Surface-tension-induced interfacial convection and its effect on rates of mass transfer

Surface-tension-induced interfacial convection (Marangoni phenomena) can appear as a result of mass and heat transfer, compression and dilatation of surface films or their non-Newtonian behaviour and owing to presence in the interface of electrostatic charges. In process engineering problems the mass transfer effect is usually predominant and, depending on the geometry of the system, leads to surface renewal or changes in interfacial area. The surface renewal phenomena can appear as instabilities or disturbances and their effect on mass transfer is presented for transfer to and from drops as well as across flat interfaces in stirred and laminar flow contactors. Mass transfer coefficients and drag coefficients of drops are compared under conditions of undisturbed (diffusional) transfer, cellular convection and interfacial turbulence for stable and unstable direction of transfer. The importance of gravitational instability is indicated.     

Study of spray cooling of a pressure vessel head of a boiling water reactor

The present paper deals with a theoretical analysis of the spray cooling of a Reactor Pressure Vessel (RPV) head in a Boiling Water Reactor (BWR). To this end a detailed computational model has been developed. The model predicts the trajectories, diameters and temperatures of subcooled droplets moving in saturated vapor. The model has been validated through comparison with experimental data, in which droplet temperatures were measured as functions of the distance that they cover in saturated vapor from the moment they leave the sprinkler outlet to the moment they impact on the RPV head inner wall. The calculations are in very good agreement with measurements, confirming the model adequacy for the present study. The model has been used for a parametric study to investigate the influence of several parameters on the cooling efficiency of the spray system. Based on the study it has been shown that one of the main parameters that govern the temperature increase in a subcooled droplet is its initial diameter. Comparisons are also made between conclusions from the theoretical model and observations made through flow and temperature measurements in the plant (Forsmark 1 and 2). One of these observations is that the rate at which the RPV head temperature decreases on the way down from hot to cold standby is constant and independent of the sprinkling flow rate as long as the flow rate is above a certain minimum value. Accordingly, the theoretical model shows that if one assumes that the cooling of the RPV head is through a water film built on the inner wall due to sprinkling, the heat removal rate is only very weakly dependent on the sprinkling flow rate.     

Characterization ofβ-carotene thermal degradation products in a model food system

A model system developed in our laboratory for the study of thermal degradation products (TDP) of carotenoids was employed.β-Carotene (10 g) in glycerol was heated at 210 C for 4 hr, 1 hr, 15 min and 5 min. The time and temperature chosen were similar to edible oil deodorization and deep fat frying. In this study, the TDP ofβ-carotene were quantified as influenced by time and temperature of heating. Results indicate that at 210 C, degradation is almost complete after 4 hr and most of the nonvolatile products are viscous, yellow-brownish material. Shorter times (1 hr, 15 min and 5 min) cause less degradation. TDP include nonpolar as well as oxidized derivatives ofβ-carotene. The results of this study provide information on the type, amount and mechanism of formation of compounds resulting from heating carotenoids. Presented at the AOCS meeting in Dallas, Texas, in 1984.     

Acrylamide formation in low-fat potato snacks and its correlation with colour development.

A recipe and technological process for the production of low-fat potato snacks (7% fat) was developed at the Institute of Food Technology of Plant Origin (Agricultural University of Poznan) using a combination of extrusion and a roasting process. Due to the character of the product, the level of acrylamide was analysed. At the same time, the influence of temperature and time of heating on acrylamide levels were monitored, as well as the correlation between colour development and acrylamide content. The level of acrylamide in low-fat potato snacks was 489 +/- 26 microg kg(-1), which is comparable to French fries, crackers and cookies but almost three times less than in potato chips, as analysed by other authors. It was also shown that temperature and heating time have a significant influence on acrylamide formation, with temperature having a stronger effect than time. Measurement of colour and acrylamide content at different temperatures and roasting times showed that there is a substantial correlation between lightness (L*), redness (a*), yellowness (b*) and acrylamide concentration as a function of time: r(2) = -0.995, r(2) = 0.996, r(2) = 0.998, respectively. Graduated increases in roasting temperature showed a correlation between lightness (L*) or redness (a*) and acrylamide concentration: r(2) = -0.947 and r(2) = 0.968. Yellowness (b*) was not correlated with acrylamide content as a function of temperature.     

Vibrational spectroscopy and periodic DFT studies of LaMg2PdH7: A material with two types of hydride

The need for a safe, reliable and cheap method for hydrogen transportation has prompted an intense effort in the synthesis of novel hydrides. To direct the search for better materials, it is essential to understand the bonding present in these systems. A newly synthesized material is LaMg₂PdH₇ which is best formulated as {La³⁺}{Mg²⁺}₂{[PdH₄]⁴⁻}{H⁻}₃. Thus hydrogen is formally present both as a free hydride ion and also as a covalently bound ligand. The combination of inelastic neutron scattering (INS), infrared and Raman spectroscopies and periodic density functional theory (DFT) has been used to characterise the material. We find that the material is less ionic than Ba₂[PdH₄], which also contains [PdH₄]⁴⁻. The charges carried by both the coordinating and free hydrides are similar which hints at a degree of covalency in the interactions between the interstitial hydrides and the lanthanum and magnesium ions.     

