Experimental and Simulation Study on Fast Cooling Method of Pulsed Magnetic Coil Based on Heat Pipe

The repeated discharge frequency is one of the important factors affecting the industrial application of pulsed magnets. In order to increase the repeated discharge frequency of pulsed magnets, a rapid cooling method based on heat pipes was proposed. By placing heat pipes between the layers of magnets, the influence of reinforcing materials with very low thermal conductivity can be overcome and the heat dissipation efficiency of magnets can be improved. An experimental model of heat pipe is established in this article. On this test bench, the heat dissipation performance of heat pipe was verified firstly. Besides, the influence of different flattening thickness, flattening length and heat load on the performance of heat pipe was investigated. The experimental results show that when the input power of a single heat pipe is 40 W, the heat source temperature can be stabilized below 65°C. Surface insulation of conductor will weaken the heat dissipation effect, but in a certain range, the heat pipe can still effectively control the temperature of the heat source. The smaller the flattening thickness and the longer the flattening length, the worse the thermal conductivity of the heat pipe. The thermal conductivity of heat pipe increases first and then decreases with the increasing input power, that is to say, the heat pipe has an optimal working power range. In this article, a rapid cooling scheme based on heat pipes was designed for 3 T saddle-shaped pulsed magnets and numerical simulation was carried out. The simulation results show that the repeated discharge frequency can reach four times per minute, which shows the effectiveness and high efficiency of heat pipes for heat dissipation of pulsed magnets.

I. Introduction

As a special-shaped magnet, saddle-shaped pulse magnet is often used to magnetize the rotor of bipolar permanent magnet motor after assembly, due to its high coupling degree of magnetic field energy [1], [2]. The structure of saddle-shaped magnet is shown in Fig. 1(a). Pulsed magnets can release hundreds of kJ of heat in tens of ms discharge time, so in order to meet the industrial application of pulsed magnets in the field of post-assembly magnetization, it is necessary to design the magnet for heat dissipation [3], [4]. Fig. 1(b) shows a 3 T saddle-shaped pulse magnet with conventional water jacket cooling method, which is cooled by wrapping a water-flowing cooling shell around the magnet. The parameters of the magnet are shown in Table I. However, the heat dissipation effect of this method is not satisfactory, and the magnet temperature still does not drop to room temperature after 5 min for single discharge. This is due to the poor thermal conductivity of the insulation reinforcing material between the layers of coils, which makes it difficult for inner heat of magnet to diffuse outwards [5], [6]. Therefore, the inner heat of magnet needs to be effectively exported to improve the heat dissipation effect. Fig. 1.

Structure diagram of saddle coil. (a) The three-dimensional structure and application scenario of the coil. (b) Traditional cooling water jacket method diagram.

TABLE I Discharge Parameters of Pulsed Magnet

Parameter	Value	Parameter	Value
Energy (kJ)	104	Peak current (kA)	10.2
Pulse duration (ms)	30	Useful volume (m3)	7.85×10-3
Minimum Magnetic field (T)	3.06	Design rep rate (min-1)	>1
Resistance (mΩ)	143.67	Inductance (mH)	4.6485
Temperature rise of a single discharge (°C)	12