Missouri University of Science and Technology
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Comparative Catalytic Pyrolysis of Wheat Straw for Enhanced Bio-oil Production
No full textCatalytic fast pyrolysis of lignocellulosic biomass is a promising thermochemical route for producing renewable biofuels and value-added chemicals. Many African countries have abundant underutilized agricultural residues whose reuse can improve waste management while reducing reliance on fossil fuels. This study used wheat straw as a representative residue to examine how two catalysts—zinc oxide (ZnO) and cement kiln dust (CKD)—affect bio-oil yield and quality. Bench-scale experiments were performed in a fixed-bed reactor under an inert nitrogen atmosphere at 500–600 °C. Each catalyst was tested separately at loadings from 0 to 7 g per 500 g of biomass to evaluate impacts on product distribution and composition. Bio-oil, biochar, and non-condensable gas yields were measured, and Gas Chromatography-Mass Spectrometry was used to characterize bio-oil chemical profiles. Without catalysts, bio-oil yield increased from 21.8 wt.% at 500 °C to 28.2 wt.% at 600 °C. With catalysts, the highest oil yield occurred at 500 °C using 5 g ZnO (30.6 wt.%), while CKD gave 26.8 wt.% under the same condition. At 600 °C, ZnO\u27s oil yield decreased to 25 wt.%, whereas CKD remained near 28.6 wt.%, so catalytic yield advantages largely disappeared at the higher temperature. Quality varied: ZnO produced lighter, less heavy-fraction oils at both temperatures, while CKD at 600 °C generated a bimodal oil dominated by a heavy halogenated aromatic, indicating post-polishing is needed; overall, ZnO (5 g) at 500 °C maximized yield, ZnO at 600 °C improved volatility, and CKD was more yield-stable at 600 °C but with quality drawbacks
Performance Evaluation of Mechanical Splicing and EB-CFRP Repairs for Impact-Damaged Prestressed Concrete Bridge Girders
No full textCollisions between over-height vehicles and prestressed concrete girders have become an increasing concern for the resilience and safety of bridge infrastructure in the United States. These collisions often lead to flexural deficiency due to damage to prestressing strands, compromising the structural integrity of the girders. Repairing damaged girders presents a cost-effective and time-efficient alternative to complete replacement, which can be very expensive with significant traffic disruptions. This study evaluates the performance of repaired girders through testing two full-scale, 46-foot MoDOT Type II prestressed concrete girders. One of the girders was subjected to lateral impact to induce a 17% loss in prestressing, simulating the damage equivalent to the failure of two strands. The second girder was damaged intentionally by cutting strands to the same ratio. Both girders were repaired using two distinct repair techniques: mechanical splicing and externally bonded carbon fiber-reinforced polymer (CFRP) composites. The repaired girders were tested under four-point flexural loading and compared against code-design calculations. The results were also compared against ACI 440 design guidelines. Both repair techniques successfully restored the flexural strength to the level of the undamaged girder, surpassing the as-built strength by 1% for the splicing technique and by 29.6% for the CFRP system. Additionally, the spliced girder demonstrated greater ductility at failure, exceeding the ductility of the CFRP-repaired girder by 23%. These findings highlight the effectiveness of both repair methods in restoring structural capacity while offering valuable insights into the trade-offs between strength and ductility in repaired prestressed concrete girders
Tomo-PIV Study of Baseline Flow Structures Behind a Strut Injector
No full textStabilizing combustion in scramjet engines is a formidable challenge due to the small-time scales afforded for air-fuel mixing. Numerous studies in this area have demonstrated the potential of strut-style platforms for fuel injection and mixing enhancement, which remains an active area of research. In the Aerodynamics Research Laboratory at Missouri S&T, a strut-style injector system has recently been installed. In this study, we characterize the baseline flow structures behind this platform absent fuel injection. The wake generated by a strut itself has an appreciable impact on the resulting air-fuel mixing, which motivates its characterization. In future studies, this characterization will help delineate the structures generated by the strut and those resulting from fuel injection or trailing edge modifications. Tomographic Particle Image Velocimetry (Tomo-PIV) is utilized to capture the flow field downstream of the strut injector platform. By establishing a versatile strut platform and Tomo-PIV as an adjoining measurement technique, this work lays the foundation for future fundamental studies in supersonic mixing
Co-calcination of Limestone and Clay Enhances the Performance of Limestone Calcined Clay Cement (LC3)
