scholarly journals Maximization of the capillary pump efficiency in microfluidics

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Wei Hua ◽  
Weidong Zhou ◽  
Wei Wang ◽  
Zhenfeng Wang ◽  
Ruige Wu ◽  
...  
Keyword(s):  
Significant Contribution ◽  
Rectangular Channel ◽  
Microfluidic Channel ◽  
Channel Width ◽  
Channel Height ◽  
Pump Efficiency ◽  
Channel Size ◽  
Rectangular Channels ◽  
Filling Time ◽  
Simulation Results

AbstractThis paper studies the efficiency of capillary pump analytically in circular, square and rectangular channels with results verified by experiment. The effect of liquid momentum is analyzed with respect to channel size and equations are developed to enable most efficient fluid pumping. It is found that the momentum term is negligible at channel cross-cut area < 0.1 mm2 while it has a significant contribution at > 0.3 mm2 region. The optimized equations show that the most efficient pumping and thereby the quickest liquid filling is accomplished in square shaped channel when compared with rectangular and circular channels. Generally, the longer the filling distance, or the longer the filling time, the larger the channel size is required after optimization, and vice versa. For the rectangular channel with channel height fixed, the channel width requirement to maximize the ability of capillary pump is obtained and discussed. Experimental verifications are conducted based on the measurement of filling distance versus time, and the simulation results are well correlated with the testing results. The equations developed in the paper provide a reference for the microfluidic channel design, such that the channel filling speed can be maximized.

scholarly journals Numerical and Theoretical Study of Performance and Mechanical Behavior of PEM-FC Using Innovative Channel Geometrical Configurations

2021 ◽  
Vol 11 (12) ◽  
pp. 5597
Author(s):  
Hussein A. Z. AL-bonsrulah ◽  
Mohammed J. Alshukri ◽  
Ammar I. Alsabery ◽  
Ishak Hashim
Keyword(s):  
Fuel Cell ◽  
Cross Section ◽  
Rectangular Channel ◽  
Compressive Load ◽  
Proton Exchange ◽  
Channel Cross Section ◽  
Channel Height ◽  
Cross Sectional ◽  
Triangular Channel ◽  
Higher Power

Proton exchange membrane fuel cell (PEM-FC) aggregation pressure causes extensive strains in cell segments. The compression of each segment takes place through the cell modeling method. In addition, a very heterogeneous compressive load is produced because of the recurrent channel rib design of the dipole plates, so that while high strains are provided below the rib, the domain continues in its initial uncompressed case under the ducts approximate to it. This leads to significant spatial variations in thermal and electrical connections and contact resistances (both in rib–GDL and membrane–GDL interfaces). Variations in heat, charge, and mass transfer rates within the GDL can affect the performance of the fuel cell (FC) and its lifetime. In this paper, two scenarios are considered to verify the performance and lifetime of the PEM-FC using different innovative channel geometries. The first scenario is conducted by adopting a constant channel height (H = 1 mm) for all the differently shaped channels studied. In contrast, the second scenario is conducted by taking a constant channel cross-sectional area (A = 1 mm2) for all the studied channels. Therefore, a computational fluid dynamics model (CFD) for a PEM fuel cell is formed through the assembly of FC to simulate the pressure variations inside it. The simulation results showed that a triangular cross-section channel provided the uniformity of the pressure distribution, with lower deformations and lower mechanical stresses. The analysis helped gain insights into the physical mechanisms that lead to the FC’s durability and identify important parameters under different conditions. The model shows that it can assume the intracellular pressure configuration toward durability and appearance containing limited experimental data. The results also proved that the better cell voltage occurs in the case of the rectangular channel cross-section, and therefore, higher power from the FC, although its durability is much lower compared to the durability of the triangular channel. The results also showed that the rectangular channel cross-section gave higher cell voltages, and therefore, higher power (0.63 W) from the fuel cell, although its durability is much lower compared to the durability of the triangular channel. Therefore, the triangular channel gives better performance compared to other innovative channels.

