| 1. |
- Etbaeitabari, Amir, et al.
(author)
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An analytical heat transfer assessment and modeling in a natural convection between two infinite vertical parallel flat plates
- 2013
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In: Journal of Molecular Liquids. - : Elsevier. - 0167-7322 .- 1873-3166. ; 188, s. 252-257
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Journal article (peer-reviewed)abstract
- Heat transfer by natural convection occurs in many physical problems and engineering applications such as geo-thermal systems, heat exchangers, petroleum reservoirs and nuclear waste repositories. These problems and phenomena are modeled by ordinary or partial differential equations. In most cases, experimental solutions cannot be applied to these problems, so these equations should be solved using special techniques. Recently, much attention has been devoted to these methods to construct analytic solutions; such as the perturbation method. Perturbation techniques are dependent upon small parameter. Thus, it is worthwhile developing a new technique independent of small parameter. The Reconstruction of Variational Iteration Method technique is a powerful and convenient algorithm in finding the solutions for the equations. While this method is capable of reducing the size of calculation, it overcomes the difficulty of the perturbation technique or Adomian polynomials by applying Laplace Transform. In this paper an analysis has been performed to study the natural convection of a non-Newtonian fluid between two infinite parallel vertical flat plates and the effects of the non-Newtonian nature of fluid on the heat transfer are studied. In order to compare with exact solution, velocity and temperature profiles are shown graphically. The obtained results are valid with significant accuracy. (C) 2013 Elsevier B.V. All rights reserved.
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| 2. |
- Harsanyi, I., et al.
(author)
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On the hydration structure of LiCl aqueous solutions : A Reverse Monte Carlo based combination of diffraction data and Molecular Dynamics simulations
- 2011
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In: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322 .- 1873-3166. ; 158:1, s. 61-67
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Journal article (peer-reviewed)abstract
- Reverse Monte Carlo (RMC) calculations have been carried out on aqueous LiCl solutions at several concentrations, comparing experimental X-ray and neutron diffraction data with partial radial distribution functions (prdf) from Molecular Dynamics (MD) simulations based on conventional ion-ion, ion-water, and water-water pair potentials. The RMC calculations indicate that the hydration shell of the Li+ ions could be even more structured than computer simulations predict, containing at high concentrations unusually few water molecules, of the order of 2 to 3. Concerning the consistency between the structures based on potential models and diffraction data: the ion-water partial radial distribution functions (prdf) from MD are found to be consistent with the experimental data whereas the water-water and ion-ion partials are more problematic. The most serious deficiency is that at high salt concentrations the O-O prdf cannot be made consistent with the present X-ray diffraction data.
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| 3. |
- Jogunola, Olatunde, et al.
(author)
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Screening of potential complexing agents in methyl formate hydrolysis
- 2014
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In: Journal of Molecular Liquids. - : Elsevier. - 0167-7322 .- 1873-3166. ; 196, s. 334-339
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Journal article (peer-reviewed)abstract
- More than 70 individual compounds, mainly amines, natural products, organophosphates and sulfur-containing organic compounds, deemed as having potentially suitable complexing strength were screened in order to determine their ability to improve the equilibrium conversion of methyl formate hydrolysis. In fact, alkylphosphates, natural products and organosulfur compounds gave lower methyl formate conversions. After careful screening and investigation of the different classes of amines, aromatic heterocyclic and some tertiary amines were chosen for further investigation. However, it was discovered that imidazoles and substituted piperazines came closest to fulfilling most of the selection criteria as a good complexing agent due to their ability to form a reversible ion pair with the acid product, in addition to their high boiling point, low nucleophilic strength, less bulkiness and thermal stability. A general procedure was proposed for the screening of potential complexing agents. This approach was proven as a rapid one, consumed fewer chemicals and could be used to estimate the complexation power of different candidate compounds in the hydrolysis-complexation process when accurate calculation tools are not available.
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| 4. |
- Nilsson, Anders, et al.
(author)
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Fluctuations in ambient water
- 2012
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In: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322 .- 1873-3166. ; 176:SI, s. 2-16
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Journal article (peer-reviewed)abstract
- We emphasize the importance in simulations of water of reproducing the isothermal compressibility, dependent on density fluctuations in the liquid, for a correct description of structural fluctuations in simulated water. From x-ray spectroscopy a strict bimodality in terms of fluctuations between high- (HDL) and low-density (LDL) forms of the liquid has been reported. The inherent structure in simulations, i.e. the structure quenched to 0 K, is found to be bimodal in terms of HDL and LDL in close correspondence to x-ray spectroscopy. This is, however, smeared out in the real structure where temperature is included. We suggest that the local minima for the HDL and LDL local structures in the simulation need to be deeper and propose that many-body electronic structure effects and non-local van der Waals interactions will be important in this respect. Much larger simulations than hitherto considered are likely necessary to catch the effects of both thermal and structural fluctuations in the simulated liquid. Since structural fluctuations can be expected to significantly affect the dynamics in the liquid it is important that these are taken properly into account when discussing hydrogen-bond breaking and reformation. Here it is essential that the model used correctly reproduces the temperature and pressure dependence in thermodynamic response functions.
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| 5. |
- Andersson, Agneta, 1968-, et al.
