External Cylinder Research Articles

Pseudoplastic natural convection flow and heat transfer in a cylindrical vertical cavity partially filled with a porous layer

PurposeThis paper aims to theoritically investigate the free convection flow and heat transfer of a non-Newtonian fluid with pseudoplastic behavior in a cylindrical vertical cavity partially filled with a layer of a porous medium.Design/methodology/approachThe non-Newtonian behavior of the pseudoplastic liquid is described by using a power-law non-Newtonian model. There is a temperature difference between the internal and external cylinders. The porous layer is attached to the internal cylinder and has a thickness of D. Upper and lower walls of the cavity are well insulated. The governing equations are transformed into a non-dimensional form to generalize the solution. The finite element method is used to solve the governing equations numerically. The results are compared with the literature results in several cases and found in good agreement.FindingsThe influence of the thickness of the porous layer, Rayleigh number and non-Newtonian index on the heat transfer behavior of a non-Newtonian pseudoplastic fluid is addressed. The increase of pseudoplastic behavior and increase of the thickness of the porous layer enhances the heat transfer. By increase of the porous layer from 0.6 to 0.8, the average Nusselt number increased from 0.15 to 0.25. The increase of non-Newtonian effects (decrease of the non-Newtonian power-law index) enhances the heat transfer rate.Originality/valueThe free convection behavior of a pseudoplastic-non-Newtonian fluid in a cylindrical enclosure partially filled by a layer of a porous medium is addressed for the first time.

Power extraction in regular and random waves from an OWC in hybrid wind-wave energy systems

A mathematical model is developed to analyse the hydrodynamics of a novel oscillating water column (OWC) in a hybrid wind-wave energy system. The OWC has a coaxial cylindrical structure in which the internal cylinder represents the mono-pile of an offshore wind turbine while the external cylinder has a skirt whose scope is to guide the wave energy flux inside the chamber. This layout is not casual, but consistent with the current approach to harnessing wave energy through hybrid systems. The device shape is rather complex and the boundary value problem is solved by applying the matching-method of eigenfunctions. Within the framework of a linearised theory, we model the turbine damping effects by assuming the airflow to be proportional to the air chamber pressure. Consequently, the velocity potential can be decomposed into radiation and diffraction problems. We study the effects of both skirt and internal radius dimensions on the power extraction efficiency for monochromatic and random waves. We show that the skirt has strong effects on the global behaviour, while the internal cylinder affects the values of the sloshing eigenfrequencies. Finally, we validate the analytical model with laboratory data and show a good agreement between analytical and experimental results.

On the post-buckling analysis of a circular column with cylindrical constraint under concentrated torque loading

With the hypotheses of small deformation and Bernoulli-Euler beam, a gap element is introduced to describe the contact between the circular column and the external cylinder. The dynamic relaxation method is used to calculate the static equilibrium of the twisted column constrained by the cylinder. The post-buckling modes of a torsional column in a cylinder are investigated for the deformation configurations of one-point, two-point, three-point, and point-line-point contact. It is found that the end constraint has an effect on the length of the two suspended sections of helical buckling mode, but has no effect on the length of the continuous contact section in the middle. The relations have been derived among critical torque, post-buckling modes, lengths of each section, and loads (including shear, bending moment, and contact force). Finally, the torsional buckling has been investigated for sucker rods and drill pipes with lengths of 1 km. It is found that the helical buckling of multiple pitches occurs. The results of the current study provide theoretical guidance for the design of centralizer spacing in oil and gas engineering applications.

Light field enhancement of particle image velocimetry measurement using a profiled window and a ray tracing method

A light field enhancement approach using a profiled window and a ray tracing method was developed to eliminate optical shadowed regions in particle image velocimetry measurements. In this approach, the profiled window was particularly designed to optimize the global illumination of tracer particles; the ray tracing method was employed to predict the illumination intensity of the light field and optimize geometry of the profiled window. To this end, two representative configurations featured by annoying optical shadows, including the internal intersection flow and external cylinder flow, were selected for demonstration. Preliminary measurements agreed with ray tracing analysis of the existing shadows; for the internal intersection flow and cylinder flow, a bi-arc window and a parallel bi-elliptic window were respectively proposed to guide the light sheet to illuminate the otherwise shadowed region. Finally, these two flows with profiled windows embedded in experimental configurations were measured, clearly capturing the unsteady vortex structures. The proposed light field enhancement approach along with high-precision machining and polishing techniques comprise a sophisticated strategy to eliminate optical shadows in particle image velocimetry measurements.

