Fluid Flow Resistance Research Articles

Entropy minimization in micro-scale evaporating thin liquid film in capillary tubes

An analysis has been provided for the entropy generated for the micro/nano scale heat and mass transfer in a capillary tube in terms of the gradients of velocity, temperature and concentration as well as the physical properties of the fluid. The heat and mass transfer rates are assumed to be uniform on the surface of the capillary tube. The optimum tube diameter that corresponds to the minimization of entropy generated and minimization of fluid flow resistance is about 1 mm. We have applied the method of thermodynamic optimization to capillary driven systems. The objective was to identify the geometric configuration that maximized performance by minimizing the entropy generated when the flow rate is prescribed.

Ultrastructure and Fluid Flow Physiology of Fetal Trabecular Meshwork Cells

Purpose: To assess the ultrastructural and fluid flow characteristics of cultured trabecular meshwork (TM) cells derived from fetal sources. Methods: Fetal eyes were carefully dissected to isolate the developing TM tissue for culture. Immunostaining was used to assess the expression of the junction-associated proteins zonula occludens-1 (ZO-1) and occludin. Fetal and adult TM cells were grown to confluence on permeable membranes for both flow and ultrastructural studies. Fluid flow resistance was measured by permeation of horseradish peroxidase (hrp) activity and hydraulic conductivity (HC) experiments. The effects of dexamethasone (Dex) on permeability and HC were also evaluated. Results: ZO-1 and occludin are expressed in the TM region of tissue sections and at cell borders in cultured fetal and adult TM cells. Transmission electron microscopy demonstrated that cultured TM cells possessed numerous mitochondria, electron-dense bodies, surface microvilli, and adherens and gap junctions. The permeation of hrp across fetal TM cell monolayers (0.030 ± 0.010) and of adult TM cells (0.031 ± 0.010) had similar values for absorbance at 470 nm (p = 0.83, 95% CI: −0.004, 0.005). Dex treatment significantly reduced the permeability to 0.022 ± 0.008 (p = 0.002) and 0.018 ± 0.009 (p = 0.004) for fetal and adult TM cells, respectively. The average HC (μ l/min/mmHg/cm2) of fetal cells (2.78 ± 1.03) and of the adult cells (2.15 ± 1.31) was not significantly different (p = 0.24, 95% CI: −1.01, 0.26). Dex treatment significantly reduced HC in both fetal (1.24 ± 0.72, p = 0.0004) and adult (1.29 ± 0.29, p = 0.00001) TM. Conclusions: Cultured fetal TM cells exhibited similar expression of junctional proteins and ultrastructural features as their adult counterparts. The permeability and HC of the fetal cells were similar to their older adult counterparts. Dex treatment induced increased fluid flow resistance in both cell types. These cells may serve as a source for in vitro studies of meshwork physiology.

Vortex sound under the influence of a piecewise porous material on an infinite rigid plane

The vortex dynamics and the sound generation by an inviscid vortex in the presence of a finite length porous material on an otherwise rigid plane are studied numerically in the present study in an attempt to understand the sound generation near the surface of a wall lining in a lined duct. The combined effects of the effective fluid density and flow resistance inside the porous material, and the length and thickness of the porous material on the sound generation process are examined in detail. Results obtained demonstrate the sound pressure is longitudinal dipole and show how seriously the above-mentioned parameters are affecting the vortex sound pressure under the influence of the porous material.

Using illumination and shadow to model aerodynamic resistance and flow separation: An isotropic study

