Isolation and identification by 18S rDNA sequence of high lipid potential microalgal species for fuel production in Hainan Dao

To exploit indigenous microalgal species with the potential for biodiesel production, 101 algal cultures were isolated from partial waters in Hainan province. Eight cultures were selected based on their high biomass, high lipid content and ease of cultivation, then identified based on morphology and 18S rDNA sequence analysis. These isolates were identified as Tetranephris brasiliensis DL12, Ankistrodesmus gracilis DL25, Ankistrodesmus sp. CJ02, Desmodesmus subspicatus WC01, A. gracilis CJ09, Chlorella vulgaris CJ15, Desmodesmus sp. WC08, Chlorella sorokiniana XS04, respectively. Desmodesmus sp. WC08 reached the highest biomass concentration (2.32 g L⁻¹) with the lipid content of 31.30%. Higher lipid content of 47.90% and 47.39% were gained by A. gracilis CJ09 and C. vulgaris CJ15, respectively. However, C. vulgaris CJ15 and Desmodesmus sp. WC08 had higher lipid productivity (117.37 mg L⁻¹ d⁻¹and 115.73 mg L⁻¹ d⁻¹, respectively) in terms of comprehensive consideration. The fatty acid compositions of these microalgal species were mainly palmitic, palmitoleic, stearic, oleic with GC–MS (gas chromatography–mass spectrometer) analysis. A. gracilis CJ09, T. brasiliensis DL12, A. gracilis DL25 and Desmodesmus sp. WC08 had the higher oleic acid content (over 50% of the total fatty acids) than the others. The results suggest that marine microalgae strain Desmodesmus sp. WC08 can be the most appropriate candidate for producing oil for biodiesel, based on its higher biomass productivity, lipid productivity and fatty acid profile.     

Kinetic study of thermophilic anaerobic digestion of solid wastes from potato processing

Anaerobic treatment of solid wastes from potato processing was studied in completely stirred tank reactors (CSTR) at 55 °C. Special attention was paid to the effect of increased organic loading rate (OLR) on the biogas yield in long-term experiments. Both biogas yield and CH₄ in the biogas decreased with the increase in OLR. For OLR in the range of 0.8 gl⁻¹ d⁻¹–3.4 gl⁻¹ d⁻¹, biogas yield and CH₄ obtained were 0.85 l g⁻¹–0.65 l g⁻¹ and 58%–50%, respectively. Biogas yield y as a function of maximum biogas yield y_m, reaction rate constant k and HRT are described on the basis of a mass balance in a CSTR and a first order kinetic. The value of y_m can be obtained from curve fitting or a simple batch test and k results from plotting y/(y_m−y) against 1/OLR from long-term experiments. In the present study values for y_m and k were obtained as 0.88 l g⁻¹ and 0.089 d⁻¹, respectively. The simple model equations can apply for dimensioning completely stirred tank reactors (CSTR) digesting organic wastes from food processing industries, animal waste slurries or biogas crops.     

Crystallographic and electrochemical characteristics of La0.7Mg0.3Ni3.5 − x(Al0.5Mo0.5)x (x = 0–0.8) hydrogen storage alloys

The crystal structure, hydrogen storage property and electrochemical characteristics of the La_0.7Mg_0.3Ni_3.5 − x(Al_0.5Mo_0.5)_x (x = 0–0.8) alloys have been investigated systematically. It can be found that with X-ray powder diffraction and Rietveld analysis the alloys are of multiphase alloy and consisted of impurity LaNi phase and two main crystallographic phases, namely the La(La, Mg)₂Ni₉ phase and the LaNi₅ phase, and the lattice parameter and the cell volume of both the La(La, Mg)₂Ni₉ phase and the LaNi₅ phase increases with increasing Al and Mo content in the alloys. The P–C isotherms curves indicate that the hydrogen storage capacity of the alloy first increases and then decreases with increasing x, and the equilibrium pressure decreases with increasing x. The electrochemical measurements show that the maximum discharge capacity first increases from 354.2 (x = 0) to 397.6 mAh g⁻¹ (x = 0.6) and then decreases to 370.4 mAh g⁻¹ (x = 0.8). The high-rate dischargeability of the alloy electrode increases lineally from 55.7% (x = 0) to 73.8% (x = 0.8) at the discharge current density of 1200 mA g⁻¹. Moreover, the exchange current density of the alloy electrodes also increases monotonously with increasing x. The hydrogen diffusion coefficient in the alloy bulk increases with increasing Al and Mo content and thus enhances the low-temperature dischargeability of the alloy electrode.     

