Concentric Cylinder System Research Articles

Radiative Transfer in Finite Concentric Cylinders by the Zonal Monte Carlo Method

Solutions to two-dimensional radiative heat transfer in a finite concentric cylinder system with a gray absorbing/emitting medium are generated using the zonal Monte Carlo method. The concept of generic exchange factors is introduced. Based on these factors, solutions for finite concentric cylinders with different geometric configurations and optical thicknesses can be generated accurately and efficiently. Numerical data are presented to demonstrate the two-dimensional effects of radiative heat transfer in finite concentric cylinder systems.

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.

Application of a BEM model with dipole elements

A potential flow code is extended to include dipole elements to handle potential flow problems for offshore structures consist of thin shell geometry with both sides exposed to ocean waves. The solution on dipole elements can be represented by the drop of fluid potential across the thin shell surface. By adjusting the porous effect parameter, such a dipole element model can be applied for the solid impervious thin shell structures, porous surfaces and even the imaginary sheets attached to the sharp edges where the local flow dissipation occurs. Special attention is paid on different approaches to evaluate the drift forces on floating bodies with porous surface, including the traditional far field and pressure integration methods as well as the control surface integration approach. The solutions from the BEM model on excitation forces, off-body kinematics and drift forces are verified against the analytical solutions for a concentric porous cylinder system fixed at the seabed. The numerical performance of a two-layer source/sink model with very small gaps is investigated, taking the results from the corresponding dipole element model as the baseline. It is suggested that the mesh size requirement from DNV-RP-C205 is too strict for the two-layer panel model in the case that the exact fluid velocity on both sides of the wall is not needed. The proposed model is demonstrated in two case studies which involve the internal fluid dynamics inside tanks with interior web frame structures of a floating barge for one case and the damping effects from the sharp edge of a box barge model for the other case.

Rheological behavior of concentrated peach puree and its dilutions in a stationary state / Comportamento reológico em estado estacionário de purê de pêssego concentrado e suas diluições

A rheometer equipped with a concentric cylinder system, was used to study the effects of temperature (15, 25, 40, 55 and 70°C) and concentration (10, 12, 15, 20, 25 and 30.5ºBrix) on the flow behavior of peach puree. The rheograms were analyzed by the Power law, Herschel-Bulkley, Bingham and Casson models. The different sample concentrations were prepared as from a concentrated peach puree at 30.5ºBrix, with absolute density of 1077.49kg/m 3 , pulp content of 60.90% and pH value of 3.51. All the puree concentrations showed pseudoplastic behavior at all the temperatures with yield stress, and the Herschel-Bulkley model adequately described the flow behavior. The temperature dependence was well described by the Arrhenius model. The flow activation energy (Ea) of the concentrated peach puree (30.5ºBrix) was 5.556kJ.mol -1 and increased with reduction in the soluble solids concentration. The exponential model was adequate to describe the effect of the puree concentration on the apparent viscosity () and on the consistency index (K). Physicochemical characterization and rheological parameters are used by the food industry to optimize the development of processes, equipment and quality control procedures for the production of pulps, nectars and fruit juices.

Non-Gray Radiative Heat Transfer in Two-Dimensional Cylindrical System

Radiative heat transfer in a concentric cylinder system with a participating medium is demonstrated to be inherently two-dimensional, even for the consideration of heat transfer to the total inner or outer surface with uniform boundary conditions. For the evaluation of two-dimensional nongray radiative heat transfer, the zonal exchange factor, together with the concept of point mean beam length, is shown to be an effective solution approach. Optimal point mean beam length for radiative heat transfer between a differential area and a finite area with different geometrical configurations within the concentric cylindrical enclosure is generated. Numerical data for an example calculation is presented to illustrate the characteristics of nongray two-dimensional radiative heat transfer.

Theoretical and experimental investigation on wave interaction with a concentric porous cylinder form of breakwater

This paper aims at deriving velocity potential for the regular wave passing through a concentric porous cylinder system, which has an arbitrary smooth section. The wave interaction with the structures, for instance wave force on them and wave elevation, are discussed with different sections and wave properties in this study. The efficiency and accuracy of present method was validated by comparing with the semi-analytical method of SBFEM first. Then an experiment with a quasi-ellipse caisson was also performed to demonstrate the effectiveness and practical potential of present method. Finally, a surface-piercing concentric cylindrical system, which consists of an impermeable inner cylinder and a coaxial single-layered perforated cylinder, was investigated by using present method. The analysis shows that the maximum wave force on the inner cylinder is reduced to some extent with a noncircular perforated cylinder around it, compared with circular cases, while the wave run-up is enlarged by the uneven spacing between the boundaries with the increasing of the wave number.