The momentum extracted from fluid flow by the underlying surface roughness is important for understanding processes of entrainment, transportation and deposition of sediments. The parameter z 0 is a length scale that characterizes the loss of wind momentum attributable to the roughness elements. However, it is very difficult to estimate accurately and precisely even under carefully controlled conditions in wind tunnels. This limits the use of the parameter over large areas and in particular across scales of roughness, e.g., grain to form scale. This is problematic for studies of wind erosion and dust dispersion which require estimates of aerodynamic resistance over very large areas. A new concept is proposed with the potential to unify the estimates of fluid flow resistance along the continuum of sparse to tightly packed object spacing and across multiple scales. It is based on the creation of shadows by the illumination of roughness elements and the assumption that flow separation is created behind roughness elements on a plane surface as a function of free-stream wind velocity and obstacle height. The concept was implemented using a computer program and validated against a wind tunnel study that estimated z 0 for configurations of spheroids. Various spheroid coverages used in the wind tunnel study were reconstructed using a digital elevation model of the surface simulated by the computer. A strong relationship was established ( R 2=0.91) over two orders of magnitude between the shadow area ratio (SAR) and z 0. Fluid drag was shown to be dependent on the arrangement of roughness elements at the surface. The configurations of spheroids were replaced by cylinders of the same basal area and computer simulations of shadow area were repeated. Object shape was evidently important to the overlap of shadow with downstream adjacent obstacles and hence aerodynamic resistance was dependent on object shape. These findings appear to contradict empirical evidence of previous studies. Illumination and shadow of objects on a plane surface appears to adequately represent z 0. Shadow appears to approximate the flow separation behind an obstacle and to represent a wake. The overlap on to downstream adjacent objects of the shadow cast from an upstream object appears to mimic the interference of wakes caused by fluid flow moving around stationary objects with close spacing. There is a compelling argument for the use of SAR as a unifying measure of aerodynamic resistance over the continuum between isolated and tightly packed objects. Furthermore, given elevation data of objects on a plane surface the results show that shadow length is a point-based measure that may be integrated for all points evaluated to provide SAR. The demonstrated angular relationship between illumination and drag (shadow and flow separation) has considerable potential for estimating aerodynamic resistance over multiple scales and for significant investigations of (i) the anisotropic nature of aerodynamic resistance and (ii) its estimation using directional measurements of reflectance and bidirectional reflectance models.

Influence of membrane support structure on the efficiency of an iron-modified silica nanofiltration membrane

Inorganic membranes are generally created by depositing a thin film separation (membrane) layer atop a supporting structure in order to provide for the physical durability of the membrane. The separation layer thickness and morphology are normally evaluated to determine their contribution to fluid flow resistance across the membrane. The supporting structure is often ignored, yet can affect the quality of the membrane formed and significantly influence the global efficiency of the membrane module. In this paper, three different support structures are compared and evaluated with respect to the efficiency (rejection and flux) of an iron-modified silica separation layer. The main difference in the supports was the nominal pore size of the surface responsible for facilitating the membrane layer. The pore sizes of the supports investigated were 5, 10, and 20 nm in diameter. It was hypothesized that the largest pore size support would produce a higher water flux. However, this support did not provide an adequate surface for the deposition of a high quality membrane layer. The formation of an intact membrane layer was successfully achieved using the other two support structures. From the results obtained from salt rejection and flux data of these two functional membrane modules, the influence of the support structure on the overall efficiency of the membrane module was assessed. The 10 nm support structure produced a water flux that was 1.6 times greater than that of the 5 nm pore size support, without sacrificing the rejection of the electrolytes studied.

Second law analysis for microscale flow and heat transfer

In phase change transport devices, capillary forces drive overall circulation of working fluid from an evaporator section to a condenser section, whereas the thin film flows at the evaporating meniscus are driven by capillary and disjoining pressure gradient. An analysis has been provided for the microscale fluid flow and heat transfer in an evaporating extended meniscus. Using the second law of thermodynamics, the entropy generated has been investigated. The geometric configuration that corresponds to the minimization of entropy generated and minimization of fluid flow resistance is identified.

Electrically enhanced dewatering (EED) of particulate suspensions

Electrically enhanced dewatering has been characterised from first principles using model kaolinite suspensions in both the coagulated and dispersed state and sludge from a potable water treatment plant. The dewatering properties, namely the compressive yield stress or extent of dewatering (quantified as the applied pressure at an equilibrium solids concentration) and the hindered settling function or the resistance of fluid flow (quantified as the rate of fluid expression at an equilibrium solids concentration), have been measured as a function of electric field strength. For both the dispersed and coagulated kaolinite suspensions, the rate of dewatering was found to improve at all applied pressures and with increasing applied electrical field strength, up to 1250 V m −1. Improvements in the extent of dewatering were also observed but only for the coagulated suspension. The greatest improvements in dewatering were observed at the lowest applied pressures. Improvement in suspension compressibility is only predicted for the specific case where the feed to the process is both coagulated and at a neutral or low pH. For the potable water sludge, improvements in the rate of dewatering were observed at all pressures above 10 kPa. At lower pressures, the low particle surface charge caused a slow onset of electro-osmotic effects. In general, the results indicate that the application of an electric field in situ during dewatering primarily helps to increase the rate of dewatering and the benefit of this methodology is predicted to be for suspensions that exhibit low permeability at low solids concentrations in applications where the pressure is low or the process is gravity driven.

