Magnetism and Temperature Essay

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i n t e r n a t i o n a l j o u r n a l o f r e f r i g e r a t i o n 3 5 ( 2 0 1 2 ) 1 0 4 3 e1 0 5 4

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Assessment of demagnetization phenomena in the performance of an active magnetic regenerator
Paulo V. Trevizoli, Jader R. Barbosa Jr.*, Pablo A. Oliveira, Fa´bio C. Canesin,
Roge´rio T.S. Ferreira
POLO Research Laboratories for Emerging Technologies in Cooling and Thermophysics, Department of Mechanical Engineering,
Federal University of Santa Catarina (UFSC), Floriano´polis, SC 88040900, Brazil

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abstract

Article history:

The primary objective of this paper is to quantify the impact of the internal magnetic field

Received 28 January 2011

and reversibility of the magnetocaloric effect on the numerical evaluation of the thermal

Received in revised form

performance of a parallel-plate active magnetic regenerator. To this end, direct measure-

24 November 2011

ments of the adiabatic temperature change of commercial-grade gadolinium samples were

Accepted 13 February 2012

carried out for an applied field change of 1.65 Æ 0.03 T (for both magnetization and

Available online 21 February 2012

demagnetization) and temperatures between 283 and 303 K. The tests were carried out in a specially constructed apparatus and the results were in good agreement with the liter-

Keywords:

ature. The data were incorporated into a mathematical model for solving the fluid flow and

Regenerator

conjugated heat transfer in the parallel-plate regenerator. It was found that if demagne-

Magnetic refrigerator

tization phenomena (i.e., the demagnetization factor and the reversibility of the magne-

Gadolinium

tocaloric effect) are not take properly into account, the thermal performance of the

Adiabatic magnetization

regenerator can be severely over-predicted.
ª 2012 Elsevier Ltd and IIR. All rights reserved.

Adiabatic demagnetization

Evaluation des phe´nome´nes de de´saimantation sur la performance d’un re´ge´ne´rateur actif magne´tique
Mots cle´s : Re´ge´ne´rateur ; Re´frige´rateur magne´tique ; Gadolinium ; Aimantation adiabatique ; De´saimantation adiabatique

1.

Introduction

The magnetocaloric effect (MCE) is the reversible temperature variation of a magnetic material subjected to a changing magnetic field. Some classes of magnetic materials exhibit a significant MCE at the vicinity of room temperature, which makes them potential candidates for utilization as refrigerants in systems based on active magnetic regeneration cycles

(Tishin and Spichkin, 2003; Gschneidner et al., 2005; Bru¨ck et al., 2008). To date, the most widely examined of such materials is gadolinium (Gd), which has an MCE around
3.5e4 K T for a magnetic field change of 1 T, at its magnetic transition (Curie) temperature (w293 K).
The MCE can be described by the magnetic entropy variation (DSM) or by the adiabatic temperature change (DTad), which can be quantified indirectly from the measurements of

* Corresponding author. Tel./fax: þ55 48 3234 5166.
E-mail address: jrb@polo.ufsc.br (J.R. Barbosa).
0140-7007/$ e see front matter ª 2012 Elsevier Ltd and IIR. All rights reserved. doi:10.1016/j.ijrefrig.2012.02.003 1044

i n t e r n a t i o n a l j o u r n a l o f r e f r i g e r a t i o n 3 5 ( 2 0 1 2 ) 1 0 4 3 e1 0 5 4

TC w Nomenclature
Roman letters
[
Characteristic dimension [mm] f Frequency [Hz]
H
Magnetic field [T]
L
Sample length [mm]
M
Magnetization [emu gÀ1]
_
m
Mass flow rate [kg hÀ1]
Demagnetization factor [-]
ND
t
Sample thickness [mm]
T
Temperature [K]

Sub and
1
2 appl cold demag hot mag res

magnetization and specific heat capacity as a function of temperature (Pecharsky and Gschneidner, 1999; Pecharsky et al., 2001). DTad can also be measured directly by means of temperature detectors, such as thermocouples or infrared thermography (Christensen et al., 2010). By definition, DTad is the difference between the
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