A theoretical study on hydrodynamics of condensate films over fluted tubes

Hydrodynamic characteristics of liquid films in downward motion on the outer surface of fluted tubes have been investigated theoretically. Velocity distribution, volumetric flow rate and friction factor are calculated from the solution of the equation of motion using bi-polar coordinate system.The results provide sufficient information pertaining to the thickness of the condensate film and its variation, thus enabling the prediction of heat transfer coefficients in desalination.     

Polyaminocarboxylic acids–Ce(IV) redox systems as an initiator in acrylamide polymerization

Acrylamide polymerization by Ce(IV)-polyaminocarboxylic acids, i.e., EDTA, DTPA, EGTA, and NTA, which have strong chelating properties, have been studied at different [H⁺], initiator concentration, and reaction time. Initiation of polymerization proceeds through the formation of the free radical after decarboxylation of the carboxyl group of polyaminocarboxylic acid. Results also indicate that the termination of the polymerization reaction is mainly mutual termination. Decrease of the rate of disappearance of the cerium(IV) is in the order of DTPA ≥ EDTA > NTA > EGTA. © 1993 John Wiley & Sons, Inc.     

Determination of polyphenolic constituents and biological activities of bark extracts from different Pinus species

BACKGROUND: The most common commercially available pine bark extract is Pycnogenol^®, a standardised extract of Pinus maritima, which has been reported to have cardiovascular benefits and enhance microcirculation. The present study was conducted to determine the chemical composition of four pine bark extracts, assess their biological activities and to compare the results with Pycnogenol^®. RESULTS: The Pinus species were analysed by LC and LC‐MS; extracts of P. brutia and P. nigra showed higher levels of phenolic constituents compared to P. sylvestris and P. pinea. In particular, P. brutia contained extremely high concentrations of taxifolin (18.5%). The highest radical scavenging activities were attained with P. pinea (88.6%), P. nigra (87.2%) and P. brutia (86.4%) bark extracts. Additionally, anticarcinogenic effects of the extracts and their kinetics were determined in four cell lines including human prostate (PC‐3, DU 145, LNCaP) and breast adenocarcinoma (MCF7) by the MTT assay. Cell viability was reduced to 40% by extracts of P. pinea, and P. sylvestris in PC‐3 cells showing a similar effect like the positive control, CPT‐11. CONCLUSION: Pinus species other than P. maritima definitively possess high biological activities, and therefore present a huge potential to be utilised in the food and the pharmaceutical industries. Copyright © 2009 Society of Chemical Industry     

A review on selected heterogeneous photocatalysts for hydrogen production

In this study, visible light‐driven heterogeneous photocatalysts for hydrogen production are comparatively assessed based on technical, environmental, and cost criteria. The photocatalysis systems are compared with respect to their (i) rate of hydrogen generation per gram; (ii) rate of hydrogen generation per m² of the specific surface area; and (iii) the band gap energy. The photocatalysis systems are also compared and discussed in terms of flammability, reactivity, and their impact on living systems' health. Furthermore, the costs of the required components of the photocatalysis systems are ranked. In addition to individual photocatalyst comparison, seven photocatalyst groups are ranked and compared. The results show that TiO₂‐C‐362 and Ag_0.03Mn_0.40Cd_0.60S show the highest in terms of µmol/h‐g_cat and µmol/h‐m²_cat, respectively, and TiO₂‐C‐362 has the highest overall rankings. The Zn/In/S‐based photocatalyst groups show the highest hydrogen production rate in terms of µmol/h‐gcat and µmol/h‐m²_cat. Overall, Cd/S/Zn has the highest rankings when cost and health and environmental impact criteria are taken into account. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis and assessment of a continuous-type hybrid photoelectrochemical system for hydrogen production

In this study, we conceptually develop and thermodynamically analyze a new continuous-type hybrid system for hydrogen production which photoelectrochemically splits water and performs chloralkali electrolysis. The system has a potential to produce hydrogen efficiently, at low cost, and in an environmentally benign way by maximizing the utilized solar spectrum and converting the byproducts into useful industrial commodities. Furthermore, by using electrodes as electron donors to drive photochemical hydrogen production, the hybrid system minimizes potential pollutant emissions. The products of the hybrid system are hydrogen, chlorine and sodium hydroxide, all of which are desired industrial commodities. The system production yield and efficiencies are investigated based on an operation temperature range of 20 °C–80 °C. A maximum energy efficiency of 42% is achieved between the temperatures of 40 °C and 50 °C.     

