Pitch Diameter Ratio Research Articles

Study of Buffeting Excitation Acting on Coil Tube Bundles in Cross Flow

Abstract The amplitudes induced by random excitation forces on the tubes bring continuous friction between the tube and supports, which results in gradual failure of the tubes due to fretting wear. Therefore, it is very important to determine the envelope lines of the random excitation force spectrum for the coil tube. To the authors' knowledge, there are no published studies on the normalized force spectrum of coil tubes. In this paper, a simplified three-layer experimental model was established. The robustness of the numerical method was demonstrated by comparing the experimental and simulated results, including the vibration response and the fluid excitation force spectrum. Then, a semi-empirical equation for predicting the dominant frequency of turbulent buffeting was constructed by employing the threshold envelope method. Through the observation of time-history and root-mean-square (RMS) data, it was found that the pitch diameter ratio between adjacent tube layers, a, had the greatest influence on the force coefficients. The smaller a is, the larger the force coefficients are. The pitch diameter ratio in the same layer, b, and helix angle, α, had little effect on the force coefficients. With the increase of α, the flow instability in the shell-side flow enhanced and the fluctuation of force coefficients became larger. Finally, the mechanisms of the tube position, Reynolds number (Re), and bundle structure on the normalized force spectrum were studied. The normalized envelope force spectrum for coil tubes was proposed as the guidelines to predict and evaluate the random excitation force acting on the tubes.

Thermal analysis for multi-conductor bundle in high voltage overhead transmission lines under the effect of strong wind

Bundle conductors are widely used in HV transmission lines to suppress the corona discharge and reduce the line reactance. To determine its current ampacity of multi-conductor bundle, the thermal analysis is indispensable. A three-dimensional flow-thermal coupling model of multi-conductor bundle considering the effect of strong wind is developed in our study. Using the finite element method, both the temperature field and the fluid field are computed; the characteristics for the multi-physics fields are discussed; the interaction between the fields as well as the mutual influence between subconductors are elucidated. Moreover, a set of sensitivity analysis have been performed, and the effects of load current, conductor spacing, wind speed on temperature field and fluid field are investigated. Based on the pitch-diameter ratio, a novel method to improve the thermal performance of multi-conductor bundle is proposed. Finally, the optimized structure is obtained, and the current ampacity is expected to be greatly enhanced.

Research on parameterized modeling and mechanical characteristics of shearer cables.

Shearer cables, subjected to large deformations and exposed to harsh working conditions during frequent back-and-forth movements, pose difficulties in achieving comprehensive mechanical performance and extended fatigue life. This study addresses parametric modeling challenges related to determining tangency within and between layers, recursively generating spiral curves from the (n-1)-th level to the n-th level, and constructing irregular surfaces for insulation and sheath. Investigating tensile and bending properties, the research explores the impact of varying pitch diameter ratios at different stranding levels, stranding directions, and monofilaments on mechanical performance across scales. The results reveal a nonlinear increase in stress in power and control conductors with growing pitch diameter ratios. The optimal combination is determined as a pitch diameter ratio of 6 for cabling, 5 for the control conductor, and 14 for the power conductor. The predicted fatigue life of the improved cable by Ncode aligns with bending test results, demonstrating functionality up to 15.12e4 cycles. Stress distribution in parallel stranding is lower and more even, tending to scatter. Conversely, counter stranding experiences relatively higher stress, ensuring a more stable structure. While maintaining a constant effective conductor cross-sectional area, finer monofilaments result in higher cross-sectional filling ratios, enhancing tensile and bending performance.

Numerical Investigation in Scale Effect on Marine Propellers for Different Pitch-Diameter Ratio

Numerical Investigation in Scale Effect on Marine Propellers for Different Pitch-Diameter Ratio

Performance evaluation of a bidirectional horizontal axis tidal turbine with S-shaped blades by the sliced section method

Understanding the flow pressure distribution on the blade airfoil of the tidal turbine is of great significance for optimising the energy harvesting performance of the blades. In this paper, a bidirectional type horizontal tidal turbine (BHTT) with special S-shaped blades is proposed, which have a larger pitch diameter ratio provide excellent performance at low oncoming flow velocity by the theoretical, numerical and experimental methods. First, it is verified that the energy harvesting efficiency is basically the same in the case of bidirectional flow, and the S-shaped blade is divided into multiple slice sections, which could quantify the energy harvesting performance of each area of the blade. Then, using the method of mathematical statistics to divide more areas, the probability density shows a skewed distribution. The results show that the energy harvesting performance is less affected by flow velocity fluctuation, and the energy harvesting efficiency could reach 0.25-0.55 when the tip speed ratio is in the range of 0.2-0.5. Furthermore, the slice section method is adopted to make the influence of axial thrust intuitive and clear to study the turbine energy harvesting performance and improve the harvesting efficiency, which could provide a reference for the engineering design of tidal turbines.