Effects of External Magnetic Field on non-Newtonian Two Phase Fluid in an Annulus with Peristaltic Pumping

This paper comprises the exact solutions of Non-Newtonian multiphase fluid through peristaltic pumping characteristics in an annulus having complaint walls and applied magnetic field. The mechanics of the geometry are defined cylindrical due to its large number of utilizations in medicine and biological apparatus. The external cylinder is having sinusoidal waves travelling along its walls. The problem is simplified by some suitable and valid approximations. The authors have obtained the accurate solutions of the velocities of two phases. The effects of appertaining parameters have been displayed through graphs of velocity for v and particulate phases and the behavior of curves are manipulated accordingly. It is concluded that applied magnetic field decreases the velocity of both the fluid and the particles flow.

Nanofluid flow and MHD mixed convection inside a vertical annulus with moving walls and transpiration considering the effect of Brownian motion and shape factor

In the present study, the exact solution of a nanofluid flow and mixed convection within a vertical cylindrical annulus with suction/injection, which is adjacent to the radial magnetic field, is presented with regard to the motion of cylinders’ walls. The impact of Brownian motion and shape factor on the thermal state of CuO–water nanofluid is also considered. The influence of such parameters as Hartmann number, mixed convection parameter, suction/injection, volume fraction of nanoparticles and motion of cylinders’ walls on flow and heat transfer is probed. The results show that the shape of the nanoparticles could change the thermal behavior of the nanofluid and when the nanoparticles are used in the shape of a platelet, the highest Nusselt number is obtained (about 2.5% increasement of Nusselt number on internal cylinders’ wall comparison to spherical shape). The results shed light on the fact that if, for example, the external cylinder is stationary and the internal cylinder moves in the direction of z axis, the maximum and minimum heat transfer take place on the walls of internal and external cylinders, respectively (for η = 300, about 15% increasement of Nusselt number on internal cylinders’ wall). Furthermore, the enhancement of radius ratio between two cylinders increases the rate of heat transfer and decreases the shear stress on the internal cylinder’s wall.

Mixed Convective Flow of Electrically Conducting Fluid in a Vertical Cylindrical Annulus With Moving Walls Adjacent to a Radial Magnetic Field Along With Transpiration

The steady, viscous flow and mixed convection heat transfer of an incompressible electrically conducting fluid within a vertical cylindrical annulus with moving walls are investigated. This annulus is under the influence of a radial magnetic field and the fluid is suctioned/injected through the cylinders' walls. An exact solution of the Navier–Stokes equations and energy equation is derived in this problem where heat is transferred from the hot cylinder walls with constant temperature to the cooler moving fluid. The role of the movement of the annulus walls is studied on the flow and heat transfer of the fluid within the annulus, for the first time. The effects of other parameters, including Prandtl number, Hartman number, mixed convection parameter, suction/injection parameter and ratio of the radius, on the behavior of the flow and heat transfer of the fluid is also considered. The results indicate that if, for example, the internal cylinder wall moves in the direction of z-axis and the external cylinder is stationary, the maximum and minimum heat transfer occur on the walls of internal and external cylinders, respectively. Moreover, the augmentation of the radius ratio between the two cylinders increases the rate of heat transfer and decreases the shear stress on the wall of the internal and external cylinders, however, the results on the wall of external cylinder are exactly the reverse. Consequently, by changing the effective parameters used in this paper, the flow of the fluid can be controlled and the heat transfer of the fluid can be improved.

Ориентационные эффекты конвекции в полости между частично нагретыми цилиндрами различной формы

This paper reports the results of numerical simulation of a steady-state convective flow of incompressible fluid in the gap between two coaxial cylinders. We assume that only one side of the inner triangular cylinder is heated, and the external circular cylinder is kept at constant temperature. It has been established that the rotation of the heater through a certain angle causes the convective plume axis to deviate. This strongly affects the flow pattern and the related heat transfer process. The maximum integral heat flux is observed when the heater is in its side position, and the minimum heat flux is observed when the heater is in the bottom position. Approximating the results, we obtain the dependence of the Nusselt number on the Rayleigh parameter and the rotation angle.

