Yuehong Su

A comprehensive review of Pt electrocatalysts for the oxygen reduction reaction: Nanostructure, activity, mechanism and carbon support in PEM fuel cells

The sluggish rate of the oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells has been a major challenge. Significantly increasing efforts have been made worldwide towards a highly active ORR catalyst with high durability. Among all the catalysts exploited, Pt electrocatalysts are still the best in terms of a comprehensive evaluation. The investigation of Pt-based ORR catalysts is necessary for a practical ORR catalyst with low Pt content. This paper reviews recent progress in the studies of the mechanism, nanostructure, size effect and carbon supports of Pt electrocatalysts for the ORR. The importance of the size and structure control of Pt ORR catalysts, related with carbon support materials, is indicated. The potential methods for such control are discussed. The progress in theoretical studies and in situ catalyst characterization are also discussed. Finally, challenges and future developments are addressed.

An Experimental Study on a Novel Heat Pipe-Type Photovoltaic/Thermal System with and without a Glass Cover

A novel heat pipe-type PV/T system was designed and constructed in the present study to solve the freezing problem associated with the traditional photovoltaic/thermal (PV/T) system. Outdoor tests were carried out from May to July 2010. The performances of the system with and without glass cover were also studied. The results showed that the average photothermal efficiency with glass cover was 41.30%, which was a little higher than that of the unglazed condition at 37.16%. However, the result of the tests on photoelectric efficiency was the opposite. The average efficiency was 9.42% with glass cover, which was lower than that without the glass cover at 11.51%. The unglazed condition efficiency curve showed a big fluctuation, whereas the glazed condition was almost a perfect parabola. The average first law efficiency of the glass-covered system was 48.52% compared with 44.24% without the glass cover. Conversely, the glass-covered system had a second law efficiency of 6.87%, which was lower than that of the unglazed condition at 8.01%.

Preliminary Experimental Comparison of the Performance of a Novel Lens-Walled Compound Parabolic Concentrator (CPC) with the Conventional Mirror and Solid CPCs

A conventional mirror compound parabolic concentrator (CPC) is limited by its half acceptance angle when pursuing a large geometrical concentration ratio with no tracking. A solid CPC, which is made from solid dielectric materials without notches, can achieve a larger half acceptance angle compared with the conventional mirror CPC of the same geometrical concentration ratio, which is attributed to the optical refraction caused by the dielectric material. However, solid CPCs are heavier and costlier. This paper presents a preliminary experiment on a novel lens-walled CPC. An experimental comparison of the conventional mirror and solid CPCs and the lens-walled CPC with the same geometrical concentration ratios of 2.5 is given for different incidence angles. Here the conventional mirror CPC chose the evaporated aluminium coating as the reflection layer, for short conventional CPC. Transparent acrylic was chosen as both the dielectric material and lens material. The three CPCs were all attached to a PV cell. Through the output characteristics of the cell, the optical performances of these CPCs can be obtained. The results showed that when the incidence angle was smaller than 35°, the optical efficiency of the lens-walled CPC remained above 46.7% and was more stable against incidence angle changes compared with the conventional CPC. It also weighed and cost less than the solid CPC. Thus, lens-walled CPC adequately combines the advantages of conventional and solid CPCs, and has great potential for use in large-scale practical applications.

Structure optimization and annual performance analysis of the lens-walled compound parabolic concentrator

ABSTRACT The primary lens-walled compound parabolic concentrator (lens-walled CPC) has a significant advantage of a larger half acceptance angle as a static solar concentrator, but it also has a drawback of a low optical efficiency. In order to overcome this drawback, in this article, series of structure parameters were investigated and compared to further improve the optical efficiency within the half acceptance angle combined with the material properties. The average optical efficiencies of the improved lens-walled CPCs could achieve more than 82% within the half acceptance angle of 35ᵒ. Experiments were adopted to verify the credibility and validity of the simulation. Moreover, annual performance of the lens-walled CPCs comparison with that of the mirror CPC for Nottingham was analyzed. Results show that the improved lens-walled CPC has a higher optical performance for actual building application.

TECHNO-ECONOMIC IMPACTS OF INNOVATIVE COMMERCIAL- INDUSTRIAL SCALE BIOENERGY PLANT IN PAKISTAN

A case study of an innovative medium sized commercial-industrial bioenergy plant is portrayed. This plant effectively runs on various agricultural waste feedstocks like; animal-manure, vegetable, poultry and sugar wastes etc. The plant design is based on anaerobic fixed dome triple digester system connected via underground lagoon. Thus system is facilitating continuous flow of the input feedstock capacity up-to four tonnes per day. This modern scheme is built on innovation with the inclusion of mechanical stirrers, gas scrubbers, filtration, compression and storage systems. This research paper highlighted the potential techno-economic impacts of such bioenergy plant for the energy stressed small-medium industrial sector in developing countries like Pakistan. It has the capability of 142 MWh energy generations per year; rate of return 15.42% and employment growth prospects in SME sector up-to 55%.

