Alternative Caloric Energy Conversions - Magnetocaloric Energy Conversion: From Theory to Applications - page 432

Z

p 2

s
o p

o

s ist ¼

ð 10 : 17 Þ

D dp

T

p 1

where p is the pressure. Furthermore, the partial derivate of the entropy with respect
to the pressure can be expressed using the Maxwell relation ð o s = o p Þ T ¼ o ð V = o T Þ p

and the isothermal entropy change can be expressed as [ 83 ]:

Z

p 2

V
o T

o

s ist ¼ dp ð 10 : 18 Þ

D

p

p 1

Moreover, the adiabatic temperature change can be expresses as:

Z

p 2

T
c p

o V

o T

T ad ¼ dp ð 10 : 19 Þ

D

p

p 1

where c p is the speci c heat at constant pressure. However, the volume changes of

barocaloric materials are very small and it is dif cult to measure them accurately

[ 82 ]. Therefore, information about the adiabatic temperature change and the iso-
thermal entropy change of the material calculated on the basis of Eqs. ( 10.18 ) and
( 10.19 ) would not be reliable [ 82 ]. Instead, direct measurement techniques, for
example, the calorimetric technique, are used to measure barocaloric effects [ 82 ]. In
Table 10.12 , some barocaloric materials with their properties are presented. The
maximum speci

ned with Eq. ( 10.10 ). It is clear
from Table 10.12 that some barocaloric materials, for example, NiMnIn [ 89 ], have
good cooling properties at room temperature. NiMnIn possesses its maximum
speci

c cooling capacity (q r,max )isde

lm ceramics presented in
Sect. 10.1.2 . However, to the best of our knowledge, no energy conversion device
based on the barocaloric effect has been presented so far. It was only Oliveira et al.
[ 90 ] who in their paper discussed a possible concept of a barocaloric cooling

c cooling capacity in the range of bulk and thick-

Table 10.12 Barocaloric properties of some materials
Material

a
(K)

Δ T ad

(K)

Δ s is

(Jkg − 1 K − 1 )

T ref p

(GPa)

q r,max
(Jkg − 1 )

Measurement
procedure

References

Pr 0.66 La 0.34 NiO 3 0.1 / 350 0.5 / Direct [ 84 ]

HoAs 0.35 / 7 0.3 / Direct [ 85 ]

CeSb 2 / 21 0.52 / Direct [ 86 ]

Ce 3 Pd 20 Ge 6 0.75 / 4.4 0.3 / Direct [ 87 ]

EuNi 2 (Si 0.15 Ge 0.85 ) 2 0.4 37 60 0.34 2,213 Direct [ 88 ]

NiMnIn 4.5 24.4 273 0.26 6,606 Direct [ 89 ]

a