Heat transfer enhancement induced by the geometry of a LHTES device

In the present contribution the authors investigate by means of numerical simulations the thermal performance of two geometries of Latent Heat Thermal Energy Storage (LHTES). The numerical model takes into account the mass, momentum and energy equations for the PCM together with an Entalphy-Porosity model for the phase change and a Bussinesq approximation for the buoyancy force. Indeed in such a system the convective motion within the melted PCM plays an important role, as confirmed by several studies. The scope of the research has been the enhancement of heat transfer performance of LHTES increasing the convection by means of modifications on the shape of the PCM enclosure. In particular, in this study two geometries have been considered to investigate the influence of the convective motion on the overall melting time. The first case consists of two concentric cylinders with the axis aligned with the vertical direction, in order to realize an internal heating of the Phase Change Material (PCM) that is confined between the internal and the external cylinder. It is a well-known ”shell-and-tube” configuration, generally adopted in LHTES systems, even in CSP applications. In the second case, the authors propose a simple cylindrical geometry filled with the PCM, with the cylinder axis aligned with the vertical position. Thus, the heated surface corresponds to the external lateral surface of the cylinder. The PCM volume (V) and the net heat transfer surface (A) have been kept constant in the two cases, in order to be able to compare them under the same operative conditions. The tests reveal a sensible difference between the thermal performance of the two proposed solutions. The external heating configuration shows an important enhancement of the convective motion within the PCM that induces a more efficient heat transfer with respect to the standard ”shell-and-tube” configuration. The complete melting time of the PCM with external heating is reduced by about 50%.

Compliant four-bar linkage synthesis with second-order flexure hinge approximation

The paper discusses an original methodology for addressing the synthesis of a compliant four-bar mechanism for prescribed finite coupler motion. The proposed method is based on the modelling of the four flexure hinges by using a planetary arrangement (two external cylinders rolling without slipping one on the other) able to accurately reproduce the relative motion between connected parts for a large range of deformation. The adopted approach allows a trade-off between accuracy and limited complexity in deducing the closure loop equations of the whole mechanism. The methodology is applied on a test case of a four-bar compliant linkage whose coupler occupies a prescribed set of finitely separated positions. The synthesized linkage has been analysed both with a pseudo-rigid model (built with mid-sized hinges) and a nonlinear finite element model.

Free convection of copper–water nanofluid in a porous gap between hot rectangular cylinder and cold circular cylinder under the effect of inclined magnetic field

Natural convection heat transfer of copper–water nanofluid in a porous gap between hot internal rectangular cylinder and cold external circular cylinder under the effect of inclined uniform magnetic field has been investigated. Domain of interest is a porous sector, where horizontal and vertical adiabatic borders are the external circular cylinder radii. Governing equations formulated in dimensionless stream function, vorticity and temperature variables using the Brinkman-extended Darcy model for the porous medium, single-phase nanofluid model with Brinkman correlation for the nanofluid viscosity and Hamilton and Crosser model for the nanofluid thermal conductivity have been solved numerically by the control volume finite element method. Effects of the Rayleigh number, Hartmann number, Darcy number, magnetic field inclination angle, nanoparticles volume fraction, nanoparticles shape factor, nanoparticles material, nanofluid thermal conductivity and dynamic viscosity models and nanofluid electrical conductivity correlation on streamlines, isotherms, local and average Nusselt numbers have been studied. Obtained results have shown the heat transfer enhancement with the Rayleigh number, Darcy number, nanoparticles volume fraction and nanoparticles shape factor, while the heat transfer rate reduces with the Hartmann number and magnetic field inclination angle. At the same time, the average Nusselt number increases at about 16% when nanoparticles volume fraction rises from 0 till 4% for Ra = 105, Ha = 25, while for Ha = 0 one can find the heat transfer rate augmentation at about 9% for the same conditions. In the case of different nanofluid thermal conductivity and dynamic viscosity models, it has been found that KKL model reflects the heat transfer rate reduction with nanoparticles volume fraction, while for the Hamilton–Crosser–Brinkman model, the heat transfer rate increases. Comparison between the Maxwell correlation for the nanofluid electrical conductivity and the base fluid electrical conductivity illustrates an intensification of the convective heat transfer rate for high values of the Rayleigh number (Ra ≥ 104) in the case of Maxwell correlation for the nanofluid electrical conductivity. At the same time, the effect of the nanoparticles volume fraction becomes more significant when nanofluid electrical conductivity is a function of nanoparticles volume fraction.

