Articles: Department of Physical Sciences

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A prototype parabolic trough solar concentrators for steam production
(Jomo Kenyatta University of Agriculture and Technology, 2012) Kawira, M.; Kinyua, R.; Kamau, J.N.
In this work, the potential for a solar-thermal concentrator to produce steam has been studied. Three parabolic trough solar concentrators (PTSCs) of dimensions: - aperture width of 1.2 m, Collector length of 5.8 m and aperture area of 6.95 m2 were investigated. The absorber pipe was a copper tube which carried water as the heat transfer fluid, were designed, fabricated, characterized and their efficiencies compared when closed and when open. The PTSCs´ were made of appropriate materials and were manually tracked. They were designed with principal focus at 0.4 m so that the receiver heat loss is minimized by covering the collectors with glass which was 0.0025 m in thickness. The concentration ratio of the solar concentrators was 128. The concentrator testing was carried out for each of the concentrators. The maximum temperature of steam obtained was 248.3oC while average temperature of steam was produced was 150oC. When closed their efficiencies were: Aluminium sheet reflector PTSC; 55.52 %, Car solar reflector PTSC; 54.65 % and Aluminium foil reflector PTSC; 51.29 %. The open solar concentrator efficiencies were 32.38 %, 34.45 % and 27.74 % respectively. The efficiency of car solar reflector when open was higher than for aluminium sheet since it was less prone to thermal degradation when exposed to weather elements. The results obtained show that production of power using the sun flux is a viable undertaking. The concentrators can be used to provide power to remote areas which are far away from the power transmission gridlines. This will make power readily available to the marginalized rural people. Improvement of the tracking system and optical efficiency can improve the efficiencies of the fabricated concentrator systems.
Cementing material from rice husk-broken bricks-spent bleaching earth-dried calcium carbide residue
(2012) Wachira, Jackson M.; Muthakia, Gerald K.; Thiong’o, Joseph K.
A cementious material, coded CSBR (Carbide residue Spent bleaching earth Broken bricks and Rice husks), was made from dried calcium carbide residue (DCCR) and an incinerated mix of rice husks (RH), broken bricks (BB) and spent bleaching earth (SBE). Another material, coded SBR (Spent bleaching earth Broken bricks and Rice husk ash), was made from mixing separately incinerated RH, SBE and ground BB in the same ash ratio as in CSBR. When CSBR was inter-ground with Ordinary Portland Cement (OPC), it showed a continued decrease in Ca(OH)2 in the hydrating cement as a function of curing time and replacement levels of the cement. Up to 45 % replacement of the OPC by CSBR produced a Portland pozzolana cement (PPC) material that passed the relevant Kenyan Standard. Incorporation of the CSBR in OPC reduces the resultant calcium hydroxide from hydrating Portland cement. The use of the waste materials in production of cementitious material would rid the environment of wastes and lead to production of low cost cementitious material.
Beneficiation of Iron in Thermal-Reduced Ilmenite by Magnetic Separation
(2013) Kariuki, Warui S.; Wachira, Jackson M.; Mutembei, Peterson K.; Waithaka, Peter N.
ncreasing demands for Iron in countries development, and lack of conventional reducing agents has resulted into sourcing of alternative ways of beneficiating the iron ore. This paper reports on the study that was done to concentrate low grade iron ores. Raw biomass / low grade iron ore mixed in the ratio of 1:10 in a reducing environment was heated in a controlled air condition to increase the magnetic susceptibility of iron in the ore. The magnetic portion of the resulting product was separated using a horse shoe-magnet. This resulted into concentrating the ore from 45.6% - 53.1 % to 76.3%- 82.2%. This gave an ore that could be fed to a blast furnace for extraction of iron.
