Papers by Nikolaos Nikolopoulos
Fuel, 2015
ABSTRACT Lignite constitutes a major energy source and has long been used for energy production d... more ABSTRACT Lignite constitutes a major energy source and has long been used for energy production despite its contribution in greenhouse gas (GHG) emissions, as a fossil fuel. For example, 27.4% of Germany’s electricity originates from lignite power plants, while in Greece more than 55% of its electric energy consumption is provided by lignite. 45% of the total global coal reserves consist of low-rank coals (LRCs) such as lignite. With this background, the utilization of lignite for energy production is expected to remain a common practice in the decades to come since the availability of lignite is considerable in many countries of Europe and the world (e.g. Germany, Poland, Greece, USA, and Australia). Therefore, problems regarding the combustion and use of lignite should be addressed in a more efficient and environmentally friendly way. One of the main existing problems is the high moisture contained in raw lignite as received from the mine. The high moisture content results in higher CO2 emissions per unit of energy produced and is responsible for high capital and transport costs as well as other technical problems such as reduction in coal friability and difficulties in its blending and pneumatic transportation. Therefore, processing of lignite through drying is considered of great interest in the implementation of energy production in lignite power plants. Taking into account the significance of the subject and the usefulness of such an attempt, an overview of the currently existing drying technologies, including both evaporative and non-evaporative drying methods is reported in the present paper.
Advances in colloid and interface science, 2014
In this study,a novel numerical implementation for the adhesion of liquid droplets impacting norm... more In this study,a novel numerical implementation for the adhesion of liquid droplets impacting normally on solid dry surfaces is presented. The advantage of this new approach, compared to the majority of existing models, is that the dynamic contact angle forming during the surface wetting process is not inserted as a boundary condition, but is derived implicitly by the induced fluid flow characteristics (interface shape) and the adhesion physics of the gas-liquid-surface interface (triple line), starting only from the advancing and receding equilibrium contact angles. These angles are required in order to define the wetting properties of liquid phases when interacting with a solid surface. The physical model is implemented as a source term in the momentum equation of a Navier-Stokes CFD flow solver as an "adhesion-like" force which acts at the triple-phase contact line as a result of capillary interactions between the liquid drop and the solid substrate. The numerical simula...
Energy and Buildings, 2011
The paper presents an extensive experimental and numerical study on a cross-ventilated building p... more The paper presents an extensive experimental and numerical study on a cross-ventilated building providing important features of the induced flow patterns at the two openings as a function of the free stream wind velocity's magnitude and its incidence angle. The experimental data are measured via anemometers across the openings, whilst the numerical methodology is based on the time-dependant solution of the governing Navier-Stokes equations. The experimental data are compared to the corresponding numerical results, revealing the unsteady character of the flow field especially at large incidence angles. Furthermore, additional information regarding the flow field near the opening edges, not easily extracted by experimental methods, provide an in depth sight in the main characteristics of the flow field both at the openings but also inside the building. Finally, a new methodology for the approximation of the volume flow rate aerating the building based on experimental measurements of the velocity field at the openings is presented.
Atomization and Sprays, 2010
This paper presents an experimental study of the impact of a single water droplet onto a stationa... more This paper presents an experimental study of the impact of a single water droplet onto a stationary liquid bulk built by the previous impact of one or two droplets. The experiments were performed with two different film thicknesses, three different Weber (We) numbers, and two surface contact angles. In both cases we have hydrophilic conditions, which do not allow for a good investigation of this parameter. The morphology of the drop impact was studied using a chargecoupled device (CCD) camera, and the corresponding qualitative and quantitative characteristics regarding the time evolution of the phenomena, such as the diameter and height of the evolving crown, were obtained by image analysis. Analysis of the experimental data evidences that the phenomenon has a strong similarity to the impact of a single drop on shallow films, although the effect of the surface wetting characteristics plays, in this case, a negligible role. The regimes of deposition and splashing are identified as a function of the We number and the maximum thickness of the steady film, which is affected by the surface wettability properties.
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Papers by Nikolaos Nikolopoulos