Teknomekanik

Enhanced durability and tribological performance of polyvinyl alcohol/layered double hydroxide/tannic acid composites under repeated swelling cycles

2024-11-27T11:47:17+00:00

In recent years, the exploration of polyvinyl alcohol (PVA) composites has garnered significant attention due to their versatility applications in aqueous environments. However, despite their promise, neat PVA exhibit limitations such as significant mechanical degradation under repeated swelling cycles. This study investigates the durability and tribological performance of polyvinyl alcohol (PVA) composites reinforced with nickel-iron layered double hydroxide (LDH) and tannic acid (TA) under repeated swelling cycles. Building on previous research that explored composite preparation and initial characterization, this research emphasizes the effects of cyclic swelling on wear resistance, friction behavior, and mechanical properties. Tribological tests were conducted to evaluate the coefficient of friction (COF) and wear rate before and after multiple swelling cycles, alongside tensile strength and strain measurements. The results revealed that the PVA/TA2/LDH2 composite, containing the highest additive content, exhibited the lowest wear rate of 11.52 × 10⁻⁵ mm³/Nm after 3 swelling cycles, demonstrating superior resistance to material degradation. Although PVA/TA2/LDH1 exhibited a slightly lower COF, its wear rate was higher due to reduced reinforcement. Compared to neat PVA, which showed a COF increase from 0.45 to 0.53, the PVA/LDH/TA composites retained their tribological stability, with only a marginal increase in COF and wear rate. Similarly, tensile strength of PVA/TA2/LDH2 decreased by only 11% after 3 cycles (from 33.3 MPa to 30 MPa), while neat PVA experienced a 25.5% reduction (from 30 MPa to 22.5 MPa). These findings highlight the potential of PVA/LDH/TA composites for applications in aqueous environments, offering significantly enhanced long-term performance and reliability.

Vapor compression refrigeration system with air and water cooled condenser: Analysis of thermodynamic behavior and energy efficiency ratio

2024-11-03T09:06:14+00:00

This study presents the analysis of thermodynamic behavior and energy efficiency of a vapor compression refrigeration system with two types of condensers: air-cooled (ACC) and water-cooled (WCC). The main objective is to assess the system performance by comparing the Coefficient of Performance (COP) and Energy Efficiency Ratio (EER) under both condenser configurations. During a 12-hour test period, data on refrigerant pressure, temperature, and electrical energy consumption were collected and analyzed. The results show that the WCC system outperforms the ACC system, showing a 5.7% increase in heat rejection and a 4.2% increase in cooling capacity. In addition, the WCC system exhibits a lower compressor duty cycle and consumes less electrical energy, resulting in a higher total EER of 5.658 compared to ACC of 1.945. These findings suggest that integrating a water-cooled condenser into a refrigeration system can significantly improve energy efficiency and reduce operating costs, making it a viable option for commercial applications in tropical regions.

Infiltration capacity based on soil geophysical constants using artificial infiltration in residential land

2024-11-04T11:37:45+00:00

Conversion of catch-land into residential land in urban areas reduces infiltration, and increases surface flow and flood risk. Artificial infiltration is a potential solution to increase infiltration capacity, but its effectiveness is highly dependent on the physical characteristics of the soil, including geophysical constants. This study aims to determine the level of infiltration capacity based on the value of soil geophysical constants using artificial infiltration in residential land in Padang. Measurements were carried out using the Horton method and double-ring infiltrometer in several residential locations. The study results show that the soil characteristics of residential land in Padang consist of the soil texture of sand, loamy sand, and sandy loam, which have high moisture content, large fill weight, and low porosity, causing low infiltration rate and high surface flow. Artificial infiltration can significantly increase the infiltration capacity, especially on sandy soils with high hydraulic conductivity. The soil geophysical constant, k, is classified according to field measurement results. In the lower range of 1.2 < k ≤ 1.9, the average infiltration capacity was found at 625.1 mm/hour. Within the interval of 1.9 < k ≤ 2.6, the mean capacity decreased to 587.7 mm/hour, but in the upper interval of 2.6 < k ≤ 3.3, the average infiltration capacity was 499 mm/hour. Large soil geophysical constants reveal higher infiltration capacity, while small geophysical constants indicate low infiltration capacity.

