Environmental Engineering Reference
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frequency and with smaller heat transfer losses. However, the AMR geometry
(hydraulic diameter) also in
ow. On one
hand, the small hydraulic diameter increases the convective heat transfer, but on the
other hand, it increases the viscous losses and the related pressure drop as well.
Therefore, the AMR geometry should be optimized with respect to both thermo-
hydraulic properties (heat transfer and pressure drop) in order to obtain the best
overall performance [ 17 , 76 ].
Figures 4.20 and 4.21 show the impact of the AMR
fl
uences the viscous losses of the
fl
uid
fl
s geometry for different
packed-bed AMRs with Gd spheres and different parallel-plate AMRs with
'
fl
at Gd
plates for a Brayton-like AMR cycle (with water as the working
fl
uid and 1 T of
magnetic
c cooling power (per
mass of Gd) and the maximum COP obtained for the optimum utilization factor for
each analysed case for two different operating frequencies at 15 K of temperature
span. For details, including the assumptions used for the geometrical analysis
presented in Figs. 4.20 , 4.21 , see Tu
eld change). The
gures show the maximum speci
ลก
ek et al. [ 17 ]. Among other assumptions, the
analysis neglects the
ow maldistribution and assumes a constant porosity in the
AMR as well as demagnetization effects in the material, which in general both
decrease the AMR
fl
'
s performance.
Fig. 4.20 a The maximum
speci c cooling power as a
function of the sphere
diameter for two different
operating frequencies (dotted
lines for 0.5 Hz and full lines
for 3 Hz) and different lengths
of the packed-bed AMR.
b The maximum COP as a
function of the sphere
diameter for two different
operating frequencies (dotted
lines for 0.5 Hz and full lines
for 3 Hz) and different lengths
of the packed-bed AMR
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