Analysis of a novel absorption refrigeration cycle using centrifugal separation

A novel absorption refrigeration cycle using centrifugal separation is described. The generator and condenser of a conventional absorption cycle are replaced with a single centrifuge and the absorbent–refrigerant solution is separated by centrifugal force. The reversible mechanical work required for separating a solution has been calculated and the coefficient of performance (COP) of the cycle determined. For an annulus centrifugal field, the separation process of the solution has been simulated. The equilibrium rotation speed and separation time required have been determined and the cooling capacity of the cycle calculated. The effects of the mass diffusion coefficient and sedimentation coefficient upon them have also been analysed.

Bioenergy recovery analysis from various waste substrates by employing a novel industrial scale AD plant

ABSTRACT In this novel industrial scale case study, the bioenergy recovery based on sole and mixed cow-buffalo (CBM) and potato waste (PW) substrates has been analyzed in real time, i.e., on-site on a full-scale operational anaerobic digestion (AD) plant. The plant employed in this study is a novel design, consisting of tri-digesters connected via an underground upflow anaerobic sludge blanket (UASB) type lagoon allowing it to function as a continuous-flow reactor. The system has been further equipped with CSTR, microwave heating, gas scrubbers, compression, and storage systems. The highest energy recovery readings were 123.9 m3/1,000 kg, 77 m3/1,000 kg, and 151.6 kWh/1,000 kg in terms of biogas, bio-methane, and electricity generated, respectively, with 75:25 ratio of CBM:PW. Operating with 100% CBM, yields of 79.9 m3/1,000 kg, 47 m3/1,000 kg, and 95 kWh/1,000 kg were obtained. The percentage of recovery in bio-methane production increased on using the mixed substrates, but it was the lowest with a 25:75 ratio of CBM:PW. The electrical power generation efficiency was found to be significantly increased, but not distinctively with the plant aggregate power rating that was probably associated with the variable quality of biogas which was fed to the power generator. A linear regression analysis had shown a significant and positive correlation between the rate of VS removal and biogas yield.

Performance Evaluation and Energy Saving Potential of Windcatcher Natural Ventilation Systems in China

Windcatcher as an architectural element is a passive cooling design to improve indoor thermal comfort without energy consumption. The performance and energy saving potential of using a windcatcher system in China are evaluated through EnergyPlus simulation of an oce building installed with commercial windcatchers. The simulation results for the climate condition in Beijing indicate that the peak indoor tem- perature can be reduced by more than 2 - C with the help of windcatchers, for approximately 50% of occupied hours it can meet the basic ventilation requirement and 28% of occupied hours can reach the purge demand. Moreover, 17% of cooling load can be reduced. The performance of windcatchers can be largely enhanced if they are used along with top-hung windows to create cross ventilation. Further investigations are carried out for various climate regions to evaluate the feasibility of windcatcher applications in China. It is found that according to the accumulative hours of meeting ventilation requirement, Harbin is the most suitable city for windcatcher applications and then Shanghai and Kunming. But, Kunming appears the best city in terms of percentage saving in cooling load, followed by Harbin and Urumqi. However, from the economic perspective, Beijing looks the most cost eective

Evaluation of Natural Ventilation and Cooling Systems using Dynamic Simulation Methods

Abstract This paper presents a simplified modelling process by using experimental results to form empirical relationships for a particular novel windcatcher natural ventilation and cooling system developed by Monodraught in the United Kingdom. In particular, the behaviour of this system, which is integrated with a DC fan and PV panel without a backup battery, is modelled for the whole year. The impact of natural and night time ventilation with thermal mass on cooling and mitigating overheating is investigated. Pressure losses from openings, louvres, ducts, dampers etc are accounted for and simplified in the modelling process. Dynamic thermal models are used to simulate natural ventilation, evaporative cooling and PV powered fans.

Thermal conductivity, structure and mechanical properties of konjac glucomannan/starch based aerogel strengthened by wheat straw

This study presents the preparation and property characterization of a konjac glucomannan (KGM)/starch based aerogel as a thermal insulation material. Wheat straw powders (a kind of agricultural waste) and starch are used to enhance aerogel physical properties such as mechanical strength and pore size distribution. Aerogel samples were made using environmentally friendly sol-gel and freeze drying methods. Results show that starch addition could strengthen the mechanical strength of aerogel significantly, and wheat straw addition could decrease aerogel pore size due to its special micron-cavity structure, with appropriate gelatin addition as the stabilizer. The aerogel formula was optimized to achieve lowest thermal conductivity and good thermal stability. Within the experimental range, aerogel with the optimized formula had a thermal conductivity 0.04641 Wm-1 K-1, a compression modulus 67.5 kPa and an elasticity 0.27. The results demonstrate the high potential of KGM/starch based aerogels enhanced with wheat straw for application in thermal insulation.