Determination of Potassium Levels in Intensive Subsistence Agricultural Soils in Nyamira County, Kenya
(2013) Kenyanya, Omanga; Wachira, Jackson M.; Mbuvi, Harun
Assessment of potassium levels in agricultural soils of Nyamira County, Kenya was necessitated by the observed progressive drops in maize acreage yields over the years despite use of phosphorus and nitrogenous fertilizers. In the study, concentration levels of potassium and other soil fertility indices such as, organic carbon, cation exchange capacity, exchangeable cations, soil pH, available nitrogen, total and available phosphorus were determined. Five composite soil samples were collected at depths of between 0-30 cm from five farms that have consistently been under intensive cultivation. Fractionation of potassium was achieved by sequential extraction of soil sampleswith distilled water, ammonium acetate and nitric acid in that order. Concentration levels of potassium in the extracts were determined using a flame photometer. Potassium concentration levels obtained from the water soluble soil extracts were used to calculate thermodynamic parameters such as free energy of replacement, potassium activity ratio and ionic strength of the soil solution. The relationship between the adsorbed and equilibrium potassium concentration, quantity/intensity was determined by plotting Freundlich adsorption isotherms. The isotherm was used to determine the buffering capacity ofpotassium and the concentration levels of potassium adsorbed on un-specific sites in the soil. The suitability of the adsorption equation was determined by applying the least square regression analysis. From the study available potassium in the soils ranged from 57 to 70 mg/kg and had amean value of 60±5.54.2 mg/kg (ammonium acetate method). The water soluble potassium ranged from 1.8 to 2.2 mg/kg with a mean of 2.02±0.16 mg/kg. Nitric acid extracted potassium had a mean of 149.±2.306 mg/kg. The mean free energy of replacement, Δ𝐹𝐹, was found to be −3572±44.98 cal/mol indicating that the soils have low supplying power of potassium. The potassium buffering capacity of the soils was found to have a mean of 1.189±0.06 mg/kg. The amount of potassium adsorbed on un-specific sites of the soilshad a mean value of 6.993±2.378 L/kg. These findingsreveal the extent of potassium depletionin the soils of this region and will form a baseline for working acreage potassium doses required for remediation.
Effects of Zeolites X and Y on the Degradation of Malathion in Water
(2013) Ogunah, Joanne A.; Kowenje, Chrispin O.; Osewe, Elly T.; Lalah, Joseph O.; Jaoko, David A.; Koigi, Robert N.
The inclusion of both zeolites X and zeolite Y significantly affected the dissipation of malathion in water. In the fresh water, malathion degradation followed a pseudo-first order kinetics with concomitant half-life dropping from 8.76 hours in fresh water to 4.44 and 6.65 hours up on the introduction of faujasite X and Y, respectively. Zeolite X had higher degradation efficiency as compared to the Y type. In pure fresh water, Malathion mainly hydrolyzed to form malathion monocarboxylic and dicarboxylic acids as the only degradation products. However, in the presence of zeolites X and Y, in addition to the degradation products obtained in the fresh water, dimethyldithiophosphate was also formed. Notably, all the degradation products obtained are environmentally benign compared to the parent malathion. Eventually, both the adsorption on the zeolite framework and zeolite catalyzed degradation processes contributed to the overall dissipation behavior of the malathion and its degradation products
Anti-Bacterialactivities And Phytochemical Screening Of Extracts Of Different Parts Of Thalictrum Rhynchocarpum
(2013) Mayeku, Philip Wafula; Hassanali, Ahmed M.; Kiremire, Bernard T.; Odalo, Josiah O.; Hertweck, Christian
Parts of the plant Thalictrum rhyncocarpum are used in herbal medicine in Kenya to treat various infections. The aim of this study was to evaluate in-vitro anti-bacteria activities and phytochemical profiles of solvent extracts of the leaves, stem bark and root of Thalictrum rhyncocarpum against Bacillus subtilis-6633, Staphylococcus aures-SG 511, Escherichia coli SG 458, Pseudomonus aeruginosa-K799/61 and Mycobacterium vaccae-10670. Anti-bacterial activity tests were carried out using disc diffusion assay and tube dilution technique, and phytochemical screening was carried out through Thin Layer Chromatography. The crude extracts showed antibacterial effects on M. vaccae, P. aeruginosa and B. subtilis. M. vaccae was most sensitive, particularly to the methanol root extract. Phytochemical screening of the extracts suggested the presence of glycosides and alkaloids in the stem bark and root extracts, and flavonoids and triterpenes in the leaf extracts. The study showed interesting levels of activities of solvent extracts of different parts of T. rhyncocarpum against some of the bacteria tested (M. vaccae, P. aeruginosa and B. subtilis). The results provide some scientific rationale for the traditional use of the plant in Kenya to treat different microbial infections.
