A Micropump Driven by Marangoni Effect

2007 ◽  
Author(s):  
Kenji Sugimoto ◽  
Kaoru Iwamoto ◽  
Hiroshi Kawamura
Keyword(s):  
Flow Structure ◽  
Marangoni Number ◽  
Marangoni Effect ◽  
Surface Forces ◽  
Present Calculation ◽  
Central Field ◽  
Liquid Region ◽  
Liquid Interfaces ◽  
Thermocapillary Force ◽  
Driven System

A micropump driven by the thermocapillary convection is proposed. The purpose of this study is to elucidate the flow structure in liquid region and the effect of the geometry on the performance of the present micropump. There are two significant advantages in the thermocapillary-driven system. First, the surface forces become more dominant than the volume forces with decreasing scale. The present micropump driven by the surface forces shows an advantage in the micro scale over a diaphragm pump driven by the volume forces. Secondary, the thermocapillary driven system contains no movable parts; thus, it allows a very simple structure compared to the diaphragm one. In the present micropump system, a number of ribs are distributed along the flow circuit between a heater and a cooler (see Fig. A-1). An appropriate amount of gas is trapped between the ribs; the gas-liquid interfaces formed between the ribs are the source of the pumping power. Since heat transfer from these ribs to the working liquid imposes temperature gradients along the gas-liquid interfaces, the flow from the hot to the cold side is induced by the Marangoni effect. Fundamental characteristics of the present micropump are studied on the basis of three-dimensional simulation conducted taking the gas, liquid and ribs into account. Since the surface tension is controlled by the temperature of the ribs, the equations for liquid and gas phases are formulated by coupling them with the heat conduction equation for the ribs. The intensity of the flow induced by the thermocapillary force can be described by using the Marangoni number. In this study, the flow structure corresponding to the temperature field was observed (see Fig. A-2). Since the high temperature fluid is convected downstream, the temperature of the central liquid region exceeds the temperature of the ribs at the same streamwise position. Therefore, the flow from the central field to the ribs is induced by the Marangoni effect on the gas-liquid interfaces. The present calculation has revealed that the flow field exhibits a transition from steady flow to oscillatory flow when the Marangoni number exceeds a critical value of about 2,000 – 2,500. An experiment was also performed. The liquid flow driven by the present micropump system was confirmed through the experiment.

Role of Capillary and Thermocapillary Forces in Laser Polishing of Metals

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Chi Zhang ◽  
Jing Zhou ◽  
Hong Shen
Keyword(s):  
Capillary Force ◽  
Molten Pool ◽  
Continuous Wave ◽  
Flow Behavior ◽  
Marangoni Effect ◽  
Cost Effective ◽  
Underlying Mechanism ◽  
Thermocapillary Force ◽  
Laser Polishing ◽  
Coupled Heat Transfer

As one of emerging novel surface treatment techniques, laser polishing offers a cost-effective and efficient solution to reduce surface roughness of precision components at micro-/mesoscale. Although it has been applied for industrial and biomedical purposes, the underlying mechanism has not been fully revealed. This paper presents a study to understand the basic fundamentals of continuous wave fiber laser polishing of Ti6Al4V samples. A two-dimensional numerical model that coupled heat transfer and fluid flow is developed to illustrate the molten flow behavior. The roles of capillary and thermocapillary flow in the process of laser polishing are investigated to assist the understanding of the contributions of surface tension (capillary force) and Marangoni effect (thermocapillary force) in the polishing process. Capillary force dominates the molten pool at the initial stage of melting, while thermocapillary force becomes predominant when the molten pool fully develops.

