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A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Chemical Processes and Systems".

Deadline for manuscript submissions: closed (30 September 2020) | Viewed by 36141

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Dr. João Mário Miranda

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Guest Editor

Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal
Interests: lab-on-a-chip devices; biomimetic particles; droplet microfluidics; blood analogues; CFD
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Dr. Rui A. Lima

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Mechanical Engineering Department, Minho University, Campus de Azurém, 4800-058 Guimarães, Portugal
Interests: biomicrofluidics; microcirculation; biofluid mechanics; blood-on-chips; conventional and confocal micro-PIV; nanofluids; energy and environment
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Dr. José Daniel Araújo

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Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal
Interests: multiphase flow; mass transport enhancement by microbubbles; Taylor bubbles; reaction, heat, and mass transport; 3D-printed reactors; computational fluid dynamics; reactor engineering; flow in oil wells
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Microfluidic devices are currently applied in multiple fields. Applications include lab-on-chips, microreactors, heat sinks, inkjet printing, microrheometers, and organs-on-chips. Microdevices are portable, minimize reactant consumption and waste production, and can be used in flexible on-demand production of small batches.

Microdevices have a high surface-to-volume ratio, which enables efficient heat and mass transport. However, the design of these devices still needs to account for heat and mass transport limitations, and solutions to optimize transport phenomena need to be developed. For example, mass transport limitations near sensors need to be minimized for the correct operation of lab-on-chip devices, and mixing is a limiting factor in lab-on-chips, microreactors, and crystallization. Solutions such as acoustic streaming promoted by piezoelectric actuators have been proposed to enhance mixing and reduce mass transport limitations. Heat transport limitations are also a reason for concern in the microprocessor industry, and the optimization of heat sinks and heat pipes is an important research topic. In this context, new nanofluids have been proposed to improve the conductivity of thermal liquids.

In a microfluidic device, heating elements, sensors, actuators, micropumps, and other elements can be integrated to control heat and mass flow rates, temperature, and solute concentrations with a high spatial and temporal resolution. High-precision temperature control, temperature gradients, and temperature cycles can be implemented. Reactions can be controlled with high precision, minimizing the production of secondary products and improving the purity of the desired products and the selectivity of the sensors. Scaling up is viable through parallelization, and microdevices are especially apt for high-throughput combinatorial chemistry applied to drug discovery, process optimization, or catalyst selection.

Microdevices present new modeling challenges for the Computational Fluid Dynamics community, since phenomena usually negligible at the macroscale level become relevant at the microscale level. At the microscale level, matter (particles and fluids) can be manipulated by sound waves, electrical interactions, light, and temperature gradients, which opens new possibilities for novel separation and manufacturing processes. On the other hand, particles and cells represent a significant fraction of the channels size, and the continuum hypothesis can no longer be applied. Therefore, new methods need to be developed to incorporate electrical and acoustic interactions and surface tension effects into conventional flow, heat and mass transport modeling and simulation.

In this Special Issue on "Flow, heat and mass transport in microdevices”, we welcome review articles and original research papers, fundamental or applied, theoretical, numerical, or experimental, on microscale transport phenomena. Topics include, but are not limited to:

Mixing;
Microreactors;
Combinatorial chemistry;
Droplet reactors;
Safe devices for reactions involving highly explosive, toxic, or flammable reactants;
Crystallization;
Acoustic streaming;
Electrowetting;
Heat Sinks;
Heat dissipation enhancement of nanofluids;
Mass transport enhancement of nanofluids;
Effect of surfactants in droplet microfluidics—effect of mass transport limitations;
Mass transport limitations in organs-on-chips;
Numerical simulation of flow, mass, and heat transport in microdevices;
Topological optimization of microdevices;
Mass transport enhancement by microbubbles and microdroplets;
Electrokinetic transport phenomena;
Cell adhesion in microchannels;
Cell and particle transport in microfluidics;
Inkjet printing;
Microjet 3D printing

Dr. João Mário Miranda
Dr. Rui A. Lima
Dr. José Daniel Araújo
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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. Processes 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 2400 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
Mass transport
Heat transport
Nanofluids
Computational Fluid Dynamics
Mixing
Inertial Microfluidics
Microreactors
Droplet Microfluidics
Heat Sinks

