Abstract
The operational rotational speeds of hydroturbines change arbitrarily within a small range, and the friction power consumption caused by the asymmetric curl represents a technical difficulty in magnetofluid sealing. In this study, the pressure-withstanding value and equations for the asymmetric curl of a magnetofluid sealing device under different rotational speeds were deduced. By considering the magnetofluid sealing device characteristics with Halbach magnetic arrays, temperature fields under a static field and low rotational speed were calculated for determining the Halbach magnetofluid sealing device with the best sealing performance. Comparisons and analyses were performed with the friction power consumption and sealing pressure-withstanding value of the selected structure under high (3000 r/min), medium (1500 r/min), and low (300 r/min) rotational speeds and alternating work conditions of ±3, ±6, and ±9. The results indicated that changes in magnetic moment caused by changes in the external magnetic field are the primary cause of friction power consumption. Heat generation occurs concurrently with the friction power consumption. Consequently, the pressure-withstanding value of the magnetofluid sealing is reduced; the friction power consumption of the magnetofluid is directly proportional to the magnetic field strength, rotational speed, and alternating amplitude. Unstable states and asymmetry of the external magnetic field lead to nonlinear increments in the friction power consumption of the magnetofluid. A stable and symmetrical magnetic effect, with a smaller rotational speed and alternating amplitude leads to lower friction power consumption, resulting in a more ideal sealing effect.
Highlights
With the rapid development of the world economy, the population of the world has increased sharply
On the basis of existing magnetofluid sealing theories, the equations for the pressure-withstanding value of the hydroturbine main shaft magnetofluid sealing device and the friction power consumption caused by asymmetric curls were deduced
It has been determined that the external magnetic field and the rotational speed have real impacts on the magnetofluid and the sealing device
Summary
With the rapid development of the world economy, the population of the world has increased sharply. The experimental results were referenced to analyze the relationship between the magnetic field and the friction power consumption to determine the optimal hydroturbine main shaft magnetofluid sealing method. The magnetofluids, which are located between the magnetic poles and main shaft, are affected by the magnetic force; these are ‘‘locked’’ in the sealing clearances, and an ‘‘O’’-shaped sealed loop is formed to prevent the medium from being leaked from the highpressure end to the low-pressure end, achieving the purpose of sealing. In terms of the magnetofluid studied here, the interior of the small-clearance magnetofluid sealing device is uniform after the magnetization of the magnetofluid is stabilized, and the radial dimensions of points A and B are to the center of rotation of the main shaft, so the values of the vertical component of magnetization intensity are equal. The difference in the magnetic induction intensity at the clearance of the magnetofluid sealing and magnetization intensity can be improved to reduce the rotational speed of the main shaft and enhance the pressure resistance of magnetofluid sealing, so as to maximize the sealing effect
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