Problem representation for refinement

In this paper we attempt to develop a problem representation technique which enables the decomposition of a problem into subproblems such that their solution in sequence constitutes a strategy for solving the problem. An important issue here is that the subproblems generated should be easier than the main problem. We propose to represent a set of problem states by a statement which is true for all the members of the set. A statement itself is just a set of atomic statements which are binary predicates on state variables. Then, the statement representing the set of goal states can be partitioned into its subsets each of which becomes a subgoal of the resulting strategy. The techniques involved in partitioning a goal into its subgoals are presented with examples.     

Effect of steam injection on pore structure and distribution in coke samples produced by delayed coking

Porous structure of the petroleum coke produced in delayed coking technique is investigated by high-resolution X-ray computed tomography imaging. Cokes analyzed for these studies were produced from decant oil with and without steam injection. Images taken at different regions along the length of the coke columns have been used to characterize and quantify porosity and pore size (>20 μm)/shape distribution within the coke samples. Fractal analysis was performed to investigate the pore complexity distribution within the coke and to compare the two coke samples produced by different methods. High-resolution X-ray computed tomography was utilized also to scan a 1.1 cm section in the middle of the steam treated coke in volume mode to scan 80 images in one scan. Multi-planar reconstruction and 3D rendering of the pores were used to understand how the flow channels are developed and the degree of connectivity.Results showed that each coke sample shows a wide range of pore sizes and shapes that vary along the length of the coke samples. This variation in the coke that is not subjected to steam is more pronounced. Quantification of macropore size distribution shows that, in each coke sample the middle sections are the most similar regions in terms of pore size distribution and porosity. In general, steam injected coke has larger pores. Box counting fractal analysis in the cokes shows that pore distribution has fractal scaling at the locations scanned and helps in the interpretation of the pores at different locations in terms of their complexity in the distribution and shapes.     

Numerical analysis of natural convection for a porous rectangular enclosure with sinusoidally varying temperature profile on the bottom wall

Numerical investigations of steady natural convection flow through a fluid-saturated porous medium in a rectangular enclosure with a sinusoidal varying temperature profile on the bottom wall were conducted. All the walls of the enclosure are insulated except the bottom wall which is partially heated and cooled. The governing equations were written under the assumption of Darcy-law and then solved numerically using finite difference method. The problem is analyzed for different values of the Rayleigh number Ra in the range 10 ≤ Ra ≤ 1000, aspect ratio parameter AR in the range 0.25 ≤ AR ≤1.0 and amplitude λ of the sinusoidal temperature function in the range 0.25 ≤ λ ≤ 1.0. It was found that heat transfer increases with increasing of amplitude λ and decreases with increasing aspect ratio AR. Multiple cells were observed in the cavity for all values of the parameters considered.     

Energy and exergy analysis of a latent heat storage system with phase change material for a solar collector

Analysis of energy and exergy has been performed for a latent heat storage system with phase change material (PCM) for a flat-plate solar collector. CaCl₂·6H₂O was used as PCM in thermal energy storage (TES) system. The designed collector combines in single unit solar energy collection and storage. PCMs are stored in a storage tank, which is located under the collector. A special heat transfer fluid was used to transfer heat from collector to PCM. Exergy analysis, which is based on the second law of thermodynamics, and energy analysis, which is based on the first law, were applied for evaluation of the system efficiency for charging period. The analyses were performed on 3 days in October. It was observed that the average net energy and exergy efficiencies are 45% and 2.2%, respectively.     

Numerical analysis of natural convection in an inclined trapezoidal enclosure filled with a porous medium

A theoretical study of buoyancy-driven flow and heat transfer in an inclined trapezoidal enclosure filled with a fluid-saturated porous medium heated and cooled from inclined walls has been performed in this paper. The governing non-dimensional equations were solved numerically using a finite-difference method. The effective governing parameters are: the orientation or inclination angle of the trapezoidal enclosure , which varies between 0° and 180°, the Rayleigh number Ra, which varies between 100 and 1000, the side wall inclination angle θ_s and the aspect ratio A. The side wall inclination parameter θ_s is chosen as 67°, 72° and 81° and the calculations are tested for two different values of A=0.5 and 1.0. Streamlines, isotherms, Nusselt number and flow strength are presented for these values of the governing parameters. The obtained results show that inclination angle is more influential on heat transfer and flow strength than that of the side wall inclination angle θ_s. It is also found that a Bénard regime occurs around =90°, which depends on the inclination of the side wall, Rayleigh number and aspect ratio.     

Crosslinked DADMAC polymers as cationic super absorbents

Loosely crosslinked cationic polyelectrolytes (polyquats) with super-water-sorption abilities are presented, for the first time. Hydrogels obtained by radically initiated copolymerization of N,N-diallyl, N,N-dimethyl ammonium chloride (DADMAC) with N-vinyl 2-pyrrolidone (NVP) in presence of N,N,N′,N′-tetraallyl piperazinium dichloride (TAP) as crosslinker showed reasonably high equilibrium swelling ratios, as high as those for poly(acrylic acid)-based super absorbents.The highest swelling ratios (up to 360) were attained by fully cationic hydrogels derived from DADMAC and 0.5% TAP. The hydrogels with 0.5–5% crosslinkers exhibited rapid expansion in neutral water, so that the equilibrium swelling values were attained within 2–3 min. The crosslinking densities of the gels were estimated by Flory-type swelling model using “phantom network elasticity” for the elastic contribution. This estimation revealed low crosslinking efficiencies of TAP (0.24–0.35) due to its double cationic charge.In the study “the salt effect” and effects of the comonomer ratios and crosslinker contents on the swellings were also investigated.     

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Minds and Machines -     

Synthesis and Characterization of Lipophilic Polymeric Adsorbent Resins for Recovery of Anthocyanins from Black Carrot

The aim of this study was to synthesize and characterize the various polymeric adsorbents which are used in the recovery of black carrot anthocyanins by the solid-phase extraction technique. In this context, acrylic and methacrylic monomers were polymerized with the free radical polymerization technique. In resin synthesis, four different crosslinker monomers, different monomer/crosslinker and monomer/diluent ratios were studied. The characterizations of the polymeric adsorbents were designed by size distribution, polymerization yield, scanning electron microscope images and swellability ratio in water and ethanol. In order to determine the best production conditions for polymer adsorbents, they were tested in a model batch system. The T-10-coded adsorbent demonstrated the best performance. The anthocyanins of the black carrot were recovered successfully from carrot juice by using the packed bed adsorption column system which is prepared with T-10. At the end of the study, 3.01 g color components were obtained from 1 L of black carrot juice.     

Speciation of selenium in vitamin tablets using spectrofluorometry following cloud point extraction

Selenium is one of the trace and essential elements for good health but required only in a very narrow range. Hence, determination of selenium in trace level is important. In this work, cloud point extraction (CPE) with non-ionic surfactant Triton X-114 and the fluorometric ligand, 2,3-diaminonaphtalene (DAN) were used for extraction of trace amounts of organic and inorganic selenium species prior to their determination by spectrofluorometry. CPE parameters affecting complexation and phase separation were optimised. The limit of detection calculated by using nine replicate measurements of 0.020 mg/L Se solution after complexing with DAN and 10-fold CPE preconcentration was 2.1 μg/L. Accuracy of the method was checked using EnviroMat Waste Water, EU-L-2 as CRM and result was found to be in good agreement with the certified value. The suggested method can be used for selenium species of selenite, selenate, and total organic selenium at μg/L level.