scholarly journals Study of Mini Channel Heat Sink with Different Internal Configuration

2020 ◽  
Vol 319 ◽  
pp. 02004
Author(s):  
Muhammad Akif Rahman ◽  
Md Badrath Tamam ◽  
Md Sadman Faruque ◽  
A.K.M. Monjur Morshed
Keyword(s):  
Nusselt Number ◽  
Thermal Performance ◽  
Heat Sink ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Heat Sinks ◽  
Maximum Temperature ◽  
Rectangular Channels ◽  
Flow Through ◽  
Internal Configuration

In this paper a numerical analysis of three-dimensional laminar flow through rectangular channel heat sinks of different geometric configuration is presented and a comparison of thermal performance among the heat sinks is discussed. Liquid water was used as coolant in the aluminum made heat sink with a glass cover above it. The aspect ratio (section height to width) of rectangular channels of the mini-channel heat sink was 0.33. A heat flux of 20 W/cm2 was continuously applied at the bottom of the channel with different inlet velocity for Reynold’s number ranging from 150 to 1044. Interconnectors and obstacles at different positions and numbers inside the channel were introduced in order to enhance the thermal performance. These modifications cause secondary flow between the parallel channels and the obstacles disrupt the boundary layer formation of the flow inside the channel which leads to the increase in heat transfer rate. Finally, Nusselt number, overall thermal resistance and maximum temperature of the heat sink were calculated to compare the performances of the modified heat sinks with the conventional mini channel heat sink and it was observed that the heat sink with both interconnectors and obstacles enhanced the thermal performance more significantly than other configurations. A maximum of 36% increase in Nusselt number was observed (for Re =1044).

scholarly journals Lamb-type waves generated by a cylindrical bubble oscillating between two planar elastic walls

2016 ◽  
Vol 472 (2188) ◽  
pp. 20160031 ◽  
Author(s):  
A. A. Doinikov ◽  
F. Mekki-Berrada ◽  
P. Thibault ◽  
P. Marmottant
Keyword(s):  
Resonance Frequency ◽  
Surface Waves ◽  
Wave Speed ◽  
Microfluidic Channel ◽  
Scattered Wave ◽  
Channel Height ◽  
Volume Oscillation ◽  
Scholte Wave ◽  
Rigid Walls ◽  
Elastic Walls

The volume oscillation of a cylindrical bubble in a microfluidic channel with planar elastic walls is studied. Analytical solutions are found for the bulk scattered wave propagating in the fluid gap and the surface waves of Lamb-type propagating at the fluid–solid interfaces. This type of surface wave has not yet been described theoretically. A dispersion equation for the Lamb-type waves is derived, which allows one to evaluate the wave speed for different values of the channel height h . It is shown that for h <λ t , where λ t is the wavelength of the transverse wave in the walls, the speed of the Lamb-type waves decreases with decreasing h , while for h on the order of or greater than λ t , their speed tends to the Scholte wave speed. The solutions for the wave fields in the elastic walls and in the fluid are derived using the Hankel transforms. Numerical simulations are carried out to study the effect of the surface waves on the dynamics of a bubble confined between two elastic walls. It is shown that its resonance frequency can be up to 50% higher than the resonance frequency of a similar bubble confined between two rigid walls.

Heat Transfer and Pressure Loss in Rectangular One-Side-Ribbed Channels With Different Aspect Ratios

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Sébastien Kunstmann ◽  
Jens von Wolfersdorf ◽  
Uwe Ruedel
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Gas Turbines ◽  
Pressure Loss ◽  
Rectangular Channel ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Aspect Ratios

