No abstract

Single-wall carbon nanotubes (SWNTs) were examined as catalysts for improving the hydrogen absorption and desorption properties of Ti/Zr-doped NaAlH4 hydride, proposed as a reversible hydrogen storage material. We studied the hydrogen charge and discharge characteristics and stability of sodium aluminium composites ball milled with carbon additives such as SWNTs, graphite or activated carbon (AX-21). The SWNT–NaAlH4 system was tested at 160 °C for up to 200 cycles, and the sorption kinetics were enhanced by a factor of four. Also, the catalyzed NaAlH4 hydride with graphite and activated carbon additives shows fast absorption and desorption kinetics. Our results indicate that by creating new hydrogen transition sites, the structure of carbon in the composites plays an important role in enhancing the hydrogen absorption and release rates.

No abstract

No abstract

There is an opportunity to improve the efficiency of flat plate solar air collectors by replacing their conventional glass covers with lightweight polycarbonate panels filled with high performance aerogel insulation. The in situ performance of a 5.4m 2 solar air collector containing granular aerogel is simulated and tested. The collector is incorporated into the external insulation of a mechanically ventilated end terrace house, recently refurbished in London, UK. During the 7 day test period, peak outlet temperatures up to 45°C are observed. Resultant supply and internal air temperatures peak at 25 30°C and 21 22°C respectively. Peak efficiencies of 22 36% are calculated based on the proposed design across a range of cover types. Measured outlet temperatures are validated to within 5% of their predicted values. Estimated outputs range from 118 166 kWh/m 2 /year for collectors with different thickness granular aerogel covers, compared to 110 kWh/m 2 /year for a single glazed collector, 140 kWh/m 2 /year for a double glazed collector and 202 kWh/m 2 /year for a collector incorporating high performance monolithic aerogel. Payback periods of 9 16 years are calculated across all cover types. An efficiency up to 60% and a payback period as low as 4.5 years is possible with an optimised collector incorporating a 10mm thick granular aerogel cover.

Effect of activated alloys on hydrogen discharge kinetics of MgH₂ nanocrystals AbstractActivated alloys synthesized by arc-melting were examined as catalysts for improving the hydrogen sorption characteristics of nanostructured magnesium hydride, proposed as a reversible hydrogen storage material. The MgH 2 -catalyst absorbing materials were prepared by ball milling of pure MgH 2 with hydrided Zr 47 Ni 53 ,Zr 9 Ni 11 , and other investigated alloys. The nanostructured MgH 2 -intermetallic systems were tested at 250 • C and catalyst addition of eutectoid Zr 47 Ni 53 resulted in the fastest desorption time and highest initial desorption rate. Also, the catalyzed Mg-hydride with activated Zr 9 Ni 11 and Zr 7 Ni 10 phases showed fast desorption kinetics. Moreover, the results demonstrated that the composition of dispersed Zr x Ni y catalysts has a strong influence on the amount of accumulated hydrogen and desorption rate of Mg-nanocomposite.

No abstract

PCM modules, constructed from a paraffin/LDPE composite, were tested in an occupied London office, in summer. Design variations tested the effect on heat transfer of a black paint or aluminium surface, the effect of different phase transition zones and the effect of discharging heat inside or outside.The modules' temperatures were monitored along with air flow rate, air temperature and globe temperature. Their small size meant any effect on room temperature was negligible.Using DSC measurements of the PCMs' thermophysical properties, in conjunction with the environmental measurements, semi-empirical models of the modules were constructed in FLUENT using an enthalpy porosity formulation to model phase change. Good validation was obtained using the temperature measurements with notable divergence noted when maximum liquid fraction was reached.The models were validated by the temperature measurements and used to generate mean liquid fraction and surface heat transfer rate profiles for performance comparisons.The broad phase transition zones of the PCMs results in wasted latent heat capacity. Black modules transfer heat and exhaust latent storage capacity significantly quicker than aluminium modules, due to radiant exchange. Discharging heat outside leads to an increase in thermal storage capacity and a higher rate of heat absorption.2