Stack Length Research Articles

Theoretical Model for Solvent-Induced Base Stacking Interactions in Solvent-Free DNA Simulations.

Ultrahigh-throughput conformational sampling of biopolymers like nucleic acids are most effectively carried out without explicit solvents, but the physical origins of almost all inter- and intramolecular interactions controlling nucleic acid structures are rooted in water. Single-stranded (ss) DNAs or RNAs in water are characterized by ensembles of diverse conformations. To properly capture solvent-induced nucleobase stacking interactions in an otherwise solvent-free Monte Carlo algorithm, theoretical models are developed here to describe the solvent entropy and dispersion terms in base stacking free energies. To validate these models, equilibrium ensembles of ss (dA) n and (dT) n sequences ( n = 30, 40, and 50) were simulated, and they quantitatively reproduced experimental small-angle X-ray scattering (SAXS) data. Simulated dA ensembles show substantial stacking. While less prevalent, stacking in dT chains is not negligible. Analysis of SAXS profiles suggests that excess features between wavevector 0.03 and 0.18 Å-1 correlate with stacking, and stacking in dA versus dT chains is chain length-dependent, where (dT)30 and (dA)30 chains have more similar structures, but longer dA chains show more stacking over dT. The average stack length in ss-dA chains is 5-10 nucleotides, yielding an estimate for the overall A|A stacking free energy at ∼1 kcal/mol.

Single-objective Optimization for Stack Unit of Standing Wave Thermoacoustic Refrigerator through Particle Swarm Optimization Method

Thermoacoustic refrigeration is being regarded as a promising alternative technology with the absence of harmful refrigerants including no or few moving parts, providing the ability to use low grade energy sources for energy conservation. However, the performances of thermoacoustic refrigerators are still low compared to their counterparts, the conventional vapor-compression ones due to involving multi-scale, even multi-field thermo-physical matters with electromagnetic or piezoelectric actuators. Therefore, design optimization of such systems has become quite necessary and significant for achieving competitive performances. In the present study, particle swarm optimization (PSO) is introduced as an intelligent method for such optimization. The stack unit as the key element responsible for thermoacoustic cooling effect, is focused in our first attempt. Coefficient of performance (COP) of the stack unit would be considered as the single-objective function to be maximized under some constraints including stack length, stack center position, blockage ratio and drive ratio. The present study had shown the capability and significant advantages of PSO through showing better optimal result compared to published literature ones. In addition, some considerations for optimization criteria were discussed. Based on this study, PSO could be possibly a favorable intelligent method suitable to the design optimization of thermoacoustic refrigerators or heat engines and their key components effectively.

STUDI EKSPERIMENTAL PENGARUH PERBEDAAN SUDUT KEMIRINGAN TERHADAP TEMPERATUR ONSET TERMOAKUSTIK GENERATOR GELOMBANG BERDIRI

Thermoacoustic generator ia one of energy conversion device that change thermal energy to acoustic form energy. This device can get many beneficial of thermal energy which banned and not be used again from industry, devices of the hospitals, geothermal, and solar energy. The device consist or two type, standing wave and traveling wave. In the research used a standing wave thermoacoustic generator because of the cost is relatively cheaper and the construction is easy to set than traveling wave type. Onset temperature is one of the most important parameter in thermoacoustic generator to be researched. In that aplication, onset temperature can representated how many the performance of this device, if seen by input energy used the system of the thermoacustic generator. Decreasing onset temperature could make decrease of thermal energy used to generator. Beside stack and resonator length, the other parameter that more important to research is tilted angles. In this researched would be done researched with variation of tilted angles -90º, 0º, dan 90º. It would be found the effective tilted angle used, the performance was presented by the least onset temperature. The result was the tilted angle decreased when the onset temperature decreased too. If seen by the input energy, the best performance of thermoacoustic generator is on 90 o tilted angle.

Numerical investigation of the effect of stack geometrical parameters and thermo-physical properties on performance of a standing wave thermoacoustic refrigerator

A thermoacoustic cooler uses sound waves to transfer heat from a cold to a hot region. The stack operates as a medium of this heat transfer and plays a vital role in the cooling performance of these systems. The present study was conducted to investigate the effect of geometrical parameters and thermophysical properties of the stack on the cooling performance of a standing wave thermoacoustic refrigerator and determine most efficient stack geometry and the material. The geometrical parameters studied are the thickness and length of stack plates and the distance between them. The thermophysical properties studied are heat capacity and thermal conductivity of stack plate. To investigate the effects of these parameters, various samples were numerically analyzed in 2D space by the use of COMSOL software. Simulation results demonstrate that reducing thickness and thermal conductivity of the stack plates lead to lower cooling temperatures and higher coefficients of performance (COPs) at an equal temperature difference. Moreover, there are optimum values for the amount of distance between two stack plates and length of the stack, in which a lower cooling temperature and higher COP at equal temperature difference will be obtained. The lowest cooling temperature obtained in simulated samples is approximately −12 °C.