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Published Papers (10 papers)

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Research

17 pages, 6387 KiB

Open AccessFeature PaperArticle

Numerical Study of Single Taylor Bubble Movement Through a Microchannel Using Different CFD Packages

by Mónica F. Silva, João B. L. M. Campos, João M. Miranda and José D. P. Araújo

Processes 2020, 8(11), 1418; https://doi.org/10.3390/pr8111418 - 7 Nov 2020

Cited by 12 | Viewed by 3347

Abstract

A Computation Fluid Dynamics (CFD) study for micro-scale gas–liquid flow was performed by using two different software packages: OpenFOAM^® and ANSYS Fluent^®. The numerical results were compared to assess the capability of both options to accurately predict the hydrodynamics of this kind of system. The focus was to test different methods to solve the gas–liquid interface, namely the Volume of Fluid (VOF) + Piecewise Linear Interface Calculation (PLIC) (ANSYS Fluent^®) and MULES/isoAdvector (OpenFOAM^®). For that, a single Taylor bubble flowing in a circular tube was studied for different co-current flow conditions (0.01 < Ca_B < 2.0 and 0.01 < Re_B < 700), creating representative cases that exemplify the different sub-patterns already identified in micro-scale slug flow. The results show that for systems with high Capillary numbers (Ca_B > 0.8) each software correctly predicts the main characteristics of the flow. However, for small Capillary numbers (Ca_B < 0.03), spurious currents appear along the interface for the cases solved using OpenFOAM^®. The results of this work suggest that ANSYS Fluent^® VOF+PLIC is indeed a good option to solve biphasic flows at a micro-scale for a wide range of scenarios becoming more relevant for cases with low Capillary numbers where the use of the solvers from OpenFoam^® are not the best option. Alternatively, improvements and/or extra functionalities should be implemented in the OpenFOAM^® solvers available in the installation package. Full article

(This article belongs to the Special Issue Flow, Heat and Mass Transport in Microdevices)

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14 pages, 3080 KiB

Open AccessArticle

Mathematical Model Based on the Shape of Pulse Waves Measured at a Single Spot for the Non-Invasive Prediction of Blood Pressure

by Lukas Peter, Jan Kracik, Martin Cerny, Norbert Noury and Stanislav Polzer

Processes 2020, 8(4), 442; https://doi.org/10.3390/pr8040442 - 9 Apr 2020

Cited by 7 | Viewed by 3832

Abstract

Background: Continuous non-invasive blood pressure (BP) measurement is a desired virtue in clinical practice. Unfortunately, current systems do not allow one for continuous, reliable BP measurement for more than a few hours per day, and they often require a complicated set of sensors to provide the necessary biosignals. Therefore we investigated the possibility of proposing a computational model that would predict the BP from pulse waves recorded in a single spot. Methods: Two experimental circuits were created. One containing a simple plastic tube for model development and a second with a silicone molded patient-specific arterial tree model. The first model served for the measuring of pulse waves under various BP (70–270 mmHg) and heart rate (60–190 beats per minute) values. Four different computational models were used to estimate the BP values from the diastolic time. The most accurate model was further validated using data from the latter experimental circuit containing a molded patient-specific silicone arterial tree. The measured data were averaged over a window of one, three, and five cycles. Two models based on pulse arrival time (PAT) were also analyzed for comparison. Results: The most accurate model exhibits a correlation coefficient of r = 0.967. The Bland–Altman plot revealed standard deviations (SD) between the model predictions and measurement of 10, 8.3, and 7.5 mmHg for the systolic BP and 8.7, 7 and 6.3 mmHg for the diastolic BP (both pressures calculated for the averaging windows of one, three, and five cycles, respectively). The best of the used PAT based model exhibited a SD of 17, 16, and 15 mmHg for the systolic BP and 14, 13, and 12 mmHg for the diastolic BP for the same averaging windows. Discussion: The proposed model showed its capability to predict BP accurately from the shape of the pulse wave measured at a single spot. Its SD was about 50% lower compared to the PAT based models which met the requirements of the Association for the Advancement of Medical Instrumentation. Full article

(This article belongs to the Special Issue Flow, Heat and Mass Transport in Microdevices)