An investigation was conducted to assess the thermal performance of W-shaped, 2W-shaped and 4W-shaped ribs in a rectangular channel. The aspect ratios (W/H) were 2:1, 4:1, and 8:1. The ribs were located on one channel wall. The rib height (e) was kept constant with a rib height-to-hydraulic diameter ratio (e/Dh) of 0.02, 0.03, and 0.06. The rib pitch-to-height ratio (P/e) was 10. The Reynolds numbers investigated (Re > 90 000) are typical for combustor liner cooling configurations of gas turbines. Local heat transfer coefficients using the transient thermochromic liquid crystal technique and overall pressure losses were measured. The rib configurations were investigated numerically to visualize the flow pattern in the channel and to support the understanding of the experimental data. The results show that the highest heat transfer enhancement is obtained by rib configurations with a rib section-to-channel height ratio (Wr/H) of 1:1. W-shaped ribs achieve the highest heat transfer enhancement levels in channels with an aspect ratio of 2:1, 2W-shaped ribs in channels with an aspect ratio of 4:1 and 4W-shaped ribs in channels with an aspect ratio of 8:1. Furthermore, the pressure loss increases with increasing complexity of the rib geometry and blockage ratio.

Theoretical Research on Two-Phase Flow Instability in Parallel Rectangular Channels Under Periodic Perturbation

2020 ◽  
Author(s):  
Libo Qian ◽  
Jian Deng ◽  
Tao Huang ◽  
Rong Cai
Keyword(s):  
Pressure Drop ◽  
Channel Model ◽  
Flow Instability ◽  
Rectangular Channel ◽  
Static Condition ◽  
Periodic Perturbation ◽  
Theoretical Research ◽  
Threshold Power ◽  
Additional Pressure ◽  
Rectangular Channels

Abstract A theoretical model for Density Wave Oscillations (DWOs) flow instability in parallel rectangular channels under periodic heaving motion is established with a lumped mathematical model based on homogenous hypothesis. The parallel rectangular channels comprise of the entrance section, the heating section, the riser section and the upper- and lower plenums, which guarantee the isobaric pressure drop condition between channels and the model consists of boiling channel model, pressure drop model, parallel channel model, additional pressure drop model generated by heaving motions, the constitutive and numerical models. The effect of periodic perturbation is introduced through additional pressure drop in the momentum equation. The model is validated with experimental data of a twin-rectangular-channel flow instability experiment under static condition. Then the flow instability in parallel-rectangular-channel system is studied under periodic perturbation and the margin of flow instability and the threshold power of the system under static condition is calculated as basis condition for comparison. The effect of the amplitude and period of perturbation is analyzed analytically and the results show that the amplitude and period of perturbation shows little effect on flow instability. While when the additional pressure difference introduced by heaving motion is comparable with that under static condition, the effect of amplitude becomes stronger. And the period of perturbation strongly effects the threshold power when it is identical to that of natural period of the system, which can be explained by resonance between the perturbation and the system. And this effect is even stronger when the asymmetric heating condition is introduced.

Flow and Heat Transfer Characteristics in Rectangular Channels With Staggered Transverse Ribs on Two Opposite Walls

2007 ◽  
Vol 129 (12) ◽  
pp. 1732-1736 ◽  
Author(s):  
Rong Fung Huang ◽  
Shyy Woei Chang ◽  
Kun-Hung Chen
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Turbulence Intensity ◽  
Flow Characteristics ◽  
Channel Height ◽  
Primary Concern ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Characteristic Flow ◽  
Rectangular Channels

The flow characteristics and the heat transfer properties of the rectangular channels with staggered transverse ribs on two opposite walls are experimentally studied. The rib height to channel height ratio ranges from 0.15 to 0.61 (rib height to channel hydraulic diameter ratio from 0.09 to 0.38). The pitch to rib height ratio covers from 2.5 to 26. The aspect ratio of the rectangular channel is 4. The flow characteristics are studied in a water channel, while the heat transfer experiments are performed in a wind tunnel. Particle image velocimetry (PIV) is employed to obtain the quantitative flow field characteristics. Fine-wire thermocouples imbedded near the inner surface of the bottom channel wall are used to measure the temperature distributions of the wall and to calculate the local and average Nusselt numbers. Using the PIV measured streamline patterns, various characteristic flow modes, thru flow, oscillating flow, and cell flow, are identified in different regimes of the domain of the rib height to channel height ratio and pitch to rib height ratio. The vorticity, turbulence intensity, and wall shear stress of the cell flow are found to be particularly larger than those of other characteristic flow modes. The measured local and average Nusselt numbers of the cell flow are also particularly higher than those of other characteristic flow modes. The distinctive flow properties are responsible for the drastic increase of the heat transfer due to the enhancement of the momentum, heat, and mass exchanges within the flow field induced by the large values of the vorticity and turbulence intensity. Although the thru flow mode is conventionally used in the ribbed channel for industrial application, the cell flow could become the choice if the heat transfer rate, instead of the pressure loss, is the primary concern.