Natural convection heat transfer from horizontal concentric and eccentric cylinder systems cooling in the ambient air and determination of inner cylinder location

Heat transfer characteristics of horizontal copper concentric cylinders in the case of natural convection was investigated numerically and experimentally. While the inner cylinder had an electric heater to keep it at a constant temperature, annulus was filled with water. There were two different test sections as bare and concentric cylinder systems located in different ambient temperatures in a conditioned room for the comparison of the results. Comparison of average Nusselt numbers for the air side of the concentric cylinder system and the effective thermal conductivity of the annulus were calculated with both experimental data, numerical results and a well-known correlation. Annulus and the air side isotherms and streamlines are shown for RaL = 9 × 105–5 × 106 and Ra = 2 × 105–7 × 105 respectively. Additionally, a numerical study was conducted by forming eccentric cylinder systems to determine the optimum location of inner cylinder to maximize the heat transfer rate. Comparison of heat transfer rates from bare and concentric horizontal cylinders were done under steady state conditions. Heat transfer enhancement, the effect of the decrease in condensing temperature of the inner cylinder surface on COP of an ideal Carnot refrigeration cycle and rise in COP were determined in the study. Also the optimum location of inner cylinder to maximize the heat transfer rate was determined as at the bottom quadrant of outer cylinder.

Rheological characteristics of mixed kaolin–sand slurry, impacts of pH, temperature, solid concentration and kaolin–sand mixing ratio

Significant amount of slurry waste is produced from mineral processing plants globally constituting high levels of both kaolin and sand in aqueous suspension. Large quantities of slurry and mine tailings require efficient handling, transportation and storage system. The transportation and treatment of kaolin–sand slurry is dependent on its rheological behaviour which is a function of temperature, total solid concentration and pH. In this study, the effects of total solid concentration, pH and temperature on rheological behaviour of kaolin–sand mixture were investigated. These parameters were varied to analyse the viscosity, yield stress, flow index and shear force requirements of the mixed kaolin–sand suspension as a function of these varying parameters. Experimental rheological investigation conducted on rotational stress-controlled rheometer equipped with Peltier concentric cylinder system showed that the kaolin–sand mixture suspension is shear thickening in nature. The shear stress-rate rheograms for the kaolin–sand suspension can be modelled by the Herschel–Bulkley model with high levels of accuracy for pH range of 4–11, temperature range of 20–50 °C and solid concentration of 5–50 %. Solid concentration of the suspension was found to significantly affect the rheological behaviour of the mixture where higher kaolin–sand slurry concentration resulted in greater viscosity and the trend becoming less predictable for solid concentration greater than 50 % by weight. pH was another factor affecting the rheological behaviour of kaolin–sand slurry. pH of 3 or less resulted in the dramatic increase of viscosity of the suspension possibly due to the isoelectric point of the mixture system found between pH of 3 and 4.

Effects of Temperature, Polymer Dose, and Solid Concentration on the Rheological Characteristics and Dewaterability of Digested Sludge of Wastewater Treatment Plant (WWTP)

The rheology of digested sludge affects the flow hydrodynamics, dewaterability, and the polymer consumption in wastewater treatment plants. The rheological characteristics of digested sludge are highly dependent on changes in total solid concentration, temperature, and polymer dose. Hence, this study aims at investigating the impacts of total solid concentration, temperature, and polymer dose on the rheological characteristics and the dewaterability of digested sludge. Investigating the relationship between rheological and physicochemical characteristics of sludge can also serve as a tool to optimize essential process parameters. Different homogenized digested sludge samples were subjected to rheological measurement on rotational stress-controlled rheometer equipped with Peltier concentric cylinder system. The shear stress–shear rate and viscosity–shear rate curves were then developed before and after polymer conditioning at various temperatures and solid concentrations. Different rheological model were fitted to the shear stress–shear rate and viscosity–shear rate rheograms, and the model with the best fitting and more practical significance was selected to determine key rheological parameters. The relationship between dewaterability and digested sludge rheology was also developed. The rheological characteristics of digested sludge during polymer conditioning and flocculation process was significantly affected by temperature and solid concentration; hence, polymer dose can be reduced by operating the dewatering process at optimum temperature condition and varying the polydose as a function of the total solid concentration and viscosity of the digested sludge. The dewaterability as measured in capillary suction time (CST) improved with increasing polymer dose up to 12 kg/t DS but further increase in polymer dose resulted in the deterioration of the dewaterability due to overdosing.