Design and Modeling of a Magnetorheological Valve with Both Annular and Radial Flow Paths

In this article, an MR valve possessing simultaneously annular fluid flow resistance channels and radial fluid flow resistance channels is designed, and its structure and working principle are described. In addition, a mathematical model for the MR valve with both annular and radial flow paths is developed and the simulation is carried out to evaluate the newly developed MR valve. The simulation results based on the proposed model indicate that the efficiency of the MR valve with circular disk-type fluid resistance channels is superior to that with annular fluid resistance channels under the same magnetic flux density and outer radius of the valve. Furthermore, the results also show that the efficiency of the MR valve can be improved significantly with two types of fluid flow resistance gaps, viz. annular fluid flow resistance gaps and circular disk-type fluid flow resistance gaps simultaneously.

Adaptive Roll Stabilization of Fishing Vessels

The application of frequency adaptive anti-roll tanks on fishing vessels is well established but currently restricted to U-tube designs. This paper concerns the initial stages of a research programme to develop a more generic anti-roll system that will be applicable to a range of tank geometries, with minimal alteration to the existing tank structure. Two possible control strategies, based on continuous and intermittent fluid flow, are assessed for a U-tube tank and the potential of extending the technique to a free-surface tank with a central partition is examined. The intermittent flow scheme was found to be most effective at longer roll periods while the continuous flow scheme was heavily reliant on a low value of fluid flow resistance.

Dendritic heat convection on a disc

In this paper we develop the optimal tree-shaped flow paths for cooling a disc-shaped body by convection. Heat is generated uniformly over the disc area. The coolant enters through the center of the disc, and exits through ports positioned equidistantly along the perimeter. The unknown is the flow architecture. The constraints are the disc size and the total volume occupied by the ducts. It is assumed that the ducts are narrow enough so that the flow is hydrodynamically and thermally fully developed. The ultimate goal is to determine flow architectures that reach simultaneously two objectives: (i) minimal global fluid flow resistance (or pumping power), and (ii) minimal global thermal resistance. When the architecture is optimized for (i), the result is a dendritic structure in which every geometric feature is uniquely determined. The corresponding thermal resistance decreases as the total mass flow rate and the pumping power increase. When the objective is (ii), the optimal architecture has radial ducts, not dendrites. The corresponding fluid-flow resistance increases as the flow rate increases and the global thermal resistance decreases. Put together, these geometric results show that methods (i) and (ii) lead to nearly the same combined performance (thermal and fluid). Examined more closely, the dendrites produced by method (i) perform progressively better as the length scales become smaller. Optimized increasing complexity is the route to high thermal and fluid-flow performance in the limit of decreasing scales.

Using Shale Gouge Ratio (SGR) to model faults as transmissibility barriers in reservoirs: an example from the Strathspey Field, North Sea

Since the onset of production in 1993, extraction and injection in Strathspey has focused on the central region of the field, around the ‘Central Fault’. Analysis of RFT measurements from intermittent, but regular drilling on either side of this fault has allowed reconstruction of footwall/hanging wall pore-pressure fields for particular time instances. Comparison of these similar age pressure fields shows the Central Fault capable of maintaining up to 1300 psi pressure differentials. The results of the pressure analysis were used to calibrate a fault seal attribute, termed Shale Gouge Ratio (SGR) which is an estimate of clay concentration within fault gouge, mapped across the surface of the Central Fault. The calibration showed that as SGR increases, so does the measured pressure differential across the fault. This positive relationship between SGR and pressure differential suggests SGR is a guide to potential fluid-flow resistance exerted by faults. We therefore suggest that SGR can potentially be used as a guide to defining differences in permeability within and between faults in a given field. This ‘scaleability’ of SGR as an indicator of fault permeability within a field could provide hitherto unachievable flexibility in the systematic modelling of the hydraulic behaviour of faults during fluid flow simulations.

