Athens, Greece
Athens, Greece

Time filter

Source Type

Kopanidis A.,University of Western Macedonia | Theodorakakos A.,Fluid Research Co | Gavaises M.,City University London | Bouris D.,University of Western Macedonia
International Journal of Thermal Sciences | Year: 2011

Flooding of the gas diffusion layer (GDL) of proton exchange membrane (PEM) fuel cells can be a bottleneck to the system's efficiency and even durability under certain operating conditions. Due to the small scale and complex geometry of the materials involved, detailed insight into the pore scale phenomena that take place are difficult to measure or simulate. In the present effort, a direct 3D microscale model of a portion of the PEM cathode channel and carbon cloth GDL is used to parametrically investigate local heat and fluid flow at the GDL's pore scale and their effects on condensation of water vapour that leads to flooding. The 3D simulation through the microscale geometry is among the first appearing in the international literature. The Navier-Stokes, energy and water vapour transport equations are solved at steady state and in three-dimensional space for a range of inlet velocities and cloth fibre material properties, using a conjugate heat transfer approach to calculate the temperature field within the solid fibres. Psychrometric calculations are applied to provide indications of the conditions and areas most prone to condensation based on the calculated local temperatures and water vapour concentration. © 2010 Elsevier Masson SAS. All rights reserved.


Kopanidis A.,University of Western Macedonia | Theodorakakos A.,Fluid Research Co. | Gavaises E.,City University London | Bouris D.,University of Western Macedonia
International Journal of Heat and Mass Transfer | Year: 2010

A 3D numerical simulation methodology for the flow and heat transfer at the pore scale level of high porosity open cell metal foam is presented. The pore scale topology is directly represented with a 3D numerical model of the geometry, which is discretised using a tetrahedral volume mesh for both its void and solid phases. The conjugate flow and temperature fields are obtained by solution of the Navier-Stokes and energy equations for two different foam pore densities under various flow and temperature conditions. Model validation is performed against macroscopic parameters such as pressure drop and heat transfer coefficient; the results are found in reasonable agreement with the experimental measurements. © 2010 Elsevier Ltd. All rights reserved.


Tonini S.,University of Bergamo | Tonini S.,City University London | Gavaises M.,City University London | Theodorakakos A.,Fluid Research Company | Cossali G.E.,University of Bergamo
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering | Year: 2010

Computational fluid dynamics results are presented providing information on the influence of multiple injection strategy on fuel vaporization characteristics under conditions typical of direct injection, turbocharged, high-speed automotive diesel engines. The fuel is assumed to be injected from a high-pressure common rail injector nozzle. Focus is given on the number of multiple injections and dwell-time on the evaporating spray plume development. Comparison between the different cases is performed in terms of liquid and vapour penetration curves, the spatial distribution of the air-fuel equivalence ratio and the fuel vapour spatial distribution difference between the cases considered. The results confirm that, under the operating conditions investigated, the liquid penetration length, known to freeze at a distance from the nozzle exit, is not significantly affected by the injection strategy, while vapour penetration follows the time-shift of the dwell-time. Longer dwell-times retard the diffusion of the vapour in the carrier gas. Although injection of small fuel quantities prior to the main pulse does not affect the liquid penetration, it contributes up to 5 per cent more stoichiometric fuel vapour present in the area of observed auto-ignition sites. Post injection and splitting of the main injection in two pulses modify the vapour distribution by creating two spatially separated fuel-rich zones. © IMechE 2010.


Strotos G.,National Technical University of Athens | Strotos G.,Technological Educational Institute of Piraeus | Gavaises M.,City University London | Theodorakakos A.,Fluid Research Co. | Bergeles G.,National Technical University of Athens
Fuel | Year: 2011

A numerical model for the complete thermo-fluid-dynamic and phase-change transport processes of two-component hydrocarbon liquid droplets consisting of n-heptane, n-decane and mixture of the two in various compositions is presented and validated against experimental data. The Navier-Stokes equations are solved numerically together with the VOF methodology for tracking the droplet interface, using an adaptive local grid refinement technique. The energy and concentration equations inside the liquid and the gaseous phases for both liquid species and their vapor components are additionally solved, coupled together with a model predicting the local vaporization rate at the cells forming the interface between the liquid and the surrounding gas. The model is validated against experimental data available for droplets suspended on a small diameter pipe in a hot air environment under convective flow conditions; these refer to droplet's surface temperature and size regression with time. An extended investigation of the flow field is presented along with the temperature and concentration fields. The equilibrium position of droplets is estimated together with the deformation process of the droplet. Finally, extensive parametric studies are presented revealing the nature of multi-component droplet evaporation on the details of the flow, the temperature and concentration fields. © 2011 Elsevier Ltd All rights reserved.