Estimation of woody biomass production from a short-rotation bio-energy system in semi-arid Australia

Short, 3–5 year, rotations of trees have been proposed as a method of regaining hydrological control of dryland farming systems (300–600 mm annual rainfall) in southern Australia and thus alleviating salinization of land and water. At the termination of the rotation, the trees will be removed and used as a bioenergy feedstock. In the absence of any tree growth data in this region, allometric relationships were developed for three prospective short-rotation species (Eucalyptus globulus, Eucalyptus occidentalis and Pinus radiata), for 3-year-old trees, at a site with a mean annual rainfall of 365 mm. Equations that related stem diameter over bark at 10 cm (D₁₀) and tree height (ht) to total tree biomass (above and below ground), leaves, stems (stemwood and bark) and roots were developed, by combining data from different planting densities (500, 1000, 2000 and 4000 stem ha⁻¹) and landscape positions (upper-slope, mid-slope and lower-slope).Mean oven-dry yields of the three species, in the high planting density treatment were not significantly different and ranged from 12 to 14 t ha⁻¹ (3 years)⁻¹. There were consistent increases in biomass yield with planting density, with this generally being greatest with the 4000 stem ha⁻¹ treatment. There were marked differences in productivity with slope position. For E. globulus and E. occidentalis the best yields were obtained in lower landscape positions with initial planting densities of 4000 stem ha⁻¹, with 16.6 and 22.2 t ha⁻¹ (3 years)⁻¹, total biomass produced, respectively. The best yield of P. radiata was 15.4 t ha⁻¹ (3 years)⁻¹ from an initial planting density of 4000 stem ha⁻¹ in an upper landscape position. These differences partly reflected site hydrology, with water accumulating in downslope positions. Partitioning of tree components was variable between species, with root:shoot (R:S) ratio being significantly (P<0.0001) higher for E. occidentalis (0.5) compared with the other two species (0.3). Results suggest that biomass productivity can be optimized in this region by using high initial planting densities and recognizing the interaction of different species with site hydrology.     

Formulation of a low-cost medium for mass production of Spirulina

A new medium was formulated for mass production of Spirulina sp. by incorporating selected nutrients of the standard Zarrouk's medium (SM) and other cost-effective alternative chemicals. This newly formulated medium (RM₆) contains single super phosphate (1.25 g l⁻¹), sodium nitrate (2.50 g l⁻¹), muriate of potash (0.98 g l⁻¹), sodium chloride (0.5 g l⁻¹), magnesium sulphate (0.15 g l⁻¹), calcium chloride (0.04 g l⁻¹), and sodium bicarbonate (commercial grade) 8 g l⁻¹. The alga was grown in an illuminated (50 μmol photons m⁻² s⁻¹ white light) growth room at 30±1 °C. Maximum growth rate in terms of dry biomass, chlorophyll and proteins in SM was recorded between 6 and 9 days of growth and values were 0.114, 0.003 and 0.068 as compared to 0.112, 0.003 and 0.069 mg ml⁻¹ d⁻¹ in RM₆,. No significant differences were observed in the protein profiles of Spirulina sp. grown in both the media. From the scale up point of view, the revised medium was found to be highly economical, since it is five times cheaper than Zarrouk's medium.     

