Porous Ring Research Articles

Experimental investigation of the effects of metal foam porous rings on non-Newtonian fluid flow in a double pipe heat exchanger

In this study, we experimentally investigate the effects of metal foam porous rings on heat transfer, pressure drop, and the heat transfer performance ratio of two non-Newtonian fluids in a double-pipe heat exchanger. Enhancing the heat transfer rate is crucial for reducing the size and cost of heat exchangers. We considered various parameters in the experiment, including the power-law index (0.91 and 0.85), porous ring thickness (4, 6, and 8 mm), and the number of porous rings (2, 4, 6). The flow is a turbulent regime, with the Reynolds number ranging from 4000 to 10,000. The test setup includes a test section with a length of 1.6 m and a diameter ratio of 0.6. Open-cell copper metal foam rings with a porosity of 0.92 are placed in the annular pipe, while the internal surface of the inner pipe is subjected to constant heat flux. The results show that, for non-Newtonian Carboxy Methyl Cellulose fluids with concentrations of 0.1% and 0.2%, the average heat transfer coefficients at Reynolds number 4000 increase by 22.0% and 32.0%, respectively. With porous rings, these coefficients increase by 80.3% and 92.7%. Additionally, the average friction factor increases by 19.2% and 35.5% without porous rings and by 320% and 280% with porous rings, respectively. Furthermore, increasing the number of porous rings from 2 to 6 increases the Nusselt number by approximately 16.8% and 17.1%, respectively. The maximum friction factor is 400% higher when using a 0.2% concentration of non-Newtonian fluid. Finally, the performance of the two non-Newtonian fluids improved by approximately 28% and 36.4%, respectively, compared to the base fluid.

Suppression of the hydroelastic responses of a composite very large floating structure by a submerged elastic ring

With the aid of the method of matched eigenfunction expansions, the hydroelastic dynamics of a composite very large floating structure on a two-layer fluid is analytically investigated in the framework of linear potential flow theory. The composite structure consists of a semi-immersed rigid cylinder fixed with a floating elastic ring and protected by a submerged flexible ring for mitigating the hydroelastic responses. A new dispersion relation for the hydroelastic waves in the two-layer fluid containing a submerged plate is derived to obtain the wave numbers with a given frequency. The coupling effect among the oscillation of rigid cylinder, the deformation of the floating and submerged plates and the motion of wave is considered by dividing the problem into scattering and radiation parts. An inner product is introduced to deduce the unknown expansion coefficients of the velocity potentials. The amplitudes of heave and pitch motions for the rigid cylinder are obtained and shown graphically. The effects of the physical parameters are explored to confirm the mitigative effect of the submerged ring on the response of the composite very large floating structure. A submerged porous ring can also eliminate the amplitudes of waves in the surrounding water region.

Wave interaction with a concentric bottom-mounted cylinder system with dual porous ring plates

The interaction between linear surface waves and a concentric bottom-mounted cylinder system has been investigated using the eigenfunction expansion approach. This system contains an outer porous cylinder and an inner impermeable cylinder, which are connected by dual porous ring plates. Both cylinders are surface-piercing and rigidly installed on the flat bottom of the ocean, while the porous ring plates are fixed below the free water surface. The analytical solution of the velocity potentials can be obtained by matching the boundary conditions. After obtaining the velocity potentials, the wave force and free surface elevation are computed. The numerical results obtained for limiting cases agreed well with the published results. The results of the study show that reducing the draft, spacing, and permeability of the dual plates all contribute to reduce the horizontal force of the inner cylinder. However, the significance of the lower plate is mainly to cope with the condition where the water surface is lower than the upper plate.

Mathematical modeling of bubble size distribution in bubble column

The bubble size plays an important role in bubble column. Therefore for proper designing of bubble columns, it is vital to understand the behaviours of bubble size and its distribution. In this research the size distribution of bubble is analysed by photo graphic method. The bubbles are generated by porous ring and spyder gas sparger. The obtained results shows that porous ring sparger generates bubble having bimodal distribution, whereas the spyder sparger generates bubble with unimodal distribution. The results also shows that size distribution curve changes as the gas flow rate and physical properties of liquid changes. The gas phase fraction is also analysed. The bubble size distribution curve is also validated using population balance model concerning simultaneous coalescence and breakup model. The results obtained in this research can be useful for scale up of bubble column operated with porous ring sparger and spyder sparger.

