Pitch Length Research Articles

Light-Reconfiguring Inhomogeneous Soft Helical Pitch with Fatigue Resistance and Reversibility.

Active engineering and modulation of optical spectra in a remote and fully reversible light is urgently desired in photonics, chemistry, and materials. However, the real-time regulation of multiple optical information such as wavelength, bandwidth, reflectance, and polarization is still a longstanding issue due to the lack of an appropriate photoresponsive candidate. Herein, we propose an additional "degree-of-freedom (DOF)" in a photo-modulated soft helix, and build up an unprecedented inhomogeneous helical pitch length with light-reconfiguring property, fatigue resistance, and reversibility. For the working model, the intrinsic chiral photoswitch LBC5 is employed as an actuator to modulate the helical pitch length, which is proportional to the irradiation intensity, and the unique broadband absorbance photo-modulator BTA-C5 is incorporated as an attenuator of the transmitted light to decrease its intensity along the sample thickness, therefore successfully adding another controlled DOF on the pitch length distribution (i.e., homogeneous or inhomogeneous) apart from the common soft helix with only a single DOF on the pitch length. The absorbance photo-modulator BTA-C5 with a unique variable broadband absorption enables the light to reconfigure the helical pitch from homogeneous to inhomogeneous, thereby achieving the robust fatigue-resistance establishment of reversible spectral programming. The established light-reconfigurable inhomogeneous helical pitch with the photoresponsive modulator BTA-C5 can provide a breakthrough to control absorbance and chirality, especially for dynamically broadening and narrowing the bandwidth on demand, and further enable the ever-desired broadband NIR circularly polarized luminescence (CPL) with a high dissymmetry factor glum of up to 1.88. The cutting-edge photoswitchable inhomogeneous soft helical pitch provides access to multi-freedom control in soft materials, optics, biophotonics, and other relevant fields.

Analysis of Heat Transfer and Flow Characteristics of a Helically Coiled Tube with Twisted Elliptical in a Low Reynolds Number Flow

In this paper, the heat transfer and flow characteristics of a helically coiled tube with twisted elliptical in a low Reynolds number (Re = 500–3000) flow were investigated numerically. The working fluid flowed in a laminar regime. Numerical results were compared with empirical correlations in the existing literature, demonstrating the accuracy of the analysis in this study. Firstly, we investigated the effects of geometric parameters and Reynolds number on the heat transfer and flow characteristics. The results showed that lower twist pitch length and semi-major axis length could induce sufficient fluid mixing and a larger temperature gradient near the tube wall, enhancing the heat exchange and producing larger friction resistance. Overall, the heat transfer performances were improved by about 1.04–1.21 times and 1.02–1.23 times for different semi-major axis lengths and different twist pitch lengths, respectively, compared to the smooth helical coil. Secondly, by changing the working fluid, it was found that the Nu when oil was chosen as the working fluid was all 6–6.8 times higher than that of water. Moreover, the effect of using Al2O3 nanofluids with a concentration of 0.10 wt.%, 0.25 wt.% and 0.50 wt.% was discussed. It can be seen that the heat transfer capacity of nanofluids increased by approximately 2–18% compared to the reference model with water as the working fluid, and the nanofluid solution with higher concentration has better heat transfer performance. Finally, Nu and f correlations are given to predict the heat transfer and pressure drop in practical applications.

Performance improvement of a cyclone separator using spiral guide vanes with variable pitch length

Performance improvement of a cyclone separator using spiral guide vanes with variable pitch length

Experimental Investigation of Rod Pitch Effect on Void Fraction in 5 × 5 Rod‐bundle under Elevated Pressure Conditions

