Helical Generator Research Articles

Limitations of the Fast Operation of Helical Magneto-Cumulative Generators

A requirement of current rise-time shortening on the final stage of a magnetocumulative generator (MCG) operation (a requirement to increase the fast operation of the generator) comes from a necessity to decrease a premature thermal or ponderomotive effect of a current pulse on loads elements. These requirements mean an increase of the MCG power, and finally, they are associated with obtaining maximum possible energy density in the loads. This paper considers different factors that limit the power of the helical MCG and experimentally shows possibility of significant increase of the helical-generator's fast operation due to application of additional elements in the stator, change of a liner shape, and use of two-sided initiation of a high-explosive charge.

A new vortex generator geometry for a counter-flow Ranque–Hilsch vortex tube

Abstract In this study, a new geometry is introduced for the cold end side (i.e. where the swirl flow is introduced into the tube), which is called ‘helical swirl flow generator’ . Effect of the helical length of the swirl flow generator on the performance of the vortex tube are investigated for varying values of other geometrical parameters as a function of the cold mass fraction, y c . Finally, it’s disclosed that the effect of the helical length on the performance changes critically according to the value of L/D .

An experimental study on the effect of the valve angle of counter-flow Ranque–Hilsch vortex tubes on thermal energy separation

An experimental study is conducted to investigate effects of the conical valve angle on thermal energy separation in a counter-flow vortex tube. A new geometry is designed for the cold end side, which is called ‘ helical swirl flow generator’. Combined and interactive effects of the helical length of the swirl flow generator, the ratio of the tube length to the tube inner diameter ( L/ D), the inlet pressure and especially the angle of the conical valve on the performance of the vortex tube are comparatively investigated as a function of the cold mass fraction, y c . Four different conical valves have been used with the angle of 30°, 45°, 60° and 75°. Finally, it is observed that the effect of the valve angle on the performance changes according to the value of L/ D and, it has a weak influence on the system performance.

The advanced helical generator

A high explosive pulsed power generator called the advanced helical generator (AHG) has been designed, built, and successfully tested. The AHG incorporates design principles of voltage and current management to obtain a high current and energy gain. Its design was facilitated by the use of modern modeling tools as well as high precision manufacture. The result was a first-shot success. The AHG delivered 16 MA of current and 11 MJ of energy to a quasistatic 80 nH inductive load. A current gain of 160 times was obtained with a peak exponential rise time of 20 micros. We will describe in detail the design and testing of the AHG.

螺旋型爆磁压缩脉冲发生器电阻及磁通损失的数值计算

螺旋型爆磁压缩脉冲发生器电阻及磁通损失的数值计算

Study on the potential use of helical swirl generators in enhancing the thermal performance of solar air heaters

SYNOPSIS The thermal performance of a solar air heater may be enhanced by means of twisted tapes, inserted inside the fluid flow tubes, which induce swirl flow acting as turbulence promoters. Experiments were carried out to investigate the effect of helical tape inserts of two different twist ratios (23 and 11) on the friction factor and heat transfer coefficient for a flow in a circular tube maintained at uniform heat flux conditions. The data were recorded at low Reynolds numbers, well in the turbulent region, for a wide range, 8.05 × 103 − 1.36 × 104. The results confirm that this system with helical tape inserts could enhance heat transfer by about 1. 15 to 1.7 times compared to that of plain tube. Also, the study shows that higher heat transfer rates were recorded for lower twist ratios.

Application of a neural network based feedwater controller to helical steam generators

In current generation pressurized water reactors (PWRs), the control of steam generator level experiences challenges over the full range of plant operating conditions. These challenges can be particularly troublesome in the low power range where the feedwater is highly subcooled and minor changes in the feed flow may cause oscillations in the SG level, potentially leading to reactor trip. The IRIS reactor concept adds additional challenges to the feedwater control problem as a result of a steam generator design where neither level or steam generator mass inventory can be measured directly. Neural networks have demonstrated capabilities to capture a wide range of dynamic signal transformation and non-linear problems. In this paper a detailed engineering simulation of plant response is used to develop and test neural control methods for the IRIS feedwater control problem. The established neural network mass estimator has demonstrated the capability to predict the steam generator mass under transient conditions, especially at low power levels, which is considered the most challenging region for a full range feed water controller.

Technology Gap Analysis on Sodium-Heated Steam Generators Supporting Advanced Burner Reactor Development

