Search results for "enthalpy"
showing 10 items of 199 documents
Integral relations, a simplified method to find interfacial resistivities for heat and mass transfer.
2007
International audience; Integral relations were used to predict interface film transfer coefficients for evaporation and condensation. According to these, all coefficients can be calculated for one-component systems, using the thermal resistivity and the enthalpy profile through the interface. The expressions were verified in earlier work using non-equilibrium molecular dynamics simulations for argon-like particles, which interacted with a short-range Lennard-Jones (LJ) spline potential, which becomes zero at about 1.7 times the LJ-diameter. In this paper we verify the validity of these relations for a long-range LJ spline potential which becomes zero at 2.5 times the diameter. In an earlie…
Charge-Induced Deformation of the 4He Solid-Superfluid Interface
1984
The interface between solid and superfluid 4He has revealed unusual dynamic properties. Characteristic of this quantum system are the very high thermal conductivity of the superfluid phase, and an extremely small heat of fusion below temperatures of about 1 K. As a result, equilibrium at the solid-superfluid 4He interface is established quite rapidly, which gives rise, e.g., to melting — crystallization waves [1,2] — similar in appearance to surface waves on a free liquid surface — and to anomalous transmission of sound [3].
Energetics of Water−Dodecyl Surfactant−Macrocyclic Compound Ternary Systems
1996
Enthalpies of dilution and osmotic coefficients of sodium dodecyl sulfate (NaDS) and dodecyltrimethylammonium bromide (DTAB) in water + 18-crown-6 ether (CR) and water + β-cyclodextrin (CD) at a fixed cosolvent concentration were measured at 298 and 310 K, respectively, as functions of the surfactant concentration (mS). Enthalpies of transfer ΔH (W → W + S) of CR (0.03 m) from water to NaDS and DTAB aqueous solutions as functions of mS were also determined at 298 K. From the enthalpies of dilution the apparent (LΦ,S) and partial (L2,S) molar relative enthalpies of both surfactants were calculated. Despite CR forms inclusion complexes with the anionic surfactant only, the L2,S vs mS profiles…
Low-pressure-MOCVD LaMnO3±δ very thin films on YSZ (100) optimized for studies of the triple phase boundary
2000
Abstract This paper deals with the preparation of LaMnO 3± δ (LM) layers by low pressure-metal organic chemical vapor deposition (LP-MOCVD) using La(tmhd) 3 and Mn(acac) 3 as organometallic precursors. By thermogravimetric analysis, these precursors were found to be suitable for LP-MOCVD in a well-defined range of total pressure and temperature of sublimation. The activation energies of the sublimation process were found to be independent of the pressure within the appropriate range (0.06–3 kPa) and their values were 177 and 100.5 kJ mol −1 for La(tmhd) 3 and Mn(acac) 3 , respectively. LM layers of various thickness ranging between a few and a few hundred nanometers with a controlled La/Mn …
Comparison of Permeation Measurements and Hybrid Density Functional Calculations on Oxygen Vacancy Transport in Complex Perovskite Oxides
2014
The oxygen vacancy (VO••) formation enthalpy (ΔHF) was determined from the effective activation energies obtained in the permeation measurements on a series of solid solutions La0.98–xSrxCo0.2Fe0.8O3−δ (x = 0.125–0.8) and compared with the results of ab initio calculations at finite temperatures based on the hybrid (PBE0) and GGA+U calculations, as well as previous thermogravimetric experiments. The Mulliken atomic charges, magnetic moments, and the Fe-VO•• and Sr-VO•• distances are analyzed. The strong dependence of formation enthalpy of VO•• on the Fe oxidation state due to variation in Sr and VO•• concentrations is discussed.
Mobility determination of lead isotopes in glass for retrospective radon measurements
2008
In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)Pb is often considered to be relatively immobile in glass after alpha recoil implanted by (222)Rn progenies. The diffusion of (210)Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if (210)Pb is mobile and can escape from glass, or lost as a result of cleaning-induced surface modification. This diffusion was studied by a radiotracer technique, where (209)Pb was used as a tracer in a glass matrix for which the elemental composition is known. Using the ion guide isotope separator on-line technique, the (209)Pb atoms were implanted into the glass with an energy of …
DSC Studies and Stability of Frozen Foods
1991
This paper discusses the role played by the “WLF decrease in viscosity” above the temperature of the glass transition (Tg) in the temperature dependence of the stability of frozen foods. In the first part, the complex features observed before the melting endotherm on DSC/DTA thermograms of sugar-water solutions are examined; they are suggested to be representative of a glass transition associated with enthalpy relaxation. In the second part, the values of Tg for some complex foods are discussed. It is shown that ice melting adds an important contribution to the WLF effect on the decrease of the viscosity of the freeze-concentrated phase. The temperature dependence of the deterioration proce…
Über die möglichkeiten zur bestimmung von mischungsenthalpien und -volumina aus der molekulargewichtsabhängigkeit der kritischen entmischungstemperat…
1977
Cloud-point curves and critical curves (Tc = f(p)) have been measured for the system trans-decahydronaphthalene/polystyrene and three different molecular weights of the polystyrene component (2,5 · 106; 3,9 · 105; 1,1 · 105). It turned out that by variation of the pressure the metastable region can be investigated up to the spinodal curve. A comparison of the theta-temperatures and the enthalpy contributions χH (to the Flory-Huggins interaction parameter χ) resulting from the measured critical temperatures according to Shultz-Flory, with the corresponding directly obtained literature data, demonstrates that, although the extrapolation of Tc to infinite molecular weight is feasible, χH obtai…
Hydration and dehydration kinetics of xylazine hydrochloride
2009
From the experiments where mixture of xylazine hydrochloride hydrate H and anhydrous X were held at constant conditions, the stable form of xylazine hydrochloride can be found out. To determine equilibrium relative humidity, the unstable form of xylazine hydrochloride was inserted in thermostated humidity chamber and its weight was recorded by weighing the sample outside the chamber. The kinetic model and the rate constant for each condition were determined. The rate constants give information regarding the speed of the process at every experimentally used relative humidity. Thus using the data in coordinates k – p for each temperature it is possible to determine the water vapor pressure of…
Thermodynamics of binding between α- and β-cyclodextrins and some p-nitro-aniline derivatives: reconsidering the enthalpy–entropy compensation effect
2004
Abstract The thermodynamics of binding between native α- and β-cyclodextrin towards several p -nitro-aniline derivatives was examined, in order to gain further insights about the occurrence of different interaction modes for the two hosts. Valuable information was achieved regarding the ‘expanded hydrophobic sphere’ of α-cyclodextrin. Furthermore, very interesting and unexpected aspects of the behavior of β-cyclodextrin were enlightened, such as the crucial role played by hydrogen bond interactions. Experimental data were examined under the perspective of the ‘enthalpy–entropy compensation effect’, and some ideas about this topic are discussed.