Comparison of rheometric devices for measuring the rheological parameters of debris flow slurry

Soil samples with clay content ranging from 15% to 31%, were taken from three debris flow gullies in Southwest China. Three debris flow slurry samples were prepared and tested with four measuring systems of an Anton Paar Physica MCR301 rheometer, including the concentric cylinder system, the parallel-plate system, the vane geometry, and the ball measuring system. All systems were smoothwalled. Flow curves were plotted and yield stress was determined using the Herschel-Bulkley model, showing differences among the different systems. Flow curves from the concentric cylinder and parallelplate systems involved two distinct regions, the low shear and the high shear regions. Yield stresses determined by data fitting in the low shear region were significantly lower than the values from the inclined channel test which is a practical method for determining yield stress. Flow curves in the high shear region are close to those from the vane geometry and the ball measuring system. The fitted values of yield stress are comparable to the values from the inclined channel test. The differences are caused by wall-slip effects in the low shear region. Vane geometry can capture the stress overshoot phenomenon caused by the destruction of slurry structure, whereas end effects should be considered in the determination of yield stress. The ball measuring system can give reasonable results, and it is applicable for rheological testing of debris flow slurries.

Dual boundary element model coupled with the dual reciprocity method to determine wave scattering by a concentric cylindrical system mounted on a conical shoal

In this study, the dual boundary element method (DBEM) is coupled with the dual reciprocity method (DRM) to investigate wave scattering by a concentric porous cylinder system, which consists of a circular inner cylinder and semicircular porous outer cylinder mounted on a conical shoal. The complex porous-effect parameter proposed by Yu and Chwang [2] is used to describe the permeability of the porous outer cylinder. The effect of topography has been considered by applying the extended mild-slope equation (EMSE) which was proposed by Chandrasekera and Cheung [10] to the entire fluid domain. The wave force, wave amplification, and increased performance configuration are illustrated through examples.

Semi-Solid State of Blast Furnace Slag Admixtures of AL2O3

Abstract The nature and properties of liquid solutions - metallurgical slags (used in the pig iron and steel production) affect the quality of the final product and processing time. The main object of the study was slag system: CaO-SiO2-MgO-Al2O3, when the content of Al2O3 was raised to ca. 25% in liquid and semi-liquid state. Measurements were performed using Searle’s method of concentric cylinder systems. Graphite measuring systems were used for testing with two types of bobs: smooth and perforated. Rheological measurements were carried out for five slag systems in the temperature range between 1310-1500°C, shear rate values were changed in the wide range between 1s-1 to 150/180s-1. FactSage application was used to calculate the mass of solid phases precipitating from the slag volume for different chemical compositions at various temperatures. In the temperature range in which the solid phases occurred in the slag the analysed systems show non-Newtonian behaviour.

S0520103 繊維懸濁液の流動配向による粘度異方性の発現([S052-01]複雑流体の流動現象(1))

Anisotropic viscosity caused by the orientation of fibers in fiber suspensions was experimentally investigated. A concentric cylinder system which is able to generate and measure a combined shear flow fields with Poiseuille flow and Couette flow has been designed and is set on a rheometer. The fiber suspensions were used for as a test sample. The matric is a silicon oil (kinematic viscosity : 1000 cSt) and the carbon fibers are dispersed into it. In the case of short fibers, the high concentration solution shows an increase of viscosity for transverse to main flow. For the long fibers, which are longer than 1/4 of the channel height, the transverse viscosity increase appears even 10 wt% solution. After cessation of the main flow, the transverse viscosity decreases to the viscosity in a no orientation state.

