The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
Cao Yang - One of the best experts on this subject based on the ideXlab platform.
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enhancing heat transfer in the Core Flow by using porous medium insert in a tube
International Journal of Heat and Mass Transfer, 2010Co-Authors: Zhifeng Huang, Akira Nakayama, Kun Yang, Cao YangAbstract:According to the concept of heat transfer enhancement in the Core Flow, porous media with a slightly smaller diameter to a tube are developed and inserted in the Core of the tube under the constant and uniform heat flux condition. The Flow resistance and heat transfer characteristics of the air Flow for laminar to fully turbulent ranges of Reynolds numbers are investigated experimentally and numerically. There are three different porous media used in the experiments with porosity of 0.951, 0.966 and 0.975, respectively. The effect of porous radius ratio on the heat transfer performance is studied in numerical simulation. Both numerical and experimental results show that the convective heat transfer is considerably enhanced by the porous inserts of an approximate diameter with the tube and the corresponding Flow resistance increases in a reasonable extent especially in laminar Flow. It shows that the Core Flow enhancement is an efficacious method for enhancing heat transfer.
Antonio Carlos Bannwart - One of the best experts on this subject based on the ideXlab platform.
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Experimental study on interfacial waves in vertical Core Flow
Journal of Petroleum Science and Engineering, 2006Co-Authors: Oscar M. H. Rodriguez, Antonio Carlos BannwartAbstract:Abstract The vertical annular pipe Flow of two immiscible liquids with very different viscosities (also known as Core Flow) provides an efficient and low cost method for producing heavy oils in vertical wells using water as a lubricant. This liquid–liquid Flow pattern is becoming attractive in the current Brazilian deep water production scenario. Understanding interfacial phenomena present in this Flow pattern is crucial for appropriate design of the production system. New experimental data on wavespeed, wave length, amplitude and wave profile of interfacial waves and holdup in heavy oil–water Core Flow (crude oil with 500 mPa s viscosity and 930 kg/m 3 density) inside a 2.84-cm-i.d. vertical glass tube at room temperature are presented and analyzed. The in-situ volumetric fraction of the oil is determined from the kinematic wave assumption and agrees very well with the measurements obtained via a proposed optical technique.
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Analytical model for interfacial waves in vertical Core Flow
Journal of Petroleum Science and Engineering, 2006Co-Authors: Oscar M. H. Rodriguez, Antonio Carlos BannwartAbstract:Abstract The vertical annular pipe Flow of two immiscible liquids with very different viscosities provides an efficient and low cost method for producing heavy oils in vertical wells using water as a lubricant. The Core Flow pattern is becoming attractive in the current Brazilian deep water production scenario. Understanding interfacial phenomena present in this Flow pattern is crucial for appropriate design of the production system. Assuming that in this axisymmetric Flow there is no net force associated with interfacial tension, a differential equation governing the shape of the liquid–liquid interface is derived. An analytical solution is proposed for the prediction of the wave geometry, which depends only on pipe geometry, physical properties and Flow rates of the fluids. The comparison between the model predictions and recent experimental data shows a reasonable agreement.
