Spiral Stream Research Articles

A CFD study on thermohydraulic characteristics of a nanofluid in a shell-and-tube heat exchanger fitted with new unilateral ladder type helical baffles

The present study aims to research the thermohydraulic characteristics and performance index for flow of the nanofluids containing varied particle shapes including cylinder, blade, brick, platelet, and Oblate Spheroid (OS) in a shell and tube heat exchanger (STHX). The STHX is equipped with new unilateral ladder-type helical baffles to develop spiral stream inside the shell side. The nanofluid is assumed as the hot fluid that passes inside the tube side. Water is selected for the cold fluid that flows within the shell side with Reynolds numbers of 5000 to 20,000. The flow pattern developed by the baffles has noticeable impacts on the STHX performance. By the rise in the Reynolds number of the shell side, the heat transfer rate, overall heat transfer coefficient, effectiveness, Number of Transfer Unit (NTU), and pressure drop increase, whereas the performance index decreases. Moreover, the highest heat transfer rate, overall coefficient, and pressure loss belong to the nanofluid containing the platelet additives, while the greatest effectiveness, NTU, and performance index happen for the nanofluid with the OS additives. The severe cross and secondary flows are completely obvious in the shell side due to the existence of the new baffles, specially at high Reynolds numbers.

Numerical research of stream analysis on helical baffles heat exchangers

In this paper, the numerical simulations for a helical baffles heat exchanger and a segmental baffles heat exchanger with component clearance are performed to reveal the features of leakage streams and their effect on heat exchanger performance. Helical baffles heat exchanger models with four different angles and segmental baffles heat exchanger model were established and calculated via Gambit and Fluent software. The results reveal that the heat exchanger with a 40° helix angle shows the best comprehensive heat transfer performance in turbulent state, and the heat exchanger with a 50° helix angle shows better comprehensive heat transfer performance in laminar flow state. The leakage streams proportion of the helical baffles heat exchanger varies from 5.5% to 6.1%, compared with the leakage streams proportion changes from 16.6% to 21.0% in the segmental baffles heat exchanger. In both turbulent flow state and laminar flow state, with the rise of shell-side Reynolds number, the main spiral stream B proportion decreases and the leakage streams proportion increases in the segmental baffles heat exchanger, while the stream B proportion increases and the leakage streams proportion decreases in helical baffles heat exchanger. The proportion of stream B increases with the increase of the helix angle β and the proportions of leakage streams decrease with the increase of β. The proportion of the tube-baffle leakage stream A increases in radial direction. Both the proportion of stream A and that of the baffle-shell leakage stream E fluctuate in the intermediate zone in axial direction; the stream A proportion decreases at the inlet and outlet zone, while the stream E proportion increases at the inlet and decreases at the outlet zone. The results of this paper could be of great significance in the optimal design and manufacture of the helical baffles heat exchanger.

Cool and luminous transients from mass-losing binary stars

Motivated by the recently established link between luminous red novae (LRN) and catastrophic phases of binary star evolution, we perform smoothed particle hydrodynamic calculations of outflows from binary stars with realistic equation of state and opacities. We focus on the case of mass loss from the outer Lagrangian point (L2), where the resulting spiral stream experiences tidal torques from the binary and becomes unbound. As the individual spiral arms merge and collide near the binary, the outflow thermalizes about 5% of its kinetic energy. For reasonable binary parameters, the outflow can produce luminosities up to 106 L⨀ with effective temperatures between 500 and 6000 K, depending on the optical depth through the outflow. This is compatible with many examples of the LRN such as V838 Mon and V1309 Sco. The luminosity and the expansion velocity are correlated, as is roughly observed in the known LRN. The outflow readily forms dust, leading to great variations of the appearance of the transient as a function of the viewing angle. Our results are relevant for a more general class of equatorial outflows with asymptotic velocity and heating rate near the binary proportional to its orbital speed.

Affecting Factors and Kinetics of New Developed Symmetrical Spiral Stream Anaerobic Bioreactor (SSSAB) for Wastewater Treatment

Affecting Factors and Kinetics of New Developed Symmetrical Spiral Stream Anaerobic Bioreactor (SSSAB) for Wastewater Treatment

