Effect of materials on the urban thermal environment a CFD simulation approach

Use of high albedo materials reduces the amount of solar radiation absorbed through building envelops and urban structures and thus keeping their surfaces cooler. The cooling energy savings by using high albedo materials have been well documented. Higher surface temperatures add to increasing the ambient temperature as convection intensity is higher. Such temperature increase has significant impacts on the air conditioning energy utilization in hot climates. This study makes use of a parametric approach by varying the temperature of building facades to represent commonly used materials and hence analyzing its effect on the air temperature through a series of CFD (Computational Fluid Dynamics) simulations. A part of the existing CBD (Central Business District) area of Singapore was selected for the study. Series of CFD simulations have been carried out using the software CFX-5.6. Wind tunnel experiments were also conducted for validation. It was found that at low wind speeds, the effect of materials on the air temperature was significant and the temperature at the middle of a narrow canyon increased up to 2.52°C with the façade material having lowest albedo.

A simple and effective method to ameliorate the interfacial properties of cellulosic fibre based bio-composites using poly (ethylene glycol) based amphiphiles

In order to overcome interfacial incompatibility issues in natural fibre reinforced polymer bio-composites, surface modifications of the natural fibres using complex and environmentally unfriendly chemical methods is necessary. In this paper, we demonstrate that the interfacial properties of cellulose-based bio-composites can be tailored through surface adsorption of polyethylene glycol (PEG) based amphiphilic block copolymers using a greener alternative methodology. Mixtures of water or water/acetone were used to form amphiphilic emulsions or micro-crystal suspensions of PEG based amphiphilic block copolymers, and their deposition from solution onto the cellulosic substrate was carried out by simple dip-coating. The findings of this study evidence that, by tuning the amphiphilicity and the type of building blocks attached to the PEG unit, the flexural and dynamic thermo-mechanical properties of cellulose-based bio-composites comprised of either polylactide (PLA) or high density polyethylene (HDPE) as a matrix, can be remarkably enhanced. The trends, largely driven by interfacial effects, can be ascribed to the combined action of the hydrophilic and hydrophobic components of these amphiphiles. The nature of the interactions formed across the fibre-matrix interface is discussed. The collective outcome from this study provides a technological template to significantly improve the performance of cellulose-based bio-composite materials.

Ecologically sustainable noise barrier – further developments

This paper reports on the second phase of a research project aimed at the development of an environmentally friendly noise barrier for urban freeways, also known as KMAK (Krezel and McManus, 2007). The concrete barrier, which has some unique capabilities to mitigate transportation noise, is made from recycled concrete (RC) aggregate and industrial by-products such as fly ash and reclaimed water. The current developmental work expands on a research project that resulted in a two-layer (2L) concrete barrier. Two prototypes of the 2L barrier were produced, followed by extensive acoustic testing and a number of simulations where standard timber and/or concrete barriers were substituted with KMAK barrier (Krezel et al, 2004). Current research investigates a variety of architectural finishes applied to the original KMAK barrier with the aim of improving its visual appearance and also fine-tuning its acoustic performance. The new three-layer (3L) barrier optimises sound absorption in a frequency range characteristic to that of transportation noise, especially road traffic noise. Three major aspects related to the development of architectural finishes were considered; environmentally responsible materials, surface features and production methods. The light-weight material used in the architectural finish is based on ordinary Portland cement (OPC) and uses very fine fraction of RC aggregate. The manufacturing process of the 3L barrier was tested in a commercial setting and two sets of prototype barrier were cast. An innovative, cost effective method of applying pattern and perforation to the surface of architectural finish was also developed and tested. The findings of the current investigation demonstrate that there is a positive correlation between surface features, percentage of perforation as well as depth of the architectural layer and increased potential of the 3L barrier to mitigate transportation noise. On average, the addition of perforated architectural finish contributes to 20% increase in sound absorption. The preliminary results also show that the sound absorbency of the 3L barrier can be better controlled and tuned to specific noise frequency. The visual appearance has been significantly improved with the addition of the architectural finish, which makes the barrier an attractive, feasible and viable alternative to road barriers made from standard concrete or timber.

