Showing papers on "Microchannel published in 2019"

The effect of using water/CuO nanofluid and L-shaped porous ribs on the performance evaluation criterion of microchannels

Abstract: The main purpose of this study is numerically investigating the flow and heat transfer of nanofluid flow inside a microchannel with L-shaped porous ribs as well as studying the effect of porous media properties on the performance evaluation criterion (PEC) of the fluid. In the present paper, in addition to the pure water fluid, the effect of using water/CuO nanofluid on the PEC of microchannel was investigated. The flow was simulated in four Reynolds numbers and two different volume fractions of nanoparticles in laminar flow regime. The investigated parameters are the thermal conductivity and the porosity rate of porous medium. The results indicate that with the existence of porous ribs, the nanofluid does not have a significant effect on heat transfer increase. By using porous ribs in flow with Reynolds number of 1200, the heat transfer rate increases up to 42% and in flow with Reynolds number of 100, this rate increases by 25%.

Highly Sensitive and Wearable Liquid Metal-Based Pressure Sensor for Health Monitoring Applications: Integration of a 3D-Printed Microbump Array with the Microchannel.

Abstract: Wearable pressure sensors capable of sensitive, precise, and continuous measurement of physiological and physical signals have great potential for the monitoring of health status and the early diagnosis of diseases. This work introduces a 3D-printed rigid microbump-integrated liquid metal-based soft pressure sensor (3D-BLiPS) for wearable and health-monitoring applications. Using a 3D-printed master mold based on multimaterial fused deposition modeling, the fabrication of a liquid metal microchannel and the integration of a rigid microbump array above the microchannel are achieved in a one-step, direct process. The microbump array enhances the sensitivity of the pressure sensor (0.158 kPa-1 ) by locally concentrating the deformation of the microchannel with negligible hysteresis and a stable signal response under cyclic loading. The 3D-BLiPS also demonstrates excellent robustness to 10 000 cycles of multidirectional stretching/bending, changes in temperature, and immersion in water. Finally, these characteristics are suitable for a wide range of applications in health monitoring systems, including a wristband for the continuous monitoring of the epidermal pulse rate for cuffless blood pressure estimation and a wireless wearable device for the monitoring of body pressure using a multiple pressure sensor array for the prevention of pressure ulcers.

Efficiency assessment of using graphene nanoplatelets-silver/water nanofluids in microchannel heat sinks with different cross-sections for electronics cooling

Abstract: This study aims to model the nanofluid flow in microchannel heat sinks having the same length and hydraulic diameter but different cross-sections (circular, trapezoidal and square).,The nanofluid is graphene nanoplatelets-silver/water, and the heat transfer in laminar flow was investigated. The range of coolant Reynolds number in this investigation was 200 ≤ Re ≤ 1000, and the concentrations of nano-sheets were from 0 to 0.1 vol. %.,Results show that higher temperature leads to smaller Nusselt number, pressure drop and pumping power, and increasing solid nano-sheet volume fraction results in an expected increase in heat transfer. However, the influence of temperature on the friction factor is insignificant. In addition, by increasing the Reynolds number, the values of pressure drop, pumping power and Nusselt number augments, but friction factor diminishes.,Data extracted from a recent experimental work were used to obtain thermo-physical properties of nanofluids.,The effects of temperature, microchannel cross-section shape, the volume concentration of nanoparticles and Reynolds number on thermal and hydraulics behavior of the nanofluid were investigated. Results are presented in terms of velocity, Nusselt number, pressure drop, friction loss and pumping power in various conditions. Validation of the model against previous papers showed satisfactory agreement.

Effects of nanofluid and radiative heat transfer on the double-diffusive forced convection in microreactors

Abstract: Understanding transport phenomena in microreactors remains challenging owing to the peculiar transfer features of microstructure devices and their interactions with chemistry. This paper, therefore, theoretically investigates heat and mass transfer in microreactors consisting of porous microchannels with thick walls, typical of real microreactors. To analyse the porous section of the microchannel, the local thermal non-equilibrium model of thermal transport in porous media is employed. A first-order, catalytic chemical reaction is implemented on the internal walls of the microchannel to establish the mass transfer boundary conditions. The effects of thermal radiation and nanofluid flow within the microreactor are then included within the governing equations. Further, the species concentration fields are coupled with that of the nanofluid temperature through considering the Soret effect. A semi-analytical methodology is used to tackle the resultant mathematical model with two different thermal boundary conditions. Temperature and species concentration fields as well as Nusselt number for the hot wall are reported versus various parameters such as porosity, radiation parameter and volumetric concentration of nanoparticles. The results show that radiative heat transfer imparts noticeable effects upon the temperature fields and consequently Nusselt number of the system. Importantly, it is observed that the radiation effects can lead to the development of a bifurcation in the nanofluid and porous solid phases and significantly influence the concentration field. This highlights the importance of including thermal radiation in thermochemical simulations of microreactors.

