An optimized magnet for magnetic refrigeration

Abstract

A magnet designed for use in a magnetic refrigeration device is presented. The magnet is designed by applying two general schemes for improving a magnet design to a concentric Halbach cylinder magnet design and dimensioning and segmenting this design in an optimum way followed by the construction of the actual magnet. The final design generates a peak value of 1.24 T, an average flux density of 0.9 T in a volume of 2 L using only 7.3 L of magnet, and has an average low flux density of 0.08 T also in a 2 L volume. The working point of all the permanent magnet blocks in the design is very close to the maximum energy density. The final design is characterized in terms of a performance parameter, and it is shown that it is one of the best performing magnet designs published for magnetic refrigeration.

Experimental and numerical results of a high frequency rotating active magnetic refrigerator

“…1) working with a 4-pole static permanent magnet and 24 rotating regenerator beds were carried out at frequencies up to 10 Hz. The permanent magnet has a peak flux magnetic density of 1.24 T in the high field regions and it is close to 0 T in the low field regions (Bjørk et al, 2010). The regenerator beds consist of commercial Gd spheres sieved to diameters between 0.25 to 0.8 mm and packed with a 0.36 porosity.…”

Development and experimental results from a 1 kW prototype AMR

“…The full length of the bore of the magnet is 250 mm, so only a small part of the magnet is presently used. The magnetic field will decrease close to the ends of the bore (Bjørk et al, 2010), but at least 200 mm could be used. Indeed, it is planned to use stacks of graded ceramic magnetocaloric materials of this length in the device.…”

“…1(b). The device concepts have previously been described in Bahl et al 2010. The regenerator consists of 24 separate compartments each operating its own AMR cycle.…”

“…The eight regions of the magnet (four high field and four low field) each cover equal angular ranges of 45°. The magnet has been built as described in Bjørk et al (2010) in order to maximise the field difference between the high and low field regions. A single pump at the hot end of the device pumps the heat transfer fluid unidirectionally around a circuit, first through a heat exchanger connected to a chiller, into regenerators in the low field regions, into the cold end where heater power is applied by an electric heater, into regenerators in the high field regions and back into the pump.…”

Magnetic Properties and Flux Distribution in the LaFeCoSi/FeCoV Hybrid Structure

“…In that case, MCE is much sensitive to operating temperature of MCM, spatial distribution of magnetic field, frequency of refrigeration cycle and other factors [12]. Temperature and frequency are strictly operating parameters while the effective value and spatial distribution of the magnetic field are design * corresponding author; e-mail: gozdur@p.lodz.pl parameters [13,14]. Improved spatial uniformity of the magnetic field in the regenerator's bed may indirectly improve the relative cooling power (RCP) of the magnetocaloric refrigeration cycle [11,12].…”