Effect of the Sm content on the structure and electrochemical properties of La1.3 − xSmxCaMg0.7Ni9 (x = 0–0.3) hydrogen storage alloys

La_1.3 − xSm_xCaMg_0.7Ni₉ (x = 0–0.3) hydrogen storage alloys were prepared by inductive melting and the effect of the Sm content on the structure and electrochemical properties was investigated in the paper. The Sm substitution for La in La_1.3 − xSm_xCaMg_0.7Ni₉ (x = 0–0.3) alloys does not change the main phase structure (the rhombohedral PuNi₃-type structure), but leads to a shrinkage of unit cell and a decrease of hydrogen storage capacity. With the increase of the Sm content in the alloys, the maximum discharge capacity of electrode decreases from 400.2 (x = 0) to 346.6 mAh g⁻¹ (x = 0.3), but the high-rate dischargeability and cycling stability is improved. After 100 cycles, the capacity retention rate increases from 75 (x = 0) to 85% (x = 0.3).     

Mass transfer coefficients associated with the mixing of a confined gas volume by the random motion of loose spheres

This investigation quantifies the change in mass transfer within a confined gas volume subjected to mixing by loose spheres. A cylindrical vessel containing between 1 and 50 Teflon spheres in a tracer gas is vigorously shaken. Extractive sampling provides time histories of tracer gas concentrations extracted from the vessel. Fitting the results from a simple 1-D mass transfer model to the experimental data yields an effective mass transfer coefficient k′ for each experimental condition. Compared to diffusive mass transfer where k′ = D_ab = 7.58 × 10⁻⁶ m²/s, k′ exhibits a cubic dependency on the number of spheres with a maximum at 17 spheres where k′ = 3.5 × 10⁻³ m²/s.     

Electrochemical behavior of polyamides with cyclic disulfide structure and their application to positive active material for lithium secondary battery

Polyamides (DTA-I, DTA-II, and DTA-III) containing cyclic disulfide structure were prepared by condensation between 1,2-dithiane-3,6-dicarboxylic acid (DTA) and alkyl diamine, NH₂–(CH₂)_n–NH₂ (DTA-I; n=4, DTA-II; n=6, DTA-III; n=8) and their application to positive active material for lithium secondary batteries was investigated. Cyclic voltammetry (CV) measurements under slow sweep rate (0.5 mV s⁻¹) with a carbon paste electrode containing the polyamide (DTA-I, DTA-II, or DTA-III) were performed. The results indicated that the polyamides were electroactive in the organic electrolyte solution (propylene carbonate (PC)-1,2-dimethoxyethane (DME), 1:1 by volume containing lithium salt, such as LiClO₄). The responses based on the redox of the disulfide bonds in the polyamide were observed.Test cells, Li/PC-DME (1:1. by volume) with 1 mol dm⁻³ LiClO₄/the polyamide cathode, were constructed and their performance was tested under constant current charge/discharge condition. The average capacity of the test cells with the DTA-III cathode was 64.3 Ah kg⁻¹ of cathode (135 Wh kg⁻¹ of cathode, capacity (Ah kg⁻¹) of the cathode×average cell voltage (2.10 V)). Performance of the cell with linear polyamide containing disulfide bond (–CO–(CH₂)₂–S–S–(CH₂)₂–CONH–(CH₂)₈–NH–, GTA-III) was also investigated and the average capacity was 56.8 Ah kg⁻¹ of cathode (100 Wh kg⁻¹ of cathode, capacity (Ah kg⁻¹) of the cathode×average cell voltage (1.76 V)). Cycle efficiency of the test cell with the DTA-III cathode was higher than that with the GTA-III cathode.     

RuxCrySez electrocatalyst loading and stability effects on the electrochemical performance in a PEMFC

The present paper presents a study of the Ru_xCr_ySe_z chalcogenide electrocatalyst based on physical–chemical characterization through scanning electron (SEM), atomic force (AFM) microscopy and energy dispersion elemental analysis (EDS), thermal stability using differential scanning calorimeter (DSC), electrochemical kinetics towards the oxygen reduction reaction (ORR) in acid media by rotating ring-disk electrode (RRDE) and single and three-stack membrane-electrode assembly (MEA) performance as a function of catalyst loading (10%, 20% and 40% W from 0.2 to 2 mg cm⁻²). Results indicate an electrocatalyst with chemical composition of Ru₆Cr₄Se₅. AFM images showed 80–160 nm nanoparticle agglomerates. Good thermal stability of the cathode Ru₆Cr₄Se₅ was established after 100 h of continuous operation. The electrochemical kinetics study (RRDE) resulted in a electrocatalyst with high activity towards the ORR, preferentially proceeding via 4e⁻ charge transfer pathway towards water formation (i.e., O₂+4H⁺+4e⁻→2H₂O), with a maximum of 2.8% H₂O₂ formation at 25 °C. Finally, MEA tests revealed a maximum power density of 220 mW cm⁻² with a catalyst loading of 20 wt% at 1.6 mg cm⁻².     