Comparison of Surface Permanent Magnet Axial and Radial Flux Coaxial Magnetic Gears

This paper provides a thorough, parametric comparison of axial and radial flux coaxial magnetic gears with surface-mounted permanent magnets. While both topologies share similar operating principles and can achieve comparable shear stresses, they exhibit different scaling trends with respect to key design parameters. Both topologies’ volumetric torque densities (VTDs) increase with the outer radius, but the axial flux topology's VTD increases with the radius at a much faster rate than the radial flux topology's VTD. Another difference between the topologies involves their cross-sectional scaling parameters. The stack length axially scales radial flux gear cross sections, and, as it increases, the impact of end-effects decreases, which improves the performance. For axial flux gears, the radii ratio scales the cross section's radial width between different radii. This fundamentally changes optimal parameter values and design performance tradeoffs. Finally, axial flux rotors experience significant axial forces, but the radial forces on radial flux rotors can be balanced out. Based on these trends, radial flux gears are superior to axial flux gears for most applications; however, axial flux gears have a significant advantage when a large radius and a small axial length are permissible or when mechanical power needs to be transmitted across a flat barrier.

Design and Performances of Multi-Tooth Stator Permanent Magnet Flux Switching Machine for Light Weight Applications

Permanent magnet flux switching machines (PMFSMs) in which their torque performance produced by interaction between armature coils and permanent magnet (PM) have been widely designed for various applications. In this regard, single-phase 8Slots-12Poles PMFSM with single tooth stator is considered the most suitable candidate for light weight applications because of their advantages of lower copper loss, high efficiency and robust rotor. However, issues of low torque performance due to weak flux linkage, high of PM volume, and high distortion in back-emf that need to be improved. In this paper, a new design of single-phase PMFSM using multi-tooth stator is proposed. Both PMFSMs have been designed using JMAG Designer version 15 and analysed through 2D-FEA. Parameters of stator outer radius, rotor outer radius, air gap, and stack length are set to 37.5mm, 22mm, 0.25mm, and 20.3mm, respectively. Based on the 2D-FEA, PM flux linkage and torque performances of the PMFSM using multi-tooth are 5 times and 38% higher than PMFSM using single-tooth. As a conclusion, single-phase 4Slot-12Poles PMFSM using multi-tooth stator considered as the best candidate for light weight applications due to the less PM volume, and good performances of toque, power and based speed of 1.44Nm, 219W, 1,062rpm, respectively.

Performance Comparison between Salient and Segmental Rotors Single-Phase FEFSM Using Non-Overlap Windings for Home Appliances

Field excitation flux switching machines (FEFSMs) in which their torque performance produced by interaction between armature and field excitation (FE) coils have been widely designed for various applications. In this regard, three-phase salient rotor FEFSM with overlap windings is considered the most suitable candidate for high speed applications because of their advantages of flux controllability, and robust due to single piece of rotor structure. However, the overlap windings cause a high copper loss, hence efficiency of the motor becomes low and higher stack length. Besides, the salient rotor structure is found to produce low torque performance due to the longer flux path in stator and rotor yielding weak flux linkage. In this paper, a new single-phase FEFSM using non-overlap windings between armature coils and FE coils is proposed. Both non-overlap windings FEFSMs with salient and segmental rotors have been designed using JMAG Designer version 15 and the investigation process is conducted via 2D finite element analysis. The proposed motor performances verification has been done by comparing the results of flux linkage, flux line and distribution, flux strengthening, various torque capability, and torque-power versus speed characteristics. As a conclusion, single-phase non-overlap windings FEFSM using segmental rotor with power, torque and speed capabilities of 277.5 W, 0.91 Nm and 2,899 rpm, respectively considered as the best candidate for low torque high speed applications.

