Numerical Study of Microchamber Filling in Centrifugal Microfluidics

2011 ◽  
Author(s):  
Nick Niedbalski ◽  
Seok-Won Kang ◽  
Debjyoti Banerjee
Keyword(s):  
Surface Tension ◽  
Numerical Model ◽  
Physical Properties ◽  
Thermal Cycle ◽  
Numerical Study ◽  
Method Comparison ◽  
Thermal Conditions ◽  
Microfluidic System ◽  
Working Fluid ◽  
Driving Mechanism

Numerical investigation of the transient, coupled hydrodynamic and thermal behavior of a novel polymerase chain reaction (PCR) centrifugal microfluidic system is presented in this study. The driving mechanism for flow within these devices is modeled as a combination of the capillary forces and rotationally induced pressure gradient working in opposition to viscous forces, which are functions of rotation speed and fluid properties. The physical properties of the working fluid are in turn functions of temperature, some of which can have significant variations over the operating temperature ranges of a PCR thermal cycle. The complex balance of viscous, capillary, and rotationally induced inertial forces are crucial factors in optimizing the design of such devices. Hence, the effects of temperature variation on the filling performance cannot be neglected. A commercial CFD code is utilized to simulate the filling of a microchamber when subjected to thermal conditions typical of a PCR thermal cycle. The numerical model accounts for the temperature dependence of the working fluid’s viscosity and surface tension by simultaneously solving the Navier-Stokes and energy equations. The free surface morphology (position, shape) and total chamber fill fraction as a function of time is predicted by using the volume of fluids (VOF) method. Comparison of the predictions from the temperature dependent numerical model to that which assume said physical properties to be constant, demonstrates the strong effect of the fluid’s viscosity and surface tension on the filling rate for various rotation speeds.

Numerical Simulation of Droplet Ejection Based on VOF Method

2014 ◽  
Vol 548-549 ◽  
pp. 1257-1264 ◽  
Author(s):  
Xiao Yong Suo
Keyword(s):  
Numerical Simulation ◽  
Surface Tension ◽  
Numerical Model ◽  
Physical Properties ◽  
Vof Method ◽  
Numerical Results ◽  
Droplet Ejection ◽  
Ejection Process ◽  
Ink Jet ◽  
Jet Nozzle

Taking ejection process of the ink droplets from ink-jet nozzle as the prototype, a similar numerical model of droplet ejection was established. The VOF method was applied to track the interface of droplet ejection process and it is shown that the numerical results simulated by the VOF method were accurate and reliable. Six kinds of liquid with different physical properties were chosen as the research object. The numerical results were analyzed and compared. Finally, the effect of the surface tension, viscosity and density on the droplet ejection process was discussed.

A Numerical Model of a Reciprocating-Mechanism Driven Heat Loop for Two-Phase High Heat Flux Cooling

2016 ◽  
Vol 8 (4) ◽  
Author(s):  
Olubunmi Popoola ◽  
Ayobami Bamgbade ◽  
Yiding Cao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Performance Optimization ◽  
Numerical Study ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
Transfer Device

An effective design option for a cooling system is to use a two-phase pumped cooling loop to simultaneously satisfy the temperature uniformity and high heat flux requirements. A reciprocating-mechanism driven heat loop (RMDHL) is a novel heat transfer device that could attain a high heat transfer rate through a reciprocating flow of the two-phase working fluid inside the heat transfer device. Although the device has been tested and validated experimentally, analytical or numerical study has not been undertaken to understand its working mechanism and provide guidance for the device design. The objective of this paper is to develop a numerical model for the RMDHL to predict its operational performance under different working conditions. The developed numerical model has been successfully validated by the existing experimental data and will provide a powerful tool for the design and performance optimization of future RMDHLs. The study also reveals that the maximum velocity in the flow occurs near the wall rather than at the center of the pipe, as in the case of unidirectional steady flow. This higher velocity near the wall may help to explain the enhanced heat transfer of an RMDHL.

scholarly journals DEVELOPMENT OF A NUMERICAL MODEL FOR THE STUDY OF AN OSCILLATING WATER COLUMN DEVICE CONSIDERING AN IMPULSE TURBINE