CFD analysis on fluid flow through multifilament woven filter cloths

The effects of woven structures on fluid flow through the basic weaves of multifilament woven filter cloths were studied numerically by using the fluid-flow software fluent™. From results of the numerical solution, the flow pattern and the resistance to flow in the interstices were obtained. Results of this work show that the construction of the fabric pores has a significant influence on the flow pattern in the interstices and the downstream. It is also shown that the plain weave gives the highest fluid-flow resistance while the satin weave gives the lowest under the same thread count. Furthermore, in the case of tightly woven filter cloths, the flow is predominantly through the yarns of the cloth; while the flow will generally be directed around the yarns of a loosely woven cloth, especially if the yarns are twisted tightly. A comparison of fluid flow through multifilament woven filter cloth with that of monofilament woven filter cloth is also discussed.

Mathematical Modeling of Iron and Steel Making Processes. Mathematical Model for Transient Erosion Process of Blast Furnace Hearth.

A mathematical model that can estimate the transient erosion process of the blast furnace hearth has been developed. This mathematical model can treat the molten iron flow, heat transfer and the brick/refractory erosion at the hearth. To verify the availability of the mathematical model, comparisons of computational final erosion profile of the hearth were made with the investigation results of the dissection blast furnace and computational results gave good agreement with the measured one. The effects of the distribution profile of the dripping molten iron flow rate into the hearth, the coke free layer size, production rate of the molten iron, thermal conductivity of the carbon brick and the fluid flow resistance through the coke packed bed were examined by using this mathematical model.

Glucocorticoids regulate transendothelial fluid flow resistance and formation of intercellular junctions.

The regulation of transendothelial fluid flow by glucocorticoids was studied in vitro with use of human endothelial cells cultured from Schlemm's canal (SCE) and the trabecular meshwork (TM) in conjunction with computer-linked flowmeters. After 2-7 wk of 500 nM dexamethasone (Dex) treatment, the following physiological, morphometric, and biochemical alterations were observed: a 3- to 5-fold increase in fluid flow resistance, a 2-fold increase in the representation of tight junctions, a 10- to 30-fold reduction in the mean area occupied by interendothelial "gaps" or preferential flow channels, and a 3- to 5-fold increase in the expression of the junction-associated protein ZO-1. The more resistive SCE cells expressed two isoforms of ZO-1; TM cells expressed only one. To investigate the role of ZO-1 in the aforementioned Dex effects, its expression was inhibited using antisense phosphorothioate oligonucleotides, and the response was compared with that observed with the use of sense and nonsense phosphorothioate oligonucleotides. Inhibition of ZO-1 expression abolished the Dex-induced increase in resistance and the accompanying alterations in cell junctions and gaps. These results support the hypothesis that intercellular junctions are necessary for the development and maintenance of transendothelial flow resistance in cultured SCE and TM cells and are likely involved in the mechanism of increased resistance associated with glucocorticoid exposure.

Characterization of fluid-flow resistance in root cultures with a convective flow tubular bioreactor

Agrobacterium transformed root cultures of Hyoscyamus muticus were grown in a recirculating 2 L tubular bioreactor system. Performance of this convective flow reactor (CFR) was compared to a bubble column (BC) reactor of the same geometry: replicated CFR experiments produced an average tissue concentration of 556 +/- 4 grams fresh weight per liter in 30 d whereas the bubble column produced only 328 +/- 5 grams per liter corresponding to 25.3 +/- 0.0 and 14.3 +/- 0.5 grams dry weight per liter, respectively. Because media nutrient levels were maintained sufficiently high to saturate growth rate, the improved performance of the CFR is attributed to enhanced convective mass transfer. The pressure drops observed for flow through roots grown within the reactors were more than an order of magnitude higher than previously obtained by placing roots grown in shake culture into defined geometries. The experimentally observed flow resistance was much higher than would be predicted from correlations using the root diameter as the characteristic diameter for flow resistance. Several lines of evidence suggest that root hairs are a substantial contributor to the observed high flow resistance in these transformed root cultures. Pressure drop increased nonlinearly with velocity which could not be adequately described by a modified form of the Ergun equation. Kyan et al's (1970) equation, although predicting such curvature, relies almost exclusively on an empirical packing deflection term to describe the hydrodynamic behavior. Implications of these results to the design of submerged reactor systems for root culture are discussed. Copyright 1998 John Wiley & Sons, Inc.