Use of Sorbent-Based Vacuum Extraction for Determination of Volatile Phenols in Beer

A novel method based on vacuum-assisted sorbent extraction (VASE) used with gas chromatography-mass spectrometry (GC-MS) for isolation of volatile phenols was described. The method is based on extraction of analytes into sorbent traps (sorbent pen) filled with Tenax in a vacuum system—vials with traps from which air was evaluated. The method was applied for extraction of volatile phenols from aqueous matrix and smoked beer was used as a food example. Methyl-, dimethyl-, and trimethylphenols, along with 4-ethylphenol, 4-methylguaiacol, 4-ethylguaiacol, 4-propylguaiacol, and eugenol, were used in method development. Optimal extraction parameters were elaborated. For the analysis of volatile phenols in beer matrix, the method was characterized with satisfactory linearity (r²?≥?0.99) in a range of 0.005–0.5 mg/L. Limits of detection (LODs) for analyzed compounds ranged from 0.0006 to 0.018 mg/L and repeatability for majority of compounds was <?5% for a single trap extraction. The detected volatile phenols in beer samples ranged from 0.003 to 0.672 mg/L.     

Synthesis and Characterization of Low Viscosity Dimethacrylic Resin Based on Isosorbide

In this article, synthesis and properties of novel dimethacrylic resin (ISETDMA) based on human friendly, biobased isosorbide was described. Its potential as a possible diluting monomer for medical applications, mainly dental restorative systems was assessed. The resin was obtained in two‐step synthesis including ethoxylation of isosorbide and subsequent methacrylation with methacryloyl chloride. ¹HNMR, FTIR, and electrospray ionization mass spectroscopy (ESI‐MS) techniques were used to identify products. ISETDMA as well as composition with 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloyloxypropoxy)phenyl]propane were polymerized using UV initiator IRGACURE 651. Double bond conversion, polymerization shrinkage, water sorption, and sol fraction of resulting polymers were determined. Selected mechanical (flexural strength and modulus, Brinell hardness) and thermomechanical (dynamic mechanical analysis) properties were also investigated. Triethylene glycol dimethacrylate and 2,2‐bis(4‐(2‐methacryloxyethyl‐1‐oxy)phenyl)propane based homopolymers and copolymers were prepared as reference for comparison of particular properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2514–2522, 2013     

Charged polaron-enhanced circular dichroism of optically nonlinear 3-nitroaniline crystal

The circular dichroism (CD) spectra in visible range of the 3-nitroaniline (m-NA) single crystal, of its solution in chloroform, and in the KBr pellet were recorded. Neither the molecular (m or C_s) nor the crystal (mm2 or C_2v) point groups belong to the chiral groups. The DFT calculation of CD spectrum of the m-NA isolated neutral molecule confirmed its chirality. The red shifted bands in the calculated CD spectrum of m-NA radical anion (charged polaron), as compared with the neutral molecule, resemble better the spectra of solids than that of the solution. It seems that these facts corroborate qualitatively the “hop and turn” model explaining the m-NA optical nonlinearity and electric conductivity proposed in Szostak et al. [M.M. Szostak, H. Chojnacki, E. Staryga, M. D?u?niewski, G. B?k, Chem. Phys. 365 (2009) 44-52].     

Influence of soil moisture on the results of surface geochemical survey applied to petroleum exploration

The quality of results obtained from surface geochemical exploration depends not only on the character of deep petroleum accumulations but also on the influence of many sub-surface factors. One of important factors is the presence of soil moisture in the sampling interval. This research presents the influence of soil moisture on concentrations of gaseous hydrocarbons in sampled soil gases. The comparative analysis was made on for two populations of gaseous hydrocarbon (methane, ethane, propane, i-butane, n-butane, propylene, 1-butene) concentrations measured in soil gas samples collected from the water-saturated (“wet” sampling interval) and water-free (“dry” sampling interval) environments. The comparison was based upon chromatographic analyses of 2974 samples of soil gas, in which 684 samples originated from “wet” sampling intervals and 2290 samples were taken from “dry” interval. Samples were collected in the areas of known gas deposits located in the Fore-sudetic Monocline (SW Poland). Samples collected from the “wet” intervals reveal higher concentrations of almost all analyzed hydrocarbons in comparison with samples from “dry” intervals. Highest differences were observed for methane concentrations and lowest — for total alkanes C₂–C₄. The increase of concentrations in “wet” sampling intervals can be explained by sub-surface accumulation of hydrocarbons caused by decreasing permeability of water-saturated soils, by the different solubilities of alkanes and alkenes in water as well as by recent generation of methane and alkenes. Considering the results obtained from the area of the Tarchaly gas deposit, it was found that surface pattern of methane anomalies does not reflect the presence of deep gas accumulations, as well as the total alkanes C₂–C₄ distribution. Hence, the procedure was proposed of elimination of soil moisture influence on the pattern of surface methane anomalies. The procedure includes normalization of measured methane concentrations to the reference levels of geochemical background, which characterize “wet” and “dry” sampling intervals. As a result, the distribution of anomalous methane concentrations was obtained, which, along with the distribution of total alkanes C₂–C₄, confirms the presence of assessed accumulation of gaseous hydrocarbons. Therefore, the proposed method is correct and supports the application of methane indicator as a petroleum exploration tool.     

Novel approach for measuring the effective shear modulus of porous materials

A new approach is proposed for the experimental study of the effective shear modulus of porous elastic materials using the uniaxial tension test. The idea is to measure strains at a few points surrounding a cluster of holes that represents the structure of the material. The representative cluster is placed in the material with the same elastic properties as those of the matrix. The measured strains lead to the properties of the equivalent circular inhomogeneity, which would produce the same elastic fields as from the cluster. An aluminum plate containing a cluster of seven circular or hexagonal holes was used. The effective shear modulus obtained from the strain data was compared with theoretical predictions and various bounds, and it was shown that the laboratory estimated values are quite accurate. The experimental technique can be used for the determination of the effective Poisson’s ratio of porous media and/or cellular solids if more detailed strain data are obtained.