Spiral Pitch Research Articles

Parametric optimization of a spiral ground heat exchanger by response surface methodology and multi-objective genetic algorithm

Horizontal spiral-coil type ground heat exchanger (HSGHE) has been increasingly used in ground source heat pump systems owing to its high heat transfer performance and low cost. This study proposes a method to optimize the design and operation parameters based on the combination of response surface methodology (RSM) and multi-objective genetic algorithm (MOGA). First, a 3D numerical model simulating the thermal–hydraulic characteristics of the HSGHE was built and the reliability of the model was validated through an indoor test rig. Subsequently, some parametric studies were performed to analyze the degree of influences that each input parameter on the outputs. On this basis, the Box-Behnken design method and RSM were used to establish response surface models between the input parameters (spiral diameter, pitch, and fluid velocity) and objective functions (net heat exchange rate and thermal performance capability) and determined the interactions between them. The results showed that the spiral diameter had the most significant influence, followed by the pitch, and fluid velocity. Finally, based on the developed models, the MOGA employing the Pareto optimum solutions were used to optimize the design and operation parameters and determine their optimal combination: spiral diameter of 0.4 m, pitch of 0.1 m, and fluid velocity of 0.4 m/s. The findings of this study may assist designers in the development of high efficiency ground heat exchangers.

Spirality: A Novel Way to Measure Spiral Arm Pitch Angle

We present the MATLAB code Spirality, a novel method for measuring spiral arm pitch angles by fitting galaxy images to spiral templates of known pitch. Computation time is typically on the order of 2 min per galaxy, assuming 8 GB of working memory. We tested the code using 117 synthetic spiral images with known pitches, varying both the spiral properties and the input parameters. The code yielded correct results for all synthetic spirals with galaxy-like properties. We also compared the code’s results to two-dimensional Fast Fourier Transform (2DFFT) measurements for the sample of nearby galaxies defined by DMS PPak. Spirality’s error bars overlapped 2DFFT’s error bars for 26 of the 30 galaxies. The two methods’ agreement correlates strongly with galaxy radius in pixels and also with i-band magnitude, but not with redshift, a result that is consistent with at least some galaxies’ spiral structure being fully formed by z=1.2, beyond which there are few galaxies in our sample. The Spirality code package also includes GenSpiral, which produces FITS images of synthetic spirals, and SpiralArmCount, which uses a one-dimensional Fast Fourier Transform to count the spiral arms of a galaxy after its pitch is determined. All code is freely available.

Reversible electron spirals by chirped attopulses at zero time delay

A class of linear, spiral phenomena is discovered in the photoelectron momentum distribution when studying photoionization of $S$-state atoms by a pair of linearly chirped, oppositely circularly polarized attosecond pulses eventually delayed in time by $\ensuremath{\tau}$. This controllable effect, dubbed. reversible electron spirals because of its energy-dependent sense of rotation, is identified and can be isolated in the absence of time delay for the case of opposite chirp rates. The astrophysical concept of spiral arm pitch angle is borrowed to gain a better insight into the energy dependence of the reversible spiral rotation, to determine the attochirp as well as the binding energy characteristic of an atomic target. Our results indicate potential applications in attochirpmetry and polarimetry.

Numerical modeling of self-compacting concrete columns longitudinally reinforced with steel tubes under axial loading

This paper presents an investigation on the efficiency of steel tubes in reinforcing self-compacting concrete (SCC) columns. A theoretical model is developed to study the axial behavior of SCC columns reinforced with steel tubes, considering the effects of confinement on the filled concrete by steel tubes and concrete core confined by spirals. The computational results are validated against the existing test results of SCC columns. The effects of various column parameters on the performance of SCC short columns under axial concentric loading are investigated. It is shown that the axial performance of SCC columns is influenced by the dimension and number of steel tubes, pitch of spirals, compressive strength of concrete, and yield stress of the steel tubes.