Single-objective optimization for stack unit of standing wave thermoacoustic refrigerator through fruit fly optimization algorithm

Thermoacoustic refrigeration is considered as a potential alternative refrigeration technology with environmentally-friendly working substance, no or few moving parts, high reliability as well as utilization of low grade energy. Optimization for thermoacoustic systems or their key components has become a crucial task to make their performances competitive over conventional vapor-compression ones. In this study, fruit fly optimization algorithm (FOA) as an intelligent method is introduced to separately maximize coefficient of performance of stack unit and cooling power produced for one standing wave thermoacoustic refrigerator, as single objective functions under optimized stack length, stack center position, blockage ratio and drive ratio. FOA had shown better optimal results, compared to published literature results. Compared to results of genetic algorithm, COP had been enhanced by 15.8%. Moreover, cooling power was first discussed as another important objective to optimize. Studied results demonstrated that FOA is an effective approach for design optimization of thermoacoustic refrigerators.

Synchronous reluctance generator with ferrite magnets for wind turbine

Synchronous reluctance generators with ferrite magnets in the rotor (PMSynRG) are a good alternative to synchronous generators (SG) with rare-earth magnets. The comparison between a SG with rare-earth magnets and a PMSynRG with ferrite magnets of the same diameter, stack length, power and speed is given in the paper. Twice as less magnets are required for the PMSynRG with ferrite magnets than for the SG with rare-earth magnets. The cost of the ferrite magnets is 4.4 times less than of the rare earth magnets. Also, the PMSynRG with ferrite magnets has much higher efficiency than the SG. The half-integer slot number per pole and phase is chosen to achieve rather low torque ripple without skewing the rotor.

Design of Power Density Improvement by Applying Novel Shape of Slit and Notch to Outer Rib of Rotor of Spoke-type Permanent Magnet Synchronous Motor

Objective:In this study, improvement of power density by applying novel shape of slit and notch to outer ribs of a rotor that reduces magnetic flux leakage in outer rib and increases air-gap magnetic flux density for spe PMSM for a washing machine, was investigated.Methods:It is important that motors for home appliance require lower manufacturing cost, high power and high efficiency. In order to increase power, rotor shape is re-designed. In the outer rib of the rotor, magnetic flux leakage occurs by permanent magnet and magnetic flux is saturated which is one of the factors that reduces the power and efficiency. However, if the outer rib is designed to be too thin, the permanent magnet may scatter during high-speed rotation. Therefore, a design considering permanent magnet scattering is necessary. Motor for a washing machine has two operating points that washing mode at constant torque point and dehydrating mode at high-speed point.Conclusion:For improvement of higher power density, 2-D finite elements analysis was performed to optimize the parameters of the shape of slit and notch to increase the torque. The torque increases by optimizing width and length of slit shape and notch shape. Finally, with the optimized parameters of shape of slit and notch, stack length was adjusted as per torque requirement for a washing machine motor and power density increases considering the safe factor from stiffness analysis.

Experimental investigation of an adjustable standing wave thermoacoustic engine

This work is primarily concerned with the experimental investigation of the performance of a standing wave thermoacoustic engine (TAE). The TAE technology converts thermal power into acoustic power which may be used to generate electricity or, to drive thermoacoustic cooling devices. Although there is a number of existing researches that suggest the link between the geometrical configuration of the device and its performance, there are no existing work that point out how to incorporate this aspect in the designing. Therefore, this study proposes the use of an adjustable TAE in order to alter the performance of the device while in operation. This new TAE model has an adjustable resonator length, which consisted of a 103 mm (4-in.) honeycomb ceramic stack sample, buffer volume and a cooling shell-tube heat exchanger was developed. Six different stacks were used to evaluate the performance of the TAE. Three different stack lengths (50, 100, and 150 mm), positioned at three different locations, were investigated. These locations were measured from the hot ends of the stack to the pressure antinode. In addition, the influence of the mean pressure and the working gas was investigated. Measurement of temperature difference across the stack and sound pressure levels at the steady state were used to determine the efficiency of the device. Through the adjustment of the resonator length, this study point out the benefit of choosing the best frequency so that TAE can work optimally and produce higher acoustic power.

