Computational Approach to the Study of Thermal Spin Crossover Phenomena

The key parameters associated to the thermally induced spin crossover process have been calculated for a series of Fe(II) complexes with mono-, bi-, and tridentate ligands. Combination of density functional theory calculations for the geometries and for normal vibrational modes, and highly correlated wave function methods for the energies, allows us to accurately compute the entropy variation associated to the spin transition and the zero-point corrected energy difference between the low- and high-spin states. From these values, the transition temperature, T 1/2, is estimated for different compounds.

Design of PCM thermal storage unit for a HVAC system

L'objectiu del projecte és el disseny d'una unitat d'emmagatzematge d'energia térmica que optimitzi i millori l'eficiència del sistema de climatització. Aquesta unitat contindrà materials de canvi de fase (PCM) per emmagatzemar l'energia i estarà acoblada a un sistema de climatització format per una bomba de calor i una unitat de tractament de l'aire.

Compact thermal storage: a-state-of-the-art review of experimental results

Thermal energy storage (TES) can increase the thermal energy effieresa, of a process by reusing the waste heat from industrial process, solar energy or other sources. There are different ways to store thermal energy: by sensible heat, by latest heat, by sorption process or by chemical reaction. This thesrs provides a-state-of-the-art review of the experimental performance of TES systems based on solid gas sorption process and chemical reactions. The importance of theses processes is that provides a heat loss free storage system with a high energy density.

Analysis of thermal properties of phase change materials (PCM) using differential scanning calorimeter (DSC)

Commercially available PCM RT 20, RT 27, SP 22, A17 and SP 25 A8. Were analyzed using dynamic and step method of heat flux DSC. The results of the dinamic and step method were compared with commercial valures. It was found that RT 20 & RT 27 showed good conforming of results with commercial values while SP 22 A17 & SP 25 A8 did not show conformity.

Improvement of the thermal performance of commercial freezers using phase change materials (PCM)

The aim of this work is to improve the thermal performance of commercial freezers using phase change materials (PCM) and the prove the importance of the correct PCM selection (melting temperature) for each application. To do this a vertical freezer with and without macro encapsulation PCM are used to assess the benefits of using PCM in minimizing temperature fluctuations and to maintain at the lowest possible temperature the freezer under heat of losses.

Thermal energy storage with phase change materials in building envelopes

Els materials de canvi de fase (PCM) han estat considerats per a l’emmagatzematge tèrmic en edificis des de 1980. Amb la inclusió dels PCM en plaques de guix, guix, formigó o altres materials que s’utilitzen per a cobrir les parets, l’emmagatzematge tèrmic pot ser part de les estructures fins i tot en edificis lleugers. Les noves tècniques de microencapsulació han obert moltes possibilitats en aplicacions per a edificis. El treball que es presenta és el desenvolupament d’un formigó innovador mesclat amb PCM microencapsulat, amb un punt de fusió de 26 oC i una entalpia de canvi de fase de 110 kJ/kg. El primer experiment va ser la inclusió del PCM microencapsulat dins del formigó i la construcció d’una caseta amb aquest nou formigó-PCM. Es va construir una segona caseta al costat de la primera amb les mateixes característiques i orientació però amb formigó convencional que serveix com a referència. Durant els anys 2005 i 2006 es va analitzar el comportament d’ambdues casetes i més tard es va edificar un mur Trombe a la paret sud de totes dues per investigar la seva influència durant la tardor i l’hivern.

Conditional equilibrium constants in multicomponent heterogeneous adsorption: The conditional affinity spectrum

The concept of conditional stability constant is extended to the competitive binding of small molecules to heterogeneous surfaces or macromolecules via the introduction of the conditional affinity spectrum (CAS). The CAS describes the distribution of effective binding energies experienced by one complexing agent at a fixed concentration of the rest. We show that, when the multicomponent system can be described in terms of an underlying affinity spectrum [integral equation (IE) approach], the system can always be characterized by means of a CAS. The thermodynamic properties of the CAS and its dependence on the concentration of the rest of components are discussed. In the context of metal/proton competition, analytical expressions for the mean (conditional average affinity) and the variance (conditional heterogeneity) of the CAS as functions of pH are reported and their physical interpretation discussed. Furthermore, we show that the dependence of the CAS variance on pH allows for the analytical determination of the correlation coefficient between the binding energies of the metal and the proton. Nonideal competitive adsorption isotherm and Frumkin isotherms are used to illustrate the results of this work. Finally, the possibility of using CAS when the IE approach does not apply (for instance, when multidentate binding is present) is explored. © 2006 American Institute of Physics.