Disruption of Saturn's ring particles by thermal stress

Spacecraft and ground-based observations show that the main rings of Saturn lack particles larger than 10 m. Tidal or collisional destruction of satellites/comets have been proposed as the origin of the main rings; however, Saturn's tide alone cannot grind km-sized fragments into submeter-sized particles because of the high mechanical strength of water ice and rock. The question arises as to why such large particles are not left in the current rings. It is known that thermal stress induced by diurnal and seasonal temperature variations can cause weathering and fragmentation of boulders and contribute to dust and regolith production on the Moon and terrestrial planets, and then such thermal stress can break particles larger than a critical radius while cannot smaller than the critical radius. In this study, we examined the role of thermal stress acting on Saturn's ring particles. We found that thermal stress can grind porous ring particles larger than 10–20 m, which explains the lack of particles larger than 10 m in Saturn's rings. Also, fragmentation by thermal stress can be adoptable for the ε rings of Uranus. Furthermore, thermal stress caused by diurnal or seasonal temperature variation acting on boulders on surfaces of icy satellites and asteroids may play an important role in the evolution of their sizes. Our calculations explain the lack of boulders on icy satellites, except in the geologically active provinces such as the tiger stripes of Enceladus, where boulders are supplied by recent geological activity. We predict that future observations can find numerous boulders around Europa's geologically active cracks.

Static and buckling characteristics of the porous ring reinforced by graphene nanofillers

The present work focuses on the static and buckling characteristics of the confined functionally graded porous (FGP) ring consolidated by graphene nanofillers (GNF). The ring is under a temperature rise field when a point load is applied on the crown position. The Halpin-Tsai micromechanics theory is used to evaluate the distribution of Young’s modulus, and the Gaussian random field theory is used to evaluate the distribution of the porosity and mass density, respectively. The influence of the thermal field on the buckling load is quantized by applying the energy function and nonlinear thin-walled shell theory. The analytical buckling load is examined numerically, and good agreement is obtained. Furthermore, the present analytical and numerical results are verified effectively by other closed-form predictions when the FGP-GNF ring reduces to a homogeneous ring. Finally, comprehensive parametric study is taken by analyzing the effect of parameters on the buckling load. These parameters include the temperature rise, porosity coefficient, weight fraction, geometric parameters of GNF, friction coefficient and Young’s modulus of the medium.

Wave diffraction from a concentric truncated cylinder system with a porous ring plate fixed inside

The diffraction problem of a concentric truncated cylinder system with a porous ring plate fixed inside is studied in the framework of linear potential theory. The system consists of a porous exterior cylinder and an impermeable interior cylinder, which are connected by an impermeable top and bottom plate, and a porous ring plate arranged below the free surface. Darcy’s law is applied to the porous boundaries under the assumption of fine pores. The velocity potential of the whole fluid domain is analytically derived by the method of variable separation and eigen-function expansion. The hydrodynamic loads of the system are obtained by integrating the pressure on the wet surface. The calculation results of the present paper are compared with the previous works with similar models to verify the correctness of the model. The effect of the dimensionless porous effect parameter of the ring plate and of the exterior cylinder, the draft–depth ratio of the ring plate, the draft–depth ratio of the system, the ratio of the interior and exterior radii are discussed. The results show that appropriate permeability and structural scale parameters can improve the hydrodynamic performance of the structure, which will provide directive guidance for engineering design.

Hydroxylamine Oxidation on Polycrystalline Gold Electrodes in Aqueous Electrolytes: Quantitative On‐Line Mass Spectrometry under Forced Convection

Herein, a method is presented that allows quantitative determination of faradaic efficiencies for dinitrogen (N2 ) generation during the electrochemical oxidation of hydroxylamine (NH2 OH), , on a polycrystalline gold Au(poly) disk electrode in aqueous electrolytes over a wide pH range. This tactic involves the use of an impinging jet electrolyte configuration incorporating a gas porous ring connected in turn to a mass spectrometer. The actual amount of N2 generated at the Au(poly) disk was assayed using the oxidation of hydrazine (N2 H4 ) in aqueous phosphate buffer (pH 7). This redox process yields N2 as the only product, allowing a direct correlation to be established between the changes in the partial pressures of N2 and the current flowing through the disk electrode. An analysis of the data collected revealed a strong dependence of both on pH and the applied potential. Although values of as high as 20 to 30 % were found in acid and neutral media over a narrow potential region, those in alkaline solution were far smaller in the entire potential range examined.

