Alternative approach in thermal analysis of plate heat exchanger

This paper presents alternative approach in heat transfer analysis of plate heat exchangers. In order to obtain heat transfer rate and effectiveness values of plate heat exchanger, neural network (NN) approach was used. Experimentally, system used in plate heat exchanger for heating and cooling applications was designed and constructed. Experimental data were used for training and testing network. The training and validation were performed with good accuracy. The correlation coefficient obtained when unknown data were applied to the networks was 0.9994 for heat transfer rate and 0.9976 for effectiveness, which is very satisfactory. Using the weights obtained from the trained network, a new formulation is presented for determination of heat transfer rate and effectiveness. This formulation can provide simplicity in thermal analysis of plate heat exchanger. The presented procedure can also help to heat exchanger designer and manufacturer.     

Structural and magnetic properties of Sc1.1Fe3.9Al8 alloy

The crystallochemical and magnetic nature of ternary Sc_1+δFe_4−δAl₈ intermetallic with a small Sc excess δ=0.1 was investigated by scanning electron microscope, X-ray powder diffraction, neutron diffraction, Mössbauer effect and superconducting quantum interference device techniques. The sample crystallizes in a tetragonal ThMn₁₂ type structure. The excess of Sc atoms substitute Fe at the (8f) positions and have a pronounced effect on the magnetic properties. The experiments carried out in temperature range 4-320 K show that below 120 K the magnetic structure of the alloy forms a double cycloid with magnetic moments rotating according to the incommensurate in-plane wave vector, which is temperature independent up to 160 K. The value of Fe magnetic moment is close to 0.9 μ_B atom⁻¹ at 4 K. Temperature dependence of unit cell dimensions can be explained within the Debye-Grüneisen approximation.     

Phenolic compounds content and antioxidant capacity in cardoon achenes from different head orders

Abstract

Cardoon inflorescences (heads) contain achenes, which are used for the production of edible oil and biodiesel but also represent a phenolic source. This research aimed at determining the level of bioactive compounds and antioxidant capacity of cardoon achenes and investigating their qualitative and quantitative variations in achenes harvested from heads having different insertion order on main stem. The head order significantly affected the number of achenes per head and one thousand weight but did not affect the achene values of antioxidant capacity and concentrations of total phenolic (107.7–117.4?g gallic acid equivalent kg^?1?dry weight), as well as the concentration of chlorogenic and 3,5-di-O-E-caffeoylquinic acids. Conversely, the absolute amounts of these metabolites differed significantly among head order when referred to a single achene or head. About 75% of their absolute values per cardoon plant were produced by achenes belonging to secondary and tertiary heads.     

Novel simple methods for the synthesis of single-phase valentinite Sb2O3

Several methods with solid and dissolved reactants were investigated as possible routes for synthesis of single-phase valentinite Sb₂O₃. The methods are based on simple chemical reaction between SbCl₃ and NaOH. The method with solid state reactants was established on self-propagating room temperature reaction (SPRT), while wet syntheses were based on the same chemical reaction, and performed in either distilled water or absolute ethanol. The prepared powders were characterized by X-ray powder diffraction, scanning electron microscopy and field emission scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction (SAED) and UV/vis diffuse reflectance spectroscopy. SPRT and aqueous solution syntheses resulted in single-phase valentinite Sb₂O₃, but with significantly different morphologies. In the case of SPRT method the obtained powder contains well crystallized prismatic shaped submicronic particles, with hexagonal or lozenge basis typical for valentinite crystal structure, while aqueous solution synthesis resulted in powder containing micronic agglomerates. The ethanolic solution synthesis product was Sb₂O₃ with cubic senarmontite as predominant phase and traces of orthorhombic valentinite. It was confirmed that not only the aggregate state, but also the choice of solvent has a great influence on the structural and optical characteristics of synthesized Sb₂O₃ powders.     

C. A. coulson and the surface energy of metals: The distribution of eigenvalues as a difficult problem in number theory

An article by Coulson on the relationhship of physics and mathematics has attracted our attention to problems already discussed by Titchmarsh, namely the distribution of quantum energy levels of a particle confined in a square or a cube with infinite potential-energy walls. These problems are identical to some classical problems in the theory of lattice points, which belongs to number theory. They are seemingly simple, but in fact they are very difficult and not yet completely solved. We summarize the most relevant results from number theory. Whereas the beautiful theorems bearing directly on the error with respect to elementary estimates only provide indications concerning the order of that error; theorems concerning mean values can be used as a basis for a physicist's guess on its asymptotic mean value. This paper has also been intended to contribute to bridging the gap between quantum mechanics and number theory.