Wojciech Lipiński

Tomography-Based Heat and Mass Transfer Characterization of Reticulate Porous Ceramics for High-Temperature Processing

Reticulate porous ceramics employed in high-temperature processes are characterized for heat and mass transfer. The exact 3D digital geometry of their complex porous structure is obtained by computer tomography and used in direct pore-level simulations to numerically calculate their effective transport properties. Two-point correlation functions and mathematical morphology operations are applied for the geometrical characterization that includes the determination of porosity, specific surface area, representative elementary volume edge size, and mean pore size. Finite volume techniques are applied for conductive/convective heat transfer and flow characterization, which includes the determination of the thermal conductivity, interfacial heat transfer coefficient, permeability, Dupuit–Forchheimer coefficient, residence time, tortuosity, and diffusion tensor. Collision-based Monte Carlo method is applied for the radiative heat transfer characterization, which includes the determination of the extinction coefficient and scattering phase function.

Design and experimental investigation of a horizontal rotary reactor for the solar thermal production of lime

We designed and tested a 10-kW solar rotary kiln reactor to effect the calcination reaction: CaCO3 → CaO+CO2. The reactor processes 1–5 mm limestone particles, producing 95% or higher purity lime with a t60 reactivity ranging from 14 s to 38 min. The degree of calcination and the reactivity both depend on the reactant’s decomposition temperature (1323–1423 K), residence time (3–7 min), and feed rate (10–50 g/min). The reactor’s efficiency, defined as the enthalpy of the calcination reaction at a specified temperature divided by the solar energy input, reached 20% for solar flux inputs of about 1200 kW m−2 and for quicklime production rates of about 1.3 kg/h. The solar lime reactor operated reliably for more than 100 h for a total of 24 sunny days, withstanding the thermal shocks that occur in solar applications.

Tomographic Characterization of a Semitransparent-Particle Packed Bed and Determination of its Thermal Radiative Properties

Keywords: computerised tomography ; extinction coefficients ; Monte Carlo methods ; particle size ; porosity ; two-phase flow Reference EPFL-ARTICLE-184803doi:10.1115/1.3109261 Record created on 2013-03-04, modified on 2017-07-28

Heat Transfer Analysis of a Novel Pressurized Air Receiver for Concentrated Solar Power via Combined Cycles

A novel design of a high-temperature pressurized solar air receiver for power generation via combined Brayton-Rankine cycles is proposed. It consists of an annular reticulate porous ceramic (RPC) bounded by two concentric cylinders. The inner cylinder, which serves as the solar absorber, has a cavity-type configuration and a small aperture for the access of concentrated solar radiation. Absorbed heat is transferred by conduction, radiation, and convection to the pressurized air flowing across the RPC. A 2D steady-state energy conservation equation coupling the three modes of heat transfer is formulated and solved by the finite volume technique and by applying the Rosseland diffusion, P1 , and Monte Carlo radiation methods. Key results include the temperature distribution and the thermal efficiency as a function of the geometrical and operational parameters. For a solar concentration ratio of 3000 suns, the outlet air temperature reaches 1000°C at 10 bars, yielding a thermal efficiency of 78%.Copyright

Heat Transfer Analysis of a Solid-Solid Heat Recuperation System for Solar-Driven Nonstoichiometric Redox Cycles

Heat transfer is predicted for a solid-solid heat recuperation system employed in a novel directly-irradiated solar thermochemical reactor realizing a metal oxide based nonstoichiometric redox cycle for production of synthesis gas from water and carbon dioxide. The system is designed for continuous operation with heat recuperation from a rotating hollow cylinder of a porous reactive material to a counter-rotating inert solid cylinder via radiative transfer. A transient heat transfer model coupling conduction, convection, and radiation heat transfer predicts temperatures, rates of heat transfer, and the effectiveness of heat recovery. Heat recovery effectiveness of over 50% is attained within a parametric study of geometric and material parameters corresponding to the design of a two-step solar thermochemical reactor.