Flow visualizations and heat transfer measurements for a rotating pin-fin heat sink with a circular impinging jet

This work experimentally investigated the fluid flow and heat transfer behaviors of jet impingement onto the rotating heat sink. Air was used as impinging coolant, while the square heat sinks with uniformly in-line arranged 5 × 5 and 9 × 9 pin-fins were employed. The side length (L) of the heat sink equaled 60 mm and was fixed. Variable parameters were the relative length of the heat sink (L/d = 2.222 and 4.615), the relative distance of nozzle-to-fin tip (C/d = 0–11), the jet Reynolds number (Re = 5019–25,096) and the rotational Reynolds number (Re_r = 0–8114). Both flow characteristics of stationary and rotating systems were illustrated by the smoke visualization. Besides, the results of heat transfer indicate that, for a stationary system with a given air flow rate, there was a larger average Nusselt number (Nu₀) for the 9 × 9 pin-fin heat sink with L/d = 4.615 and C/d = 11. For a rotating system, a bigger Re_r meant a more obvious heat transfer enhancement (Nu_Ω/Nu₀) in the case of smaller Re, but Nu_Ω/Nu₀ decreased with increasing Re. In this work, Nu_Ω/Nu₀ in L/d = 2.222 is higher than in L/d = 4.615; among the systems in L/d = 2.222, bigger Nu_Ω/Nu₀ exists in the case of C/d = 9–11, but among the systems in L/d = 4.615, bigger Nu_Ω/Nu₀ exists in the case of C/d = 1–3. Finally, according to the base of Nu_Ω/Nu₀ ? 1.1, the criterion of the substantial rotation was suggested to be Re_r/Re ? 1.154.     

Effects of platinum loading on performance of proton-exchange membrane fuel cells using surface-modified Nafion® membranes

The interface between the electrolyte and electrode catalyst plays an important role in determining the performance of proton-exchange membrane fuel cells (PEMFCs) since the electrochemical reactions take place at the interface in contact with the reactant gases. To enhance catalyst activity by enlarging the interfacial area, the surface of a Nafion^® membrane is roughened by Ar⁺ ion beam bombardment that does not change the chemical structure of the membrane, as confirmed by FT-IR spectra. Among the membranes treated with ion dose densities of 0, 10¹⁵, 10¹⁶, 5 × 10¹⁶ and 10¹⁷ ions cm⁻² at ion energy of 1 keV, the membrane treated at ion dose density of 5 × 10¹⁶ ions cm⁻² exhibits the highest performance. Using the untreated and the treated membrane with 5 × 10¹⁶ ions cm⁻², the effects of platinum loading on cell performance are examined with Pt loadings of 01, 0.2, 0.3, 0.4 and 0.55 mg cm⁻². Except for a Pt loading of 0.55 mg cm⁻² where mass transport limits the cell performance, the single cell using a treated membrane gives a higher performance than that using an untreated membrane. This implies that the cell performance can be improved and the Pt loading can be reduced by ion beam bombardment.     

Heat transfer behavior in a rotating aluminum foam heat sink with a circular impinging jet