The conversion of nata de coco bacterial cellulose into cellulose nanofibers using high shear mixer with eco-friendly fluid dynamics method

2024-12-14T05:52:00+00:00

Nanocellulose is widely applied in various fields due to its superior characteristics. Several methods have been developed to synthesize it, but they still have limitedness as being non-eco-friendly and inefficient use. Therefore, the synthesis of nanocellulose from sustainable sources is being developed using a simple and eco-friendly method. This study successfully produced a low viscosity gel suspension of cellulose nanofibers (CNF) from bacterial cellulose (BC) derived from Nata de Coco using a high shear mixer (HSM). The mixture of BC and water in a 1:1 ratio was processed with various rotational speeds and times in the HSM. The suspension result was characterized using an Ostwald viscometer, UV-vis spectrophotometer, lux meter, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), particle size analyzer (PSA), and x-ray diffraction (XRD). Based on the characterization, it was confirmed that higher rotational speeds and extended processing times reduced the suspension viscosity and increased light transmittance, indicating a reduction in BC size to the submicron/nanometer scale. The best light transmittance was achieved with the HSM at 4500 rpm for 180 min, resulting in a viscosity drop from 232.67 mPa.s to 1.45 mPa.s. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis showed that the CNF retained its fibrous structure with nanometer-scale widths and high porosity without significant changes in crystallinity.

Transformative process: Crafting imines from nitrobenzene and benzyl alcohol coupling with cerium oxide modified mesoporous SBA-15

2024-12-18T12:33:22+00:00

A low-cost and eco-friendly cerium oxide modified mesoporous SBA-15 catalyst was developed by wet impregnation. It enables sequential oxidation of benzyl alcohol and reduction of nitrobenzene, followed by imine formation in a single and solvent-free system. Characterization confirms homogeneous cerium oxide dispersion, high stability, and enhanced redox properties. The optimized catalyst demonstrates excellent conversion and selectivity, attributed to the mesoporous SBA support, acidic properties, and cerium's redox functionality. Elevated temperatures enhance benzyl alcohol dehydration and hydrogen diffusion, facilitating intermediate aniline formation by a borrowing-hydrogen mechanism and followed by imine synthesis. It eliminates solvents, reduces byproducts, and achieves high atom economy and renewability. It presents a significant advance in sustainable catalysis. The catalyst's robustness and ease of recovery strengthen its practicality for repeated cycles. The findings provide a scalable and energy-efficient solution for greener imine synthesis with potential applications in industrial processes requiring efficient and eco-friendly chemical production. It ensures minimal environmental impact and offers a cost-effective pathway for high-value chemical synthesis. This study supports the SDGs by promoting sustainable industrial practices through the development of a low-cost and eco-friendly catalyst that reduces environmental impact, enhances energy efficiency, and contributes to greener chemical production.

Classifying four maturity categories of coffee cherry using CNN-VGG19

2024-10-05T04:07:32+00:00

The local coffee farmers employ manual inspection to identify the maturity of coffee cherries that are inefficient in labor and time. Thus, the objective of this study is to develop a CNN-VGG19 algorithm model that can accurately detect the maturity image of coffee cherry samples, and classify them into: unripe, semi-ripe, ripe, and overripe categories. The proposed solution will provide local coffee farmers with an automated and more accurate classification of the quality of coffee cherries. The visual geometry group-19 was employed to increase the object recognition model performance of the proposed algorithm while maintaining higher accuracy and quicker throughput, thus increasing revenues. The images are utilized as training and test set data. They were then processed by using the feature extraction of CNN-VGG19 deep learning model, and got four coffee cherry maturity classes. The model architecture attained a 90.00 % accuracy. Furthermore, the increase in both the validation and training accuracy graph with a corresponding decrease in both the validation and training loss graph propounds that the model performance has improved.