An Analysis of The Influence of Viscosity on The Numerical Simulation of Temperature Distribution, as Demonstrated by the CC Process

Abstract The numerical modelling of casting processes is based on complex software packages, which most often use the finite element method. But the degree of complexity of the applied model may cause an occurrence of numerical errors. These errors may be generated both by an incorrect finite element mesh and by the use of incorrect material characteristics. The ProCAST numerical software package was used for numerical calculations. A 3D model was developed on the basis of the process parameters of an actual continuous steel casting process. The temperature distribution of a solidifying strand, with dimensions of 220x1100mm, was analysed for two steel grades: F320 and S235. A series of numerical simulations were performed where the influence of the applied viscosity values on the solidifying strand temperature distribution was presented. Viscosity values from rheological examinations that were performed with an FRS1600 high-temperature rheometer were used in the numerical simulations of the CC process. The aforementioned rotational measurements were carried out for the F320 and S235 steels in the liquid and in the semi-solid statesto examine the influence of temperature on the viscosity value changes obtained. A concentric cylinder systems working in accordance with Searle’s method was used for the measurements. Numerical calculations that were based on the viscosity values from the CompuTherm LLC, thermodynamic database were compared with one other in the project. The calculated temperature distribution of the solidifying CC strand was verified on the basis of a database that was created during measurements which were conducted in industrial conditions.

Hydroelastic analysis of surface wave interaction with concentric porous and flexible cylinder systems

The present study deals with the hydroelastic analysis of gravity wave interaction with concentric porous and flexible cylinder systems, in which the inner cylinder is rigid and the outer cylinder is porous and flexible. The problems are analyzed in finite water depth under the assumption of small amplitude water wave theory and structural response. The cylinder configurations in the present study are namely (a) surface-piercing truncated cylinders, (b) bottom-touching truncated cylinders and (c) complete submerged cylinders extended from free surface to bottom. As special cases of the concentric cylinder system, wave diffraction by (i) porous flexible cylinder and (ii) flexible floating cage with rigid bottom are analyzed. The scattering potentials are evaluated using Fourier–Bessel series expansion method and the least square approximation method. The convergence of the double series is tested numerically to determine the number of terms in the Fourier–Bessel series expansion. The effects of porosity and flexibility of the outer cylinder, in attenuating the hydrodynamic forces and dynamic overturning moments, are analyzed for various cylinder configurations and wave characteristics. A parametric study with respect to wave frequency, ratios of inner-to-outer cylinder radii, annular spacing between the two cylinders and porosities is done. In order to understand the flow distribution around the cylinders, contour plots are provided. The findings of the present study are likely to be of immense help in the design of various types of marine structures which can withstand the wave loads of varied nature in the marine environment. The theory can be easily extended to deal with a large class of problems associated with acoustic wave interaction with flexible porous structures.

Short-crested waves interaction with a concentric porous cylinder system with partially porous outer cylinder

In this paper, based on the linear wave theory, the interaction of short-crested waves with a concentric dual cylindrical system with a partially porous outer cylinder is studied by using the scaled boundary finite element method (SBFEM), which is a novel semi-analytical method with the advantages of combining the finite element method (FEM) with the boundary element method (BEM). The whole solution domain is divided into one unbounded sub-domain and one bounded sub-domain by the exterior cylinder. By weakening the governing differential equation in the circumferential direction, the SBFEM equations for both domains can be solved analytically in the radial direction. Only the boundary on the circumference of the exterior porous cylinder is discretized with curved surface finite elements. Meanwhile, by introducing a variable porous-effect parameter G, non-homogeneous materials caused by the complex configuration of the exterior cylinder are modeled without additional efforts. Comparisons clearly demonstrate the excellent accuracy and computational efficiency associated with the present SBFEM. The effects of the wide range wave parameters and the structure configuration are examined. This parametric study will help determine the various hydrodynamic effects of the concentric porous cylindrical structure.

Experimental and numerical study of natural convection heat transfer from horizontal concentric cylinders

Natural convection heat transfer from horizontal concentric cylinders is studied experimentally and numerically. Concentric cylinders were formed with two test cylinders made of copper, and the annulus was filled with water. Concentric cylinder system was located in the ambient air and the inner horizontal cylinder was kept at a constant temperature. Experimental study was carried out at different ambient temperatures in a conditioned room which can be maintained at a stable required value and inside a sufficiently designed test cabin. The ambient and inner copper cylinder surface temperatures (T ∞ and T c) varied between 20 °C–30 °C and 30 °C–60 °C respectively. Also, experiments were performed for bare cylinder at the same conditions as concentric cylinders to compare results. On the basis of the experimental data average Nusselt numbers for the air side of the concentric cylinders were calculated and compared with numerical results. The effective thermal conductivity ( k e f f ) of the annulus was calculated by using the experimental data and numerical solution results and also compared with the well known correlation. Isotherms and streamlines are presented in the annulus and the air side for Ra L = 9 × 10 5–5 × 10 6 and Ra = 2 × 10 5–7 × 10 5 respectively. It is seen that numerical and experimental results are in a good agreement. Heat transfer rates under steady-state conditions from bare and concentric horizontal cylinders were compared and heat transfer enhancement was determined. Also the effect of the decrease in the temperature of the inner copper cylinder surface (condensation temperature) on COP was investigated considering an ideal Carnot refrigeration cycle. It is found that the enhancement in COP of a Carnot refrigeration cycle is 42.6% under steady-state conditions.

