Research

14 pages, 5126 KiB

Open AccessArticle

Study on the Stability of Functionally Graded Simply Supported Fluid-Conveying Microtube under Multi-Physical Fields

by Tao Ma and Anle Mu

Micromachines 2022, 13(6), 895; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13060895 - 03 Jun 2022

Cited by 5 | Viewed by 1390

The stability of functionally graded simply supported fluid-conveying microtubes under multiple physical fields was studied in this article. The strain energy of the fluid-conveying microtubes was determined based on strain gradient theory, and the governing equation of the functionally graded, simply supported, fluid-conveying [...] Read more.

The stability of functionally graded simply supported fluid-conveying microtubes under multiple physical fields was studied in this article. The strain energy of the fluid-conveying microtubes was determined based on strain gradient theory, and the governing equation of the functionally graded, simply supported, fluid-conveying microtube was established using Hamilton’s principle. The Galerkin method was used to solve the governing equation, and the effects of the dimensionless microscale parameters, temperature difference, and magnetic field intensity on the stability of the microtube were investigated. The results showed that the dimensionless microscale parameters have a significant impact on the stability of the microtube. The smaller the dimensionless microscale parameters were, the stronger the microscale effect of the material and the better the microtube stability became. The increase in the temperature difference decreased the eigenfrequency and critical velocity of the microtube and reduced the microtube stability. However, the magnetic field had the opposite effect. The greater the magnetic field intensity was, the greater the eigenfrequency and critical velocity were, and the more stable the microtube became. Full article

(This article belongs to the Special Issue Fluid Dynamics and Heat Transport in Microchannels)

► Show Figures

Figure 1

18 pages, 26022 KiB

Open AccessArticle

Snowflake Bionic Flow Channel Design to Optimize the Pressure Drop and Flow Uniform of Proton Exchange Membrane Fuel Cells

by Yuting Li, Jingliang Bi, Miao Tang and Gui Lu

Micromachines 2022, 13(5), 665; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13050665 - 24 Apr 2022

Cited by 4 | Viewed by 2228

Abstract

The flow channel design of bipolar plates plays a significant role in the proton exchange membrane fuel cells operation, particularly in thermal and water management. The pursuit of low-pressure drop supply and flow field uniformity in PEM fuel cells has not stopped, resulting [...] Read more.

The flow channel design of bipolar plates plays a significant role in the proton exchange membrane fuel cells operation, particularly in thermal and water management. The pursuit of low-pressure drop supply and flow field uniformity in PEM fuel cells has not stopped, resulting in numerous new bipolar plate flow channel designs. The biomimetic leaf vein shape-based flow channel and lung flow channel designs can significantly improve gas supply uniformity and reduce pressure drop. Therefore, we propose a snowflake-shaped bionic channel design by integrating the advantages of the leaf vein shape and lung shape channel. A 3D multi-physics fuel cell model is used to verify the feasibility and superiority of the bionic snowflake design in improving fuel cell performance, especially in reducing the pumping work. The local pressure distribution, oxygen distribution, water distribution, and current density distribution are used to reveal the enhancement mechanism of the new snowflake flow channel. The flow uniformity is further enhanced by using multi-objective (13 target parameters) and multi-parameter (18 independent variables) genetic algorithm optimization. The general goal of this work is to provide a new strategy for the thermal and water management of PEM fuel cells. Full article

(This article belongs to the Special Issue Fluid Dynamics and Heat Transport in Microchannels)

► Show Figures

Figure 1

24 pages, 10770 KiB

Open AccessArticle

Large-Eddy Simulation on the Aerodynamic and Thermal Characteristics in a Micropipe of the Hypersonic Engine Precooler

by Junqiang Zhang, Zhengping Zou and Yifan Wang

Micromachines 2022, 13(4), 637; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13040637 - 17 Apr 2022

Cited by 3 | Viewed by 1934

Abstract

The precooling air-breathing technique has become a study focus in the aerospace field. Research on the internal flow and heat-transfer mechanism of the precooler is important for design and optimization. A large-eddy simulation was used to study the aerodynamic and thermal characteristics in [...] Read more.

