Further Studies of a Low-Melting Point Alloy Used in a Liquid Metal Current Collector

Maribo, D.; Sondergaard, Neal A.

doi:10.1109/tchmt.1987.1134745

Cited by 9 publications

(6 citation statements)

References 1 publication

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“…The last critical issue is the viscous power losses associated with the turbulent drag acting on the outer sliding contacts at high shear rates. These losses can be estimated as Q = Sτ v ≈ 7 kW, where S ≈ 2πdR o the area of the outer sliding contact, τ = c 4 ρv 2 2 is the turbulent shear stress, and c ≈ 0.02 is the Darcy friction factor for turbulent pipe flow with the Reynolds number Re ∼ 10 5 [14].…”

Section: Feasible Setupmentioning

confidence: 99%

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Feasible homopolar dynamo with sliding liquid-metal contacts

Priede¹,

Avalos-Zuniga²

2013

Physics Letters A

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We present a feasible homopolar dynamo design consisting of a flat, multi-arm spiral coil, which is placed above a fast-spinning metal ring and connected to the latter by sliding liquid-metal electrical contacts. Using a simple, analytically solvable axisymmetric model, we determine the optimal design of such a setup. For small contact resistance, the lowest magnetic Reynolds number, Rm ≈ 34.6, at which the dynamo can work, is attained at the optimal ratio of the outer and inner radii of the rings R i /R o ≈ 0.36 and the spiral pitch angle 54.7• . In a setup of two copper rings with the thickness of 3 cm, R i = 10 cm and R o = 30 cm, self-excitation of the magnetic field is expected at a critical rotation frequency around 10 Hz.

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Section: Feasible Setupmentioning

confidence: 99%

“…2 is the turbulent shear stress, and c ≈ 0.02 is the Darcy friction factor for turbulent pipe flow with the Reynolds number Re ∼ 10 5 [14].…”

Section: Feasible Setupmentioning

confidence: 99%

Feasible homopolar dynamo with sliding liquid-metal contacts

Priede¹,

Avalos-Zuniga²

2013

Physics Letters A

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“…where the second term is analogous to a friction force but with negative coefficient When this negative friction outweighs the electromagnetic damping with the coefficient (12), stationary dynamo state becomes unstable giving rise to periodic oscillations as in the original Bullard dynamo model. This instability is illustrated in Fig.…”

Section: Extended Disc Dynamo Modelmentioning

confidence: 99%

“…We overcome this problem by using sliding liquid-metal electrical contacts which are similar to those employed previously in the homopolar motors and generators [11,12,13] as well as in the laboratory model of Herzenberg dynamo [14] built by Lowes and Wilkinson [15,16]. The set-up consists of a coil made of a stationary copper disc which is divided in spiral-shaped sections by thin slits [17].…”

Section: Introductionmentioning

confidence: 99%

Realization of Bullard's disc dynamo

Avalos-Zuniga¹,

Priede²

2022

Preprint

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We report experimental results from three successful runs of a Bullard-type homopolar disc dynamo. The set-up consisted of a copper disc with a radius of 30 cm and thickness of 3 cm which was placed co-axially beneath a flat, multi-arm spiral coil of the same size and connected to it electrically at the centre and along the circumference by sliding liquid-metal contacts. The magnetic field was measured using Hall probes which were fixed on the top face of the coil. We measured also the radial voltage drop across the coil. When the disc rotation rate reached Ω ≈ 7 Hz, the magnetic field increased steeply approaching B 0 ≈ 40 mT in the central part of the coil. This field was more than two orders of magnitude stronger than the background magnetic field. In the first two runs, the electromagnetic torque braking the disc in the dynamo regime exceeded the breakdown torque of the electric motor driving the disc. As a result, the motor stalled and the dynamo was interrupted. Stalling did not occur in the third run when the driving frequency was set higher and increased faster. We also propose an extended disc dynamo model which qualitatively reproduces the experimental results.

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“…This results in unrealistically high rotation rates which are required for dynamo to operate. To overcome this problem Priede et al [5] proposed a theoretical design of homopolar disc dynamo which uses liquid-metal sliding electrical contacts similar to those employed in homopolar motors and generators [6,7]. The design consists of a flat multi-arm spiral coil placed above a fast-spinning copper disc and connected to the latter by sliding liquid-metal electrical contacts.…”

Section: Introductionmentioning

confidence: 99%

A homopolar disc dynamo experiment with liquid metal contacts

Avalos-Zuniga¹,

Priede²,

E.³

2017

MHD

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We present experimental results of a homopolar disc dynamo constructed at CICATA-Querétaro in Mexico. The device consists of a flat, multi-arm spiral coil which is placed above a fast-spinning metal disc and connected to the latter by sliding liquid-metal electrical contacts. Theoretically, self-excitation of the magnetic field is expected at the critical magnetic Reynolds number Rm ≈ 45, which corresponds to a critical rotation rate of about 10 Hz. We measured the magnetic field above the disc and the voltage drop on the coil for the rotation rate up to 14 Hz, at which the liquid metal started to leak from the outer sliding contact. Instead of the steady magnetic field predicted by the theory we detected a strongly fluctuating magnetic field with a strength comparable to that of Earth's magnetic field which was accompanied by similar voltage fluctuations in the coil. These fluctuations seem to be caused by the intermittent electrical contact through the liquid metal. The experimental results suggest that the dynamo with the actual electrical resistance of liquid metal contacts could be excited at the rotation rate of around 21 Hz provided that the leakage of liquid metal is prevented.

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Further Studies of a Low-Melting Point Alloy Used in a Liquid Metal Current Collector

Cited by 9 publications

References 1 publication

Feasible homopolar dynamo with sliding liquid-metal contacts

Feasible homopolar dynamo with sliding liquid-metal contacts

Realization of Bullard's disc dynamo

A homopolar disc dynamo experiment with liquid metal contacts

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