Browsing by Author "Kivevele, Thomas"

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Activated Bentonite for Physical, Mechanical, and Durability Properties of Concrete—A Review
(Wiley, 2024-12) Fode, Tsion; Jande, Yusufu; Kivevele, Thomas
Bentonite mostly exists in many counties and studies reported employment of activated bentonite in the concrete improves concrete performance more than using raw bentonite. However, it is not well-known which range of bentonite activation temperature and employment dose gives the best concrete performance for the sustainability of activated bentonite in construction materials. Therefore, the present study detail reviewed the effect of activated bentonite at different heating temperatures and replacement doses of bentonite on the durability, physical, mechanical, and microstructural properties of concrete. Also, environmental and economic beneficiary of employing activated bentonite in concrete is evaluated. As the review of various studies reveals, activation of bentonite between 201 and 800°C increases the pozzolanic reactivity of bentonite. Hence, the activated pozzolana can easily consume free calcium hydroxide to form a secondary C–S–H gel that can improve the mechanical, microstructural, and durability properties of activated bentonite blended concrete in addition to lessening energy consumption compared to conventional concrete. Besides these, adding 15%–20% of activated bentonite in concrete significantly improves the mechanical properties; specifically, most studies found the optimum activated bentonite dose is 15% by weight of cement in concrete. This replacement indicates lessened energy consumption by around 45% compared to the total employment of ordinary Portland cement in concrete production.
An Analysis of Fuel Properties of Fatty Acid Methyl Ester from Manketti Seeds Oil
(Taylor & Francis Online, 2014-11-20) Kivevele, Thomas; Huan, Zhongjie
The fatty acid methyl esters (FAME)produced from vegetable oils, animal fats, or waste oils known as biodiesel has attracted attention as possible replacement of fossil fuels. The fuel properties of biodiesel are similar to that of conventional petro-diesel and it is more environmentally friendly. This study investigated in detail the fuel properties of biodiesel from less common edible oil produced from Manketti seeds (Schinziophyton rautanenii). Manketti Oil Methyl Ester (MOME) was produced by transesterification process using an alcohol in the presence of a catalyst. The fuel related properties of MOME were determined and compared with the global biodiesel standards such as ASTM 6751 and EN 14214. Also, the effects of different antioxidants; 1, 2, 3 tri-hydroxy benzene (Pyrogallol, PY), 3,4,5-tri hydroxy benzoic acid (Propyl Gallate, PG) and 2-tert butyl-4-methoxy phenol (Butylated Hydroxyanisole, BHA) were investigated on oxidation stability, kinematic viscosity and cetane number (CN) of MOME. The results showed that, most of the determined fuel properties fulfilled the minimum requirement of global biodiesel standards. Among antioxidants used in this study, PY and PG were more effective compared to BHA on oxidation stability. Also, addition of antioxidants on MOME showed positive results on CN which was increased and kinematic viscosity was decreased. In summary, biodiesel produced from manketti seeds oil indigenous to Southern Africa can be used as partial substitute of mineral diesel.
Applications of Natural Rocks as Heat-Storage Materials for Food Drying in Sub-Saharan Africa
(Trans Tech Publications Ltd, 2025-10-03) Loemba, Aldé; Kichonge, Baraka; Kivevele, Thomas
Natural rocks are emerging as a viable solution for solar heat storage in Sub-Saharan Africa due to their low cost and accessibility, as well as their ability to reduce energy costs and reliance on solar energy. This study review research on applications of natural rocks as heat-storage materials for food drying in Sub-Saharan Africa. Findings of this study indicate that current research on the combination of drying systems with thermal energy storage systems using natural rocks as storage material focuses on indirect solar dryers (66.67%), mixed mode solar dryers (16.67%), and solar-assisted heat pump dryers (16.67%). These dryers perform admirably, particularly in extreme weather conditions and when there is no sunlight. The findings show that using natural rocks as a storage medium can increase the efficiency of dryers by up to 17.48%, reduce drying time by as much as 50%, and extend the drying operation by 2 to 4 hours after sunset. This study also identifies and proposes key areas for further research. In particular, more attention is needed to characterize the thermal properties of the storage materials used, as this aspect is often underexplored in African studies. Understanding these properties is essential for optimizing the performance of solar dryers and making informed choices about which materials to use. In addition, the techno-economic analysis of all these dryers is neglected, making it difficult to assess the economic impacts of these technologies and facilitate their adoption in communities. Exergoeconomic analysis should also be carried out in order to facilitate optimization and understand the actual efficiency of these dryers.
