Volume 35, Issue 1

Thermodiffusion along with molecular diffusion occurs in many engineering systems and in nature. Thermodiffusion has a great effect on concentration distribution in binary mixtures. A new approach to predicting the Soret coefficient in binary mixtures of linear chain and aromatic hydrocarbons using the thermodynamics of irreversible processes is presented. In particular, this approach is based on free volume theory, which explains the diffusivity in diffusion-limited systems. Free volume states that the transfer kinetics of molecules depends greatly on molecular size and shape. The proposed model, combined with Shukla and Firoozabadi's model, was applied to predict the Soret coefficient. The perturbed chain statistical associating fluid theory equation of state (PCSAFT-EoS) was used to calculate the related thermodynamic properties. Comparisons of the theoretical results with experimental data show good agreement.

A model based on non-equilibrium thermodynamics has been extended for investigation of energy transduction in biological systems. Rate of free energy loss and efficiency of some mitochondria in energetic and thermogenic modes have been determined by means of this model. The theoretical results are in agreement with previous experimental ones indicating that the rate of free energy loss is greater in mitochondria with thermogenic function while the efficiency of oxidative phosphorylation appears to be less than energetic ones. Therefore, the model illustrates the principle that mitochondria with energetic role are able to store more energy in the form of adenosine triphosphate (ATP), while mitochondria with thermogenic function release more energy as heat and are thus less efficient in energy storage. Furthermore, the model introduces some thermodynamic criteria that can provide valuable information on whether the mitochondrion is functioning properly. After evaluation of some parameters for each mitochondrion, these criteria can be easily determined by means of the presented equations. Hence, the developed model can be widely used in medical, pharmaceutical, and biological studies.

We describe the stochastic rotational dynamics and magnetization curves of a suspension of interacting magnetic colloidal particles of a ferrofluid under an external magnetic field. The orientation of the magnetic dipole moments of these particles is considered as a fluctuating variable, so within the framework of mesoscopic irreversible thermodynamics, we derive an equivalent Fokker–Planck equation (FPe), which gives us the orientational distribution function (Odf) of the magnetic dipole moments of these particles. The numerical solution of the FPe allows us to observe the temporal evolution of the orientation of the magnetic dipoles to the equilibrium limit, once an external magnetic field is applied to the ferrofluid. We observe that the dipoles orient better in the direction of the field when the particles are bigger or the temperature of the solvent is decreased. Decreasing the average distance between the magnetic particles does not give us an important improvement in their orientation with respect to the external magnetic field. Finally, with the solution of the FPe and the partition function, we determine an average magnetic dipole moment of the particles and, changing the magnetic field applied to the ferrofluid, we obtain a set of magnetization curves which fits to experimental results by tuning the interactions among the particles. These results are useful for different applications of magnetizable composite particles.

Following the non-equilibrium thermodynamics approach, we develop expressions for the calculation of the thermal diffusion coefficients in a ternary system. On the basis of some physical justifications, we approximate the net heat of transport with the activation energy of viscous flow. In parallel, we revisit the Kempers model and propose new expressions for the estimation of the thermal diffusion factors in a ternary mixture. The proposed expressions are based on a dynamic modeling approach, as they incorporate the activation energy of viscous flow, which is a fluid flow property and contains the effects of some of the parameters that govern thermodiffusion. The proposed expressions, the Kempers and Ghorayeb–Firoozabadi–Shukla models are evaluated against the experimental data. Our expression which was developed on the basis of the Kempers approach has the best performance.

The Onsager heat of transport, Q *, for nitrous oxide at the surface of water has been measured by using high-resolution diode-laser spectroscopy to monitor the partial pressure of N 2 O as a function of the temperature difference across a 5-mm vapour gap above the water surface. The metal surface above the vapour gap was conditioned with ammonia prior to the measurements, to enable efficient thermal accommodation at that surface, which allowed the temperature difference to be as large as 15 K. We find Q * = –6.6 ± 0.85 kJ mol –1 , so that Q */ RT is –2.9 at T = 275.15 K. These experiments are a necessary preliminary to a planned series of measurements of Q * for CO 2 at the surface of simulated sea water.