breakup. The LL-Rhombus configuration yielded higher kla values for an equivalent pressure drop when compared to the LL-Triangle geometry. The Lockhart–Martinelli model provided good pressure drop predictions for the entire range of experimental data (AARE < 8.1%), but the fitting parameters are dependent on the mixing unit geometry and fluid phase properties. The correlation of kla with the energy dissipation rate provided a good fit for the experimental data in the bubble flow regime (AARE < 13.9%). The presented experimental data and correlations further characterize LL microreactors, which are part of a toolbox for fine chemical synthesis involving immiscible fluids for applications involving reactive gas–liquid flows. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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26 pages, 3351 KiB  
Article
Overview of Void Fraction Measurement Techniques, Databases and Correlations for Two-Phase Flow in Small Diameter Channels
by Álvaro Roberto Gardenghi, Erivelto dos Santos Filho, Daniel Gregório Chagas, Guilherme Scagnolatto, Rodrigo Monteiro Oliveira and Cristiano Bigonha Tibiriçá
Fluids 2020, 5(4), 216; https://doi.org/10.3390/fluids5040216 - 20 Nov 2020
Cited by 14 | Viewed by 6016
Abstract
Void fraction is one of the most important parameters for the modeling and characterization of two-phase flows. This manuscript presents an overview of void fraction measurement techniques, experimental databases and correlations, in the context of microchannel two-phase flow applications. Void fraction measurement techniques [...] Read more.
Void fraction is one of the most important parameters for the modeling and characterization of two-phase flows. This manuscript presents an overview of void fraction measurement techniques, experimental databases and correlations, in the context of microchannel two-phase flow applications. Void fraction measurement techniques were reviewed and the most suitable techniques for microscale measurements were identified along its main characteristics. An updated void fraction experimental database for small channel diameter was obtained including micro and macrochannel two-phase flow data points. These data have channel diameter ranging from 0.5 to 13.84 mm, horizontal and vertical directions, and fluids such as air-water, R410a, R404a, R134a, R290, R12 and R22 for both diabatic and adiabatic conditions. New published void fraction correlations as well high cited ones were evaluated and compared to this small-diameter void fraction database in order to quantify the prediction error of them. Moreover, a new drift flux correlation for microchannels was also developed, showing that further improvement of available correlations is still possible. The new correlation was able to predict the microchannel database with mean absolute relative error of 9.8%, for 6% of relative improvement compared to the second-best ranked correlation for small diameter channels. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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19 pages, 5512 KiB  
Article
Modelling Microlayer Formation in Boiling Sodium
by Giovanni Giustini, Hyungdae Kim, Raad I. Issa and Michael J. Bluck
Fluids 2020, 5(4), 213; https://doi.org/10.3390/fluids5040213 - 19 Nov 2020
Cited by 5 | Viewed by 2456
Abstract
During boiling at a solid surface, it is often the case that a liquid layer of a few microns of thickness (’microlayer’) is formed beneath a bubble growing on the heated surface. Microlayers have been observed forming beneath bubbles in various transparent fluids, [...] Read more.
During boiling at a solid surface, it is often the case that a liquid layer of a few microns of thickness (’microlayer’) is formed beneath a bubble growing on the heated surface. Microlayers have been observed forming beneath bubbles in various transparent fluids, such as water and refrigerants, subsequently depleting due to evaporation, thus contributing significantly to bubble growth and possibly generating the majority of vapor in a bubble. On the other hand, boiling of opaque fluids, such as liquid metals, is not amenable to optical observations, and microlayers have not yet been observed in liquid metals. Among that class of fluids is sodium, suitable as a coolant for nuclear reactors and as the working fluid in phase-change solar power receivers. In order to support these applications, it is necessary to understand the boiling behavior of sodium and identify the parameters that might influence microlayer formation during boiling of this important fluid. This paper presents simulations of the hydrodynamics of sodium vapor bubble growth at a surface. An interface capturing flow solver has been implemented in the OpenFOAM code and used to predict the behavior of a sodium vapor bubble near a solid surface in typical boiling conditions. The methodology has been validated using recently reported direct experimental observations of microlayer formation in water and then applied to sodium boiling cases. Simulations indicate that microlayers are formed in sodium in a similar fashion to water. Comparison of simulation results with an extant algebraic model of microlayer formation showed good agreement, which increases confidence in the current predictions of microlayer formation. Typical values of microlayer thickness thus computed indicate that the microlayer is likely to play an important role during bubble growth in sodium. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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18 pages, 3913 KiB  
Article
Analysis of Hydraulic Mixing Efficiency in Widespread Models of Micromixers
by Andrey V. Minakov, Alexander S. Lobasov, Anna A. Shebeleva and Alexander V. Shebelev
Fluids 2020, 5(4), 211; https://doi.org/10.3390/fluids5040211 - 18 Nov 2020
Cited by 3 | Viewed by 1827
Abstract
In this paper, we present the results of a systematic numerical study of the flow and mixing modes of fluids in micromixers of various configurations, in particular, an analysis of passive micromixers, the most widely used in practice, as well as the main [...] Read more.
