Numerical simulation and experiment of droplet formation in circular cross-section micro-channels

2019 ◽  
Vol 33 (18) ◽  
pp. 1950200
Author(s):  
Hongcheng Wang ◽  
Chengxin Tang ◽  
Miaomiao Zhao ◽  
Liqun Wu ◽  
Baohua Yu
Keyword(s):  
Interfacial Tension ◽  
Cross Section ◽  
Droplet Size ◽  
Flow Rate ◽  
Microfluidic Chip ◽  
Capillary Number ◽  
Circular Cross Section ◽  
Continuous Phase ◽  
Micro Channel ◽  
Micro Channels

In recent decades, microfluidics in biological applications have experienced significant growth due to their advantages of small volume, low cost, short reaction time and high throughput. Almost all cross-section shapes of micro-channels in microfluidic chips are rectangular or triangular by the existing chip fabricating technologies, including hot embossing, lithography, etching and injection molding, etc. However, compared with the above micro-channel shapes, the circular one has the advantages in aspects of fluid flow, droplet generating, heat transfer and its replication for blood vessels. This paper presents a T-junction droplet microfluidic chip with circular cross-section micro-channels. The effect of micro-channel wettability, interfacial tension, velocity and flow rate of continuous phase on droplet size are simulated and mechanism of droplets generating process is explored. Comparing with continuous phase viscosity and interfacial tension, flow rate plays a decisive role in determining the droplet size which is in the range of 100–350 [Formula: see text]m according to the simulation result. The Capillary number is affected by the above three parameters and an estimating numerical method for generated droplet size was proposed according to the above simulation results and calculated by Capillary number. The droplets, the sizes of which were in the range of 20–400 [Formula: see text]m, were produced by varying the parameters of water and oil flow rates in the designed T-junction droplet microfluidic chip with circular cross-section micro-channels.

Fabrication of sandwich-like microfluidic chip with circular cross-section micro-channels

2018 ◽  
Vol 32 (26) ◽  
pp. 1850288 ◽  
Author(s):  
Hong Cheng Wang ◽  
Miao Miao Zhao ◽  
Li Qun Wu
Keyword(s):  
Cross Section ◽  
Microfluidic Chip ◽  
Low Cost ◽  
Circular Cross Section ◽  
Middle Layer ◽  
Channel Cross Section ◽  
Heating Process ◽  
Micro Channel ◽  
Micro Channels ◽  
Glass Capillaries

In microfluidic chips, most micro-channel cross-section shapes are rectangular or triangular in existing chip fabricating technologies, including hot embossing, lithography, etching, injection molding, etc. However, compared with the above micro-channel shapes, a circular shape has advantages in aspects of fluid flow, droplet generation, heat transfer and blood vessel replication. This paper presents a sandwich-like microfluidic chip with circular cross-section micro-channels. The sandwich-like structure includes three layers. The top and bottom layers are PDMS material while the middle layer is composed of micron glass capillaries (used as micro-channels) with circular cross-sections. The glass capillaries are made of borosilicate tube by a glass heating process. Sphere shaped paraffin wax is used as a sacrificial material to form micro-channel junctions. To test the functions of the fabricated micro sandwich-like microfluidic chip, a droplet generating experiment was conducted in the T-junction chip. The droplet size can be controlled in the range of 20–400 [Formula: see text]m by varying the water and oil flow rates. This proposed microfluidic chip structure has the advantages of short processing cycle, low cost and small flow resistance.

scholarly journals Lattice Boltzmann Simulation of Droplet Generation in a Microfluidic Cross-Junction

2011 ◽  
Vol 9 (5) ◽  
pp. 1235-1256 ◽  
Author(s):  
Haihu Liu ◽  
Yonghao Zhang
Keyword(s):  
Droplet Size ◽  
Flow Rate ◽  
Lattice Boltzmann ◽  
Capillary Number ◽  
Rate Ratio ◽  
Viscosity Ratio ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Viscous Force ◽  
Flow Rate Ratio

AbstractUsing the lattice Boltzmann multiphase model, numerical simulations have been performed to understand the dynamics of droplet formation in a microfluidic cross-junction. The influence of capillary number, flow rate ratio, viscosity ratio, and viscosity of the continuous phase on droplet formation has been systematically studied over a wide range of capillary numbers. Two different regimes, namely the squeezinglike regime and the dripping regime, are clearly identified with the transition occurring at a critical capillary number Cacr. Generally, large flow rate ratio is expected to produce big droplets, while increasing capillary number will reduce droplet size. In the squeezing-like regime (Ca ≤ Cacr), droplet breakup process is dominated by the squeezing pressure and the viscous force; while in the dripping regime (Ca ≤ Cacr), the viscous force is dominant and the droplet size becomes independent of the flow rate ratio as the capillary number increases. In addition, the droplet size weakly depends on the viscosity ratio in both regimes and decreases when the viscosity of the continuous phase increases. Finally, a scaling law is established to predict the droplet size.

