Narrow Annulus Research Articles

Experimental and numerical investigation of heat transfer from a narrow annulus to supercritical pressure water

Heat transfer characteristics of supercritical pressure water in a narrow annulus with vertically upward and downward flows were investigated experimentally and numerically. The outer diameter of the inner heated rod is 8mm with an effective heated length of 620mm. Experimental parameters covered the pressure of 23–28MPa, mass flux of 400–1000kg/m2s and heat flux on the outer surface of the heated rod from 200 to 1000kW/m2. The general heat transfer behaviors were discussed with respect to various mass fluxes and pressures. According to the experimental data, it was found that the effect of flow direction on heat transfer depends on the heat-flux to mass-flux ratio (q/G). Heat transfer is much improved in the downward flow compared to that of upward flow at high q/G ratios. At the pressure of 25MPa, low-mass-flux deteriorated heat transfer occurred in the upward flow but not in the downward flow. At the same test parameters, however, heat transfer deterioration was observed at both of the two flow directions when the pressure was lowered to 23MPa. The experimental results indicate that buoyancy plays an important role for this type of deterioration, but is not the only mechanism that leads to the heat transfer deterioration. Three turbulence models were assessed against the annulus test data, it was found that the SST k-ω model gives a satisfying prediction of heat transfer deterioration especially for the case of downward flow. The mechanisms for the low-mass-flow heat transfer deterioration were investigated from the viewpoints of buoyancy and property variations of the supercritical water.

Lack of Diamagnetism and the Little–Parks Effect

When a superconducting sample is submitted to a sufficiently strong external magnetic field, the superconductivity of the material is lost. In this paper we prove that this effect does not, in general, take place at a unique value of the external magnetic field strength. Indeed, for a sample in the shape of a narrow annulus the set of magnetic field strengths for which the sample is superconducting is not an interval. This is a rigorous justification of the Little-Parks effect. We also show that the same oscillation effect can happen for disc-shaped samples if the external magnetic field is non-uniform. In this case the oscillations can even occur repeatedly along arbitrarily large values of the Ginzburg--Landau parameter $\kappa$. The analysis is based on an understanding of the underlying spectral theory for a magnetic Schr\"{o}dinger operator. It is shown that the ground state energy of such an operator is not in general a monotone function of the intensity of the field, even in the limit of strong fields.

Structure of the hexameric HerA ATPase reveals a mechanism of translocation-coupled DNA-end processing in archaea.

The HerA ATPase cooperates with the NurA nuclease and the Mre11-Rad50 complex for the repair of double-strand DNA breaks in thermophilic archaea. Here we extend our structural knowledge of this minimal end-resection apparatus by presenting the first crystal structure of hexameric HerA. The full-length structure visualises at atomic resolution the N-terminal HerA-ATP Synthase (HAS) domain and a conserved C-terminal extension, which acts as a physical brace between adjacent protomers. The brace also interacts in trans with nucleotide-binding residues of the neighbouring subunit. Our observations support a model in which the coaxial interaction of the HerA ring with the toroidal NurA dimer generates a continuous channel traversing the complex. HerA-driven translocation would propel the DNA towards the narrow annulus of NurA, leading to duplex melting and nucleolytic digestion. This system differs substantially from the bacterial end-resection paradigms. Our findings suggest a novel mode of DNA-end processing by this integrated archaeal helicase-nuclease machine.

The Research on the Annulus Electromagnetic Stirring for Preparing the Semisolid A356 Aluminum Alloy Slurry

The effects of annulus gap width, stirring power and stirring frequency on the microstructure of the semi-solid A356 aluminum alloy slurry have been investigated by the annulus electromagnetic stirring (AEMS) technology The results show that narrow annulus gap , strong stirring power and high stirring frequency are advantageous to obtain the small spherical primarymicrostructure, the smaller the annulus gap width is, the bigger the stirring power is, and the higher the stirring frequency is, the more uniform, the smaller and the more spherical the microstructure is. So the high stirring frequency, narrow annulus gap, strong stirring power are beneficial to obtain the fine and spherical semisolid microstructure in AEMS. Also the results indicate that the primary particles are globular, small and distribute homogeneously in the AEMS.

