Refrigeration and air conditioning overall consume around 20% of theenergy budget in developed countries.Most conventional air conditioners and refrigerators achieve cooling through a mechanical vapor compression cycle (VCC). These systems suffer low efficiency and there does not appear to be any economically viable avenue to markedly improve the efficiency of these VCC systems. Further, air conditioning is a major contributor to electric utility peak loads, which are also a major factor in poor grid reliability.  A related problem with today’s VCC cooling technology is the adverse environmental impact of the refrigerant gases employed, which contribute about 25% of green house gases.These factors necessitate a search for new approaches to increase the energy efficiency of these cooling technologies which are meanwhile environmentally friendly and low cost. Among various technologies, cooling technologies based on the electrocaloric effect (ECE) hold great potential and promise in realizing these goals.

The electrocaloric effect is the induced change in the entropy and temperature in a dielectric material by an applied voltage.Although ECE has been studied for many decades, the relatively small ECE observed, i.e.,adiabatic temperature change DT<2.5 ^oC, made it unsuitable for practical applications. Recently, it was discovered that in a class of ferroelectric polymers, a giant electrocaloric effect can be achieved. That is, these polymers can exhibit an adiabatic temperature change DT ~ 20 K and isothermal entropy change DS ~ 100 J/kgK at room temperature.^1,2 This talk will review the earlier works in the ECE, present the basic materials considerations and experimental results of ECE in both normal ferroelectric and in the relaxor ferroelectrics. It will be shown that although ECE exhibits a sharp peak around the ferroelectric-paraelectric phase transition, the relaxor ferroelectric polymer displays a nearly flat ECE response over a broad temperature range, which is very attractive for practical cooling device applications.  Besides the materials works, I will also present recent advances in developing practical cooling devices based on the advanced ECE materials. Moreover, the materials with giant ECE create totally new cooling device design paradigms for a broad range of applications.

 

References:

1. Bret Neese, Baojin Chu, Sheng-Guo Lu, Yong Wang, E. Furman, and Q. M. Zhang, Science, 321, 821-823 (2008).

2. S. G. Lu, B. Rozic, Q. M. Zhang, Z. Kutnjak, Xinyu Li, E. Furman, Lee J. Gorny, Minren Lin,B. Malic, M. Kosec, R. Blinc, and R. Pirc. Appl. Phys. Lett.  97, 162904 (2010).