A Precise Calculation Method of Conductor Current Based on FEM

The demand for electricity in society is increasing. It is necessary to continuously strengthen the construction of transmission capacity. This article establishes a precise calculation method for the current carrying capacity of wires based on finite element analysis, taking into account the aluminum core diameter, steel core diameter, pitch diameter ratio, rotation angle, etc., which has higher calculation accuracy and is suitable for calculating the current carrying capacity in different meteorological environments. It is of great significance for fully tapping the power supply potential of transmission lines and improving the capacity of transmission channels.

Variation of Flow Hydrodynamic Parameters and Prediction of Particle Separation Indices in the Spiral Concentrator with the Regulation of Pitch-Diameter Ratio

The pitch-diameter ratio is an important design indicator affecting the separation performance of spirals. Based on the numerical simulation method, this paper systematically investigated the variation of flow hydrodynamic parameters in the spiral concentrator with the regulation of the pitch-diameter ratio. The radial distribution and variation trend of hematite and quartz particles with different particle sizes are further analyzed. Additionally, the separation indices of hematite and quartz with different particle size combinations were predicted. The results show that the tangential velocity, maximum radial velocity, velocity shear rate, and Reynolds number of fluid in each region decrease with the increase of the pitch-diameter ratio. The range of laminar flow gradually expands as the pitch-diameter ratio increases. There are significant differences in depth of water, ratio of inward and outward flows, and secondary flow velocity in different regions. Some flow hydrodynamic parameters at the inner trough reach relative equilibrium at a pitch-diameter ratio of 0.675. Hematite and quartz particles form a selective distribution in the trough surface, which comprehensively reflects the density effect, particle size effect, following flow effect of fine particles, and the effect of interstitial trickling of high-density fine particles. Fine hematite and coarse quartz form a large amount of misplaced material, and there is a corresponding mixing area. With the increase in pitch-diameter ratio, coarse and fine hematite particles migrate inward and outward, respectively. With the increase in pitch-diameter ratio, the misplaced amount of quartz on the inner trough decreases, but the outward migration distance of coarse quartz is smaller. Increasing the pitch-diameter ratio is beneficial to the separation of combined feedings of coarse hematite and quartz but unfavorable to that of fine hematite and quartz. The maximum separation efficiency of coarse hematite and fine quartz can reach 85.74%, and the iron grade of the inner product can reach 65.96% when the pitch-diameter ratio is 0.675 and the splitter location is 115 mm. The changing trend of separation indices in this feeding is closely related to the variation of fluid parameters and the change in the radial distribution of single mineral particles. The research results can provide references for the structural design of spirals, the selection of feed particle size, and the adjustment of splitter location.

Optimization of the Energy Capture Performance of the Lift-Drag Hybrid Vertical-Axis Wind Turbine Based on the Taguchi Experimental Method and CFD Simulation

In order to improve the energy capture performance of vertical axis lift wind turbines in a low wind speed environment, the drag wind turbine is employed to couple with the design of existing vertical axis lift wind turbines. In contrast to the existing literature, in this work, a computational model is proposed that can simulate the interaction between the turbine and the fluid. The effects of pitch angle (β), installation angle (θ), overlap ratio (ε) and diameter ratio (DL) on the energy capture performance of hybrid vertical axis wind turbines are systematically analyzed based on Taguchi and CFD methods. The results show that under the optimized parameter combination, the peak energy capture coefficient of the lift-drag hybrid wind turbine can be increased to 0.2328, compared with 0.0309 and 0.0287 of the pure lift and drag turbine, respectively. In addition, the result of the prototype test show that the optimized hybrid wind turbine not only has a better-starting performance but also has 2.0 times the output power of that of the lift wind turbine.