In this paper, we present the results of a systematic numerical study of the flow and mixing modes of fluids in micromixers of various configurations, in particular, an analysis of passive micromixers, the most widely used in practice, as well as the main methods to intensify mixing. The advantages of microstructure reactors can significantly reduce reaction times and increase productivity compared to traditional bulk reactors. Four different geometries of micromixers, including the straight T-shaped microchannel, were considered. The effect of the geometrical patterns of micromixers, as well as of the Reynolds number on flow regimes and mixing efficiency were analyzed. The Reynolds number varied from 1 to 300. Unlike other studies, the efficiency of the considered mixers was for the first time compared with the cost of pressure loss during pumping. As a result, the efficiency of the most optimal micromixer in terms of hydraulic mixing and the optimal operation ranges were determined. It was shown that the maximum normalized mixing efficiency in the entire range of Re numbers was noted for mixer, in which a vortex-based intensification of mixing occurs due to the flow swirling in cylindrical chambers. This mixer allows mixing the fluids 600 times more efficiently than a straight T-mixer, while all other conditions being equal. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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23 pages, 7074 KiB  
Article
Influence of Hydrodynamic Conditions on Micromixing in Microreactors with Free Impinging Jets
by Rufat Sh Abiev and Alexey A Sirotkin
Fluids 2020, 5(4), 179; https://doi.org/10.3390/fluids5040179 - 13 Oct 2020
Cited by 20 | Viewed by 2346
Abstract
An experimental study and mathematical modeling of micromixing in a microreactor with free impinging jets (MRFIJ) with a diameter of 1 mm was carried out. In the experimental part, the iodide-iodate technique was used (involving parallel competing Villermaux–Dushman reactions with the formation of [...] Read more.
An experimental study and mathematical modeling of micromixing in a microreactor with free impinging jets (MRFIJ) with a diameter of 1 mm was carried out. In the experimental part, the iodide-iodate technique was used (involving parallel competing Villermaux–Dushman reactions with the formation of I3). Theoretical assessment revealed that more than 50% of the introduced energy is dissipated in the jets collision region. Through the use of differentiated sampling, an uneven quality distribution of micro mixing in the central and peripheral zones of the reactor was found: at moderate flow rates (700–1000 mL/min, jets velocity of 15–21 m/s) the micromixing in the central part of reactor is up to 12 times better than that in the periphery. Furthermore, the weight fraction of the probes in the central zones of MRFIJ is reduced with increasing jet velocity; this effect is attributed to a more intense formation of ligaments and droplets upon collision of jets and their secondary mixing on the walls of the apparatus. In terms of the weighted average concentration, the best quality of micromixing in the samples is achieved at a flow rate of 300 mL/min. With an increase in the flow rate (and velocity) of the jets, the dependence of the I3 concentration on the flow rate has a nonmonotonic character, which is explained by a change in the nature of the flow in the collision zone of the jets: the transition from the formation of a liquid sheet to the intensive formation of ligaments and drops and secondary mixing of the liquid film formed on the walls of the reactor. The effect of “freshness” of solutions on the concentration of reaction products was studied. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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16 pages, 4377 KiB  
Article
Condensation of an Azeotropic Mixture inside 2.5 mm ID Minitubes
by Andrea Diani and Luisa Rossetto
Fluids 2020, 5(4), 171; https://doi.org/10.3390/fluids5040171 - 2 Oct 2020
Cited by 5 | Viewed by 1941
Abstract
The ongoing miniaturization of air conditioning and refrigeration systems, in order to limit, as much as possible, the refrigerant charge, calls for smaller and smaller heat exchangers. Besides, the new environmental regulations are calling for new pure refrigerants or refrigerants mixtures with lower [...] Read more.
The ongoing miniaturization of air conditioning and refrigeration systems, in order to limit, as much as possible, the refrigerant charge, calls for smaller and smaller heat exchangers. Besides, the new environmental regulations are calling for new pure refrigerants or refrigerants mixtures with lower values of global warming potentials (GWPs). In this context, this paper analyzes the possible implementation of minitubes during condensation of the azeotropic mixture R513A. Two minitubes are tested: a smooth tube with an inner diameter of 2.5 mm, and a microfin tube with an inner diameter at the fin tip of 2.4 mm. The effects of vapor quality (varied in the range 0.10–0.99), of mass velocity (varied in the range 200–1000 kg m−2 s−1), and of saturation temperature (30 °C and 40 °C) on the heat transfer coefficient are investigated. The experimental results indicate that the heat transfer coefficient increases as both vapor quality and mass velocity increase, both in the case of the smooth tube and of the microfin tube, but the slope of the heat transfer coefficient trend respect to vapor quality is higher in the case of the microfin tube. The microfin tube shows, on average, heat transfer coefficients are 79% higher than those of the smooth tube under the same working conditions. Since R513A is a possible substitute of R134a, some experimental data during condensation heat transfer are also compared against those for R134a. Finally, the experimental results are compared against values estimated by empirical correlations available in the open literature. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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13 pages, 3932 KiB  
Article
Temperature Uniformity in Cross-Flow Double-Layered Microchannel Heat Sinks
by Carlo Nonino and Stefano Savino
Fluids 2020, 5(3), 143; https://doi.org/10.3390/fluids5030143 - 28 Aug 2020
Cited by 4 | Viewed by 2071
Abstract
An in-house finite element method (FEM) procedure is used to carry out a numerical study on the thermal behavior of cross-flow double-layered microchannel heat sinks with an unequal number of microchannels in the two layers. The thermal performance is compared with those yielded [...] Read more.
An in-house finite element method (FEM) procedure is used to carry out a numerical study on the thermal behavior of cross-flow double-layered microchannel heat sinks with an unequal number of microchannels in the two layers. The thermal performance is compared with those yielded by other more conventional flow configurations. It is shown that if properly designed, i.e., with several microchannels in the top layer smaller than that in the bottom layer, cross-flow double-layered microchannel heat sinks can provide an acceptable thermal resistance and a reasonably good temperature uniformity of the heated base with a header design that is much simpler than that required by the counter-flow arrangement. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels)
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