Showing papers on "Pressure drop published in 2004"
TL;DR: In this paper, a series of experiments are presented which demonstrate significant drag reduction for the laminar flow of water through microchannels using hydrophobic surfaces with well-defined micron-sized surface roughness.
Abstract: A series of experiments is presented which demonstrate significant drag reduction for the laminar flow of water through microchannels using hydrophobic surfaces with well-defined micron-sized surface roughness. These ultrahydrophobic surfaces are fabricated from silicon wafers using photolithography and are designed to incorporate precise patterns of microposts and microridges which are made hydrophobic through a chemical reaction with an organosilane. An experimental flow cell is used to measure the pressure drop as a function of the flow rate for a series of microchannel geometries and ultrahydrophobic surface designs. Pressure drop reductions up to 40% and apparent slip lengths larger than 20 μm are obtained using ultrahydrophobic surfaces. No drag reduction is observed for smooth hydrophobic surfaces. A confocal surface metrology system was used to measure the deflection of an air–water interface that is formed between microposts and supported by surface tension. This shear-free interface reduces the ...
970 citations
TL;DR: In this paper, the authors investigated the effect of flow rates, fluid viscosities and interfacial tension on the droplet size and observed the dynamics of satellite drop generation at a capillary tip in laminar flow.
456 citations
TL;DR: In this paper, the effect of channel diameter on two-phase flow was investigated to identify the phenomena which distinguish microchannels from minichannels, and a new slug flow model was also proposed to gain physical insight into the observed flow characteristics in micro-channels.
394 citations
TL;DR: In this paper, high-resolution Navier-Stokes simulations and laboratory measurements of fluid flow in a natural sandstone fracture were conducted, where epoxy casts were made of the two opposing fracture surfaces, and the surface profiles were then measured at a vertical resolution of ±2 μm, every 20 μm in the x and y-directions, over 2 cm × 2 cm regions of the fracture.
368 citations
TL;DR: In this paper, the effect of mass flux, pressure, and heat flux on the heat transfer coefficient and pressure drop was measured for four horizontal cooling tubes with different inner diameters ranging from 1 to 6 mm.
Abstract: Heat transfer of supercritical carbon dioxide cooled in circular tubes was investigated experimentally. The effect of mass flux, pressure, and heat flux on the heat transfer coefficient and pressure drop was measured for four horizontal cooling tubes with different inner diameters ranging from 1 to 6 mm. The radial distribution of the thermophysical properties (i.e. specific heat, density, thermal conductivity and viscosity) in the tube cross-section was critical for interpreting the experimental results. A modified Gnielinski equation by selecting the reference temperature properly was then developed to predict the heat transfer coefficient of supercritical carbon dioxide under cooling conditions. This proposed correlation was accurate to within 20% of the experimental data.
342 citations
TL;DR: In this article, continuous SAPO-34 membranes with low concentrations of non-zeolite pores were synthesized by in situ crystallization on porous stainless steel and α-Al2O3 supports.
334 citations
TL;DR: In this paper, a two-phase flow map and transition lines between flow regimes are examined and bubble velocity and slip ratio between liquid and gas are measured in 200 and 525 µm square microchannels made of glass and silicon.
Abstract: Liquid/gas flows are experimentally investigated in 200 and 525 μm square microchannels made of glass and silicon. Liquid and gas are mixed in a cross-shaped section in a way to produce steady and homogeneous flows of monodisperse bubbles. Two-phase flow map and transition lines between flow regimes are examined. Bubble velocity and slip ratio between liquid and gas are measured. Flow patterns and their characteristics are discussed. Local and global dry out of the channel walls by moving bubbles in square capillaries are investigated as a function of the flow characteristics for partially wetting channels. Two-phase flow pressure drop is measured and compared to single liquid flow pressure drop. Taking into account the homogeneous liquid fraction along the channel, an expression for the two-phase hydraulic resistance is experimentally developed over the range of liquid and gas flow rates investigated.
329 citations
TL;DR: In this article, the transition to turbulent flow is studied for liquids of different polarities in glass microtubes having diameters between 50 and 247 µm, and the onset of transition occurs at Reynolds numbers of ~1,800-2,000, as indicated by greater thanlaminar pressure drop and micro-PIV measurements of mean velocity and rms velocity fluctuations at the centerline.