Prediction of acoustic wave parameters of thermoacoustic prime mover through artificial neural network technique: Practical approach for thermoacoustics

Thermoacoustic prime movers are considered new alternative heat engines to traditional ones. For good performance of such a heat engine, a careful apparatus design is required. To predict the acoustic wave parameters responding to geometrical parameters of stack and resonator, is important for such a design. Artificial neural network (ANN) model is first proposed to predict the oscillating frequency and acoustic pressure amplitude, under given resonator length, stack length, stack plate spacing and thickness. ANN models for one standing wave thermoacoustic prime mover had been developed based on published experimental data, and evaluated based on some criteria such as least mean square error between the predicted and actual outputs during the testing phase. Concerning oscillating frequency, ANN model with the configuration of 4-4-4-1 was adopted whilst 4-4-1 for acoustic pressure amplitude, namely 4 neurons representing the four input design parameters, one or two hidden layers each with optimal four hidden neurons and one neuron representing the output oscillating frequency or acoustic pressure amplitude. Moreover, a statistical analysis has been conducted to show the contribution percentages of the proposed geometrical parameters of resonator and stack where it was found that the resonator length has the largest contribution effect with the approximate percentage of 76% on the two considered acoustic wave parameters. Compared to both experimental and DeltaEC model results, the determined ANN models had been proven to be desirable in their prediction accuracy with the error percentages of 2.26% and 0.78% for predicted oscillating frequency and acoustic pressure amplitude, respectively. This research work provides a promising practical modeling approach based on ANN technique for complex design problems in thermoacoustic systems.

Design of a Stator for a High-Speed Turbo-Generator With Fixed Permanent Magnet Rotor Radius and Volt–Ampere Constraints

This paper investigates high-speed surface PM machine design for portable turbo-generator applications. The rotor radius is fixed to achieve certain optimal characteristics of the magnet retention mechanism. The objective of this paper is to design and select the stator. The stator designs are populated by different slot/pole combinations, winding arrangements, and over a range of possible stack lengths. However, the design is constrained by physical diameter, stack length, and electrical volt–ampere constraints. A large number of preliminary machine designs do not satisfy the specified turbo-generator torque/speed requirements under the given volt–ampere constraints and therefore it is ineffective to perform finite element analysis on all preliminary design variations. In order to establish the feasibility of a machine design to fulfill the specified turbo-generator torque/speed requirements, the concept of inductance-limits is presented and then linked with stator design parameters. By application of this analysis strategy, a confined optimal set of stator designs are obtained and are subjected to detailed finite element simulations. A final machine design is selected and fabricated. Experimental results are presented for the validation of the final machine design.

Virtual Material Method for Enabling a Single 2D-FEA Simulation of Electrical Machine Sets

When two or more electrical machines are electrically and mechanically interconnected, the implementation of a single two-dimensional finite element analysis (2D-FEA) of the whole system is complex or even impossible. This is mainly due to the feature of commercially available 2D-FEA software to use a domain depth equal for all the electrical machines drawn in the geometrical 2-D model. For any typology of rotating electrical machines, the proposed “ virtual material method ” easily consents to change the actual axial stack length to an arbitrary value, opening the way to describe all the machines in a single geometrical model. In the paper, the complete theory of this original approach is reported and validated on permanent magnet, induction, and field-wound synchronous machines. The cases of study with two and three interconnected machines are also presented and the results compared with the cosimulation technique of their separated bidimensional models. The perfect agreements observed in the comparisons definitely prove the feasibility of the proposed solution.

Optimization of standing-wave thermoacoustic refrigerator stack using genetic algorithm

The main focus of this work is the optimization of a thermoacoustic plate stack in a standing-wave thermoacoustic refrigerator using genetic algorithm. A numerical model of the thermoacoustic stack and its iterative solving process are firstly presented. A comparison to DeltaEC modelling shows that the presented method is effective in predicting the acoustic field and the energy flow. Based on the numerical model, the stack is optimized in terms of four and five variables for both single objective and multiple objectives. In the four-variable models, the length and position of the stack, the plate spacing and the stack porosity are investigated. In the five-variable model, the acoustic frequency is considered additionally. In the single-objective optimization, the objective function is either the cooling power or the coefficient of performance of the stack, and the multi-objective model has two objective functions, namely, the coefficient of performance of the stack and the cooling power. For the optimization, genetic algorithm hybridized by pattern search and implemented in Matlab is adopted. The optimal values of the stack length and the stack position, obtained from the single-objective optimization, agree with those in the published work. The extended multi-objective models present the Pareto optimal, which provides more design choices depending on the preference.