Precipitation variability differently affects radial growth, xylem traits and ring porosity of three Mediterranean oak species at xeric and mesic sites

In the Mediterranean basin, diffuse-porous, semi-ring-porous and ring-porous tree species coexist in the same regions. Climate change might differently affect these types, but a mechanistic understanding of drought effects on their xylem structure is lacking. We investigated tree-ring width and xylem functional traits in ring-porous Quercus boissieri, semi-ring-porous Q. ithaburensis and diffuse-porous Q. calliprinos, at xeric (Galilee) and mesic (Golan) sites in the South-Eastern Mediterranean basin. We quantitatively assessed how dry and wet years affect growth and xylem traits in different porosity type oaks, and evaluated whether porosity type is preserved or altered during these years. We measured, counted or computed tree-ring width, vessel number, maximum lumen area, frequency, tree-ring and xylem theoretical hydraulic conductivity along 40-year ring series of 50 trees in total. We also quantified ring porosity in each year using two indices, the Gini coefficient and the porosity ratio of vessel area, and described vessel area intra-ring variations by distribution profiles. We then compared these parameters in the five driest and five wettest years of the 40-year period. Radial growth and functional trait variations were more similar between species in the same site (strong drought effects in Q. ithaburensis and Q. calliprinos in Galilee, moderate effects in Q. boissieri and Q. calliprinos in Golan) than between sites for the same species (Q. calliprinos was more affected in Galilee than in Golan). Ring porosity indices and distribution profiles showed that diffuse-porous xylem structure of Q. calliprinos was maintained even under dry conditions at both sites. However, Q. boissieri xylem shifted from ring-porous in wet and normal years to semi-ring-porous in dry years, i.e. the porous ring cannot be completely built under water constraint. This suggests that ring porous strategy, typical of temperate regions with strong seasonality, might not be realized under future drier conditions in the Mediterranean basin.

Analytical consideration and numerical verification of the confined functionally graded porous ring with graphene platelet reinforcement

The present work is concerned with the stability behavior of the functionally graded porous (FGP) ring with graphene platelet (GPL) reinforcement. The ring is surrounded by an elastic medium and a point load is introduced at the crown position. Assuming no interface friction between the ring and medium, the buckling load of the ring with a “single-lobe” deformation is obtained analytically. Afterward, the numerical examination is developed by comparing the critical buckling load from the numerical and analytical results. The good comparison indicates the analytical solutions are applicable to the nine cases by combining three porous distributions and three GPL dispersion patterns, respectively. It is explored that the combination of symmetrical pores and symmetrical GPL to the mid-surface can resist the highest external load of the confined FGP–GPL ring, and this case is successfully compared with other closed-form expressions for the homogeneous ring without pores and GPL. Finally, the effects of porosity coefficient, and weight fraction of the GPL are examined and discussed in terms of the load capacity, the hoop force, the bending moment, the hoop stress and strain, and the geometric shapes of the GPL.

Damper with Porous Anisotropic Ring

<p class="1Body">The solution of a problem of coefficient of damper drive with a double-layer porous ring and squeeze film of lubrication is presented at its combined feed, and also the account of permeability of porous layers. Novelty of the solution is simultaneous introduction in analytical model of variety of variable factors which were considered separately earlier.</p>

Dаmреr with а pоrоus element fоr bearing arrangements

A solution to the problem of damper gain with a porous ring and compressible film of lubricant has been given. A feature of the solution is the combined assumption of a set of variable factors, which were previously only considered for particular cases.

Numerical Study of the Influence of a Porous Ring Insert on the Structure of a Swirling Flow

The influence of a porous ring insert on the structure of a swirling flow in a channel is investigated. In a strongly swirling flow the main part of the flow from the porous layer is expelled into the near-wall region and only a small part is expelled into the axial region. The maximum of the tangential velocity in the axial zone decreases with growth of the porosity. In the near-wall region the influence of the porosity on the distribution of the tangential velocity is insubstantial. With increase of the porosity the process of expulsion of gas from the porous layer becomes less intense; a zone of return flows arises at smaller swirl angles; the size of this zone increases with growth of the porosity.

Automatic control of bubble size in a laboratory flotation column

Gas dispersion properties play an important role on determining the metallurgical performance of flotation processes. Indeed, bubble surface area flux (Sb) has been found to correlate with the collection zone flotation rate constant and is therefore a potential variable to regulate in order to achieve a target performance. Sb can be calculated as a combination of two other gas dispersion properties, namely, gas superficial velocity and the Sauter bubble mean diameter. This communication describes the design and implementation of a feedback control system for the Sauter bubble mean diameter in an attempt towards controlling Sb. In order to track changes on bubble size, the Sauter bubble mean diameter was derived from an adaptive bubble size probability density function (PDF). A Gaussian mixture model was used to represent the bubble size PDF and its parameters were updated on-line and in real-time by a dedicated computer from sequentially incoming images. To improve bubble size controllability, a frit-and-sleeve sparging device was installed. This device allows modifying bubble size by manipulating the water flow rate circulating through a sleeve surrounding a porous ring (shear water). A Wiener model is used to represent the dynamic relationship between the shear water flow rate and the Sauter bubble mean diameter. A nonlinear control, based on the internal model control (IMC) structure, was designed and implemented. Tracking and regulation performance against gas velocity and unmeasured frother concentration variations were then successfully evaluated in a two-phase system.