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16 pages, 981 KiB

Open AccessArticle

Variable Wall Permeability Effects on Flow and Heat Transfer in a Leaky Channel Containing Water-Based Nanoparticles

by Aamir Shahzad, Wael Al-Kouz and Waqar A. Khan

Processes 2020, 8(4), 427; https://doi.org/10.3390/pr8040427 - 3 Apr 2020

Cited by 1 | Viewed by 2488

Abstract

This work presents the effects of variable wall permeability on two-dimensional flow and heat transfer in a leaky narrow channel containing water-based nanoparticles. The nanofluid is absorbed through the walls with an exponential rate. This situation arises in reverse osmosis, ultrafiltration, and transpiration cooling in industry. The mathematical model is developed by using the continuity, momentum, and energy equations. Using stream function, the transport equations are reduced and solved by using regular perturbation method. The expressions for stream function and temperature distribution are established, which helps in finding the components of velocity, wall shear stress, and heat transfer rate inside the channel. The results show that velocity components, temperature, wall shear stress, and rate of heat transfer are minimum at the entrance region due to the reabsorption of fluid containing nanoparticles. Additionally, with increasing volume fraction of nanoparticles, the rate of heat transfer enhances at all positions inside the channel. Titanium dioxide (TiO

_{2}

) nanoparticles show higher wall shear stress compared to copper and alumina. The streamlines confirms that all the fluid is reabsorbed before reaching the exit region of the channel for high reabsorption. Full article

(This article belongs to the Special Issue Flow, Heat and Mass Transport in Microdevices)

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13 pages, 2609 KiB

Open AccessArticle

Isolated Taylor Bubbles in Co-Current with Shear Thinning CMC Solutions in Microchannels—A Numerical Study

by Ana I. Moreira, Luís A. M. Rocha, João Carneiro, José D. P. Araújo, João B. L. M. Campos and João M. Miranda

Processes 2020, 8(2), 242; https://doi.org/10.3390/pr8020242 - 20 Feb 2020

Cited by 10 | Viewed by 3825

Abstract

Slug flow is a multiphase flow pattern characterized by the occurrence of long gas bubbles (Taylor bubbles) separated by liquid slugs. This multiphase flow regime is present in many and diversified natural and industrial processes, at macro and microscales, such as in eruption of volcanic magmas, oil recovery from pre-salt regions, micro heat exchangers, and small-sized refrigerating systems. Previous studies in the literature have been mostly focused on tubular gas bubbles flowing in Newtonian liquids. In this work, results from several numerical simulations of tubular gas bubbles flowing in a shear thinning liquid in microchannels are reported. To simulate the shear thinning behavior, carboxymethylcellulose (CMC) solutions with different concentrations were considered. The results are compared with data from bubbles flowing in Newtonian liquids in identical geometric and dynamic conditions. The numerical work was carried out in computational fluid dynamics (CFD) package Ansys Fluent (release 16.2.0) employing the volume of fluid (VOF) methodology to track the volume fraction of each phase and the continuum surface force (CSF) model to insert the surface tension effects. The flow patterns, the viscosity distribution in the liquid, the liquid film thickness between the bubble and the wall, and the bubbles shape are analyzed for a wide range of shear rates. In general, the flow patterns are similar to those in Newtonian liquids, but in the film, where a high viscosity region is observed, the thickness is smaller. Bubble velocities are smaller for the non-Newtonian cases. Full article

(This article belongs to the Special Issue Flow, Heat and Mass Transport in Microdevices)

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26 pages, 6642 KiB

Open AccessArticle

Numerical Investigation of Design and Operating Parameters of Thermal Gradient Continuous-Flow PCR Microreactor Using One Heater

