Introducing a proper hydrogen liquefaction concept for using wasted heat of thermal power plants-case study: Parand gas power plant

A hydrogen liquefaction concept with an innovative configuration and a capacity of 4 kg·s^-1 (345.6 t·d^-1) is developed. The concept involves an ammonia absorption refrigeration system for the pre-cooling of hydrogen and MR streams from 25 ℃ to -30 ℃. The ammonia absorption refrigeration system is fed by exhaust gases of the Parand gas power plant that are normally dissipated to the environment with a temperature of 546 ℃. The simulation is performed by Aspen HYSYS V9.0, using two separate equations of state for simulating hydrogen and MR streams to gain more accurate results especially for ortho-para conversion. Results show that conversion enthalpy estimated by Aspen HYSYS, fits very well to the experimental data. Determining the important independent variables and composition of MRs are done using trial and error procedure, a functional and straightforward method for complicated systems. The minimum temperature limit in the cooling section is lowered, and an ortho-para converter is implemented in this section. The proposed concept performs well from energy aspects and leads to COP and SEC equal to 0.271 and 4.54 kW·h·kg^-1, respectively. The main advantage of this study is in the low SEC, eliminating the losses of the distribution network, and improving the ability of the hydrogen liquefaction for energy storage in off-peak times.     

Study the flashover voltage for outdoor polymer insulators under desert climatic conditions

This work presents a study of flashover voltage for outdoor polyester and composite insulators under some desert climatic conditions. Cylindrical polyester composite samples have been prepared after incorporated with different concentrations of inorganic fillers e.g., alumina trihydrate [ATH], boric acid [H₃BO₃] and magnesium hydroxide [Mg(OH)₂] to improve the electrical, mechanical and thermal properties in addition to maximize the surface flashover voltage and decrease the tracking phenomena.Results showed that flashover voltage reaches to 38 kV for samples without filler and 47 kV for samples containing 50% of ATH filler in dry condition. A comparison between inorganic fillers under various environmental conditions showed higher flashover voltage values for samples containing ATH filler than that of samples containing H₃BO₃ and Mg(OH)₂ fillers at all filler concentrations. Flashover voltage increases 24% by adding ATH filler for polyester samples under sandstorm conditions. Also, in this study, the effects of sandstorm, ultra violet (UV) radiation, mechanical strength (compressive and tensile strengths) and thermal performance with respect to surface of the sample under test have been investigated in detail.     

Modeling of nucleate boiling heat transfer under an impinging free jet

A model using an analytical/empirical approach has been developed to predict the rate of heat transfer in the stagnation region of a planar jet impinging on a horizontal flat surface. The model has been developed based on the hypothesis that bubble-induced mixing would result in enhanced or additional diffusivity. The additional diffusivity has been included in the diffusion term of the conservation equations. The value of the effective diffusivity has been correlated with jet parameters (velocity and temperature) and surface temperature using experimental data. The important aspects of the bubble dynamics (generation frequency and average bubble diameter) have been acquired using high-speed imaging and an intrusive optical probe. The applicability of the proposed model has been investigated under conditions of partial and fully-developed nucleate boiling. Experiments have been carried out using water at atmospheric pressure, mass flux in the range of 388–1649 kg/m² s, degree of sub-cooling in the range of 10–28 °C, and surface temperature in the range of 75–120 °C. Results showed that the proposed model is able to predict the surface heat flux with reasonable accuracy (+30% and ?15%).     

NUMERICAL SIMULATION OF FLOW OVER TWO CIRCULAR CYLINDERS IN TANDEM ARRANGEMENT

In this article,the 2-D unsteady viscous flow around two circular cylinders in a tandem arrangement is numerically simulated in order to study the characteristics of the flow in both laminar and turbulent regimes.The method applied alternatively is based on the finite volume method on a Cartesian-staggered grid.The great source term technique is employed to identify the cylinders placed in the flow field.To apply the boundary conditions,the ghost-cell technique is used.The implemented computational method is firstly validated through simulation of laminar and turbulent flows around a fixed circular cylinder.Finally,the flow around two circular cylinders in a tandem arrangement is simulated and analyzed.The flow visualization parameters,the Strouhal numbers,and drag and lift coefficients are comprehensively presented and compared for different cases in order to reveal the effect of the Reynolds number and gap spacing on the behavior of the flow.The obtained results have shown two completely distinct flow characteristics in laminar and turbulent regimes.     

Micromechanics of spatially uniform heterogeneous media: A critical review and emerging approaches

Outside of the classical microstructural detail-free estimates of effective moduli, micromechanical analyses of macroscopically uniform heterogeneous media may be grouped into two categories based on different geometric representations of material microstructure. Analysis of periodic materials is based on the repeating unit cell (RUC) concept and the associated periodic boundary conditions. This contrasts with analysis of statistically homogeneous materials based on the representative volume element (RVE) concept and the associated homogeneous boundary conditions. In this paper, using the above classification framework we provide a critical review of the various micromechanical approaches that had evolved along different paths, and outline recent emerging trends. We begin with the basic framework for the solution of micromechanics problems independent of microstructural representation, and then clarify the often confused RVE and RUC concepts. Next, we describe classical models, including the available RVE-based models, and critically examine their limitations. This is followed by discussion of models based on the concept of microstructural periodicity. In the final part, two recent unit cell-based models, which continue to evolve, are outlined. First, a homogenization technique called finite-volume direct averaging micromechanics theory is presented as a viable and easily implemented alternative to the mainstream finite-element based asymptotic homogenization of unit cells. The recent incorporation of parametric mapping into this approach has made it competitive with the finite-element method. Then, the latest work based on locally-exact solutions of unit cell problems is described. In this approach, the interior unit cell problem is solved exactly using the elasticity approach. The exterior problem is tackled with a new variational principle that successfully overcomes the non-separable nature of the overall unit cell problem.     