Phenolic and Monoterpenoid Mosquito Repellent Constituents of Headspace Vapors of Conyza newii
(2013-01) Mayeku, Philip Wafula; Sauda, Swaleh; Ahmed, Hassanali
The plant Conyza newii has been reported to posses, mosquito repellent and fumigant toxicity properties. In this study headspace vapors emitted by the plant were obtained by adsorption on porapak Q® through headspace trapping under field conditions in West Pokot (35oE, 1oN) and Kericho (35oE, 0o) and analyzed using Gas Chromatography-Mass Spectrometry and co-injection with authentic standards. Mosquito repellency bioassays of volatiles and their synthetic blend were carried out according to the World Health Organization protocol for evaluation of repellents. Five major compounds identified in the volatiles were trans-limonene oxide, cislimonene oxide, cis-dihyrocarvone, 4-methoxyphenol and 3-ethoxy-2-methyl phenol (2:2:2:2:1). Authentic standards of the compounds were bioassayed against Anopheles gambiae s.s and the three of them, trans-limonene oxide, cis-dihyrocarvone and 4-methoxyphenol exhibited repellency of RD50 = 9.2 × 10-5 mg cm,-2, 95% CL, RD50 = 5.4 × 10-4 mg cm,-2, 95% CL and RD50 = 6.7 × 10-4 mg cm,-2, 95% CL respectively.Synthetic blend of the three compounds in their natural ratio (1:1:1) exhibited higher repellency (6.2 × 10-5 mg cm-2) than the individual compounds and even the oil of the plant obtained through steam distillation.
Influence of alkaline earth metal cations; Ca2+, Sr2+ and Ba2+ on the structural and optical properties of MAl2O4: Eu2+, Nd3+ phosphors.
(2014) Wako, Ali Halake; Dejene, F. B.; Swart, H.C.
Eu2+ doped and Nd3+ co-doped MAl2O4:Eu2+, Nd3+ (M = Ca, Sr, and Ba) phosphors were prepared by a solution-combustion method. The obtained powders were investigated in terms of their phase composition, particle morphology and photoluminescence (PL) by X-Ray diffraction (XRD), Scanning Electron Microscope (SEM) and Ultraviolet-Visible Spectroscopy (UV-VIS) techniques respectively. XRD analysis depicts a monoclinic phase for CaAl2O4:Eu2+, Nd3+ and SrAl2O4:Eu2+, Nd3+ and a hexagonal structure for BaAl2O4:Eu2+, Nd3+ phosphor. SEM results showed generally agglomerated particles with non-uniform shapes and sizes with irregular network structures having lots of voids and pores. PL excitation revealed broadband spectra with peaks corresponding to the crystal field splitting of the Eu2+ d-orbital. The emission spectra were also broadband with peaks at 447 nm for CaAl2O4:Eu2+, Nd3+, at 507 nm for SrAl2O4:Eu2+, Nd3+ and at 497 nm for BaAl2O4:Eu2+, Nd3+ due to the 4f65d1-4f7 emission of Eu2+. Sharp emission lines were observed arising from the f-f transitions of the Eu3+ ions. The differences in emissions from the three phosphors arise from the crystal field splitting of the 5d electron shell due to the changes in the crystalline environment of the Eu2+ ions caused by the substitution of the divalent alkaline earth metal cations with different ionic sizes in the MAl2O4 host lattice. UV-VIS spectra showed absorption edges at 330, 342 and 340 nm in agreement with the observed PL excitation peaks. The luminescence decay characteristics showed that these materials possess persistent luminescence whereby BaAl2O4: Eu2+; Nd3+ gave a longer afterglow as compared to the other two phosphors.