No full textLimestone-calcined clay cements (LC3) reduce the environmental impact of cement production and accelerate the industry transition toward carbon neutrality. While conventional LC3 with 50% clinker replacement (LC3-50) demonstrate long-term performance comparable to ordinary Portland cement (OPC) in concrete, early-age performance is generally compromised. This study explores for the first time, joint thermal treatment—that is, co-calcination—of limestone (LS) and bulk kaolinitic clay in mass ratios of 1:1 to 1:4 under a calcination regime specifically designed to ensure activation of the clay mineral. The co-calcination converts a small fraction of LS to metastable CaO, thus providing an additional reactive calcium source during hydration. Microstructural, kinetic, and thermodynamic studies on systems with 50% clinker replacement are used to quantify enhanced early-stage in situ formation of portlandite, which promotes the precipitation of C−A−S−H and carboaluminate hydrates, that refine the pore structure and improve early-age strength—even in systems with low calcined clay content. A performance-efficiency index is used to indicate the improved mechanical and environmental performance of co-calcined blends as compared to traditional LC3. The approach offers a potential pathway to achieving higher clinker substitution levels
Flow Regime-independent Two-group Interfacial Area Concentration Model for Dispersed Gas-liquid Flows in Large-diameter Pipes
No full textIn many power plants, boiling can result in two-phase flows during normal and accident conditions. Heat and mass transfers through the gas-liquid interface in a two-phase flow process are proportional to the interfacial area concentration (IAC). These calculations for nuclear systems are typically performed using advanced system analysis codes such as TRACE. TRACE uses a two-group (2G) model, where bubbles are divided into two groups according to their drag coefficients. Correlations are used to calculate the group-wise void fractions (VFs) and IACs. This study evaluates the accuracy of the TRACE 2G VF and IAC models for vertically upward dispersed flows in large-diameter (LD) pipes. 2G experimental data in a wide range of dispersed flows from a VF of 0.16–0.68 in LD pipes were used for the model evaluation. Results showed that the TRACE 2G VF and IAC models could be replaced with more advanced models. Therefore, the second part of this study aims to advance the TRACE 2G IAC model while the formulation framework of the model is preserved. Thus, the advanced relations can be implemented in the TRACE code. An approach based on the 2G drift-flux model (DFM) is proposed to calculate group-wise VFs. Furthermore, this study improves the TRACE 2G Sauter mean diameter (SMD) correlation for LD pipes. The mean absolute relative errors (MAREs) of proposed models for the group one (G1) and group two (G2) VFs and total IAC predictions were improved from 42.9 %, 52.0 %, and 40.1 % to 21.6 %, 22.8 %, and 19.2 %, respectively
In-operando Imaging for Mechanistic Insights and Process Optimization in the Biofuel-driven Combustion Synthesis of Cement and Precursor Phases
No full textBiofuel-based combustion synthesis (BCS) is a promising low-carbon pathway for decarbonizing cement production, providing an alternative to the fossil-fuel-driven clinkering process typically conducted at ∼1450 °C. Understanding microscale combustion mechanisms is essential to efficiently transfer biofuel-generated heat to cement precursors for targeted phase formation. Unlike previous studies focusing on macro-scale parameters such as fuel content/type, porosity, and holding temperature, this work provides mechanistic insights into microscale combustion behavior, linking microstructural phenomena with macro-scale processing conditions to guide parameter optimization. In-operando microscale imaging was employed to examine combustion wave propagation, spatio-temporal temperature evolution, and microstructural transformations within reactive pellets. Two combustion modes were observed: surface combustion wave (SCW) and continuous combustion wave (CCW) near fuel ignition, and rapid volumetric heating followed by CCW at elevated input temperatures. Optimizing pellet properties—porosity (8–10 %) and fuel calorific value—resulted in reduced cracking and wave velocity dispersion (∼0.1–0.2 mm s−1), enabling more uniform wave propagation (0.5–0.75 mm s−1) and temperature stability (±25–50 °C) for sustained durations (∼1–2 min). These conditions allowed reliable synthesis of multiple cement phases. At 450 °C, ∼90–95 % limestone-to-lime conversion was achieved while maintaining calcination temperatures of ∼950 °C. At 700 °C, volumetric heating generated transient peaks of ∼1200 ± 100 °C, producing belite-rich cement (∼90 % C2S). At 800 °C, BCSA-type cement was formed (∼25 % ye\u27elimite, ∼50 % belite). At 900 °C, surface temperatures reached ∼1300 ± 100 °C, but limited dwell time restricted alite (C3S) formation (∼20 %), indicating further optimization is needed. These findings provide mechanistic insights and a foundation for scalable, energy-efficient, and low-carbon cement production via BCS
Temperature Compensation in Loop and Patch FSS Strain Sensors: Analysis and Experimental Validation