Bacterial Diversity Dynamics in Sandy Loam Soils in Tanzania Under Varying Fertilizer-Derived Uranium Concentrations
(Microorganisms, 2025-08-13) Mwalongo, Dennis; Lisuma, Jacob; Haneklaus, Nils; Maged, Ali; Brink, Hendrik; Carvalho, Fernando; Wacławek, Stanisław; Mpumi, Nelson; Amasi, Aloyce; Mwimanzi, Jerome; Chuma, Furaha; Kivevele, Thomas; Mtei, Kelvin
The presence of radiotoxic uranium (U) in mineral fertilizers is of global concern. A pilot study was conducted in Tabora (Tanzania) to determine the release of U from three brands of phosphate fertilizers and its impact on soil bacteria. The experiment used three types of fertilizer: Minjingu Powder (MP), Nafaka Plus (NP), a mixed and granulated fertilizer made from Minjingu Phosphate Rock (MPR), and YaraMila Cereal (YC) fertilizer. There was also a control treatment that was not fertilized (NF). Alpha diversity and the R tool were used to analyze bacterial diversity in four samples within an average sequencing depth of 74,466 reads, using metrics like ASVs, Shannon index, and Chao1. The results showed that the number of amplicon sequence variants (ASVs) in the DNA from soil bacteria decreased, specifically to 400 ASVs, in the NP treatment, which was in line with the higher U concentration (3.93 mg kg−1) in the soils. In contrast, the MP fertilizer treatment, associated with a lower U concentration (3.06 mg kg−1) in soils, exhibited an increase in ASVs within the DNA of soil bacteria, reaching 795; the highest ASV value (822) was observed in the NF treatment. Higher amounts of U in the soil plots seemed to have resulted in more types of bacteria, with the Actinobacteriota phylum being the most common in all of the treatments. The NP (3.93 mg kg−3 U concentration) and MP (3.06 mg kg−3 U concentration) treatments were the only ones that showed Halobacteriota and Crenarchaeota phyla. Nonetheless, bacterial diversity may also account for the alterations in soil phosphorus and nitrogen following fertilizer application. The YaraMila Cereal treatment did not seem to be linked to any particular bacterial phylum. This means that in this study it did not have any measurable effect on the soil bacteria species compared to the MP and NP treatments
Bacterial Diversity Dynamics in Sandy Loam Soils in Tanzania Under Varying Fertilizer-Derived Uranium Concentrations
(MDPI, 2025-08-13) Mwalongo, Dennis; Lisuma, Jacob; Haneklaus, Nils; Maged, Ali; Brink, Hendrik; Carvalho, Fernando; Wacławek, Stanisław; Mpumi, Nelson; Amasi, Aloyce; Mwimanzi, Jerome; Chuma, Furaha; Kivevele, Thomas; Mtei, Kelvin
The presence of radiotoxic uranium (U) in mineral fertilizers is of global concern. A pilot study was conducted in Tabora (Tanzania) to determine the release of U from three brands of phosphate fertilizers and its impact on soil bacteria. The experiment used three types of fertilizer: Minjingu Powder (MP), Nafaka Plus (NP), a mixed and granulated fertilizer made from Minjingu Phosphate Rock (MPR), and YaraMila Cereal (YC) fertilizer. There was also a control treatment that was not fertilized (NF). Alpha diversity and the R tool were used to analyze bacterial diversity in four samples within an average sequencing depth of 74,466 reads, using metrics like ASVs, Shannon index, and Chao1. The results showed that the number of amplicon sequence variants (ASVs) in the DNA from soil bacteria decreased, specifically to 400 ASVs, in the NP treatment, which was in line with the higher U concentration (3.93 mg kg−1) in the soils. In contrast, the MP fertilizer treatment, associated with a lower U concentration (3.06 mg kg−1) in soils, exhibited an increase in ASVs within the DNA of soil bacteria, reaching 795; the highest ASV value (822) was observed in the NF treatment. Higher amounts of U in the soil plots seemed to have resulted in more types of bacteria, with the Actinobacteriota phylum being the most common in all of the treatments. The NP (3.93 mg kg−3 U concentration) and MP (3.06 mg kg−3 U concentration) treatments were the only ones that showed Halobacteriota and Crenarchaeota phyla. Nonetheless, bacterial diversity may also account for the alterations in soil phosphorus and nitrogen following fertilizer application. The YaraMila Cereal treatment did not seem to be linked to any particular bacterial phylum. This means that in this study it did not have any measurable effect on the soil bacteria species compared to the MP and NP treatments.