Environmentally friendly sound absorbing noise barrier made from concrete waste - further developments

This paper reports on the second phase of a research project aimed at the development of an environmentally friendly noise barrier for urban freeways, also known as KMAK [1]. The concrete barrier, which has some unique capabilities to mitigate transportation noise, is made from recycled concrete (RC) aggregate and industrial by-products such as fly ash and reclaimed water. The current developmental work expands on a research project that resulted in a two-layer (2L) concrete barrier. Two prototypes of the 2L barrier were produced, followed by extensive acoustic testing and a number of simulations where standard timber and/or concrete barriers were substituted with KMAK barrier [2]. Current research investigates a variety of architectural finishes applied to the original KMAK barrier with the aim of improving its visual appearance and also fine-tuning its acoustic performance. The new three-layer (3L) barrier optimizes sound absorption in a frequency range characteristic similar to that of transportation noise, especially road traffic noise. Three major aspects related to the development of architectural finishes were considered; environmentally responsible materials, surface features, and production methods. The findings of the current investigation demonstrate that there is a positive correlation between surface features, percentage of perforation as well as depth of the architectural layer, and increased potential of the 3L barrier to mitigate transportation noise. On average, the addition of perforated architectural finish contributes to a 20% increase in sound absorption. The preliminary results also show that the sound absorbency of the 3L barrier can be better controlled and tuned to specific noise frequency than the 2L type. The visual appearance has been significantly improved with the addition of the architectural finish, which makes the barrier an attractive, feasible, and viable alternative to road barriers made from standard concrete or timber.

Triethyl and tributyl phosphite as flame-retarding additives in Li-ion batteries

This study examined the influence of triethyl and tributyl phosphite (TEP and TBP) additives on the electrochemical performance of lithium-ion cells. The cell performance of the TEP- and TBP-containing electrolytes was evaluated by cyclic voltammetry, thermogravimetric analysis, electrochemical impedance spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. The flammability of the electrolytes was also investigated by measuring the self-extinguishing time of the electrolytes. The results showed that the TEP and TBP additives suppressed the flammability of the electrolyte, with a significant improvement in cell performance observed for the TEP additive. In addition, TEP and TBP additives improved the thermal stability of the battery and its electrochemical cell performance. Overall, 5 wt% TEP and TBP can be used as a flame-retarding additive to improve the cell performance of Li-ion batteries due to the decrease in cell impedance and SEI formation.

Amine enrichment of thin-film composite membranes via low pressure plasma polymerization for antimicrobial adhesion

Thin-film composite membranes, primarily based on poly(amide) (PA) semipermeable materials, are nowadays the dominant technology used in pressure driven water desalination systems. Despite offering superior water permeation and salt selectivity, their surface properties, such as their charge and roughness, cannot be extensively tuned due to the intrinsic fabrication process of the membranes by interfacial polymerization. The alteration of these properties would lead to a better control of the materials surface zeta potential, which is critical to finely tune selectivity and enhance the membrane materials stability when exposed to complex industrial waste streams. Low pressure plasma was employed to introduce amine functionalities onto the PA surface of commercially available thin-film composite (TFC) membranes. Morphological changes after plasma polymerization were analyzed by SEM and AFM, and average surface roughness decreased by 29%. Amine enrichment provided isoelectric point changes from pH 3.7 to 5.2 for 5 to 15 min of plasma polymerization time. Synchrotron FTIR mappings of the amine-modified surface indicated the addition of a discrete 60 nm film to the PA layer. Furthermore, metal affinity was confirmed by the enhanced binding of silver to the modified surface, supported by an increased antimicrobial functionality with demonstrable elimination of E. coli growth. Essential salt rejection was shown minimally compromised for faster polymerization processes. Plasma polymerization is therefore a viable route to producing functional amine enriched thin-film composite PA membrane surfaces.