Impact of secondary flow on the single-phase flow in spiral microchannels: An experimental study

Spiral microchannels have a wide range of applications, such as microscale cooling, fluid mixing and particle sorting, in micro-fluidic devices. The flow characteristics of spiral microchannels play an important role in the design and operation of these devices. An experimental study of the laminar flow characteristics in spiral microchannels is conducted for different Reynolds numbers from 51 to 985. Microchannels have rectangular cross sections and follow Archimedean spiral pathways with different spiral and cross-section parameters. The results show that the pressure drop of the spiral microchannel increases with increasing spiral diameter and aspect ratio, but decreases with spiral pitch and hydrodynamic diameter. In addition, the effect of the spiral and cross-section parameters on pressure drop is evident at the high Reynolds number. Under the influence of additional friction caused by the secondary flow, the friction factor of the spiral microchannel is higher than that of the straight channel, and its value increases with the increase in curvature of the microchannel. The correlation of the Poiseuille number in the spiral microchannel is established on the basis of the experimental results, and 95.3% of the experimental data fall within the error band of ±18%.

Numerical Analysis of the Installation Process of Screw Piles Based on the FEM-SPH Coupling Method

The installation of screw piles can cause damage to the soil, which is a dynamic and large deformation problem. In this paper, a FEM-SPH numerical model for the analysis of this large deformation problem was developed in LS-DYNA to simulate the installation process of screw piles. In addition, field installation tests of screw piles were carried out. By comparing the FEM-SPH simulation results with the experimental results and traditional FEM simulation results, it was found that the FEM-SPH coupling method has higher efficiency and accuracy in dealing with the large deformation problems caused by the installation of screw piles. Then, numerical simulations of screw piles with various parameters were conducted to analyze the differences in the installation process. The results show that the spiral pitch and pile diameter have a significant effect on the installation torque, soil stress and soil pressure during the installation process. During the installation process, the interaction between the screw pile and the soil is transferable. The installation of the screw pile will lead to the movement of soil particles in the radial and axial directions, resulting in heave damage to the shallow soil and cylindrical shear damage to the middle and deep soil. The influence range on the soil by the heave failure mechanism (HFM) and the cylindrical shear failure mechanism (CSFM) caused by the installation of screw piles is affected by pile parameters. The change in pile diameter will act on both HFM and CSFM, whereas the variation in spiral pitch will only have an influence on CSFM.

Optimization Analysis of Pretreatment Device Structural Parameters for Low-Concentration CBM Utilization

The unstable concentration of the difficulty in utilizing low-concentration CBM causes a large amount of CBM to be discharged into the atmosphere. In order to ensure the safe and stable operation of the CBM utilization device, the gas mixing unit is used to stabilize the concentration of feed gas. Generally, the resistance of the gas mixing unit is not higher than 500 Pa and the uniformity of gas is not less than 90%. In order to solve the problems of heavy resistance and low uniformity of the existing CBM mixing unit, a three-dimensional calculation model is established, and the structural parameters such as the number of spiral blades, blade length, and pitch in the gas mixing unit are adjusted and verified by experiments to achieve optimal performance. The dimensionless mathematical correlation between the resistance loss and the uniformity of gas is refined, and the maximum error between the resistance loss and the simulation results is controlled within 10%; it provides a theoretical basis for the uniformity and low resistance mixing of different gases in the gas industry. When the flow is 7000 Nm3/h, 50000 Nm3/h, and 160000 Nm3/h, respectively, the optimal structural parameters of the mixing zone are as follows: the number of blades is 3, 3, and 2, respectively, the pitch is 1000 mm, 2000 mm, and 2636 mm, respectively, and the length of blades is 500 mm, 1600 mm, and 1845 mm, respectively. The optimal structural parameters of the small pipe area are as follows: the mixing device with a flow of 50000 Nm3/h is not equipped with blades, the number of blades of the other two devices is 4, the pitch is 1400 mm, and the length of blades is 700 mm.