(author)
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Plasma Alkylresorcinol Concentrations Correlate with Whole Grain Wheat and Rye Intake and Show Moderate Reproducibility over a 2- to 3-Month Period in Free-Living Swedish Adults
- 2011
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In: Journal of Nutrition. - Rockville Pike, Bethesda : American Society of Nutrition. - 0022-3166 .- 1541-6100. ; 159, s. 1712-1718
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Journal article (peer-reviewed)abstract
- Plasma alkylresorcinols (AR) are useful as dietary biomarkers of wheat and rye whole grain (WG) during interventions but need to be validated in free-living populations. This study estimated the medium-term reproducibility and relative validity of plasma AR as biomarkers of WG and cereal fiber intake. Seventy-two Swedish adults kept 3-d weighed food records on 2 occasions 2-3 mo apart. Of these men and women, 51 provided a fasting blood sample at the end of each occasion. In addition, 18 participants provided 3 fasting and 3 nonfasting samples for 3 consecutive days on the first and second occasions, respectively. Dietary and blood variables did not differ between the 2 occasions. Nonfasting plasma total AR concentration [210 nmol/L (95% CI: 140, 314)] was higher than fasting [99 nmol/L (95% CI: 72, 137)] (P < 0.0001). Mean WG intake was 70 ± 61 g/d (41% from rye) and the intra-class correlation coefficient was 0.44 (95% CI: 0.26, 0.63) for total WG intake and 0.47 (95% CI: 0.27, 0.67) for the fasting plasma total AR concentration, suggesting moderate reproducibility. Fasting plasma total AR moderately correlated with WG rye + wheat (r(s) = 0.53; P < 0.001) and cereal fiber intake (r(s) = 0.32; P < 0.05) when using mean values from both occasions. This suggests that plasma AR concentration in fasting samples can be used as a biomarker of rye + wheat WG intake in free-living populations with a high and consistent WG intake.
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| 6. |
- Brodin, A., et al.
(author)
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Dipolar interaction and molecular ordering in liquid propylene carbonate: Anomalous dielectric susceptibility and Raman non-coincidence effect
- 2011
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In: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322. ; 164:1-2, s. 17-21
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Journal article (peer-reviewed)abstract
- Dielectric constant of non-associating fluids normally exhibits a 1/T temperature dependence according to Curie's law. Kirkwood correlation factor in such cases is close to unity and almost independent of the temperature. Recent broadband dielectric studies of a well-known solvent propylene carbonate (PC) revealed anomalous behavior of its loss spectrum, whose amplitude somewhat increases at high temperatures contrary to Curie's law, while it is known from the literature that its Kirkwood factor is close to unity. We analyze the origin of this discrepancy and find, based on recent literature data, that the Kirkwood factor of PC is strongly temperature dependent and significantly differs from unity, which signals the presence of temperature dependent molecular ordering. We find other signatures of this ordering in vibrational spectra of PC, where it leads to splitting of molecular vibrations due to interaction between the transition dipoles of neighboring molecules (the so-called non-coincidence effect). Spectroscopic and dielectric results agree well with each other and reveal the presence of significant temperature-dependent anti-parallel dipolar arrangement. Based on these results, it is likely that other polar liquid:; with large and localized molecular dipoles, albeit traditionally classified as non-associating, in fact do possess significant local molecular order due to dipolar interactions.
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| 7. |
- Lindman, Björn, et al.
(author)
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On the mechanism of dissolution of cellulose
- 2010
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In: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322. ; 156:1, s. 76-81
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Journal article (peer-reviewed)abstract
- Cellulose is insoluble in water and many organic solvents, but can be dissolved in a number of solvents of intermediate properties, like N-methylmorpholine N-oxide (NMMO) and ionic liquids (ILs). It can also be dissolved in water at high and low pHs, in particular if a cosolute of intermediate polarity is added. The insolubility in water is often referred to strong intermolecular hydrogen bonding between cellulose molecules. However, an examination of the interactions involved reveals another picture, which suggests that cellulose is significantly amphiphilic and that hydrophobic interactions are important for explaining the solubility pattern of cellulose. (C) 2010 Elsevier B.V. All rights reserved.
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| 8. |
- Söderman, Olle, et al.
(author)
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NMR diffusometry applied to liquids
- 2010
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In: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322. ; 156:1, s. 38-44
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Journal article (peer-reviewed)abstract
- Gradient based nuclear magnetic resonance spectroscopy provides a convenient method to determine self-diffusion coefficients especially in liquid samples. The method has many advantages including short experiment time, sensitivity, molecular resolution, and accuracy - all without the need for adding perturbing probes or chemically introducing isotopes. In this contribution we introduce the method and discuss through several examples its uses. We discuss how the method provides diffusion coefficients in supercooled water and alcohol-water mixtures. In ionic liquids the method conveys information about single ion mobilities and cluster formation. In self-assembling systems possible aggregate growth can be conveniently investigated. We demonstrate, based on self-diffusion coefficients, that there is little evidence for aggregation in aqueous solutions of cyclodextrins. Finally, we demonstrate how NMR diffusometry can be used to determine the diffusion of water inside a biological cell. It goes without saying that such data are very important in the understanding of transport properties in cells, where diffusion plays a major role. (C) 2010 Elsevier B.V. All rights reserved.
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