by Usama Perwez, Imran Aziz, Faisal Ahmed and Mohsin Raza Khan

Processes 2019, 7(12), 919; https://doi.org/10.3390/pr7120919 - 4 Dec 2019

Cited by 4 | Viewed by 3420

Abstract

To respond to the dire need for miniaturization and process simplification of continuous-flow PCR (CF-PCR) device, this paper represents design and operation guide of a novel metal alloy assisted hybrid microdevice (polydimethylsiloxane (PDMS) and glass) for CF-PCR employing one heater. In this research, the specific objectives are to determine whether one heater chip design will be flexible enough when the size of DNA base pair is varied and to investigate whether one heater CF-PCR device will be able to resolve the longstanding problem of thermal crosstalk. Furthermore, the parametric study is performed to determine which of the fourteen parameters have the greatest impact on the performance of one heater CF-PCR device. The main objective of this parametric study is to distinguish between the parameters that are either critical to the chip performance or can be freely specified. It is found that substrate thickness, flow rate, channel spacing, aspect ratio, channel pass length and external heat transfer coefficient are the most limiting parameters that can either improve or deteriorate the chip’s thermal performance. Overall, the impact of design and operating parameters are observed to be least on thermocycling profile at low Reynolds number (≤0.37 Re). However, in addition to the primary metric advantages of CF-PCR, one heater chip design helps in minimizing the thermal crosstalk effects by a factor of 4 in comparison to dual heater PCR while still maintaining a critical criteria of chip flexibility in terms of handling various sizes of DNA fragments. Hence, the proposed scheme paves the way for low-cost point-of-care diagnostics, system integration, and device miniaturization, realizing a portable microfluidic device applicable for on-site and direct field uses. Full article

(This article belongs to the Special Issue Flow, Heat and Mass Transport in Microdevices)

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12 pages, 3293 KiB

Open AccessArticle

Numerical Solutions of Heat Transfer for Magnetohydrodynamic Jeffery-Hamel Flow Using Spectral Homotopy Analysis Method

by Asad Mahmood, Md Faisal Md Basir, Umair Ali, Mohd Shareduwan Mohd Kasihmuddin and Mohd. Asyraf Mansor

Processes 2019, 7(9), 626; https://doi.org/10.3390/pr7090626 - 17 Sep 2019

Cited by 20 | Viewed by 3803

Abstract

This paper studies heat transfer in a two-dimensional magnetohydrodynamic viscous incompressible flow in convergent/divergent channels. The temperature profile was obtained numerically for both cases of convergent/divergent channels. It was found that the temperature profile increases with an increase in Reynold number, Prandtl number, Nusselt number and angle of the wall but decreases with an increase in Hartmann number. A relatively new numerical method called the spectral homotopy analysis method (SHAM) was used to solve the governing non-linear differential equations. The SHAM 3rd order results matched with the DTM and shooting, showing that SHAM is feasible as a technique to be used. Full article

(This article belongs to the Special Issue Flow, Heat and Mass Transport in Microdevices)

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Graphical abstract

14 pages, 3048 KiB

Open AccessArticle

Effect of the Marangoni Convection in the Unsteady Thin Film Spray of CNT Nanofluids

by Ali Rehman, Taza Gul, Zabidin Salleh, Safyan Mukhtar, Fawad Hussain, Kottakkaran Sooppy Nisar and Poom Kumam

Processes 2019, 7(6), 392; https://doi.org/10.3390/pr7060392 - 24 Jun 2019

Cited by 16 | Viewed by 4117

Abstract

The gradient of surface temperature is known as Marangoni convection and plays an important role in silicon melt, spray, atomic reactors, and thin fluid films. Marangoni convection has been considered in the liquid film spray of carbon nanotube (CNT) nanofluid over the unsteady extending surface of a cylinder. The two kinds of CNTs, single-wall carbon nanotubes (SWCNTs) and multiple-wall carbon nanotubes (MWCNTs), formulated as water-based nanofluids have been used for thermal spray analysis. The thickness of the nanofluid film was kept variable for a stable spray rate and pressure distribution. The transformed equations of the flow problem have been solved using the optimal homotopy analysis method (OHAM). The obtained results have been validated through the sum of the total residual errors numerically and graphically for both types of nanofluids. The impact of the physical parameters versus velocity, pressure, and temperature pitches under the influence of the Marangoni convection have been obtained and discussed. The obtained results are validated using the comparison of OHAM and the (ND-solve) method. Full article

(This article belongs to the Special Issue Flow, Heat and Mass Transport in Microdevices)