In the present study, void fraction distributions in 5 × 5 rod-bundle test sections were investigated. Two different rod-bundle test sections with different rod pitch lengths were constructed. Experiments were carried out using unheated rod-bundle test sections equipped with 10 mm rod diameter with rod-pitch lengths of 13 and 12 mm, respectively. The HUSTLE (Hitachi Utility Steam Test Leading Facility) facility supplied steam and water with an inlet mass flux (G) ranging from 75 to 500 kg/m2/s at 5.0 to 7.5 MPa system pressure. These inlet and boundary conditions simulate the prototypic BWR at natural circulation conditions. For the measurement of void fraction, the X-ray CT system was newly developed for the three-dimensional time-averaged void fraction measurement, and 3D void fraction distributions were successfully obtained for various pressure conditions. The volume-averaged void fraction was also measured using differential pressure transmitters. Based on the newly developed void fraction database, the assessment was carried out using state-of-the-art drift-flux correlations applicable for rod-bundle. Existing correlations tend to show good void fraction prediction at high mass flux conditions for both geometries, poorer performance was shown for the narrow rod test sections with low mass flux conditions. Furthermore, the effect of the rod-pitch lengths on void fraction distribution in rod-bundle flow field was assessed. It was observed that narrower rod bundle configuration tends to have higher void fraction at given mass flux. Narrowed pitch-length enhances wall-friction against two-phase flow, which likely suppress the central phase fraction peak tendency. This promotes lower distribution parameter values, results in increased area-averaged void fraction for narrower pitch test section. However, the present study revealed that no existing correlations could clearly capture the void fraction trend for the narrow rod test section.

Examination of Twisted Elliptical Tube Heat Enhancement Within the Mixed Convective Zone

Previously, the investigation of the heat transfer performance of twisted elliptical tubes has been restricted to the effects of forced convective conditions without considering the impact of buoyancy conditions. Therefore, this work investigates heat transfer enhancement of twisted elliptical tubes of different pitch lengths at different mixed convective regimes. The model continuity, momentum, and energy equations were solved using the finite volume technique and validated using both analytical and experimental results. Under the variation of Gr and Re, the results show that twisted elliptical tubes are better than smooth elliptical tubes for heat transfer but with a corresponding high drag coefficient. The heat enhancement of 48% was obtained at a twisted pitch length of 200 mm and Re of 2000 as compared to the plain tube. In addition, on the effect of twist pitch length, the results show that the more twisted a tube is the more its Nu and F. This indicates that induced secondary flow by the twist has a high impact on the Nu and F. The results show that heat enhancement of the elliptical tube depends on P, Gr, and Re. Similarly, there is a fluid-thermal-structure interaction interplay in the hydrothermal behavior of elliptical tubes.

A finite element study and mathematical modeling of lumbar pedicle screw along with various design parameters

BackgroundLumbar pedicle screw is one of the most common and important elements in the field of lumbar surgery. It plays a great role in rectifying the spinal alignment and stabilization providing strength and stability to the affected area of spine. In spinal surgery, minimally invasive techniques and minor incisions are made which makes it less painful for the patients than the traditional methods. Moreover, the screws are not needed to be removed after the surgery which is yet another great advantage of the pedicle screw. MethodIn this study, 3D Finite Element (FE) model of human L4 vertebrae is taken for analysis using image processing tool. Pedicle screw design with varying mechanical and geometrical properties has been carried out at different applied loads on it along with considering the effect of frictional forces between all contact surfaces. ResultMathematical relationship among stress, strain, pitch of the screw and diameter have been developed for different thread profiles which will be beneficial for researchers for further development of pedicle screw implants. ConclusionResults from the different analysis shows that bending stress on the screw for different loads at triangular pitch is higher than the trapezoidal. Hence, trapezoidal thread is efficacious than triangular thread. In case of vertebral bone, the magnitude of stress is less for trapezoidal screw than triangular and stress has a linear relationship with pitch length. In term of strain, triangular thread develops more strain than trapezoidal thread. A set of mathematical relation has been developed for different thread profile based on pitch length, stress and strain which gives the idea about von Mises stress and strain.