Technical feasibility of a proton battery with an activated carbon electrode

The technical feasibility of a small-scale ‘proton battery’ with a carbon-based electrode is demonstrated for the first time. The proton battery is one among many potential contributors towards meeting the gargantuan demand for electrical energy storage that will arise with the global shift to zero greenhouse emission, but inherently variable, renewable energy sources. Essentially a proton battery is a reversible PEM fuel cell with an integrated solid-state electrode for storing hydrogen in atomic form, rather than as molecular gaseous hydrogen in an external cylinder. It is thus a hybrid between a hydrogen-fuel-cell and battery-based system, combining advantages of both system types. In principle a proton battery can have a roundtrip energy efficiency comparable to a lithium ion battery. The experimental results reported here show that a small proton battery (active area 5.5 cm2) with a porous activated carbon electrode made from phenolic resin and 10 wt% PTFE binder was able to store in electrolysis (charge) mode very nearly 1 wt% hydrogen, and release on discharge 0.8 wt% in fuel cell (electricity supply) mode. A significant design innovation is the use of a small volume of liquid acid within the porous electrode to conduct protons (as hydronium) to and from the nafion membrane of the reversible cell. Hydrogen gas evolution during charging of the activated carbon electrode was found to be very low until a voltage of around 1.8 V was reached. Future work is being directed towards increasing current densities during charging and discharging, multiple cycle testing, and gaining an improved understanding of the reactions between hydronium and carbon surfaces.

On Calculating the Stopping Time of a Cylindrical Body Rotating in a Viscous Continuum and the Time of Entrainment of a Coaxial External Cylinder

The velocity distribution in the vicinity of the surface of an axisymmetric body rotating in a viscous medium at frequency ω directed along its axis is determined. The dissipative function has been calculated and used for deriving the equation of motion, from which an analytic expression for the stopping time of the body (until its complete stoppage) is obtained. The time of entrainment of an external stationary cylinder coaxial with the body is calculated by solving the time-dependent Navier–Stokes equation.

Effect of viscous dissipation in two-dimensional Stokes flow between rotating cylinders – preliminary numerical investigation

This paper introduces the modelling of two-dimensional laminar flow of Newtonian fluid in a system of concentric or eccentric rotating cylinders with regards to viscous dissipation. Viscous dissipation is a main part, where the viscosity is large for example in oils. The dependence of the Nusselt number on the ratio of the radius of the inner cylinder to the radius of the external cylinder for the selected distance of the cylinder axes was investigated. In order to determine the velocity fields and the temperature distribution, the boundary element method was used. The results of the calculations were presented in the form of diagrams.

Stationary heat transfer in helicoidal flows of a rarefied gas

The paper focuses on a stationary problem in a rarefied gas confined between two coaxial cylinders kept at different constant temperatures. It is assumed that the external cylinder is at rest, while the internal one rotates around its axis and contemporaneously moves upwards with a constant axial velocity, so that a helicoidal motion of the fluid is generated. The equations of Rational Extended Thermodynamics are introduced to study the physical effects due to the combination of both helicoidal flow and heat transfer. It turns out that, although only a radial temperature gradient is prescribed, both the tangential and the axial components of the heat flux do not vanish. Moreover, all the components of the stress tensor are not null, even though the radial and the axial velocity of the gas depend only on the radial coordinate. The results are compared with the prediction of the corresponding Classical Thermodynamics model and significative differences are observed. The role of the helicoidal motion is also analyzed through a comparison with the cases of only rotation or only axial flows.