Nikolopoulos N.,Technological Educational Institute of Piraeus | Strotos G.,Technological Educational Institute of Piraeus | Nikas K.-S.,Technological Educational Institute of Piraeus | Theodorakakos A.,Fluid Research Company | And 3 more authors.
Atomization and Sprays | Year: 2010

The impact of a spherical water droplet onto a stationary sessile droplet lying on a solid wall is studied numerically using the volume-of-fluid methodology. The governing Navier-Stokes equations are solved both for the gas and liquid phase coupled with an additional equation for the transport of the liquid interface. An unstructured numerical grid is used along with an adaptive local grid refinement technique, which enhances the accuracy of the numerical results along the liquid-gas interface and decreases the computational cost. The stationary sessile droplet has been created from the prior impact of one or two water droplets falling onto the solid wall, while two solid walls have been studied-an aluminum substrate and a glass substrate. The material of the wall plays an important role because it has an impact on the droplet's wetting behavior. The numerical model is validated against corresponding experimental data presented in the first part of the present work (Nikolopoulos et al., 2010), showing good agreement. Furthermore, the numericalinvestigation sheds light on the governing physics of the phenomenon. © 2010 by Begell House, Inc.


Nikolopoulos N.,Technological Educational Institute of Piraeus | Strotos G.,Technological Educational Institute of Piraeus | Nikas K.S.,Technological Educational Institute of Piraeus | Gavaises M.,University of London | And 3 more authors.
Atomization and Sprays | Year: 2010

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 theWe number and the maximum thickness of the steady film, which is affected by the surface wettability properties © 2010 by Begell House, Inc.


Strotos G.,Technological Educational Institute of Piraeus | Aleksis G.,Technological Educational Institute of Piraeus | Gavaises M.,City University London | Nikas K.-S.,Technological Educational Institute of Piraeus | And 2 more authors.
International Journal of Thermal Sciences | Year: 2011

The conjugate problem of fluid flow and heat transfer during the impact of water droplets onto a heated surface is studied numerically using the Volume of Fluid (VOF) methodology; adaptive grid refinement is used for increased resolution at the droplet moving interface. The phenomenon is assumed to be 2D-axisymmetric and the wall temperature is moderated to prevent the onset of nucleate boiling. Parametric studies examine the effect of Weber number, droplet size, wall initial temperature and liquid thermal properties on the cooling process of the heated plate during the impaction period. The main variables describing the evolution of the phenomenon are non-dimensionalised with expressions arising from the transient conduction theory. It is proved that for all cases examined, these non-dimensional expressions can be grouped together for describing the hydrodynamic and thermal behavior in a similar manner. Additionally, semi-analytic expressions are derived, which, for a given range of variation, describe the spatial distribution and the temporal evolution of the temperature of the wall as well also the heat flux absorbed from the droplet, cooling effectiveness and mean droplet temperature. © 2011 Elsevier Masson SAS. All rights reserved.


Trademark
Fluid Research Corporation | Date: 2014-01-13

INDUSTRIAL MACHINES FOR MIXING, DISPENSING, AND MIXING AND DISPENSING LIQUIDS AND OTHER FLOWABLE MATERIALS, NAMELY, PASTES AND POWDERS, ALL IN MEASURED AMOUNTS.


Trademark
Fluid Research Corporation | Date: 2015-05-26

Automated liquid dispending machines; Fluid power component kit for machine control comprising pumps and valves; Machine parts that heat and maintain temperature in machine piping systems, namely, steam jacketing, electrical tracing, and insulation sold as integral components of finished machines.


Trademark
Fluid Research Corporation | Date: 2011-11-15

INDUSTRIAL MACHINES FOR MIXING, DISPENSING, AND MIXING AND DISPENSING LIQUIDS AND OTHER FLOWABLE MATERIALS, NAMELY, PASTES AND POWDERS, ALL IN MEASURED AMOUNTS.

Loading Fluid Research Co. collaborators
Loading Fluid Research Co. collaborators