1. High-frequency Magnetocaloric
Modules with Heat Gates Operating
with Péltier Effect
Peter W. Egolf
University of Applied Sciences of Western Switzerland
Institute of Thermal Sciences and Engineering
HEIG-VD / Hes-so

2. In collaboration with:
Institute of Micro and Nanotechniques
Laurent Gravier
Thibault Francfort
Anne-Gabrielle Pawlowski
Gilles Courret
Mirco Croci

3. Table of content
1) The operation principle of magnetic
refrigeration
2) The frequency problem
3) The thermal switch technology
4) Overall device: An engineer’s estimate
5) Conclusions and outlook

4. 1) The operation principle

5. 2) The frequency problem
A provocative personal statement:
We are not competitive enough with present developments
(feasibility was demonstrated, good efficiency is possible, but
still high cost)! Approaching luxury refrigerator sector!
Demanded:
3-5 x higher magnetocaloric effect of materials
or
3-5 x higher frequency of the machines
(seems to me more realistic!)

6. 2) The frequency problem
1
10
100
1000
10
4
105
0.01 0.1 1
Frequencyf(Hz)
Thickness of structure s (mm)
Heat diffusion in and
out of solid structure!
Density:
ρ=7900 kg m-3
,
Thermal conductivity:
k=10.5 W m-1
K-1
,
Heat capacity:
cH= 886 J kg-1
K-1
,
Thermal diffusivity:
a= 1.5 10-6
m2
s-1
.
Example:
s=0.25 mm
f =100 Hzmax

7. 2) The frequency problem
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1
L=25 mm
L=50 mm
L=100 mm
L=200 mm
Maximalfrequencyf(Hz)
Velocity v (m/s)
Safety factor: 10
L=25 mm
L=50 mm
L=100 mm
L=200 mm
Safety factor: 10
Carry-over leakage
Example:
L=25 mm
v=0.25 m/s
Result:
f ≤ 1 Hz

8. 3) The thermal switch technology
Advantage: Constant fluid flows with alternating cold/heat
inputs (no carry over leckage, no fluid switches)
Magnetic
field
No
field
Gate closed
A. Kitanovski and P.W. Egolf, Int. J. Refr. 33 (3), 449-464:

9. 3) The thermal switch technology
Kitanovski and Egolf, Int. J. Refr. 33 (3), 449-464:
The basic plates:

10. 3) The thermal switch technology
Three main elements:
1) Magnetocaloric layered bed
2)Thermoelectric switches
3) Micro channel heat exchangers
Overall system and its performance
1
32

11. 3) The thermal switch technology
Characteristic diameter of the
Ni wires is 200 nm
SME: Dr. Anne-Gabrielle Paw-
lowski, MNT
Nanowires:

12. 3) The thermal switch technology
Thermal switches and experimental device:

13. 0
20
40
60
80
100
0 10 20
Θ = 0
Θ = 10
Θ = 20
Θ = 30
Θ = 40
Θ = 50
COP
Θ2
1
1
1
1
1
1
2
1
1
2
Θ+
Θ−
= CarnotCOP
COP
Entire theory outlined
in Thermag V paper.
Main result:
( )chT
R
TT
RI
P
P
−
==Θ
α
2
thT
I
IRP
Q
α
1
1 ==Θ

( )ch TT
A
Z
−ΘΘ
=
21
1
Z: Figure of merit
Coefficient of performance of a thermal switch:
3) The thermal switch technology

14. 4) Overall device: An engineer’s estimate
Thermal switches (3 layers):
20 Surface area of thermal switches A --- 800 cm2
21 Temperature difference Th-Tc --- 2 x 2.5 K
22 Thermal resistance, Eq. (7d), Table 2 Rth --- ∞ +++
23 Carnot coefficient of perf. (13a,b) COPCarnot --- 216…254
24 Power thermoelectric effect, Eq. (3a) PT --- 10 mW
25 Power electric loss, Eq. (3b) PR --- 122 mW
26 Total power of source, Eq. (3c) PS --- 132 mW
27 Heat flux, Eq. (10c) --- 0 +++
28 First non-dim. variable, Eq. (11a,b) Q1 --- 0 +++
29 Sec. non-dim. variable, Eq. (11c,d) Q2 --- 12
30 Coeff. of perf. (Eq.(13c)) COP --- 17-20 +++
IQ

15. 4) Overall device: An engineer’s estimate
No. Quantity Symbol ULMR
(usual type)
TSMR
(thermal switch)
Overall machine:
1 Nominal cooling power Pn 50 W* 50 W
2 Max. cooling power Pmax 96 W 96 W
3 Magnetic field strength (ind.) H 2 T* 2 T
4 Frequency f 2 Hz* 10 Hz
5 Heat source temperature Tc -5 °C* -5 °C
6 Heat sink temperature Th 45 °C* 45 °C
7 Adiabatic temp. diff. ∆Tad
5 K* 5 K
8 Temp. Diff. Mat.-Fluid ∆T 1 K* 2.5 K
9 Coeff. of perf. Carnot COPCarnot 5.4* 5.4
10 Coefficient of performance COP 2.8* 2.8
11 Exergy efficiency ξ 52 %* 52 %
12 Number of layers (layered bed) N 10 10
13 Specific cooling power pc 2.5 kW kg-1
** 15 kW kg-1
**
14 Mass of magnetoc. mat. mmagneto 384 g 64 g
15 Volume of magnetoc. material V 49 cm3
8 cm3
16 Thickness of plates (FIG. 1) s ≈ 0.2 mm* 0.2 mm
17 Surface area heat exchange A 4900 cm2
400 cm2
18 Demanded heat transf. coeff. h 392 W m2
K 1920 W m2
K
19 Estimate of magnets mass mmag 18 kg* 4-6 kg
(*) Kitanovski et al. (2008a), (**) Kitanovski and Egolf (2008b) based on pure gadolinium.

16. 5) Conclusions and outlook
1) First nanowire thermal switches have been success-
fully produced following secret recipes (patent)
2) A substiantial Péltier effect was experimentally deter-
mined
3) The electric resistance can be further decreased
4) The thermal resistance has not yet been successfully
determined
5) Thermal switches are high-frequency devices
6) A physical model for the thermal switches has been
developed (see Thermag V proceedings)
7) The energy demand of the switches is of small influence

17. 5) Conclusions and outlook
1)If this technology works, it will be possible to beat
conventional refrigeration in numerous important
refrigeration markets
2)This technology is so promising that even automobile
refrigeration, where a high mass is very critical, could
become feasible!

18. Final slide
Thank you for your attention!
FINISH