Determination of the complexing capacity of synthetic and real wine for Zn using Absence of Gradients and Nerstian Equilibrium Stripping technique

The complexing capacity of synthetic (0.011 M tartrate in 13.5% ethanol) and real wine (Raimat Abadia) in titrations with added total Zn concentrations up to 0.03 M has been determined following the free Zn concentrations with AGNES (absence of gradients and Nernstian equilibrium stripping) technique. A correction to find the preconcentration factor or gain (Y1) really applied at each one of the ionic strengths reached due to Zn additions along the titration has been applied. The standard implementation of AGNES to real wine led to the observation of two anomalous behaviors: (a) an increasingly negative current in the deposition stage (labeled as “HER” effect) and (b) a minimum in the currents of the stripping stage plot (labeled as the “dip” effect). A practical strategy to apply AGNES avoiding the dip effect has been developed to quantify properly free Zn concentrations. The van den Berg–Ružic–Lee linearization method (assuming the existence of just 1:1 complexes) has been adapted to consider the dilution effect and the ionic strength changes. Aggregated stability constants and total ligand concentrations have been calculated from synthetic and wine titration data. The found complexing capacity in the studied wine (cT,L = 0.0179 ± 0.0007 M) indicates the contribution of ligands other than tartrate (which is confirmed to be the main one).

Comblike poly(a-alkyl g glutamate)s: computer simulation studies of an intermediate thermal phase.

Monte Carlo (MC) simulations have been used to study the structure of an intermediate thermal phase of poly(R-octadecyl ç,D-glutamate). This is a comblike poly(ç-peptide) able to adopt a biphasic structure that has been described as a layered arrangement of backbone helical rods immersed in a paraffinic pool of polymethylene side chains. Simulations were performed at two different temperatures (348 and 363 K), both of them above the melting point of the paraffinic phase, using the configurational bias MC algorithm. Results indicate that layers are constituted by a side-by-side packing of 17/5 helices. The organization of the interlayer paraffinic region is described in atomistic terms by examining the torsional angles and the end-to-end distances for the octadecyl side chains. Comparison with previously reported comblike poly(â-peptide)s revealed significant differences in the organization of the alkyl side chains.

Relaxation and derelaxation of pure and hydrogenated amorphous silicon during thermal annealing experiments

The structural relaxation of pure amorphous silicon a-Si and hydrogenated amorphous silicon a-Si:H materials, that occurs during thermal annealing experiments, has been analyzed by Raman spectroscopy and differential scanning calorimetry. Unlike a-Si, the heat evolved from a-Si:H cannot be explained by relaxation of the Si-Si network strain but it reveals a derelaxation of the bond angle strain. Since the state of relaxation after annealing is very similar for pure and hydrogenated materials, our results give strong experimental support to the predicted configurational gap between a-Si and crystalline silicon.

Coarse-graining and thermodynamics in far-from-equilibrium systems

Lying at the core of statistical physics is the need to reduce the number of degrees of freedom in a system. Coarse-graining is a frequently-used procedure to bridge molecular modeling with experiments. In equilibrium systems, this task can be readily performed; however in systems outside equilibrium, a possible lack of equilibration of the eliminated degrees of freedom may lead to incomplete or even misleading descriptions. Here, we present some examples showing how an improper coarse-graining procedure may result in linear approaches to nonlinear processes, miscalculations of activation rates and violations of the fluctuation-dissipation theorem.