The goals of the Global Nuclear Energy Partnership (GNEP) are to expand the use of nuclear energy to meet increasing global energy demand in an environmentally sustainable manner, to address nuclear waste management issues without making separated plutonium, and to address nonproliferation concerns. The Advanced Burner Reactor (ABR) is a fast reactor concept that supports the GNEP fuel cycle system. Since the Integral Fast Reactor (IFR) and Advanced Liquid Metal Reactor (ALMR) projects were terminated in 1994, there has been no major development on sodium-cooled fast reactors in the United States. Therefore, in support of the GNEP ABR program, the history of sodium-cooled reactor development was reviewed to support the initiation of this technology within the United States and to gain an understanding of the technology gaps that may still remain for sodium fast reactor technology.A sodium-heated steam generator is one of the key components in the fast reactor system since it provides interface between sodium and water. In this gap analysis, information of fabrication and operation experiences in reactor plant steam generators and prototype steam generators was carefully reviewed, for example the Enrico Fermi Atomic Power Plant, the Prototype Fast Reactor (PFR), and Phénix steam generators; the Babcock & Wilcox helical coil tube, 70 MW; the Westinghouse double-wall tube, 70 MW; the Clinch River Breeder Reactor (CRBR) full-scale evaporator; the Superphénix prototype helical coil tube, 45 MW; the SNR-300 prototype straight tube, 50 MW; the SNR-300 prototype helical coil tube, 50 MW; and the Monju prototype helical coil tube, 50 MW. The results of this evaluation indicate that straight and helical coil tube steam generators are the best immediate candidate designs for producing reliable steam generators for future sodium fast reactor applications. Though the design comparison suggested that the straight tube type has the advantages of compactness and ease of inspection, prototype tests revealed more technical problems than the helical modules. From the viewpoint of tube material, 2¼Cr steel has been well established, and Incoloy® 800, 9Cr, and 12Cr steels are available as higher-performance materials.

Influence of the Hall effect on the plasma dynamics in an MTF/MAGO chamber

The role of the Hall effect in experiments on the magnetic implosion of a D-T plasma in a cylindrical MTF/MAGO chamber fed from a helical explosive magnetic generator is investigated. The plasma dynamics is simulated numerically by a 2D code developed for solving the set of MHD equations with account of the Hall effect. In simulations, the generator, the break switch, and other units were replaced with LR circuits. It is shown that taking into account the Hall effect provides better agreement between numerical simulations and experimental data.

A lumped parameter dynamic model of the helical coiled once-through steam generator with movable boundaries

A lumped parameter mathematical model of the helical coiled once-through steam generator of the 10 MW high-temperature gas-cooled reactor (HTR-10) is developed based upon the fundamental conservation of fluid mass, energy, and momentum. The steam generator is handled with single tube concept and is divided into three regions as subcooled region, boiling region, and superheater region. And these regions have movable boundaries to simulate the change of the region lengths. A lot of numerical experiments are investigated using the developed model. The steady-state simulation results agree well with the design data. The transient simulation results show that the model can properly predict the steam generator dynamics.

Modeling of a Small Helical Magnetic Flux-Compression Generator

In order to gain experience in explosive pulsed power and to provide experimental data as the basis for computer modeling, a small high-explosive-driven helical magnetic flux-compression generator (FCG) was designed at the Swedish Defence Research Agency. The generator, of which three have been built, has an overall length of 300 mm and a diameter of 70 mm. It could serve as the energy source in a pulse-forming network to generate high-power pulses for various loads. This paper presents a simulation model of this helical FCG. The model, which was implemented in Matlab-Simulink, uses analytical expressions for the generator inductance. The model of resistive losses takes into account the heating of the conductors and the diffusion of the magnetic field into the conductors. The simulation results are compared with experimental data from two experiments with identical generators but with different seed currents, influencing the resistive losses. The model is used to analyze the performance of the generator.

Experimental validation of the helical steam generator model in the TASS/SMR code

The transients and setpoint simulation/system-integrated modular reactor (TASS/SMR) code has been used to identify the safety margin of a 65-MWt advanced integral reactor and to evaluate its design performance. Although, the code has been verified by using simplified and analytical problems as well as a reliable system code, its validation has not been fully established. This paper deals with a validation of the TASS/SMR code by using two kinds of separate effect tests related to heat transfer at a helically coiled steam generator. The heat transfer experiments were performed by using a full-scale prototype of the steam generator cassette of the advanced integral reactor and a scaled-down steam generator cassette. Analytical results show that the TASS/SMR code predicts the thermal hydraulic parameters, including the system pressure and fluid temperature at the primary and secondary sides of the steam generator cassette, and the heat transfer rate through the steam generator cassette well. The validation results in this study show that the TASS/SMR code is applicable for heat transfer calculations related to the helically coiled steam generator of the advanced integral reactor.

Generation of soft X-ray emission by Z-pinches powered from helical explosive magnetocumulative generators

Results are presented from experiments on the implosion of wire arrays powered from 100-and 200-mm-diameter helical explosive magnetocumulative generators with explosive opening switches. The experiments were performed at load currents of up to 4 MA, the current rise time being 0.3–0.4 μs. The maximum soft X-ray yield of ∼ 100 kJ was achieved at a pinch plasma temperature of 55 eV. A two-dimensional MHD code was developed to simulate the process of liner implosion and the generation of X-ray emission. The results of computer simulations agree satisfactorily with the experimental data.