The Eccentric Compression Performance of Spirally Stiffened Thin-Walled Square Concrete-Filled Steel Tubular Laminated Composite Members

To enhance the local buckling resistance of thin-walled steel pipes and enhance their fire and corrosion resistance, a new spirally stiffened thin-walled square concrete-filled steel tubular laminated composite member with transverse ribs is proposed. Through the four forms of combined members for eccentric pressure testing, it was found that: ordinary thin-walled steel pipe concrete drum buckling is more severe; with spiral ribs, the buckling is limited between the stiffening ribs; and the deformation is significantly reduced. By addressing the problem of cooperative work between the inner and outer structural layers of new components, it was found that, after setting constraints such as steel bars, the integrity of the two can be ensured, and the stress performance is significantly improved; compared to ordinary steel pipe concrete, the load-carrying capacity is 17.9% higher, and the deformation capacity is roughly equivalent. Spiral ribs as a new form of spatial restraint, in addition to increasing the local bending stiffness, manifest an overall restraint role in limiting lateral deformation of the steel pipe, whereas the role of vertical stiffness is insignificant. Based on test evidence, the influences of the width to thickness ratio of spiral ribs and pitch were determined, and reasonable structural measures for the members were given. Through the N–M relationship curve, the limit of damage in compression and tension under eccentricity was obtained at an eccentricity of about 0.9. Finally, a method for calculating the eccentric compressive ultimate load capacity of this new composite member was proposed.

Acoustic Meta-Lens for Enhanced Sensing Consisting of Single-Helicoid Array

Magnifying lenses based on acoustic metamaterials (MMs) play an important role in many practical applications requiring acoustic focusing and amplification detection. However, the current 3D meta-lenses are still plagued by low flexibility, huge volumes, and high manufacture costs. We report a 3D meta-lens composed of discretely distributed meta-helicoid element that can solve the above problems. We improve the traditional helical MMs by reducing the number of blades to increase the distance between blades, achieving higher transmission efficiency and avoiding blade adhesion during manufacture. In order to eliminate the uneven phase and pressure of single-helicoid MMs at the outlet, pipe extension method is used to unify the phase and pressure. Via adjusting the spiral pitch, the meta-helicoid can generate 0- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 \boldsymbol {\pi }$ </tex-math></inline-formula> phase delay with a fixed outline size while maintaining transmittance greater than 90%. Based on the small single-helicoid meta-element, we design and manufacture a low-cost 3D magnify meta-lens with compact size. We demonstrate, both theoretically and experimentally, the acoustic meta-lens can make the normally incident signals focus on the prescribed point, enhances pressure amplitude about three times, and can flexibly manipulate focus point. Moreover, the bandwidth of the meta-lens is as wide as about 5.6 kHz. Our new strategy may offer an alternate route to the design of novel meta-lens and devices for acoustic focusing and amplification detection.

Current-driven spiral domain wall in a ferrimagnet near the magnetization compensation point

A spiral domain wall emerges when the Dzyaloshinskii-Moriya vector is along the easy axis. While the ferromagnetic spiral wall has been well studied, its ferrimagnetic counterpart has nevertheless not been explored. Here, using the collective variable approach, we derive the spiral domain-wall solutions in a ferrimagnetic nanostrip with a longitudinal easy axis and a bulk Dzyaloshinskii-Moriya interaction. At the magnetization compensation point, the wall rotates and propagates steadily in a wide current range. The (angular) velocity of this wall increases almost linearly with the experimentally feasible currents. Also, the wall exhibits a relativistic-like contraction with increasing velocity. Near this point, the wall moves smoothly with its velocity linearly depending on the current below the Walker breakdown. Above this critical current, all the internal parameters of the wall, such as the azimuthal angle, width, and spiral pitch, as well as their rates of change, oscillate periodically. The wall moves forward with its velocity varying periodically. These different behaviors at or near the compensation point are ascribed to the tunable demagnetization effect. The adjustability of FiM parameters, combining with the twist induced by the Dzyaloshinskii-Moriya interaction, can effectively change the DW's propagation and rotation.