Abstract: The transition to turbulent flow is studied for liquids of different polarities in glass microtubes having diameters between 50 and 247 µm. The onset of transition occurs at Reynolds numbers of ~1,800–2,000, as indicated by greater-than-laminar pressure drop and micro-PIV measurements of mean velocity and rms velocity fluctuations at the centerline. Transition at anomalously low values of Reynolds number was never observed. Additionally, the results of more than 1,500 measurements of pressure drop versus flow rate confirm the macroscopic Poiseuille flow result for laminar flow resistance to within −1% systematic and ±2.5% rms random error for Reynolds numbers less than 1,800.
290 citations
TL;DR: In this article, the fluid flow and heat transfer features of cellular metal lattice structures made from copper by transient liquid phase (TLP) bonding and brazing of plane weave copper meshes (screens) were experimentally characterized under steady-state forced air convection.
282 citations
TL;DR: In this paper, the fundamental heat transfer data and two-phase flow patterns present during flow boiling in microchannels were obtained and the measured single-phase, adiabatic pressure drop agreed with the conventional theory within the experimental error.
Abstract: Microchannels are being considered in many advanced heat transfer applications including automotive and stationary fuel cells as well as electronics cooling. However, there are a number of fundamental issues from the heat transfer and fluid mechanics perspectives that still remain unresolved. The present work focuses on obtaining the fundamental heat transfer data and two-phase flow patterns present during flow boiling in microchannels. An experimental investigation is performed for flow boiling using water in six parallel horizontal microchannels with a hydraulic diameter of 207 μm. The ranges of parameters are: mass flux from 157 to 1782 kg/m 2 s, heat flux from 5 to 930 kW/m 2 , inlet temperature of 22°C, quality from sub-cooled to 1.0. and atmospheric pressure at the exit. The corresponding single-phase, all-liquid flow Reynolds number range at the saturation conditions is from 116 to 1318. The measured single-phase, adiabatic pressure drop agreed with the conventional theory within the experimental error
268 citations
TL;DR: In this paper, the laminar convective heat transfer and pressure drop characteristics in tree-like microchannel nets are numerically investigated and compared to the corresponding characteristics in traditional serpentine flow patterns, by solving the Navier-Stokes and energy equation for an incompressible fluid with constant properties in three dimensions.
TL;DR: The amplification performance of the CFPCR as a function of linear velocity was assessed using 500 and 997 base pair fragments from lambda-DNA, and the longer amplification time required for detection of the 997 bp fragment was due to the device being operated at its enzyme kinetic limit.
Abstract: Continuous flow polymerase chain reaction (CFPCR) devices are compact reactors suitable for microfabrication and the rapid amplification of target DNAs. For a given reactor design, the amplification time can be reduced simply by increasing the flow velocity through the isothermal zones of the device; for flow velocities near the design value, the PCR cocktail reaches thermal equilibrium at each zone quickly, so that near ideal temperature profiles can be obtained. However, at high flow velocities there are penalties of an increased pressure drop and a reduced residence time in each temperature zone for the DNA/reagent mixture, that potentially affect amplification efficiency. This study was carried out to evaluate the thermal and biochemical effects of high flow velocities in a spiral, 20 cycle CFPCR device. Finite element analysis (FEA) was used to determine the steady-state temperature distribution along the micro-channel and the temperature of the DNA/reagent mixture in each temperature zone as a function of linear velocity. The critical transition was between the denaturation (95 °C) and renaturation (55 °C–68 °C) zones; above 6 mm s−1 the fluid in a passively-cooled channel could not be reduced to the desired temperature and the duration of the temperature transition between zones increased with increased velocity. The amplification performance of the CFPCR as a function of linear velocity was assessed using 500 and 997 base pair (bp) fragments from λ-DNA. Amplifications at velocities ranging from 1 mm s−1 to 20 mm s−1 were investigated. The 500 bp fragment could be observed in a total reaction time of 1.7 min (5.2 s cycle−1) and the 997 bp fragment could be detected in 3.2 min (9.7 s cycle−1). The longer amplification time required for detection of the 997 bp fragment was due to the device being operated at its enzyme kinetic limit (i.e., Taq polymerase deoxynucleotide incorporation rate).