No full textFrequency selective surfaces (FSSs) are arrays of conductive elements or apertures that exhibit frequency-dependent reflection and transmission properties. Their electromagnetic response is influenced by geometry and environmental conditions, making them attractive for wireless strain-sensing applications. However, temperature variations can produce frequency shifts similar to those caused by strain, reducing measurement accuracy. This work investigates the effects of intrinsic temperature compensation on two common FSS unit cell geometries—loop and patch—through comprehensive simulation analysis. The results show that loop-based cells offer superior thermal stability, while patch-based cells provide greater strain sensitivity, illustrating the trade-off between thermal robustness and mechanical responsiveness. A patch-type FSS strain sensor was designed, fabricated, and characterized under varying temperature and strain. The sensor achieves a strain sensitivity of ~150 MHz per 1 %εl, while temperature-induced drift is limited to ~12 MHz over a 200 °C range, confirming the effectiveness of the intrinsic compensation strategy. The results provide valuable insights for optimizing FSS-based sensor design in structural health monitoring applications and balancing thermal stability with mechanical sensitivity to ensure reliable performance in thermally dynamic environments
Robust and High-efficiency Demodulation of Ultra-weak FBG Arrays in OFDR-Based Distributed Sensing
No full textA robust and high-efficiency demodulation scheme for optical frequency domain reflectometry (OFDR) based ultra-weak fiber Bragg grating (UWFBG) array detection system, originating from the Buneman frequency estimation (BFE) algorithm, is proposed and experimentally demonstrated. Due to the current limitations and imperfections of FBG inscription technology, the quasi-continuous inscription approach, along with its less-than-ideal outcomes, gives rise to problems of grating spectrum splitting and spectral distortion during the grating demodulation process. This renders the traditional approach of directly applying the BFE algorithm for grating demodulation ineffective, despite its significant enhancement of demodulation efficiency. To address this issue, we propose utilizing the BFE algorithm for the demodulation of rough cross-correlation spectra of FBGs. This approach leverages the inherent noise resistance of the cross-correlation algorithm while also capitalizing on the efficiency improvements offered by the BFE algorithm, ultimately achieving a simultaneous enhancement in demodulation efficiency while ensuring robust demodulation performance. In the demonstration experiments, by employing the proposed algorithm, we achieved demodulation results that were virtually indistinguishable from those of traditional demodulation methods, while simultaneously enhancing the demodulation efficiency by 15.3 times (10-m measurement range). This algorithm facilitates the progress of OFDR-based UWFBG sensing towards practical applications
First-principles Study on Pressure Induced Structural and Electronic Properties of Mg 1−xFexO using HSE06 and GGA+U Methods, a Combined Study
No full textWe investigate the pressure-induced spin crossover in ferropericlase (Mg1 − xFex O, x = 0.031 25–0.25) using first-principles calculations with generalized gradient approximation (GGA+U) and HSE06 methods. By analyzing spin transition pressures, structural distortions, and electronic properties, we establish a correspondence between the Hubbard U and hybrid mixing parameter α. Both methods predict a linear increase in transition pressure with Fe concentration and show weak sensitivity to Fe distribution. Our findings clarify the strengths and limitations of each approach and provide guidance for modeling spin transitions in mantle materials
Near-wall Void Distribution Characterization in Pebble Bed Reactor using Gamma-ray CT and DEM Simulation
No full textAccurate characterization of void-fraction distributions in pebble-bed reactors (PBRs) is essential for predicting flow, heat transfer, and neutronic behavior. High-fidelity experimental benchmark data for validating such predictions remain scarce, largely due to the challenges of non-invasive measurements. In this study, gamma-ray computed tomography (CT) was employed to measure radial and cross-sectional porosity in a laboratory-scale pebble bed containing 6cm graphite pebbles. A Discrete Element Method (DEM) simulation was implemented and validated against these measurements, then applied to the full-scale geometry of the Xe-100 high-temperature gas-cooled pebble-bed reactor. Analyses included radial and axial void-fraction profiles in the cylindrical section and conical base, with particular attention to near-wall oscillations at multiple axial levels. Both axially averaged profiles, integrating over extended bed sections, and locally resolved profiles, capturing fine-scale oscillations, were evaluated. Additional analyses examined cross-sectional void distributions and the effect of pebble recirculation. The DEM results reproduced the expected near-wall oscillatory layering with a characteristic wavelength of ∼1 dp and bulk void fractions near 0.40 and further showed that oscillatory patterns persist into the conical region, where the first trough shifts outward, and a broader near-wall gap develops. Recirculation studies, corresponding to 5,10, and 15 complete bed inventory cycles, showed that structural rearrangements occur mainly during the initial passes, after which the bed attains a quasi-steady configuration. Recirculation intensified near-wall oscillations, particularly in the lower regions, but had negligible impact on bulk porosity in the cylindrical section. In the cone, however, the void fraction was elevated during dynamic operation due to pebble drainage and upward void propagation. The findings support improved neutronic and thermal-hydraulic modeling and contribute to the design and safety assessment of next-generation pebble-bed systems