Microchannels for applications in liquid dosing and flow-rate measurement (original) (raw)
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Journal of Micromechanics and Microengineering, 2003
Experimental observations of liquid microchannel flows are reviewed and results of computer experiments concerning channel entrance, wall slip, non-Newtonian fluid, surface roughness, viscous dissipation and turbulence effects on the friction factor are discussed. The experimental findings are classified into three groups. Group I emphasizes 'flow instabilities' and group II points out 'viscosity changes' as the causes of deviations from the conventional flow theory for macrochannels. Group III caters to studies that did not detect any measurable differences between micro- and macroscale fluid flow behaviors. Based on numerical friction factor analyses, the entrance effect should be taken into account for any microfluidic system. It is a function of channel length, aspect ratio and the Reynolds number. Non-Newtonian fluid flow effects are expected to be important for polymeric liquids and particle suspension flows. The wall slip effect is negligible for liquid flows in microconduits. Significant surface roughness effects are a function of the Darcy number, the Reynolds number and cross-sectional configurations. For relatively low Reynolds numbers, Re < 2000, onset to turbulence has to be considered important because of possible geometric non-uniformities, e.g., a contraction and/or bend at the inlet to the microchannel. Channel-size effect on viscous dissipation turns out to be important for conduits with Dh < 100 µm.
Pressure drop measurements in a microchannel
AIChE Journal, 2000
Recent de®elopments in micro-energy and micro-chemical systems ha®e produced a need for greater understanding of flow in small channels. Se®eral recent studies of friction factors and transition Reynolds numbers in rectangular microchannels ha®e produced results that differ from classical theory. In this work, friction factors and laminar flow friction constants were determined for water flowing in high aspect ratio channels with depths ranging from 128 to 521 m. Reynolds numbers were between 60 and 3,450. Pressure drops were measured within the channel itself to exclude entrance and exit losses. Transitions to turbulence were obser®ed with flow ®isualization. Uncertainties in measured ®ariables were quantified and propagated into the estimated friction constants. Friction factors were also determined in a 1,050-m-deep channel that ser®ed as a control. After considering experimental uncertainties and systematic errors, significant differences remained between the results and classical theory.
Μpiv Measurement and Numerical Computation of the Velocity Profiles in Microchannels
scientificbulletin.upb.ro
Lucrarea de faţă prezintă rezultatele obţinute în urma studiilor numerice şi experimentale dedicate măsurării şi modelării profilurilor de viteze în micro-canale, atât pentru fluide pur vâscoase newtoniene cât şi pentru fluidele complexe ce prezintă un caracter pseudoplastic. Cinematica mişcărilor studiate în microbifurcaţii tip Y este determinată cu ajutorul unui sistem micro-PIV, simulările corespunzătoare fiind realizate cu ajutorul codului FLUENT. Soluţiile numerice în configuraţii 3D, confirmate calitativ şi cantitativ de măsurătorile experimentale, permit extinderea studiului în aplicaţii specifice micro-fluidicii: amestecul fluidelor imiscibile, analiza fenomenului de difuzie, transportul fluidelor bifazice. The present paper is dedicated to the experimental investigations and numerical simulations of the velocity distributions in micro-channels geometry, for pure viscous Newtonian fluids and complex fluids characterized by the shear thinning behavior. The steady flow kinematics in Y-micro-bifurcation is determined with a micro-PIV measurement system, the simulations being performed with the FLUENT commercial code. Numerical solutions obtained in 3D configurations, validated from qualitative and quantitative by experiments, can be extended to more complex specific micro-fluidics applications: mixing of immiscible fluids, analysis of diffusion process, transport of biphasic fluids.
Development of an Experimental Facility for Investigating Single-Phase Liquid Flow in Microchannels
Heat Transfer Engineering, 2006
An experimental facility has been developed to investigate single-phase liquid heat transfer and pressure drop in a variety of microchannel geometries. The facility is capable of accurately measuring the fluid temperatures, heater surface temperatures, heat transfer rates, and differential pressure in a test section. A microchannel test section with a silicon substrate is used to demonstrate the capability of the experimental facility. A copper resistor is fabricated on the backside of the silicon to provide heat input. Several other small copper resistors are used with a four-point measurement technique to acquire the heater temperature and calculate surface temperatures. A transparent pyrex cover is bonded to the chip to form the microchannel flow passages. The details of the experimental facility are presented here. The experimental facility is intended to support the collection of fundamental data in microchannel flows. It has the capability of optical visualization using a traditional microscope to see dyes and particles. It is also capable of performing micro-particle image velocimetry in the microchannels to detect the flow field occurring in the microchannel geometries. The experimental uncertainties have been carefully evaluated in selecting the equipment used in the experimental facility. The thermohydraulic performance of microchannels will be studied as a function of channel geometry, heat flux, and liquid flow rate. Some preliminary results for a test section with a channel width of 100 micrometers, a depth of 200 micrometers, and a fin thickness of 40 micrometers are presented.
