Thermodynamics

The ecosphere and its components (atmosphere, hydrosphere, lithosphere and biosphere) are considered as open thermodynamic systems far away from equilibrium. In this regard, maximum power principle, dissipative structures emergence and associated negentropy production are recalled and illustrated by the behavior of Bénard cells. Similarities and differences between BOLTZMAN thermodynamic entropy and SHANNON information entropy are also reviewed. Their relative usefulness in complex and highly organized macrosystems are underlined. The closely related concepts of exergy, information and matter are also included into the discussion.

The specific properties and dynamics of both solar and geothermic energy inflows are forcing the structures of the humid tropical ecosphere to develop the most dissipative power of the planet. Acid pedogenesis results from hydrolysis which is catalyzed by the respiration, evapotranspiration and photosynthesis activities taking place within the biosphere. These reactions consume the surface orolithomass (rocky mineral mass and its relief) during a period of several thousands years to form soils highly concentrated in exchangeable aluminium (HA soils, High Aluminium status). In these soils, the biosphere evolution is characterized by a large forest biodiversification as a natural maximization process of solar energy dissipation under poor growth conditions. This thermodynamic interpretation is deduced from increase of stems’ densities and decrease of food crops growth rates in HA soils. The agricultural production systems support the same hypothesis: yields decreases of food crops constrain farmers to slash and burn shifting cultivation, burned rangeland practices, perennial cropping of species like rubber, palm, tea, etc.

Maximum use of exergy inflows as thermodynamic stability criterion should also explain the darwinian evolution of species towards more and more complex and organized organisms. Satisfying the same thermodynamic principle should finally be considered as a natural law condition and technological challenge for agrarian sustainable development.

Equilibrium vapour pressures of sodium and potassium over a KxNa1−xNbO3 solid solution within its whole compositional range at temperatures between 1173 K and 1303 K were determined by Knudsen Effusion Mass Spectrometry. It should be noted that the thermodynamic equilibrium between the condensed and the vapour phase could be established only after prolonged annealing (more than 10 h at 1263 K). The equilibrium vapour pressure of potassium over K0.5Na0.5NbO3 (KNN) is a few times larger than that of sodium, i.e., 8 × 10−3 Pa as compared to 3 × 10−3 Pa at 1263 K. From the obtained results, the excess thermodynamic functions for the pseudo-binary KNbO3–NaNbO3 system were evaluated. The excess Gibbs energy was found to be positive, the excess enthalpy is close to zero, while the negative excess entropy indicates a partial ordering of alkaline ions in the solid solution. The comparison of the obtained results to the well-established lead-based piezoelectric systems revealed, that the vapour pressure of alkalis over the respective niobates at 1200 K is almost three orders of magnitude lower as compared to the values reported for lead oxide over Pb(Zr,Ti)O3.

CFD Analysis of one side dimpled plate heat exchanger is done in comparison with the experimental results for channel height to diameter ratio of H/D 0.5 with a Reynolds No. of 10200. Dimpled and Flat Plates were heated to a constant surface heat flux of 940 W/m2. Results were com-pared against normalized values of Nusselt Numbers to Baseline Nusselt Numbers of Flat Plate. Fully developed flow was ensured by employing a reducing duct, outlet profile of which was mapped on to the flat and dimpled surfaces. Simulations were run at turbulent intensity levels of 0.5%, 5% and 15%, each of which resulted in similar results due to properly modeled duct for developing a fully developed flow. Normalized Nusselt No. study over specific dimple areas show that the Nusselt No. increases when flow is entering    and leaving a dimple. This effect of increased Nusselt No. is due to vortex mixing of the flow due to separation. Similarly, while flowing out of the dimple depth, the heat transfer is also high due to reattachment of the flow to the main stream line flow. The values of normalized Nusselt No. reach to a nearly of 2.8, indicating that the heat transfer is almost 3 times more than that of flat plate. Whereas, on the flat sections of the dimpled plate, the Normalized Nusselt Number is nearly equal to 1 showing that the heat transfer is equivalent to that of a flat plate. The above mentioned values are in agreement to the experimental analysis by P.M.Ligrani. This leads to the conclusion that the heat transfer is directly proportional to the surface area of the convection surface. But more than this, if the foot print area is to be kept constant than turbulent mixing is most effective in efficient heat transfer where fluid properties cannot be changed with obvious compromise over pressure drops as the geometry gets more irregular.