Chris N Christodoulou - Academia.edu (original) (raw)

Papers by Chris N Christodoulou

ChemInform, 2010

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Renewable Energy

Abstract Compression is one of the most critical issues related to almost all hydrogen storage me... more Abstract Compression is one of the most critical issues related to almost all hydrogen storage methods and its subsequent usage. Hydrogen compression is only part of the so-called “Hydrogen Value Chain”, but it is crucial for overcoming the entry barriers for a “Hydrogen Economy”. It is widely accepted that there is a strong need for significant improvements in efficiency, durability and reliability of hydrogen compressors as well as for cost reductions, The basic scope of this work is to present the current developments on Metal Hydride Hydrogen Compressors (MH2C) and try to evaluate from both technical and economical point of view the potential integration of MH2C in real power systems comprising Renewable Energy Sources and Hydrogen technologies. In this work, certain target markets for the MH2 compressor are identified, while all technical and financial issues of its integration in complete power systems have been assessed. Through a preliminary analysis of potential markets for the MH2 Compressor, it is shown that there are three major niche markets: (i) Chemical industry, by utilisation of waste industrial and/or available renewable heat; (ii) Hydrogen filling stations for vehicles and (iii) RES & H2 autonomous power systems for remote communities (e.g. off-grid islands). A specific case study (the Greek island of Milos) is analysed in detail (using the HOMER software tool) with the aim of increasing RES penetration. A RES & hydrogen storage power supply system is proposed and examined from an economic, environmental and social perspective drawing the relevant conclusions.

ABSTRACT Power Plant (VPP) is one of the aggregation models suggested for Distributed Generation ... more ABSTRACT Power Plant (VPP) is one of the aggregation models suggested for Distributed Generation (DG) and controllable or flexible loads. This paper aims to show the increased benefits that the end-users of DG units can enjoy if they formulate a VPP with increased flexibility of controllable loads. In this study, data from a pilot VPP formulated by three experimental sites with DGs are used. The results presented are based on actual measurements of consumption and temperature combined with a variety of market prices and demand patterns for different seasons.

International Journal of Hydrogen Energy

Transportation and the Environment, 2016

Journal of Alloys and Compounds, 1995

The i~reparation of Sm2FelTN3 involves the slow diffusion of nitrogen atoms from the surface to t... more The i~reparation of Sm2FelTN3 involves the slow diffusion of nitrogen atoms from the surface to the bulk of the material. The atomic diffusion mechanism operating in this case is voidal diffusion. The nitrogen atoms are located inside the 9(e) octahecra, which share Sm corners but no faces between them. Nitrogen atoms migrate by jumping from a 9(e) site into a thermodynamically unstable tetrahedral 18(g) site, and subsequently into a new 9(e) site. an such a migration path, nitrogen atoms have to contend with an enormous energy barrier, accounting for the energy needed to overcome the strong bonding from its nearest neighbors (Fe and, especially, the Sm atoms) and, more importantly, for the strain energy needed to break out through the octahedral face (Fe(f)-Sm(c)-Fe(h)) and in through the tetrahedral face (Fe(h)-Sm(c)-Fe(h)). Although the 18(g) sites cannot accommodate nitrogen atoms in an equilibrium fashion, their presence plays a key role for the diffusion of the nitrogen atoms. The diffusion of nitrogen atoms is anisotropic, as a result of the anisotropic crystal structure of Sm2Fe17. Bitter domain patterns have been used to map the nitrogen diffusion fields of nitrogenated particles, and clearly show the expected anisotropic behavior of the diffusivity. Grain boundaries with their open structure provide free paths, behaving essentially the same way as free surfaces exposed to nitrogen gas. The presence of hydrogen facilitates nitrogen diffusion but, more importantly, it fractures the particles such that nitrogen effectively penetrates towards the centre of the particles. The use of :ammonia gas causes severe morphological changes to the grains, resulting in very distinct fine microstructures.

Materials Letters, 1988

ABSTRACT Differential scanning calorimetry (DSC) has been employed to study low-temperature therm... more ABSTRACT Differential scanning calorimetry (DSC) has been employed to study low-temperature thermal oxidation of Fe-Nd-B powders. The three exothermic reactions observed cause a significant deterioration of the hard magnetic properties of the resulting magnets. X-ray photoelectron data demonstrate that at least two forms of oxygen are present on such powders.