TL;DR: In this article, a comparison of the results in terms of flow pattern and mixing/segregation kinetics of binary mixtures of particles is performed with different model formulations and different equations for quantifying the particle−fluid interaction.
Abstract: Discrete particle simulation has been recognized as a useful numerical technique for elucidating the fundamentals of granular matter. For gas−solid two-phase flow in fluidization, such simulations are achieved by combining the discrete flow of the particle phase with the continuum flow of the gas phase. However, differences exist in the actual implementation of this idea in the literature. This paper attempts to rationalize this matter by discussing important aspects including the governing equations in relation to the so-called models A and B, which use different treatments of pressure drop in the well-established two-fluid model, different coupling schemes between the gas and solid phases, and different equations for quantifying the particle−fluid interaction. For the purpose of quantitative analysis, gas fluidization of binary mixtures of particles is simulated with different model formulations, and a comparison of the results in terms of flow pattern and mixing/segregation kinetics shows a significant...
TL;DR: In this article, a high-density polyethylene (pe) pipe-rig was used to collect pressure and circumferential strain data, and the pipe material presented a typical viscoelastic mechanical behaviour with a sudden pressure drop immediately after the fast valve closure, a major dissipation and dispersion of the pressure wave, and transient mechanical hysteresis.
Abstract: The mechanical behaviour of the pipe material determines the pressure response of a fluid system during the occurrence of transient events. in viscoelastic pipes, typically made of polyethylene (pe), maximum or minimum transient pressures are rapidly attenuated and the overall pressure wave is delayed in time. this is a result of the retarded deformation of the pipe-wall. this effect has been observed in transient data collected in a high-density pe pipe-rig, at imperial college (london, uk). several transient tests were carried out to collect pressure and circumferential strain data. the pipe material presented a typical viscoelastic mechanical behaviour with a sudden pressure drop immediately after the fast valve closure, a major dissipation and dispersion of the pressure wave, and transient mechanical hysteresis. the creep-function of the pipe material was experimentally determined by creep tests, and, its order-of-magnitude was estimated based on pressure-strain data collected from the pipe-rig. a goo...
TL;DR: In this article, the characteristics of two kinds of fibrous materials are discussed: randomly stacked fibers and metallic foams that are used in industrial systems, and the transport properties are analyzed for both materials: permeability, friction factors and effective thermal conductivity.
TL;DR: In this article, the effects of fin spacing on four-row annular-finned tube bundles in staggered and in-line arrangements are investigated by the three-dimensional numerical study.
TL;DR: In this article, a computational fluid dynamics (CFD) calculation was performed to predict and evaluate the effects of temperature and inlet velocity on the pressure drop of gas cyclones, and the numerical solutions were carried out using spreadsheet and commercial CFD code Fluent 6.1.
Abstract: This work presents a computational fluid dynamics (CFD) calculation to predict and to evaluate the effects of temperature and inlet velocity on the pressure drop of gas cyclones. The numerical solutions were carried out using spreadsheet and commercial CFD code Fluent 6.1. This paper also reviews four empirical models for the prediction of cyclone pressure drop, namely [Air pollution control: a design approach, in: C. David Cooper, F.C. Alley (Eds.), Cyclones, second ed., Woveland Press Inc., Illinois, 1939, p. 127–139] [Chem. Eng. (1983) 99] [Doctoral Thesis, Havarad University, USA, 1988], and [Chem. Eng. Progress (1993) 51]. All the predictions proved to be satisfactory when compared with the presented experimental data. The CFD simulations predict excellently the cyclone pressure drop under different temperature and inlet velocity with a maximum deviation of 3% from the experimental data. Specifically, results obtained from the computer modelling exercise have demonstrated that CFD is a best method of modelling the cyclones operating pressure drop.
TL;DR: In this article, the authors describe the numerical investigations concerning the combustion enhancement when a cavity is used for the hydrogen fuel injection through a transverse slot nozzle into a supersonic hot air stream.
