Razmig Kandilian

The pyroelectric energy harvesting capabilities of PMN–PT near the morphotropic phase boundary

This paper reports on direct thermal to electrical energy conversion by performing the Olsen cycle on pyroelectric materials. The energy harvesting capability of commercially available [001] oriented 68PbMg1/3Nb2/3O3?32PbTiO3 (PMN?32PT) single crystal capacitors was measured experimentally. An energy density of 100? mJ?cm?3/cycle, corresponding to 4.92?mW?cm?3, was obtained by successively dipping the material in oil baths at temperatures 80 and 170??C and cycling the electric field between 2 and 9? kV?cm?1. Similarly, an energy density of 55?mJ?cm?3/cycle was obtained between 80 and 140??C. An estimated 40% of this energy resulted from the strain polarization due to the rhombohedral to tetragonal phase transition. The strain from this transition disappeared when the maximum operating temperature exceeded the Curie temperature of about 150??C. The optimal low electric field used in the Olsen cycle maximizing the energy harvested was found to be around 2?kV?cm?1. In addition, the material suffered from (i)?dielectric breakdown for electric fields larger than 9? kV?cm?1 and (ii)?cracking from thermal stress for operating temperature differences in excess of 90??C. A physical model predicting the total amount of energy harvested was also derived, accounting for thermal expansion as well as temperature dependent dielectric constant and spontaneous polarization. The model predictions fell within 20% of the experimental results in the temperature range between 80 and 170??C and electric fields ranging from 2 to 9?kV?cm?1.

Radiation and optical properties of Nannochloropsis oculata grown under different irradiances and spectra

This paper reports accurate measurements of the radiation characteristics and optical properties of Nannochloropsis oculata in the photosynthetically active radiation (PAR) region. These marine microalgae were grown in 2 cm thick culture bottles with vented caps exposed, on one side, to either white fluorescent light bulbs or red LEDs emitting at 630 nm. The illuminance varied from 2000 to 10,000 lux. The microalgae average equivalent diameter ranged from 2.52 to 2.63 μm. Their radiation characteristics and optical properties were statistically identical over most of the PAR region. Other N. oculata grown with 2 vol.% CO2 injection in 1cm thick flat bottles exposed to light from both sides reached a significantly larger mass concentration and featured lower pigment concentration and smaller absorption cross-sections. This was due to nutrient limited growth conditions. The refraction index was independent of illuminance, spectrum, and growth conditions and featured resonance at wavelengths corresponding to absorption peaks.

Waste heat energy harvesting using the Olsen cycle on 0:945Pb.Zn 1=3 Nb 2=3 /O 3 - 0:055PbTiO 3 single crystals

This paper reports on direct thermal to electrical energy conversion by performing the Olsen (or Ericsson) cycle on [001]-poled 0:945PbZn1=3Nb2=3O3‐0:055PbTiO3 (PZN-5.5PT) single crystals. The cycle consists of two isothermal and two constant electric field processes. The energy density was found to decrease with increasing cycle frequency while the power density increased. The maximum energy density obtained was 150 J=l=cycle for temperatures between 100 and 190 C and electric field between 0 and 1:2 MV m 1 at frequency 0.034 Hz. The maximum power density reached 11:7 W l 1 at 0.1 Hz for temperatures between 100 and 190 C and electric fields between 0.2 and 1:5 MV m 1 . Moreover, the dielectric constant and saturation polarization of PZN-5.5PT are reported for the first time at 0.1 Hz for temperatures between 100 and 190 C. Finally, the experimental results agree relatively well with predictions by a recently developed temperature-dependent property model already validated with PMN-32PT. Inter-sample variability and sample durability are also discussed. (Some figures may appear in colour only in the online journal)

Influence of light absorption rate by Nannochloropsis oculata on triglyceride production during nitrogen starvation.

This study aims to understand the role of light transfer in triglyceride fatty-acid (TG-FA) cell content and productivity from microalgae during nitrogen starvation. Large amounts of TG-FA can be produced via nitrogen starvation of microalgae in photobioreactors exposed to intense light. First, spectral absorption and scattering cross-sections of N. oculata were measured at different times during nitrogen starvation. They were used to relate the mean volumetric rate of energy absorption (MVREA) per unit mass of microalgae to the TG-FA productivity and cell content. TG-FA productivity correlated with the MVREA and reached a maximum for MVREA of 13 μmol hν/gs. This indicated that TG-FA synthesis was limited by the photon absorption rate in the PBR. A minimum MVREA of 13 μmol hν/gs was also necessary at the onset of nitrogen starvation to trigger large accumulation of TG-FA in cells. These results will be instrumental in defining protocols for TG-FA production in scaled-up photobioreactors.

Screening of freshwater and seawater microalgae strains in fully controlled photobioreactors for biodiesel production.

Strain selection is one of the primary hurdles facing cost-effective microalgal biodiesel production. Indeed, the strain used affects both upstream and downstream biodiesel production processes. This study presents a screening procedure that considers the most significant criteria in microalgal biodiesel production including TAG production and wet extraction and recovery of TAGs. Fourteen freshwater and seawater strains were investigated. Large variation was observed between the strains in all the screening criteria. The overall screening procedure ultimately led to the identification of Parachlorella kessleri UTEX2229 and Nannochloropsis gaditana CCMP527 as the best freshwater and seawater strains, respectively. They featured the largest areal TAG productivity equal to 2.7×10(-3) and 2.3×10(-3)kgm(-2)d(-1), respectively. These two strains also displayed encouraging cell fragility in a high pressure bead milling process with 69% and 98% cell disruption at 1750bar making them remarkable strains for TAG extraction in wet environment.