Noncontact Bubble Manipulation in Microchannel by Using Photothermal Marangoni Effect

2009 ◽  
Author(s):  
Hiroyuki Takeuchi ◽  
Masahiro Motosuke ◽  
Shinji Honami
Keyword(s):  
Bubble Size ◽  
Channel Wall ◽  
Silicone Oil ◽  
Optical Power ◽  
Marangoni Effect ◽  
Scanning Speed ◽  
Surface Tension Gradient ◽  
Resistance Force ◽  
Fluid Viscosity ◽  
Thermocapillary Force

A novel method of noncontact bubble manipulation by optically-induced local surface tension gradient is described in this paper. In microfluidic devices, the effects of interfacial phenomena become dominant with decreasing of a length scale. An unexpected adhesion of a bubble on the channel wall is a serious problem which can cause the large pressure loss and the deterioration of the device. Thus, the removal or manipulation technique of the bubble is strongly required. In this study we controlled the thermocapillary force around the bubble by means of optical technique. The purpose of this study is the verification of the optical manipulation method of bubble. Particularly, the detail of migration process including the effect of bubble size, fluid viscosity and optical power is discussed. The manipulation experiments were conducted for the bubble with the diameter of 40 to 140 μm in a microchannel filled with silicone oil. An FEP (fluorinated ethylene propylene copolymer) tube with the inner diameter of 200 μm was used as the microchannel. The optical system for the heating is composed of a scanning setup and a compact laser diode. In this technique, two types of motion for the bubble transport are possible. One motion is the detachment of the bubble from the channel wall. When a laser beam is irradiated into the liquid in the vicinity of the bubble attached to the wall, the Marangoni convection is induced and the difference of pressure is generated around the bubble. The bubble is detached from the wall when the pressure difference overcomes the anchoring force between the bubble and the wall. Then, the bubble detached from the wall is suspended in the liquid at the balanced position between the thermocapillary and buoyancy force. This position can be controlled by adjusting the laser power. The other motion is the manipulation of the bubble along the channel. When the focal spot is scanned along the channel, it is possible to manipulate the bubble as if the bubble follows the light. In addition, the minimum optical power necessary to transport the bubble along the microchannel was measured. The minimum optical power strongly depends on bubble size, liquid viscosity, and scanning speed. These results show the relationship between the driving force induced by photothermal Marangoni effect and the resistance force related with the viscosity and the scanning speed.

scholarly journals Surface forces measurement for materials science

2019 ◽  
Vol 91 (4) ◽  
pp. 707-716 ◽  
Author(s):  
Kazue Kurihara
Keyword(s):  
Soft Matter ◽  
Materials Science ◽  
Resonance Method ◽  
Surface Force ◽  
Surface Forces ◽  
Liquid Interfaces ◽  
Science Field ◽  
Confined Liquids ◽  
History Of ◽  
Solid Liquid

Abstract This article reviews the surface forces measurement as a novel tool for materials science. The history of the measurement is briefly described in the Introduction. The general overview covers specific features of the surface forces measurement as a tool for studying the solid-liquid interface, confined liquids and soft matter. This measurement is a powerful way for understanding interaction forces, and for characterizing (sometime unknown) phenomena at solid-liquid interfaces and soft complex matters. The surface force apparatus (SFA) we developed for opaque samples can study not only opaque samples in various media, but also electrochemical processes under various electrochemical conditions. Electrochemical SFA enables us to determine the distribution of counterions between strongly bound ones in the Stern layer and those diffused in the Gouy-Chapman layer. The shear measurement is another active area of the SFA research. We introduced a resonance method, i.e. the resonance shear measurement (RSM), that is used to study the effective viscosity and lubricity of confined liquids in their thickness from μm to contact. Advantages of these measurements are discussed by describing examples of each measurement. These studies demonstrate how the forces measurement is used for characterizing solid-liquid interfaces, confined liquids and reveal unknown phenomena. The readers will be introduced to the broad applications of the forces measurement in the materials science field.

Scaling Thermocapillary Surface Velocity in Weld Pool

2011 ◽  
Author(s):  
P. S. Wei ◽  
C. L. Lin ◽  
C. N. Ting
Keyword(s):  
Prandtl Number ◽  
Low Power ◽  
Power Density ◽  
Marangoni Number ◽  
Surface Velocity ◽  
Beam Power ◽  
Scale Analysis ◽  
Free Surface Velocity ◽  
Thermocapillary Force ◽  
Beam Heating

In this study, the peak surface velocity driven by thermocapillary force in melting or welding pool irradiated by a distributed low-power-density beam is determined from a scale analysis. In view of different distances of diffusion between momentum and energy, the effects of Prandtl number on surface velocity are of interest. A low-power-density-beam heating implies no deep and narrow cavity (or keyhole) taking place in the pool. The results find that the peak surface velocity is proportional to the first power and 2/3 power of the surface tension coefficient or Marangoni number for high and low Prandtl number, respectively. The free surface velocity is determined by Prandtl and Marangoni numbers for given dimensionless beam power and Peclet numbers. The predictions agree with numerical computations.