Fluid Flow Through Basic Weaves of Monofilament Filter Cloth

The effects of woven structures on fluid flow through basic weaves of monofilament filter cloths are studied numerically using the fluid-flow software FLUENT. The flow pattern and resistance to flow in the interstices are obtained as results of the numerical solution. The results show that the construction of the fabric pores has a significant influence on flow pattern in the interstices and downstream. Plain weave gives the highest fluid flow resistance, while satin weave has the lowest with the same thread count.

Estimation of Fluid Flow Resistance of Elastic Tube

Estimation of Fluid Flow Resistance of Elastic Tube

Effects of adhesion on microbial cell physiology

Most studies on microbial adhesion are concerned with either direct effects on the surfaces, such as in dental caries or metal corrosion, or indirect effects of microbial biofilms on fluid flow, heat exchange, substrate transformations, and biocide resistance of the microorganisms on pipelines or on biomaterials implanted in human patients. However, there are indications that certain microorganisms immobilised at surfaces possess physiological properties not evident when the organisms are in the aqueous phase. In the past, difficulties have been encountered in studying the physiology of such immobilised organisms because of the need to remove them from the surface in order to examine their physiological properties by conventional methods. This physical disturbance to the organisms may result in further alterations to their physiology. The application of reporter gene technology to such studies has allowed in situ studies of gene expression directly at surfaces and has provided possibilities of cloning and identification of a range of genes “switched on” or “switched off” at surfaces, as well as for defining the physicochemical factors that induce the changes in gene expression at solid-liquid interfaces. A reporter gene can be traced by a specific chemical reaction and can be inserted into the genome of a recipient organism where its expression is controlled by the promoter of the target gene. Applications discussed include examples of genes “switched on” on semisolid media, on solid substrata, and within a biofilm environment.

A collapsible-tube oscillator is not readily enslaved to an external resonator

Previous experiments on collapsed-tube self-excited oscillation have shown that the resistance to flow downstream of the tube controls whether a given operating point is stable, oscillatory or divergent. This paper extends the documentation of those experiments by reporting the results of measuring the frequency-dependent complex impedance to flow up- and downstream of the collapsed tube. Both up- and downstream there was a shallow resonant impedance peak. To test whether such resonance might have governed the frequency of self-excited oscillation through entrainment, both resonant frequencies were increased approximately three times, maintaining as exactly as possible the same fluid inertia and flow resistance, and approximately the same sharpness of resonant peak. Whereas the frequency of the original resonances corresponded to the broad fundamental-frequency range of the dominant mode to self-excited oscillation, the altered resonances did not attract self-excited oscillations at those frequencies. With the increased resonant frequency downstream, the transient collapse and recovery once per cycle of the self-excited oscillation gave rise to rapidly decaying ringing, clearly visible in pressure and cross-sectional area recordings. Nevertheless, the higher-frequency system was not conducive to entrained oscillation. This suggests, in turn, that entrainment was unlikely to have been responsible for setting the frequency of self-excited oscillation in the previous experiments.

Fluid Flow and Interpolar Resistance Measurements in Advanced Hall-Heroult Cells

Abstract This paper describes electrode design, velocity and interpolar resistance measurements in a physical model of advanced Hall-Heroult cells that use inert anodes and aluminum wcttable cathodes. The principal experimental tool has been a “water” model wherein gas generation was simulated by forcing compressed air through porous graphite and the fine bubbles characteristic of inert anodes were produced by adding butanol to water. Measurements were carried out with two different anode designs—one that is flat and the other that has grooves. The results show that energy-efficient operation of advanced Hall cells can be achieved by using grooved anodes that are fully submerged in the electrolyte in the near-horizontal electrode configuration.