Journal of Material and Process Technologies

Experimental Investigation of Direct Heated Rock Bed Thermal Energy Storage for Application in Small Scale Power Generation

2025-09-06T03:02:02+00:00

Thermal energy storage is essential for power generation using renewable energy sources like solar and wind, addressing the intermittent nature of these resources and the fluctuating power demand by users. This study experimentally investigates using a new approach of direct heated packed rock-air bed thermal energy storage for small-scale power generation. The experimental setup comprised a cylindrical steel tank (6 mm thickness, 0.45 m diameter, 1.0 m height) with a 25 mm air gap and 200 mm (Castable, Refractory and Fiber glass) insulation. Two granite rock sizes (average diameters of 1.5 cm and 3.5 cm) were tested. An electric heat source maintained a temperature of approximately 550 °C at the bottom of the storage for charging, while thermocouples monitored temperatures at various positions. Thermal decay characteristics were studied under no-load conditions, and discharging was tested by circulating water through an embedded coiled pipe within the storage. During the first 10 h of charging, temperatures between 100 °C and 400 °C were achieved for both 1.5 cm and 3.5 cm rocks. For the 1.5 cm rocks, temperatures reached 400 °C at the bottom, 225 °C in the middle, and 115 °C at the top, while the 3.5 cm rocks reached 395 °C, 180 °C, and 93 °C, respectively. These results show that smaller rocks (1.5 cm) provided better thermal performance, reaching higher temperatures throughout the storage than larger rocks (3.5 cm). The system reached steady state in about 10 hours, after which heat transfer slowed due to the low thermal conductivity of the rocks, with conduction as the dominant mode. During discharging without load, the 3.5 cm rocks cooled to near ambient within 40 hours, while the 1.5 cm rocks maintained 75 °C over the same period. The storage fully discharged within two days, while water circulation at 25 L/h produced steam for 5 h before temperatures dropped below boiling for the smaller rock size. Significant heat losses from all surfaces highlighted the need for better insulation. Overall, the study demonstrates the potential of packed air-rock bed thermal energy storage for small-scale applications, with recommendations to apply forced convection and improve insulation to enhance efficiency.

Effect of Basalt Aggregate Size Distribution and Specific Surface Area on High-Performance Concrete

2025-09-06T02:23:50+00:00

Optimizing concrete mix design requires understanding how coarse aggregate size distribution and specific surface area (SSA) modulate mechanical response and durability. Using basalt aggregates (9.5, 12.5, 19, and 25 mm) characterized by laser diffraction and BET, this study shows that mixtures with larger aggregates (19–25 mm) achieved up to ≈17% higher 28‑day compressive strength (37.93 MPa for 25 mm vs. 32.39 MPa for 9.5 mm) and ≈18% lower water absorption (1.90% for 19 mm vs. 2.31% for 9.5 mm), while mixtures with smaller aggregates (9.5–12.5 mm) exhibited ≈56% greater flexural strength (4.87 MPa vs. 3.13 MPa), ≈38% higher splitting tensile (4.23 vs. 3.07 MPa), and ≈49% higher shear strength (4.04 vs. 2.72 MPa). Pull‑out resistance increased with aggregate size (≈48% higher for 25 mm vs. 9.5 mm), consistent with enhanced mechanical anchorage. BET confirmed an inverse SSA–size relation (≈580→≈200 cm²/g), clarifying ITZ area demand and paste requirements. These outcomes provide a rational basis for tailoring aggregate gradation to balance compressive capacity, flexural/tensile response, and transport resistance for durable, resource‑efficient concrete design.

Extraction and Modification of Starch from Purple Taro Tuber, Colocasia esculenta B. Tini, Through Acetylation Method: Optimization of the Acetylation Process

2025-10-14T07:01:41+00:00

In this study, starch was extracted from non‒conventional purple taro tuber, Colocasia esculenta B. Tini and modified via acetylation method. The extracted starch was acetylated under varying acetic anhydride concentrations, reaction temperature, and time. The acetylation experiments were designed by Box–Behnken Design (BBD) whereas the effects of the variables on the acetylation process were studied at a significance of p < 0.05 with response surface methodology (RSM). The experimental results were subjected analysis of variance to come up with a quadratic model equation. The quadratic model showed that an acetic anhydride concentration of 9.70%, reaction temperature of 30.94 ^oC, and reaction time of 15.17 min, were found to be optimal to obtain a maximum yield of 40.31% acetyl content and 2.34 degree of substitution (DS). The amylose and amylopectin content, as well as the proximate composition of the native starch of purple taro tuber were determined according to the Association of Official Analytical Chemists (AOAC). The proximate composition of native and acetylated starches of purple taro tuber showed the moisture, crude protein, crude fat, ash, amylose, and amylopectin contents of 64.60 ± 3.68 & 2.95 ± 0.24%, 3.90 ± 0.33 & 0.97 ± 0.09 %, 2.96 ± 0.17 & 0.60 ± 0.22 %, 4.30 ± 0.47 & 0.50 ± 0.29 %, and 30.18 ± 0.67% & 69.82 ± 0.33% contents, respectively. On a dry weight basis, the purple taro tuber yielded 16.7 ± 0.16 % starch. The native starch (NS) and acetylated purple taro tuber starch (APTS) were characterized by determining their pH, hydration capacity, swelling power and solubility, FTIR, SEM, and XRD. The pH and hydration capacity of APTS were found to be 7.30 and 2.90 ± 1.17, respectively. The FTIR spectrum showed a successful introduction of the acetyl group as confirmed by the peak intensity improvements at 1720 cm^-1, 1395 cm^-1, and 1260 cm^-1wavenumbers. The SEM image showed the native and acetylated purple taro tuber starches had a polygonal, semi‒oval, and irregular shapes. The native and acetylated purple taro tuber starch showed a B‒type XRD pattern.

Keywords: Acetylation, BBD, Characterization, DS, Proximate analysis, Purple taro tuber, RSM

Petro-stratigraphy and Geochemistry of volcanic rocks from the eastern escarpment of Main Ethiopian Rift

2025-11-10T09:09:31+00:00

The Dera-Sire section is located in the eastern escarpment of the Central Main Ethiopian Rift. The section consists of, from bottom to top, lower flood basalt (Oligocene), lower ignimbrite, tuff and ash, upper basalt (Pliocene), and upper ignimbrite. The lower flood basalts are characterized by phyric to aphyric textures. The lower and upper ignimbrite units contain crystals of quartz, plagioclase, and lithic fragments embedded within a glassy groundmass. The upper basalts are aphyric to plagioclase phyric in texture. The lower flood basalts and upper basalts are alkaline and sub-alkaline (tholeiitic) in composition, respectively. The geochemical variations suggest at least two dominant mantle components that require the production of both upper tholeiitic and lower alkaline basalts. The components are an OIB-like component, which might be similar to the Afar plume composition, and an E-MORB-like component in the asthenosphere, indicating that there were no temporal mantle source variations from Oligocene to Pliocene magma generations. However, the alkaline affinity of the lower flood and tholeiitic nature of the upper basalts suggest that the depth of melting of the lower flood basalt is relatively deeper than that of the upper basalts. The fractionated mineral assemblages of the lower flood basalts (plagioclase-olivine-minor clinopyroxene) and upper basalts (dominant plagioclase with minor clinopyroxene) suggest that the mantle-derived magma rose, accumulated, and fractionated in the lower crustal and upper crustal chambers, respectively. Subsequently, the fractionated magma from the lower and upper crustal chambers rose to the surface and produced lower flood basalts and upper basalts, respectively.