2019 ◽  
Vol 18 (1) ◽  
pp. 99
Author(s):  
A. L. dos Santos ◽  
L. A. Isoldi ◽  
L. A. O. Rocha ◽  
M. N. Gomes ◽  
R. S. Viera ◽  
...  
Keyword(s):  
Numerical Model ◽  
Energy Conversion ◽  
Water Column ◽  
Numerical Study ◽  
Velocity Ratio ◽  
Power Coefficient ◽  
Working Fluid ◽  
Speed Ratio ◽  
Oscillating Water Column ◽  
Impulse Turbine

The present work brings a numerical study of an energy conversion device which takes energy from the waves through an oscillating water column (OWC), considering an impulse turbine with rotation in the chimney region through the implementation of a movable mesh model. More precisely, a turbulent, transient and incompressible air flow is numerically simulated in a two-dimensional domain, which mimics an OWC device chamber. The objectives are the verification of the numerical model with movable mesh of the impulse turbine in the free domain from the comparison with the literature and, later, the study of the impulse turbine inserted in the geometry of the OWC device. In order to perform the numerical simulation on the generated domains, the Finite Volume Method (FVM) is used to solve the mass and momentum conservation equations. For the closure of the turbulence, the URANS (Unsteady Reynolds Averaged Navier-Stokes) model k-ω SST is used. To verify the numerical model employed, drag coefficients, lift, torque and power are obtained and compared with studies in the literature. The simulations are performed considering a flow with a Reynolds number of ReD = 867,000, air as the working fluid and a tip speed ratio of λ = 2. For the verification case, coefficients similar to those previously predicted in the literature were obtained. For the case where the OWC device was inserted it was possible to observe an intensification of the field of velocities in the turbine region, which led to an augmentation in the magnitude of all coefficients investigated (drag, lift, torque and power). For the case studied with the tip velocity ratio λ = 2, results indicated that power coefficient was augmented, indicating that the insertion of the turbine in a closed enclosure can benefit the energy conversion in an OWC device.

Thermal Performance of the U-Tube Solar Collector Using Computational Fluid Dynamics Simulation

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Rim Farjallah ◽  
Monia Chaabane ◽  
Hatem Mhiri ◽  
Philippe Bournot ◽  
Hatem Dhaouadi
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Numerical Model ◽  
Flow Rate ◽  
Solar Collector ◽  
Numerical Study ◽  
Numerical Results ◽  
Dynamics Simulation ◽  
Working Fluid ◽  
Discrete Ordinates

In this paper, we propose a numerical study of a tubular solar collector with a U-tube. A three-dimensional numerical model is developed. It was first used in order to study the efficiency of the solar collector and to evaluate the validity of the developed computational fluid dynamics (CFD) model by comparison with experimental results from the literature. For the numerical simulations, the turbulence and the radiation were, respectively, modeled using the standard k–ε model and the discrete ordinates (DO) model. This numerical model was then used to carry out a parametrical study and to discuss the effect of selected operating parameters such as the fluid mass flow rate, the absorber selectivity, and the material properties. Numerical results show that with the increase of the working fluid flow rate from 0.001 kg/s to 0.003 kg/s, the efficiency of the solar collector is improved (from 30% to 35%). Numerical results also show that the filled-type evacuated tube with graphite presents a best result in comparison with those found using the copper fin tube (η increases from 54% to 64%). Finally, we noted that the use of a high selective absorber surface adds to better performance in comparison with the black absorber tube. This is mainly due to the radiation losses reduction.

USAGE OF A DIATOMITE-CONTAINING NANOFLUID AS THE WORKING FLUID IN A WICKLESS LOOP HEAT PIPE: EXPERIMENTAL AND NUMERICAL STUDY

2018 ◽  
Vol 49 (17) ◽  
pp. 1721-1744 ◽  
Author(s):  
Adnan Sözen ◽  
Erdem Çiftçi ◽  
Selçuk Keçel ◽  
Metin Gürü ◽  
Halil Ibrahim Variyenli ◽  
...  
Keyword(s):  
Heat Pipe ◽  
Numerical Study ◽  
Working Fluid ◽  
Loop Heat Pipe

Real-time Red Blood Cell Counting and Osmolarity Analysis using a Photoacoustic-based Microfluidic System

Lab on a Chip ◽  
2021 ◽  
Author(s):  
Wenxiu Zhao ◽  
Haibo Yu ◽  
Yangdong Wen ◽  
Hao Luo ◽  
Boliang Jia ◽  
...  
Keyword(s):  
Blood Cell ◽  
Physical Properties ◽  
Red Blood Cell ◽  
Blood Cells ◽  
Diagnostic Procedure ◽  
Microfluidic System ◽  
Cell Counting ◽  
Blood Samples ◽  
System P ◽  
Blood Cell Counting

