Magnetic minibars

A new material featuring a big temperature jump when subjected to a magnetic field will enable competitive magnetic cooling.

Hotel minibars are probably the first market to adopt magnetic cooling on a large scale. These machines currently use silent but very inefficient thermoelectric Peltier cooling. Replacing those machines by equally silent magnetocaloric fridges would save lots of energy, while adding to the hotel’s green credentials.

Dr Nguyên Thàn Trung, a former PhD student at the faculty of Applied Sciences, has developed a material featuring a ‘giant magnetocaloric effect’. Its temperature rise under the application of a magnetic field is ten times greater than in other materials. Trung’s PhD supervisor, Professor Ekkes Brück, says Trung’s new material is the first of a second generation. An unnamed industrial partner is even considering introducing magnetocaloric fridges, based on Trung’s alloy, on the market next year.

By applying an intermittent magnetic field, the magnetocaloric effect can be used for cooling. Switch the field on, and the magnetocaloric material will heat up. Switch the magnets off, and the temperature will drop, so that the material can absorb heat from its surrounding. A clever cycle results in magnetic refrigeration. However, until now, the effect was too small to compete with the standard compressor-driven fridges (in which expanding gas will absorb heat, and compressed gas will release it).

The magic of the new material, an alloy of manganese, cobalt, and germanium with boron doping, is the synchronisation of two phase transitions: the magnetic phase change plus a structural one. “The material can switch from hexagonal into orthorhombic crystal structure [‘square’, ed.] ones”. Prof. Brück explains. When the material changes from hexagonal to orthorhombic, entropy falls and heat is given off. Normally, this happens at relatively high temperatures, but by inserting boron atoms into the crystal, Trung has succeeded in stabilising the hexagonal form at lower temperatures, and coinciding the structural change with the magnetic phase change, resulting in a giant magnetocaloric effect.

Nguyên Thàn Trung, First-order phase transitions and giant magnetocaloric effect, PhD supervisor Professor Ekkes Brück.

Clash of the Cover Bands is a simple concept. Bands get thirty minutes on stage to play their songs, and then the winners of a professional jury review, and the public’s vote, go to the next round, with the best ones ultimately winning their fifteen minutes of fame by performing in the national semifinals at Amsterdam’s Paradiso concert hall.

Having recently attended a quarterfinal cover band clash, I can report that not all these bands are worth hearing, not every random bunch of guys can produce good music, but it’s always fascinating to see people chasing their dreams and being passionate about something – even if they stink at it. Like the band CargoVibes – no voice, lousy music, zero charisma.
Some of these cover bands dare to step into the shoes of real musical heroes, like ‘Echo Bowie’ for example; although skeptical at first, I was pleasantly surprised when this band loosened up after several songs, and by the time they got to the Space Oddity, they were rocking! Just like the real thing. Well… almost.

And then there are the really good bands. ‘Peen uit Hellevoetsluis’, an 11-member ska band, gives their all on stage, playing, as they say, “the most fun songs from the past forty years of reggae and ska”. Peen won their quarterfinal by a landslide.

Attending Clash of the Cover Bands is a chance to hear plenty of music in one night. The regional quarterfinals are at Rotterdam’s Plan C on Friday nights – November 6, 13 and 20. For just 10 euro, you help determine who’ll be the next ‘Best Cover Band of the Netherlands’. And if you get inspired, you can always register for next year’s competition.

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