Cool and luminous transients from mass-losing binary stars

We study transients produced by equatorial disk-like outflows from catastrophically mass-losing binary stars with an asymptotic velocity and energy deposition rate near the inner edge which are proportional to the binary escape velocity v_esc. As a test case, we present the first smoothed-particle radiation-hydrodynamics calculations of the mass loss from the outer Lagrange point with realistic equation of state and opacities. The resulting spiral stream becomes unbound for binary mass ratios 0.06 < q < 0.8. For synchronous binaries with non-degenerate components, the spiral-stream arms merge at a radius of ~10a, where a is the binary semi-major axis, and the accompanying shock thermalizes about 10% of the kinetic power of the outflow. The mass-losing binary outflows produce luminosities reaching up to ~10^6 L_Sun and effective temperatures spanning 500 < T_eff < 6000 K, which is compatible with many of the class of recently-discovered red transients such as V838 Mon and V1309 Sco. Dust readily forms in the outflow, potentially in a catastrophic global cooling transition. The appearance of the transient is viewing angle-dependent due to vastly different optical depths parallel and perpendicular to the binary plane. We predict a correlation between the peak luminosity and the outflow velocity, which is roughly obeyed by the known red transients. Outflows from mass-losing binaries can produce luminous (10^5 L_Sun) and cool (T_eff < 1500 K) transients lasting a year or longer, as has potentially been detected by Spitzer surveys of nearby galaxies.

Radial and Spiral Stream Formation in Proteus mirabilis Colonies

The enteric bacterium Proteus mirabilis, which is a pathogen that forms biofilms in vivo, can swarm over hard surfaces and form a variety of spatial patterns in colonies. Colony formation involves two distinct cell types: swarmer cells that dominate near the surface and the leading edge, and swimmer cells that prefer a less viscous medium, but the mechanisms underlying pattern formation are not understood. New experimental investigations reported here show that swimmer cells in the center of the colony stream inward toward the inoculation site and in the process form many complex patterns, including radial and spiral streams, in addition to previously-reported concentric rings. These new observations suggest that swimmers are motile and that indirect interactions between them are essential in the pattern formation. To explain these observations we develop a hybrid model comprising cell-based and continuum components that incorporates a chemotactic response of swimmers to a chemical they produce. The model predicts that formation of radial streams can be explained as the modulation of the local attractant concentration by the cells, and that the chirality of the spiral streams results from a swimming bias of the cells near the surface of the substrate. The spatial patterns generated from the model are in qualitative agreement with the experimental observations.

ITER FW cooling by a flat channel, adapted to low flow rate and high pressure drop

Application of hypervapotron (HV) to cool in-vessel components of ITER – divertor and first wall (FW) – is characterized by the same design load (5 MW/m 2) but water flow rate for FW is 8–9 times (almost by order!) less for parallel feeding elements so it seems it would be better to use other design. Several variants of a flat channel design different from HV are suggested that enable to adapt a channel to pressure quota up to 1 MPa and higher. A main feature of the suggested variants is a spiral or multi-spiral stream (flat multi spiral––FMS) that improves heat rejection and can be obtained both by exciting of such mode and forced by channel geometry. Comparison of the variants was carried out in simulations (Ansys CFX) as well as in experiments on the TSEFEY-M facility with electron-beam gun. It is shown that excitation of a spiral stream in a channel significantly reduces a temperature of a loaded surface of a channel. Miniature thermocouples were used to measure temperature near the surface.

Influence of spiky twisted tape insert on thermal fluid performances of tubular air–water bubbly flow

An experimental study that comparatively examined the two-phase flow structures, pressure drops and wall-to-fluid heat transfer properties between the plain tube and the enhanced tube with the spiky twisted-tape insert (swirl tube), was performed to disclose their differential thermal-fluid performances with air–water flows. On-line and post-processed high-speed digital images of air–water two-phase phenomena in plain and swirl tubes were detected to ensure the bubbly flow pattern in plain tube and to visualize their characteristic interfacial structures. Superficial liquid Reynolds number ( Re L) and air-to-water mass flow ratio (AW), which were respectively controlled in the ranges of 5000–15,000 and 0.0004–0.01, were selected as the controlling parameters of heat transfer performances. The dispersed rising air bubbles in the plain tube and the centrifugal-force induced coherent spiral stream of coalesced bubbles in the swirl-tube core considerably modify the pressure-drop and heat-transfer performances from the single-phase conditions. Selected results of pressure-drop and heat-transfer measurements, flow images and tube-averaged void fractions detected from the plain and swirl tubes with air–water two-phase flows were cross-referenced to illustrate the mechanisms responsible for the modified thermal-fluid performance due to the spiky twisted-tape insert. Empirical heat transfer correlations which evaluate the Nusselt numbers over the developed flow regions of the plain and swirl tubes with air–water two-phase flows were generated for industrial applications.

