B.T. Chew

Synthesis of polyethylene glycol-functionalized multi-walled carbon nanotubes with a microwave-assisted approach for improved heat dissipation

In order to improve the dispersibility of multi-walled carbon nanotubes (MWCNT) in aqueous media, MWCNT were functionalized with tetrahydrofurfuryl polyethylene glycol (TFPEG) in a one-pot, fast and environmentally friendly method. To reduce defects and eliminate the acid-treatment stage, an electrophonic addition reaction under microwave irradiation was employed. Surface functionalization was analyzed by FTIR, Raman spectroscopy, thermogravimetric analysis (TGA). In addition, the morphology of TFPEG-treated MWCNT (PMWCNT) was investigated by transmission electron microscopy (TEM). After the functionalization phase, the convective heat transfer coefficient and pressure drop in PMWCNT-based water nanofluids with various weight concentrations were analyzed and compared with that of the base fluid. The results suggest that the addition of PMWCNT into the water improved the convective heat transfer coefficient significantly. The pressure drop of prepared PMWCNT-based water nanofluids showed an insignificant variation as compared with the base fluid and could result from good dispersivity of PMWCNT. According to the laminar flow results, as the weight concentration and Reynolds number increase, the convective heat transfer coefficient and pressure drop increase.

Microwave-Assisted Synthesis of Highly-Crumpled, Few-Layered Graphene and Nitrogen-Doped Graphene for Use as High-Performance Electrodes in Capacitive Deionization

Capacitive deionization (CDI) is a promising procedure for removing various charged ionic species from brackish water. The performance of graphene-based material in capacitive deionization is lower than the expectation of the industry, so highly-crumpled, few-layered graphene (HCG) and highly-crumpled nitrogen-doped graphene (HCNDG) with high surface area have been introduced as promising candidates for CDI electrodes. Thus, HCG and HCNDG were prepared by exfoliation of graphite in the presence of liquid-phase, microwave-assisted methods. An industrially-scalable, cost-effective, and simple approach was employed to synthesize HCG and HCNDG, resulting in few-layered graphene and nitrogen-doped graphene with large specific surface area. Then, HCG and HCNDG were utilized for manufacturing a new class of carbon nanostructure-based electrodes for use in large-scale CDI equipment. The electrosorption results indicated that both the HCG and HCNDG have fairly large specific surface areas, indicating their huge potential for capacitive deionization applications.

Transformer oil based multi-walled carbon nanotube–hexylamine coolant with optimized electrical, thermal and rheological enhancements

In a one-pot microwave-assisted method, multi-walled carbon nanotubes (MWNT) are functionalized with hexylamine (HA). Based on FT-IR, TGA-DTG, Raman, EDS, CHNS/O and TEM results, the functionalization of MWNT with HA was confirmed . The effect of microwave-assisted functionalized MWNT with HA charged transformer oil at different concentrations was experimentally investigated for electrical, thermal and rheological properties. According to the breakdown voltage, flash point, density, electrical conductivity, thermal parameters and viscosity results of the synthesized transformer oil-based coolants they could be an appropriate alternative for different transformers operating at a nominal voltage less than 170 kV.

Mass production of highly-porous graphene for high-performance supercapacitors

This study reports on a facile and economical method for the scalable synthesis of few-layered graphene sheets by the microwave-assisted functionalization. Herein, single-layered and few-layered graphene sheets were produced by dispersion and exfoliation of functionalized graphite in ethylene glycol. Thermal treatment was used to prepare pure graphene without functional groups, and the pure graphene was labeled as thermally-treated graphene (T-GR). The morphological and statistical studies about the distribution of the number of layers showed that more than 90% of the flakes of T-GR had less than two layers and about 84% of T-GR were single-layered. The microwave-assisted exfoliation approach presents us with a possibility for a mass production of graphene at low cost and great potentials in energy storage applications of graphene-based materials. Owing to unique surface chemistry, the T-GR demonstrates an excellent energy storage performance, and the electrochemical capacitance is much higher than that of the other carbon-based nanostructures. The nanoscopic porous morphology of the T-GR-based electrodes made a significant contribution in increasing the BET surface as well as the specific capacitance of graphene. T-GR, with a capacitance of 354.1 Fg−1 at 5 mVs−1 and 264 Fg−1 at 100 mVs−1, exhibits excellent performance as a supercapacitor.

