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ABSTRACT
The electrocaloric effect in thin films of electrocaloric material has the potential to be used for efficient cooling systems. We numerically calculated the effect of the parameters in electrocaloric refrigeration with multi-layers of electrocaloric material films and thermal switches by changing the contact thermal conductance to improve thermal performance. It was found that the average heat transfer efficiency was 10% and the average heat flux transferred to the cold side of the system was 2.4 × 104 W/m2 for the standard conditions of a frequency of 100 Hz and a temperature difference between the hot side and the cold side of the system of 20 K. The average heat flux transferred to the cold side of the system was maximum when the thickness of the electrocaloric material was 70 µm and thickness of the heat storage material 100 µm. The average heat transfer efficiency was maximum at the two layers of the electrocaloric material.
Nomenclature
| b | = | thickness of film, m |
| ba | = | distance of thermal switch, m |
| be | = | thickness of electrocaloric material, m |
| bf | = | thickness of heat storage material, m |
| Ca | = | thermal conductance of thermal switch, W/m K |
| c | = | specific heat, J/kg K |
| F | = | frequency, Hz |
| N | = | number of layers of electrocaloric material, dimensionless |
| Qb | = | heat transfer rate per unit volume at boundaries, W/m3 |
| Qe | = | generated heat per unit volume due to the electrocaloric effect, W/m3 |
| Qg | = | generating heat energy per unit volume for each change of electric field, J/m3 |
| q | = | heat flux, W/m2 |
| qc | = | heat flux transferred to cold side of system, W/m2 |
| qc-ave | = | average heat flux transferred to cold side of system, W/m2 |
| qe | = | generated heat flux in each layer of electrocaloric material, W/m2 |
| qe-ave | = | average generated heat flux in multi-layers of electrocaloric material, W/m2 |
| qfi | = | heat flux transferred from electrocaloric material to ith heat storage material, W/m2 |
| qf(i+1) | = | heat fluxes transferred to upper (i + 1)th heat storage material, W/m2 |
| qg | = | average heat flux of generated heat energy, W/m2 |
| qh | = | heat flux transferred to hot side of system, W/m2 |
| T | = | temperature, K |
| Tc | = | temperature of cold side of system, K |
| Tei | = | temperature of ith electrocaloric material, K |
| Tfi | = | temperature of ith heat storage material, K |
| Tf(i+1) | = | temperature of upper (i + 1)th heat storage material, K |
| Th | = | temperature of hot side of system, K |
| t | = | time, s |
| tc | = | time constant, s |
| te | = | time interval to generate heat, s |
| z | = | coordinate in direction to cross electrocaloric material film, m |
Greek symbols
| ΔP | = | pressure, Pa |
| ΔT | = | temperature change, K |
| η | = | average heat transfer efficiency, dimensionless |
| λ | = | thermal conductivity, W/m K |
| λa | = | thermal conductivity of air, W/m K |
| ρ | = | density, kg/m3 |
Subscripts
| e | = | electrocaloric material |
| f | = | heat storage material |
Additional information
Notes on contributors
Shigeki Hirasawa
Shigeki Hirasawa received his Ph.D. from Department of Physical Engineering, Tokyo Institute of Technology, Japan. He is working as Professor in Kobe University, Japan. His area of research is thermal engineering and heat transfer in equipment.
Tsuyoshi Kawanami
Tsuyoshi Kawanami received his Ph.D. from Department of Mechanical Engineering, Hokkaido University, Japan. He is working as Associate Professor in Kobe University, Japan. His area of research is thermal engineering, refrigeration and air conditioning.
Katsuaki Shirai
Katsuaki Shirai received his Ph.D. from Faculty of Electrical and Computer Engineering, Dresden University of Technology, Germany. He is working as Assistant Professor in Kobe University, Japan. His area of research is flow measurement and laser diagnostics.