Household cooking fuels and technologies in developing economies

A major energy challenge of the 21^st century is the health and welfare of 2.7 billion people worldwide, who currently rely on burning biomass in traditional household cooking systems. This Special Issue on Clean Cooking Fuels and Technologies in Developing Economies builds upon an IAEE workshop on this subject, held in Istanbul in 2008 ( Foell et al., 2008). It includes several papers from that workshop plus papers commissioned afterwards. The major themes of that workshop and this Special Issue are:     

Performance of Counterflow Microchannel Heat Exchangers Subjected to External Heat Transfer

This article analyzes the effect of external heat transfer on the thermal performance of counterflow microchannel heat exchangers. Equations for predicting the axial temperature and the effectiveness of both fluids as well as the heat transferred between the fluids, while operating under external heating or cooling conditions, are provided in this article. External heating may decrease and increase the effectiveness of the hot and cold fluids, respectively. External cooling may improve and degrade the effectiveness of the hot and cold fluids, respectively. For unbalanced flows, the thermal performance of the microchannel heat exchanger subjected to external heat transfer depends on the fluid with the lowest heat capacity. At a particular number of transfer units (NTU), the effectiveness of both the fluids increased with decrease in heat capacity ratio when the hot fluid had the lowest heat capacity. When the cold fluid had the lowest heat capacity, the effectiveness of both fluids increased with decrease in heat capacity ratio at low values of NTU but at high values of NTU the effectiveness increased with increase in heat capacity ratio. A term called the “performance factor” has been introduced in this article to assess the relative change in effectiveness due to external heat transfer.     

A novel approach for computing tertiary current distributions based on simplifying assumptions

A novel yet efficient method for the computation of simplified tertiary current density and surface concentration distributions in electrochemical processes is presented. The method is rooted in the important physiochemical property that the activation potential is constant and uniform for given electrode material during the electrolysis. The technique is attractive because it involves a single iterative procedure against the conventional doubly iterative procedure. The initial assumption of current distribution along the electrode is also not necessary, as it involves only an assumption of a suitable power series to solve steady state laminar convective diffusion. Accordingly the method is relevant only for electrodes of constant activation polarization, but this holds good for situations where the electrode configurations are such that the primary current density distribution is almost uniform and for situations where the Wagner number is high. To illustrate the utility of the technique the procedure is applied to some realistic problems encountered in electrochemical engineering such as the current distribution either in plane-parallel plate electrode with electrolyte flowing between them or a moving electrode with the electrolyte stationary.     

Functional expression of three isoforms of human nitric oxide synthase in baculovirus-infected insect cells

Complementary DNAs encoding three human isoforms (neuronal, inducible, and endothelial) of nitric oxide synthase were cloned into the baculovirus expression vector pVL1392/1393. Transfection of Sf-9 insect cells with the recombinant baculovirus resulted in the expression of high levels of nitric oxide synthases. The expressed proteins of neuronal and inducible nitric oxide synthase were predominantly soluble, whereas the endothelial enzyme was for the most part, particulate. Recombinant enzymes were purified with 2',5'-ADP Sepharose affinity chromatography. The effects of reference enzymatic inhibitors (NG-methyl-L-arginine, NG-nitro-L-arginine and N-iminoethyl-L-ornithine) on recombinant expressed proteins were not significantly different from native nitric oxide synthase enzyme preparations. L-aminoguanidine was found to be much less potent in inhibiting recombinant or native human inducible nitric oxide synthase compared to the murine isoform. These findings indicate previously unappreciated interspecies differences in the action of nitric oxide synthase enzymatic inhibitors. The functional expression of human nitric oxide synthase isoforms in a heterologous expression system allowed screening of novel inhibitors. Studies indicated that S-ethylisothiourea and 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine were potent novel inhibitors of human nitric oxide synthases.     

MODELING OF ETHANOL BIOPRODUCTION IN THREE-PHASE FLUIDIZED BED REACTORS

A time dependent and one-dimensional model is developed to analyze the performance of three-phase fluidized reactors and is applied to the fermentation of glucose to ethanol. The reactor model takes into consideration the presence of three different phases; the yeast (solid) which is continuously fluidized by the liquid stream, the gas bubbles which greatly enhance mixing and the wake phase which follows the tracks of the gas bubbles. The reactor performance is analyzed as a function of major operating conditions. The analysis includes variations in dispersion of glucose and yeast inside the reactor, the concentration of glucose in feed, and of the yeast mass inside the reactor, reaction temperature, velocities of gas and liquid feeds, and reactor aspect ratio. Computed glucose conversion is presented as a function of reactor length and time. The results indicate that high glucose conversions can be obtained at high gas velocities, low liquid flow rates, large aspect ratios, high yeast concentration, and an optimum operating temperature of 36°C,     