Pr_2Co_ {14}B-based permanent magnets have been prepared by using both the rapid quenching and po... more Pr_2Co_ {14}B-based permanent magnets have been prepared by using both the rapid quenching and powder metallurgy techniques. The rapidly quenched magnets have been found to be initially in an amorphous state exhibiting soft magnetic properties. Subsequent heat-treatment above the crystallization temperature (560^circC) causes the initial crystallization of the Pr_2 Co_{14}B phase which is responsible for the observed high value of the intrinsic coercivity (greater than 15 kOe). The corresponding maximum energy product of the produced isotropic rapidly quenched magnets was 4-5 MGOe. The final phases present in the magnets were the Pr_2Co _{14}B, PrCo_4B and a minor amount of PrCo_5 or PrCo_{12}B_6 depending on the composition of the starting alloy. The crystallographically anisotropic Pr _2Co_{14}B -based sintered magnets exhibited an intrinsic coercivity of 5.2 kOe and a maximum energy product of 10.3 MGOe. The above sintered magnets were found to contain 1.2 wt% oxygen. The phases present in the same magnets were the Pr _2Co_{14}B, PrCo_4B and a minor amount of PrCo _{12}B_6 . The metallurgical behavior (microstructural characteristics and phases present) of the alloys used to prepare rapidly quenched and sintered magnets were found to be in a complete agreement with the experimentally determined Co-Pr-B (Co -rich) phase diagram in terms of the liquidus projection surface and the isothermal section at 1000^ circC. The Co-Pr-B phase diagram was found to be very different from that of Fe-Nd-B. The Pr_2 Co_{14}B phase forms peritectically around the Pr_2Co _{17} phase according to the pseudo-binary peritectic reaction: Pr_2 Co_{17} + Liquid rightarrow Pr_2 Co_{14}B. In the case of Fe-Nd-B system, the Nd_2Fe _{14}B phase forms during the reaction: alpha-Fe + Liquid rightarrow Nd_2 Fe_{14}B. Also, it was found that the Pr_2Co _{14}B phase can be in equilibrium with the Co-Pr_2Co_ {17},Pr_2Co _{17}-PrCo_5, PrCo_5-PrCo_4B, PrCo_4B-PrCo_{12 }B_6 and PrCo _{12}B_6 -Co phases. The magnetic hysteresis of the Pr_2 Co_{14}B-based permanent magnets exhibited a sharp decrease in the magnetization (shoulder) at small reverse fields. Also, the magnetization vs. temperature behavior of the Pr_2Co _{14}B-containing alloys exhibited a "spike" type of transition at 410^ circC on heating. The above features of the magnetic hysteresis and magnetization vs. temperature behavior have been interpreted by employing the "non-interacting" single-domain particle (SDP) theoretical model.

7th Mediterranean Conference and Exhibition on Power Generation, Transmission, Distribution and Energy Conversion (MedPower 2010), 2010

ABSTRACT Wider use of fossil fuels is prohibited by unfavourable recent climate change phenomena ... more ABSTRACT Wider use of fossil fuels is prohibited by unfavourable recent climate change phenomena as well as constraints from greenhouse gasses emissions, regulated strictly by the European Union. Fuel demanding sectors, such as transportation, impose utilisation of environmentally friendly technologies which will contribute in increased hydrogen production, which is considered as energy carrier for future applications. The state-of-the-art of solar/thermal power plants, and technologies for hydrogen production, storage and application are briefly reviewed. The utilisation of solar/thermal power plants from technical and economical point of views, for electricity production which will subsequently be exploited for hydrogen production is examined. It is argued that use of hydrogen to empower internal combustion engine vehicles, as well as fuel cell vehicles, can extensively satisfy the energy requirements of the transportation sector in the near future. Hydrogen usage can subsequently decrease the dependency on fossil fuel imports of local economies of southern Mediterranean insular areas with high solar radiation. Recent statistical data both for fuel demands for transportation, as well as pertinent CO2 emissions are illustrated for the case study of the island of Cyprus. In the case study, the energy requirements for the transportation sector are used and the exploitation of solar/thermal power plants is analysed. From the case study results and findings, conclusions are drawn and recommendations are provided for the type and size of solar/thermal power plants, and the appropriate hydrogen technologies to be adapted in the near future for limiting dependency on fuel imports and largely decreasing CO2 emissions.