This work experimentally studied heat transfer associated with an impinging jet onto a rotating heat sink. Air was used as the impinging coolant, and a square Al-foam heat sink was adopted. The variable parameters were the jet Reynolds number (Re), the relative nozzle-to-foam tip distance (C/d), the rotational Reynolds number (Re_r) and the relative side length of the square heat sink (L/d). The effects of Re, C/d, Re_r and L/d on the dimensionless temperature distributions and the average Nusselt number were considered. For a stationary system, the results reveal that the average Nusselt number (Nu₀) with Al-foam was two to three times that without Al-foam. Nu₀ increased with Re. A larger L/d responded to a larger Nu₀ based on the same jet flow rate. The effect of C/d on Nu₀ was negligible herein. For a rotating system, when Re and L/d were small and C/d was large, the average Nusselt number (Nu_Ω) increased considerably with Re_r. Additionally, for Nu_Ω/Nu₀ ? 1.1, the results suggest that rotation was substantial at Re_r/Re ? 1.13 when L/d = 4.615 with C/d = 0–5 and at Re_r/Re ? 1.07 when L/d = 3.0 with C/d = 0–5. For L/d = 2.222, rotation was substantial at Re_r/Re ? 1.44 when C/d = 0 and was always substantial when C/d ? 1.     

Time evolution of double-diffusive convection in a vertical cylinder with radial temperature and axial solutal gradients

The characteristics of transient double-diffusive convection in a vertical cylinder are numerically simulated using a finite element method. Initially the fluid in the cavity is at uniform temperature and solute concentration, then constant temperature and solute concentration, which are lower than their initial values, are imposed along the sidewall and bottom wall, respectively. The time evolution of the double-diffusive convection is investigated for specific parameters, which are the Prandtl number, Pr = 7, the Lewis number, Le = 5, the thermal Grashof number, Gr_T = 10⁷, and the aspect ratio, A = 2, of the enclosure. The objective of the work is to identify the effect of the buoyancy ratio (the ratio of solutal Grashof to thermal Grashof numbers: N = Gr_S/Gr_T) on the evolution of the flow field, temperature and solute field in the cavity. It is found that initially the fluid near the bottom wall is squeezed by the cold flow from the sidewall, a crest of the solute field forms and then pushed to the symmetry line. In the case of N > 0, a domain with higher temperature and weak flow (dead region) forms on the bottom wall near the symmetry line, and the area of dead region increases when N varies from 0.5 to 1.5. More crests of the solute field are formed and the flow near the bottom wall fluctuates continuously for N < 0. The frequency of the fluctuation increases when N varies from −0.5 to −1.5. Corresponding to the variety of the thermal and solutal boundary layers, the average rates of heat transfer (Nu) at the sidewall remain almost unchanged while the average rates of mass transfer (Sh) at the bottom wall change much in the cases of N = 1, 0, −1.     

LiMn2O4 cathode materials synthesized by the cellulose–citric acid method for lithium ion batteries

A new technique was employed to synthesize spinel LiMn₂O₄ cathode materials by adding cellulose and citric acid to an aqueous solution of lithium and manganese salts. Various synthesis conditions such as the calcination temperature and the citric acid-to-metal ion molar ratio (R) were investigated to determine the ideal conditions for preparing LiMn₂O₄ with the best electrochemical characteristics. The optimal synthesis conditions were found to be R = 1/3 and a calcination temperature of 800 °C. The initial discharge capacity of the material synthesized using the optimal conditions was 134 mAh g⁻¹, and the discharge capacity after 40 cycles was 125 mAh g⁻¹, at a current density of 0.15 mA cm⁻² between 3.0 and 4.35 V. Details of how the initial synthesis conditions affected the capacity and cycling performance of LiMn₂O₄ are discussed.     

Thermal management using the bi-disperse porous medium approach

Thermal management of distributed electronics similar to data centers is studied using a bi-disperse porous medium (BDPM) approach. The BDPM channel comprises heat generating micro-porous square blocks, separated by macro-pores. Laminar forced convection cooling fluid of Pr = 0.7 saturates both the micro- and macro-pores. Bi-dispersion effect is induced by varying the macro-pore volume fraction ?_E, and by changing the number of porous blocks N², both representing re-distribution of the electronics. When 0.2 ? ?_E ? 0.86, the heat transfer Nu is enhanced twice (from ～550 to ～ 1100) while the pressure drop Δp¹ reduces almost eightfold. For ?_E < 0.5, Nu reduces quickly to reach a minimum at the mono-disperse porous medium (MDPM) limit (?_E → 0). Compared to N² = 1 case, Nu for BDPM configuration is high when N² ? 1, i.e., the micro-porous blocks are many and well distributed. The Nu increase with Re changes from non-linear to linear as N² increases from 1 to 81, with corresponding insignificant pumping power increase.     