Diffusivity of Chloride Ion in Mortar Cubes Made Using Ordinary Portland and Portland Pozzolana Cements
(2014) Wachira, Jackson M.; Mutitu, D.K.; Karanja, J.K.
Cement is subject to degradation by aggressive media. This study investigated chloride diffusivity in mortar made from Kenyan cements which included three brands of Ordinary Portland Cements (OPC) and three brands of Portland Pozzolana Cements (PPC) sampled within Kenyan markets. The test cements were used to make mortar prisms at different water/cement ratios. Compressive strength was determined at the 7th and 28th day of curing. The mortars were subjected to laboratory prepared 3.5 % by mass of sodium chloride solution under accelerated ion migration test method for a period of thirty six hours using a 12V DC power source. The compressive strength before subjecting to aggressive media was found to increase with curing duration as well as on decreasing w/c. Compressive strength at all w/c ratios was found to increase after the aggressive media ingress. After subjecting the mortar cubes to Cl- media, they were sliced and the cores from the slices analyzed for Cl- content. From these results, Dapp was approximated from solutions to Fick’s 2nd law using the error function. PPC at all w/c ratios showed lower Dapp than OPC. Cl- ingress for both cement types across all cement categories, increased with the increase in w/c ratio.
Diffusivity of Sulphate Ion in Selected Ordinary Portland and Portland Pozzolana Cements Mortar
(Kenya Chemical Society, 2014) Wachira, Jackson M.; Mutitu, D.K.; Karanja, J.K.
Cement is subject to degradation by aggressive media. This study investigated sulphate diffusivity in mortar made from selected Kenyan cements which included three brands of Ordinary Portland Cements (OPC) and three brands of Portland Pozzolana Cements (PPC) sampled within Kenyan markets. The test cements were used to make mortar prisms at different water/cement ratios. Compressive strength was determined at the 7th and 28th day of curing. The mortars were subjected to laboratory prepared 3.5 % by mass of sodium sulphate solution under accelerated ion migration test method for a period of thirty six hours using a 12V DC power source. The compressive strength before subjecting to aggressive media was found to increase with curing duration as well as on decreasing w/c. Compressive strength at all w/c ratios was found to increase after the aggressive media ingress, however, prolonged exposure or exposure to high levels of sulphate is known to be deleterious to cement/concrete. After subjecting the mortar cubes to SO4 2- media, they were sliced and the cores from the slices analyzed for SO4 2- content. From these results, apparent diffusion coefficient, Dapp, was approximated from solutions to Fick’s 2nd law using the error function. PPC at all w/c ratios showed lower Dapp than OPC. SO4 2- ingress for both cement types across all cement categories, increased with the increase in w/c ratio. Chemical analysis results showed that the Kenyan Cement meet the minimum chemical and phase requirements.
Thalictramine, A new alkaloid from Thalictrum rhyncocarpum (Dill & Rich) and its anti-bacterial activity
(2014) Mayeku, Philip Wafula; Odalo, J. O.; Hassanali, A.; Kiremire, B. T.; Hertweck, C.
Thalictrum rhyncocarpum, a creeping plant with fern-like leaves, is used in herbal medicine to treat various infections in parts of Africa. Previously, we reported In-vitro anti-bacterial activity of different parts (root, stem bark and leaves) of the plant. In this study, bioassay-guided chromatography of an active fraction of ethanol extract of the plant against Staphylococcus aures-SG 511, Pseudomonus aeruginosa-K799/61 and Mycobacterium vaccae- 10670 (using tube dilution method) was undertaken. Two bioactive constituents were isolated from an active fraction of the extract and characterized using spectrometric methods as thalictramine (1) and berberine. In addition, 6-O-β-D-glucopyranosyl-D-glucose (gentiobiose) was also isolated from the same fraction. The antibacterial activities of the active fraction, thalictramine and berberine against P. aeruginosa and M. vaccae were higher than that of ciprofloxacin.