Analysis of Drilling Fluid Circulating Pressure Loss in Hole Annulus for Microhole Drilling

The microhole drilling (MHD) technology is one of cutting-edge drilling technologies with wellbore diameter less than 88.9 mm and taking coiled tubing (CT) as drilling string to deliver the bottomhole assembly to drill ahead. The normal circulation of drilling fluid is affected because of huge annulus drilling fluid circulating pressure loss (ADFCPL) caused by small diameter wellbore, narrow hole annulus and deep well. For three flow regimes of power-law fluid in MHD, the computing models of ADFCPL are built by analyzing the relationships among annulus drilling fluid parameters according to power law fluid flow state equation. The ADFCPL with different flow rate, CT diameter, well depth, eccen- tricity and so on is calculated for the hole annulus of MHD. The calculation results show that: in 89mm diameter MHD, the ADFCPL is huge. It increases with the increase of outer diameter of CT and average flow rate of drilling fluid, and in- creases linearly with the increase of well depth, and decreases with the increase of eccentricity. The bigger the hole annu- lus is, and the lower the flow rate is, the less the impact of eccentricity acts on the ADFCPL is. Thus, the ADFCPL can be reduced by decreasing the outer diameter of CT and the average flow rate of drilling fluid in hole annulus. Only low flow rate can be used to drill deep well. The research results may be useful for MHD parameter selections related to the ADFCPL.

Heat transfer and flow characteristics of nanofluid in a narrow annulus: Numerical study, modelling and optimisation

AbstractThis study attempts to evaluate the flow and heat transfer characteristics of water–Al2O3 nanofluid in a narrow annulus. The effects of volume fraction, the size of particles and the ratio of inner wall heat flux to outer wall heat flux were investigated on the convective heat transfer coefficients and friction coefficients at inner and outer walls of the annulus. Using smaller particles caused a greater heat transfer coefficient. Meanwhile, at higher volume fractions, changing the size of particles led to more considerable changes in the convective heat transfer coefficient and friction coefficient. As per the observation made, the value of heat transfer coefficient at the inner wall was larger than that of the outer wall. In contrast with the results of applying constant properties, changing the volume fraction will change the friction coefficient in the case of using variable properties. Moreover, genetic algorithm was used in combination with compromise programming in order to find the optimum values of the input parameters using neural network correlation.

Unusual right ventricle aneurysm and dysplastic pulmonary valve with mitral valve hypoplasia

We report a newborn with an unusual combination of aneurysmally dilated thin-walled right ventricle with hypertrophy of the apical muscles of the right ventricle. There was narrow pulmonary annulus, pulmonary regurgitation, and hypoplasia of the mitral valve and left ventricle. We propose that this heart represents a partial form of Uhl's anomaly.

Optical polarization of quasars and the Balmer edge feature revealed by ultraviolet and polarized visible to near-infrared emissions

Polarized emission from a quasar is produced by wavelength-independent electron scattering surrounding its accretion disc, and thus avoid the contamination from its host galaxy and reveal the intrinsic emission spectrum of the accretion disc. Ultra-violet (UV) emission from a quasar is normally free from the contamination from its host galaxy. Polarization fraction of the quasar's disc emission can therefore be determined by comparing total UV emission with polarized visible to near-infrared (NIR) emission; and the resulting continuum spectrum from UV to infrared can reveal the theoretically expected Balmer edge absorption feature. We fit the polarized spectra in visible and NIR bands together with the total UV spectra of two type-1 quasars (3C 95, 4C 09.72), to an extended geometrically thin and optically thick accretion disc model. In addition to the standard model, we include the Balmer edge absorption due to co-rotational neutral gas on a narrow annulus of the accretion disc. We find that the extended thin accretion disc model provides adequate description on the continuum spectra of the two quasars from UV to NIR wavelengths. A Monte-Carlo-Markov-Chain fitting to the continuum spectra is able to well constrain the true polarization fraction of the disk emission, which allows the Balmer edge feature to be completely revealed from polarized visible to UV continua. The Balmer edge feature is prominent in both quasars' spectra, and is significantly broadened due to the orbital motion of gas in the accretion disc. The broadening of the Balmer edge feature is therefore related to the quasar's inclination. This work proves the concept of determining quasar's inclination from the Balmer edge feature in their continuum spectra.

Needles of longitudinally polarized light: guidelines for minimum spot size and tunable axial extent

Optical beams exhibiting a long depth of focus and a minimum spot size can be obtained with the tight focusing of a narrow annulus of radially polarized light, leading to a needle of longitudinally polarized light. Such beams are of increasing interest for their applications, for example in optical data storage, particle acceleration, and biomedical imaging. Hence one needs to characterize the needles of longitudinally polarized light obtained with different focusing optics and incident beams. In this paper, we present analytical expressions for the electric field of such a nearly nondiffracting, subwavelength beam obtained with a parabolic mirror or an aplanatic lens. Based on these results, we give expressions of the transverse and longitudinal full widths at half maximum of the focal lines as a function of the width of the incident annular beam and we compare the performances of the two focusing systems. Then, we propose a practical solution to produce a needle of longitudinally polarized light with a tunable axial extent and a transverse width reaching the theoretical limit of 0.36λ.