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Wettability alteration of internal surfaces of pipelines for use in the transportation of heavy oil via Core-Flow
Journal of Petroleum Science and Engineering, 2006Co-Authors: Renata Costa Ribeiro Da Silva, Rahoma Sadeq Mohamed, Antonio Carlos BannwartAbstract:Abstract A promising technique for heavy oil transportation is the use of water-assisted Flow, such as Core-annular Flow. It is based upon the lubrication of pipeline walls with a thin water film and thereby confining the oil to the central portion of the pipe. Oil adhesion to the pipe wall has, however, been pointed out as a possible hindrance to the efficient employment of this method. A solution to this problem is the utilization of hydrophilic and/or oleophobic material as internal coatings for the pipe wall. This work examines the modification of surfaces as a way to minimize or eliminate altogether the heavy oil adherence to pipeline inner walls in the Core-Flow method. To obtain hydrophilic/oleophobic surfaces, the oxidation of surfaces and the alteration of the wall roughness were carried out and their effects quantified. The changes in the wetting behavior of the pipe wall are described through contact angle measurements (in the aqueous phase) for oil/water/surface systems. The surfaces examined included PVC, stainless steel, enameled steel, galvanized steel and commercial steel. Salt, pH and temperature effects on the wetting behavior were also investigated. The results indicated a decrease in contact angles upon the oxidation of the pipeline surface as well as the increase of its roughness. Surface oxidation and increase in roughness resulted in the increase of the hydrophilic character of the surfaces. PVC and steels surfaces, without oxidation showed contact angles around 113–150° (i.e., oleophilic behavior). After oxidation, the steels show angles around 14–20° and PVC an angle of 65°. Stainless steel with roughness of 0.24 μm displayed a contact angle of 35°; roughness increase to 2.28 μm resulted in a contact angle down to 13°. The enameled steel showed a contact angle of 20°, being therefore effective to avoid oil adhesion. Na 2 SiO 3 was effective to lower contact angles of all surfaces being, therefore, effective in reducing fouling. The presence of Na 2 SiO 3 in the solution decreased the contact angles to around 25°, 45° and 20° for systems with glass, PP and stainless steel, respectively. Low temperature and solution pH outside the 4–8 range resulted in lower contact angles. Enameled steel, stainless steel with 2.5 μm roughness, oxidized polymers or oxidized commercial steel can all be used to better the effectiveness of Core-Flow in the transportation of heavy oils.
Ming Tingzhen - One of the best experts on this subject based on the ideXlab platform.
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Analysis on Heat Transfer Enhancement in the Core Flow of a Tube Filled With Swirling Flow Vanes and Its Structure Optimization
2009Co-Authors: Ming TingzhenAbstract:The conventional method of heat transfer enhancement for turbulent Flow in tube is to increase the heat transfer area,but it will increase the pressure drop across the tube significantly.Based on the theory of heat transfer enhancement in the Core Flow in this article,a kind of vane-swirling Flow tube with relatively higher heat transfer efficiency and lower Flow resistance was presented in this paper,and accordingly the physical and mathematical models for the vane-swirling Flow tube were established.Numerical simulation results show that significant effect of heat transfer enhancement for turbulent Flow appears in the tube filled with certain amount of swirling Flow units,while the increase amplitude of pressure drop is lower than that of enhanced heat transfer.When Re number is in the scope of 3 000～15 000,and water with normal temperature Flows through the tube filled with 4 groups of 4-blade swirling Flow units,the performance evaluation criteria numbers SPEC are higher than 1.5,and the maximum SPEC is around 1.9.
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Analysis for Heat Transfer Enhancement in the Core Flow of a Tube Filled With Porous Media at different Layers
2008Co-Authors: Ming TingzhenAbstract:Based on the concept of heat transfer enhancement in the Core Flow, the Core of the fully-developed laminar tube Flow was filled with high-porosity metallic porous media divided into layers, and mathematical models to describe its Flow and heat transfer characteristic were established. Numerical simulation results show that: Compared with those in clear tube, the temperature of the Core Flow in tube, which is filled with metallic porous media, is more uniform, the temperature gradient is larger in the boundary Flow, and the average synergy angle of the whole tube is less than 36°, which shows that heat transfer between the wall and the Flow is enhanced greatly. In addition, in order to increase the performance evaluation criteria value of the two types of enhanced tube, it is appropriate to fill the Core Flow where the velocity is large with relatively lower prosity metallic porous media, while the Core Flow where the velocity gradient is large need to be filled with relatively higher prosity metallic porous media.
Kun Yang - One of the best experts on this subject based on the ideXlab platform.
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enhancing heat transfer in the Core Flow by using porous medium insert in a tube
International Journal of Heat and Mass Transfer, 2010Co-Authors: Zhifeng Huang, Akira Nakayama, Kun Yang, Cao YangAbstract:According to the concept of heat transfer enhancement in the Core Flow, porous media with a slightly smaller diameter to a tube are developed and inserted in the Core of the tube under the constant and uniform heat flux condition. The Flow resistance and heat transfer characteristics of the air Flow for laminar to fully turbulent ranges of Reynolds numbers are investigated experimentally and numerically. There are three different porous media used in the experiments with porosity of 0.951, 0.966 and 0.975, respectively. The effect of porous radius ratio on the heat transfer performance is studied in numerical simulation. Both numerical and experimental results show that the convective heat transfer is considerably enhanced by the porous inserts of an approximate diameter with the tube and the corresponding Flow resistance increases in a reasonable extent especially in laminar Flow. It shows that the Core Flow enhancement is an efficacious method for enhancing heat transfer.