Catalytic hydrothermal liquefaction of orange peels into biocrude: An optimization approach by central composite design
(Elsevier B.V., 2023-08) Kariim, Ishaq; Waidi, Yusuf; Swai, Hulda; Kivevele, Thomas
Global instability, persistent increase in pump-price, inflation and depletion of fossil fuel resources amidst the continuous discharge of greenhouse gases from fossil fuels combustion call for urgent attention. The application of novel catalyst towards an improved biocrude production and enhanced biomass conversion are required for effective performance of hydrothermal liquefaction of biomass feedstocks. In the present study, iron supported carbon nanospheres (Fe/CNSs) catalyst has been developed using wet impregnation approach and explored for its catalytic potency in improving yield of biocrude using an optimization approach; central composite design. Hydrothermal liquefaction (HTL) was adopted as a process route where the catalyst dosage (3–6 wt%) and the reaction temperature (330–430 °C) were optimized on the constant weight of orange feedstock (10 g), reaction time of (15 mins) and solvents’ ratio of 3:1 (acetone to ethanol). The performance of the catalyst was found to be aided with the even dispersion of the Fe on the surfaces of the CNSs support and improved surface area. The effects of reaction temperature were observed to be more progressive on biocrude yield formation over the catalyst loading. The optimum biocrude yield, solid residue, biomass conversion and gas yield were obtained to be 71.09 wt%, 28.18 wt%, 71.82 wt% and 40.14 mL/g at 430 °C and 3 wt% catalyst loading. The obtained analysis of variance suggests a good correlation between the experimental and predicted data in all responses. The selectivity of Fe/CNSs catalyst to high yield of phenolics and aromatic compounds in the biocrude suggest that, the biocrude can be further be upgraded into transportation fuel through hydrodeoxygenation process. The findings have further suggested the viability of the developed Fe/CNSs as an effective catalyst for improved HTL products in a batch reactor.
Catalytic hydrothermal liquefaction of orange peels into biocrude: An optimization approach by central composite design
(Elsevier, 2023) Kariim, Ishaq; Waidi, Yusuph; Swai, Hulda; Kivevele, Thomas
Global instability, persistent increase in pump-price, inflation and depletion of fossil fuel resources amidst the continuous discharge of greenhouse gases from fossil fuels combustion call for urgent attention. The application of novel catalyst towards an improved biocrude production and enhanced biomass conversion are required for effective performance of hydrothermal liquefaction of biomass feedstocks. In the present study, iron supported carbon nanospheres (Fe/CNSs) catalyst has been developed using wet impregnation approach and explored for its catalytic potency in improving yield of biocrude using an optimization approach; central composite design. Hydrothermal liquefaction (HTL) was adopted as a process route where the catalyst dosage (3–6 wt%) and the reaction temperature (330–430 °C) were optimized on the constant weight of orange feedstock (10 g), reaction time of (15 mins) and solvents’ ratio of 3:1 (acetone to ethanol). The performance of the catalyst was found to be aided with the even dispersion of the Fe on the surfaces of the CNSs support and improved surface area. The effects of reaction temperature were observed to be more progressive on biocrude yield formation over the catalyst loading. The optimum biocrude yield, solid residue, biomass conversion and gas yield were obtained to be 71.09 wt%, 28.18 wt%, 71.82 wt% and 40.14 mL/g at 430 °C and 3 wt% catalyst loading. The obtained analysis of variance suggests a good correlation between the experimental and predicted data in all responses. The selectivity of Fe/CNSs catalyst to high yield of phenolics and aromatic compounds in the biocrude suggest that, the biocrude can be further be upgraded into transportation fuel through hydrodeoxygenation process. The findings have further suggested the viability of the developed Fe/CNSs as an effective catalyst for improved HTL products in a batch reactor.
Catalytic hydrothermal liquefaction of orange peels into biocrude: An optimization approach by Central Composite Design
(Elsevier B.V., 2023-06-01) Kariim, Ishaq; Waidi, Yusuf; Swai, Hulda; Kivevele, Thomas
Global instability, persistent increase in pump-price, inflation and depletion of fossil fuel resources amidst the continuous discharge of greenhouse gases from fossil fuels combustion call for urgent attention. The application of novel catalyst towards an improved biocrude production and enhanced biomass conversion are required for effective performance of hydrothermal liquefaction of biomass feedstocks. In the present study, iron supported carbon nanospheres (Fe/CNSs) catalyst has been developed using wet impregnation approach and explored for its catalytic potency in improving yield of biocrude using an optimization approach; central composite design. Hydrothermal liquefaction (HTL) was adopted as a process route where the catalyst dosage (3-6 wt.%) and the reaction temperature (330-430 oC) were optimized on the constant weight of orange feedstock (10 g), reaction time of (15 mins) and solvents’ ratio of 3:1 (acetone to ethanol). The performance of the catalyst was found to be aided with the even dispersion of the Fe on the surfaces of the CNSs support and improved surface area. The effects of reaction temperature were observed to be more progressive on biocrude yield formation over the catalyst loading. The optimum biocrude yield, solid residue, biomass conversion and gas yield were obtained to be 71.09 wt.%, 28.18 wt. %, 71.82 wt.% and 40.14 mL/g at 430 oC and 3 wt.% catalyst loading. The obtained analysis of variance suggests a good correlation between the experimental and predicted data in all responses. The selectivity of Fe/CNSs catalyst to high yield of phenolics and aromatic compounds in the biocrude suggest that, the biocrude can be further be upgraded into transportation fuel through hydrodeoxygenation process. The findings have further suggested the viability of the developed Fe/CNSs as an effective catalyst for improved HTL products in a batch reactor.
