Band 37, Heft 4

Abstract. The thermodynamics of oxygen desorption from TiO 2 crystals under steady light excitation is investigated. The non-equilibrium photo-induced processes are explicitly accounted for by considering the rate of entropyproduction. The adsorption/desorption properties of oxygen on anatase nanocrystals are investigated as a function of the pressure of the experimental room and a generalized Langmuir–Fowler equation is obtained for the case of photo-assisted surface processes. The kinetic scheme used for this study involves color centers and surface centers on the sites. In particular, oxygen depletion is forced by recombinations of electrons trapped in bonding sites and holes trapped in color centers ( centers).

Abstract. Thermodiffusion in complex mixtures, such as associating, molten metal, and polymer mixtures is difficult to model usually owing to the occurrence of a sign change in the thermodiffusion coefficient when the mixture concentration and temperature change. A mixture comprised of a nonpolar hydrocarbon and an alcohol is a complex and highly non-ideal mixture. In this paper an existing binary non-equilibrium thermodynamics model (Eslamian and Saghir, Physical Review E 80, 061201, 2009) developed for aqueous mixtures of alcohols is examined against the experimental data of binary nonpolar hydrocarbon and alcohol mixtures. For ternary mixtures, non-equilibrium thermodynamic expressions developed by the authors for aqueous mixtures of alcohols (Eslamian and Saghir, Canadian Journal of Chemical Engineering, DOI 10.1002/cjce.20581) is used to predict thermodiffusion coefficients of ternary nonpolar hydrocarbon and alcohol mixtures. The rationale behind the sign change is elucidated and attributed to an anomalous change in the molecular structure and therefore viscosity of such mixtures. Model predictions of thermodiffusion coefficients of binary mixtures predict a sign change consistent with the experimental data although the model is still too primitive to capture all structural complexities. For instance, in the methanol–benzene mixture where the model predictions are poorest, the viscosity data show that when concentration varies, the mixture's molecular structure experiences a severe change twice, the first major change leading to a maximum in the thermodiffusion coefficient, whereas the second change causes a sign change.

Abstract. The framework of non-equilibrium thermodynamics (NET) is used to derive heat and mass transport equations for pervaporation of a binary mixture in a membrane. In this study, the assumption of equilibrium of the sorbed phase in the membrane and the adjacent phases at the feed and permeate sides of the membrane is abandoned, defining the interface properties using local equilibrium. The transport equations have been used to model the pervaporation of a water–ethanol mixture, which is typically encountered in the dehydration of organics. The water and ethanol activities and temperature profiles are calculated taking mass and heat coupling effects and surfaces into account. The NET approach is deemed good because the temperature results provided by the model are comparable to experimental results available for water–alcohol systems.

Abstract. A nonlinear model of anisotropic rigid heat conductor is developed in the framework of weakly nonlocal Extended Irreversible Thermodynamics.The restrictions placed on the constitutive functions by the principles of dissipation and material frame indifference are investigated. Nonlinear anisotropic Guyer–Krumhansl and Maxwell–Cattaneo equations are derived. Comparison is made with some other models existing in the literature.

Abstract. Bridging the regime between fully irreversible and fully reversible dynamics as represented by the two paradigmatic evolution equations for diffusion and wave propagation became possible by the use of fractional diffusion equations based on time- or space-fractional differential operators. These bridges are each characterized by a one-parameter family of distribution functions. In both cases one encounters a counter-intuitive behavior: the closer one gets to the reversible case, the larger the entropy production becomes. This feature is known as the entropy production paradox, and could be partly resolved for the time-fractional case by using the distribution mean as a way to characterize the internal quickness of the process, while for the space-fractional case a special location parameter was used. Here we are able to present a unified approach based on the distribution modes as the appropriate measure for the internal quickness of the processes.

Abstract. This paper focuses on the research of an evaporator with a binary mixture of organic working fluids in the organic Rankine cycle. Exergoeconomic analysis and performance optimization were performed based on the first and second laws of thermodynamics, and the exergoeconomic theory. The annual total cost per unit heat transfer rate was introduced as the objective function. In this model, the exergy loss cost caused by the heat transfer irreversibility and the capital cost were taken into account; however, the exergy loss due to the frictional pressure drops, heat dissipation to surroundings, and the flow imbalance were neglected. The variation laws of the annual total cost with respect to the number of transfer units and the temperature ratios were presented. Optimal design parameters that minimize the objective function had been obtained, and the effects of some important dimensionless parameters on the optimal performances had also been discussed for three types of evaporator flow arrangements. In addition, optimal design parameters of evaporators were compared with those of condensers.