1,720,975 research outputs found
A study of the loss characteristics of a single cell PEM electrolyser for pure hydrogen production
No full textIn this paper the losses of a proton exchange membrane (PEM) single cell electrolyser were investigated. The ohmic, activation and mass transfer losses are the most prominent losses in a PEM electrolyser. The Electrochemical Impedance Spectroscopy (EIS) method was applied to identify these losses. A parametric study of each loss component was performed by changing a component or condition responsible for the loss. The membrane thickness was varied in the Membrane Electrode Assembly (MEA) to identify the ohmic loss and the temperature was changed to capture the activation loss. Two different diffusion media were used to investigate the mass transfer effect. The results were confirmed with polarisation curves and Tafel plot
PEM Water Electrolysis: Preliminary Investigations Using Neutron Radiography
No full textThe quasi-dynamic water distribution and performance of a proton exchange membrane (PEM) electrolyzer at both a small fuel cell's anode and cathode was observed and quantitatively measured in the in-plane imaging geometry direction(neutron beam parallel to membrane and with channels parallel to the beam) by applying the neutron radiography principle at the neutron imaging facility (NIF) of NIST, Gaithersburg, USA. The test section had 6 parallel channels with an active area of 5 cm2 and in-situ neutron radiography observation entails the liquid water content along the total length of each of the channels. The acquisition was made with a neutron cMOS-camera system with performance of 10 sec per frame to achieve a relatively good pixel dynamic range and at a pixel resolution of 10 x 10 μm2. A relatively high S/N ratio was achieved in the radiographs to observe in quasi real time the water management as well as quantification of water / gas within the channels. The water management has been observed at increased steps (0.2A/cm2) of current densities until 2V potential has been achieved. These observations were made at 2 different water flow rates, at 3 temperatures for each flow rate and repeated for both the vertical and horizontal electrolyzer orientation geometries. It is observed that there is water crossover from the anode through the membrane to the cathode. A first order quantification (neutron scattering correction not included) shows that the physical vertical and horizontal orientation of the fuel cell as well as the temperature of the system up to 80 °C has no significant influence on the percentage water (∼18%) that crossed over into the cathode. Additionally, a higher water content was observed in the Gas Diffusion Layer at the position of the channels with respect to the land
Characterisation tools development for PEM electrolysers
No full textElectrochemical impedance spectroscopy (EIS), current interrupt (CI) and current mapping (CM) were investigated as in-situ characterisation tools for PEM electrolysers. A 25 cm2 cell with titanium anode and carbon cathode plates were utilised in this study. A commercial MEA consisting of 1 mg IrO2/cm2 on the anode and 0.3 mg Pt/cm2 on the cathode was used. The electrocatalyst was deposited on Nafion® membranes. The electrochemical losses in a PEM electrolyser namely: activation, ohmic and mass transfer losses were identified using EIS and CI and both the advantages and disadvantages of the methods were discussed. The current distribution over the membrane electrode assembly (MEA) at different current densities was measured using the current mapping method. It is also shown that under the given experimental conditions the current density decreases along the serpentine flow fiel
Evaluation of MEA manufacturing parameters using EIS for SO2 electrolysis
No full textMembrane electrode assembly (MEA) manufacturing parameters such as hot pressing pressure and pressing time were investigated for the use in a SO2 electrolyser. The SO2 electrolysis was optimised in terms of cell temperature, membrane thickness and catalyst loading. The electrolysis efficiency was evaluated using polarisation curves while electrochemical impedance spectroscopy (EIS) was used to determine the membrane resistance, activation energy and mass transport limitations. An electrical circuit, which included inductance, ohmic resistance, charge transfer, constant phase and Warburg elements, was used to fit the experimental data. The optimum hot pressing conditions were 50 kg cm−2 for 5 min at 120 °C. Increased cell temperature (80 °C) resulted in a reduction of mass transport, while thicker membranes resulted in an increased mass transport due to lower water transport through the membrane. Increased catalyst loading (from 0.3 to 1 mgPtC.cm−2) improved the cell performance due to improved kinetics confirmed by the EIS dataDST (Department of Science and Technology, South Africa) under project KP5 – IO3 managed by HySA Infrastructure Co
Informal Production Networks
Full text linkMini Dissertation MArch(Prof)--University of Pretoria, 2017.The relationship between industry and the city is a damaged
one. However, with its existing mix of residents, industry
and commerce (albeit segregated from one-another)
Pretoria West holds the potential for a unique relationship
between industry and the citizens of Pretoria. Only by understanding
the role that these industries play within the
greater context of the city can the rich character and culture
of a place be ampli ed and solidi ed in a development
plan. Catalyzed by its heritage, development becomes
a manifestation of the character of place that will attract
further growth and simultaneously embrace the existing
stakeholders.