TL;DR: In this paper, an experimental study was performed to measure the heat transfer distributions and frictional losses in rotating ribbed channels with an aspect ratio of 4:1, where the ribs are placed on both the leading and trailing surfaces of the channel, and they are oriented 45° to the mainstream flow.
Abstract: An experimental study was performed to measure the heat transfer distributions and frictional losses in rotating ribbed channels with an aspect ratio of 4:1. Angled, discrete angled, V-shaped, and discrete V-shaped ribs were investigated, as well as the newly proposed W-shaped and discrete W-shaped ribs. In all cases, the ribs are placed on both the leading and trailing surfaces of the channel, and they are oriented 45° to the mainstream flow. The rib height-to-hydraulic diameter ratio (e/D) is 0.078, and the rib pitch-to-height ratio (P/e) is 10. The channel orientation with respect to the direction of rotation is 135°. The range of flow parameters includes Reynolds number (Re = 10000–40000), rotation number (Ro = 0.0–0.15), and inlet coolant-to-wall density ratio (Δρ/ρ = 0.12). Both heat transfer and pressure measurements were taken, so the overall performance of each rib configuration could be evaluated. It was determined that the W-shaped and discrete W-shaped ribs had the superior heat transfer performance in both non-rotating and rotating channels. However, these two configurations also incurred the greatest frictional losses while the discrete V-shaped and discrete angled ribs resulted in the lowest pressure drop. Based on the heat transfer enhancement and the pressure drop penalty, the discrete V-shaped ribs and the discrete W-shaped ribs exhibit the best overall thermal performance in both rotating and non-rotating channels. These configurations are followed closely by the W-shaped ribs. The angled rib configuration resulted in the worst performance of the six configurations of the present study.Copyright © 2004 by ASME
TL;DR: In this paper, a fractal analysis combined with a modified Richardson-Zaki approach is proposed for prediction of agglomerate size and voidage, and the results showed that the bed appeared to exhibit a fluidlike behavior at velocities much lower than the minimum fluidization velocity.
Abstract: Vigorous homogeneous fluidization of 12-nm silica particles was easily achieved by coupling aeration with vibration. Vibration (with frequency in the range of 30 to 200 Hz, and vibrational acceleration in the range of 0 to 5 g) was found to be necessary to achieve smooth fluidization. The minimum fluidization velocity, defined as the lowest gas velocity at which the pressure drop across the bed reaches a plateau, was approximately 0.3‐0.4 cm/s, and essentially independent of the vibrational acceleration. However, the bed expanded almost immediately after the air was turned on, reaching bed expansions of three times the initial bed height or higher. Thus the bed appeared to exhibit a fluidlike behavior at velocities much lower than the minimum fluidization velocity. Fluidization of nanoparticles was achieved as a result of the formation of stable, relatively large, and very porous agglomerates. Practically no bubbles or elutriation of particles was observed. A fractal analysis combined with a modified Richardson‐Zaki approach is proposed for prediction of agglomerate size and voidage. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1776 –1785, 2004
TL;DR: In this article, the rheological properties of hydrate suspension are analyzed depending on the oil phase and flow loop experiments are performed to determine the modification of the friction factor under turbulent conditions.
Abstract: The problem of hydrate blockage of pipelines in offshore production is becoming more and more severe with the increase of the water depth. Conventional prevention techniques like insulation or methanol injection are reaching their limits. Injection of antiagglomerant additives and/or presence of natural surfactants in crude oils give us a new insight into hydrate prevention methods. Hydrate crystals are allowed to form but size of the particles is limited and transportation within the hydrocarbon phase is possible as a suspension. Solid particles formation in the liquid modifies the flowing properties. The pressure drop is controlled by the friction factor under turbulent flow conditions or by the apparent viscosity in the case of laminar flow regime. In a first part, the rheological properties of hydrate suspension are analysed depending on the oil phase. Results of flow loop experiments are then reported and allow us to determine the modification of the friction factor under turbulent conditions. Effect of hydrate particles is analysed in terms of rheological properties of the system in the laminar regime and in terms of friction factor modification in the turbulent regime.