Chemical composition and mosquito repellency of essential oil of Conyza newii propagated in different geographical locations of Kenya
(John Wiley & Sons, 2014) Mayeku, Philip Wafula; Omollo, N. I.; Odalo, O. J.; Ahmed, Hassanali
Previously, essential oil of Conyza newii (Asterale: Asteracea, Oliv. & Hiern) growing in the northern part of West Pokot (35◦E, 1◦N) of Kenya was shown to be highly repellent [RD50 =8.9×10−5 mg/cm2, 95% confidence interval (CL)] to Anopheles gambiae s.s. Fumigant toxicity of the oil to the mosquito was also demonstrated. The major constituents of the oil were found to be monoterpenoids, including (S )-(-)-perillyl alcohol, (S )-(-)-perillaldehyde, geraniol, (R)-(+)-limonene, trans-β-ocimene and 1,8-cineol. In this study, the chemical composition and repellency of essential oils of the plant seedlings collected from West Pokot (35◦E, 1◦N) and propagated in seven different geographical regions of Kenya [West Pokot (35◦E, 1◦N), Kilome (37◦E, 1◦S), Naivasha (36◦E, 0◦), Webuye (34◦E, 1◦N), Nyakach (34◦E, 0◦), Kericho (35◦E, 0◦) and Nairobi (36◦E, 1◦S)] were compared. There were significant variations (P <0.01, 95% CL) in the relative proportions of the six constituents and this was reflected in the repellency of the essential oils (P <0.01, 95% CL). Higher repellency of the oil was associated with greater proportions of (S )-(-) perillyl alcohol, (S )-(-)-perillaldehyde and geraniol, and lower repellency was associated with an increased proportion of (R)-(+)-limonene. The results suggest significant epigenetic (chemotypic) variations in the repellency and composition of C. newii essential oils growing in different regions of Kenya.
Performance of Potential Pozzolanic Cement in Chloride media
(2014-04) Marangu, J.M.; Wachira, Jackson M.; wa- Thiong‟o, J.K.
The paper presents finding of the pozzolanic activity of calcined clays from selected regions of Embu County – Kenya. The results are also presented for the compressive strength development and Chloride ingress resistance of the blend of the calcined clays with Ordinary Portland Cement (OPC), vis a vis commercial OPC and Portland Pozzolana cement (PPC). The objective of the study was to investigate the viability of using locally available materials to make affordable cementitious materials. Sampled clays were activated at different temperatures and time and blended with OPC at different replacement levels. The blends were subjected to accelerated chloride ingress. The blended cement and commercial PPC showed lower chloride ingress, in terms of apparent diffusion coefficients, compared to OPC with the blended cement exhibiting least chloride ingress
Roles of doping ions in afterglow properties of blue CaAl2O4:Eu2+,Nd3+ phosphors
(2014-04) Wako, Ali Halake; Dejene, B. F.; Swart, H.C.
Eu2+ doped and Nd3+ co-doped calcium aluminate (CaAl2O4:Eu2+,Nd3+) phosphor was prepared by a urea-nitrate solution combustion method at furnace temperatures as low as 500 °C. The produced CaAl2O4:Eu2+,Nd3+ powder was investigated in terms of phase composition, morphology and luminescence by X-Ray diffraction (XRD), Scanning Electron Microscope (SEM), Fourier Transform Infra Red spectroscopy (FTIR) and Photoluminescence (PL) techniques respectively. XRD analysis depicts a dominant monoclinic phase that indicates no change in the crystalline structure of the phosphor with varying concentration of Eu2+ and Nd3+. SEM results show agglomerates with non-uniform shapes and sizes with a number of irregular network structures having lots of voids and pores. The Energy Dispersive X-ray Spectroscopy (EDS) and (FTIR) spectra confirm the expected chemical components of the phosphor. PL measurements indicated one broadband excitation spectra from 200 to 300 nm centered around 240 nm corresponding to the crystal field splitting of the Eu2+ d-orbital and an emission spectrum in the blue region with a maximum on 440 nm. This is a strong indication that there was dominantly one luminescence center, Eu2+ which represents emission from transitions between the 4f7 ground state and the 4f6–5d1 excited state configuration. High concentrations of Eu2+ and Nd3+ generally reduce both intensity and lifetime of the phosphor powders. The optimized content of Eu2+ is 1 mol% and for Nd3+ is 1 mol% for the obtained phosphors with excellent optical properties. The phosphor also emits visible light at around 587 and 616 nm. Such emissions can be ascribed to the 5D0–7F1 and 5D0–7F2 intrinsic transition of Eu3+ respectively. The decay characteristics exhibit a significant rise in initial intensity with increasing Eu2+ doping concentration while the decay time increased with Nd3+ co-doping. The observed afterglow can be ascribed to the generation of suitable traps due to the presence of the Nd3+ ions.