Fe2O3/TUD-1: an efficient catalysts for Friedel–Crafts alkylation of aromatics

Three-dimensional mesoporous (Fe-TUD-1) catalysts with different Si/Fe ratios (100, 50, 20 and 10) are prepared using triethanolamine as template. Physicochemical and textural measurements by XRD, elemental analysis, N₂ adsorption, UV–Vis spectroscopy and HR-TEM imaging indicate the formation of pure solid mesoporous materials and the presence of Fe₂O₃ nanoparticles in the prepared Fe-TUD-1 samples. The catalytic performance of Fe-TUD-1 catalysts is tested in Friedel–Crafts alkylations of single-ring aromatic compounds [e.g. toluene (T), ethyl benzene (EB) and cumene (C)] by benzyl alcohol (BnOH). Dispersion of Fe(III) in the mesoporous matrix of TUD-1 enhanced the catalytic activity of Fe-TUD-1 in the alkylation of aromatic compounds compared to pure Fe₂O₃ and TUD-1 catalysts. The catalytic activity further increases by the decreasing of Si/Fe ratio. Sample loaded with Si/Fe ratio = 10 (Fe-10) showed almost complete conversion of BnOH in a relatively very short reaction time (<30 min) with 95 % selectivity. The catalytic performance of Fe-TUD-1 was superior to other metal-containing TUD-1 (e.g. Ga, Sn, and Ti) catalysts, or other Fe-containing catalysts (e.g. Fe-MCM-41, ZSM-5 and Fe-HMS). Alkylation of C is the fastest among the three aromatic substrates investigated (at temperatures very close to their boiling points) due to the largest inductive effect by the isopropyl group compared to the methyl group of T and the ethyl group in EB. Dibenzyl ether is formed as a byproduct only in the early times of the reaction and proved to act as alkylating agent after being hydrolyzed backwards to reform BnOH. Leaching experiments show the Fe-TUD-1 materials are very stable and can be reused as alkylation catalyst.     

Tamarind Fruit Fiber and Glass Fiber Reinforced Polyester Composites

Polyester-based hybrid composites were developed by combining the tamarind fruit (Tf) and glass fibers into a polyester matrix. Hardness, impact strength, frictional coefficient, and chemical resistance of hybrid composites with and without alkali treatments were studied. Variation of the aforementioned mechanical properties and chemical resistance was studied with different fiber lengths, such as 1, 2, and 3 cm. A 9 vol% of the tamarind and glass fibers was reinforced into the polyester matrix. The aforementioned mechanical properties were optimally improved at 2-cm fiber length when compared with 1- and 3-cm fiber lengths. Chemical resistance was also significantly improved for all chemicals except toluene. A 3°C rise in decomposition temperature while a 2°C rise in glass transition temperature was observed from TGA and DSC micrograms, respectively.     

Effect of heat-treatment on the electrical and dielectric properties of a TiO2-containing lithia–calcia–silica glass and glass ceramics

The glass 65 SiO₂, 20 CaO, 15 Li₂O (mol%) containing 4 g TiO₂/100 g glass was prepared. Samples of this glass were heat treated at temperatures pre-determined by DTA to produce crystalline samples which were characterized by IR, XRD and SEM. The dielectric constant (?′), dielectric loss (?″) and conductivity σ_ac over a wide range of frequency and temperatures were measured. Optical absorption and values of the absorption edge were also determined for the transparent samples. Li–calcium silicate was found to crystallize at 964 °C as the main phase with lithium disilicate and quartz as minor phases. An enhancement in conductivity of about 1–3 orders of magnitude was obtained in the heat treated samples as compared to parent glass. Conduction takes place through an electronic mechanism in the low temperature region. In crystalline samples, the electronic conduction is extended to high temperature regions. Crystallized samples show high ?′ values, particularly at low frequencies. The values of (?′) reached 60–300 at 300 °C. The capacitance results indicated that these materials can be used in capacitors. Dielectric loss bands appeared in the range 0.32–5 MHz and the conduction relaxation times were calculated.     

Correlating the phenotypic and molecular diversity in Jatropha curcas L.

Thirty four Jatropha germplasm accessions, selected based on unique phenotypic traits from 180 accessions collected from diverse geographical regions were subjected to field evaluation and molecular analysis. The field evaluation using eight quantitative traits showed significant variation among the germplasm. The molecular analysis using 56 RAPD and 40 ISSR primers resulted in 7 and 8 clusters, respectively. The accession IC541633 from Bastar (Chattisgarh) emerged as the most diverse accession. An attempt has been made to correlate the clustering based on molecular data with the quantitative traits. There was partial correlation between the quantitative traits and molecular data. Interestingly, the diverse accessions according to molecular diversity were characterized by unique phenotypes. Time of flowering, inflorescence type and number, leaf colour and texture were the traits contributing to variation. These traits may be used in identification of diverse accessions during germplasm exploration surveys or short listing of accessions for crossing in Jatropha improvement programmes.