Microchannel Fabrication on Glass Materials for Microfluidic Devices

Abstract: Microchannels are the main features that characterize microfluidic devices. Also, glass is given priority in selecting a substrate material in the development of microfluidic devices due to its high degree of transparency, high chemical resistance, inertness to most substances, ability to sustain higher temperature, biological compatibility, and relatively low non-specific adsorption. However, the high cost and time-consuming labor for fabricating microchannels on glass limit the development of glass-based microfluidic devices, especially for point-of-care test devices. Therefore, it is important to have a capability for fabricating microchannels on glass more efficiently. In this context, the present paper reviews the processes applicable for fabricating microchannels on glass, which include chemical, mechanical, laser-based, and other processes. The state of the art for these processes, and their advantages and limits are also addressed, which will guide in selecting the processes suitable for constructing glass-based microfluidic devices.

Entropy generation analysis of magneto-nanoliquids embedded with aluminium and titanium alloy nanoparticles in microchannel with partial slips and convective conditions

Abstract: Purpose Outstanding features such as superior electrical conductivity and thermal conductivity of alloy nanoparticles with working fluids make them ideal materials to be used as coolants in microelectromechanical systems (MEMSs). This paper aims to investigate the effects of different alloy nanoparticles such as AA7075 and Ti6Al4V on microchannel flow of magneto-nanoliquids with partial slip and convective boundary conditions. Flow features are explored with the effects of magnetism and nanoparticle shape. Heat transport of fluid includes radiative heat, internal heat source/sink, viscous and Joule heating phenomena. Design/methodology/approach Suitable dimensionless variables are used to reduce dimensional governing equations into dimensionless ordinary differential equations. The relevant dimensionless ordinary differential systems are computed numerically by using Runge–Kutta–Fehlberg-based shooting approach. Pertinent results of velocity, temperature, entropy number and Bejan number for assorted values of physical parameters are comprehensively discussed. Also, a closed-form solution is obtained for momentum equation for a particular case. Analytical results agree perfectly with numerical results. Findings It is established that the entropy production can be improved with radiative heat, Joule heating, convective heating and viscous dissipation aspects. The entropy production is higher in the case of Ti6Al4V-H2O nanofluid than AA7075-H2O. Further, the inequality Ns(ξ)Sphere > Ns(ξ)Hexahedran > Ns(ξ)Tetrahydran > Ns(ξ)Column > Ns(ξ)Lamina holds true. Originality/value Effects of aluminium and titanium alloy nanoparticles in microchannel flows by using viscous dissipation and Joule heating are investigated for the first time. Flow features are explored with the effects of magnetism and nanoparticle shape. The results for different alloy nanoparticles such as AA7075 and Ti6Al4V have been compared.

Thermal performance improvement in water nanofluid/GNP–SDBS in novel design of double-layer microchannel heat sink with sinusoidal cavities and rectangular ribs

Abstract: In this numerical study, laminar flow of water nanofluid/GNP–SDBS (graphene nanoplatelet–sodium dodecylbenzene sulfonate) for 0–0.1% solid nanoparticles mass fraction was investigated for Reynolds numbers of 50–1000 in 3D space via finite volume method. In the newly proposed microchannel design, the cooling fluid is moving in countercurrent in the upper and lower layers of the microchannels, and there are cavities and sinusoidal routes on the solid walls of the microchannel, and the presence of rectangular ribs on the flow centerline along the fluid path enhances mixing for cooling fluid and creates better heat transfer for warm surfaces. The results of this study show that this special design of the microchannel can have a substantial increase in Nusselt number and heat transfer so that in the considered geometry by adding solid nanoparticles mass fraction it is possible to increase average Nusselt number for each Reynolds number by approximately 20%. Also, the mixing of the fluid because of formation of secondary flows has a strong effect on making the temperature distribution uniform in the cooling fluid and solid bed (wall) of the microchannel, especially in the lower layer. The upper layer of the microchannel always has a lower temperature due to indirect contact with heat flux compared with the lower layer. In this study, by increasing Reynolds number and mass fraction of solid nanoparticles the Nusselt number is increased and heat resistance of the lower wall of the microchannel is reduced. Based on the investigation of flow field and heat transfer, the use of the proposed design of the microchannel is recommended for Reynolds number less than 300.

