The Thermodynamics of Magnetocaloric Energy Conversion - Magnetocaloric Energy Conversion: From Theory to Applications - page 14

Ericsson, the Carnot, and the magnetic Stirling cycles. All these thermodynamic
cycles, or at least their approximation, can be obtained from the variations in the
magnetic

ow. We will not focus here on the passive regenerative
process, since active regeneration represents a more ef

eld and the fl uid fl

cient solution.

Magnetic Brayton Thermodynamic Cycle

Figure 1.5 shows the magnetic Brayton thermodynamic cycle, which is operated
between two constant magnetic elds and two isentropic (adiabatic) processes of

magnetization and demagnetization. For this particular cycle, the speci c cooling

capacity can be de ned as follows:

Z Z Z

a a a

q R ¼ T ds ¼ c H dT ¼ dh ¼ h a h d ð 1 : 38 Þ

d d d

The speci c work, performed within the cycle equals:

I Z Z Z Z

c a c a

w ¼ dq ¼ T ds þ T ds ¼ c H dT þ c H dT

b d b d

ð 1 : 39 Þ

Z Z

c a

¼ dh þ dh ¼ ð h c h d Þþ ð h a h b Þ

b d

Fig. 1.5 The magnetic Brayton refrigeration cycle in a T s diagram (with gadolinium as the

-

refrigerant)