No abstract

No abstract

Optimal thermo-physical properties of nanofluids provide an opportunity to overcome energy associated difficulties, in addition to providing new alternatives to catch, store and exchange of energy. A significant reduction in energy consumption is possible by improving the performance of a heat exchanger circuit, and may in part alleviate current energy related challenging issues such as global warming, climate change, and the fuel crisis. The objective of this work is to gain an insight into the overall stability of nanofluids with respect to pH, zeta potential, particle size distribution, and its effect on viscosity and thermal conductivity. For the purpose of this study two nanofluids were selected (water based alumina and copper oxide). Various nanoparticles concentrations as well as anionic surfactants (sodium dodecylbenzene sulfonate) were investigated for their stability, viscosity as well as thermal conductivity. The results clearly showed that nanofluid stability has a strong relation with viscosity and thermal conductivity. The stability of the nanofluid was found to be improved with a decrease in viscosity and an increase in thermal conductivity.

The increasing demand for oxygen combined with the need for improved economic performance necessitates the search for alternative methods of oxygen production. Chemical looping air separation (CLAS) is one of these alternatives with a relatively small energy footprint. The present paper describes the results of a comprehensive thermodynamic study conducted by our group to identify suitable oxygen carriers for CLAS at medium to low temperatures. The thermodynamic simulations were carried out using Fact-Sage 6.1 for 20 different metal oxides forming 40 oxygen carrier systems. An Ellingham diagram was developed to relate the Gibbs free energy of the relevant reactions to the temperature for all metal oxide systems. Furthermore, the equilibrium partial pressure of oxygen was calculated at elevated temperatures. The mass balance calculations were also performed for identifying the steam/CO 2 requirements for the reduction reactor. On the basis of the comprehensive thermodynamic study, oxides of manganese, cobalt, and copper have been found most suitable for the CLAS process. Additionally, the possibility of carbonate and hydroxide formation during the reduction with CO 2 and steam, respectively, was calculated. The formation of the mixed oxide phases or the spinel structures between the metal oxides and various supports (such as SiO 2 and Al 2 O 3 ) has also been thermodynamically investigated. Several other important factors were also qualitatively assessed. The Cu oxides with SiO 2 and the Co oxides with Al 2 O 3 were found to be the most suitable oxygen carriers for CLAS.

No abstract