Piezoelectric peristaltic micropump integrated on a microfluidic chip

Abstract: Micropump is extremely useful in miniature biochemical analysis systems for its abilities of manipulating and transporting minute liquid. We developed a novel peristaltic micropump to pump fluids in microfluidic chip in this article. The micropump consists of three piezoelectric actuators, and part of a microfluidic chip as a compressible microchannel. The fluid in the microchannel is transported owning to a series of impacting actions on the microchannel by the piezoelectric actuators. The microchannel is integrated fabricated with the microfluidic chip, which ensures a tiny dead volume less than 300 nL. Being beneficial from the plug-and-play design of the microfluidic chip, there is no cross-contamination for the reagent has no contact with the reusable actuators. Calibration shows the micropump can transport liquid at a high resolution of 8.4 nL/s, a maximum flow rate of 102 nL/s, and backpressure of up to 2.0 K Pa. A demonstration of mixing liquids on a chip was carried out using two micropumps, indicating its great potential for manipulating microamount reagent in biochemical application.

Energetic and entropic analyses of double-diffusive, forced convection heat and mass transfer in microreactors assisted with nanofluid

Abstract: This paper investigates the energetic and entropic characteristics of a microchannel with thick walls. A first-order, catalytic chemical reaction is imposed on the inner surfaces of the microchannel walls, and local thermal non-equilibrium approach is employed to analyse heat transfer within the porous section of the microchannel. Further, endo-/exothermic physicochemical processes are incorporated into the fluid phase and solid structure of the microchannel. Two models describing the fluid–porous interface conditions known as Models A and B are incorporated. It is shown that for both interface models, and with the considered parametric values, the optimum thickness of the porous insert to achieve the maximum Nu is around 0.6. However, when PEC is considered, this optimum thickness may vary between 0 and 0.5. It is further shown that depending on the specification of the microreactor, either Model A or B may result in the prediction of the minimum total entropy generation rate. It is also demonstrated that by altering the endothermicity of the microreactor it is possible to find an optimal value, which minimizes the total rate of entropy generation.

Microchannel Structural Design For a Room-Temperature Liquid Metal Based Super-stretchable Sensor.

Abstract: Room-temperature liquid metal has been widely used in flexible and stretchable sensors, focusing on embedding liquid metal in microchannels, liquid metal microdroplets formation, captive sensors, and liquid metal nanoparticles, etc. In this paper, a facile Eutectic Galium-Indium (EGaln) liquid-based microfluidic high-sensitivity, skin-mountable, and ultra-soft stretchable sensor is developed. It comprises Ecoflex microfluidic assembly filled with EGaln, which serves as the working fluid of the stretchable sensor. The lithography method is applied to achieve microfluidic channel. The microfluidic channel is optimized by using topology method and finite element analysis, making this device with high conformability and high stretchability. This method achieved an outstanding effect on elastomer-encapsulated strain gauge, which displays an approximately linear behavior with a gauge factor (GF). The GF could reach as high as 4.95 when the strain ultimately reached 550%. Applications of detection of the joints, fingers, and wrists has been conducted and showed excellent results. This work can further facilitate the exploration and potential realization of a functional liquid-state device technology with superior mechanical flexibility and conformability.

A comprehensive review on liquid–liquid two-phase flow in microchannel: flow pattern and mass transfer

Abstract: Liquid–liquid two-phase flow in microchannel is very common in micro-chemical and micro-biological system, etc. Deep understanding of the liquid–liquid two-phase flow mechanisms and mass transfer in microchannel can promote industrial applications significantly. To summarize the recent research progress on the liquid–liquid two-phase flow in microchannel, this paper collects research work about this topic, especially focusing on flow pattern and mass transfer. To begin with, flow patterns observed in various conditions are identified and factors which influence the flow patterns are analyzed. Then, mass transfer in liquid–liquid two-phase flow is discussed, especially the mass transfer during droplet flow, with both experiments and simulations. Furthermore, energy dissipation involved in liquid–liquid two-phase flow in microchannel is also briefly discussed. Finally, future needs are proposed for extending the researches on liquid–liquid two-phase flow and enlarging its application fields.