Search results for "Heat capacity"
showing 10 items of 90 documents
Derivation of a Homogenized Two-Temperature Model from the Heat Equation
2014
This work studies the heat equation in a two-phase material with spherical inclusions. Under some appropriate scaling on the size, volume fraction and heat capacity of the inclusions, we derive a coupled system of partial differential equations governing the evolution of the temperature of each phase at a macroscopic level of description. The coupling terms describing the exchange of heat between the phases are obtained by using homogenization techniques originating from [D. Cioranescu, F. Murat: Coll\`ege de France Seminar vol. 2. (Paris 1979-1980) Res. Notes in Math. vol. 60, pp. 98-138. Pitman, Boston, London, 1982.]
Single Enantiomer’s Urge to Crystallize in Centrosymmetric Space Groups: Solid Solutions of Phenylpiracetam
2017
A detailed thermochemical and structural study of the phenylpiracetam enantiomer system was performed by characterizing the solid solutions, rationalizing the structural driving force for their formation, as well as identifying a common structural origin responsible for the formation of solid solutions of enantiomers. Enantiomerically pure phenylpiracetam forms two enantiotropically related polymorphs (enant–A and enant–B). The transition point (70(7) °C) was determined based on isobaric heat capacity measurements. Structural studies revealed that enant–A and enant–B crystallize in space groups P1 (Z′ = 4) and P212121 (Z′ = 2), respectively. However, pseudoinversion centers were present res…
Volcanic plume and bomb field masses from thermal infrared camera imagery
2013
International audience; Masses erupted during normal explosions at Stromboli volcano (Italy) are notoriously difficult to measure. We present a method that uses thermal infrared video for cooling bomb fields to obtain the total power emitted by all hot particles emitted during an explosion. A given mass of magma (M) will emit a finite amount of thermal power, defined by M cp(Te−T0), cp and Te being magma specific heat capacity and temperature, and T0 being ambient temperature. We use this relation to convert the total power emitted by the bomb field to the mass required to generate that power. To do this we extract power flux curves for the field and integrate this through time to obtain to…
ON THE CALCULATION OF THE HEAT CAPACITY IN PATH INTEGRAL MONTE CARLO SIMULATIONS
1992
In Path Integral Monte Carlo simulations the systems partition function is mapped to an equivalent classical one at the expense of a temperature-dependent Hamiltonian with an additional imaginary time dimension. As a consequence the standard relation linking the heat capacity Cv to the energy fluctuations, <E2>−<E>2, which is useful in standard classical problems with temperature-independent Hamiltonian, becomes invalid. Instead, it gets replaced by the general relation [Formula: see text] for the intensive heat capacity estimator; β being the inverse temperature and the subscript P indicates the P-fold discretization in the imaginary time direction. This heatcapacity estimator…
Thermodynamic properties of a liquid–vapor interface in a two-component system
2010
Abstract We report a complete set of thermodynamic properties of the interface layer between liquid and vapor two-component mixtures, using molecular dynamics. The mixtures consist of particles which have identical masses and diameters and interact with a long-range Lennard-Jones spline potential. The potential depths in dimensionless units for like interactions is 1 (for component 1) and 0.8 (for component 2). The surface excess entropy decreases when the temperature increases, so the surface has a negative excess heat capacity. This is a consequence of the fact that the surface tension decreases to zero at the critical point, proportional to ( T C , i − T ) 2 ν . The surface entropy decre…
Thermodynamic properties of N-octyl- and N-dodecylnicotinamide chlorides in water
1990
Densities, heat capacities and enthalpies of dilution at 25°C and osmotic coefficients at 37°C were measured for N-octyl- and N-dodecylnicotinamide chlorides in water over an extended concentration region. Partial molar volumes, heat capacities, relative enthalpies and nonideal free energies and entropies at 25°C were derived as a function of the surfactant concentration. For both surfactants, plots of volumes, enthalpies and free energies vs. concentration are regular whereas those of heat capacities and entropies present anomalies at about 0.8 and 0.1m for the octyl and dodecyl compounds, respectively. Changes in the slope of a plot of osmotic coefficients times molality vs. molality were…
Thermodynamic and19F NMR studies of antimony trifluoride in water
1993
Densities, specific heat capacities per unit volume and enthalpies of dilution at 25°C and osmotic coefficients at 37°C were measured for antimony trifluoride in water as functions of concentration. From the first three properties the apparent and partial molar volumes, heat capacities and relative enthalpies were derived. As well, pH measurements in water at 25°C and19F NMR spectra in water and methanol at 33°C were also carried out. All the thermodynamic properties together with the chemical shifts abruptly change in the very dilute concentration region (<0.1m) and, then, tend to a constant value. These trends have been rationalized through a simple model based on an equilibrium of dissoc…
Volumes, heat capacities and solubilities of amyl compounds in decyltrimethylammonium bromide aqueous solutions
1989
Apparent molar heat capacities and volumes of amylamine (PentNH2) 0.02m, capronitrile (PentCN) 0.02m and nitropentane (PentNO2) 0.009m in decyltrimethylammonium bromide (DeTAB) micellar solutions, in water and in octane were measured at 25°C. By assuming that their concentration approaches the standard infinite dilution state, heat capacities and volumes were rationalized by means of previously reported equations following which the distribution constant between the aqueous and the micellar phase and heat capacity and volume of the additives in both phases are simultaneously derived. The present results are compared to those we have previously obtained for pentanol (PentOH). The thermodynam…
Binding between (Ethylene Oxide)13−(Propylene Oxide)30−(Ethylene Oxide)13 and Sodium Decanoate. Volume, Enthalpy, and Heat Capacity Studies
2002
Volume, enthalpy, and heat capacity of transfer (ΔYt) of (ethylene oxide)13−(propylene oxide)30−(ethylene oxide)13 (L64), at some concentrations, from water to the aqueous sodium decanoate (NaDec) solutions as functions of the surfactant concentration (mS) were determined at 298 K. The copolymer was studied in both the unassociated and associated forms. For a given L64 concentration (mC), the ΔYt vs mS profiles for the volume and the enthalpy are equal but different from that of the heat capacity because the latter contains also the relaxation terms. The experimental data were analyzed by assuming the distribution of L64 between the aqueous and the micellar phases and the shift of micelliza…
Heat Capacity of Transfer of (Ethylene oxide)13-(propylene oxide)30-(ethylene oxide)13 from Water to the Aqueous Anionic Surfactant Solutions at 298 …
2004
Heat capacities of transfer (ACpt) of unimeric (ethylene oxide)(13)-(propylene oxide)(30)-(ethylene oxide)(13) from water to the aqueous surfactant solutions as functions of the surfactant concentrations (m(S)) were determined at 298 K. The surfactants investigated are sodium hexanoate, sodium heptanoate, sodium octanoate, sodium undecanoate, and sodium dodecanoate. For short alkyl chain surfactants, the profiles of the DeltaCp(t) versus ms curves show maxima and minima; for long alkyl chain surfactants, the maximum becomes sharper and moved to lower ms values whereas the minimum tends to disappear. These experimental trends are different from those of the enthalpy in agreement with the fac…