Effect of Rotation on Heat Transfer in Narrow Rectangular Cooling Channels (AR = 8:1 and 4:1) With Pin-Fins

2003 ◽  
Author(s):  
Lesley M. Wright ◽  
Eungsuk Lee ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Pin Fin ◽  
Aspect Ratios ◽  
Rectangular Channels ◽  
Smooth Channel ◽  
Pin Fins

The effect of rotation on smooth narrow rectangular channels and narrow rectangular channels with pin-fins is investigated in this study. Pin-fins are commonly used in the narrow sections within the trailing edge of the turbine blade; the pin-fins act as turbulators to enhance internal cooling while providing structural support in this narrow section of the blade. The rectangular channel is oriented at 150° with respect to the plane of rotation, and the focus of the study involves narrow channels with aspect ratios of 4:1 and 8:1. The enhancement due to both conducting (copper) pin-fins and non-conducting (plexi-glass) pins is investigated. Due to the varying aspect ratio of the channel, the height-to-diameter ratio (hp/Dp) of the pins varies from two, for an aspect ratio of 4:1, to unity, for an aspect ratio of 8:1. A staggered array of pins with uniform streamwise and spanwise spacing (xp/Dp = sp/Dp = 2.0) is studied. With this array, 42 pin-fins are used, giving a projected surface density of 3.5 pins/in2 (0.543 pins/cm2), for the leading or trailing surfaces. The range of flow parameters include Reynolds number (ReDh = 5000–20000), rotation number (Ro = 0.0–0.302), and inlet coolant-to-wall density ratio (Δρ/ρ = 0.12). Heat transfer in a stationary pin-fin channel can be enhanced up to 3.8 times that of a smooth channel. Rotation enhances the heat transferred from the pin-fin channels 1.5 times that of the stationary pin-fin channels. Overall, rotation enhances the heat transfer from all surfaces in both the smooth and pin-fin channels. Finally, as the rotation number increases, spanwise variation increases in all channels.

Forced Convective Liquid Cooling of Arrays of Protruding Heated Elements Mounted in a Rectangular Duct

1998 ◽  
Vol 120 (3) ◽  
pp. 243-252 ◽  
Author(s):  
A. Gupta ◽  
Y. Jaluria
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Correlation Coefficients ◽  
Small Variation ◽  
Transport Processes ◽  
Spanwise Direction ◽  
Channel Height ◽  
Water Cooling ◽  
Algebraic Equations

Experiments are performed to study forced convection water cooling of arrays of protruding heat sources with specified heat input. Each array has four rows, with three elements in each row. The arrays are mounted at the top or at the bottom of a rectangular channel. The Reynolds number, based on channel height, is varied from around 2500 to 9000. Flow visualization and temperature measurements revealed that the flow over the arrays was fully turbulent, even at the smallest Reynolds number. Different channel heights (ranging from 3 to 4 times the height of each element), different heat inputs to the modules, and different streamwise spacings between the elements are employed. The spanwise spacing between the elements is kept constant. It is found that the average Nusselt number is higher for smaller channel heights and streamwise spacing, at constant Reynolds number. The effect of buoyancy on the average heat transfer rate from the arrays is found to be small over the parametric ranges considered here. A small variation in the heat transfer coefficient is found in the spanwise direction. The observed trends are considered in terms of the underlying transport processes. The heat transfer data are also correlated in terms of algebraic equations. High correlation coefficients attest to the consistency of results. The data are compared with previous air and water cooling studies, wherever possible, and a good agreement is obtained.