e existing industrial built-environment is often misshapen
and illegible and whilst it is di cult to organize
(and navigate) the seemingly disorganized site, it is possible
to resolve; through understanding historic boundaries and
development patterns that can be utilized as organizational
grids. In this case historic erf divisions and consolidations
can be utilized as an organizational tool at a large scale and
should serve as a guide to where future structures should be
erected in order to maintain a legible built environment.
When designing future additions, understanding the historic
expansion of these industrial buildings holds the key
to a harmonious relationship between old and new. With
minimal architectural intent these buildings supply little
for the architect to grapple onto, but with material spans
and structural repetition forming the underlying ordering
principle; it is possible to create a logical and ordered extension
of the past.Die verhouding tussen industrie en die stad is beskadig
en as gevolg word industrië stelselmatig verwyder van die
stad. Die mengsel tussen inwoners, industrie en handel in
Pretoria Wes (albeit geissoleer van mekaar) gun egter die
potensiaal tot ‘n unieke verbandskap tussen industrie en
die inwoners van Pretoria. Slegs deur die rol te erken wat
die industrië speel ten opsigte van die stad se groter konteks,
kan die karakter en kultuur van so ‘n omgewing versterk en
vasgevang word in ‘n ontwikkelings plan. Erfenis dien as
katalisator vir ontwikkeling van die karakter van plek wat
in beurt verdere nansiële groei sal aanhits.
Die bestaande industriële bou-omgewing is misvorm en onvoorspelbaar.
Alhoewel so ‘n omgewing nie aan die individie
toeleen om weg te vind of organiseer nie, is dit moontlik
deur die ontginning van historiese grense en ontwikkelings
patrone wat kan dien as organiseerings mates. Historiese erf
indelings en konsolodasies kan gebruik word om te dien as
‘n gids vir toekomstige toevoegings, om sodoende die nuwe
argitektuur uit die bestaande te laat vloei. Die resultaat is
‘n leesbare en geordende bou-omgewing.
Die ontwerp van die nuwe verbeelding steun op die
morfologie van die bestaande omgewing om ‘n harmoniese
verhouding tussen oud en nuut te skep. Materiale se span
afstande neem die rol van die onderliggende orde stelsels
aan as gevolg van die gebrek aan aansienlike argitektoniese
bedoelings in die bestaande omgewing. Sodoende is
‘n leesbare en logiese uitbreiding van die verlede en na die
toekoms moontlik in ‘n omgewing wat ontstaan het sonder
ontwerp vir ervaring van mense.ArchitectureMArch(Prof)Unrestricte
Transformasie van die gevonde: \u27n Alchemiese proses
No full textDie beginsel van transformasie kan beskou word as \u27n maatstaf vir die herkenning van kuns as kuns (alhoewel die debat hieroor onbeslis bly). In \u27n artikel waarin aspekte van die werk van filosowe soos Heidegger, Harries, Gadamer en Marcuse ondersoek word in \u27n poging om kriteria vir kuns op te stel, som Olivier ( 1987: 16) sy bevinding as volg op: \u27to the extent that art reveals an aesthetically transformed world, it also has the capacity to transform the (moral, political) life of the spectator. This, it is suggested, constitutes a criterion for art.\u27 Volgens hierdie stelling is transformasie \u27 n sleutelbegrip en deurlopend ter sprake binne die konteks van kuns . Die beginsel van transformasie is dus omvattend. Dit word egter in hierdie artikel ondersoek spesifiek met betrekking tot die rekonstruksie van die gevonde objek/voorwerp
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
South African hydrogen infrastructure (HySA infrastructure) for fuel cells and energy storage: overview of a projects portfolio
No full textThe paper provides brief introduction to the National South African Program, branded HySA (Hydrogen South Africa) as well as discusses potential business cases for deployment of hydrogen and fuel cell technology in South Africa. This paper also describes some key activities in the area of hydrogen production and storage within HySA Infrastructure Center of Competence in South Africa. The content of this paper is based on the presentation given during the recent WHEC 2016 Congress in Zaragoza, Spain. More specifically, the discussion of activities at HySA Infrastructure Center of Competence in the paper includes hydrogen production and storage
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