Study of blood flow behaviour in microchannels
2008
Microfluidic (also known as lab-on-a-chip) devices offer the capability of manipulating very low volumes of fluids (of the order of micro litres) for several applications including medical diagnostics. This property makes microfluidic devices very attractive when the fluid, such as blood, has a limited supply because the patients cannot easily and frequently provide a large sample. This is typically the case for aged, diseased patients that do require frequent sampling during acute care or of older people that have the option of being treated and cared for at home [1]. Prototype lab-on-a-chip devices for medical diagnostics comprise a number of elements which separately perform different functions within the system. Activity within the research community is focusing on the better integration of device functionalities with the long term goal of creating fully integrated, portable, affordable clinical devices. However, engineering these solutions for the large volume production of lab...
Sensors and Actuators A: Physical, 2003
A rectangular straight microchannel was fabricated with dimensions of 57 mm H Â 200 mm W Â 48,050 mm (L), in which the resistance temperature detectors (RTDs) were integrated on the inner surface of the channel wall to measure the temperatures of the¯uid more accurately. Platinum (Pt) was used as RTD material. The values of the temperature coef®cient of resistance (TCR) of the fabricated Pt-RTDs without annealing ranged about 2800±2900 ppm/8C and the variation of the TCR values in the range of 0±110 8C was less than 2%. A microheater was also installed at the outlet/inlet of the channel to generate the heat¯ux. Effects of the temperature-dependent properties on the laminar¯ow characteristics in the microchannel were investigated experimentally using the fabricated microchannel device. DI water was used as the working¯uid. The pressure drop was measured as the mass¯ow rate and the applied heating power were increased. The microparticle image velocimetry (micro-PIV) was used to measure the detailed velocity ®elds along the microchannel having various wall temperatures. The pressure drop and micro-PIV measurements revealed that the variation of the¯uid properties along the microchannel has a signi®cant effect on the¯ow resistance but not a considerable effect on the velocity pro®le. Also, the measured¯ow resistance and velocity ®eld showed a high degree of consistency with those estimated by the macro-laminar¯ow theory under our experimental conditions. The proposed microchannel device is expected to be useful in the ®eld of micro¯uidics. #
Parametric Analysis of Flow through Microchannels
International Journal of Science and Research (IJSR), 2016
This paper attempts to provide the extensive discussions based on the experimental work performed on a microchannel heat exchanger setup. The discussion begins with the description of the experimental setup and the requisite procedure which is followed by the results obtained during the course of work. The paper signifies the various conditions which somehow affect the flow and heat transfer characteristics in microchannels. The application of fluid flow in microchannels is used for thermal management in the various fields which include biotechnology, aerospace, mechatronics, and microelectronic devices. It is expected that the work provided in this paper will help the reader to analyse the practical design problems, where these results can be applied. Moreover, the information provided would be useful and of interest to the readers in this new domain.
Experimental Study on Liquid Film Thickness of Annular Flow in Microchannels
2014
Many studies were carried out to investigate the flow and heat transfer characteristics of two-phase flow in microchannels because of its advantage in improving heat exchange performance, it has been well revealed that liquid film thickness and flow pattern play important roles in determining the heat transfer characteristics. However, these data is still limited to understanding properties of two-phase flow in microchannels because both the effect of tube size, geometry and physical property of working fluids have be taken into account. In this study, visual observation of flow pattern by using a high-speed camera and direct measurement of liquid film thickness by using a laser displacement meter for annular flow inside microchannels with inner diameter of 0.5 mm, 1 mm and 2 mm were conducted. 5 fluids with different surface tension and viscosity (water, ethanol, FC72, KF-96L-0.65cs, KF-96L-2cs) were selected to investigate the effect of physical properties on the flow pattern and liquid film thickness. Experimental results were compared with numerical simulation model results to provide better understanding of two phase flow and heat transfer characteristics at various tube scales and working fluid physical properties.