Numerical Investigation of Thermal-Hydraulic Performance of Printed Circuit Heat Exchanger with Different Fin Shape Inserts

The printed circuit heat exchanger is one of the most recent important heat exchangers, especially in the nuclear power plant and aerospace applications, due to its very compact geometry and small print foot. This paper presents a 3D numerical investigation of the thermo-hydraulic performance of PCHE with a new non-uniform channel design configuration. The new channel design consists of two different fins and shape inserts: the diamond and biconvex shapes. The influence of two design parameters on the heat exchanger performance was studied and optimized, the longitudinal and transverse pitch length (Pl) and (Pt). Air with constant properties as the working fluid with constant heat flux at the walls envelope. The Reynolds number varied from 200 to 2000. Different Pitch lengths were used (Pl=20, 30, 40, and 50) mm and (Pt=3, 4, and 5) mm. Three performance parameters were studied the Nusselt number, friction factor, and the overall performance evaluation factor. Results show that the thermal performance enhanced with decreasing the pitch lengths, and it was shown that this enhancement was found only at high Reynolds numbers above 1400. The higher enhancement factor was with NACA 0020 airfoil fins at pt=3 mm and pl=20mm of η=2.75 at Re=2000, while the worst performance was obtained with biconvex fins. The main reason behind the enhancement is the disruption of the boundary layer and the good mixing induced in the fluid flow.

Intrinsically chiral ferronematic liquid crystals: An inversion of the helical twist sense at the chiral nematic – Chiral ferronematic phase transition

The ferroelectric nematic phase is a unique example of a polar phase without positional order of the constituent molecules. The properties of the ferronematic phase formed by intrinsically chiral molecules are discussed. Chirality makes the phase structure helical with the similar pitch length in the N* and N F * phases, but with opposite sense. The materials show strong non-linear optical properties. • Intrinsically chiral mesogens forming ferroelectric fluidic nematic, N F *, phase were obtained and studied. • In both, paraelectric and ferroelectric nematic phases, molecular chirality leads to helical structure. • Inversion of helix twist sense was observed at the N*-N F *phase transition. • Giant dielectric permittivity, above 10 4 , was determined in ferroelectric nematic phase. • Strong nonlinear optical properties were confirmed for ferronematic phase. Strongly dipolar mesogenic compounds with a chiral center located in a lateral alkyl chain were synthesized, and shown to form the ferroelectric nematic phase. The presence of molecular chirality induced a helical structure in both the N* and N F * phases, but with opposite helix sense in the two phases. The relaxation frequency of the polar fluctuations is only weakly affected by helical structure, it was found to be slightly lower for the chiral N F * phase than for its achiral, non-branched counterpart with the same lateral chain length.

Performance Optimization of Helicopter Rotor in Hover Based on CFD Simulation

An optimization method of helicopter rotor hovering performance is proposed, which is mainly carried out by means of CFD simulation. This method can be used to obtain the rotation speed of any blade model under the designed hovering tension through several iterations, and then, the tension, torque, power, and power load of the rotor under the rotation speed can be obtained. By comparing different blade pitch, radius, twist, and chord length, the blade parameters at the highest power load can be selected. A series of new rotor models are obtained by changing the model parameters on the basis of C-T rotor. NASA has carried out a lot of experiments on the C-T rotor model and published detailed experimental reports. The transient simulation is carried out by the embedded grid method.

Performance enhancement and optimization for rod‐baffle heat exchangers with twisted oval tubes

AbstractTwisted oval tubes were proposed to be installed in rod‐baffle heat exchangers (RBHXs) to enhance heat transfer performance. A comparison between RBHXs with twisted oval tubes and those with circular tubes is performed. The results show that the heat transfer coefficient (h) per unit pressure drop (Δp) of RBHXs with twisted oval tubes is larger than 36.01%~100.24% compared with that of circular tubes when Reynolds numbers are 4577~22 889, and heat transfer enhancement is more obvious under lower inlet velocity. Then the structural parameters of RBHXs with twisted oval tubes are optimized using the response surface model and genetic algorithms. The results show that the h decreases first and then remains constant with the increase of the twisted pitch length, and decreases first and then rises again with the increase of the ratio of long axis to short axis. The Δp almost keeps constant with increasing twisted pitch length and decreases by 36.67% with the increase in the ratio of long axis to short axis. The comprehensive performance index h/Δp of the RBHXs with twisted oval tubes is enhanced by an average of 26.42% compared with that of original structure. The research results have a good guideline for heat transfer enhancement and the structural design of RBHXs.

