Sun, 16 Jun 2002
The magnetocaloric effect is when a material changes its temperature upon exposure of a magnetic field. This is due to a change in the elecrons spin orientation, somewhat similar to magnetoresistive materials. The material heats up when moved into a magnetic field and gets cold moving it out of the field. What's more intresting is that it does not require any additional force to move it in and out of the magnetic field. This can be used for a highly effcient heatpump, refrigerator or airconditioner whithout the high energy consumption that todays machines needs.
Currently there are several intresting materials that exhibit a gigantic magnetocaloric effect: highly pure gadolinium, and some compounds using gadolinium, silica or germanium (Gd5Si4 or Gd5Si2Ge2). The effect can be as large as 7 Kelvin per Tesla and it works best around the curie temperature of the material (room temperature for gadolinium, the other compounds can be adjusted by the amount of silica).
An experimental setup can look like this:
Small gadolinium spheres (grey) is flushed around in a system by a pump. The magnet (red/blue) heats the gadolinium and the heat is transferred to the fluid medium. The heat is extracted at flow f2 and led to a heatexchanger. The flow f3 is used to preheat the incomimg gadolinium to a useful temperature (sort of bootstrap heating) is reached at f2. The topmost heatexchanger is the intake of cold fluid (seawater or similar).