Solar energy harvesting and self-cleaning of surfaces by an impacting water droplet

The self-cleaning of surfaces via impacting water droplets is examined pertinent to solar energy applications. The mechanism of spreading and retraction of the impacting droplet onto the dust and cleaned hydrophobic surfaces is considered in the analysis. The spreading factor of the impacting droplet is formulated incorporating the energy balance on the hydrophobic surface. High-speed photography is used to monitor the impacting droplet behavior. The functionalized silica particles coating is introduced towards generating hydrophobic wetting state on the glass surfaces. Environmental dust particles are characterized prior to self-cleaning impacting tests. It is found that spreading rate predicted for the impacting droplet agrees well with that obtained from the experiments. The droplet Weber number incorporated in the experiments does not result in droplet breaking on the surface upon impacting. The dusts are dissimilar in shapes and consist of several elements. Impacting droplet gives rise to cloaking of the dust on the surface during spreading and retraction. Almost all the dusts are removed from the surface through the impacting droplets; however, few dust residues are left on the impacting surface, which cover only 0.03% of the total surface area. Hence, we have demonstrated that self-cleaning of a surface can be achieved by an impacting droplet for renewable energy applications.     

Numerical investigation of laminar forced convection of water upwards in a narrow annulus at supercritical pressure

In the present work, convection heat transfer of water at supercritical pressure in a narrow annulus at low Reynolds numbers (less than 1500) has been investigated numerically. The continuity, momentum and energy equations have been solved simultaneously using computational fluid dynamics techniques with the inlet Reynolds number ranging from 250 to 1000, Grashof number from 2.5 × 10⁵ to 1 × 10⁶ and the inlet fluid temperature from 360 °C to 380 °C. In all of the case studies, a sub-cooled water flow at supercritical pressure (25 MPa) and a temperature close to the pseudo-critical point enters the annular channel with constant heat flux at inner wall surface and insulated at outer wall. To calculate the velocity and temperature distributions of the flow, discretized form of the governing equations in the cylindrical coordinate system are obtained by the finite volume method and solved by the SIMPLE algorithm. It has been shown that the effect of buoyancy is strong and causes extensive increase in velocity near the inner wall, and consequently an increase in the convective heat transfer, which is desirable. Besides, the effects of inlet Reynolds number, Grashof number and inlet temperature on the velocity distribution and also on the heat transfer have been investigated.     

Two stage biodiesel and hydrogen production from molasses by oleaginous fungi and Clostridium acetobutylicum ATCC 824

In the present study biodiesel was produced by various fungal species isolated from Egypt using sugarcane molasses as substrate. In the first stage 6 oleaginous fungi, namely, Alternaria alternata, Cladosporium cladosporioides, Epicoccum nigrum, Fusarium oxysporum, Aspergillus parasiticus and Emericella nidulans var. lata were used for lipid production. Subsequent to fungal cultivation on sugarcane molasses the cultures were filtered and biodiesel was prepared by direct esterification of dry fungal biomass. Methyl esters of palmitic, stearic, linoleic and elaidic represented the major components while palmitoleic represented a minor component of biodiesel produced from tested oleaginous fungi. In the second stage, the spent medium of fungal culture was used as the fermentation medium for hydrogen production by Clostridium acetobutylicum ATCC 824. The maximum total H₂ yield was obtained with the spent medium of E. nigrum and A. alternata. The results presented in this study suggest a possibility of interlinking the biodiesel production technology by fungi with hydrogen production by C. acetobutylicum ATCC 824 to exploit the residual sugars in the spent media and therefore increase the economic feasibility of the biofuel production from molasses.     

The temperature dependence of the spectral and efficiency behavior of Si solar cell under low concentrated solar radiation

Relative spectral response of monocrystalline silicon solar cell is measured at different cell temperatures. At room temperature, the spectral response is found to have its maximum peak in the infrared (IR) range (800–1100 nm). By increasing the cell temperature, modification in the shape of the spectral response is observed and a shift of the peak towards the IR part of the spectrum is found. This behavior is of special importance that the temperature of highly illuminated thin film coated solar cells will be elevated. Other cell parameters as maximum power, fill factor, and cell efficiency are also studied at five illumination levels, viz., 1154, 1329, 1740, 2812, and 4010 W/m² and temperature ranging from −3 to 90°C.     

Numerical and experimental study of free convection through a horizontal open‐ended axisymmetric cavity

This paper summarizes a numerical and experimental investigation of free convective heat transfer in an open‐ended cavity between two horizontal parallel circular plates. The upper plate is maintained at an ambient temperature and the lower one is heated. Air is used as the heat transfer medium. The numerical model equations are solved using a control volume‐based finite differences method, and the experimental study was performed using holographic interferometry. Streamlines and isotherm patterns are presented and discussed for different aspect ratios (A) and Rayleigh numbers (Ra). Heat transfer at the surface of the lower plate is thoroughly inspected in the ranges and . Useful correlations of Nusselt numbers in terms of and A are given with their validity ranges. Also, an investigation of both numerical and experimental results is performed. It shows similar temperature field aspect with some differences in the radial boundary layer thickness and a small deviation in the heat transfer.     