Non-isothermal axial flow of a rarefied gas between two coaxial cylinders

A stationary problem of heat transfer in a rarefied gas confined between two coaxial cylinders is presented. The two cylinders are maintained at two different constant temperatures, so that a radial temperature gradient is created. The external cylinder is at rest, while the internal one moves in the axial direction with a constant velocity. A flow of the gas in the z -direction, orthogonal to the temperature gradient, is created by the motion of the internal boundary. Instead of the classical Navier-Stokes and Fourier theory, the field equations of extended thermodynamics with 13 moments are used in order to describe this physical problem. It turns out that, although only a radial temperature difference is imposed, the heat flux presents also an axial component. Moreover, some components of the stress tensor do not vanish, even though the axial velocity of the gas depends only on the radial coordinate r . The solution here obtained is compared with the classical one. Furthermore, the dependence of the solution on the boundary velocity is investigated.

Determination of the fracture cause in an aircraft motor cylinder

Abstract One of the six cylinders of an aircraft four-cycle motor was fractured in two pieces between the 13th–14th cooling fins. To determine the root cause of the fracture, it was necessary a preliminary observation of the whole motor to verify the state of valves, spark plugs, seats, and their disposition in order to determine a possible motor malfunction previous to the failure. Afterwards, a chemical and mechanical material characterization and a fracture surface fractographic study were carried out determining the heat treatment state using metallography and microscopy techniques. Observations of the external and inner cylinder surface were made to detect the possible presence of cracks or pitting. Some pitting were observed in the cylinder external wall. It was determined that material was a quenched and tempered steel, type AISI 4140, and the fracture was brittle presenting fractographic signs of a progressive fracture, concluding that the fracture was originated by a corrosion pit localized in the cylinder external wall that progressed by a fatigue mechanism.

MHD liquid metal flow and heat transfer between vertical coaxial cylinders under horizontal magnetic field

Direct numerical simulations are presented of MHD liquid metal flow and heat transfer in vertical annuli. Three annular gaps and four ratios of annular height to annular gap are considered. The walls of the external and internal cylinders are isothermal with the temperature of the outer cylinder being higher and, thus, buoyancy is the driving force. The results show that the fluid motion increases as the aspect ratio and the annular gap become larger. The presence of the magnetic field results to fluid deceleration and, thus, to flow stabilization. Additionally, non symmetric flow patterns develop, due to the magnetic field, resulting in differently sized normal and parallel wall layers, namely the Hartmann and the Roberts layers, respectively. For all annular gaps considered, the highest spatially averaged heat transfer rates are obtained for aspect ratios equal to 1.

Coupled Hydraulic System for Tensile Testing in Compression-only Machines

Fracture theory for normal strength concrete has thoroughly been studied over the past decades. Through indirect and direct tensile testing techniques, the post-peak softening response of conventional concrete has been established and utilized in analysis and design. However, for more recently developed concrete materials (e.g. fiber reinforced, high performance) under complex loading conditions, the required fracture properties to predict response are extremely limited. Considering this lack of knowledge, the objective of this research was to develop a uni-axial tensile testing technique to attain the post-peak softening response for ultra-high performance concrete for ultimate use in conjunction with an applied confining pressure system. Specifically, this research was conducted for implementation into an existing, large compression-only machine at the US Army Engineer Research and Development Center (ERDC). The new methodology enabled the existing testing frame to apply a stiffening force, while an external hydraulic plunger cylinder performed the tensile test. The scheme enables tensile testing under confining pressures in the compression-only machine.

Numerical simulation of the optimal spacing for a radial finned tube cooled by a rectangular jet. I – Average thermal results

The present work investigates the average heat transfer on a finned cylinder cooled by a rectangular jet of height H. The diameter of the external cylinder, without fins, is D and the cylinder to slot ratio D/H is equal to 1. Numerical simulations are carried on with two turbulent models, RNG k–ɛ and SST k–ω. The jet flow can be characterized by the Reynolds number, defined with the diameter of the external cylinder without fins, D, or with the hydraulic diameter of the rectangular slot, Dhydr ≈ 2H. Two turbulent flows are investigated at ReD = 7100, or ReDhydr = 13,200, and at ReD = 19,700, or ReDhydr = 36,700. The main goal of the paper is to evaluate the optimal spacing, s, between the fins, and the optimal slot-to-cylinder distance, S/H, which maximize the average heat transfer on the finned cylinder. The optimization process is performed for a pitch of 3 mm and at a given value of the fin volume. The numerical simulations show that an optimal configuration is obtained when the ratio s/l of the spacing, s, to fin height, l, is maximum, and the cylinder is set at the slot-to-cylinder distance, S/H = 3.