Thermal comfort study of hospital workers in Malaysia

UNLABELLED This article presents findings of the thermal comfort study in hospitals. A field survey was conducted to investigate the temperature range for thermal comfort in hospitals in the tropics. Thermal acceptability assessment was conducted to examine whether the hospitals in the tropics met the ASHRAE Standard-55 80% acceptability criteria. A total of 114 occupants in four hospitals were involved in the study. The results of the field study revealed that only 44% of the examined locations met the comfort criteria specified in ASHRAE Standard 55. The survey also examined the predicted percentage of dissatisfied in the hospitals. The results showed that 49% of the occupants were satisfied with the thermal environments in the hospitals. The field survey analysis revealed that the neutral temperature for Malaysian hospitals was 26.4 degrees C. The comfort temperature range that satisfied 90% of the occupants in the space was in the range of 25.3-28.2 degrees C. The results from the field study suggested that a higher comfort temperature was required for Malaysians in hospital environments compared with the temperature criteria specified in ASHRAE Standard (2003). In addition, the significant deviation between actual mean vote and predicted mean vote (PMV) strongly implied that PMV could not be applied without errors in hospitals in the tropics. PRACTICAL IMPLICATIONS The new findings on thermal comfort temperature range in hospitals in the tropics could be used as an important guide for building services engineers and researchers who are intending to minimize energy usage in heating, ventilating and air conditioning systems in hospitals operating in the tropics with acceptable thermal comfort level and to improve the performance and well-being of its workers.

In vitro and in vivo study of hazardous effects of Ag nanoparticles and Arginine-treated multi walled carbon nanotubes on blood cells: application in hemodialysis membranes.

One of the novel applications of the nanostructures is the modification and development of membranes for hemocompatibility of hemodialysis. The toxicity and hemocompatibility of Ag nanoparticles and arginine-treated multiwalled carbon nanotubes (MWNT-Arg) and possibility of their application in membrane technology are investigated here. MWNT-Arg is prepared by amidation reactions, followed by characterization by FTIR spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The results showed a good hemocompatibility and the hemolytic rates in the presence of both MWNT-Arg and Ag nanoparticles. The hemolytic rate of Ag nanoparticles was lower than that of MWNT-Arg. In vivo study revealed that Ag nanoparticle and MWNT-Arg decreased Hematocrit and mean number of red blood cells (RBC) statistically at concentration of 100 µg mL(-1) . The mean decrease of RBC and Hematocrit for Ag nanoparticles (18% for Hematocrit and 5.8 × 1,000,000/µL) was more than MWNT-Arg (20% for Hematocrit and 6 × 1000000/µL). In addition, MWNT-Arg and Ag nanoparticles had a direct influence on the White Blood Cell (WBC) drop. Regarding both nanostructures, although the number of WBC increased in initial concentration, it decreased significantly at the concentration of 100 µg mL(-1) . It is worth mentioning that the toxicity of Ag nanoparticle on WBC was higher than that of MWNT-Arg. Because of potent antimicrobial activity and relative hemocompatibility, MWNT-Arg could be considered as a new candidate for biomedical applications in the future especially for hemodialysis membranes.

Cadmium ion sorption from aqueous solutions by high surface area ethylenediaminetetraacetic acid- and diethylene triamine pentaacetic acid-treated carbon nanotubes

A novel and rapid microwave-assisted approach along with Friedel–Crafts acylation has been successfully introduced for functionalization of carbon nanotubes (CNT) via aliphatic and aromatic carboxylic acids. This green and efficient route may play an essential role for realizing miscellaneous functionalizations of CNT, which were successfully functionalized via ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA). Qualitative (FT-IR) and quantitative (TGA, Raman, XPS) characterization has been employed to investigate the degree of functionalization. The N2 adsorption isotherm shows significant increases of 270% and 262% in specific surface area in the low partial pressure region after functionalization of CNT with EDTA and DTPA, respectively, which resulted from eliminating the tube ends or caps. By looking at the potential of EDTA and DTPA for sequestering metal ions, EDTA- & DTPA-treated CNT were used to evaluate the aqueous cadmium(II) adsorption efficiency. Then, the effects of solution temperature, pH and contact time on the adsorption of Cd2+ ions onto the treated samples and pristine CNT were investigated. The adsorption performance of Cd2+ ions by functionalized samples showed dramatic growth when compared with the pristine sample, which was effectively pH dependent. The pseudo second-order model precisely captured the kinetic analyses of adsorption. This study suggested that the functionalization method not only enhanced the effective surface area including active adsorption sites on the CNT structure, but also decreased the functionalization time and cost significantly and proposed a promising material for capacitive deionization.