Heat transfer enhancement in circular tubes using helical swirl generator insert at the entrance

This paper presents an experimental study of heat transfer and friction characteristics in decaying turbulent swirl flow generated by a short helical tape placed at the entrance of the test section. In the experiments, total mass flux was varied from 160 kg m −2 s −1 to 1628 kg m −2 s −1 and the momentum ratio ( M h / M T ) was varied from 0 to 8.6. The experiments were conducted for water flow rates in the range of 5000 ⩽ Re ⩽ 30 000 . Three different helical tapes with helical angels of 30°, 45° and 60° were used. Experimental results confirm that, the use of a helical tape inserted to the tube leads to a higher heat transfer rate than the non-swirling flow. The local heat transfer coefficients were found to be increasing to very high values along the downstream of the helical tape, and then decreasing with the distance ( x / L ). The augmentation of heat transfer was found to be the function of the momentum ratio, M h / M T and Reynolds number. No pronounced effect of the number of the helical channels ( N h ), and helical angle ( α) on heat transfer was observed. It is found that using the helical tape can help to increase the heat transfer rate up to 20% depending on M h / M T and Re at constant pumping power. Enhancement efficiency increases with increasing momentum ratio and decreases with increasing Reynolds number.

Vladimir Konstantinovich Chernyshev

Vladimir Konstantinovich Chernyshev

Helical wave-front laser beam generated with a microelectromechanical systems (MEMS)-based device

We report a novel helical wave-front laser beam generator based on microelectromechanical systems (MEMS) technology. The device consists of a circular array of micromirrors; each can be electrostatically actuated to move perpendicular to the substrate to modulate the phase of an incident laser beam. A prototype device has been developed using the polysilicon multiuser MEMS processes. The ability of the device to transform a plane wave into an l=3 helical wave-front laser beam has been experimentally demonstrated. Additionally, the device is faster by two orders of magnitude or more than conventional liquid crystal spatial light modulators. In combination with a rapid optical beam steering system, the proposed device might provide new capabilities for fast-scanned optical tweezer arrays, allowing them to combine optical vortices and conventional traps together to trap, guide, and rotate a wide variety of particles.

An Electrical-Explosion Opening Switch Powered from a Magnetic-Explosion Generator

The results from experiments with powering an electrical-explosion opening switch (EEOS) from a high-speed helical magnetic explosion generator are presented. The energy capacity of this generator is ∼1 kJ, the total operating time is 25 µs, and the characteristic current rise time is ∼2 µs. In experiments with thin copper wires used in EEOSs, voltage pulses with an amplitude of ∼180 kV and a rise time of ∼50 ns were formed across a 25-Ω resistive load connected in parallel to the EEOS.

Enhancement of heat transfer in a tube with regularly-spaced helical tape swirl generators

Influence of helical tapes inserted in a tube on heat transfer enhancement is studied experimentally. A helical tape is inserted in the tube with a view to generating swirl flow that helps to increase the heat transfer rate of the tube. The flow rate of the tube is considered in a range of Reynolds number between 2300 and 8800. The swirling flow devices consisting of: (1) the full-length helical tape with or without a centered-rod, and (2) the regularly-spaced helical tape, are inserted in the inner tube of a concentric tube heat exchanger. Hot air is passed through the inner tube whereas cold water is flowed in the annulus. The experimental data obtained are compared with those obtained from plain tubes of published data. Experimental results confirmed that the use of helical tapes leads to a higher heat transfer rate over the plain tube. The full-length helical tape with rod provides the highest heat transfer rate about 10% better than that without rod but it increased the pressure drop. To overcome this, different free-spacing ratio ( s = L s/ L h) of 0.5, 1.0, 1.5, and 2.0 were examined. It was found that the space ratio value should be about unity for Re < 4000. The regularly-spaced helical tape inserts at s = 0.5 yields the highest Nusselt number which is about 50% above the plain tube.

Control of spring back for helically coiled steam generator tube

A study has been performed to control the amount of the spring back from tubes of the helical steam generator, which is to be installed in the integral reactor SMART. The analytical calculation was done on the basis of beam theory and elastic-perfectly plastic material property. The analysis model has considered the effect of the plastic hardening and the effect of the tensile force on the spring back phenomena. Apart from the analytical approach, finite element analysis was carried out to investigate methodological comparison and the quantitative evaluation of the spring back. Coiling process was simulated utilizing commercial finite element analysis program ABAQUS. The application of the tensile force has reduced a considerable amount of spring back. However, the application of the tensile force may cause ovality and excessive thickness reduction. From the finite element analysis based on the present design conditions, the range of the axial tensile force to be applied in order to satisfy the required criteria of the spring back phenomena, the ovality, and the thickness reduction has been suggested. As an alternative approach of reducing the amount of spring back, the stress relieving heat treatment was also studied. After the coiling of the tube, the heat treatment was simulated in finite element analysis and the effect of heat treatment on the spring back was confirmed by an experiment.

Studies of a Magnetocumulative Source of Electromagnetic Pulses with a Double Inductive Energy Storage

An energy source based on a helical magnetocumulative generator with simultaneous initiation of an explosive charge on the axis was developed. The generator operates on a double inductive energy storage with current circuit breakers in each storage. The main analytical dependences of the pulse amplitude and shape on the parameters of the double inductive energy storage were obtained. In an experiment with such an energy source, a voltage pulse of 770 – 800 kV was obtained on a breaker made of electrically exploding wires. The voltage at possible load points was 1300 – 1350 kV. The duration of the voltage pulse edge from 0.1Umax to 0.9Umax did not exceed 0.5 μsec.