Seasonal changes of fatty acids of cuttlefish Sepia officinalis L. (Mollusca: Cephalopoda) in the north eastern Mediterranean sea

The total lipids and seasonal variations in the fatty acids of the mantle of cuttlefish (Sepia officinalis) captured in the north eastern Mediterranean were investigated and the mantle was found to be a good source of polyunsaturated fatty acids (ω3 PUFAs, in particular). In all seasons, the major fatty acids in the cuttlefish mantle were observed to be palmitic acid (16:0), stearic acid (18:0), eicosapentaenoic acid (EPA, 20:5ω3) and docosahexaenoic acid (DHA, 22:6ω3). A comparison of the saturated fatty acid (29.5–36.8%), monounsaturated fatty acids (7.81–9.84%) and polyunsaturated fatty acids (43.7–49.6%) of the cuttlefish mantle revealed that polyunsaturated fatty acids (PUFA) constituted the highest proportion. The levels of DHA in the cuttlefish mantle in autumn, winter, spring and summer were 27.6%, 28.5%, 29.5% and 23.9%, while those of EPA were 16.8%, 15.4%, 14.7% and 13.9%, respectively.     

Biochemical and thermal properties of β-galactosidase enzymes produced by artisanal yoghurt cultures

β-Galactosidases, produced by pure and mixed cultures of Streptococcus thermophilus 95/2 (St 95/2) and Lactobacillus delbrueckii ssp bulgaricus 77 (Lb 77) isolated from the Toros mountain region of Turkey, were characterised with respect to their biochemical and thermal properties. Optimum pH and temperature for maximum activity were determined and these enzymes were stable in the pH range 7–9 and in the temperature range 20–37 °C, retaining 80–90% of their initial activities. The inactivation energies of β-galactosidase from Lb 77, St 95/2 and mixed culture (Lb 77 and St 95/2) were 51.3, 44.0 and 48.3 kcal mol⁻¹, respectively. Moreover, thermodynamic (ΔG, ΔS, ΔH) and kinetic constants (K_m and V_max) were determined and effects of metal ions were investigated. As a result, these enzymes could be considered as potential candidates for lactose hydrolysis of milk and milk products.     

A comprehensive evaluation of energy storage options for better sustainability

Due to ever increasing global energy demand and the limited nature of fossil fuel reserves, there has been tremendous research and development studies in the literature, focusing on alternative and clean energy resources and systems. Renewables are the promising choice when it comes to addressing some critical energy issues such as climate change and energy security. However, renewables have intermittent and discontinuous supplies; hence, they need to be stored in ways that are affordable, reliable, flexible, clean, safe, and efficient. As a result, energy storage is becoming a crucial step to build innovative energy systems for a sustainable future. Energy can be stored in many forms, from electrical to chemical (eg, hydrogen), or electrochemical, thermal, electromagnetic, etc. Each form consists of different technologies, some of which are already commercially mature while others are at early research and development stages. Each of these options can be tailored to meet different end users' needs at different scales. Therefore, this study aims to conduct a comprehensive review on the most recent status of energy storage options, along with the requirements of various end users, and characteristics of smart energy storage systems. The main objective is to summarize the performance evaluation statuses of mechanical, electrochemical, chemical, thermal, and electromagnetic energy storage technologies. The selected performance measures are capacity flexibility, energy arbitrage, system balancing, congestion management, environmental impact, and power quality. In the end, some key recommendations and future directions for energy storage systems are provided.     

MHD flow in a rectangular duct with a perturbed boundary

The unsteady magnetohydrodynamic (MHD) flow of a viscous, incompressible and electrically conducting fluid in a rectangular duct with a perturbed boundary, is investigated. A small boundary perturbation $\epsilon$ is applied on the upper wall of the duct which is encountered in the visualization of the blood flow in constricted arteries. The MHD equations which are coupled in the velocity and the induced magnetic field are solved with no-slip velocity conditions and by taking the side walls as insulated and the Hartmann walls as perfectly conducting. Both the domain boundary element method (DBEM) and the dual reciprocity boundary element method (DRBEM) are used in spatial discretization with a backward finite difference scheme for the time integration. These MHD equations are decoupled first into two transient convection–diffusion equations, and then into two modified Helmholtz equations by using suitable transformations. Then, the DBEM or DRBEM is used to transform these equations into equivalent integral equations by employing the fundamental solution of either steady-state convection–diffusion or modified Helmholtz equations. The DBEM and DRBEM results are presented and compared by equi-velocity and current lines at steady-state for several values of Hartmann number and the boundary perturbation parameter.