Catalytic supercritical water gasification of biomass waste using iron-doped alkaline earth catalysts
(Springer Nature Switzerland AG., 2022-05-18) Bakari, Ramadhani; Kivevele, Thomas; Huang, Xiao; Jande, Yusufu
The objective of this study is to optimise the process of supercritical water gasification of rice husk biomass utilising a low-cost catalyst made from alkaline-earth materials. The interactions between catalyst loading and Fe content on gasification yield were investigated using response surface methodology. The catalyst characterisation findings revealed that the catalysts’ predominant reactive site is on iron oxide, calcium ferrite, and calcium oxide. Under all the conditions tested, the manufactured catalyst was highly active in promoting char gasification, gas volume, and gasification efficiency whilst the tar yield was substantially elevated. The maximum gasification efficiency of 69.57%, gas yield of 402.8 mL/g biomass, char yield 24.68 wt%, and gravimetric tar yield of 57.5 mg/g were obtained under the catalytic conditions of 15% catalyst loading with 5%Fe/limestone, 492 °C, 120-min residence time, and 9.5 wt% feed concentrations. Thus, the manufactured catalyst showed a potential for optimising gasification outputs.
Catalytic tar conversion and the prospective use of iron-based catalyst in the future development of biomass gasification: a review
(Springer Nature Switzerland AG., 2020-06-27) Ramadhani, Bakari; Kivevele, Thomas; Kihedu, Joseph; Jande, Yusufu
Biomass is a promising renewable energy source which is available globally, mostly in developing countries where access to clean and affordable energy is a critical problem. Biomass gasification is an interesting technology that can convert biomasses to a more versatile fuel known as syngas, the energy which can substitute conventional fossil fuels in the future. Syngas can amenably be combusted to produce power and heat as well as a feedstock for synthesis of chemicals and other fuels. The biomass gasification is facing severe operational challenges, one of the problems being tar formation and its removal techniques. Tar condenses at reduced temperature, thus causing blockage in the downstream equipment such as compressors and engines. Many studies have considered syngas cleaning by physical removal and thermal cracking unsuitable as they need downstream processing of scrub liquor and utilizes a part of the produced gas in maintaining the thermal cracking temperature, respectively. The utilization of catalysts has been an interesting focus; however, it has not yet been fruitful as many of the developed catalysts deactivate rapidly, and they are expensive or toxic. The motives of the current study are to review tar formation characteristics and trends on catalytic conversion. In addition, the study elucidates the fascinating behaviour of metallic and oxides of the iron-based catalyst under different syngas composition (oxidizing and reducing environments). The behaviours of the iron-based catalyst indicate its fundamental role in developing a catalyst for tar cracking with respect to less toxic, inexpensive, abundant, and regenerable alternatives.
