The Thermodynamics of Magnetocaloric Energy Conversion - Magnetocaloric Energy Conversion: From Theory to Applications - page 17

Fig. 1.7 The magnetic Carnot refrigeration cycle in a T - s diagram (with gadolinium as the
refrigerant)

T R Z T R Z

a a

M
o

l 0 o q R ¼ ds ¼ T R D s a d ¼ dH ð 1 : 46 Þ

T

H

d d

The speci c work can be de ned with the following relation:

I

w ¼ dq ¼ T R D s a d þ T H D s c b ð 1 : 47 Þ

where s a − d = s c − b. Therefore, the COP can be de ned as:

Δ −Δ

q R
w

T R
T H

COP ¼

jj ¼

ð 1 : 48 Þ

T R

Magnetic Stirling Thermodynamic Cycle
Such a cycle (Fig. 1.8 ) is very dif cult to operate in real situations. It is necessary to

keep the iso-magnetization and iso-demagnetization processes (constant magneti-
zation), which require a particular magnetic eld variation with a simultaneous fl uid

fl ow. The speci c cooling power for this cycle can be de ned as:

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 : 49 Þ

T

H

d d