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Mechanism and numerical analysis of heat transfer enhancement in the Core Flow along a tube
Science China-technological Sciences, 2008Co-Authors: Kun YangAbstract:The present study introduces the principles of enhanced heat transfer in the Core Flow to form an equivalent thermal boundary layer in the fully developed laminar tube Flow, which consequently enlarges the temperature gradient of the fluid near the tube wall, and thereby enhances the heat transfer between the fluid and the tube wall. At the same time, the increase of Flow resistance in the tube is not so obvious. Mechanism analysis and numerical calculation based on air and water have been carried out to verify the principle and method presented in this paper, which may bring positive effects to the design of heat exchanger with high heat transfer efficiency and low Flow resistance.
Hagay Amit - One of the best experts on this subject based on the ideXlab platform.
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Geomagnetic jerk features produced using synthetic Core Flow models
Physics of the Earth and Planetary Interiors, 2019Co-Authors: Katia Pinheiro, Hagay Amit, Filipe Terra-novaAbstract:Abstract Geomagnetic jerks are the shortest temporal variations of the magnetic field generated in the Earth's Core. The physical mechanism producing such abrupt changes as well as their spatio-temporal characteristics are not well understood. In order to explore geomagnetic jerks generation and their characteristics, we use a set of synthetic Core Flow models to solve the radial magnetic induction equation. We analyze changes of trend in the secular variation time series using a cubic polynomial fit, by invoking a new formalism of jerk amplitude per unit duration time. A new visualization scheme allows interpreting jerk amplitudes and occurrences in space and time. We find that a mild time-dependence of Flow amplitude, while keeping a fixed pattern, reproduces geomagnetic jerk amplitudes. The polynomial fits were compared with two line-segments fits at ten sampled magnetic observatories about historical jerk occurrences. The differences between the misfits in the two approaches are small, which may question the definition of geomagnetic jerks as sharp “V-shape”. The local time series in our models exhibit secular acceleration changes of sign that reproduce some main observed characteristics of geomagnetic jerks: (i) a range of amplitudes that encompass those observed in geomagnetic jerks, (ii) non-simultaneous occurrence, (iii) non-global occurrence, (iv) spatial variability of amplitudes and (v) strongest amplitudes in the radial component.
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accounting for magnetic diffusion in Core Flow inversions from geomagnetic secular variation
Geophysical Journal International, 2008Co-Authors: Hagay Amit, Ulrich R. ChristensenAbstract:SUMMARY We use numerical dynamos to investigate the possible role of magnetic diffusion at the top of the Core. We find that the contribution of radial magnetic diffusion to the secular variation is correlated with that of tangential magnetic diffusion for a wide range of control parameters. The correlation between the two diffusive terms is interpreted in terms of the variation in the strength of poloidal Flow along a columnar Flow tube. The amplitude ratio of the two diffusive terms is used to estimate the probable contribution of radial magnetic diffusion to the secular variation at Earth-like conditions. We then apply a model where radial magnetic diffusion is proportional to tangential diffusion to Core Flow inversions of geomagnetic secular variation data. We find that including magnetic diffusion does not change dramatically the global Flow but some significant local variations appear. In the non frozen-flux Core Flow models (termed ‘diffusive’), the hemispherical dichotomy between the active Atlantic and quiet Pacific is weaker, a cyclonic vortex below North America emerges and the vortex below Asia is stronger. Our results have several important geophysical implications. First, our diffusive Flow models contain some Flow activity at low latitudes in the Pacific, suggesting a local balance between magnetic field advection and diffusion in that region. Second, the cyclone below North America in our diffusive Flows reconciles the difference between mantle-driven thermal wind predictions and frozen-flux Core Flow models, and is consistent with the prominent intense magnetic flux patch below North America in geomagnetic field models. Finally, we hypothesize that magnetic diffusion near the Core surface plays a larger role in the geomagnetic secular variation than usually assumed.
