Assessment of powder flow characteristics in incoherent soup concentrates

Soup mixtures represent specific flow characteristics while particles of different sizes and properties form a homogeneous mixture. In such mixtures, particle–particle interactions differ with addition of different fat types. This study was done to present a characterization and comparison of the cohesion index, powder flow speed dependency and caking properties of four different aggregates of fat particles with three different moisture contents, used in various compositions of powdered soup concentrates. ESEM micrographs have shown that different fat types bind particles differently. The moisture content of cream soup concentrates has a significant influence on cake height ratio of all cycles – more moisture causes higher cake height ratios (from r_s = 0.86 to r_s = 0.76; p < 0.05). Cream soup concentrates cake strength values are also significantly influenced by the mixtures moisture content – higher moisture content samples showed higher cake strength values (r_s = 0.73, p < 0.05). There is a significant correlation between compaction coefficients of all speeds and cake height ratios of all cycles for the cream soup concentrates. Combination of measuring techniques (Powder Flow Analyzer, ESEM and Mastersizer) together with Spearman’s Rank Order Correlation, as a method of non-parametric statistics, provides parturient results in characterization of extremely non-homogenous powder mixtures.     

Flame acceleration in channels with obstacles in the deflagration-to-detonation transition

It was demonstrated recently in Bychkov et al. [Bychkov et al., Phys. Rev. Lett. 101 (2008) 164501], that the physical mechanism of flame acceleration in channels with obstacles is qualitatively different from the classical Shelkin mechanism. The new mechanism is much stronger, and is independent of the Reynolds number. The present study provides details of the theory and numerical modeling of the flame acceleration. It is shown theoretically and computationally that flame acceleration progresses noticeably faster in the axisymmetric cylindrical geometry as compared to the planar one, and that the acceleration rate reduces with increasing Mach number and thereby the gas compressibility. Furthermore, the velocity of the accelerating flame saturates to a constant value that is supersonic with respect to the wall. The saturation state can be correlated to the Chapman-Jouguet deflagration as well as the fast flames observed in experiments. The possibility of transition from deflagration-to-detonation in the obstructed channels is demonstrated.     

A correlation to describe interfacial heat transfer coefficient during solidification of Al–Si alloy casting

A thin wall Al–9 wt.% Si alloy casting was made in a sand mold prepared by CO₂ process. The thermal history obtained from the experiment was used to solve an inverse heat conduction problem (IHCP). The IHTC was estimated by an iterative algorithm based on the function specification method. Acquired IHTC values are given as a function of time and as a function of the casting surface temperature at the interface. It has been found that pattern of IHTC variation with casting surface temperature can be described by an equation which has been proposed as a new correlation model. In order to verify broader applicability of the proposed correlation, its use is demonstrated on the IHTC results taken from the literature.     

Simulation of droplet impact on a solid surface using the level contour reconstruction method

We simulate the three-dimensional impact of a droplet onto a solid surface using the level contour reconstruction method (LCRM). A Navier-slip dynamic contact line model is implemented in this method and contact angle hysteresis is accounted for by fixing the contact angle limits to prescribed advancing or receding angles. Computation of a distance function directly from the tracked interface enables a straightforward implementation of the contact line dynamic model in the LCRM. More general and sophisticated contact line models are readily applicable in this front tracking approach with few modifications, since complete knowledge of the geometrical information of the interface in the vicinity of the wall contact region is available. Several validation tests are performed including 2D planar droplet, 2D axisymmetric droplet, and full three-dimensional droplet splashing problems. The results show good agreement compared with existing numerical and experimental solutions.     

Soybean oil‐chitosan emulsion affects internal quality and shelf‐life of eggs stored at 25 and 4 °C

Effects of soybean oil (SO), chitosan solution (CH) and their emulsions (SO:CH = 60:40, 50:50 and 40:60 ratios) as coatings on internal quality of eggs stored at 25 and 4 °C, respectively, for 7 and 20 weeks, were evaluated. Eggs coated with SO and SO:CH emulsions maintained grade AA and/or A quality up to 7 weeks at 25 °C and 20 weeks at 4 °C, while noncoated eggs changed from AA to B grade after 2 weeks at 25 °C. Compared with noncoated eggs, shelf‐life of eggs stored at 25 °C was extended for 5 weeks by all SO:CH emulsions. Weight loss of eggs coated with SO:CH emulsions was <3% after 7 weeks at 25 °C and <5% after 20 weeks at 4 °C. SO:CH emulsion is alternatively an effective coating with possible shorter drying times for reducing weight loss and preserving the internal quality of eggs.     