Properties of blue emitting CaAl2O4:Eu2+, Nd3+ phosphor by optimizing the amount of flux and fuel
(Elsevier, 2014-04) Wako, Ali Halake; Dejene, B. F.; Swart, H.C.
Long afterglow CaAl2O4:0.03Eu2+, 0.03Nd3+ phosphor was prepared by solution-combustion synthesis. The active role of boric acid (H3BO3) as a flux in enhancing the Eu2+ photoluminescence and the effect of a varied amount of urea (CO (NH2)2) as a fuel on the morphological, structural and photoluminescent (PL) properties of the CaAl2O4:0.03Eu2+, 0.03Nd3+ systems were investigated. The results of X-ray diffraction, scanning electron microscopy, and PL spectra revealed the influence of the dosage of urea and hence the heated process on the crystallinity, morphology, and luminescence of the phosphor. The addition of H3BO3 favoured the formation of a monoclinic CaAl2O4 phase while the variation of the amount of CO (NH2)2 showed mixed phases although still predominantly monoclinic. Both H3BO3 and CO(NH2)2 to some extent influence the luminescence intensity of the obtained phosphor but unlike the case of CO(NH2)2, the presence of H3BO3 did not evidently shift the emission peak due to no obvious change in the energy level difference of the 4f–5d levels. The broad blue emissions consisting mainly of symmetrical bands having maxima between 440 and 445 nm originate from the energy transitions between the ground state (4f7) and the excited state (4f65d1) of the Eu2+ ions while the narrow emissions in the red region (600–630 nm) arise from the 5D0→7F2 transitions of the remnant unreduced Eu3+ions. Higher concentrations of H3BO3 (0.228 mol and 0.285 mol) reduce both intensity and lifetime of the phosphor. The optimized content of H3BO3 was 0.171 mol for the obtained phosphor with the best optical properties.
Effects of Temperature on Ilmenite During Concentration of Iron in Laterites Using Charcoal and Separation using Magnetic Separation
(IJSET, 2014-06) Mutembei, Peterson K.; Muriithi, Naftali T.; Njoroge, Peter W.; Muthengia, Jackson W.