Magnetically Arrested Disks and the Origin of Poynting Jets: A Numerical Study

The dynamics and structure of accretion disks, which accumulate a vertical magnetic field in their centers, are investigated using two- and three-dimensional MHD simulations. The central field can be built up to the equipartition level, where it disrupts a nearly axisymmetric outer accretion disk inside a magnetospheric radius, forming a magnetically arrested disk (MAD). In the MAD, the mass accretes in the form of irregular dense spiral streams, and the vertical field, split into separate bundles, penetrates through the disk plane in low-density magnetic islands. The accreting mass, when spiraling inward, drags the field and twists it around the axis of rotation, resulting in collimated Poynting jets in the polar directions. These jets are powered by the accretion flow with an efficiency of up to ~1.5% (in units of inc2). The spiral flow pattern in the MAD is dominated by modes with low azimuthal wavenumbers m ~ 1–5 and can be a source of quasi-periodic oscillations in the outgoing radiation. The formation of the MAD and the Poynting jets can naturally explain the observed changes of spectral states in galactic black hole binaries. Our study is focused on black hole accretion flows; however, the results can also be applied to accretion disks around nonrelativistic objects, such as young stellar objects and stars in binary systems.

A Multiwavelength Campaign on γ Cassiopeiae. IV. The Case for Illuminated Disk‐enhanced Wind Streams

On 1996 March 14¨15 we conducted a campaign with the Hubble Space Telescope GHRS to observe the Si IV jj1394, 1403 lines of the B0.5e star c Cas at high temporal and spectral resolution. As a part of this D22 hr campaign, the Rossi X-Ray T iming Explorer (RXT E) was also used to monitor this stars copious and variable X-ray emission. In this fourth paper of a series we present an analysis of the rapid variations of the discrete absorption components (DACs) of the Si IV doublet. The DACs attain a maximum absorption at (1280 km s~1, taper at higher velocities, and extend to (1800 km s~1. The DACs in this stars resonance lines have been shown to be correlated with a yr cycle in the Balmer Z6 line emission V /R ratio, and in 1996 this DAC strength was near its maximum. We derive hydrogen densities of 109¨1010 cm~3 in the DAC material using a curve-of-growth method and —nd that the plasma becomes marginally optically thick near (1280 km s~1. The ii mean DAC ˇˇ probably represents a broad ii plateau ˇˇ with a volume density intermediate between the stars midlatitude wind and equato- rial disk. We also follow the blueward evolution of subfeatures in the DACs. These features appear to emanate primarily from one or two discrete azimuths on the star and accelerate much more slowly than expected for the background wind, thereby exhibiting an enhanced opacity spiral stream pattern embed- ded within the structure forming the DAC. In the —rst two papers in this series, we suggested that active X-ray centers are associated with at least two major cool clouds forced into corotation. Several corre- lations of —ickering in the Si IV DACs are found in our data, which support the idea that changes in X-ray ionizing —ux cause changes in the ionization of material at various sectors along the spiral pattern. We demonstrate that similar —ickering is visible in archival IUE data from 1982 and may also be responsible for earlier reports from Copernicus of rapid changes in this stars UV and optical lines. Finally, we discovered that —ickering of the DAC —uxes in the 1982 data is correlated with rotation phase and shows a modulation with a 7.5 hr cyclical cessation of X-ray —ares that was observed recently by RXT E. This con—rms our basic picture that lulls in X-ray activity close to the stars surface cause both a lower Si V ionization fraction and an increase in Si IV variability within the DAC structures. Subject headings: circumstellar matterline: pro—lesstars: early-typestars: emission-line, Be ¨ stars: individual (c Cassiopeiae) ¨ stars: winds, out—ows