The Formation of Mars: Building Blocks and Accretion Time Scale

In this review paper I address the current knowledge of the formation of Mars, focusing on its primary constituents, its formation time scale and its small mass compared to Earth and Venus. I argue that the small mass of Mars requires the terrestrial planets to have formed from a narrow annulus of material, rather than a disc extending to Jupiter. The truncation of the outer edge of the disc was most likely the result of giant planet migration, which kept Mars’ mass small. From cosmochemical constraints it is argued that Mars formed in a couple of million years and is essentially a planetary embryo that never grew to a full-fledged planet. This is in agreement with the latest dynamical models. Most of Mars’ building blocks consists of material that formed in the 2 AU to 3 AU region, and is thus more water-rich than that accreted by Earth and Venus. The putative Mars could have consisted of 0.1 % to 0.2 % by mass of water.

Enlargement of the narrow aortic annulus: valid, but not much sought-after technique

Enlargement of the narrow aortic annulus: valid, but not much sought-after technique

Age validation and growth of Micropogonias furnieri (Pisces - Sciaenidae) in a temporally open coastal lagoon (South-western Atlantic - Rocha - Uruguay) based on otolith analysis

Summary In this work 228 individuals of the whitemouth croaker Micropogonias furnieri collected in the Rocha coastal lagoon (Uruguay) from October 1997 to September 1998 were analysed. The species formed annuli in the otolith (sagitta) associated with the opaque zone (narrow opaque annulus), mainly in early winter when water temperature decreased, and reached the lowest values in July–August. The period of greatest growth occurred from December to June, partially overlapping with the spawning period (December–March) and in coincidence with the increase in marginal increment. Growth parameters determined for all individuals were K = 0.19, L∞ = 30.2 and t0 = −2.12. Annual growth increments showed that individuals grew rapidly and attained over 50% of their maximum observed size in the second year of life. In the third year, individuals attained sizes of first maturity at 11–12 cm less than estimates for the Rio de la Plata spawning area and coastal areas of Brazil. The increment in length-at-age in the Rocha coastal lagoon was smaller than in individuals inhabiting the continental shelf (up to 50 m depth).

On the axial drift of free pistons in acoustic systems.

Unlike the pistons in car engines, or other devices with crankshafts and other mechanical linkages, the pistons in acoustic devices such as pressure-wave generators, thermoacoustic coolers, or Stirling engines are part of a resonant system. The motion is induced by the overall dynamics of the system, but is not rigidly proscribed. It is therefore possible, and exceedingly common, for these pistons to experience axial “drift” from their nominal rest position while running. This most often occurs in devices that use radial “clearance seals” in which the working fluid flows in a very narrow annulus between the piston and the piston cylinder. There is no guarantee that the mass of fluid that “blows by” one way during one-half of the cycle equals the the mass that blows by during the second half; and in general these devices experience net mass transfer through the clearance seal, resulting in a buildup of dc pressure across the piston. This dc pressure tends to force the piston away from its natural center, shortening its useful stroke. Through our work with clearance seal devices, we have learned how to quantify the processes that cause this piston drift, and how to passively suppress it.

Optimal Cover of Points by Disks in a Simple Polygon

Let $P$ be a simple polygon, and let $Q$ be a set of points in $P$. We present an almost-linear time algorithm for computing a minimum cover of $Q$ by disks that are contained in $P$. We then generalize the algorithm so that it can compute a minimum cover of $Q$ by homothets of any fixed compact convex set ${\cal O}$ of constant description complexity that are contained in $P$. This improves previous results of Katz and Morgenstern [Lecture Notes in Comput. Sci. 5664, 2009, pp. 447-458]. We also consider the minimum disk-cover problem when $Q$ is contained in a (sufficiently narrow) annulus and present a nearly linear algorithm for this case, too.

Heat Transfer Enhancement in a Narrow Concentric Annulus in Decaying Swirl Flow

Heat Transfer Enhancement in a Narrow Concentric Annulus in Decaying Swirl Flow

The analytical solution of natural convection in a micro size horizontal cylindrical annulus with periodic volumetric heat flux

We consider the two-dimensional problem of steady natural convection in a narrow (micro size) horizontal cylindrical annulus filled with viscous fluid and periodic volumetric heat flux. The solution is expanded in powers of a single combined similarity parameter, which is the product of the gap ratio to the power of four, and Rayleigh number and the series extended by means of symbolic calculation up to 16 terms. Analysis of these expansions allows the exact computation for arbitrary accuracy up to 50,000 figures. Although the range of the radius of convergence is small, the Pade approximation leads our result to be good even for much higher values of the similarity parameter. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/htj.20323

Numerical investigation of laminar forced convection of water upwards in a narrow annulus at supercritical pressure

