The Thermodynamics of Magnetocaloric Energy Conversion - Magnetocaloric Energy Conversion: From Theory to Applications - page 10

The exergy concept is well known and often applied by engineers in different
domains. The term exergy was suggested by Rant in 1956 [ 50 ]. According to Rant
[ 50 ], energy can be divided into two parts, from which the part that is fully
transformable (available) into other kinds of energy is named the

, and the
part that is not transformable (e.g. the internal energy of the ambient) is called the
“

“ exergy ”

. There have been just a few publications on exergy analyses for mag-
netocaloric energy conversion [ 21 , 51

anergy ”

54 ].

-

ciency of the magnetic refrigerator represents the ratio between
the exergy of the cooling energy and the work (i.e. electric energy, which is pure
exergy).

The exergy ef

E j W ¼ D e R

w

n ¼ ð 1 : 30 Þ

The speci c exergy of the cooling energy can be de ned by the following relation

(see also Eq. ( 1.12 )):

¼ ð Þ ð 1 : 31 Þ

de dh T amb ds

eld (i.e. the Brayton process, where the
temperature T R is not constant), the enthalpy is equal to the heat (exergy of heat),
and therefore:

In the case of a constant magnetic

ð T R T amb Þ

de ¼ ð T R T amb Þ ds ¼ dq ð 1 : 32 Þ

T R

and the integration of the exergy between the states a and b (which, e.g. correspond
to the cooling process) corresponds to:

Z Z dq

b b

T amb
T R

D e R ¼ de ¼ 1 ¼ q R T amb D s R ð 1 : 33 Þ

a a

where the second part of Eq. ( 1.33 ) represents the anergy. The exergy ef ciency can

be de ned as:

q R T amb D s R

n ¼ ð 1 : 34 Þ

q H q R

In the Carnot cycle, the Ericsson cycle or the Stirling cycle, in the case of an
isothermal demagnetization, the speci c exergy of the cooling energy can be

de ned as: