Thermodynamic Analyses of Fuel Production Via Solar-Driven Ceria-Based Nonstoichiometric Redox Cycling: A Case Study of the Isothermal Membrane Reactor System

A thermodynamic model of an isothermal ceria-based membrane reactor system is developed for fuel production via solar-driven simultaneous reduction and oxidation reactions. Inert sweep gas is applied on the reduction side of the membrane. The model is based on conservation of mass, species, and energy along with the Gibbs criterion. The maximum thermodynamic solar-to-fuel efficiencies are determined by simultaneous multivariable optimization of operational parameters. The effects of gas heat recovery and reactor flow configurations are investigated. The results show that maximum efficiencies of 1.3% (3.2%) and 0.73% (2.0%) are attainable for water splitting (carbon dioxide splitting) under counter- and parallel-flow configurations, respectively, at an operating temperature of 1900 K and 95% gas heat recovery effectiveness. In addition, insights on potential efficiency improvement for the membrane reactor system are further suggested. The efficiencies reported are found to be much lower than those reported in literature. We demonstrate that the thermodynamic models reported elsewhere can violate the Gibbs criterion and, as a result, lead to unrealistically high efficiencies. The present work offers enhanced understanding of the counter-flow membrane reactor and provides more accurate upper efficiency limits for membrane reactor systems. © 2019 by ASME.Australian Research Council (Wojciech Lipiński, Future Fellowship, Award No. FT140101213, Funder ID. 10.13039/501100000923). China Scholarship Council (Sha Li, Grant No. [2015] 3022, 201506020092, Funder ID. 10.13039/501100004543)

Absorption of Short-Pulsed Laser Radiation in Superficial Human Tissues: Transient Vs Quasi-Steady Radiative Transfer

Transient radiative transfer effects are pertinent to thermal treatment of superficial cancer via short-pulsed laser irradiation. The transient effects become particularly important due to relatively strong scattering and long attenuation path of radiation in human tissues in the therapeutic window until the complete absorption. Our analysis is based on transport approximation for scattering phase function and the Monte Carlo method for radiative transfer. One-dimensional radiative transfer problem is considered, which was proved to be applicable for simulation of heat transfer and thermal destruction of tumors in superficial human tissues in the case of indirect heating strategy. A series of Monte Carlo calculations enables us to find the threshold of the steady-state approach applicability. In the biomedical problem under consideration, the steady-state solution for absorbed radiation power is sufficiently accurate at duration of laser pulse more than about 10 ps. The calculations for human tissues with embedded gold nanoshells, which are used to increase the local volumetric absorption of the radiation, showed that overheating of the nanoshells with respect to the ambient biological tissue is strongly dependent of the laser pulse duration. This effect is quantified for short pulses by solving the unsteady radiative transfer problem

Optical Design of Multisource High-Flux Solar Simulators

We present a systematic approach to the design of a set of high-flux solar simulators (HFSSs) for solar thermal, thermochemical, and materials research. The generic simulator concept consists of an array of identical radiation modules arranged in concentric rows. Each module consists of a short-arc lamp coupled to a truncated ellipsoidal specular reflector. The positions of the radiation modules are obtained based on the rim angle, the number of concentric rows, the number of radiation modules in each row, the reflector radius, and a reflector spacing parameter. For a fixed array of radiation modules, the reflector shape is optimized with respect to the source-to-target radiation transfer efficiency. The resulting radiative flux distribution is analyzed on flat and hemispherical target surfaces using the Monte Carlo ray-tracing technique. An example design consists of 18 radiation modules arranged in two concentric rows. On a 60-mm dia. flat target area at the focal plane, the predicted radiative power and flux are 10.6 kW and 3.8 MW m(-2), respectively, and the predicted peak flux is 9.5MW m(-2)

Radiative characterization of random fibrous media with optically large long cylindrical fibers