Abstract In the present work, convection heat transfer of water at supercritical pressure in a narrow annulus at low Reynolds numbers (less than 1500) has been investigated numerically. The continuity, momentum and energy equations have been solved simultaneously using computational fluid dynamics techniques with the inlet Reynolds number ranging from 250 to 1000, Grashof number from 2.5 × 10 5 to 1 × 10 6 and the inlet fluid temperature from 360 °C to 380 °C. In all of the case studies, a sub-cooled water flow at supercritical pressure (25 MPa) and a temperature close to the pseudo-critical point enters the annular channel with constant heat flux at inner wall surface and insulated at outer wall. To calculate the velocity and temperature distributions of the flow, discretized form of the governing equations in the cylindrical coordinate system are obtained by the finite volume method and solved by the SIMPLE algorithm. It has been shown that the effect of buoyancy is strong and causes extensive increase in velocity near the inner wall, and consequently an increase in the convective heat transfer, which is desirable. Besides, the effects of inlet Reynolds number, Grashof number and inlet temperature on the velocity distribution and also on the heat transfer have been investigated.

An Alternative Method of Dealing With Pressure: Friction Reducer for Water Packing of Long Horizontal Open Holes in Low-Fracturing-Gradient Environments

Summary Water packing is the most commonly used gravel-packing technique for openhole horizontal completions. With this technique, the packing of a horizontal well occurs through two sequential events, called the α wave and the β wave. Because the carrier fluid is diverted into and must travel through the narrow annulus between the screen base pipe and the wash pipe all the way to the toe, pressure builds up steadily during the β wave as the packing proceeds from toe to heel because of high friction pressures in that annulus. This rise in pressure may result in exceeding the fracturing pressure of the reservoir, which in turn causes a premature screenout and an incomplete gravel pack. This is a well-known problem, which in the past, often limited the horizontal well length that can be gravel packed in many deep-water developments because of a narrow operating window. Today, various methods are available to solve this problem, including mechanical solutions that create a short cut for fluid returns and the use of lightweight gravel that allows pumping at lower rates without having to worry about gravel settling in the work string but still having an α-wave height that will cover the screens. In this paper, we present an alternative method of dealing with the pressure rise during the β wave, reducing the friction pressures through addition of a friction reducer to brine carrier fluid. We first detail the laboratory-scale experiments used for screening of many additives considered, including laboratory-scale friction pressure measurements, compatibility with high-density brines, gravel settling, formation, and gravel-pack damage. We then discuss the results from full-scale friction tests conducted in pipe and annular geometries, using the best-candidate friction reducer selected on the basis of laboratory tests. The results indicate that a drag reduction of 20 to 70% is attained with an environmentally friendly friction reducer, with gravel-pack retained permeability in the range of 75 to 90%, depending on test conditions, and with minimal to no impact on gravel settling and, thus, on α-wave height.

Faces of Poisson–Voronoi mosaics

For a stationary Poisson–Voronoi tessellation in Euclidean d-space and for \({k\in \{1,\dots,d\}}\), we consider the typical k-dimensional face with respect to a natural centre function. We express the distribution of this typical k-face in terms of a certain Poisson process of closed halfspaces in a k-dimensional space. Then we show that, under the condition of large inradius, the relative boundary of the typical k-face lies, with high probability, in a narrow spherical annulus.

THE POINCARÉ SERIES OF THE HYPERBOLIC COXETER GROUPS WITH FINITE VOLUME OF FUNDAMENTAL DOMAINS

The discrete group generated by reflections of the sphere, or the Euclidean space, or hyperbolic space are said to be Coxeter groups of, respectively, spherical, or Euclidean, or hyperbolic type. The hyperbolic Coxeter groups are said to be (quasi-)Lannér if the tiles covering the space are of finite volume and all (resp. some of them) are compact. For any Coxeter group stratified by the length of its elements, the Poincaré series is the generating function of the cardinalities of sets of elements of equal length. Around 1966, Solomon established that, for ANY Coxeter group, its Poincaré series is a rational function with zeros somewhere on the unit circle centered at the origin, and gave an implicit (recurrence) formula. For the spherical and Euclidean Coxeter groups, the explicit expression of the Poincaré series is well-known. The explicit answer was known for any 3-generated Coxeter group, and (with mistakes) for the Lannér groups. Here we give a lucid description of the numerator of the Poincaré series of any Coxeter group, the explicit expression of the Poincaré series for each Lannér and quasi-Lannér group, and review the scene. We give an interpretation of some coefficients of the denominator of the growth function. The non-real poles behave as in Eneström's theorem (lie in a narrow annulus) though the coefficients of the denominators do not satisfy theorem's requirements.