The precooling air-breathing technique has become a study focus in the aerospace field. Research on the internal flow and heat-transfer mechanism of the precooler is important for design and optimization. A large-eddy simulation was used to study the aerodynamic and thermal characteristics in a micropipe of the hypersonic engine precooler with supercritical methane as coolant and fuel. Under the effect of buoyancy, the high-temperature and low-density fluid near the wall in the circumferential direction gradually accumulate to the top wall. The accumulation of low-density fluid enhances the thermal acceleration effect at the top wall, which intensifies the local turbulent relaminarization and forms an M-shaped velocity distribution, resulting in the weakening of the heat transfer. On the other hand, the high-density fluid gathers to the bottom wall under the influence of gravity, the local thermal acceleration effect is weakened, and the flow heat transfer is enhanced. The influence of the relationship between the turbulent burst and the turbulent heat transfer under the effect of buoyancy is analyzed. It is found that the low-speed ejection events and high-speed sweep events are strengthened at the bottom wall, especially the low-speed ejection. However, the occurrence of these events at the top wall is restrained to a certain extent. Full article

(This article belongs to the Special Issue Fluid Dynamics and Heat Transport in Microchannels)

► Show Figures

Figure 1

11 pages, 3508 KiB

Open AccessArticle

Impact of Channels Aspect Ratio on the Heat Transfer in Finned Heat Sinks with Tip Clearance

by Elena Martin, Alejandro Valeije, Francisco Sastre and Angel Velazquez

Micromachines 2022, 13(4), 599; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13040599 - 12 Apr 2022

Cited by 4 | Viewed by 1536

Abstract

A 3D numerical study is used to analyze the flow topology and performance, in terms of heat transfer efficiency and required pumping power, of heat sink devices with different channel aspect-ratio in the presence of tip-clearance. Seven different channel aspect ratios

A R

[...] Read more.

A 3D numerical study is used to analyze the flow topology and performance, in terms of heat transfer efficiency and required pumping power, of heat sink devices with different channel aspect-ratio in the presence of tip-clearance. Seven different channel aspect ratios

A R

, from 0.25 to 1.75, were analyzed. The flow Reynolds numbers

R e

, based on the average velocity evaluated in the device channels region, were in the range of 200 to 1000. Two different behaviors of the global Nusselt were obtained depending on the flow Reynolds number: for

R e < 600

, the heat transfer increased with the channels aspect ratio, e.g., for

R e = 400

, the global Nusselt number increased by 14% for configuration

A R = 1.75

when compared to configuration

A R = 0.25

. For

R e > 600

, the maximum Nusselt is obtained for the squared-channel configuration, and, for some configurations, flow destabilization to a unsteady regime appeared. For

R e = 700

, Nusselt number reduced when compared with the squared-channel device, 11% and 2% for configurations with

A R = 0.25

and 1.75, respectively. Dimensionless pressure drop decreased with the aspect ratio for all cases. In the context of micro-devices, where the Reynolds number is small, these results indicate that the use of channels with high aspect-ratios is more beneficial, both in terms of thermal and dynamic efficiency. Full article

(This article belongs to the Special Issue Fluid Dynamics and Heat Transport in Microchannels)

► Show Figures

Graphical abstract

17 pages, 10978 KiB

Open AccessArticle

The Influence of the Unit Junction on the Performance of a Repetitive Structure Micromixer

by He Zhang, Shuang Yang, Rongyan Chuai, Xin Li and Xinyu Mu

Micromachines 2022, 13(3), 384; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13030384 - 27 Feb 2022

Cited by 3 | Viewed by 1446

Abstract

In order to investigate the influence of the unit junction on the micromixer performance, a repetitive structure micromixer with a total length of 12.3 mm was proposed. This micromixer consists of a T-shape inlet channel and six cubic mixing units, as well as [...] Read more.

In order to investigate the influence of the unit junction on the micromixer performance, a repetitive structure micromixer with a total length of 12.3 mm was proposed. This micromixer consists of a T-shape inlet channel and six cubic mixing units, as well as junctions between them. Numerical simulations show that, when the junctions are all located at the geometric center of the cubic mixing unit, the outlet mixing index is 72.12%. At the same flow velocity, the best mixing index achieved 97.15% and was increased by 34.68% when the junctions were located at different corners of the cubic mixing unit. The improvement in the mixing index illustrated that the non-equilibrium vortexes generated by changing the junction location to utilize the restricted diffusion by the mixing unit’s side wall could promote mixing. Visual tests of the micromixer chip prepared by 3D printing were consistent with the simulation results, also indicating that the junction location had a significant influence on the mixer’s performance. This article provides a new idea for optimizing the structural design and improving the performance of micromixers. Full article