An Investigation on Micro Slip Flows in Micro Channels

2010 ◽  
Author(s):  
Gh. Reza Salehi ◽  
Masoud JalaliBidgoli ◽  
Saeed ZeinaliDanaloo ◽  
Kazem HasanZadeh
Keyword(s):  
Flow Rate ◽  
Pressure Ratio ◽  
Slip Flow ◽  
Accommodation Coefficient ◽  
Flow Rate Ratio ◽  
Numerical Representation ◽  
Micro Channel ◽  
Parallel Plates ◽  
Dimensionless Numbers ◽  
Micro Channels

In this paper, distributions of velocity and flow rate of micro channels are studied. Moreover, the parameters which influence them were also discussed, as well as their effects and relevant curves. In the Analytical study, the governing equation in specific micro flows is obtained. This equation is specifically investigated for slip flow in two micro parallel plates (micro channel).At the next step numerical representation shows the influence of the related parameters in micro channel flow such as Knudsen number, thermal -accommodation coefficient, mass flow rate ratio and pressure ratio (outlet to inlet), Tangential Momentum Accommodation Coefficient with relative curves, and flow rate distribution in slippery state to no slip state has been compared as the another part of this solution. Finally, the results of investigating parameters and dimensionless numbers in micro channels are reviewed.

Integrated Micro-Channel Cooling in Industrial Applications

2004 ◽  
Author(s):  
C. C. S. Nicole ◽  
R. Dekker ◽  
A. Aubry ◽  
R. Pijnenburg
Keyword(s):  
Forced Convection ◽  
Flow Rate ◽  
Single Phase ◽  
Industrial Applications ◽  
Experimental Results ◽  
Junction Temperature ◽  
Micro Channel ◽  
Cooling Device ◽  
Micro Channels ◽  
Cooling Of Electronics

Experiments and simulations have been performed in order to assess the feasibility of integrated single phase forced convection in silicon micro-channels for the cooling of electronics. A silicon micro-channel device has been fabricated with channel size of 100 by 300 μm. Cooling has been achieved with a heater dissipating up to 370 W (750 W/cm2) with a flow rate of 0.1 1/min. In this case the maximum junction temperature was 130°C. This paper presents characteristics of such a cooling device as well as its description and fabrication. Experimental results are shown and compared with simulations. A description of a rough optimization of the channels size is given followed by comments describing the main advantages and drawbacks regarding industrial feasibility.

Unsteady Laminar Duct Flow With a Given Volume Flow Rate Variation

1999 ◽  
Vol 67 (2) ◽  
pp. 274-281 ◽  
Author(s):  
D. Das ◽  
J. H. Arakeri
Keyword(s):  
Cross Section ◽  
Flow Rate ◽  
Volume Flow Rate ◽  
Circular Cross Section ◽  
Volume Flow ◽  
Rate Variation ◽  
Two Dimensional ◽  
Duct Flow ◽  
Fully Developed Flow ◽  
Gradient Variation

In this paper we give a procedure to obtain analytical solutions for unsteady laminar flow in an infinitely long pipe with circular cross section, and in an infinitely long two-dimensional channel, created by an arbitrary but given volume flow rate with time. In the literature, solutions have been reported when the pressure gradient variation with time is prescribed but not when the volume flow rate variation is. We present some examples: (a) the flow rate has a trapezoidal variation with time, (b) impulsively started flow, (c) fully developed flow in a pipe is impulsively blocked, and (d) starting from rest the volume flow rate oscillates sinusoidally. [S0021-8936(00)01702-5]

Optimization of Micro Channel Morphology

2006 ◽  
Author(s):  
Aleksander Vadnjal ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Media ◽  
Cross Section ◽  
Channel Morphology ◽  
Channel Cross Section ◽  
Micro Channel ◽  
Parallel Plates ◽  
Conservation Of Energy ◽  
Micro Channels