Optimization of hydrogen production from pretreated rice straw waste in a mesophilic up‐flow anaerobic staged reactor

This study was carried out to assess the efficiency of a mesophilic up‐flow anaerobic staged reactor for continuous H₂ production from pretreated rice straw waste. The reactor was operated at different hydraulic retention times (HRTs) of 20, 16, 12, 8 and 4 h. The organic loading rate and sludge residence time were kept constant at 30 g chemical oxygen demand (COD)/L/day, and 1.9 days, respectively. The results showed that increasing the HRT from 4 to 20 h increased the H₂ production from 0.4 ± 0.1 to 3.6 ± 0.3 L H₂/day, respectively. This corresponds to a H₂ yield of 2.1 ± 0.2 mol H₂/g COD_removed at an HRT of 20 h and 0.03 ± 0.002 mol H₂/g COD_removed at an HRT of 4 h. Likewise, carbohydrate and COD removal efficiency was strongly dependant on HRT. The removal efficiency decreased from 76.5 ± 3.4% to 40 ± 2.2% for carbohydrate and from 77.7 ± 4.3% to 12.2 ± 2.1% for COD when the HRT is reduced from 20 to 4 h, respectively. The addition of presettled sewage sludge to pretreated rice straw at a mixing ratio of 1:4 (v/v) increased the volumetric H₂ production from 3.6 ± 0.3 to 8.2 ± 2.5 L/day and the H₂ yield from 2.1 ± 0.2 to 2.8 ± 0.3 mol H₂/g COD_removed. Moreover, the removal efficiency of COD, volatile solids and carbohydrate was significantly improved. Copyright © 2013 John Wiley & Sons, Ltd.     

Hydrogen generation from hydrolysis of sodium borohydride by cubic Co–La–Zr–B nano particles as novel catalyst

Cubic Co–La–Zr–B nano particles were prepared in situ for the first time from the reduction of Co(II), La(III) and Zr(IV) chloride by sodium borohydride in methanol under reflux condition. Poly N-vinyl-2-pyrrolidone (PVP) as stabilizing agent was used for preparation of Co–La–Zr–B nano particles. Obtained powders were characterized by XRD, BET, ICP, SEM, TEM and UV–vis techniques. XRD patterns declare that under argon atmosphere only metalboride phase has been crystallized and it was not seen any oxide phase of metals. TEM image depicts that PVP stabilized nano particles are square shaped particles that containing many nanoclusters. Cubic Co–La–Zr–B nano particles were also confirmed by SEM image. Co–La–Zr–B is highly active catalysts for hydrogen generation from the hydrolysis of sodium borohydride. The reported work also includes the full experimental details for the collection of a wealth of kinetic data to determine the activation energy (E_a = 53 kJ mol⁻¹) and effects of the catalyst dosage, amount of NaBH₄, and temperature on the rate of the catalytic hydrolysis of sodium borohydride. Catalytic hydrolysis of NaBH₄ is first order with respect to the catalyst concentration and also first order to the NaBH₄ concentration in the case of cubic Co–La–Zr–B nano particles.     

Effects of pH, glucose and iron sulfate concentration on the yield of biohydrogen by Clostridium butyricum EB6

A local bacterial isolate from palm oil mill effluent (POME) sludge, identified as Clostridium butyricum EB6, was used for biohydrogen production. Optimization of biohydrogen production was performed via statistical analysis, namely response surface methodology (RSM), with respect to pH, glucose and iron concentration. The results show that pH, glucose concentration and iron concentration significantly influenced the biohydrogen gas production individually, interactively and quadratically (P < 0.05). The center composite design (CCD) results indicated that pH 5.6, 15.7 g/L glucose and 0.39 g/L FeSO₄ were the optimal conditions for biohydrogen production, yielding 2.2 mol H₂/mol glucose. In confirmation of the experimental model, t-test results showed that curve fitted to the experimental data had a high confidence level, at 95% with t = 2.225. Based on the results of this study, optimization of the culture conditions for C. butyricum EB6 significantly increased the production of biohydrogen.     

Semi-automatic measurement of rigid gas-permeable contact lens movement in keratoconus patients using blinking images

Purpose

To introduce a method for estimation of the rigid gas-permeable contact lens (RGP) movement.

Antibacterial activity of Lactobacillus acidophilus strains isolated from honey marketed in Malaysia against selected multiple antibiotic resistant (MAR) Gram-positive bacteria

A total of 32 lactic acid bacteria (LAB) were isolated from 13 honey samples commercially marketed in Malaysia, 6 strains identified as Lactobacillus acidophilus by API CHL50. The isolates had antibacterial activities against multiple antibiotic resistant's Staphylococcus aureus (25 to 32 mm), Staphylococcus epidermis (14 to 22 mm) and Bacillus subtilis (12 to 19 mm) in the agar overlay method after 24 h incubation at 30 °C. The crude supernatant was heat stable at 90 °C and 121 °C for 1 h. Treatment with proteinase K and RNase II maintained the antimicrobial activity of all the supernatants except sample H006-A and H010-G. All the supernatants showed antimicrobial activities against target bacteria at pH 3 and pH 5 but not at pH 6 within 72 h incubation at 30 °C. S. aureus was not inhibited by sample H006-A isolated from Libyan honey and sample H008-D isolated from Malaysian honey at pH 5, compared to supernatants from other L. acidophilus isolates. The presence of different strains of L. acidophilus in honey obtained from different sources may contribute to the differences in the antimicrobial properties of honey.