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geomagnetic dipole tilt changes induced by Core Flow
Physics of the Earth and Planetary Interiors, 2008Co-Authors: Hagay Amit, Peter OlsonAbstract:The tilt of the geomagnetic dipole decreased from about 11.7 ◦ in 1960 to 10.5 ◦ in 2005, following more than a century when it remained nearly constant. The recent poleward motion of the dipole axis is primarily due to a rapid decrease in the equatorial component of the dipole moment vector. Using maps of the equatorial dipole moment density and its secular change derived from Core field models, we identify regions on the Core–mantle boundary where the present-day tilt decrease is concentrated. Among the possible causes of equatorial dipole moment change on the Core–mantle boundary, tangential magnetic diffusion is negligible on these time scales, and although radial magnetic diffusion is potentially significant, the rapid changes in equatorial moment density indicate it is not the dominant mechanism. We show that magnetic flux transport can account for most of the observed equatorial dipole moment change. Frozen-flux Core Flow models derived from geomagnetic secular variation reveal a nearly balanced pattern of advective sources and sinks for the equatorial dipole moment below the Core–mantle boundary. The recent tilt decrease originates from two advective sinks, one beneath Africa where positive radial magnetic field is transported westward away from the equatorial dipole axis, the other beneath North America where negative radial magnetic field is transported northward away from the equatorial dipole axis. Each of these sinks is related to a prominent gyre that has evolved significantly over the past few decades, indicating the strong variability of the large-scale circulation in the outer Core on this time scale. © 2008 Elsevier B.V. All rights reserved.
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Tests of Core Flow imaging methods with numerical dynamos
Geophysical Journal International, 2007Co-Authors: Hagay Amit, Peter Olson, Ulrich R. ChristensenAbstract:SUMMARY We test the quality of a new Core Flow imaging method that incorporates constraints on Flow helicity, using synthetic magnetic secular variation data from 3-D self-consistent numerical dynamo models. Comparison with the dynamo model Flows reveals that our imaging method delineates most of the main large-scale Flow features, both in pattern and magnitude. The dynamo model Flows are characterized by high-latitude vortices, some equatorial symmetry, columnar convection and a significant amount of Flow along radial magnetic field contours. Our inversion method correctly images these aspects of the Flows. The correlation coefficient between the dynamo velocity and the imaged velocity exceeds 0.5 in cases with large-scale Flow and magnetic field pattern, but degrades substantially in more complex cases when the scale of the secular variation is small. The magnitude of the imaged velocity depends on the a priori-assumed ratio of tangential divergence to radial vorticity k, in some resemblance to the damping parameter in spectral methods, although with our method the misfit is insensitive to k-values. Including tangential magnetic diffusion in Core Flow inversion improves the quality of the imaged velocity pattern. The largest artefacts in the imaged velocities are due to unmodelled radial magnetic diffusion and truncation of the input magnetic field.
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Time-average and time-dependent parts of Core Flow
Physics of the Earth and Planetary Interiors, 2006Co-Authors: Hagay Amit, Peter OlsonAbstract:Abstract We infer fluid motions below the Core–mantle boundary by inverting geomagnetic secular variation data over a 150 years, assuming helical-geostrophic Flow. We obtain snapshot images of Core Flow at 5-year intervals, which we combine to give time-average and time-dependent parts of the motion over this time interval. The most prominent time-average Flow structure is a large anti-cyclonic vortex in the southern hemisphere beneath the Atlantic and Indian Oceans. The time-average zonal Core Flow outside the inner Core tangent cylinder is significantly westward in the southern hemisphere but nearly zero in the northern hemisphere. Westward polar vortices occur inside the tangent cylinder in both hemispheres, particularly in the north. In terms of mantle versus Core origins, mantle driving appears to be responsible for the mid-latitude asymmetry in the zonal Core Flow, whereas Core driving appears to be responsible for the Flow at high latitudes. We also compare changes in the Core’s angular momentum calculated from our time-dependent Core Flow with changes in the mantle’s angular momentum derived from decade-scale length-of-day variations and find adequate agreement. A fit of our time-dependent Core Flow to a torsional oscillations model yields dominant periods of 110 and 53 years.