Neural-Genetic Optimization of Temperature Control in a Continuous Flow Polymerase Chain Reaction Microdevice

2005 ◽  
Author(s):  
Hing Wah Lee ◽  
Parthiban Arunasalam ◽  
Ishak A. Azid ◽  
Kankanhally N. Seetharamu
Keyword(s):  
Polymerase Chain Reaction ◽  
Reaction Zone ◽  
Temperature Control ◽  
Continuous Flow ◽  
Microfluidic Channel ◽  
Microfluidic Channels ◽  
Genetic Optimization ◽  
Chain Reaction ◽  
Polymerase Chain ◽  
Simulation Results

In this study, a hybridized neural-genetic optimization methodology realized by embedding finite element analysis (FEA) trained artificial neural networks (ANN) into genetic algorithms (GA) is used to optimize temperature control in a ceramic based continuous flow polymerase chain reaction (CPCR) device. The CPCR device requires three thermally isolated zones of 94°C, 65°C and 72°C for the corresponding process of denaturing, annealing and extension to complete a cycle of polymerase chain reaction. Three separately addressable heaters provide heat input to each zone, microfluidic channels allow for the transport of fluid between zones and thermal isolation between the zones is maintained by machining air-gaps into the device. The most important aspect of temperature control in the CPCR is to maintain temperature distribution at each reaction zone with a precision of ±1°C or better irrespective of changing ambient conditions. Results obtained from the FEA simulation are compared with published experimental work. Simulation results show good comparison with experimental work for the temperature control in each reaction zone of the microfluidic channels. The data is then used to train the ANN to predict the temperature distribution of the microfluidic channel for new heater input power and fluid flow rate. Using these data, optimization of temperature control in the CPCR device is achieved by embedding the trained ANN results as a fitness function into GA. The objective of the optimization is to minimize the temperature difference in each reaction zone of the microfluidic channel while satisfying the residence time requirement. Finally, the optimized results for the CPCR device are used to build a new FEA model for numerical simulation analysis. The simulation results for the neural-genetic optimized CPCR model and the initial CPCR model are then compared. The neural-genetic optimized model shows a significant improvement from the initial model establishing the optimization methods superiority.

Development of a Novel Micro-Manipulation Device and Its Simulation Using COMSOL

2009 ◽  
Author(s):  
Hsiu-hung Chen ◽  
Dayong Gao
Keyword(s):  
Microfluidic Channel ◽  
Groove Depth ◽  
Flow Speed ◽  
Fluid Mixing ◽  
Microfluidic Channels ◽  
Channel Depth ◽  
Multiphysics Modeling ◽  
Modeling Software ◽  
Simulation Results ◽  
Channel Systems

The manipulation of particles in fluids using microfluidic devices is a fundamental task in Lab-on-a-Chip applications. Grooved structures have been widely studied in particle handling and fluid mixing in microfluidic channel systems. In this study, we report use of patterning flows produced by a series of grooved surfaces with different geometrical setups integrated into a microfluidic device, to continuously manipulate the flowing particles, ranging from 6 to 20 μm in diameters, of comparable sizes to the depth of the channel. COMSOL, a multiphysics modeling software that can help predict engineering trends, is used to systematically quantify the following parameters: 1) channel depth, 2) groove width, 3) groove depth, 4) groove angle, and 5) flow speed, which may affect the performance of separation for flowing particles inside the channel. The device is fabricated using softlithographic techniques and is composed of inlets, microfluidic channels, and outlets for loading, manipulating and retrieving cell suspensions, respectively. Experimental results indicated that the particles were evenly distributed in the entrance of the microchannel and illustrate patterns of enriching, focusing, or size-selective profiles after passing through the grooved area. The preliminary simulation results also demonstrated that particles tend to bias towards the sidewall after flowing through the grooves.

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