AN ANALYSIS OF HEATING UNIFORMITY IN WOOD HIGH-FREQUENCY DRYING

The high-frequency heating temperature field simulation model was built using finite element method and validated by experiments. Under the premise of ensuring model accuracy, the model parameters (plate spacing and area, wood dielectric constant, stack length and width, and heating time) were individually varied to assess the impact of these parameters on wood heating uniformity. The results showed the following: 1) The model has good accuracy as verified by experiments. 2) In the thickness direction, the middle layer temperature was higher than the upper and lower surface temperatures; in the length and width directions, the center temperature was lower than those of both ends and both sides, and the temperature at the corners was the highest. 3) The smaller the distance between the plates, the better the heating uniformity; with the plate area increasing, the heating uniformity first increased and then decreased; the smaller the wood dielectric constant, the better the heating uniformity; as the continuous heating time increased, the heating uniformity first decreased, then increased, and then again decreased; as the length and width of the stack increased, the heating uniformity decreased first, then increased, and then again decreased; when they were the same size as the plate, the heating uniformity was the best.

Characteristic Analysis of Interior Permanent Magnet Synchronous Machine by considering Magnetization Patterns

This paper deals with the comparative investigation on the electromagnetic field characteristics of interior permanent magnet synchronous motors (IPMSMs) based on finite element method. With identical magnetic structure, this paper proposes newly designed PM magnetization patterns for the cogging torque reduction. Based on this method, in spite of the longer stack length of the rotor and stator core, the torque characteristics can be much more improved in comparison with the conventional model. Along with the torque characteristics, the performance evaluation is also addressed based on the analyzed power loss values.

Design and analysis of acoustically-driven 50 W thermoacoustic refrigerators

The design of loudspeaker-driven 50 W cooling power thermoacoustic refrigerators operating with helium at 3% drive-ratio and 10 bar pressure for a temperature difference of 75 K using the linear thermoacoustic theory is discussed. The dimensional normalization technique to minimize the number of parameters involved in the design process is discussed. The variation in the performance of the spiral stack-heat exchangers’ at 75% porosity as a function of the normalized stack length and center position is discussed. The resonator optimization is discussed, and the optimized one-third-wavelength (tapered, small diameter tube and divergent section with hemispherical end), and one-fourth-wavelength (tapered and divergent section with hemispherical end) resonator designs show 41.3% and 30.8% improvements in the power density compared to the published 10 W designs, respectively. The back volume gas spring system for improving the performance of the loudspeaker is discussed. The one-third-wavelength and one-fourth-wavelength resonator designs are validated using the DeltaEC software, which predicts the cold heat exchanger temperature of − 3.4 °C at 0.882 COP, and − 4.3 °C at 0.841 COP, respectively.

The Influence of the Density of Coconut Fiber as Stack in Thermo-Acoustics Refrigeration System

An experimental study of using coconut fiber as stack with varying density in thermo-acoustics refrigeration system has been done. Stack is a device which is described as the “heart” in thermo-acoustics refrigeration system. The length of stack is a fix parameter in this experiment. The performance of the coconut fiber was evaluated from the density of stack (varied from 30%, 50% and 70%), position of stack (varied from 0 to 34 cm from the sound generator), and frequency of sound generator (varied from 150 Hz, 200Hz, 250Hz and 300Hz). The inside, outside, and environment temperatures were collected every second using Data Acquisition (DAQ). The result showed that the increase of stack density will increase the performance of thermo-acoustics refrigeration system. The higher density produced temperature differences in cold side and hot side of 5.4°C. In addition, the position of stack and frequency of sound generator have an important role in the performance of thermo-acoustics refrigeration system for all variations of the density.

A Study on the Maximum Flux Linkage and the Goodness Factor for the Spoke-Type PMSM

In this paper, we propose a goodness factor that shows how the output density of a Spoke-type permanent-magnet synchronous motor (PMSM) is improved than that of the conventional surface permanent-magnet synchronous motor (SPMSM). The application of the goodness factor, which is defined as the ratio of the total flux between different motor configurations, enables a comparison of the total flux between the SPMSM and spoke-type PMSM. A performance comparison analysis between the two motor configurations with the same rotor diameter, air gap length, stack length, permanent-magnet usage, and materials was performed using the proposed goodness factor. In order to improve the performance prediction accuracy, furthermore, the effect of both the bridge leakage and the axial leakage was included during the analysis process of the spoke-type PMSM. Finally, in order to verify the proposed method, SPMSM and Spoke-type PMSM with the same outer diameter size and permanent-magnet usage were fabricated and evaluated.