An increasing demand for a higher heat flux removal capability within a smaller volume for high power electronics led us to focus on micro channels in contrast to the classical heat fin design. A micro channel can have various shapes to enhance heat transfer, but the shape that will lead to a higher heat flux removal with a moderate pumping power needs to be determined. The standard micro-channel terminology is usually used for channels with a simple cross section, e.g. square, round, triangle, etc., but here the micro channel cross section is going to be expanded to describe more complicated and interconnected micro scale channel cross sections. The micro channel geometries explored are pin fins (in-line and staggered), parallel plates and sintered porous micro channels (see Fig.1). The problem solved here is a conjugate problem involving two heat transfer mechanisms; 1) porous media effective conductivity and 2) internal convective heat transfer coefficient. Volume averaging theory (VAT) is used to rigorously cast the point wise conservation of energy, momentum and mass equations into a form that represents the thermal and hydraulic properties of the micro channel (porous media) morphology. Using the resulting VAT based field equations, optimization of a micro channel heated from one side is used to determine the optimum micro channel morphology. A small square of 1 cm 2 is chosen as an example and the thermal resistance, 0C/W, and pressure drop are shown as a function of Reynolds number.

scholarly journals Drop formation in microfluidic cross-junction: jetting to dripping to jetting transition

2019 ◽  
Vol 23 (8) ◽  
Author(s):  
Nina M. Kovalchuk ◽  
Masanobu Sagisaka ◽  
Kasparas Steponavicius ◽  
Daniele Vigolo ◽  
Mark J. H. Simmons
Keyword(s):  
Interfacial Tension ◽  
Capillary Number ◽  
Continuous Phase ◽  
Flow Rate Ratio ◽  
Dispersed Phase ◽  
Flow Focusing ◽  
Jet Formation ◽  
Relative Contribution ◽  
Power Law Function ◽  
Dispersed Phases

AbstractThe regimes of drop generation were studied in a Dolomite microfluidic device which combined both hydrodynamic and geometrical flow focusing over a broad range of flow rates. A series of aqueous dispersed phases were used with a viscosity ratio between continuous and dispersed phases of close to unity. Surfactants were added to alter the interfacial tension. It was shown that the transition from dripping to jetting is well described by the capillary numbers of both the dispersed and continuous phases. Only the jetting regime was observed if the capillary number of the dispersed phase was above a critical value, whereas at smaller values of this parameter a jetting → dripping → jetting transition was observed by increasing the capillary number of the continuous phase. The analysis performed has shown that the conditions for a dripping to jetting transition at moderate and large values of the capillary number of the continuous phase can be predicted theoretically by comparison of the characteristic time scales for drop pinch-off and jet growth, whereas the transition at small values cannot. It is suggested that this transition is geometry mediated and is a result of the interplay of jet confinement in the focusing part and a decrease of confinement following entry into the main channel. The flow fields inside the jet of the dispersed phase were qualitatively different for small and large values of the capillary number of the continuous phase revealing the relative contribution of the dispersed phase flow in jet formation. The volume of the drops formed in the jetting regime increased as a power law function of the flow rate ratio of the dispersed to continuous phase, independent of the interfacial tension.

Parametric Study of Droplet Formation and Characteristics Within Microfluidic Devices — A Case Study

2020 ◽  
Vol 12 (07) ◽  
pp. 2050077
Author(s):  
Seyedeh Sarah Salehi ◽  
Amir Shamloo ◽  
Siamak Kazemzadeh Hannani
Keyword(s):  
Interfacial Tension ◽  
Physical Properties ◽  
Flow Rate ◽  
Viscosity Ratio ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Phase Flow ◽  
Phase Density ◽  
Size And Shape ◽  
The Impact