Influence of bottom regiment distributions on the mixing efficiency in a BOF converter

ABSTRACT Within steelmaking processes, the required energy is consistently transferred from the bottom gas into the melt, which assures the mixing efficiency of the bath. In this paper, physical experiment and numerical simulation are established to investigate the influence of bottom nozzles with different arrangements and blowing gas intensities on the dynamic conditions of a 260-t converter. The results indicate that the shortest mixing time was achieved as the outer regiments maintained a pitch circle diameter ratio (PCD) of 0.6 at an angle of 15°. Under the gas flowrate of 960 Nm3·h−1, the minimum mixing time was 40 s, and the minimum proportion of inactive zone was 0.022. Meanwhile, the synergy of bottom-blowing gas flows can help drive the rapid motion of molten steel. It is concluded that 0.5–0.6 PCD is the rational location for the outer regiments to enhance the synergistic effect of flow streams in a BOF converter.

Computational Study and Enhancement of Heat Transfer Rate by Using Inserts Introduced in a Heat Exchanger

The research provides a numerical and computational analysis of improving heat transfer rate in heat exchangers employing obstructing geometries such as Circular Ring, Circular Ring with` clearance, and Hexagonal ring tabulators with different pitch diameter ratios (PDR). All geometries were evaluated with flow obstruction areas of 0.3, 0.4, and 0.5. Flow obstruction area and Reynolds number were the variables that changed during the testing. The pitch diameter ratio employed in the investigation is one. The Reynolds number was changed between 6000 and 21000. For numerical examination, k--ε technique was used in this study. The use of flow obstruction geometry as a turbulator improves heat transmission derived from the hot surface of the pipe to the air throughout the test region substantially. In this research work, the tested designs, a circular ring separated from the tube wall and a hexagonal ring with the same flow blockage area improve heat transmission. Hexagonal rings incur a lower fluid friction cost than circular rings and circular rings with clearance. The maximal heat transfer enhancement (Nut/Nup) for the diameter ratio of the insert of 0.6.3 is 2.28–3.01.

Effect of various structures on the shell-side flow over coil tube bundles

In response to the increasing number of applications and safety considerations for coil tube bundles, an investigation on the influence of structural parameters (the pitch diameter ratio between adjacent tube layers, a, the pitch diameter ratio in the same layer, b, and the helix angle, α) on the flow in the shell side over simplified three-layer bundles was carried out using detached-eddy simulation (DES), which was verified by previous studies. In this study, the local flow structures were discussed by observing a zoomed-in view of the gaps, which revealed that irregularly distributed vortices appeared. The spiral wound structure made the flow structures asymmetric and increased the lateral velocity between tubes of the same layer. By applying power spectral density (PSD) and continuous wavelet transform (CWT) functions, the time–frequency data of velocity fluctuations were analyzed to obtain the flow and evolution of coherent structures over time, revealing vortex shedding frequency bands and Strouhal numbers (St). In addition, multimodal Gaussian distribution approximations (MGDA) were employed to indicate that the shell-side flow was composed of multiple flow modes.

Fluidelastic instability research of tube bundles by a two-way fluid-structure interaction simulation

Fluidelastic instability (FEI) could cause serious damage to the tube bundle, and streamwise FEI has attracted more attention in recent years. Water tunnel experiments have been conducted to investigate streamwise and transverse FEI in a parallel triangular tube bundle with a single elastic tube in center. RMS displacement-reduced velocity relationship diagram, vibration time-history curve and frequency spectrum response in streamwise and transverse directions are obtained. A Two-way fluid-structure simulation method was developed to calculate the streamwise and transverse FEI. The motion of the elastic tube was controlled by a User-Defined Function (UDF) coupled with dynamic mesh. The FEI tendency of simulation is consistent with experiment results but the values of predicted critical reduced velocities are more conservative. The process of FEI was analyzed. Finally, the model was extended to explore the effect of pitch diameter ratio, elastic tube arrangement and natural frequency ratio of streamwise and transverse.

Numerical investigation on flow-induced vibration and heat transfer of fuel rods in a small pitch-diameter ratio (P/D) channel

The Korea Atomic Energy Research Institute developed a dual-cooled annular fuel rod bundle structure to enhance the core power of the nuclear reactor and improve its heat transfer efficiency. The structure also reduced the pitch-diameter ratio (P/D) of the channel. In this study, a four-subchannel model is taken as the research object, and the Reynolds stress model (RSM) is applied to calculate the flow-solid-thermal tri-physical field coupling for a typical bare rod beam channel. The accuracy of the numerical calculation method used in this study was first verified by comparing it with the experimental data in the literature. Then, the channel flow field under different P/D conditions was simulated, and the formation conditions and influencing factors of the vortex-street structure were studied. Axial flow-induced vibrations of a cylindrical structure in a channel were investigated using a weak coupling algorithm. Finally, the influence of the vortex-street structure on the heat transfer efficiency of the fluid in the channel is discussed. The results show that the anisotropy-based RSM turbulence model can accurately capture the vortex-street structure in small P/D channels. When P/D < 1.050, a stable vortex-street structure appeared in the channel, which led to the stable micro-amplitude vibration of the cylindrical structure in the channel. The presence of the vortex-street structure significantly improves the heat transfer efficiency of the fluid in the channel.