Machinability of metallic and ceramic biomaterials : a review

The machining process is the most common method for metal cutting, especially in the fabrication of biomaterials and artificial implants. In modern industry, the goal of production is to manufacture products at a low cost, with the highest quality in the shortest time. The main focus of the research presented here is to provide a review of the machinability of metallic and ceramic biomaterials in traditional machining processes, such as turning, milling and grinding. Thereafter, machining strategies, machinability and surface characteristics post machining are discussed. To provide a better understanding of the machining process, various cutting tools and fluids are analysed. Finally, the current research gap and directions of prospect investigations are highlighted.

Anaerobic degradation of organic materials - significance of the substrate surface area

In anaerobic degradation of substrates containing mainly particulate organic matter, solids hydrolysis is rate-limiting. In these investigations, the particle size of various substrates was reduced by comminution to support hydrolysis. Two positive effects of comminution were observed. For substrates with high fibre content, which are particularly resistant to biodegradation, a significant improvement of the degradation degree was observed as a result of comminution. Secondly, for all substrates tested, and particularly for those rich in fibres, the degradation rate of comminuted samples was significantly higher. The first reason for both effects is an increase of the sample surface area. Several methods for measuring the specific surface area of organic materials, including particle size analysis, Nitrogen-adsorption and enzyme adsorption, were used and compared for the purpose of this study, where the surface area accessible to microbial enzymes is critical. The significance of the surface area in anaerobic degradation of particulate substrates was investigated through a kinetic model where the hydrolysis rate was based on the sample surface area. Good agreements were obtained between model and experiments carried out with samples of various specific surface areas. These results reinforced the significance of the sample surface area in anaerobic degradation processes. However, other effects of comminution responsible for the increased degradation degree and degradation rate were identified and discussed. These include: the increase of dissolved compounds due to cell rupture, exposition of surface areas previously inaccessible for microbial degradation, and alteration of the sample structure such as the lignin-cellulose arrangements.

Surface modification of biocompatible metallic materials for bone tissue engineering

Titanium, zirconium and TiZr binary alloy were fabricated using a powder metallurgical method. Appropriate surface modifying techniques were conducted on the metals to render an ability for apatite formation. Their biocompatibility has also been assessed. These materials showed potential for biomedical applications because of their excellent bioactivity and biocompatibility which may improve bonding of the implants to juxtaposed bone.

Surface forces and their action in ceramic materials

A descriptive account is given of the surface forces acting between two solids. Different contributions to the force are outlined, with particular attention paid to the underlying mechanisms, and how they are affected by the nature of the medium between the surfaces. This is followed by a discussion of the areas of ceramic science and engineering in which surface forces play a role.

Potential of 129Xe NMR spectroscopy of adsorbed xenon for testing the chemical state of the surface of mesoporous carbon materials illustrated by the example of aggregates of diamond and onion-like carbon nanoparticles

The chemical shift in the 129Xe NMR spectrum of adsorbed xenon is very sensitive to the presence of oxygen-containing functional groups on the surface of mesoporous carbon materials. Well-characterized, structurally similar nanodiamond and onion-like carbon samples are considered here as model objects.

A nitrocarburising and low-temperature chromising duplex surface treatment

A duplex surface treatment has been developed involving the pre-treatment of hardened and tempered AISI H13 chromium hot-work tool steel by a ferritic nitrocarburising process, and a subsequent treatment of the nitrocarburised surface by a low-temperature chromium thermo-reactive deposition process.  The process formed a thin and hard chromium carbonitride surface layer above a hardened diffusion zone, and the low processing temperature allowed the properties of the core material to be retained. It is expected this surface treatment will find application in the treatment  of tooling used for aluminium forming operations.