INFLUENCE OF SOME GEOMETRICAL PARAMETERS ON THE CHARACTERISTICS OF PREFILMING TWIN-FLUID ATOMIZATION

Geometries are considered to have a great influence on the spray characteristics of atomizers. In the present study, we studied a prefilming twin-fluid atomizer patented by Sadatomi and Kawahara (2012), in which liquid atomization is implemented by supplying compressed air alone into an internal mixing chamber, and water is automatically sucked by the negative pressure induced by an orifice. In the experiments, we studied spray characteristics influenced by the geometrical parameters, such as orifices in different opening area ratios and different shapes, porous rings with different porous diameters, and different atomizer sizes. Higher spray performance can be obtained by a small sized atomizer with a circular orifice in opening area ratio of 0.429 and a porous fiber ring with porosity of 25 μm. The present results provide a significant guidance for practical applications with different requirements of spray characteristics.

Numerical Investigation of Convection Heat Transfer in Pipes with Sintered Porous Metal Rings

Fully developed turbulence single phase convection heat transfer of water in pipes filled with sintered porous metal inner rings or solid inner rings was investigated numerically respectively. Numerical calculations were conducted with the Fluent 6.3 code, using the SST k-ω turbulence model. Comparing to solid-ring turbulator pipes, porous-ring turbulator pipes have better comprehensive heat transfer effect. The maximum PEC for porous-ring turbulator pipes is 4.4 and the PEC of solid-ring turbulator pipes is less than 1. It was also analyzed effect of geometric structures on porous-ring turbulator pipe performance. f/f0 for porous-ring turbulator pipes increases with the increasing of Re while Nu/Nu0 decreases with the increasing of Re ,and PEC decreases with the increasing of Re. With the same Re, if the width of the porous ring is equal to the width of groove, f/f0, Nu/Nu0 increases and PEC decreases with the increasing height of porous ring. When the height of porous ring is constant, the f/f0, Nu/Nu0 and PEC decreases with the increasing height of porous ring under the same Re.

Magnetohydrodynamics Flow and Heat Transfer Around a Solid Cylinder Wrapped With a Porous Ring

The problem of the effect of an external magnetic field on fluid flow and heat transfer characteristics is relevant to several physical phenomena. In this paper, flow and heat transfer of an electrically-conductive fluid around a cylinder, wrapped with a porous ring and under the influence of a magnetic field, is studied numerically. The ranges of the Stuart (N), Reynolds (Re), and Darcy (Da) numbers are 0–7, 1–40, and 10−8–10−1, respectively. The Darcy–Brinkman–Forchheimer model was used for simulating flow in the porous layer. The governing equations provide a coupling between flow and magnetic fields. The governing equations, together with the relevant boundary conditions, are solved numerically using the finite-volume method (FVM). The effect of the Stuart, Reynolds, and Darcy numbers on the flow patterns and heat transfer rate are explored. Finally, two empirical equations for the average Nusselt number were suggested, in which the effect of a magnetic field and the Darcy numbers are taken into account. It was found that in the presence of a magnetic field, the drag coefficient and the critical radius of the insulation increases, while the wake length and Nusselt number decrease.

Porous Ring Disk Electrode Model for Oxygen Reduction By Non-Precious Electrocatalysts

not Available.

Reducing the Radial Error Motion of an Aerostatic Journal Bearing to a Nanometre Level: Theoretical Modelling

Ultra-precision air bearings could enable novel and more accurate precision applications. In this paper we report on the design of an ultra-precision air-bearing system, intended to reduce the radial error motion, i.e. the deviation from perfectly centric motion, to a nanometre level (i.e.<10 nm). To this end, the influence of several manufacturing errors, bearing parameters and feeding geometries is analysed on the radial error motion of an aerostatic journal bearing. This finally leads to the formulation of several design guidelines. On this basis, a numerical gas film model is developed and validated. Increasing the number of feedholes proves to be a promising solution as it results in an evenly distributed air film. The latter is confirmed by the fact that the radial error motion of an aerostatic journal bearing with a porous ring feeding geometry, which can be seen as a limiting case of infinite number of feedholes, is only 1 nm.

Investigation of filtration convection in a near-critical Van-der-Waals gas for substantial temperature differences

The qualitative mechanisms of stationary filtration convection in a near-critical Van-der-Waals gas with substantial temperature variations are investigated. The object of the study is a thin porous ring in a vertical heat-conducting plane, saturated with the gas. An adequate mathematical model, based on the averaging of the two-dimensional equations over the ring thickness, is proposed. The dependence of natural-convection characteristics on the non-Boussinesq parameters (compressibility criteria, temperature difference, and proximity to the critical point) is found. The limits of applicability of the previously known regularities related to the conditions of onset and the properties of stationary convection are discussed.