Spin wave stiffness and damping in a frustrated chiral helimagnet Co8Zn8Mn4 as measured by small-angle neutron scattering

Multiple intriguing low-temperature phenomena have recently been discovered in the family of chiral cubic Co-Zn-Mn compounds with a $\ensuremath{\beta}$-Mn-type structure. In particular, ${\mathrm{Co}}_{8}{\mathrm{Zn}}_{8}{\mathrm{Mn}}_{4}$ displays a reduction of the helical spiral pitch on cooling along with lattice shape transformations of metastable skyrmions and the manifestation of peculiar magnetic textures due to strong magnetocrystalline anisotropy. Here we report on temperature-dependent measurements of helimagnon excitations in the field polarized regime ${\mathrm{Co}}_{8}{\mathrm{Zn}}_{8}{\mathrm{Mn}}_{4}$ using the spin-wave (SW) small-angle neutron-scattering technique. By applying a new analytical expression to interpret the data, quantitative estimates for both SW stiffness and damping are extracted across a wide temperature range between 70 and 250 K. We speculate that their nontrivial temperature dependencies arise due to the effects of magnetic frustration arising from Mn magnetic moments, which is further reflected in continuous variations of both exchange and Dzyaloshinskii-Moriya interactions.

Effect of high-strength spirals on eccentric compression behavior of square CFST columns

In this study, the eccentric compressive performance of square CFST columns with high-strength internal spirals (HSS) was systematically investigated. First, an eccentric compression test was conducted on spiral-confined CFST columns with influential parameters of yield strength and pitch of the steel spiral and load eccentricity. It was found that the strength and ductility of square CFST columns were significantly improved by incorporating the contribution of the confined HSS. The improvements were more pronounced for columns with lower load eccentricity ratios. Subsequently, detailed finite element analyses were conducted to investigate the performance and mechanisms of the HSS-CFST columns, i.e., the distributions of axial stress and confining pressure of concrete, the interaction between concrete and steel tube, and load versus deformation responses. It was observed that the internal spirals could not only enhance the axial stress of the concrete they confined but also improve the interaction between the concrete and steel tube. Moreover, a parametric study was performed to investigate the influence of confined steel spiral layouts on the mechanical performance of HSS-CFST columns. Decreasing the steel spiral pitch improved the strength and ductility of square CFST columns more effectively than increasing the diameter of the steel spiral. Finally, design recommendations for eccentrically loaded spiral-confined square CFST columns are provided.

Thermal and flow characteristics in a vertical spiral-type ground heat exchanger based on linear non-equilibrium thermodynamic principle

The thermal and flow performances in a single spiral-type ground heat exchanger in one-week operation were numerically simulated by considering the coupled thermal and moisture migration model for backfill and soil fields. The main factors involved Reynolds number (3000–10000), inlet temperature (30–40 °C), initial volumetric moisture content (6.95–20.8%), backfill materials (native sand, and sand/kaolin blend with 5% adding ratio of kaolin), spiral diameters (0.4–0.8 m), spiral pitches (0.1–0.8 m) and operation modes. The thermal performance of the heat exchanger without considering the coupled thermal and moisture migration model in unsaturated soil could be overestimated in long-term operation. The average temperatures in the blend enhanced by about 2% compared with the sand field, but the change degrees for the moisture content in the blend field were about 33% lower than that in the sand field, which imply that the kaolin additive could simultaneously enhance the thermal migration and water-holding capacity of the sand. The heat transfer rate of the heat exchanger in the blend enhanced by 24–36% with widening the spiral diameter from 0.4 to 0.8 m or narrowing the spiral pitch from 0.8 to 0.1 m, while the pressure drop rose by 50–92% and 4–5 times, respectively. 3-h-on/3-h-off mode among three intermittent operation modes (12-h-on/12-h-off, 6-h-on/6-h-off and 3-h-on/3-h-off) for the blend was more effective one to urge the soil temperature restoration. The intermittent operation mode should be also a feasible technique for prompting the thermal performance of the ground heat exchanger.

