Volume 30, Issue 2

The main feature of this paper was to recognize struvite crystallization in the metastable region of supersaturation. Thermodynamic equilibria of struvite were simulated to identify the minimum struvite solubility limit, thereafter validated by existing thermodynamic modelling packages such as PHREEQC and the derived data from existing struvite solubility curve. Using laser light scattering detection, spontaneous nucleation was identified by the slow increase of pH in a supersaturated solution of struvite. The crystallization experiment, conducted close to the saturation region in metastable zone, initiated struvite growth. The conducted experiment showed that mother crystal (struvite) was more effective as seeds for struvite crystallization.

We revisit the simple model of the cyclic endoreversible heat engine with linear heat transfer. With W being the delivered work, t , the total contact time with the reservoirs and α the total heat transfer coefficient, we (i) introduce the regime of maximum W /α given the contact times with each reservoir; (ii) reinterpret the regime of maximum W / t for given t and α as a regime of maximum W /( t α); and (iii) introduce the regime of maximum W /γ (where the total contact coefficient γ is the sum of the product of each contact time and the corresponding heat transfer coefficient). We conclude that to compare cyclic and stationary operation with regard to the performance in using time and heat transfer coefficients, the regime of maximum W /γ is the most adequate, because γ accounts only for the resources that are actually employed during the cycle.

We explain that the path of minimum entropy production in a system with nonlinear flux-force relations, which do not depend explicitly on the state variables of the system, can be characterised by equipartition of driving forces and equipartition of entropy production. The explanation is based on an optimal control theory formulation of the optimisation problem. The finding helps explaining recent numerical observations on the second law optimal state of chemical reactions.

The effect of a constant magnetic field on the stability of a compressible, electrically conducting fluid contained in a duct with an axial temperature gradient is studied. A plausible physical model of the phenomenon is presented and its linear stability is analyzed. The study includes the consideration of a general state equation for the working fluid and the variation of its physical properties with temperature. An expression for the critical thermal gradient required to generate thermoacoustic standing waves is found as a function of the external magnetic field. The potential application of this work is in the context of thermoacoustic prime movers with magnetohydrodynamic transducers.

Oxygen delivery to the tissues is crucial to survival but our understanding of the processes involved in the transport of oxygen from blood to tissue is incomplete. The aim of the present work is to illustrate a long-standing paradox regarding such transport by reporting new state-of-the-art measurements and by analyzing the results in several ways, thereby exploring possible resolutions of the paradox. Our model calculations show that slight extensions of system parameters are sufficient to overcome the apparent inconsistencies. Alternatively, so far unappreciated mild effects like flow-assisted diffusion in the interstitium will explain the supernormal diffusion of oxygen.

The spectroscopic impedance associated with a localized linear redox reaction distributed across irregular boundaries is studied. Taking advantage of recent results in the literature, we present a real space renormalization scheme for the calculation of the coefficients of the impedance in the Makarov regime. It is predicted that the impedance diminishes for successive prefractal generations of the same fractal generator, so that the final fractal object is expected to dissipate less than all previous ones.

Within the postulates of linear irreversible thermodynamics, the Onsager reciprocity relations between the thermal diffusion and diffusion thermo effect coefficients in a multiple mixture of inert dilute gases obtained via the kinetic theory of gases are shown to hold true when the proper representation is chosen. Differences in the identification of transport coefficients in other representations are discussed both from the theoretical as well as the experimental point of view.