Characteristics of briquettes from plastic pyrolysis by-products
(MESI, 2023) Sunaryo, Sunaryo; Sutoyo, Sutoyo; Suyitno, Suyitno; Arifin, Zainal; Kivevele, Thomas; Petrov, Artur
Pyrolysis has been proven as a method to reduce plastic waste and produce useful products, especially liquid fuels. However, plastic pyrolysis also produces gases and char as by-products which are being investigated for useful products. Therefore, our present study aims to investigate the char characteristics of plastic pyrolysis for further use as briquettes. Seven samples of char by- products from the pyrolysis process of low-density polyethylene (LDPE) plastic at various reaction temperatures and catalyst types were studied. The proximate test is used to determine the properties of char such as moisture content, ash, volatile matter, and fixed carbon while the bomb calorimeter is used to determine the calorific value. Briquettes are formed by mixing 4 grams of char and 0.5-1 gram of binder (1% starch and 90% water). The briquettes were formed into solid cylinders with a diameter of 1.75 cm and formed with a pressure of 10 kg/cm2. Furthermore, the impact resistance index (IRI) was used to test the performance of the briquettes and showed an IRI value between 100 and 200. However, of the seven char samples tested, three of them were impossible to process into briquettes because they melted during the combustion test
Clustering and Fuzzy Logic-Based Demand-Side Management for Solar Microgrid Operation: Case Study of Ngurudoto Microgrid, Arusha, Tanzania
(Hindawi, 2021-02-15) Philipo, Godiana; Jande, Yusufu; Kivevele, Thomas
Permanent electricity availability should not be taken for granted since grid sustainability and reliability are at stake when there is no balance between supply and demand. This paper employs a load balancing demand-side management (DSM) approach based on fuzzy logic, considering the low energy users who have insignificant influence on system peaks. Through the K-means clustering algorithm, suitable candidates for DSM are identified, and the control mechanism is based on energy utilization and load priority. The results reveal that about 3.7 kW in power saving was achieved per month. This result indicates that, with a proper energy management strategy for an individual customer, almost a flatter load profile and power saving can be achieved.
Comprehensive Analysis of Fuel Properties of Adansonia digitata Methyl Ester with the Influence of Nanoparticle Additives Extracted from an Agricultural Waste
(SpringerLink, 2022-02-06) Kapile, Fredrick; Bereczky, Akos; Ntalikwa, Justin; Kivevele, Thomas
Purpose This paper reports the results of experimental investigations on the influence of the addition of silica nanoparticles extracted from rice husk (an agricultural waste) on the major physicochemical properties of biodiesel derived from Adansonia digitata. Methods The physicochemical properties of the base fuel and the modified fuel formed by dispersing the nanoparticles by ultrasonic agitation were measured using ASTM and EN standard testing methods. The effects of manufactured silica nanoparticles on the fuel properties of Adansonia digitata methyl esters (ADME) that were produced by the transesterification process were investigated. Silica nanoparticles which were produced by the extraction process from rice husk were doped at the dosing levels of 400–1000 ppm. The produced silica was characterized by Thermogravimetry analysis (TGA), Barrett Emmett Teller (BET), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM), X-ray fluorescence (XRF), and Xray diffractometer (XRD) methods. Results The silica was found to have BET specific surface area, Barret-Joyner Halenda (BJH) pore diameter, and pore volume of 502.24 m2 /g, 19.3 nm, and 0.761 cm3 /g respectively. At 400 ppm and 800 ppm silica dosages, the oxidation induction period increased significantly from 5.2 h to a high of 10.3 h. These findings showed that ADME's oxidation stability had improved significantly to satisfy the ASTM D6751 and EN 14,214 standard limits of > 3 h and > 8 h, respectively. The kinematic viscosity of ADME dropped as the additive content increased, from 4.62 mm2 /s for pure biodiesel to 2.21 mm2 /s for 400 ppm. Furthermore, it was discovered that the largest increase in viscosity occurs at high doses of 600–1000 ppm. The flash point increased linearly as the amount of nanoparticle addition was increased. Higher flash point temperatures are desirable for improving engine performance and for safety issues. Also, results showed that cetane number (CN) increases from 60 to 64 simultaneously at the dosing level between 400 and 800 ppm and dropped to 63 at dosing levels beyond 800 ppm. The blending of Silica/Alumina showed the best improvement of CN of ADME about 33.6%. Commercial additive (Al2O3) showed an improvement of oxidation stability up to a dosing level of 800 ppm. Fuel blending of (B100 + SiO2), (B20 + SiO2), and (B20 + Al2O3) was also performed and the results showed that the oxidation induction period (OIP) increases from 3.8 to 10.3 h for (B100 + SiO2) blending up to dosing level of 800 ppm but decreases at 1000 ppm. However, blending (B20 + SiO2) showed significant improvement on OIP from 47.2% to 64.16% at 0 to 1000 ppm respectively but blending of B20 and Al2O3 showed the best improvement about 71.7% at 1000 ppm but slightly decreased at 600 ppm (15.7 h). Kinematic viscosity showed slight improvement (decrease by 32.6%) at 400 ppm, but increases at 600 ppm (4.16 mm2 /s) for B20 + SiO2 fuel blending. However, at higher dosing level decreases by 3.85% up to 1000 ppm. Dosing of Al2O3 additive on B20 fuel blend displayed the improvement decreasing by 36.9% at 600 ppm but at higher dosage (1000 ppm) increases to 5.2 mm2 /s for Al2O3. Conclusion Generally, from this study it has been observed that rice husk nano-particle is considered as a potential fuel-borne catalyst than the commercial one to improve the fuel properties, owing to their enhanced surface area to volume ratio probably due to its 3-dimensional tetrahedral coordination and covalent nature of silicon atom.