Thermal–hydraulic characteristics and structure optimization of Z-channel printed circuit heat exchanger

Printed circuit heat exchanger (PCHE) is a compact equipment, which has the characteristic of high heat exchange efficiency. In practical application, the Z-type microchannel PCHE has shown unique advantage, and its structural parameters, such as pitch angle, pitch length, and channel diameter, have significant impact on its thermal–hydraulic characteristics. In this study, a series of PCHE models with a pitch angle of 5° to 45°, a pitch length of 12.3 mm to 24.6 mm, and a channel diameter of 1.25 mm to 2.25 mm are built by numerical method. Using a working medium of helium, we in detail analyze effects of these structural parameters of the PCHE on the related thermal–hydraulic characteristics. More importantly, to obtain the optimized structure of the PCHE, the response surface analysis of the simulation data is present. It shows that both the pitch angle and the inlet Reynolds number have greater effects on the flow and heat transfer performance of the PCHE. The quadratic polynomials of Nu and f are fitted by DesignExpert and the genetic algorithm is used for the multiobjective optimization. Three sets of optimized structures are given and also verified by the numerical simulations. The study could provide a guidance for the design and application of the PCHE in related engineering.

A Tunable, Particle-Based Model for the Diverse Conformations Exhibited by Chiral Homopolymers

Chiral block copolymers capable of hierarchical self-assembly can also exhibit chirality transfer─the transfer of chirality at the monomer or conformational scale to the self-assembly. Prior studies focused on experimental and theoretical methods that are unable to fully decouple the thermodynamic origins of chirality transfer and necessitate the development of particle-based models that can be used to quantify intrachain, interchain, and entropic contributions. With this goal in mind, in this work, we developed a parametrized coarse-grained model of a chiral homopolymer and extensively characterized the resulting conformations. Specifically, the energetic parameter in the angular and dihedral potentials, the angular set point, and the dihedral set point are systematically varied to produce a wide range of conformations from a random coil to a nearly ideal helix. The average helicity, pitch, persistence length, and end-to-end distance are measured, and correlations between the model parameters and resulting conformations are obtained. Using available experimental data on model polypeptoid-based chiral polymers, we back out the required parameters that produce similar pitch and persistence length ratios reported in the experiments. The conformations for the experimentally matched chains appear to be somewhat flexible, exhibiting some helical turns. Our model is versatile and can be used to perform molecular dynamics simulations of chiral block copolymers and even sequence-specific polypeptides to study their self-assembly and to gain thermodynamic insights.

(Digital Presentation) Development of a Low-Torque Transfer System Using a Progressive Cavity Pumps with Gels

Progressive cavity pumps (PCPs) consist of a rotor and a stator. The extrusion process of PCPs is governed by a single-helical rotor which rotates eccentrically within a double-helical stator of twice the pitch length. Between the seal lines (the contact lines of rotor and stator), there are cavities which are constantly moved towards the discharge end of the pump. As one cavity is eliminated, another cavity develops, keeping the cross-sectional area of the cavities constant. The process makes a continuous non-pulsating flow in the PCPs. The developed pushing–and–suction action allows PCPs to exert significantly lower shear rates on the pumped material, compared to other pump types, such as membrane pumps or peristaltic pumps. However, the sliding of the rotor and stator in the pump causes a biting phenomenon [1-3]. Therefore, the degradation of particles in the fluid occurs. In this study, we adopted a flexible, low-friction gels as the stator material. By using gels materials as stator, we could make a pump that could discharge at low torque as previously reported by our group [4]. In this work, the rubber stator and the gels stator fabricated by 3D printing were compared and evaluated by performing discharge and torque test.

Vocal Characteristics Influence Women's Perceptions of Infidelity and Relationship Investment in China.

