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# Harvesting Nanoscale Thermal Radiation Using Pyroelectric Materials

[+] Author and Article Information
Jin Fang, Hugo Frederich

Department of Mechanical and Aerospace Engineering, Henri Samueli School of Engineering and Applied Science, University of California, Los Angeles, Los Angeles, CA 90095-1597

Laurent Pilon1

Department of Mechanical and Aerospace Engineering, Henri Samueli School of Engineering and Applied Science, University of California, Los Angeles, Los Angeles, CA 90095-1597pilon@seas.ucla.edu

1

Corresponding author.

J. Heat Transfer 132(9), 092701 (Jun 30, 2010) (10 pages) doi:10.1115/1.4001634 History: Received October 31, 2009; Revised March 24, 2010; Published June 30, 2010; Online June 30, 2010

## Abstract

Pyroelectric energy conversion offers a way to convert waste heat directly into electricity. It makes use of the pyroelectric effect to create a flow of charge to or from the surface of a material as a result of heating or cooling. However, an existing pyroelectric energy converter can only operate at low frequencies due to a relatively small convective heat transfer rate between the pyroelectric materials and the working fluid. On the other hand, energy transfer by thermal radiation between two semi-infinite solids is nearly instantaneous and can be enhanced by several orders of magnitude from the conventional Stefan–Boltzmann law as the gap separating them becomes smaller than Wien’s displacement wavelength. This paper explores a novel way to harvest waste heat by combining pyroelectric energy conversion and nanoscale thermal radiation. A new device was investigated numerically by accurately modeling nanoscale radiative heat transfer between a pyroelectric element and hot and cold plates. Silica absorbing layers on top of every surface were used to further increase the net radiative heat fluxes. Temperature oscillations with time and performances of the pyroelectric converter were predicted at various frequencies. The device using 60/40 porous poly(vinylidene fluoride–trifluoroethylene) achieved a 0.2% efficiency and a $0.84 mW/cm2$ electrical power output for the cold and hot sources at 273 K and 388 K, respectively. Better performances could be achieved with $0.9Pb(Mg1/3Nb2/3)–0.1PbTiO3$ (0.9PMN-PT), namely, an efficiency of 1.3% and a power output of $6.5 mW/cm2$ between the cold and hot sources at 283 K and 383 K, respectively. These results are compared with alternative technologies, and suggestions are made to further improve the device.

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## Figures

Figure 2

Comparison between results obtained in the present study with results reported by Mulet (28) for the heat transfer coefficient between two semi-infinite bodies of SiC at 300 K and 301 K as a function of distance d(λmax≃104 nm)

Figure 3

Temperature oscillation of the PE plate made of 60/40 P(VDF-TrFE) as a function of time oscillating at 1 Hz between cold and hot plates at Tc=273 K and Th=388 K, with and without SiO2 absorbing layers

Figure 4

Temperature oscillation of PE plate made of 60/40 P(VDF-TrFE) with SiO2 absorbing layers as a function of time with Tc=273 K and Th=388 K at frequencies of (a) f=0.6 Hz and (b) f=1.2 Hz

Figure 5

Minimum and maximum temperatures of oscillation as a function of frequency for PE plate made of 60/40 P(VDF-TrFE) film with SiO2 absorbing layers for Tc=273 K and Th=388 K

Figure 1

Schematic of the PE plate as it oscillates between the hot and cold plates, with or without SiO2 absorbing layers (not to scale)

Figure 6

Minimum and maximum temperatures of oscillation as a function of frequency for PE plate made of 0.9PMN-PT thin films with SiO2 absorbing layers for Tc=283 K and Th=383 K

Figure 7

Efficiency ratios η/ηCarnot and η/ηCA as a function of frequency for PE plates made (i) of 60/40 P(VDF-TrFE) for temperature oscillations shown in Fig. 5 and (ii) of 0.9PMN-PT (Tmax−Tmin=10 K) with SiO2 absorbing layers

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