小気球のコマ取り撮影による都市キャニオン内の空気循環の測定

The simplest expression of the urban surface is alternation of buildings and streets. The space above a street between buildings is called an urban canyon. Air circulation in an urban canyon, which affects the behavior of air pollutants emitted by motor vehicles, is a significant factor in investigating the urban environment. However, because of the difficulty in installing observation equipment, few observational studies on air circulation have been conducted in actual urban canyons. In the present study, in order to detect three-dimensional air circulation in an urban canyon quantitatively, three wind vector components were measured using interval camera and tracer balloons with a known ascending rate. The three-dimensional position of the tracer balloons was determined by microscopic measurements of the position and diameter of the balloons on the negatives taken at an interval of two seconds (Fig. 2, Photo 1). Thereafter, wind vectors that drive the tracer balloons were calculated by subtracting the ascending rate of the respective balloons from the vectors of balloon movement. The direction and length of the target canyon, located on the former campus of Hiroshima University in Hiroshima City, are NNW-SSE and about 80 m, with canyon height and width of about 18 m and 25 m, respectively (Fig. 1). During the observation periods, wind at 3 m above the rooftop level blew obliquely to the canyon direction, and wind velocity ranged from 1.6 to 2.3 m/s (Table 2). The results of observations can be summarized as follows: 1) Measurement of air circulation using tracer balloons and interval camera is a simple method for the set-up of observation equipment, and can be used without serious error (Table 1). Therefore, this method is applicable to actual urban canyons. 2) Although there were marked contrasts in the distribution of air and surface temperatures in a canyon, no significant difference was observed in air circulation between approximately noon and during the afternoon (Fig. 4). Therefore, the air circulation detected in this study could be induced mechanically by downward air motion due to the blocking effect of leeward buildings. Air flow parallel to the canyon direction was in a spiral stream (Fig. 3). Moreover, the intensity of circulation defined as wind vorticity (Fig. 5) in the cross-section of the canyon correlated positively and significantly with the wind component perpendicular to the canyon direction at 3 m above the rooftop level (Fig. 6). 3) Wind velocity parallel to the canyon direction increased toward the leeward canyon direction (Fig. 3 (b), (c)). The increase in the wind component rate parallel to the canyon direction was nealy proportional to the downward wind velocity at the canyon top (Fig. 7), i. e., the net downward air flow from the canyon top should accelerate wind velocity in the canyon along the canyon direction. In conclusion, it was observationally confirmed that air circulation in the urban canyon spirals with descending and ascending motions on the leeward and windward sides of the canyon versus to the wind aloft, respectively. Moreover, the intensity of air circulation varies according to the wind velocity aloft, and wind velocity parallel to the canyon direction is accelerated by net inflow from the canyon top. Since the wind conditions in the present observation were rather limited, further observations are needed for various wind velocities and directions.

Intracardiac flow patterns in early embryonic life. A reexamination.

Microangiography, using methylene blue injected at eight vitelline vein sites, was performed on 156 developing chick embryos at Hamburger-Hamilton stages 14-22. Two stream patterns were observed. Type A coursed sequentially through the dorsal portion of the sinus venosus, the cranial segments of the primitive atrium and atrioventricular canal, the ventral parts of the primitive ventricle and conus cordis, and, finally, the left branchial arches. Type B coursed through the ventral portion of the sinus venosus, the caudal segments of the primitive atrium and atrioventricular canal, the dorsal parts of the primitive ventricle and conus cordis, and, finally, the right branchial arches. Both streams flowed in parallel fashion in the conus cordis. At Hamburger-Hamilton stages 17-18, the dye stream from the right lateral vitelline vein was chiefly type A, whereas that from the left lateral vitelline vein was type B. At Hamburger-Hamilton stages 19-22, those patterns reversed, i.e., the right lateral vitelline vein stream ran as type B, whereas the left lateral vitelline vein stream assumed type A pattern. The cranial-caudal relationship of the two streams at the primitive atrium and atrioventricular canal is not consistent with the hypothesis that these streams separately expand the future right atrium and left atrium. Their parallel direction at the conus cordis does not support the theory that spiral septation is initiated by two spiral streams. The longitudinal separation of the two streams at and beyond the branchial arches also argues against aortico-pulmonary septation as a consequence of flow streaming. Our observations do not support the traditional flow-molding theory.

Velocity field of a liquid stream in a spiral channel of rectangular cross section

The equations for the velocity distribution of an ideal incompressible liquid in a rectangular tube twisted along a spiral line are established within the framework of the theory of a uniform spiral stream [1]. On the basis of the equations obtained, a numerical calculation is made of the velocity field in a hydroseparator [2] designed for the enrichment of valuable minerals. The results obtained are compared with the available experimental data, indicating their satisfactory qualitative agreement. Secondary flows develop during the flow of a liquid in curvilinear channels. The liquid near the upper and lower walls flows toward the inner side wall while the liquid in the central part of the stream flows from the inner to the outer walls. A qualitative explanation of this phenomenon is given in [3, 4]. Despite the fact that viscous forces play an important role in the formation of the secondary flow, a correct description of the flow structure can be obtained within the framework of the Gromeka equation. Good qualitative and quantitative agreement between experimental data and theoretical calculations of vortex flows made on the basis of the Gromeka equation has been obtained in many reports ([1, 5], for example).

The presence and influence of two spiral streams in the heart of the chick embryo

The presence and influence of two spiral streams in the heart of the chick embryo

The Shadow of a Mist

THE reticulated rippling shadow of the mist described in Mr. Fawcett's letter (NATURE, January 5, p. 224) reminds me of a somewhat parallel phenomenon seen by me a few years ago. I saw a snow-storm some miles away crossing the valley between the Mendips and the Quantocks. It hung like a long, heavy curtain partially obscuring the bright western sky. The light shining through the shower showed a fairly regular pattern. On a reddish-brown ground the darker, because denser, parts of the shower took the form indicated roughly by the accompanying diagram. Was the snow falling in spiral streams, and would a similar explanation apply to the shadow of the mist seen by Mr. Fawcett?