Comprehensive Analysis of Fuel Properties of Adansonia digitata Methyl Ester with the Influence of Nanoparticle Additives Extracted from an Agricultural Waste
(Springer Nature Link, 2022-02-06) Kapile, Fredrick; Bereczky, Akos; Ntalikwa, Justin; Kivevele, Thomas
Purpose This paper reports the results of experimental investigations on the influence of the addition of silica nanoparticles extracted from rice husk (an agricultural waste) on the major physicochemical properties of biodiesel derived from Adansonia digitata. Methods The physicochemical properties of the base fuel and the modified fuel formed by dispersing the nanoparticles by ultrasonic agitation were measured using ASTM and EN standard testing methods. The effects of manufactured silica nanoparticles on the fuel properties of Adansonia digitata methyl esters (ADME) that were produced by the transesterification process were investigated. Silica nanoparticles which were produced by the extraction process from rice husk were doped at the dosing levels of 400–1000 ppm. The produced silica was characterized by Thermogravimetry analysis (TGA), Barrett Emmett Teller (BET), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM), X-ray fluorescence (XRF), and X-ray diffractometer (XRD) methods. Results The silica was found to have BET specific surface area, Barret-Joyner Halenda (BJH) pore diameter, and pore volume of 502.24 m2/g, 19.3 nm, and 0.761 cm3/g respectively. At 400 ppm and 800 ppm silica dosages, the oxidation induction period increased significantly from 5.2 h to a high of 10.3 h. These findings showed that ADME's oxidation stability had improved significantly to satisfy the ASTM D6751 and EN 14,214 standard limits of > 3 h and > 8 h, respectively. The kinematic viscosity of ADME dropped as the additive content increased, from 4.62 mm2/s for pure biodiesel to 2.21 mm2/s for 400 ppm. Furthermore, it was discovered that the largest increase in viscosity occurs at high doses of 600–1000 ppm. The flash point increased linearly as the amount of nanoparticle addition was increased. Higher flash point temperatures are desirable for improving engine performance and for safety issues. Also, results showed that cetane number (CN) increases from 60 to 64 simultaneously at the dosing level between 400 and 800 ppm and dropped to 63 at dosing levels beyond 800 ppm. The blending of Silica/Alumina showed the best improvement of CN of ADME about 33.6%. Commercial additive (Al2O3) showed an improvement of oxidation stability up to a dosing level of 800 ppm. Fuel blending of (B100 + SiO2), (B20 + SiO2), and (B20 + Al2O3) was also performed and the results showed that the oxidation induction period (OIP) increases from 3.8 to 10.3 h for (B100 + SiO2) blending up to dosing level of 800 ppm but decreases at 1000 ppm. However, blending (B20 + SiO2) showed significant improvement on OIP from 47.2% to 64.16% at 0 to 1000 ppm respectively but blending of B20 and Al2O3 showed the best improvement about 71.7% at 1000 ppm but slightly decreased at 600 ppm (15.7 h). Kinematic viscosity showed slight improvement (decrease by 32.6%) at 400 ppm, but increases at 600 ppm (4.16 mm2/s) for B20 + SiO2 fuel blending. However, at higher dosing level decreases by 3.85% up to 1000 ppm. Dosing of Al2O3 additive on B20 fuel blend displayed the improvement decreasing by 36.9% at 600 ppm but at higher dosage (1000 ppm) increases to 5.2 mm2/s for Al2O3. Conclusion Generally, from this study it has been observed that rice husk nano-particle is considered as a potential fuel-borne catalyst than the commercial one to improve the fuel properties, owing to their enhanced surface area to volume ratio probably due to its 3-dimensional tetrahedral coordination and covalent nature of silicon atom
Comprehensive assessment of heat pump dryers for drying agricultural products
(Wiley Online Library, 2022-11-22) Loemba, Aldé; Kichonge, Baraka; Kivevele, Thomas
Fruits and vegetables are agricultural products that require preservation to enhance and protect shelf life, encapsulate natural flavour, and retain nutritional content. Globally, agricultural products are preserved by a range of means, the most prevalent of which is the heat pump dryer, which produces the best results even in unfavourable climatic conditions. Heat pump dryers come in different types and their performance varies depending on the type. This study aims to evaluate recently developed heat pump dryers based on key performance indicators, impacts on food colour and nutritional content, techno-economic, exergoeconomic, and environmental issues associated with the development of heat pump dryers, which are underrepresented in most of the existing heat pump dryers' reviews. This study also discusses mathematical drying kinetic models, and regulation or policy aspects related to the development of heat pump dryers. In the present study, the results on performance analysis indicate that heat pump dryers examined were effective in reducing drying time and obtaining high coefficients of performance ranging from 1.94 to 5.338 and specific moisture extraction rate ranging from 0.156 to 9.25 kg/kWh, as well as significantly reducing energy consumption by up to 80%. The nutritional composition and colour results show that heat pump dryers maintain the maximum nutrient content while also improving colour. The expansion valve has the lowest exergoeconomic factor of all heat pump dryer components, whereas the compressor has the highest cost of exergy destruction in general, according to the results of exergoeconomic analysis. Techno-economic analysis results demonstrated that most developed heat pump dryers have short payback periods ranging from 1.6 to 3.6 years. However, due to a lack of research in this field, the environmental implications of heat pump dryers are unknown. As per the findings of this study, future research in this field should focus on the design of simple and low-energy heat pump dryers, life cycle, techno-economic, and exergoeconomic assessments.