Vocal characteristics are important cues to form social impressions. Previous studies indicated that men with masculine voices are perceived as engaging in higher rates of infidelity and being less committed to their relationship. In the current study, we examined how women in China perceive information regarding infidelity and relationship investment conveyed by the voices (voice pitch and vocal tract length) of males, and whether different vocal characteristics play a similar role in driving these impressions. In addition, we examined whether these perceptions are consistent in Chinese and English language contexts. The results indicated that women perceived men with more masculine voices (lower voice pitch and longer vocal tract length) as showing a lower likelihood of infidelity and higher relationship investment; further, women who preferred more masculine voices in long-term relationships, but not in short-term relationships, were more likely to perceive men with masculine voices as less likely to engage in infidelity and more likely to invest in their relationship. Moreover, the participants formed very similar impressions irrespective of whether the voices spoke native (Chinese) or foreign (English) languages. These results provide new evidence for the role of the voice in women's choices in selecting long-term partners.

Effects of trapezoidal and twisted trapezoidal tapes on turbulent heat transfer in tubes

Trapezoidal and twisted trapezoidal tape elements which are used for heat transfer enhancement in tubes are experimentally investigated. The effects of the tapes on heat transfer, pressure drop, and overall performance factor are analyzed. Three different thread heights are used in the experiments, which are obtained by dividing the tape width by 4, 6, and 10. Pitch length is kept constant for the trapezoidal tapes, while the constant twisting ratio is used for the twisted trapezoidal ones. Tapes were held in the tube with no wall contact by stretching mechanically. Experiments were conducted under constant heat flux boundary condition and for Reynolds number interval of 5000–25,000, targeting turbulent flow at which overall performance factor values reported in literature are relatively small comparing to laminar flow. The experimental results show that trapezoidal tape elements enhance heat transfer and increase pressure drop with changing rates depending on thread heights. Overall performance factor in the tested interval is detected over unity for two twisted trapezoidal inserts, making them significant alternatives comparing to the literature. The best thermal performance of 1.164 is obtained with the twisted trapezoidal tape element with the maximum thread height, while Nu is 90.52 and friction factor is 0.12. A maximum Nu of 118.46 is achieved with the proposed twisted trapezoidal tape, which is 1.9 times higher than the plain tube case and 1.57 times higher than the conventional twisted tape case. Since the twisted trapezoidal tapes perform better than the plain trapezoidal ones, it is concluded that the combination of the twisted and trapezoidal forms may be favorable in terms of heat transfer enhancement and overall performance factor regarding combination of swirl flow effect and periodical flow disturbance effect.

Multi-objective optimization of a bidirectional-ribbed microchannel based on CFD and NSGA-II genetic algorithm

The bidirectional rib (BR) has been recognized as one effective heat transfer enhancement technique for the microchannel heat sink (MCHS) since it can realize the heat transfer improvement in both vertical and spanwise directions. However, the utilizing of BR causes a large pressure drop penalty in the microchannel due to its broader obstruction area. For the engineering application, the heat transfer and pressure drop penalty of MCHS are two key metrics to evaluate its overall performance. To address this optimization problem, 144 sample points of the microchannels with different BRs are generated by CFD simulation, and the NSGA-II has been utilized to search for the optimal solutions in-terms of both objectives. For most optimal solutions, the length of SR and rib pitch are 200 μm and 800 μm, respectively, while the other two parameters, the width and height of SR, almost cover the entire value range. Subsequently, the best compromise solutions have been determined from the Pareto fronts by the TOPSIS and LINMAP methods according to the decision maker's preference. Finally, the selected optimum solutions are verified by numerical and experimental methods.

Physical relationship between resonant frequency and structure parameters of a normal mode helix dipole antenna for an ultra-high frequency radio frequency identification tag thread

