Magnetic refrigeration systems for cryogenic applications

A cryogenic refrigeration system for cooling and liquefying on the order of about 3 kg to about 300 kg per day of hydrogen, the cryogenic refrigeration system comprising a liquid nitrogen first stage, a magnetocaloric refrigeration system as a second stage, a closed-loop heat transfer fluid flow system, and at least four heat exchangers, wherein;

• a liquid nitrogen first stage comprises a liquid nitrogen filled tank wherein hydrogen gas is configured to be cooled to 77K through heat exchange with liquid nitrogen in the liquid nitrogen filled tank prior to entering a first heat exchanger of the at least four heat exchangers;
• and wherein
• the magnetocaloric refrigeration second stage comprises- magnetocaloric beds;
• and wherein
• the at least four heat exchangers are configured to cool the hydrogen gas after the liquid nitrogen first stage by transferring heat from the hydrogen gas to the heat transfer fluid, such that upon exit from a last heat exchanger of the at least four heat exchangers, the hydrogen gas is cooled to below its boiling point so that the hydrogen gas is at least partially condensed into liquid hydrogen;
• and wherein
• the closed-loop heat transfer fluid flow system is configured to circulate a heat transfer fluid comprising helium gas through the liquid nitrogen first stage, the magnetocaloric beds of the magnetocaloric refrigeration second stage, the at least four heat exchangers, and a compressor which transfers the heat transfer fluid into a pressurized tank so that it can be re-circulated in the closed-loop heat transfer system;
• and wherein
• the magnetocaloric beds of the magnetocaloric refrigeration second stage comprise magnetocaloric materials, wherein the magnetocaloric materials comprise:
• (AxB1−x)Si1−y−z(CryMnz)
• wherein A and B are selected from the group consisting of Ce, Nd, or Gd,
• wherein x is in a range of about 0 to about 1,
• wherein y is in arange of about 0.05 to about 0.3,
• wherein z is in a range of about 0 to about 0.3, and wherein 0.05≤y+≤0.3;
• and
• an oscillating permanent magnetic field configured to operating operate at a pre-defined frequency of between about 0.1Hz and about 10Hz, wherein the frequency of oscillation includes magnetizing the magnetocaloric material at a predefined magnetic field ramp-up speed, maintaining the magnetic field on the magnetocaloric beds for a specified holding time, demagnetizing the magnetocaloric material at a predefined ramp-down speed, and maintaining zero magnetic field on the magnetocaloric bed for a specified removed time;
• and wherein
• application of the permanent magnetic field to the magnetocaloric beds is configured to cause the magnetocaloric material to heat up, and removal of the permanent magnetic field from the magnetocaloric beds causes the magnetocaloric material to cool down;
• and wherein
• flow of the heat transfer fluid into and out of the magnetocaloric beds is coupled with the oscillation of the permanent magnetic field so that portions of the helium heat transfer fluid are configured to be cooled below 80K and flowed through the at least four heat exchangers to provide enough cooling at the last heat exchanger of the at least four heat exchangers to cool the hydrogen gas to below the boiling point of hydrogen so that the hydrogen gas is at least partially condensed into liquid hydrogen.

A cryogenic refrigeration system for cooling a medium to temperatures below 80K comprising a dual stage system, a closed-loop heat transfer fluid flow system, and at least one heat exchanger, wherein:

• a first stage of the dual stage system acts to cool from room temperature down to 80K, and a second stage of the dual stage system acts to cool from 80K down to a desired temperature below 80K, and wherein the first stage comprises either a vapor compression refrigeration system, or a liquid nitrogen tank, or a combination thereof;
• and wherein the second stage of the dual stage system comprises a magnetocaloric refrigeration system;
• and wherein
• a heat transfer fluid circulates through the closed-loop heat transfer fluid flow system, wherein the closed-loop heat transfer fluid flow system is configured to the heat transfer fluid using the first stage, then flow the heat transfer fluid through the magnetocaloric refrigeration system where a portion of the heat transfer fluid is cooled and then flowed through the at least one heat exchanger to provide cooling to the medium, and then return the heat transfer fluid to a compressor which is configured to transfer the heat transfer fluid into a pressurized tank so that is can be re-circulated in the closed-loop heat transfer fluid flow system;
• and wherein
• the magnetocaloric refrigeration system comprises at least one magnetocaloric bed and an oscillating permanent magnetic field operating at a pre-defined frequency, wherein a frequency of oscillation includes magnetizing a magnetocaloric material in the at least one magnetocaloric bed at a predefined magnetic field ramp-up speed, maintaining the magnetic field on the at least one magnetocaloric bed for a specified holding time, demagnetizing the at least one magnetocaloric bed at a predefined ramp-down speed, and maintaining zero magnetic field on the at least one magnetocaloric bed for a specified removed time;
• and wherein
• application of the permanent magnetic field to the at least one magnetocaloric bed is configured to cause the magnetocaloric material to heat up, and removal of the permanent magnetic field from the at least one magnetocaloric bed is configured to cause the magnetocaloric material to cool down;
• and wherein
• the flow of the heat transfer fluid into and out of the at least one magnetocaloric bed is coupled with the oscillation of the permanent magnetic field so that a portion of the heat transfer fluid is configured to be cooled to the desired temperature below 80K and flowed through the at least one heat exchanger;
• and wherein
• the at least one heat exchanger is configured to transfer heat from the medium to the heat transfer fluid such that the medium is cooled to the desired temperature below 80K;
• and wherein
• the at least one magnetocaloric bed comprises a magnetocaloric material with a composition of:
• (AxB1−x)Si0.8Cr0.2
• wherein A and B are selected from the group consisting of Ce, Nd, or Gd, and
• wherein x is in a range of about 0 to about 1.