Hydrodynamic performance of a dual cylindrical caisson breakwater

The hydrodynamic performance of a dual cylindrical caisson breakwater (DCBW) formed by a row of caissons each of which consisting of a porous outer cylinder circumscribing an impermeable inner cylinder has been theoretically investigated. The theoretical formulation is based on the eigenfunction expansion method proposed by Spring and Monkmeyer (1974) which was further modified by Linton and Evans [Linton, C.M., Evans, D.V., 1990. The interaction of waves with arrays of vertical circular cylinders. Journal of Fluid Mechanics 215, 549–569] for an array of impermeable cylinders. The present formulation is an extension of the work of Wang and Ren [Wang, K.H., Ren, X., 1994. Wave interaction with a concentric porous cylinder system. Ocean Engineering 21(4), 343–360], wherein; the interaction of linear waves with a single concentric porous cylinder system was studied. In the present study, the formulation has been extended to the case of a group of porous dual cylinder system. Parametric studies are carried out to study the influence of porosity ( G 0) on the outer caisson, width of the doughnut chamber ( a/ b) and the angle of wave incidence on the variation in the hydrodynamic loading, wave run-up, free-surface elevation in its vicinity as well as the transmission on its lee-side. The importance of the presence of the inner cylinder in achieving the required hydrodynamic performance in terms of either protection or providing tranquility on its lee side keeping higher stability for the breakwater system is highlighted.

Effect of measuring geometries and of exocellular polymeric substances on the rheological behaviour of sewage sludge

In biological Wastewater Treatment Plants operated with the activated sludge process, the resulting suspension is a very complex non-Newtonian material. A better understanding of sludge flows could lead to improvements in the process itself. For the purpose of sludge characterisation, rheology is a well-known relevant investigation tool. In this study, rheological measurements have been carried out on sewage sludge with different total suspended solid (TSS) contents ranging from 4 to 43 g/L. Three measuring geometries, a concentric cylinders (CC) system, a double concentric cylinders (DCC2) system and a helical ribbon impeller (HRI) have first been compared in their ability to accurately characterise the rheological properties of sludge suspensions. The Herschel–Bulkley model has then been chosen to represent the flow curves. The evolution of the model parameters drawn as a function of TSS content for CC and HRI systems showed that, with both geometries, viscoplastic (VP) and shear-thinning (ST) behaviours increased with increasing TSS. Finally, the role of exocellular polymers in terms of adsorbed exopolysaccharides (EPS) concentration has also been investigated. As the sludge ages, the results showed that a decrease in EPS concentration induced a decrease in both VP and ST properties.

Interaction of regular waves with a group of dual porous circular cylinders

Diffraction of linear waves around a group of dual porous cylinders consisting of a thin and porous outer cylinder with an impermeable inner cylinder is investigated analytically based on the eigenfunction expansion method proposed by Spring and Monkmeyer [Spring BH, Monkmeyer PL. Interaction of plane waves with vertical cylinders. In: Proceedings 14th international coastal engineering conference. 1974. p. 1828–47] and further modified by Linton and Evans [Linton CM, Evans DV. The interaction of waves with arrays of vertical circular cylinders. Journal of Fluid Mechanics 1990;215:549–69]. The present formulation is an extension of the work of Wang and Ren [Wang KH, Ren X. Wave interaction with a concentric porous cylinder system. Ocean Engineering 1994;21(4):343–60], wherein; the interaction of linear waves with a single concentric porous cylinder system was studied. This paper aims at investigating the influence of multiple interactions between the cylinders in the group on the hydrodynamic wave forces, wave run-up and free-surface elevation in their vicinity. Further, the study focuses on the variation of the forces and run-up on the individual cylinders within the group compared to that on isolated cylinders.