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Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2017;140(1):012001-012001-11. doi:10.1115/1.4037365.

This paper depicts the results of a detailed energy audit, analysis, and implementation of energy efficient operations and maintenance strategies in a large commercial mall in Kuwait. Initially, the cooling towers (CTs) operated only at high speed, and on a typical summer day, nearly one-fourth of the make-up water was used for self-cooling of air. The study based on measured data and analysis, for a period of one year, revealed that the use of variable frequency drive (VFD) could reduce the water wastage for self-cooling of air by as much as 75% and overall water consumption by 18.6% while keeping the cooling system performance at the design level. An optimization model was developed, suitable exclusively for arid climatic conditions. Implementation of various energy efficient operation and maintenance strategies (EEO&MS) with ventilation and air-conditioning (VAC), and lighting systems obtained an overall reduction of 9879 MWh/y, equivalent to a percentage reduction of 11.7% in the annual energy consumption and a 345 kW in peak power demand. The study estimated an economical benefit of 19,958 KD/y for the owners and to the Ministry of Electricity and Water, in addition to a considerable environmental benefit of deduction in CO2 emissions by 6990 t/y.

Commentary by Dr. Valentin Fuster

Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2017;140(1):012201-012201-8. doi:10.1115/1.4037367.

Utilization of oxygenated fuels has proven to be able to significantly control diesel engine exhaust emissions. Presented in this paper is a new oxygenated fuel di-(2-methoxypropyl) carbonate (DMPC), which was produced through transesterification reaction using dimethyl carbonate (DMC) and propylene glycol monomethyl ether (PGMME) as reactants as well as potassium hydroxide (KOH) as catalyst. Its structure characterization was completed through analyses with Fourier transform infrared (FT-IR), 1H nuclear magnetic resonance (NMR), and GC-MS analytical techniques. Further study was made about the effect of the oxygenate addition to diesel fuel on chemicophysical properties, combustion performances, and exhaust emissions characteristics. Experimental results displayed that the oxygenated fuel is mutually soluble with diesel fuel in any proportion at ambient temperature around 25 °C. With DMPC introduced to diesel fuel, kinematic viscosity decreases linearly, smoke point increases linearly, and flash point declines remarkably even under low content 5 vol %. Results of combustion test carried out on a single cylinder, DI diesel engine running at 1600 rpm and 2000 rpm showed that CO can be reduced by up to 60.0%, smoke can be lessened by up to 90.2%, while NOx increases by 4.4–14.0% as 15 vol % and 25 vol % of the oxygenate was added to a diesel fuel. Engine in-cylinder peak pressure increases somewhat and ignition delay duration becomes a little shorter. Both engine in-cylinder pressure rising rate and heat release rate increase noticeably during the premixed combustion.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2017;140(1):012202-012202-8. doi:10.1115/1.4037370.

The objective of this experimental work is to design an original microfluidic mixer for continuous emulsification of small fractions of water in a lipid phase. This system is aimed to be integrated on-line in the process so as to avoid the use of a surfactant. The currently targeted application is a better combustion of water-supplemented alternative biofuels in boilers, turbines, or internal combustion engines in general. Therefore, mean size of droplets of water in the emulsion should be 5–10 μm, and the water content should not exceed ∼20%. Microsystems developed in this work are designed so as to enhance different flow perturbations that are favorable for the emulsification process. The microchannels for the fluids admittance have different sections: 300 × 300 μm2 and 600 × 600 μm2. As a consequence, an impinging flow is developed at the crossing of the inlet microchannels of the two phases which has for effect a significant stretching of the fluids. Then, depending on the continuous phase, Rayleigh instabilities can be developed in the straight parts of the outlet channels (600 × 600 μm2) and/or the enhancement of fluid splitting is obtained; thanks to a singularity (bend) located in the same outlet channels. Two different continuous phases are tested (gasoil and sun flower oil) for which the flow rate is about (65–100 ml/min). The water fraction is varied in the range 7–24%. It is shown that the length of the outlet microchannels is a crucial parameter. Considering an oil phase with low viscosity, such as gasoil, a too long channel can promote coalescence. On the opposite, longer outlet channels are needed with more viscous fluids (like sunflower oil) in order to develop Rayleigh instabilities which is, in this case, the more efficient way to obtain emulsions in this kind of microsystem. On a general point of view, concerning the size of the water droplets, dispersion of water is much more efficient with this microsystem using gasoil rather than vegetable oil as the continuous phase. Considering the targeted application, emulsions with an average size of water droplets of about 10 μm were obtained with gasoil as the continuous phase.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Engineering

J. Energy Resour. Technol. 2017;140(1):012901-012901-12. doi:10.1115/1.4037366.

In recent years, colloidal gas aphron (CGA) fluids have been much attended by researchers for their possible application in infill drilling, due to their pore blockage ability. In this study, the possible synergistic effect of silica nanoparticle hydrophobicity in the presence of sodium dodecyl sulfate (SDS), as a surface active agent, on enhancement of properties of CGA fluids was experimentally investigated. Results revealed that the hydrophobicity of nanoparticles, adsorbed at the bubble interface, plays an important role in improving stability and blockage ability at low as well as high pressure/temperature conditions, low shear rate viscosity (LSRV), and return permeability ability of CGA dispersion measured in a special radial sand pack apparatus at different levels of surfactant concentration. It was observed that partially hydrophobic SiO2 nanoparticles (nanosilica coated with KH550-Silane) yield a better performance than both strongly hydrophilic and hydrophobic nanoparticles (silicon dioxide nanopowder coated with 2 wt. % Silane) which confirms what is expected from the particle detachment theory. Optimal SDS concentrations equal to 0.25 wt. % for strongly hydrophilic, and 0.33 wt. % for both strongly hydrophobic and partially hydrophobic SiO2 nanoparticles were also found, which maximize the improving effect of CGA fluids. The superiority of the aphronized fluid improved by partially hydrophobic nanoparticles of SiO2 to CGA fluid stabilized only by surfactant makes the CGA fluids attractive for some industrial and drilling applications.

Commentary by Dr. Valentin Fuster

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