A review on predicted mean vote and adaptive thermal comfort models

This paper presents a literature review of the Fanger’s predicted mean vote and adaptive thermal comfort models developed in different buildings and climates. An important premise of this paper is the fact that Fanger’s model underestimates the thermal impression in the actual case and thus is no longer valid for use in certain climates. As a consequence, many researchers have developed adaptive models from field studies for different climates and countries. However, there is still no adaptive model that can be applied in designing air-conditioning systems for different buildings in all tropical climate countries. Based on this comprehensive review, an internationally recognized adaptive model is needed to achieve better thermal conditions in a variety of buildings such as hospitals, offices, factories, lecture halls, museums, hotels and libraries in the tropics. Practical application: The new conclusions from the comprehensive review on an adaptive thermal comfort model in buildings in the tropics could be used as an important guide for building service engineers and researchers. Their intentions are to minimize energy usage in heating, ventilation and air conditioning (HVAC) systems in buildings such as hospitals, offices and lecture halls operating in the tropics while maintaining an acceptable thermal comfort level and thus improving the performance and well-being of the occupants.

A Field Study on Thermal Comfort of Occupants and Acceptable Neutral Temperature at the National Museum in Malaysia

A field study was conducted to investigate the thermal environment and occupants’ comfort in the National Museum of Malaysia. The occupants’ thermal perceptions in the museum were measured and characterised. The response of the occupants has indicated that the thermal conditions inside the museum did not satisfactorily fulfil the ASHRAE Standard 55, because only 78% of the occupants were satisfied with their environment. Besides, actual mean vote (AMV) and predicted mean vote (PMV) were compared. The Fanger’s model gave a neutral operative temperature of 22.2°C from the PMV, whereas the questionnaire data used in the mean thermal sensation vote (MTSV) of the present study gave a higher value (22.5°C) for the neutral operative temperature. The preferred operative temperature was found to be 22.3°C. The minimum air temperature in three galleries was below the lower limit of the temperature range of 18–22°C as recommended by Museums Australia Victoria. The mean indoor humidity was too high compared to the optimal range of 55 ± 5% relative humidity (RH). The mean air velocity, ≤0.15 m·s−1, in each gallery was satisfactory. Findings of this study are very useful for designing heating, ventilating and air-conditioning (HVAC) systems with energy-saving methodology for museum buildings in tropical regions.

Heat transfer enhancement of water-based highly crumpled few-layer graphene nanofluids

Backward-facing step heat transfer of transitional and turbulent flows occurs in many industrial applications. The heat transfer performances of different multiphase working fluids over a backward-facing step in the transitional and turbulent flow regimes, however, have not been fully investigated experimentally. Recently, highly crumpled few-layer graphene (HCFLG) with a high surface area has been introduced as a promising additive for preparing nanofluids for high performance heat transfer applications. In this work, the heat transfer properties of the HCFLG nanofluids were studied experimentally. The HCFLG was prepared by exfoliation of graphite in the presence of liquid-phase using microwave-assisted methods, which was shown to be industrially-scalable, cost-effective, and simple. Then the HCFLG was used for fabricating a new class of water-based graphene nanofluid for use in large-scale heat transfer equipment. The prepared water-based HCFLG nanofluids were shown to be stable with less than 2% sedimentation after 30 days. In addition, the measured thermophysical properties indicated that the water-based HCFLG nanofluids have huge potential for high performance heat transfer applications. Finally, the water-based HCFLG nanofluids were shown to be significantly more effective in the duct with a backward-facing step in terms of overall thermal performance including the local Nusselt number (Nu), convective heat transfer coefficient, performance index, pumping power, and rheological properties such as effective viscosity in comparison to distilled water.