Counting the number of red blood cells (RBCs) in blood samples is a common clinical diagnostic procedure, but conventional methods are unable to provide the size and other physical properties...

scholarly journals Numerical Analysis of Air Vortex Interaction with Porous Screen

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 70
Author(s):  
Xudong An ◽  
Lin Jiang ◽  
Fatemeh Hassanipour
Keyword(s):  
Physical Properties ◽  
Vortex Ring ◽  
Numerical Study ◽  
Flow Behavior ◽  
Industrial Applications ◽  
Moving Mesh ◽  
Vortex Flows ◽  
Vortex Interaction ◽  
Piston Cylinder ◽  
Porous Screen

In many industrial applications, a permeable mesh (porous screen) is used to control the unsteady (most commonly vortex) flows. Vortex flows are known to display intriguing behavior while propagating through porous screens. This numerical study aims to investigate the effects of physical properties such as porosity, Reynolds number, inlet flow dimension, and distance to the screen on the flow behavior. The simulation model includes a piston-cylinder vortex ring generator and a permeable mesh constructed by evenly arranged rods. Two methods of user-defined function and moving mesh have been applied to model the vortex ring generation. The results show the formation, evolution, and characteristics of the vortical rings under various conditions. The results for vorticity contours and the kinetic energy dissipation indicate that the physical properties alter the flow behavior in various ways while propagating through the porous screens. The numerical model, cross-validated with the experimental results, provides a better understanding of the fluid–solid interactions of vortex flows and porous screens.

scholarly journals Pool Boiling of Nanofluids on Biphilic Surfaces: An Experimental and Numerical Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 125
Author(s):  
Eduardo Freitas ◽  
Pedro Pontes ◽  
Ricardo Cautela ◽  
Vaibhav Bahadur ◽  
João Miranda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Heat Dissipation ◽  
Numerical Study ◽  
Pool Boiling ◽  
Temperature Drop ◽  
Surface Cooling ◽  
Average Temperature ◽  
Gold Silver

This study addresses the combination of customized surface modification with the use of nanofluids, to infer on its potential to enhance pool-boiling heat transfer. Hydrophilic surfaces patterned with superhydrophobic regions were developed and used as surface interfaces with different nanofluids (water with gold, silver, aluminum and alumina nanoparticles), in order to evaluate the effect of the nature and concentration of the nanoparticles in bubble dynamics and consequently in heat transfer processes. The main qualitative and quantitative analysis was based on extensive post-processing of synchronized high-speed and thermographic images. To study the nucleation of a single bubble in pool boiling condition, a numerical model was also implemented. The results show an evident benefit of using biphilic patterns with well-established distances between the superhydrophobic regions. This can be observed in the resulting plot of the dissipated heat flux for a biphilic pattern with seven superhydrophobic spots, δ = 1/d and an imposed heat flux of 2132 w/m2. In this case, the dissipated heat flux is almost constant (except in the instant t* ≈ 0.9 when it reaches a peak of 2400 W/m2), whilst when using only a single superhydrophobic spot, where the heat flux dissipation reaches the maximum shortly after the detachment of the bubble, dropping continuously until a new necking phase starts. The biphilic patterns also allow a controlled bubble coalescence, which promotes fluid convection at the hydrophilic spacing between the superhydrophobic regions, which clearly contributes to cool down the surface. This effect is noticeable in the case of employing the Ag 1 wt% nanofluid, with an imposed heat flux of 2132 W/m2, where the coalescence of the drops promotes a surface cooling, identified by a temperature drop of 0.7 °C in the hydrophilic areas. Those areas have an average temperature of 101.8 °C, whilst the average temperature of the superhydrophobic spots at coalescence time is of 102.9 °C. For low concentrations as the ones used in this work, the effect of the nanofluids was observed to play a minor role. This can be observed on the slight discrepancy of the heat dissipation decay that occurred in the necking stage of the bubbles for nanofluids with the same kind of nanoparticles and different concentration. For the Au 0.1 wt% nanofluid, a heat dissipation decay of 350 W/m2 was reported, whilst for the Au 0.5 wt% nanofluid, the same decay was only of 280 W/m2. The results of the numerical model concerning velocity fields indicated a sudden acceleration at the bubble detachment, as can be qualitatively analyzed in the thermographic images obtained in this work. Additionally, the temperature fields of the analyzed region present the same tendency as the experimental results.

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