Magnetic Refrigeration

Currently, refrigeration cycles typically use a fluid as the working substance undergoing a compression and expansion cycle. Efficiencies are limited due to irreversibilities in the compression and heat transfer process. A cycle that has the potential to be an efficient means of producing refrigeration at cryogenic temperatures is the Active Magnetic Regenerative (AMR) cycle. This cycle makes use of solid magnetic refrigerants typically composed of rare earth elements and alloys ordering ferromagnetically. The magnetic materials display a characteristic temperature rise when the magnetic flux density is increased known as the magnetocaloric effect (MCE). Near the ordering temperature, this temperature change can be highly reversible. When used in an AMR cycle the magnetic refrigerant acts as a thermal storage medium (a regenerator) as well as the means of work input.

In our lab two parallel programs are underway, one for cryogenic and the other one for room temperature application. For the low temperature case, the objective is to increase understanding of the AMR cycle and to develop an efficient refrigerator stage operating between 77 K and 20 K. Ultimately, we aim to develop of a compact liquefier for hydrogen. Work is conducted experimentally, using the Active Magnetic Regenerator Test Apparatus (AMRTA), and numerically through AMR modeling. Room temperature testing, so far, has been performed with the same device. A new apparatus, using a novel design (RTPMR) is under development and will be soon used for room temperature refrigeration.