Histologic evaluation of thermal damage produced on soft tissues by CO2, Er,Cr:YSGG and diode lasers

Objective: The aim of this in vitro experimental study was to perform histological evaluation of the thermal effect produced on soft tissue irradiated with CO2, Er,Cr:YSGG or diode lasers. Study design: Porcine oral mucosa samples were irradiated with Er,Cr:YSGG laser at 1 W with and without water / air spray, at 2 W with and without water / air spray, and at 4 W with water / air spray, with CO2 laser at 1 W, 2 W, 10 W, 20 W continuous mode and 20 W pulsed mode and diode laser at 2W, 5W, and 10W pulsed mode. The thermal effect was evaluated measuring the width of damaged tissue adjacent to the incision, stained positively for hyalinized tissue with Hematoxylin-Eosin and Masson Trichrome stains. Besides, histological changes in the irradiated tissue were described using subjective grading scales. Results: The evaluated lasers developed a wide range of thermal damage with significant differences between groups. The samples with lowest thermal effect were those irradiated with Er,Cr:YSGG laser using water / air spray, followed by CO2 and diode lasers. Conclusions: Emission parameters of each laser system may influence the thermal damage inflicted on the soft tissue, however, the wave length of each laser determines the absorption rate characteristics of every tissue and the thermal effect

Studying the non-thermal lobes of IRAS 16547-4247 through a multi-wavelength approach

In recent years, massive protostars have turned out to be a possible population of high-energy emitters. Among the best candidates is IRAS 16547-4247, a protostar that presents a powerful outflow with clear signatures of interaction with its environment. This source has been revealed to be a potential high-energy source because it displays non-thermal radio emission of synchrotron origin, which is evidence of relativistic particles. To improve our understanding of IRAS 16547-4247 as a high-energy source, we analyzed XMM-Newton archival data and found that IRAS 16547-4247 is a hard X-ray source. We discuss these results in the context of a refined one-zone model and previous radio observations. From our study we find that it may be difficult to explain the X-ray emission as non-thermal radiation coming from the interaction region, but it might be produced by thermal Bremsstrahlung (plus photo-electric absorption) by a fast shock at the jet end. In the high-energy range, the source might be detectable by the present generation of Cherenkov telescopes, and may eventually be detected by Fermi in the GeV range.

Equilibrium of the simultaneous etherification ofisobutene and isoamylenes with ethanol inliquid-phase

The simultaneous etherification of isobutene and isoamylenes with ethanol has been studied using macroreticu-lar acid ion-exchange resins as catalyst. Most of the experiments were carried out over Amberlyst-35. In addition,Amberlyst-15 and Purolite CT-275 were also tested. Chemical equilibrium of four chemical reactions was studied:ethyl tert-butyl ether formation, tert-amyl ethyl ether formation from isoamylenes (2-methyl-1-butene and 2-methyl-2-butene) and isomerization reaction between both isoamylenes. Equilibrium data were obtained in a batchwisestirred tank reactor operated at 2.0 MPa and within the temperature range from 323 to 353 K. Experimental molarstandard enthalpy and entropy changes of reaction were determined for each reaction. From these data, the molarenthalpy change of formation of ethyl tert-butyl ether and tert-amyl ethyl ether were estimated. Besides, the chemical equilibrium between both diisobutene dimers, 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene, wasevaluated. A good agreement between thermodynamic results for the simultaneous etherification carried out in thiswork and those obtained for the isolated ethyl tert-butyl ether and tert-amyl ethyl ether systems was obtained.

Response of the Thermal Conductivity as a Function of Water Content of a Burnt Mediterranean Loam Soil

The purpose of this research is to explore the variability on the soil thermal conductivity -λ- after a prescribe fire, and to assess the effects of the ashes on the heat transfer once it"s were incorporated into the soil matrix. Sampling plot was located in the Montgrí Massif (NE of Spain). A set of 42 soil samples between surface and 5 cm depth was collected before and after the fire. To characterize the soil chemical and physical variables were analyzed. To determine the vari-ability on the soil λ a dry-out curve per scenario (before and after fire) was determined. SoilRho® method based on ASTM D-5334-08 which was validated by LabFerrer was used. Soil thermal conductivity has shown changes in their values. Indeed, in all moisture scenarios the values of soil λ decreased after soil was burnt. The critical point in the rela-tionship ϴ (λ) for the soil after fire which always was stronger than soil before to be burnt. Soil with"white" ashes showed a high thermal conductivity. An X-Ray diffractometry analysis allowed to clarify and to verify these results. To sum up, we could say that thermal conductivity presents changes when the scenario changes, i.e. before and after to be burnt. On the other hand, the volume of ashes incorporated on the soil increased the differences between no burnt and burnt soil, showing even some improvements on the heat transfer when water content started to govern the process.