Active Magnetic Regeneration - Magnetocaloric Energy Conversion: From Theory to Applications - page 144

Fig. 4.29 The magnetic eld pro les and the corresponding fl uid fl ow periods for the AMR

thermodynamic cycles investigated in the experiment

The ˄ mag = 0.75 s was taken in all the experimental analyses shown in this section.

The s thermodynamic cycle

(information about this period is provided in the text below). In addition to

˄ f was changed for a particular test of the AMR '

˄ mag and
˄ f , the response time of the data acquisition and control elements was, in all the
cases, equal to

˄ 0 = 0.2 s per cycle. The frequency of the operation was therefore

de ned by the duration of the total period. In the case of the Brayton-like AMR

refrigeration cycles this equals to 1/(2 ˄ 0 ). However, in the case of the

Ericsson-like AMR cycle, the frequency of operation was de

˄ mag +2 ˄ f +

ned as 1/(2 ˄ f + ˄ 0 ),

since the ow was performed during all the thermodynamic processes. In the

Hybrid AMR cycle the frequency was de

fl uid fl

˄ f + ˄ mag/2 )+ ˄ 0 ).

ned as 1/(2(

rst tests were performed for no cooling load conditions in order to measure
the maximum possible temperature span for a given AMR thermodynamic cycle.
For this purpose, the utilization factor and the working frequency were varied.
Figure 4.30 shows the ratio between the maximum no-load temperature spans
(obtained at U = optimum, which has been de

The

ned at the maximum temperature

span) and the adiabatic temperature change ʔ T ad for different frequencies (we

denote this as the regeneration factor). As can be seen from Fig. 4.30 , the largest
regeneration factor (6.6 at f = 0.3 Hz and

˄ f = 0.85 s) was obtained with the Hybrid

Fig. 4.30 The experimentally obtained no-load maximum temperature span as a function of the
operating frequency for a parallel-plate gadolinium AMR