TL;DR: Friction factor data from two recent pipe flow experiments are combined to provide a comprehensive picture of the friction factor variation for Reynolds numbers from 10 to 36,000,000 as mentioned in this paper. But this is not the case for all pipe flows.
Abstract: Friction factor data from two recent pipe flow experiments are combined to provide a comprehensive picture of the friction factor variation for Reynolds numbers from 10 to 36,000,000.
TL;DR: In this paper, high-speed photographic methods were used to determine dominant flow patterns and explore as well as characterize hydrodynamic instabilities in micro-channel convective boiling in small, parallel coolant passages.
Abstract: The design and reliable operation of a two-phase micro-channel heat sink require a fundamental understanding of the complex transport phenomena associated with convective boiling in small, parallel coolant passages. This understanding is the primary goal of this paper. This goal is realized by exploring the following aspects of boiling in micro-channels: hydrodynamic instability, two-phase flow patterns, pressure drop, and convective boiling heat transfer. High-speed photographic methods were used to determine dominant flow patterns and explore as well as characterize hydrodynamic instabilities. Two types of dynamic instability were identified, a severe pressure drop oscillation and a mild parallel channel instability, and a simple method is recommended to completely suppress the former. Predictions of three popular two-phase pressure drop models and correlations were compared to micro-channel water data, and only a separated flow (Lockhart-Martinelli) correlation based on the assumption of laminar flow in both phases gave acceptable predictions. Several popular heat transfer correlations were also examined and deemed unsuitable for micro-channel heat sinks because all these correlations are based on turbulent flow assumptions, and do not capture the unique features of micro-channel flow such as abrupt transition to slug flow, hydrodynamic instability, and high droplet entrainment in the annular regime. These findings point to the need for further study of boiling behavior and new predictive tools specifically tailored to micro-channel heat sinks.Copyright © 2002 by ASME
TL;DR: In this article, the measured heat transfer coefficients and pressure drop during evaporation process of carbon dioxide in a horizontal smooth tube were investigated by experiment and analysis in transcritical refrigeration cycle using carbon dioxide.
Abstract: Carbon dioxide among natural refrigerants has gained considerable attention as an alternative refrigerant due to its excellent thermophysical properties. In this study, transcritical refrigeration cycle using carbon dioxide is of great interest, and the evaporation process is investigated by experiment and analysis. This paper presents the measured heat transfer coefficients and pressure drop during evaporation process of carbon dioxide in a horizontal smooth tube. The test section was made of a seamless stainless steel tube with the inner diameter of 7.53 mm, and length of 5 m. Heat is provided by a direct heating method to the test section. Experiments were conducted at saturation temperatures of −4 to 20 °C, heat fluxes of 12 to 20 kWm −2 and mass fluxes of 200 to 530 kgm −2 s −1 . A comparison of different heat transfer correlations applicable to evaporation of carbon dioxide has been made. Based on the experiments for the evaporation heat transfer, useful correlation is developed.
TL;DR: In this article, a simulation of two-dimensional wavy-plate-fin channels with sinusoidal wall corrugations is numerically simulated, where velocity and temperature fields, isothermal Fanning friction factor, and Colburn factor are presented for different flow rates, wall-corrugation severity, and fin spacing.
TL;DR: In this article, a three-dimensional, steady-state mathematical model is described to investigate the fluid flow, species transport and electrochemical reaction in the PEM fuel cells with conventional and inter-digitated flow fields.
TL;DR: In this article, an experimental study of the pressure loss and endwall heat transfer in a highly porous, ultralightweight, multifunctional lattice-frame material (LFM) subjected to forced air convection is examined in detail.
TL;DR: In this article, a three-regime correlation is developed for the excess bend loss coefficient as a function of Reynolds number, aspect ratios, curvature ratios and spacer lengths between the channels.
TL;DR: In this paper, the authors present a theoretical approach for the design of multi-scale fluid distributors based on fractal tree networks, which allows to design such distributors optimally, within certain constraints.
TL;DR: In this article, a two-phase flow pressure drop analysis by ranging several mass flow rates for a chosen heat flux provided to the minichannel has been performed, and two kinds of upstream conditions have been investigated to show up the confinement influence on boiling.