John Anagnostopoulos

Prof. Dr. John Anagnostopoulos

School of Engineering, Bahrain Polytechnic, Madīnat ‘Īsá, Al Janūbīyah, Bahrain
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Academic Career Length

16Years (2011-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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22 September 2023 in Advanced Functional Materials
Verified
Journal Article
Open access
PSPanagiotis Sarkiris
Panagiotis Sarkiris
Vassilios ConstantoudisVassilios Constantoudis
Vassilios Constantoudis
Kosmas EllinasKosmas Ellinas
Kosmas Ellinas
CLCheuk Wing Edmond Lam
Cheuk Wing Edmond Lam
AMAthanasios Milionis
Athanasios Milionis
EGEvangelos Gogolides
Evangelos Gogolides
An effective pathway to enhance the heat transfer process is to induce the formation of highly mobile condensate droplets, employing micro‐nanoengineered superhydrophobic surfaces. However, the design of the topography of these surfaces for sustained high performance constitutes a significant scientific and technological challenge. Herein, the critical role of the correlation length of topography is demonstrated as an important factor when designing superhydrophobic surfaces for heat transfer applications. Specifically, it is shown that a) a high correlation length value corresponds to increased space between surface structures and higher lateral distances between nucleating droplets, which results in lower droplet departure diameter and significantly delayed flooding of the surface and b) correlation length has to surpass a critical value for dropwise condensation (DWC) to be sustained in hierarchical structured surfaces, when the droplets are growing in a partial Cassie state. Following this rationale, droplets are categorized in three different energy and wetting states (Wenzel droplets, Cassie droplets of low kinetic energy and high energy jumping droplets), depending on the correlation length of the topography. Heat transfer experiments demonstrate an increase of 126% in the heat transfer coefficient (HTC) of surfaces exhibiting the maximum correlation length when compared to the flat hydrophobic surface.
12 March 2023 in Energies
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Journal Article
Open access
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PKPhoevos Koukouvinis
Phoevos Koukouvinis
JAJohn Anagnostopoulos
John Anagnostopoulos
The expanding role of renewable energy sources in the electricity market share implies the increasing role of hydropower and the exploitation of unharnessed hydraulic potential, in the scope of sustainability and net zero emissions. Hydro-turbine design practices are expected to expand beyond achieving high efficiency goals, to multi-objective criteria ranging from efficient reversible operation to fish-friendly concepts. The present review paper outlines fundamental characteristics of hydropower, summarizing its potential impact toward aquatic life. Estimates of lethality for each damage mechanism are discussed, such as barotrauma, blunt impact and shearing, along with relevant advances in experimental techniques. Furthermore, numerical techniques are discussed, ranging from simple particle tracking to fully coupled six-degree-of-freedom tracking, which can be used to investigate candidate designs and their fish-friendly performance, presenting their advantages and disadvantages. Subsequently, a link to the individual damage mechanisms is established, to proposed holistic performance metrics, useful for providing estimates of fish-friendliness of a given hydropower installation. Finally, recent developments and design practices for fish-friendly turbine concepts are presented.
1 May 2011 in Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy
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Journal Article
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FSF G Stamatelos
F G Stamatelos
JAJohn Anagnostopoulos
John Anagnostopoulos
DPD E Papantonis
D E Papantonis
Pelton hydraulic turbines are impulse-type turbomachines commonly used in hydroelectric plants with medium-to-high water head and in various energy recovery applications. The aim of the present work is to provide detailed performance measurements on a Pelton turbine model, along with the design and geometrical dimensions of its runner/buckets and injectors. Such a complete set of data would be useful for further development and evaluation of numerical modelling tools of the complex unsteady free-surface flow developed in the turbine, and is missing from the literature. The two-nozzle Pelton model was designed using standard guidelines and was fully constructed in the Laboratory of Hydraulic Turbomachines, NTUA. The measurements include the net water head and flowrate, the injector characteristic curves, and the torque and rotation speed of the runner, from which the corresponding overall efficiency and shaft power are computed. The model was tested with one injector (upper or lower) and with both injectors in operation, using either constant or variable rotation speed mode. The comparative results were satisfactory and in line with the theory, verifying similarity and repeatability, and allowing for an estimation of mechanical losses. The measurements covered the entire operation range of the turbine, in order to draw complete hillcharts for various operation modes.
27 April 2013 in Acta Mechanica
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PKPhoevos Koukouvinis
Phoevos Koukouvinis
JAJohn Anagnostopoulos
John Anagnostopoulos
DPDimitris E. Papantonis
Dimitris E. Papantonis
10 January 2023 in Energies
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Journal Article
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PKPhoevos Koukouvinis
Phoevos Koukouvinis
JAJohn Anagnostopoulos
John Anagnostopoulos
Utilization of unharnessed hydro-power necessitates designing fish-friendly hydraulic machinery. Towards this effort, the present work investigates various methods for tracking fish motion, ranging from particle tracking methods to accurate, but computationally expensive, body tracking methods, such as immersed boundaries and overset meshes. Moreover, a novel uncoupled 6-Degree of Freedom tracking technique is proposed, based on an approximated pressure field around the tracked body of interest, using steady-state flow field data, and including collision detection to walls. The proposed method shows promising results in terms of accuracy, being comparable to the more computationally expensive fully coupled methods at a tiny fraction of the execution time. The new method reveals location of fish–blade impact, as well as statistics of forces, pressure and flow shear that a passing fish is subjected to, both in the normal and reverse operation of the turbine. The low computational cost of the proposed method renders it attractive for optimization studies.
13 August 2024 in Energies
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Open access
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MMMichalis Mentzos
Michalis Mentzos
IKIoannis Kassanos
Ioannis Kassanos
JAJohn Anagnostopoulos
John Anagnostopoulos
AFAndronikos E. Filios
Andronikos E. Filios
Operating centrifugal pumps under two-phase flow conditions presents challenges such as phase separation, cavitation, and flow instabilities, compromising reliability and performance. A specialized design is crucial to mitigate these issues. This study utilized computational fluid dynamics (CFDs) to understand two-phase flow behavior and assess the impact of different blade geometries on pump performance under such conditions. For this purpose, the inhomogeneous multiphase model was employed, wherein the momentum and continuity flow equations were individually solved for each phase across three different impellers with varying blade angle distributions. The computational results indicated higher gas concentrations on the pressure side of the blade, with gas pocket size correlating with flow rate and inlet gas concentration. The blade angle distribution’s effect was more pronounced with increased gas concentrations, while a tendency of gas bubbles to coalesce towards the impeller shroud was also observed. The presence of gas promoted flow recirculation and separation, substantially reducing impeller performance. Blade angle distribution critically influenced the flow field, affecting flow separation, stability, efficiency, and overall performance, highlighting the importance of optimized blade design for enhanced centrifugal pump performance in liquid–gas two-phase flow conditions.