A novel approach for real-time prediction and prevention of tool chipping in intermittent turning machining

An integrated tool condition monitoring system, based on a novel signal processing approach, for online prediction and prevention of tool chipping in intermittent turning is presented. It identifies the unstable crack propagation features of the prefailure phase, independent of the cutting parameters and workpiece material. A correlation between the chipping size and these features was developed for decision making, to protect machined surfaces. Experimental validation results confirmed the accuracy of the proposed system. The time required for signal processing, decision making and communication with the machine controller allows stopping the operation before part damage. No such system is presently available.     

Intramolecular hydrogen bond controlled coordination of N-thiophosphorylated thiourea 2,6-Me2C6H3NHC(S)NHP(S)(OiPr)2 with Ni(II)

Reaction of O,O′-diisopropylthiophosphoric acid isothiocyanate (iPrO)₂P(S)NCS with 2,6-dimethylaniline 2,6-Me₂C₆H₃NH₂ leads to the new N-thiophosphorylated thiourea 2,6-Me₂C₆H₃NHC(S)NHP(S)(OiPr)₂ (HL). Reaction of the potassium salt of HL with Ni(II) in aqueous EtOH leads to the complex of formula [Ni(L-N,S)₂]. The molecular structures of the thiourea HL and the complex [Ni(L-N,S)₂] were elucidated by single crystal X-ray diffraction analysis, ¹H and ³¹P NMR spectroscopy and microanalysis. In the complex [Ni(L-N,S)₂], the metal center is found to be in a square-planar N₂S₂ environment formed by the CS sulfur atoms and the P–N nitrogen atoms of two deprotonated L ligands. The ligands are in a trans-configuration.     

Numerically assisted analysis of flat and corrugated plate solar collectors thermal performances

The paper presents the results of experimentally supported numerical analysis performed in order to investigate the possibilities to improve the thermal efficiency of plate solar collectors. Different numerical models were developed in order to asses the influence of design and operating parameters such as bond conductance between absorber plate and tube, tube diameter, glass cover to absorber plate distance, optical properties of absorber and flow rate on thermal efficiency of collectors. Following the results, two designs of collector without tubes, with parallel flat and corrugated absorber plates of chevron type, is further considered and shown to be an effective way to increase the thermal efficiency of solar energy conversion beyond that of commercial glazed and unglazed solar water heaters. Based on the results, the guidelines for design of a new collector prototype consisting of chevron type corrugated plates normally used in plate heat exchangers are provided.     

Comparative study of commercially available cocoa products in terms of their bioactive composition

Recent trends in food marketing suggest that cocoa products, besides being favourite sweets among consumers, also present multiple-benefit foodstuffs, which are becoming objects of increased scientific research, mainly because of their interesting phytochemical composition. UV/VIS spectrophotometric and high-performance liquid chromatography (HPLC-PDA) methods were applied in order to compare the composition of polyphenols and methylxanthines in commercial cocoa products affected by different extraction solvents. Antioxidant capacity of water and methanol extracts was evaluated using DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) and FRAP (ferric reducing/antioxidant power) assays. The obtained results confirmed that the content of polyphenols and methylxanthines, as well as the antioxidant capacity of cocoa products depend on the content of their cocoa solids. Among the tested cocoa products, the highest content of bioactive compounds (polyphenols and methylxanthines) was determined in extracts of cocoa products with the highest content of cocoa solids (cocoa liquor, cocoa powder and dark chocolate with 88% cocoa solids), while the lowest content was determined in milk chocolate and cocoa bar extracts. The most abundant phenolic compound in cocoa extracts was (?)-epicatechin, while the most abundant methylxanthine was theobromine. In comparison with water, 70% methanol demonstrated higher efficiency for the extraction of the studied bioactive compounds from cocoa products.     

NPV-based decision support in multi-objective design using evolutionary algorithms

Optimum design problems are frequently formulated using a single excellence criterion (minimum mass or similar) with evolutionary algorithms engaged as decision-support tools. Alternatively, multi-objective formulations are used with a posteriori decision-making amongst the Pareto candidate solutions. The former typically introduces excessive simplification in the decision space and subjectivity, the latter leads to extensive numerical effort and postpones the compromise decision-making. In both cases, engineering excellence metrics such as minimum mass can be misleading in terms of performance of the respective design in the given operational environment. This paper presents an alternative approach to conceptual design where a compound objective function based on the Net Present Value (NPV) and Internal Rate of Return (IRR) aggregate performance metrics is developed. This formulation models the integral value delivered by the candidate designs over their respective life-cycles by applying value-based NPV discounting to all objectives. It can be incorporated as an a priori compromise and consequently viewed as a weighted sum of individual objectives corresponding to their economically faithful representation over the entire operational life-time of the designs. The multi-objective design optimization is consequently expanded from purely engineering terms to coupled engineering–financial decision support.