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15 pages, 4577 KiB

Open AccessArticle

Computational Study of MHD Nanofluid Flow Possessing Micro-Rotational Inertia over a Curved Surface with Variable Thermophysical Properties

by Zahid Ahmed, Ali Al-Qahtani, Sohail Nadeem and Salman Saleem

Processes 2019, 7(6), 387; https://doi.org/10.3390/pr7060387 - 21 Jun 2019

Cited by 26 | Viewed by 3382

Abstract

This work presents a numerical investigation of viscous nanofluid flow over a curved stretching surface. Single-walled carbon nanotubes were taken as a solid constituent of the nanofluids. Dynamic viscosity was assumed to be an inverse function of fluid temperature. The problem is modeled with the help of a generalized theory of Eringen Micropolar fluid in a curvilinear coordinates system. The governing systems of non-linear partial differential equations consist of mass flux equation, linear momentum equations, angular momentum equation, and energy equation. The transformed ordinary differential equations for linear and angular momentum along with energy were solved numerically with the help of the Keller box method. Numerical and graphical results were obtained to analyze the flow characteristic. It is perceived that by keeping the dynamic viscosity temperature dependent, the velocity of the fluid away from the surface rose in magnitude with the values of the magnetic parameter, while the couple stress coefficient decreased with rising values of the magnetic parameter. Full article

(This article belongs to the Special Issue Flow, Heat and Mass Transport in Microdevices)

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15 pages, 3854 KiB

Open AccessArticle

Simulation of the Gas Filling and Evacuation Processes in an Inertial Confinement Fusion (ICF) Hohlraum

by Liangyu Wu, Hua Zhou, Cheng Yu and Feng Yao

Processes 2019, 7(5), 269; https://doi.org/10.3390/pr7050269 - 8 May 2019

Cited by 2 | Viewed by 3293

Abstract

In indirect inertial confinement fusion (ICF), the prediction of gas pressures and mass flow rates in the hohlraum is critical for fielding the hohlraum film and the support tent. To this end, it is desirable to understand the gas filling and evacuation process through the microcapillary fill tube and the support tent. In this work, a unified flow simulation of the filling and evacuation processes through the microcapillary fill tube and the support tent in an ICF hohlraum was conducted to study the gas pressure and mass flow rate in the hohlraum. The effects of the support tent size and the microcapillary fill tube size on the critical pressure variation and pressure difference across the hole on the support tent are examined. The results indicate that an increase in the diameter of the hole and the hole number leads to a smaller pressure difference across the hole on the support tent. If the diameter of the hole on the support tent is larger than 0.06 mm, the critical pressure variation rate is nearly independent of the diameter and the hole number. Increases in the diameter and decreases in the length of the microcapillary fill tube induce a larger critical pressure variation rate and pressure difference across the hole, which is conductive to fielding the hohlraum film. Full article

(This article belongs to the Special Issue Flow, Heat and Mass Transport in Microdevices)

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18 pages, 4137 KiB

Open AccessArticle

Unsteady Nano-Liquid Spray with Thermal Radiation Comprising CNTs

by Taza Gul, Waqar A Khan, Mehwish Tahir, Rubi Bilal, Ilyas Khan and Kottakkaran Sooppy Nisar

Processes 2019, 7(4), 181; https://doi.org/10.3390/pr7040181 - 28 Mar 2019

Cited by 9 | Viewed by 3525

Abstract

Carbon nanotubes play a significant role in improving the thermal efficiency of common liquids. The objective of this research is to examine the thin film spray over the surface of a vertical tube through carbon nanotubes (CNTs) nanofluids. Processes for the preparation of the nanofluid and the stable dispersion of the CNTs in water were followed from the available experimental literature. The thickness of the spray pattern was kept variable to control the stability of the spray pattern and to accomplish the suitable heat transmission under the effects of a magnetic field. The pressure supply and rate of the spray were also calculated as a function of the liquid film thickness. The basic governing equations were transformed into nonlinear differential equations by using suitable similarity transformations. The numerical outcomes were obtained by means of the BVPh 2.0 package of the optimal scheme. The influences of the physical quantities like spray rate and variable thickness on the dimensionless velocity, temperature, pressure distribution, Nusselt number were investigated and the results are compared with the existing literature. The comparison was found to be in good agreement. The present results showed that the single-walled carbon nanotubes are more efficient in the enhancement of heat transfer rate compared to the multi-walled carbon nanotubes. Full article

(This article belongs to the Special Issue Flow, Heat and Mass Transport in Microdevices)

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