Effect of temperature on ilmenite minerals found in laterites has been investigated. It was found that during reduction of iron minerals in laterites to magnetite using charcoal at temperatures of about 500-700oC, ilmenite minerals were not reduced. However when temperatures were raised to about 850-1200oC using acetylene flame, ilmenite minerals were reduce to rutile and iron. Currently, the mineral ilmenite (FeTiO3) is responsible for about 85% of the world’s titanium requirements. The methods used to upgrade ilmenite are high temperature reduction and direct acid-leaching methods. Extraction of titanium from ores containing iron still remains a challenge. Laterite soils are currently being used mainly for surfacing roads. It has been proven that laterites can be a potential source of iron. This study set out to investigate whether the heat treatment that converts hematite in laterite to magnetite is adequate to decompose ilmenite. Laterite samples were concentrated by heating charcoal/laterite mixtures in the ratios of 1:10 by mass in a slow current of air and in the temperature range of 500-700oC. Elemental analysis was carried out on both the raw laterites and the concentrated samples using Atomic Absorption Spectroscopy (AAS). The minerals present were determined using a CubiX3 Powder Diffractometer from PANanalytical Company. The results of elemental analysis showed that, raw laterites contain 28-31% iron and 1-2% titanium (IV) oxide depending on source. After the concentration, the level of iron in the heat-treated sample had increased to 55-64%, and titanium oxide increased to 3-5%. The X-ray diffraction data confirmed that, iron in the raw laterites was present predominantly as the minerals goethite, hematite and ilmenite since these are known to have diffraction peaks at angles 2θ= 21.51˚, 2θ= 54.11˚ and 2θ=32.7, respectively. After reduction (at 500-700oC), goethite and hematite peaks disappeared in the heat-treated magnet-separated samples and instead, a strong peak was observed at angle 2θ= 36˚and 2θ=32.7, which represents peaks for magnetite and ilmenite respectively. From the observation, this temperature (500-700oC), had no significant effect to ilmenite hence, was collected together with magnetite by a magnet. When reduction was done at temperature range of 850-1200oC, the ilmenite peak disappeared and a peak at 2θ=27.4, 2θ= 36˚and 2θ=44.6 appeared, attributed to rutile, magnetite and metallic iron respectively. The XRD of the tailing (non-magnetic waste) show distinct peak at 2θ=27.4 and 2θ=54.3 attributed by rutile. This shows that ilmenite minerals are reduced at high temperatures to rutile (non-magnetic) and metal iron (magnetic).
Investigating a Prototype Heat Exchanger for Steam Storage
(2014-07) Kawira, M.K.; Kinyua, R.; Kamau, J.N.
A coiled tube single pass counter flow heat exchanger was designed and fabricated using locally available materials and its capacity to transmit heat to water to make steam was tested. The heat exchanger was part of components used in solar thermal power production using a parabolic trough solar concentrator. The design of the heat exchanger storage system was done using Auto CAD 2010 software. Higher temperatures of steam were realized when the heat exchanger was used as a steam storage system. The heat transfer fluids used were locally available and they were water, sunflower oil, Rina oil, used engine oil, unused engine oil, 2 M sodium chloride salt solution, 4 M sodium chloride salt solution and 6 M sodium chloride solution. For each of the heat transfer fluids, heat exchanger operating points were obtained and it was operated between 1 Nm-2 to 1.0 Nm-2 of pressure. In the study the number of heat transfer units of the heat exchanger obtained was 0.61 and the thermal efficiency was found as 0.91. The average rates of heat transfer were 68.4 J for 6M sodium chloride solution, 62.8 J for 4 M sodium chloride solution, 57.9 J for 2M sodium chloride solution, 55.4 J for water, 49.1 J for sunflower oil, 46.3 J for Rina vegetable oil, 59.7 J for unused engine oil and 54.1 J for used engine oil. Thermal conductivity of the salt solutions was better than for other heat transfer fluids although they were more corrosive on the system. Thermal efficiencies of the heat transfer fluids were 6 M sodium chloride solution; 0.89, for 4 M sodium chloride solution ; 0.84, for 2 M sodium chloride solution ; 0.80, water ; 0.78, sunflower; 0.69, Rina oil ; 0.66, unused engine oil ; 0.75 and used engine oil; 0.71. Storage of solar thermal energy will address the problem of low solar density and its variability. The heat exchanger storage system achieved a thermal capacity of 3.26 kJ at a maximum temperature of 249.4 oC and at a pressure of 7.2 Nm-2. The use of heat exchangers in solar thermal storage will increase the overall efficiency of total system
Magnetic Concentration of Iron in Lateritic Soils from Kamahuha, Murang’a County, in Kenya using Carbon Monoxide Generated In-Situ
(IJSET, 2014-08) Njoroge, P. W.; Mutembei, Peterson K.; Wachira, Jackson M.; Wanjau, R.