Cryptogamic Packed Biofilter as Potential Adsorbent for CO2, NH3, and H2S Impurities from Biogas
(Hindawi, 2020-07-07) Temba, Norbert W.; Kivevele, Thomas; Pogrebnaya, Tatiana
The presence of elevated concentrations of carbon dioxide, hydrogen sulfide, ammonia, and trace impurities in biogas affect its caloric value as well as causes corrosion and is extremely toxic. There are various methods in existence for removal of these impurities, but most are chemically based and expensive and are limited in use. In our work, cryptogams (moss) integrated with soil and biochar packed in a filter have been employed for simultaneous removal of CO2, H2S, and NH3, from biogas. Different soil types rich in metallic oxides at different masses of 100 g, 150 g, and 200 g with a fixed mass of moss and biochar were tested in an on-site experiment to determine the removal efficiency (RE) and sorption capacity (SC). The adsorption dynamics of the filters were investigated at two flow rates, 80 ml/min and 100 ml/min, by determining removal efficiency. For the contribution of each substrate, sorption capacity and breakthrough time were determined by considering 5 g of each substrate that made up the filter. The soils with a high content of extractable cations showed excellent adsorption capacity for H2S by about 20 g S/100 g, which was higher than other adsorbents tested. It was found that integrated biofilter made up of bed arrangement of the soil, biochar, and moss plant improved the quality of biogas with SC of 11 g S and RE of 93% for H2S, 72% for NH3, and 68% for CO2.
Demand-SideManagement of Solar Microgrid Operation: Effect of Time-of-Use Pricing and Incentives
(Hindawi, 2020-06-05) Philipo, Godiana Hagile; Jande, Yusufu; Kivevele, Thomas
Over 17% of the world’s population lack access to electricity, the majority being in rural areas of sub-Saharan Africa and South Asia. Microgrid technologies are a promising solution towards rural and remote area electrification; however, ever-increasing electricity demand remains a big challenge leading to pronounced power outages. Demand-side management is an indispensable tool towards addressing the challenges. is paper employs a mathematical model based on incentives and time-of-use rates to simulate daily power usage pattern of residential customers using data collected from an isolated village Ngurdoto solar microgrid, Arusha, Tanzania. Customer responsiveness on the increase in price was evaluated based on the concept of price elasticity of demand. Using two demand response strategies, namely, load shifting (LS) and scheduled load reduction (SLR), the results reveal that LS can achieve up to 4.87% energy-saving, 19.23% cost-saving, and about 31% and 19% peak reduction and power factor improvement, respectively. SLR method resulted in about 19% energy-saving, 49% cost-saving, and 24% power factor improvement. us, the results presented in this study may lead to a more efficient and stable system than the current state in developing countries’ utility
Design and Performance Analysis of Composite Airfoil Wind Turbine Blade
(University of Dar es Salaam, 2021) Mwanyika, Hegespo; Jande, Yusufu; Kivevele, Thomas
Small horizontal axis wind turbine rotors with composite airfoil rotor blades were designed and investigated in the present study in order to improve its performance in low wind speed and low Reynolds number (Re) conditions for standalone system. The geometrical and aerodynamic nature of a single airfoil small horizontal axis wind turbine blade curtails efficient energy harnessing of the rotor blade. The use of composite airfoil rotor blade improves energy production but imposes uncertainty in determining an optimal design angle of attack and the off design aerodynamic behaviour of the rotor. This research investigated the effects of two airfoils used at different sections in a composite blade and determined the blade’s optimal design angle of attack for maximum power generation. The wind turbine rotor blades were designed using blade element momentum (BEM) method and modelled by SolidWorks software. The SG6042 and SG6043 airfoils were used for the composite airfoil blades. Five wind turbines were designed with rotor blades of design angles of attack from 3° to 7°. The five wind turbine blades were simulated in computational fluid dynamics to determine the optimal design angle of attack. The composite airfoil wind turbine blade showed improved performance, whereas, the wind power generated ranged from 4966 W to 5258 W and rotor power coefficients ranged from 0.443 to 0.457. The blade with design angle of attack of 6° showed highest performance
Design and performance analysis of portable solar powered cooler for vaccine storage