Diffusion of benzene and toluene into aqueous nitric acid-sulphuric acid mixtures

Diffusion coefficients of toluene and benzene into aqueous mixtures of nitric and sulphuric acids have been measured at 30°C by use of a laminar jet technique. Equations are presented which correlate the data in terms of the acid concentrations and permit extrapolation to acid mixtures of interest for industrial mononitration reactions. The results show the expected dependence on viscosity of the acid phase and are in agreement with values predicted by the Wilke and Chang correlation.     

The potential use of alkaline protease from Streptomyces albidoflavus as an eco-friendly wool modifier

The main task of this study is to search for the proper conditions of the enzymatic treatment using an alkaline bacterial protease, as an eco-friendly option, to improve some performance properties and dyeability of grey wool fabric with acid dyes. The efficiency of the enzymatic treatment has been improved by prewashing in the presence of a nonionic wetting agent alone and in combination with H₂O₂. The enhancement in wool performance properties as well as in the extent of post-acid dyeing is determined by pretreatment regime, enzyme dosage, as well as enzymatic treatment conditions. For modified wool fabric samples, as the weight loss increases, the nitrogen content decreases, the whiteness index as well as the dyeability with the acid dye improves compared with the prewashed fabric samples. Proper conditions for maximising the efficiency of enzymatic treatment along with attaining better performance properties and minimal wool damage are: prewashing in the presence of a nonionic surfactant along with H₂O₂ followed by enzymatic treatment using the enzyme dosage (3?ml/g fabric), pH (9), incubation time (45?min), temperature (40?°C), LR (1/20) and rotational speed (40?rpm). The enzyme inactivation was performed at 100?°C for 5?min, followed by thoroughly rinsing, neutralising and air-drying before testing. SEM images also provide evidence that pretreatment of the wool substrate enhanced the proteolysis of cuticle layers, their degradation and potential removal by the subsequent protease treatment.     

Study of the nutritional value of black cumin seeds (Nigella sativaL)

The nutritional value of five samples of black cumin seeds from five different sources available in the local market were studied. The average values of the proximate analysis on dry matter basis were 216 g kg⁻¹ for crude protein, 406 g fat, 45 g ash, 84 g crude fibre and 249 g of nitrogen-free extract, whereas moisture content was 38 g kg⁻¹. The mineral and vitamin analyses showed that black cumin seeds contained iron, (105 mg kg⁻¹) copper (18 mg), zinc (60 mg) phosphorus (527 mg), calcium (1860 mg), thiamin (15·4 mg), niacin (57 mg), pyridoxine (5·0 mg) and folic acid (160 μg). The protein quality of black cumin seeds was evaluated using net protein utilisation (NPU), protein efficiency ratio (PER) and net dietary protein energy percent (NDPE %) for two samples imported from Syria and Turkey, while PER was determined for the Syrian sample only. The results indicated that the NPU standardised of Turkish black cumin seeds was significantly higher than that of Syrian type (P<0·05). The mean results (±SD) were 54·6±2·72 for the Syrian type and 63·1±3·74 for the Turkish type. The NDPE% mean results (±SD) were 5·3±0·79 and 5·6±0·26 for the Syrian and the Turkish samples, respectively. The PER adjusted value for the Syrian samples was 1·9. The results of protein quality evaluation and those of the nutrient composition suggest that black cumin is of relatively good nutritional value. © 1998 SCI.     

Investigating the electromagnetic shielding effectiveness of copper/cotton full Milano and 1 × 1 rib weft-knitted fabrics

In recent decades, the use of conductive textile structures for electromagnetic shielding effectiveness has been increased. In order to reduce, mitigate or completely eliminate destructive and adverse effects of these waves. For this purpose, the Copper/Cotton core spun yarn was manufactured and the copper wires with various diameters (0.06, 0.07, 0.08?mm) as core component were used. Copper/cotton core spun yarns were knitted with two knit structures, Full Milano and 1?×?1 Rib, at machine gauge (8, 10, and 12 per inch). The electromagnetic shielding effectiveness (EMSE) was examined using ASTM D4935-10 standard at frequency range between 0.03 to 1.5?GHz. The results show that heavier and thicker samples with larger stitch density have the higher EMSE values and also Full Milano knit structure with miss stitches provide larger shielding effectiveness values than 1?×?1 Rib knit structures.     

Chemical Composition and Antibacterial Activity of Essential Oils of Iranian Herbs Against Staphylococcus Aureus Isolated from Milk

Chemical composition and antibacterial activity of essential oils from three endemic plants including, Thymus daenensis Celak, Dracocephalum multicaule Montbr & Auch., Satureja bachtiarica Bunge and one native plant, Tanacetum polycephalum Schultz-Bip were determined. Volatile oils analyzed using gas chromatography and gas chromatography-mass spectrometry. The in-vitro antibacterial activity was performed by agar disc diffusion and micro-dilution assays. The results revealed distinct differences in the compounds depending on sample plant. Among the plant species screened, essential oils of S. bachtiarica and T. daenensis showed highest antibacterial activity against Staphylococcus aureus.