José William Restrepo

High direct normal irradiation and a large residual stream from oil-palm processing make the Colombian Caribbean an attractive site for firm renewable power, yet the balance between thermal energy storage (TES) and biomass backup for supercritical CO₂ (sCO₂) plants in tropical climates remains unresolved. This work evaluates a 120 MWe solar tower plant based on a re-heated recompression sCO₂ Brayton cycle bottomed by a dual-pressure organic Rankine cycle (DORC) and hybridized with palm biomass. A Python 3.12/CoolProp 8.0 design model supplies temperature-dependent performance maps to an 8760 h quasi-steady dispatch layer with dry-cooling ambient coupling and part-load derating. Solar multiple, storage capacity, biomass capacity fraction and turbine inlet temperature are sized simultaneously with NSGA-II against levelized cost of electricity (LCOE) and capacity factor (CF), subject to a regional feedstock availability of 210 kt/yr, and the selected design is propagated through Monte Carlo simulation and Sobol analysis; biomass heat supplies 36–43% of the delivered electricity across the selected designs. The combined cycle attains 51.25% thermal efficiency at the 720 °C salt limit, while the cost-optimal designs deliver 47.9–49.6% at the turbine inlet temperatures selected, of which the bottoming cycle contributes 2.13 percentage points. The feedstock constraint is active along the Pareto front except at its fully firm corner: optimal designs saturate the biomass budget and reach firmness with solar multiples of 2.9–3.5 and 7–10 h of storage. Capacity factor rises from 0.888 to 0.998 for an LCOE penalty of 2.6% (108.5 to 111.3 USD/MWh), while the levelized cost spans P50 = 107 to P90 = 122 USD/MWh and the discount rate alone accounts for 78% of its variance. Near-baseload operation is therefore inexpensive for this class of plant, and financing terms rather than component costs govern its economic risk.

Renewable energy sources, such as solar and biomass, represent sustainable alternatives to meet the growing energy demands of the residential sector. This study evaluated the energy, exergy, and environmental performance of two Brayton configurations using supercritical carbon dioxide: a recompression cycle (SRC) and a recompression cycle with intercooling in the main compression (SMC), both coupled to a dual-loop organic Rankine cycle (DORC) and powered by a hybrid solar-biomass thermal system. Mass, energy, and exergy balances were developed, and a life cycle assessment was performed to quantify the environmental impact. The systems were designed to cover a cooling load of 130 kW corresponding to 200 dwellings constructed with Asbestos cement in the Colombian Caribbean region. The results show that both configurations meet the required demand; the SMC-DORC cycle operates at 650 °C, while the SRC-DORC requires 750 °C. The SRC-DORC exhibits higher thermal efficiency (53.24%), while the SMC-DORC achieves a slightly higher exergy efficiency (28.15%). Environmental analysis shows that the construction phase accounts for the majority of the total impact, exceeding 95% of emissions. Overall, both configurations are technically feasible, with the SRC-DORC standing out for its balance between efficiency and environmental impact.

Cellular structures, formed by periodic two- or three-dimensional cells, offer weight reduction without compromising mechanical performance and are commonly fabricated via additive manufacturing. This study investigates the compressive behaviour of three polymer lattice structures—gyroid, diamond, and octet truss—fabricated by fused filament fabrication (FFF). A Box–Behnken experimental design was used to systematically evaluate the influence of three key parameters: cell size, strut/wall thickness, and layer thickness. A total of 225 samples were produced using PLA and subjected to compression testing in accordance with ASTM D1621. Linear regression and response surface methodology were employed to determine the statistical significance and impact of each factor. The results indicate that cell size has the strongest influence on both maximum force and displacement, followed by strut/wall thickness and layer thickness. Among the configurations, gyroid structures had the highest strength-to-density ratio, while diamond structures had the highest deformation capacity. These findings provide design insights for optimising lattice structures in lightweight applications and highlight the importance of carefully balancing geometric and printing parameters in FFF-based polymer components.

In the context of the circular economy and the adoption of one of its business models, namely ”resource recovery”, this study presents an opportunity to valorize industrial and urban wastes using alkaline activation technology to produce hybrid binders. Several alkali-activated binders were produced using response surface methodology based on a mixture of 45/45/10 clay brick waste, fly ash, and Portland cement. The compressive strength and setting time of each were evaluated. The hybrid cementitious pastes achieved up to 45 MPa after 28 days of setting. Based on the experimental data, two binders were selected as the cementitious matrix for composites, with paper sludge as the lightweight aggregate. Incorporating up to 45% volume of paper sludge allowed extrusion of the materials. The addition of paper sludge reduced the compressive and flexural strength. These results were explained by the decrease in density and the increase in porosity. However, there was an improvement in the thermal properties of the composites; in particular, the thermal conductivity range between 0.35 and 0.49 W/mK. Finally, it was found that the composites with 25% volume of paper sludge had the best combination of properties, positioning them as potential construction materials.

The results presented in this paper belong to the mechanical characterization of vegetal woven fabric reinforced composites with polyester resin as the matrix and fabrics made of cotton, jute and flax fibers. Test specimens were manufactured using a simple hand lay-up molding process. A group of test specimens was reinforced with the woven fabrics as delivered by the supplier, while another group was reinforced with woven fabrics that were chemically treated with Sodium hydroxide NaOH at 6% w/v for 48 hours. The fabrics were then neutralized and dried in an oven. Mechanical characterizations were performed using traction, compression, in-plane shear and interlaminar (out of plane) shear tests. Results show that the untreated flax fiber composite has the best specific properties among the three vegetal composites.

Contexto: Se realizó una búsqueda local de tejidos de fibras vegetales para determinar la composición de los grupos funcionales y morfología de su superficie antes y después de un tratamiento alcalino con miras a su empleo como refuerzo en compuestos de matriz polimérica.Método: La búsqueda se desarrolló dentro del área metropolitana del Valle de Aburrá, Colombia. Las fibras se trataron por inmersión en NaOH disuelto al 6 % w/v por 48 horas, seguida por una neutralización en ácido acético al 1 % v/v por una hora. Posteriormente fueron secadas a 60 °C por 24 horas. Las técnicas empleadas para los análisis fueron la espectroscopía infrarroja por transformada de Fourier (FTIR) y la microscopía electrónica de barrido (SEM).Resultados: Se seleccionaron tejidos de fique, yute, corteza de coco, lino y algodón. Los análisis FTIR muestran una tendencia a la disminución de ácidos grasos, hemicelulosas, ligninas y enlaces β en la superficie de las fibras, mientras que las imágenes SEM demuestran la remoción de impurezas, la exposición de rugosidades y la creación de espacios interfibrales.Conclusiones: El tratamiento alcalino podría favorecer el mecanismo de anclaje del polímero termofijo a la superficie de las fibras y la creación de enlaces entre las moléculas polares de las fibras y el polímero termofijo, disminuyendo el deslizamiento relativo entre matriz y refuerzo durante la aplicación de cargas.

Laser marking of architectural materials is nowadays an attractive technique for industrial and decorative applications. We report the clay brick pavers marking by vitrification with a continuous-wave Nd:YAG laser (λ=1.064 μm), at different output powers and scan speeds of the laser beam. The marked lines resulted in a dark green glassy phase. The width, depth, and cross-section area of the lines grow with the impinging laser energy density. It was found that the energy density determines the volume per length unit of glassy phase formed. However, the width and depth of the lines can present small differences depending on the particular combination of power and speed.