Radiative heat transfer is analyzed in participating media consisting of long cylindrical fibers with a diameter in the limit of geometrical optics. The absorption and scattering coefficients and the scattering phase function of the medium are determined based on the discrete-level medium geometry and optical properties of individual fibers. The fibers are assumed to be randomly oriented and positioned inside the medium. Two approaches are employed: a volume-averaged two intensities approach referred to as multi-RTE approach as it has been done in several other papers, and a homogenized single intensity approach referred to as the single RTE approach. Both approaches require effective properties determined by utilizing Monte Carlo ray tracing techniques. The macroscopic radiative transfer equations (for single intensity or volume averaged two intensities) with the corresponding effective properties are solved by Monte Carlo techniques and allow for the determination of the radiative flux distribution as well as overall transmittance and reflectance of the medium. The results are compared against predictions by the direct Monte Carlo simulation on the exact morphology. The effects of optical properties of the fiber substance and volume fraction on the effective radiative properties and the overall slab radiative characteristics are investigated. The single RTE approach gives accurate prediction for high porosity fibrous media (porosity about 95%). Advanced radiative transfer models such as the multi-RTE approach are more suitable for isotropic fibrous media with porosity in the range 79−95%

High-flux optical systems for solar thermochemistry

High-flux optical systems (HFOSs) are optical concentrators used to increase the radiative flux of the natural terrestrial solar irradiation. High radiative flux concentration leads to high energy density in solar receivers which allow to obtain high temperatures. In solar thermochemical applications, the high-temperature heat drives endothermic thermochemical reactions. HFOSs have been deployed for research and development of solar thermochemical devices and systems, from solar reacting media to solar reactors. Here, we review the designs and characteristics of HFOSs as well as challenges and opportunities in the area of high-flux optical systems for solar thermochemical applications

Effect of non-stoichiometry on optical, radiative, and thermal characteristics of ceria undergoing reduction

The complex refractive index of ceria has been determined at ambient temperature using variable angle spectroscopic ellipsometry for two chemical states—fully oxidized and partially reduced. The ellipsometric model is corroborated with complementary measurements of thickness, surface roughness, and chemical composition. Partially reduced ceria is shown to have a larger absorption index over a broad spectral range than fully oxidized ceria, including the visible and near IR regions. We use a simple model of a directly irradiated particle entrained in a gas flow to demonstrate the consequences of accounting for changes in chemical state when modeling ceria-based thermochemical process.Australian Research Council (FT140101213)

Experimental and Numerical Characterization of a New 45 kWel Multisource High-Flux Solar Simulator

The performance of a new high-flux solar simulator consisting of 18 × 2.5 kWel radiation modules has been evaluated. Grayscale images of the radiative flux distribution at the focus are acquired for each module individually using a water-cooled Lambertian target plate and a CCD camera. Raw images are corrected for dark current, normalized by the exposure time and calibrated with local absolute heat flux measurements to produce radiative flux maps with 180 µm resolution. The resulting measured peak flux is 1.0–1.5 ± 0.2 MW m−2 per radiation module and 21.7 ± 2 MW m−2 for the sum of all 18 radiation modules. Integrating the flux distribution for all 18 radiation modules over a circular area of 5 cm diameter yields a mean radiative flux of 3.8 MW m−2 and an incident radiative power of 7.5 kW. A Monte Carlo ray-tracing simulation of the simulator is calibrated with the experimental results. The agreement between experimental and numerical results is characterized in terms of a 4.2% difference in peak flux and correlation coefficients of 0.9990 and 0.9995 for the local and mean radial flux profiles, respectively. The best-fit simulation parameters include the lamp efficiency of 39.4% and the mirror surface error of 0.85 mrad

Micronutrient Status of Winter Wheat in Poland

The aim of this study was to investigate the scale of the deficiency of the six basic micronutrients: B, Cu, Fe, Mn, Mo and Zn in the fields of wheat grown in Poland. In the years of 2010 – 2011, 357 samples of winter wheat crops were collected from fields located in the averagely intensive farms in 16 provinces of Poland. Plants were collected in the beginning of stem elongation/first node stage (whole aboveground part), and then the contents of individual micronutrients were determined and evaluated on the basis of critical values developed for cereals by Schnug and Haneklaus. It has been shown that the wheat cultivated in Poland is characterized by low Zn (38% of the samples), and Mn (29%) contents, followed by Cu (21%) and B (18%). Almost no deficiencies of Mo (3%), and only few of Fe (11%) were observed in the collected samples. Regional differences in terms of occurrence of deficiencies of the analyzed elements were also quite significant