The present research work is focused on the effect of activation procedure on the hydrogen absorp... more The present research work is focused on the effect of activation procedure on the hydrogen absorption-desorption properties of new rare earth -transition metal compound based on Sm(Co 0.6 Fe 0.2 Zr 0.16 B 0.04 ) 7.5 composition. Crystal structure and composition is always connected to the maximum capacity of the intermetallic hydrides. For composite materials the thermodynamic properties of hydrogenationdehydrogenation procedure are mostly explained through microstructuremicrochemistry characteristics. Efficient hydrogen storage is direct connected to the desorbed hydrogen amount. The as hydrogenated material Sm(Co 0.6 Fe 0.2 Zr 0.16 B 0.04 ) 7.5 seems to have in the desorption a pressure plateau below the atmospheric pressure at room temperature while the absorbed hydrogen almost remains in the material having capacity of ~0.8 wt. % at 0.1 MPa -30 o C. After the proper activation procedure, the hydrogenated material desorbs very high amount of hydrogen ~1.9 wt. % at 0.1 MPa -100 o C. Subsequently, the treatment of the composite materials before hydrogenationdehydrogenation procedures could play a crucial role on the efficiency.

Summary The "Cluster Pilot Project for the Integration of Renewables into European Energy Se... more Summary The "Cluster Pilot Project for the Integration of Renewables into European Energy Sectors using Hydrogen" (RES2H2 in brief) is concerned with the design, installation, operation and optimisation of two different wind-hydrogen systems. This paper focuses on the current status of system engineering for the unit to be installed near Athens, Greece. Furthermore, market opportunities for "green" hydrogen, i.e. hydrogen

In this work, the (Zr-Ti)(Fe-Cr) 2 based compounds have been synthesized while charging-dischargi... more In this work, the (Zr-Ti)(Fe-Cr) 2 based compounds have been synthesized while charging-discharging hydrogen ability has been examined. Relatively low hydrogen pressure has been used for the hydrogenation of the samples. After following the discharging procedure, a high desorbed amount of hydrogen ~180 (ml of H 2 )/(gr of the alloy) has been measured on the first 15 min by using a volumetric device. The crystal structure has been analyzed by means of x-ray diffraction (XRD) while a Rietveld analysis has been performed on the x-ray diffraction patterns and the characteristic MgZn 2 type of structure has found to be the dominant phase in both compounds. The scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX) have been used for microstructural studies and quantitative analysis, respectively. Magnetic measurements have been performed on the samples and a paramagnetic behaviour has found to be at room temperature.

Materials Letters, 1988

Journal of Nanoscience and Nanotechnology, 2012

Metal hydrides (MH) are often preferred to absorb and desorb hydrogen at ambient temperature and ... more Metal hydrides (MH) are often preferred to absorb and desorb hydrogen at ambient temperature and pressure with a high volumetric density. These hydrogen storage alloys create promising prospects for hydrogen storage and can solve the energetic and environmental issues. In the present research work, the goal of our studies is to find the influence of partial substitution of small amounts of vanadium and tantalum on the hydrogenation properties of TiFe 0 7−x Mn 0 3 V x (x = 0 05, and 0.1) and Ti 1−y Ta y Fe 0 7 Mn 0 3 (y = 0 2, and 0.4) alloys, respectively. The nominal compositions of these materials are TiFe 0 65 Mn 0 3 V 0 05 , TiFe 0 6 Mn 0 3 V 0 1 , Ti 0 8 Ta 0 2 Fe 0 7 Mn 0 3 , and Ti 0 6 Ta 0 4 Fe 0 7 Mn 0 3 . All samples were synthesized by arc-melting high purity elements under argon atmosphere. The structural and microstructural properties of the samples were studied by using XRD and SEM, respectively, while the corresponding microchemistry was determined by obtaining EDS measurements at specific regions of the samples. Mapping was obtained in order to investigate atomic distribution in microstructure. Moreover, to ensure the associations between the properties and structure, all samples were examined by an optical microscope for accessional characterization. From all these microscopic examinations a variety of photomicrographs were taken with different magnifications. The hydrogenation properties were obtained by using a Magnetic Suspension Balance (Rubotherm). In this equipment, the hydrogen desorption and re-absorption, can be investigated at constant hydrogen pressures in the range of 1 to 20 MPa (flow-through mode). At least 3.43 wt.% of absorbed hydrogen amount was measured while the effect of substitutions was investigated at the same temperature.

ChemInform, 2010

Renewable Energy

International Journal of Hydrogen Energy

Transportation and the Environment, 2016

Journal of Alloys and Compounds, 1995

Materials Letters, 1988

7th Mediterranean Conference and Exhibition on Power Generation, Transmission, Distribution and Energy Conversion (MedPower 2010), 2010

Materials Letters, 1988

Journal of Nanoscience and Nanotechnology, 2012