Design of a new 45 kWe high-flux solar simulator for high-temperature solar thermal and thermochemical research

In this paper, we present a systematic procedure to design a solar simulator for high-temperature concentrated solar thermal and thermochemical research. The 45 kW e simulator consists of seven identical radiation units of common focus, each comprised of a 6.5 kW e xenon arc lamp close-coupled to a precision reflector in the shape of a truncated ellipsoid. The size and shape of each reflector is optimized by a Monte Carlo ray tracing analysis to achieve multiple design objectives, including high transfer efficiency of radiation from the lamps to the common focal plane and desired flux distribution. Based on the numerical results, the final optimized design will deliver 7.5 kW over a 6 cm diameter circular disk located in the focal plane, with a peak flux approaching 3.7 MW/m 2 .

Multitube Rotary Kiln for the Industrial Solar Production of Lime

We designed and tested a scaleable solar multitube rotary kiln to effect the endothermic calcination reaction CaCO 3 →CaO+CO 2 at above 1300 K. The indirect heating 10-kW reactor prototype processes 1-5 mm limestone particles, producing high purity lime of any desired reactivity and with a degree of calcination exceeding 98%. The reactors efficiency, defined as the enthalpy of the calcination reaction at ambient temperature (3184 kJ kg -1 ) divided by the solar energy input, reached 30%-35% for solar flux inputs of about 2000 kW m -2 and for quicklime production rates up to 4 kg h -1 . The use of concentrated solar energy in place of fossil fuels as the source of process heat has the potential of reducing by 20% CO 2 emissions in a state-of-the-art lime plant and by 40% in a conventional cement plant.

Quantitative Comparison of Photothermal Heat Generation between Gold Nanospheres and Nanorods.

Gold nanoparticles (GNPs) are widely used for biomedical applications due to unique optical properties, established synthesis methods, and biological compatibility. Despite important applications of plasmonic heating in thermal therapy, imaging, and diagnostics, the lack of quantification in heat generation leads to difficulties in comparing the heating capability for new plasmonic nanostructures and predicting the therapeutic and diagnostic outcome. This study quantifies GNP heat generation by experimental measurements and theoretical predictions for gold nanospheres (GNS) and nanorods (GNR). Interestingly, the results show a GNP-type dependent agreement between experiment and theory. The measured heat generation of GNS matches well with theory, while the measured heat generation of GNR is only 30% of that predicted theoretically at peak absorption. This then leads to a surprising finding that the polydispersity, the deviation of nanoparticle size and shape from nominal value, significantly influences GNR heat generation (>70% reduction), while having a limited effect for GNS (<10% change). This work demonstrates that polydispersity is an important metric in quantitatively predicting plasmonic heat generation and provides a validated framework to quantitatively compare the heating capabilities between gold and other plasmonic nanostructures.

Tomography-based analysis of radiative transfer in reacting packed beds undergoing a solid-gas thermochemical transformation

A reacting packed-bed undergoing a high-temperature thermochemical solid-gas trans-formation is considered. The steam- and dry-gasification of carbonaceous materials tosyngas is selected as the model reaction. The exact 3D digital geometrical representationof the packed-bed is obtained by computer tomography and used in direct pore-levelsimulations to characterize its morphological and radiative transport properties as afunction of the reaction extent. Two-point correlation functions and mathematical mor-phology operations are applied to calculate porosities, specific surfaces, particle-sizedistributions, and representative elementary volumes. The collision-based Monte Carlomethod is applied to determine the probability distribution of attenuation path length anddirection of incidence at the solid-fluid boundary, which are linked to the extinctioncoefficient, scattering phase function, and scattering albedo. These effective propertiescan be then incorporated in continuum models of the reacting packed-bed.

Heat Transfer Analysis of a Solid-Solid Heat Recuperation System for Solar-Driven Non-Stoichiometric Redox Cycles

Heat transfer is analyzed numerically for a solid-solid heat recuperation system employed in a novel directly-irradiated solar thermochemical reactor realizing a metal oxide based non-stoichiometric redox cycle for production of synthesis gas from water and carbon dioxide. The system is designed for continuous operation with heat recuperation from a rotating hollow cylinder of a porous reactive material to a counter rotating inert solid cylinder via radiative transfer. A transient heat transfer model coupling conduction, convection, and radiation heat transfer modes is developed to predict temperatures of both components, rates of heat transfer, and the effectiveness of heat recuperation. Heat recovery effectiveness of over 50% is attained within a parametric study of geometric and material parameters corresponding to the design of a two-step solar thermochemical reactor.Copyright