Effect of (Al,Mg) substitution in LiNiO2 electrode for lithium batteries

Stabilized lithium nickelate is receiving increased attention as a low-cost alternative to the LiCoO₂ cathode now used in rechargeable lithium batteries. Layered LiNi_1−x−yM_xM_yO₂ samples (M_x = Al³⁺ and M_y = Mg²⁺, where x = 0.05, 0.10 and y = 0.02, 0.05) are prepared by the refluxing method using acetic acid at 750 °C under an oxygen stream, and are subsequently subjected to powder X-ray diffraction analysis and coin-cell tests. The co-doped LiNi_1−x−yAl_xMg_yO₂ samples show good structural stability and electrochemical performance. The LiNiAl_0.05Mg_0.05O₂, cathode material exhibits a reversible capacity of 180 mA h g⁻¹ after extended cycling. These results suggest that the threshold concentration for aluminum and magnesium substitution is of the order of 5%. The co-substitution of magnesium and aluminium into lithium nickelate is considered to yield a promising cathode material.     

Optimal design of geometric parameters of double-layered microchannel heat sinks

This work uses an optimization procedure consisting of a simplified conjugate-gradient method and a three-dimensional fluid flow and heat transfer model to investigate the optimal geometric parameters of a double-layered microchannel heat sink (DL-MCHS). The overall thermal resistance R_T is the objective function to be minimized, and the number of channels N, channel width ratio β, lower channel aspect ratio α_l, and upper channel aspect ratio α_u are the search variables. For a given bottom area (10 × 10 mm) and heat flux (100 W/cm²), the optimal (minimum) thermal resistance of the double-layered microchannel heat sink is about R_T = 0.12 °C/m²W. The corresponding optimal geometric parameters are N = 73, β = 0.50, α_l = 3.52, and, α_u = 7.21 under a total pumping power of 0.1 W. These parameters reduce the overall thermal resistance by 52.8% compared to that yielded by an initial guess (N = 112, β = 0.37, α_l = 10.32, and α_u = 10.93). Furthermore, the optimal thermal resistance decreases rapidly with the pumping power and then tends to approach an constant value. As the pumping power increases, the optimal values of N, α_l, and α_u increase, whereas the optimal β value decreases. However, increasing the pumping power further is not always cost-effective for practical heat sink designs.     

Synthesis and electrochemical properties of Mo-doped Li[Ni1/3Mn1/3Co1/3]O2 cathode materials for Li-ion battery

The layered Li[Ni_(1−x)/3Mn_(1−x)/3Co_(1−x)/3Mo_x]O₂ cathode materials (x = 0, 0.005, 0.01, and 0.02) were prepared by a solid-state pyrolysis method (700, 800, 850, and 900 °C). Its structure and electrochemical properties were characterized by XRD, SEM, XPS, cyclic voltammetry, and charge/discharge tests. It can be learned that the doped sample of x = 0.01 calcined at 800 °C shows the highest first discharge capacity of 221.6 mAh g⁻¹ at a current density of 20 mA g⁻¹ in the voltage range of 2.3–4.6 V, and the Mo-doped samples exhibit higher discharge capacity and better cycle-ability than the undoped one at room temperature.     

Heat conduction in fractal tree-like branched networks

The geometric structures and fractal dimensions of fractal tree-like branched networks have the significant influence on the efficiency of physiological, communication and transport processes. We analyze the heat conduction through symmetric fractal tree-like branched networks. We obtain the expression of thermal conductivity in the networks and analyze the relationship between the effective thermal conductivity (ETC) and the geometric structures of the networks. We have found that the ETC of the networks is always less than that of a single channel, and the value of the thermal conductivity of the network can tend to zero under certain conditions; as long as the branching number N is fixed, the heat conduction reaches the fastest rate at the same diameter ratio β_m which is corresponding to the fractal dimension D_d = 2.0. We have also found that the heat conduction in the networks is rather different from Murray’s law both for laminar regime (2^−1/3) and for turbulent flow regime (2^−3/7).