Experimental Investigation of Large-Scale Eccentrically Loaded GFRP-Reinforced High-Strength Concrete Columns

Ten large-scale high-strength concrete (HSC) circular columns were constructed and tested to failure. Nine columns were internally reinforced with glass fiber-reinforced polymer (GFRP) bars and spirals, whereas one was reinforced with steel bars and spirals to serve as a reference. All columns had a diameter of 350 mm. The variables tested were reinforcement type, spiral pitch, slenderness ratio, eccentricity-to-diameter ratio (e/D), and type of loading (axial or four-point bending). Experimental results showed that both reinforcement types (steel or GFRP) and the spiral pitch did not have a significant effect on the behavior of GFRP-reinforced HSC columns up to the peak load. In addition, a decrease in the axial capacity of the columns as the e/D ratio increased was observed. This was consistent for specimens of both slenderness ratios of 14 and 20. Columns with a higher slenderness ratio showed a lower axial capacity for all specimens tested under the same e/D ratio. Furthermore, slender columns with higher e/D ratio underwent much larger deformations; both axially and laterally. For columns of both slenderness ratios, axial load–bending moment interaction diagrams were produced using the experimental results and were compared to the predictions of available codes and guidelines.

Seismic performance of GFRP-RC circular columns with different aspect ratios and concrete strengths

The available code provisions for seismic design of confinement reinforcement in fiber-reinforced polymer-reinforced concrete (FRP-RC) columns, even their most recent versions, are overly conservative. This is due to the limited available research data, particularly those related to high-strength concrete (HSC) columns and those with different aspect ratios. That is, the linear-elastic behavior of FRP could be of concern when combined with the brittle nature of HSC or implemented in shorter columns, which could be significantly influenced by shear stresses. Therefore, this study was conducted to investigate the effects of concrete compressive strength and column aspect ratio on the seismic performance of glass FRP (GFRP)-RC circular columns with variation of spiral pitch and axial load level. Nine full-scale GFRP-RC column-footing connections were cast and tested under concurrent axial loading and reversed-cyclic lateral drifts. Test results proved the conservativeness of the seismic design requirements of the Canadian standards for confinement reinforcement in GFRP-RC circular columns with regard to the effects of HSC and different aspect ratios.

Numerical investigation of thermal-hydraulic performance of a heat exchanger tube with helical dimples

This study proposes a novel type of tube with helical dimples. Turbulent heat transfer and flow resistance in a heat exchanger tube with helical dimples were numerically investigated. Furthermore, the effects of the geometric parameters, including spiral pitch, transverse length, number of starts, depth, and radius on the performance were investigated. The results demonstrated that the longitudinal swirling flow and vortex generated behind the helical dimples result in adequate fluid mixing between the mainstream and near-wall regions. Therefore, the thermal performance of the tube with helical dimples was enhanced by 120–270% in comparison with the plain tube. Both Nu/Nu0 and f/f0 increased with increasing dimple starts, depth, and radius and decreasing spiral pitch and transverse length. Additionally, a maximum PEC = 1.93 was obtained by employing the geometric model with P = 30 mm, L = 6.9 mm, N = 4, D = 2 mm, and R = 2 mm in all cases.

Bond behavior of spirally confined bar splices in grout

Despite various studies on the bond behavior of Glass-Fiber Reinforced Polymer (GFRP), an available literature on the bond behavior of GFRP bars in grouted confined by spiral is limited. In the present study, the bond behaviour of deformed steel and GFRP reinforcing bars connected by a grouted spiral connection was investigated. Flexural pull-out test was performed on 24 beam specimens to evaluate the bar bond strength. The test parameters were the spiral diameter and pitch distance. The test results showed that the spiral confinement significantly improved the bond performance of GFRP bars and deformed steel main bars. The bond strength of GFRP was decreased by damage of the outer layer of GFRP bars due to detachment of sand grains on the GFRP bar surface. As the spiral diameter decreased from 45 to 25 mm, the bond strength increased by 9.7 ∼ 14.5% due to higher confinement stress. In the deformed steel reinforcing bars, the reduced spiral diameter increased the bond strength by 40%.