Computer-Aided Development of Multicomponent Metallic Glasses

2002 ◽  
Vol 754 ◽  
Author(s):  
Akira Takeuchi ◽  
Akihisa Inoue
Keyword(s):  
Glass Transition ◽  
Metallic Glasses ◽  
Crystallization Temperature ◽  
Experimental Results ◽  
Heat Of Mixing ◽  
Present Calculation ◽  
Liquid Region ◽  
Thermodynamic Quantities ◽  
Calculation Methods ◽  
Binary Model

ABSTRACTAsynthesized calculation model for developing metallic glasses has been created by taking into account criteria for the achievement of high glass-forming ability (GFA) and viscosity. The model deals with amorphous-forming composition region (AFCR), crystallization temperature (Tx) and three GFA factors: critical cooling rate (Rc), reduced glass-transition temperature (Tg/Tm) and supercooled liquid region (ΔTx=Tx-Tg) where Tg and Tm are glass transition and melting temperature, respectively. The principle of the model is based on thermodynamic functions for multicomponent systems, i.e., mismatch entropy and mixing enthalpy which express the criteria in terms of the number of elements, atomic size differences and the heat of mixing. By combining these thermodynamic quantities with the Miedema's semi-empirical model, AFCR was calculated, and was compared with the experimental results. The GFA factors were also analyzed from viscosity. The Rc was derived from transformation diagram of metallic glasses for crystallization while ΔTx was calculated by solving a differential equation expressing the change in free volume with temperature. As a result of these analyses, Rc-Tg/Tm and R-ΔTx diagrams were found to fit with the experimental results qualitatively. Furthermore, crystallization temperature (Tx) was also calculated for multicomponent metallic glasses by the modification of the Miedema's binary model for the calculation of Tx. The reduced crystallization temperature (Tx/Tl), where Tl is liquidus temperature, was calculated for evaluating GFA of metallic glasses instead of Tg/Tm. Some of the calculation methods used in the present study have theadvantage giving results as a function of composition; thus, there exists possibility to lead to the prediction of glassy alloys compositions. In this sense, the present calculation methods are completely different to the current method for the development of new metallic glasses relying on the empirical criteria which suggest only appropriate systems and/or elements of the alloysfor the achievement of high GFA. In near future, this kind of calculation technique can be used for the prediction of optimal compositions of the metallic glasses with high GFA.

Experiments on Melting of Unfixed Ice in a Horizontal Cylindrical Capsule

1987 ◽  
Vol 109 (2) ◽  
pp. 454-459 ◽  
Author(s):  
B. W. Webb ◽  
M. K. Moallemi ◽  
R. Viskanta
Keyword(s):  
Natural Convection ◽  
Flow Structure ◽  
Close Contact ◽  
Flow Regimes ◽  
Melting Process ◽  
Contact Melting ◽  
Cylinder Wall ◽  
Liquid Region ◽  
Inversion Point ◽  
Heated Cylinder

Melting of unrestrained ice in a horizontal cylindrical capsule has been investigated experimentally to determine the interaction of fluid flow induced by motion of the solid and natural convection with density inversion of the water–ice system. During the melting process the ice is drawn by buoyancy to the top of the heated cylinder where close-contact melting occurs. Natural convection-dominated melting whose intensity depends on wall temperature prevails in the liquid region below. Three distinct flow regimes were identified for the cylinder wall temperatures of 3.5, 7, and 12° C studied. The flow structure for temperatures below the inversion point is similar to that for melting of unfixed n-heptadecane reported previously. Photographs of flow regimes are presented, and dependence of the solid–liquid interface morphology on the flow structure is discussed.

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