Precise determination of R134a boiling bundle effect on a column of reentrant cavity tubes

The boiling bundle effect was investigated on a column of reentrant cavity tubes to reveal the heat transfer coefficient (HTC) variation for a tube which is affected by other tubes. All experimental data were obtained on the specific tube, which is the distinct difference between the adopted homologous method and the routine method. Two columns of eight horizontal tubes were submerged in R134a liquid, and each tube was specifically heated by an ethylene glycol–water mixture. The saturation temperature was 6.0 °C, the heat flux ranged from 10.0 kW/m2 to 28.0 kW/m2, and the row number ranged from 1 to 7. The tube length in the test section was 500 mm, and the pitch–diameter ratio was 1.32. Results showed that the uncertainty of the bundle effect using the homologous method was less than ± 4.4%, which decreased by at least 80% compared with that using the routine method. The values were from 1 to 1.32, indicating that the upward bubbles from the lower heated tubes positively influenced the boiling HTC. Moreover, the bundle effect increased with the increase in row number and decreased with the increase in heat flux. Correlations of the single-tube HTC and the bundle effect with vapor film Reynolds number and effective row number were established to predict the experimental data. The current study can offer a reference for further investigations of film or convective boiling on tube bundles.

Numerical analysis of flow and heat characteristic around micro-ribbed tube in heat exchanger system

In order to improve the energy utilization rate, this paper analyzes the flow around the cylinder in the tube-row channel heat exchanger through numerical simulation. Effects of micro-rib structure types (vertical rib and ring rib), number of ribs (N = 0, 4, 6, 8), height of ribs (H = 2, 3, 4 mm), pitch diameter ratio (ST/D = 1.5, 2, 2.5), mass fractions (ω = 0–0.5%) and Reynolds numbers (Re = 514–1205) on the flow and heat transfer characteristics of tube-row channel heat exchangers are analyzed. Results showed that TiO2-H2O nanofluids can improve the comprehensive performance of heat exchanger, and when the mass fraction is 0.4%, the tube-row channel heat exchanger has the best performance. For heat exchangers with different types and structural parameters, the adjustment of the number of ribs, the height of ribs, the ratio of transverse pitch diameter and the use of nanofluids can increase Nusselt numbers by 53.63%, 57.25%, 52.38% and 12.93% at maximum, respectively.

Thermal Performance Exploration of Air Foil Shape of Pillars using Impinging Jet in Heat Sink

Objectives: The current investigation introduces the concept of heat sink with combination of jet impingement, micro – channel and air foil shaped pillars. A numerical model is designed to explore the thermal performance of jet impingement with constant heat flux. The steady state conditions are assumed for the laminar and incompressible flow. For the purpose of study dimensionless variables are formed. The performance of jet impingement was predicted in terms of different parameters like temperature rise, drop in pressure and coefficient of heat transfer. Augmentation in pitch diameter ratio, leads to increase in temperature for a particular value of height diameter ratio. Also the heat transfer coefficient gets lowered with the increase in pitch diameter ratio. So proper selection of dimensionless parameters to increase the heat dissipation is of utmost importance.

Numerical investigation on the shell and tube heat exchanger with baffle leakage zones blocked

A novel type of shell and tube heat exchanger with modified fold helical baffles and twisted oblate tubes (STHXsFBTB) is proposed to seal the leakage areas in the shell center of the shell and tube heat exchanger with fold helical baffles (STHXsFB). The thermal and hydraulic properties of STHXsFB and STHXsFBTB for water chiller systems are investigated by numerical simulation. The influences of the configuration factors (screw pitch and tube diameter ratio, length width ratio and cutting ratio) on the thermal and hydraulic properties of STHXsFBTB are studied. Compared with STHXsFB, the heat transfer coefficient (h) of STHXsFBTB increases by 3.88%–8.05%, while the pressure loss (△P) decreases by 6.50%–7.38%, and the comprehensive heat transfer performance (Nu·f−1/3) increases by 6.38%–10.35%. Moreover, as screw pitch and tube diameter ratio, length width ratio and cutting ratio increase, both h and Nu·f−1/3 decrease. The influences of the length-width ratio and the cutting ratio on thermal and hydraulic properties of STHXsFBTB are tremendous, while the screw pitch and tube diameter ratio has a negligible effect. When the screw pitch and tube diameter ratio is 10, the length width ratio is 1.5 and cutting ratio is 0.35, the optimum configuration of STHXsFBTB is obtained.