Novel FRP micro-bar reinforced UHPC permanent formwork for circular columns: Concept and compressive behavior

In this study, a novel form of tubular permanent formwork that is made of ultra-high-performance concrete (UHPC) internally reinforced with fiber-reinforced polymer (FRP) micro-bars (herein referred to as FRP-UHPC tubular permanent formwork or simply FRP-UHPC tubular column) is developed. The axial compression test results of FRP-UHPC tubular columns with and without in-filled concrete are presented and discussed. Effects of the FRP micro-bar spiral pitch, the steel fiber addition in the UHPC, the tube thickness and the presence of external FRP confinment are investigated. The test results confirmed that the FRP-UHPC tubular columns have an excellent compressive strength, and the strength and ductility of existing concrete columns jacketed with an FRP-UHPC composite tube are substantially enhanced due to the confinement and axial contribution of the FRP-UHPC tube. The proposed FRP micro-bar-reinforced UHPC composite tubes are attractive in structural applications as pipelines or permanent formworks for columns, as well as external jackets (can be prefabricated in the form of two halves of composites tubes) for strengthening deteriorated reinforced concrete columns.

Reinforcement corrosion of circular concrete columns under sustained load

This paper presents the results of an experimental study of the axial capacity of circular spirally-reinforced concrete columns that were subjected to accelerated corrosion while sustaining a constant compressive service load. Two sets of columns of five columns each were designed with different spiral pitch to investigate the effect of concrete confinement on the corrosion propagation. Columns with non-confining spiral reinforcement had only their longitudinal reinforcing steel corroded, whereas in the other set of specimens, the spiral reinforcement was corroded and isolated from the vertical reinforcing steel. The cracking initiation, pattern, and widening of the concrete cover were monitored for a period of 4-10 months, and relations obtained between the crack widening and propagation and the elastic shortening of the column and steel mass loss were established. After the accelerated corrosion period, eight columns were tested to failure under either concentric or eccentric load; the vertical deformation, cracking pattern and failure type were monitored and recorded. The failure of specimens with non-confining spiral reinforcement was characterized by sudden crushing of the concrete and longitudinal reinforcement buckling, with a reduction in load capacity of 30-40%. Columns with confinement reinforcement failed in a ductile manner by progressive spalling of the concrete cover, maintaining their load capacity in spite of the corroded spiral reinforcement.

Experimental investigation for the spiral coiled capillary tube for various spiral pitches for the flow of refrigerant R32

ABSTRACT The experimental investigation was carried out for the spiral coiled capillary tube having a spiral pitch of 32 mm, 48 mm, and 64 mm to study the mass flow rate of R32. A wooden spiral pattern was used to get the spiral shape of the capillary tube. Three wooden patterns were prepared for three different spiral pitches. The spiral convolutions are calculated for the capillary tube length of 1000 mm, 1500 mm, and 2000 mm. The variation in mass flow rate for all three spiral pitches was studied, and the results were shown on a graph. The effect of variation of capillary inlet pressure and degree of subcooling were observed. From the data comparison, it can be concluded that if the spiral pitch increases from 32 mm to 48 mm, for all the diameters for similar operating conditions, the mass flow rate increases from 3.89% to 5.05%. If the spiral pitch increases from 32 mm to 64 mm, for all the diameters for similar operating conditions, the flow rate increases from 6.49% to 11.64%. The measured mass flow and predicted mass flow rate is well within the accepted range. The percentage deviation of the mass flow rate is compared with the other researchers and found between +30% and −34%. The mass flow rate was higher for the higher spiral pitch, a higher degree of subcooling, higher capillary inlet pressure, and higher capillary diameter.