The thread-based ultra-high frequency radio frequency identification (UHF RFID) tag with a normal mode helix dipole antenna (NMHDA) shows great potential in anti-theft and implant wireless sensors; for the engineered and digitized design of the high-performance tag, it is necessary to know the physical relationship between the resonant frequency and structure parameters of the NMHDA. Previous work for the design of the NMHDA structure is based on the self-resonant principle, that is, zero port reactance, while the port impedance of the NMHDA in the UHF RFID tag thread at resonant frequency is ideally conjugate matching to the chip. Under the requirement of conjugate matching, this study built the physical relationship between the resonant frequency and structural parameters of the NMHDA (helical radius, helical pitch, and single arm length) by linking the chip impedance with the NMHDA impedance. Meanwhile, the reported equivalent impedance model of the NMHDA, consisted of a lumped inductor and a linear dipole antenna, was utilized and modified by considering the distributed capacitance deviation from the NMHDA geometry simplification as part of the lumped inductor. Finally, the physical relationship was put into practice for the design of an UHF RFID tag thread with expected resonant frequency, and the long reading range of the prototype (over 14 m) demonstrated the rationality of the modification. In addition, the discussion on the structure parameter of the NMHDA clarified the efficiency of our proposed method. Generally, the built physical relationship explicitly gives the physical effects of the structural parameters and provides a parametric method for the structure design of a NMHDA for the UHF RFID tag thread.

Effects on collective behaviour and locomotor and neuromuscular response in young players by varying the length of the pitch in 11-a-side football

The aim of this study was to describe the effects on collective behaviour and the physical response of young elite football players (Under 15) in the same 11 versus 11 task in three different pitch lengths (100, 75 and 50 m, LSG100, LSG75 and LSG50, respectively), keeping the width constant (60 m). The intra-team variables were: convex hull (CH), stretch index (SI), width (W), length (L) and length/width (L/W). The inter-team variables were calculated by using the 20 outfield players: CH2, W2, L2, L/W2 and DC (distance between centroids). The physical variables were: maximum speed (Vmax), number of accelerations (Acc) and decelerations (Dec) and total distance (TD). The results showed small (LSG100 > LSG75) and moderate–long differences (LSG100 > LSG50) for CH, SI and L. There was a moderate increase in DC and W2 (LSG50 > LSG75) and a moderate decrease in SI2, CH2, SI, L and CH (LSG75 > LSG50). The entropy was higher in SSG50 > LSG75 > LSG100. On a conditional level, the values showed differences between the three formats studied, showing more similarities between LSG50 and LSG100 than with LSG75. The main conclusion of the study was that the variation in the dimensions of the pitch caused a non-linear variation in the behavioural and conditional response in teams and players.

Understanding and Manipulating Helical Nanofilaments in Binary Systems with Achiral Dopants.

Here, we report the relationship between helical pitch of the helical nanofilament (HNF) phase formed by bent-core molecule NOBOW and the concentration of achiral dopants 5CB and octane, using linearly polarized resonant soft X-ray scattering (RSoXS). Utilizing theory-based simulation, which fits well with the experiments, the molecular helices in the filament were probed and the superstructure of helical 5CB directed by groove of HNFs was observed. Quantitative pitch determination with RSoXS reveals that helical pitch variation is related to 5CB concentration with no temperature dependence. Doping rodlike immiscible 5CB led to a pitch shortening of up to 30%, which was attributed to a change in interfacial tension. By shedding light not only on phase behavior of binary systems but also enabling control over pitch length, our work may benefit various applications of HNF-containing binary systems, including optical rotation devices, circularly polarized light emitters, and chirality transfer agents.

Dynamically actuated soft heliconical architecture via frequency of electric fields

Dynamic electric field frequency actuated helical and spiral structures enable a plethora of attributes for advanced photonics and engineering in the contemporary era. Nevertheless, leveraging the frequency responsiveness of adaptive devices and systems within a broad dynamic range and maintaining restrained high-frequency induced heating remain challenging. Herein, we establish a frequency-actuated heliconical soft architecture that is quite distinct from that of common frequency-responsive soft materials. We achieve reversible modulation of the photonic bandgap in a wide spectral range by delicately coupling the frequency-dependent thermal effect, field-induced dielectric torque and elastic equilibrium. Furthermore, an information encoder prototype without the aid of complicated algorithm design is established to analogize an information encoding and decoding process with a more convenient and less costly way. A technique for taming and tailoring the distribution of the pitch length is exploited and embodied in a prototype of a spatially controlled soft photonic cavity and laser emission. This work demonstrates a distinct frequency responsiveness in a heliconical soft system, which may not merely inspire the interest in field-assisted bottom-up molecular engineering of soft matter but also facilitate the practicality of adaptive photonics.