Experimental Investigation of Inclined Circular Ring Turbulators on Heat Transfer and Fluid Flow Characteristics

This paper demonstrates influence of various inclination of Circular Ring Turbulator (CRT) on thermal characteristics in circular type heat exchanger. “A wall linked circular inserts were analyzed having constant inner diameter to achieve uniform flow blockage area (FBA) of 40%”. These CRTs located within the tube to prevailed different angular patterns (-10°, -15°, - 20° and -25°) w. r. t. horizontal of tube. Influence of these geometries on fluid friction and heat performance were studied. Parameter constant throughout the investigation was diameter ratio and Pitch Diameter Ratio (PDR). Modified parameters throughout study were the angular inclinations of CRT and Reynolds number. Inner side of tube is preserved at constant heat flux having air as working medium at atmospheric temperature with variation of Reynolds number from 6,000 to 24,000 respectively.Implementation of CRT as turbulator favorably improves rate of heat exchange within heated enclosure of tube to fluid domain throughout the test model. Out of all studied inserts, CRT having angular deflection of -25° gives peak value of heat transfer at extreme Reynolds number and at slightest Reynolds number CRT having angle inclination of -10° offers greater friction factor which is at 2.5 and 5.5 times than smooth tube. CRT with angular inclination of -25° at minimum Reynolds number offers extreme thermal performance factor is 1.7.

Horizontal flow reactor optimization for biogas recovery during high solid organics fermentation: Rheological characteristic analyses

Continuous improvements in human living standards, water supply quality, and poor solid waste collection systems in China has led to increased production of municipal sewage sludge and organic solid waste (MOSW), which incurs a potential risk for human health and the environment. Solid anaerobic fermentation, which has exhibited advantageous energy recovery and biosolid stabilization, has been considered for urban organic solid waste treatment. The primary objective of this study was to optimize horizontal flow reactor operations for the efficient fermentation of high solid organics and subsequent biogas production via rheological characteristic analyses. The effects of operational parameters, such as paddle type, paddle diameter, pitch diameter ratio, stirring efficiency, torque, and power consumption, on the reactor performance were simulated using computational fluid dynamics (CFD). The solid content greatly influenced the rheological characteristics of the MOSW; increasing the solid content (5 %–30 %) of the MOSW led to a significant decline in the rheological index (0.532 to 0.224). The optimized parameters simulated by CFD included a screw-type stirring paddle with a pitch of 0.6 D, pitch of the screw with the value of 0.75 D, stirring shaft (set vertically and eccentrically downward) with the value of 0.15 D, and stirring speed less than 10 rpm. Moreover, the higher the consistency coefficient, the lower the rheological index and required power consumption. The reactor energy consumption analysis indicated that the average energy consumption can reach 48.20 kJ/m3 with an efficient operation.

Research on low-temperature heat exchange performance of hydrogen preheating system for PEMFC engine

The durability of membrane electrodes, which are the core components of the Proton Exchange Membrane fuel cell (PEMFC), seriously affects the service life of the stack. Under the action of long-term low temperature, the gas diffusion layer at the entrance will be aged and its micro-porous layer structure will be destroyed, which will hinder the removal of liquid water and gas transport, so it is necessary to preheat the anode hydrogen. In the present study, the influence of different pitch ratio and diameter ratio on heat transfer of corrugated tube heat exchanger is simulated by means of thermal-fluid coupled numerical simulation and periodic unit model, the effects of coolant flow rate and temperature on the overall heat transfer performance were also studied. The validity of the simulation results is verified by experiments, and the effect of hydrogen preheating on the stack performance is also tested. The simulation results show that the corrugated joint will disturb the flow of hydrogen, which increases the temperature gradient along the radial direction of the main flow and enhances the heat transfer. When Re is lower than 4000, the friction factor decreases quickly and then gradually flattens out. Compared with 0.5 for bellows with a pitch ratio of 1, the friction factor increases by 17%. With the increase of Re, the j values of different pitch ratios differ greatly and decrease linearly. For every 5 cm increase in the length of the corrugated tube, the total heat exchange capacity is increased by about 20%，and the total heat transfer increases about 100 W with the increase of the coolant flow 0.04 kg/s.