Droplet-based microfluidics technologies hold great attention in a wide range of applications, including chemical analysis, drug screening, and food industries. This work aimed to describe the effects of different physical properties of the two immiscible phases on droplet formation in a flow-focusing microfluidic device and determining proper flow rates to form a droplet within the desired size range. A numerical model was developed to solve the governing equations of two-phase flow and the results were validated with previous experimental results. The results demonstrate different types of droplet formation regimes from dripping to jetting and different production rates of droplets as a consequence of the impact of each property on fluid flow, including the viscosity ratio, density, interfacial tension, and the flow rate ratio. Based on the results, flow rate, viscosity, and interfacial tension strongly affect the droplet formation regime as well as its size and shape. Droplet diameter increases by increasing the dispersed to continuous phase flow rate as well as the interfacial tension while it decreases by increasing the viscosity ratio and the continuous phase density. Moreover, the formation of satellite droplets was modeled, and the effect of interfacial tension, the viscosity of the dispersed phase and the continuous phase density were found to be important on the conditions that the satellite droplets are suppressed. Since the formation of the satellite droplets induces polydispersity in droplet size, this phenomenon is avoided. Collectively, choosing appropriate aqueous and oil phases with proper physical properties is crucial in forming monodisperse droplets with defined size and shape.

Numerical Study on Bubble Formation in a Microchannel Flow-Focusing Device Using the VOF Method

2011 ◽  
Author(s):  
Shobeir Aliasghar Zadeh ◽  
Rolf Radespiel
Keyword(s):  
Surface Tension ◽  
Disperse Phase ◽  
Flow Rate ◽  
Capillary Number ◽  
Bubble Formation ◽  
Continuous Phase ◽  
Glycerol Solution ◽  
Flow Focusing ◽  
Injection Angle ◽  
Bubble Length

The liquid-gas two-phase flow in a flow-focusing device are numerically investigated and the results are compared with experimental data. The geometries and the structured meshes were generated using the Gridgen software, while the computations were conducted with Fluent. N2 (disperse phase) and Water-Glycerol solution (continuous phase) at standard atmospheric conditions are considered as fluids. Based on dimensional analysis, the effects of various parameters such as the flow rates of both phases (effect of CQ = Qd/Qc), the viscosities of both phases (effect of the respective Reynolds number Re), the surface tension (effect of the capillary number) and the geometrical properties of the channel (channel width W and injection angle β) on the bubble formation and its length are compared to available experimental results. The break-up mechanism of the bubbles in various capillary regimes is explained. The computed length of the generated bubbles as a function of the capillary number (varying the flow rate of the continuous phase) are in good agreement with the experiments. Further studies indicate that at a constant flow rate of the continuous phase, the bubble length rises strongly as the flow rate of the disperse phase increases. In contrast, the relative effects of the viscosity and the surface tension on the length of the bubbles are moderate. The numerical results using various injection angles show that the bubble length increases, as the injection angle is raised from β = 45° to β = 90°.

SIMULATIONS OF DROPLET FORMATION IN A T-JUNCTION MICRO-CHANNEL USING THE PHASE FIELD METHOD

2014 ◽  
Vol 11 (04) ◽  
pp. 1350096 ◽  
Author(s):  
L. L. WANG ◽  
G. J. LI ◽  
H. TIAN ◽  
Y. H. YE
Keyword(s):  
Contact Angle ◽  
Flow Rate ◽  
Capillary Number ◽  
Rate Ratio ◽  
Droplet Formation ◽  
Field Method ◽  
Leakage Rate ◽  
Phase Field Method ◽  
Flow Rate Ratio ◽  
Micro Channel

Micro-fabrication techniques are developed rapidly because they offer numerous benefits for chemical and biological industries. Numerical simulations (based on incompressible Navier–Stokes equations) are presented of the two-phase flow in a cross-flowing T-junction micro-channel using the phase field method and the results are in agreement with experimental measurements. The leakage rate in the gap between the droplet and lower wall decreases during the droplet formation, the relationship between the leakage rate and the derivative of the up-stream droplet size is obtained, which is applicable when the droplet contacts with the lower wall on the wetted conditions or expands to the up-stream in the main channel. The droplet formation is related to several factors, including the capillary number, the contact angle, the flow rate ratio, and the micro-channel shape. The critical capillary number could distinguish between the squeezing and dripping regimes for the generation of different kinds of droplets. The simulations show that the critical capillary number is 0.012. Influence of those factors on the droplet length is related to the leakage rate. The leakage rate of the continuous phase decreases slowly as the flow rate ratio decreases or contact angle increases. In the squeezing regime, the leakage rate is weakly influenced by the contact angle at the small flow rate ratio and is different in three type micro-channels, the droplet length increases with the increase in contact angle which intensifies growth at the big flow rate ratio, and the longest droplet is obtained in the Y-junction micro-channel. In the dripping regime, at the big flow rate ratio the leakage rate is almost independent to the contact angle and micro-channel shape, and the droplet length also is same.

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