The Thermodynamics of Magnetocaloric Energy Conversion - Magnetocaloric Energy Conversion: From Theory to Applications - page 15

Now the COP can be de ned as follows:

q R
w

h a h d

COP ¼

jj ¼

ð 1 : 40 Þ

ð

h c

Þþ ð

h a

Þ

j h d h b j

ned using Eq. ( 1.37 ). The maximum
refrigeration capacity of the magnetic Brayton refrigeration cycle is denoted by the
surface 1

Now, the exergy ef ciency can by de

2 (note that points 1 and 2 should correspond to a temperature of
0 K). The speci

a d

- - -

c magnetic work is denoted by the surface a b c d.

- - -

Magnetic Ericsson Thermodynamic Cycle
Figure 1.6 shows the magnetic Ericsson thermodynamic cycle in a T - s diagram.
During this cycle, the processes of magnetization and demagnetization are per-
formed by an isothermal process. This can be provided by the simultaneous fl uid

fl ow (i.e. heat transfer) and demagnetization.

The cooling process and the related speci

c cooling capacity can be de ned as

follows:

T R Z

Z

a a

M
o

l 0 o

q R ¼ ds ¼ T R D s a d ¼ T R dH ð 1 : 41 Þ

T

H

d d

Fig. 1.6 The magnetic Ericsson refrigeration cycle in a T - s diagram (with gadolinium as the
refrigerant)