(This article belongs to the Special Issue Fluid Dynamics and Heat Transport in Microchannels)

► Show Figures

Figure 1

16 pages, 3763 KiB

Open AccessArticle

Simulation of Gold Nanoparticle Transport during MHD Electroosmotic Flow in a Peristaltic Micro-Channel for Biomedical Treatment

by Muneerah Al Nuwairan and Basma Souayeh

Micromachines 2022, 13(3), 374; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13030374 - 26 Feb 2022

Cited by 20 | Viewed by 2067

Abstract

The study of gold nanoparticles (AuNPs) in the blood flow has emerged as an area of interest for numerous researchers, due to its many biomedical applications, such as cancer radiotherapy, DNA and antigens, drug and gene delivery, in vitro evaluation, optical bioimaging, radio [...] Read more.

The study of gold nanoparticles (AuNPs) in the blood flow has emerged as an area of interest for numerous researchers, due to its many biomedical applications, such as cancer radiotherapy, DNA and antigens, drug and gene delivery, in vitro evaluation, optical bioimaging, radio sensitization and laser phototherapy of cancer cells and tumors. Gold nanoparticles can be amalgamated in various shapes and sizes. Due to this reason, gold nanoparticles can be diffused efficiently, target the diseased cells and destroy them. The current work studies the effect of gold nanoparticles of different shapes on the electro-magneto-hydrodynamic (EMHD) peristaltic propulsion of blood in a micro-channel under various effects, such as activation energy, bioconvection, radiation and gyrotactic microorganisms. Four kinds of nanoparticle shapes, namely bricks, cylinders and platelets, are considered. The governing equations are simplified under the approximations of low Reynolds number (LRN), long wavelength (LWL) and Debye–Hückel linearization (DHL). The numerical solutions for the non-dimensional equations are solved using the computational software MATLAB with the help of the bvp4c function. The influences of different physical parameters on the flow and thermal characteristics are computed through pictorial interpretations. Full article

(This article belongs to the Special Issue Fluid Dynamics and Heat Transport in Microchannels)

► Show Figures

Figure 1

20 pages, 12338 KiB

Open AccessArticle

Numerical Simulations of Magnetohydrodynamics Natural Convection and Entropy Production in a Porous Annulus Bounded by Wavy Cylinder and Koch Snowflake Loaded with Cu–Water Nanofluid

by Abed Mourad, Aissa Abderrahmane, Obai Younis, Riadh Marzouki and Anas Alazzam

Micromachines 2022, 13(2), 182; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13020182 - 26 Jan 2022

Cited by 21 | Viewed by 2128

Abstract

The current paper presents a numerical study of the magnetohydrodynamics natural convection and entropy production of Cu–water nanofluid contained in a porous annulus between a heated Koch snowflake and wavy cylinder with lower temperature with respect to the Koch snowflake. The numerical algorithm [...] Read more.

The current paper presents a numerical study of the magnetohydrodynamics natural convection and entropy production of Cu–water nanofluid contained in a porous annulus between a heated Koch snowflake and wavy cylinder with lower temperature with respect to the Koch snowflake. The numerical algorithm is based on the Galerkin Finite Element Method. The impacts of Rayleigh number (Ra = 10³, 10⁴, 10⁵, and 10⁶), Hartman number (Ha = 0, 25, 50, and 100), Darcy number (Da = 10⁻², 10⁻³, 10⁻⁴, and 10⁻⁵), nanoparticle volumetric fraction (φ = 2%, 3%, 4%, and 5%), and the undulations number of the outer wavy cylinder (three cases) on the distributions of isotherms, streamlines, mean Nusselt number (Nu_avg), as well as on total entropy production and Bejan number are thoroughly examined. The computational outcomes disclose that dispersing more Cu nanoparticles in the base fluid and creating a flow with higher intensity inside the annulus by raising the Rayleigh number bring about a boosted natural convective flow in the cavity, which improves the heat transmission rate. In addition, it can be noted that owing to the peculiar form of the heated Koch snowflake, nanofluid gets trapped between the angled parts, resulting in uneven temperature profiles with higher values in these places. Full article

(This article belongs to the Special Issue Fluid Dynamics and Heat Transport in Microchannels)