(SCI, 2024-10-31) Marwa, Vicent; Kivevele, Thomas; Kichonge, Baraka; Selemani, Juma
The efficacy of vaccine storage is significantly impacted by temperature fluc- tuations within the cooler, often exacerbated by using phase change materials in existing cooler designs for remote areas. These materials can undergo uneven melting and phase separation, leading to temperature instability and vaccine potency loss. In response to this challenge, the present study intro- duces a novel design of a portable, locally‐made solar‐powered cooler opti- mized for longer storage periods. The cooler's performance in terms of tem- perature distribution, airflow dynamics, and the coefficient of performance (COP) is meticulously examined through computational fluid dynamics (CFD) simulations. The simulated results were validated using experimental data from the open literature, ensuring accuracy and reliability. The findings indicate that the developed cooler achieves significant improvements over traditional models. For instance, the current model reaches a temperature of +12°C in just 84 min, compared to 208 min, as reported in the literature results. Moreover, the current model reaches a temperature of −12°C in 195 min and it has energy efficient with a COP of 4.5. Statistical analysis further confirms the reliability of the simulation results, with root mean square and mean absolute percentage errors of 6.587 and 24.2%, respectively. Additionally, a comparative study of five insulative materials highlights polyurethane (Po) as the top performer, with a heat transfer performance of 14.3%, followed by feather fiber (Fe) (18.7%), fly ash (Fl) (19.8%), fiberglass (Fi) (21.9%), and coconut fiber (Co) (25.9%). Notably, net present value (NPV) of $689.336 and $448.01 was obtained for economic analysis of the current model over the existing model, showing the feasibility of the study. Hence, the cooler's effectiveness in storing vaccines in isolated regions exceeds that of conventional models, providing a hopeful solution to tackle vital challenges in vaccine distribution and preservation.
Development and Performance Evaluation of a Novel Solar Dryer Integrated with Thermal Energy Storage System for Drying of Agricultural Products
(American Chemical Society, 2023-11-14) Kivevele, Thomas; Kichonge, Baraka; Marwa, Janeth; Rulazi, Evordius
Passive solar dryers play a crucial role in reducing postharvest losses in fruits and vegetables, especially in regions like sub-Saharan Africa with low electrification rates and limited financial resources. However, the intermittent nature of solar energy presents a significant challenge for these dryers. Passive solar dryers integrated with thermal energy storage (TES) can reduce intermittence and improve the drying efficiency. Currently, phase change materials (PCMs) are popular heat storage materials in dryers, and paraffin wax dominates. The main problem with the use of PCMs is that it is necessary to closely constrain the temperature range of the process during charging and discharging. This can be a difficult condition to meet in simple solar dryers due to the variable availability of solar radiation. Instead, solid-phase materials, such as sand and rocks, are often used. Soapstone is one of the natural rocks with good thermal properties, but it has yet to be used as a TES material in solar dryers for drying agricultural products. Therefore, the main objective of the present study was to develop a novel solar dryer integrated with soapstone as a TES material and evaluate its performance. The proximate analysis to examine the quality of dried products using the developed technology was also carried out. The comparative experiments for the developed dryer were conducted in two modes: dryer with TES materials and without TES materials, and the results were compared with open sun drying (OSD) by drying 50 kg of fresh pineapple and carrot at different times. The drying times for pineapples in the dryer with TES, without TES, and OSD were 13, 24, and 52 h, respectively. However, the drying times for carrots in the dryer with TES, without TES, and OSD were 12, 23, and 50 h, respectively. Notably, the dryer integrated with TES materials could supply heat for around 3–4 h after sunset. The thermal efficiency of the dryer, collector efficiency, and storage efficiency of TES materials were calculated and found to be 45, 43, and 74.5%, respectively. Proximate analysis indicated that the dryer integrated with TES materials effectively maintained the quality of the dried products compared to OSD. Solar dryer integrated with soapstone showed great promise as sustainable and efficient solutions for reducing postharvest losses and enhancing food security in resource-constrained regions like sub-Saharan Africa.