Chemical and Mineral Analyses of laterites from selected sites in Kamahuha area of Murang’a County, in the Republic of Kenya, have been carried out with particular interest in the levels of iron and the type of minerals the iron is present in. A laterite/charcoal mixture was heated in the temperature range 500-700OC as a slow current of air was passed through the hot mixture, the material cooled and the iron-containing mineral picked with a permanent magnet. Elemental Analysis, which was done on both the raw and concentrated samples was carried out using, Atomic Absorption Spectroscopy (AAS). The Analyses also showed that whereas the level of iron in the raw laterites was in the range 28-35, in the magnet –separated product, the level had increased to 55-62% depending on several factors such as how efficiently the laterite-charcoal mixture had been mixed and the length of time of heating.The nature of the minerals present was determined using a Brucker D2 PhaserDiffractometer. In the raw laterites, iron was present as the minerals goethite, FeO.OH and haematite, Fe2O3. These minerals have diffraction peaks at angles 2θ=21.51˚ and 2θ = 54.11, respectively. On the other hand, iron in the magnetpicked product was present predominantly as the mineral magnetite, Fe3O4, as shown by presence of a characteristic peak at 2θ = 36˚. The results of this study show that iron in laterites can be concentrated by magnetic separation after passing compressed air over hot charcoal laterite mixture.
A Prototype Steam Storage System for Power Production
(2014-08-01) Kawira, M.; Kinyua, R.; Kamau, J.N.
Use of solar energy on a large scale is mainly limited to the sun duration hours, weather conditions and adequate solar thermal storage technology. A means of addressing this problem using local materials is provided. A prototype pressure storage system was designed using auto cad 2010 and fabricated using locally available materials. The steam storage system was tested using ASME 2000b guidelines for boiler and pressure vessels at a small scale. The maximum continuous rating for the storage system was 60 kg maximum instantaneous demand 40 kg , storage capacity 50 kg and mean off peak load of 100 W was realized. The maximum test temperatures of operation obtained using seamless galvanized iron pipe was 264.7 o C and 140 o C using polypropylene pipes. The steam storage system operated between 1.0 Pa and 1.0 Pa. Its charging duration was twenty minutes and would discharge at the rate of 50 l continuously after full charge with solar irradiance between 800 W/ and 1020 W/ . The length of complete discharge for the heat transfer fluids was found to range between 4.4 hours. and 6.9 hours. The power output for the heat transfer fluids were in the range of 251.8 W and 486.9W. The steam storage system was found to have an efficiency of 93.5 % and a thermal capacity of 4.54 k J. This system presents a means of storing solar energy in form of steam during low energy demand and its conversion to power during high peak demand twenty four hours a day depending on the size of the storage and application and hence addressing the problem of variability and low density of solar energy.
Combustion synthesis, characterization and luminescence properties of barium aluminate phosphor
(Elsevier, 2014-09) Wako, Ali Halake; Dejene, F. B.; Swart, H.C.
The blue-green emitting Eu2+ and Nd3+ doped polycrystalline barium aluminate (BaAl2O4:Eu2+,Nd3+) phosphor, was prepared by a solution-combustion method at 500 °C without a post-annealing process. The characteristic variation in the structural and luminescence properties of the as-prepared samples was evaluated with regards to a change in the Ba/Al molar ratio from 0.1:1 to 1.4:1. The morphologies and the phase structures of the products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), while the optical properties were investigated using ultra-violet (UV) and photoluminescence (PL) spectroscopy, respectively. The XRD and TEM results revealed that the average crystallite size of the BaAl2O4:Eu2+,Nd3+ phosphor was about 70 nm. The broad-band UV-excited luminescence of the phosphors was observed at λmax=500 nm due to transitions from the 4f65d1 to the 4f7 configuration of the Eu2+ ion. The PL results indicated that the main peaks in the emission and excitation spectrum of phosphor particles slightly shifted to the short wavelength due to the changes in the crystal field due to the structure changes caused by the variation in the quantity of the Ba ions in the host lattice.

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