► Show Figures

Figure 1

15 pages, 6059 KiB

Open AccessArticle

Thermal Analysis of 3D Electromagnetic Radiative Nanofluid Flow with Suction/Blowing: Darcy–Forchheimer Scheme

by Hammad Alotaibi and Mohamed R. Eid

Micromachines 2021, 12(11), 1395; https://0-doi-org.brum.beds.ac.uk/10.3390/mi12111395 - 13 Nov 2021

Cited by 19 | Viewed by 1576

Abstract

This paper discusses the Darcy–Forchheimer three dimensional (3D) flow of a permeable nanofluid through a convectively heated porous extending surface under the influences of the magnetic field and nonlinear radiation. The higher-order chemical reactions with activation energy and heat source (sink) impacts are [...] Read more.

This paper discusses the Darcy–Forchheimer three dimensional (3D) flow of a permeable nanofluid through a convectively heated porous extending surface under the influences of the magnetic field and nonlinear radiation. The higher-order chemical reactions with activation energy and heat source (sink) impacts are considered. We integrate the nanofluid model by using Brownian diffusion and thermophoresis. To convert PDEs (partial differential equations) into non-linear ODEs (ordinary differential equations), an effective, self-similar transformation is used. With the fourth–fifth order Runge–Kutta–Fehlberg (RKF45) approach using the shooting technique, the consequent differential system set is numerically solved. The influence of dimensionless parameters on velocity, temperature, and nanoparticle volume fraction profiles is revealed via graphs. Results of nanofluid flow and heat as well as the convective heat transport coefficient, drag force coefficient, and Nusselt and Sherwood numbers under the impact of the studied parameters are discussed and presented through graphs and tables. Numerical simulations show that the increment in activation energy and the order of the chemical reaction boosts the concentration, and the reverse happens with thermal radiation. Applications of such attractive nanofluids include plastic and rubber sheet production, oil production, metalworking processes such as hot rolling, water in reservoirs, melt spinning as a metal forming technique, elastic polymer substances, heat exchangers, emollient production, paints, catalytic reactors, and glass fiber production. Full article

(This article belongs to the Special Issue Fluid Dynamics and Heat Transport in Microchannels)

► Show Figures

Figure 1

15 pages, 5526 KiB

Open AccessArticle

A Computational Fluid Dynamic Study on Efficiency of a Wavy Microchannel/Heat Sink Containing Various Nanoparticles

by Yacine Khetib, Hala M. Abo-Dief, Abdullah K. Alanazi, S. Mohammad Sajadi, Mohsen Sharifpur and Josua P. Meyer

Micromachines 2021, 12(10), 1192; https://0-doi-org.brum.beds.ac.uk/10.3390/mi12101192 - 30 Sep 2021

Cited by 9 | Viewed by 1652

Abstract

In this paper, a common and widely used micro-heat sink (H/S) was redesigned and simulated using computational fluid dynamics methods. This H/S has a large number of microchannels in which the walls are wavy (wavy microchannel heat sink: WMCHS). To improve cooling, two [...] Read more.

In this paper, a common and widely used micro-heat sink (H/S) was redesigned and simulated using computational fluid dynamics methods. This H/S has a large number of microchannels in which the walls are wavy (wavy microchannel heat sink: WMCHS). To improve cooling, two (

A l_{2} O_{3}

and

C u O

) water-based nanofluids (NFs) were used as cooling fluids, and their performance was compared. For this purpose, studies were carried out at three Reynolds numbers (Re) of 500, 1000, and 1500 when the volume percent (φ) of the nanoparticles (NPs) was increased to 2%. The mixture two-phase (T-P) model was utilized to simulate the NFs. Results showed that using the designed WMCHS compared to the common H/S reduces the average and maximum temperatures (T-Max) up to 2 °C. Moreover, using the

A l_{2} O_{3}

NF is more suitable in terms of WMCHS temperature uniformity as well as its thermal resistance compared to the

C u O

NF. Increasing the φ is desirable in terms of temperature, but it enhances the pumping power (PP). Besides, the Figure of Merit (FOM) was investigated, and it was found that the value is greater at a higher volume percentage. Full article

(This article belongs to the Special Issue Fluid Dynamics and Heat Transport in Microchannels)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Fluid Dynamics and Heat Transport in Microchannels

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (9 papers)

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI