Pressure drop measurements in a microchannel (original) (raw)
Related papers
Single-phase liquid friction factors in microchannels
International Journal of Thermal Sciences, 2006
The validity of friction factor theory based upon conventional sized passages for microchannel flows is still an active area of research. Several researchers have reported significant deviation from predicted values, while others have reported general agreement. The discrepancies in literature need to be addressed in order to generate a set of design equations to predict the pressure drop occurring in microchannel flow devices.
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.
Single phase pressure drop in microchannels
International Journal of Heat and Fluid Flow, 2007
This article focuses on investigating fully developed liquid and vapor flow through rectangular microchannels with hydraulic diameters varying from 69.5 to 304.7 lm and with aspect ratios changing from 0.09 to 0.24. R134a liquid and vapor were used as the testing fluids. During the experiments, the Reynolds numbers were varied between 112 and 9180. Pressure drop data are used to characterize the friction factor in the laminar region, the transition region and the turbulent region. When the channel surface roughness was low, both the laminar friction factor and the critical Reynolds number approached the conventional values, even for the smallest channel tested. Hence, there was no indication of deviation from the Navier-Stokes flow theory for rectangular microchannels. The friction factor data in the turbulent region were larger than the predictions from the [Churchill, S.W., 1977, Friction factor equations spans all fluid-flow regimes, Chemical Engineering 45, 91-92] equation for smooth tubes, even for the smoothest channel tested (R a /D h = 0.14%). In addition, it was likely that surface roughness was responsible for higher laminar flow friction and earlier transition to turbulent flow in one of the channels tested.
Experimental characterization of water flow through smooth rectangular microchannels
Physics of Fluids, 2005
This article presents experimental results obtained in water flows through smooth rectangular microchannels. The experimental setup used in the present study enabled the investigation of both very small length scales ͑21-4.5 m͒ and a wide range of Reynolds numbers ͑0.1-300͒. The evolution of the friction coefficient was inferred from pressure drop versus flow-rate measurements for two types of water with different electrical conductivities. The channels were made of a silicon engraved substrate anodically bonded to a Pyrex cover. In these structures, pressure losses were measured internally with micromachined C u-N i strain gauges. When compared to macroscale correlations, the results demonstrate that in smooth silicon-Pyrex microchannels larger than 4 m in height, the friction law is correctly predicted by the Navier-Stokes equations with the classical no-slip boundary conditions, regardless of the water electrical conductivity ͑Ͼ0.1 S cm −1 ͒.
Single phase flow characteristics in rectangular microchannel: entrance length and friction factor
International Journal of Innovation and Applied Studies, 2014
A three-dimensional model with the COMSOL Multiphysics software was used to simulate the flow behavior in straight rectangular microchannels of 500µm width, 100µm depth and 30mm length. The model uses the Navier-Stokes equations with no slip velocity at the wall boundary condition. The influences of structural parameters on velocity distribution, entrance length and pressure drop among microchannels were analyzed. The numerical simulations are done with a variation of hydraulic diameter, aspect ratio on a wide range of the Reynolds number (Re). The simulation results showed that geometric parameters have an effect on the velocity distribution in rectangular microchannels and it agreed well the he Poiseuille laminar flow theory. Decreasing the hydraulic diameter and aspect ratio accelerate the fully development condition; in addition, the Re increase causes to postpone the flow development. For the friction factor in rectangular can be determined by the classic correlations. But, the variation of the normalized friction factor shows that the transition to turbulent flow occurs at low Reynolds.
SpringerReference, 2011
Fluid mechanics in small channels, i.e. channels of micrometer size, is dominated by surface effects and often exhibits striking differences of flow characteristics when compared with macro scale. One of important microfluidic problems is flow destabilization and occurrence laminarturbulent transition. In this paper we describe our experimental and numerical attempts to understand growth of flow instabilities and development of turbulent structures in small channels. In the first configuration flow of water through 1mm long and 0.4mm high microchannel formed between two planes is investigated varying Reynolds number from 1000 to 6770. Fluorescent traces are used for flow visualization and microPIV acquisition of temporary velocity fields. The microPIV data are used to evaluate turbulent flow characteristics. Our experimental study shows that destabilization of flow in such a micro-channel does not necessarily occurs when it is usually expected. Nearly laminar flow structure is present within the channel even for the highest investigated flow Reynolds number. These findings are confirmed by numerical simulation performed using finite volume code. On the other hand it appears possible to achieve unstable flow pattern even for quite low Reynolds number flow regime by proper modification of the channel walls. In the second experimental and numerical study we demonstrate that appropriately chosen wall waviness of the micro-channel may lead to flow destabilization already at quite low flow Reynolds number (~100).
Characterization of frictional pressure drop of liquid flow through curved rectangular microchannels
Experimental Thermal and Fluid Science, 2012
This paper experimentally investigated the behavior of water through curved rectangular microchannels with different aspect ratios and curvature radii for Re numbers ranging from 10 to 600. The experimental data were compared with the results obtained from numerical analyses and the available correlations. The experimental results indicated that classical Navier-Stokes equations were applicable for the incompressible laminar flow passing through curved microchannels. Geometrical parameters, such as aspect ratio and curvature ratio, were found to have important effects on fluid flowing through curved rectangular microchannels.
An Experimental Study of Water Flow in Smooth and Rough Rectangular Micro-Channels
2004
This paper presents experimental results concerning water flow in smooth and rough rectangular micro-channels. It is part of a work intended to test the classical fluid mechanics laws when the characteristic length scale of inner liquid flows falls below 500μm. The method consists in determining experimental friction coefficients as a function of the Reynolds number. This implies simultaneous measurements of pressure drop and flow rates in microstructures. The two experimental apparatus used in this study enabled us to explore a wide range of length scales (7μm to 300μm) and of Reynolds number (0.01 to 8,000). Classical machining technologies were used to make micro-channels of various heights down to a scale of 100μm. Smaller silicon-Pyrex micro-channels were also made by means of silicon-based micro technologies. In these structures, friction coefficients have been measured locally with Cu -Ni strain gauges. For every height tested, both smooth and rough walls were successively us...
Prediction and Measurement of Pressure Drop of Water Flowing in a Rectangular Microchannel
This paper presents experimental results of pressure drop measurement and prediction of water flowing through a copper rectangular microchannel with a hydraulic diameter of 437 µm. The aim of this work is to identify discrepancies between experimental data and macrochannel theory. An inlet temperature of 60 o C was kept constant at the channel entrance and the experiments were performed with Reynolds numbers (based on the mean velocity and hydraulic diameter) ranging up to 4500. The results show that the pressure drop prediction agrees with the theory. However, the trend of Poiseuille number with the Reynolds number was not constant for laminar flow. This could be due to the entrance effect. Moreover, the friction factor theory could predict the experimental data for turbulent flow. Thus, in this experiment, the theory for flow in macro passages is still applicable.
Effects of compressibility and transition to turbulence on flow through microchannels
A detailed experimental study of flow through long microchannels of hydraulic diameter ranging from 60.5 to 211 lm has been carried out. The internal pressure distribution along the length of the channel has been measured to analyze the local flow behaviour. The effects of compressibility and transition to turbulence occurring in the microchannel flow were investigated in detail. In addition, the resulting flow has been analyzed numerically using a commercially available CFD code, FLUENT. It has been shown that there are no special micro-scale effects, including early transition to turbulence at least in the present range of hydraulic diameters after the significant effects of compressibility are accounted appropriately.