M.A. Amalina

Effective ultrasonication process for better colloidal dispersion of nanofluid

Improving dispersion stability of nanofluids through ultrasonication has been shown to be effective. Determining specific conditions of ultrasonication for a certain nanofluid is necessary. For this purpose, nanofluids of varying nanoparticle concentrations were prepared and studied to find out a suitable and rather mono-dispersed concentration (i.e., 0.5 vol.%, determined through transmission electron microscopy (TEM) analyses). This study aims to report applicable ultrasonication conditions for the dispersion of Al2O3 nanoparticles within H2O through the two-step production method. The prepared samples were ultrasonicated via an ultrasonic horn for 1-5h at two different amplitudes (25% and 50%). The microstructure, particle size distribution (PSD), and zeta potentials were analyzed to investigate the dispersion characteristics. Better particle dispersion, smaller aggregate sizes, and higher zeta potentials were observed at 3 and 5h of ultrasonication duration for the 50% and 25% of sonicator power amplitudes, respectively.

Adsorption of divalent heavy metal ion by mesoporous-high surface area chitosan/poly (ethylene oxide) nanofibrous membrane

In this study, chitosan/poly (ethylene oxide) nanofibres were fabricated at different chitosan:PEO weight ratio by electrospinning process. The effects of chitosan/PEO composition onto adsorption capability for Cu(II), Zn(II) and Pb(II) ions were studied. Formation of beadless fibres were achieved at 60:40 chitosan:PEO ratio. Average fiber diameter, maximum tensile strength and the specific surface area of the beadless fibres were found to be 115±31nm, 1.58MPa and 218m2/g, respectively. Chitosan/PEO composition that produced beadless fibres tend to possess higher hydrophilicity and maximum specific surface area. These characteristics lead the beadless fibres to the maximum adsorption capability. Adsorption equilibrium data were analysed by Langmuir and Freundlich isotherm. Freundlich isotherm showed the better fit with the experimental data and proved the existence of the monolayer adsorption conditions. The maximum adsorption capacity of the beadless fibres for Cu(II), Zn(II) and Pb(II) ions were found to be 120, 117 and 108mgg-1, respectively.

Effects of Jatropha biodiesel on the performance, emissions, and combustion of a converted common-rail diesel engine

An experimental investigation into the effects of Jatropha biodiesel fuels on the engine performance, emissions, and combustion characteristics of a single-cylinder high-pressure common-rail diesel engine was performed under six different load operations (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 MPa). The test fuels included a conventional diesel fuel and three different blends of Jatropha biodiesel fuel (JB10, JB30, and JB50). The results revealed that the biodiesel blended fuels had a significant influence on the brake specific fuel consumption (BSFC) at all of the engine load conditions examined. In general, the use of Jatropha biodiesel blends resulted in a reduction in brake specific nitrogen oxide (BSNOx), brake specific carbon monoxide (BSCO), and smoke emissions, regardless of the load conditions. A large reduction of 20.2% in BSNOx emissions and 69.5% in smoke opacity were found for the engine when it was fuelled with the biodiesel blends. In terms of the engine combustion characteristics, a slightly shorter ignition delay (ID) and faster combustion duration were found to occur with the use of biodiesel blends under all loading operations. It was revealed that the peak apparent heat release rate (AHRR) for biodiesel blends is lower during low load operation; the AHRR was found to be comparable to that of baseline diesel during high-load operation. Finally, the vibration results demonstrated that the largest reduction, 11.3%, in the root mean square (RMS) of acceleration in comparison with the baseline diesel was obtained with JB50 at an engine load of 0.5 MPa.

Optimization of ultrasonication period for better dispersion and stability of TiO2–water nanofluid

Nanofluids are promising in many fields, including engineering and medicine. Stability deterioration may be a critical constraint for potential applications of nanofluids. Proper ultrasonication can improve the stability, and possibility of the safe use of nanofluids in different applications. In this study, stability properties of TiO2-H2O nanofluid for varying ultrasonication durations were tested. The nanofluids were prepared through two-step method; and electron microscopies, with particle size distribution and zeta potential analyses were conducted for the evaluation of their stability. Results showed the positive impact of ultrasonication on nanofluid dispersion properties up to some extent. Ultrasonication longer than 150min resulted in re-agglomeration of nanoparticles. Therefore, ultrasonication for 150min was the optimum period yielding highest stability. A regression analysis was also done in order to relate the average cluster size and ultrasonication time to zeta potential. It can be concluded that performing analytical imaging and colloidal property evaluation during and after the sample preparation leads to reliable insights.

Global Effects of MWCNT-W Nanofluid in a Shell & Tube Heat Exchanger

Global warming and other problems can be reduced by effectively using the available materials and facilities. Heat exchangers play an important part of the field of energy conservation, conversion and recovery. Shell & tube heat exchangers are widely using in industrial processes and power plants. Suspension of small amounts of nanoparticles into the base fluid called nanofluid can reduce the global energy losses. Thermal conductivity of Multi Walled Carbon Nanotube (MWCNT) is highest among the different nano materials [1]. Therefore, in this paper, the overall performance of a shell & tube heat exchanger has been analytically investigated by using MWCNT-W nanofluid with 0.02-0.1 vol. fractions of MWCNT and compared with water. Mathematical formula, specifications of heat exchanger and nanofluid properties were taken from the literatures to analyze the energy performance and other effects within the system. It is found that for certain mass flow rates of nanofluid and base fluid, the convective heat transfer coefficient increased around 4% to 17% compared to pure water, respectively for 0.02-0.1 vol. fractions of MWCNT in water. However, for constant vol. fractions of MWCNT, convective heat transfer coefficient of the above nanofluid negligibly changed for different mass flow rates. Furthermore, energy effectiveness of the heat exchanger also improved approximately by 3% to 14%, respectively. This energy effectiveness again improved with the decrease of the mass flow rates of nanofluids (tube side) and increase of the mass flow rates of base fluid (shell side). As energy effectiveness is increased by using MWCNT-W nanofluid, therefore, a significant amount of heat losses will be reduced. As a result, with the reduced heat emissions, global warming and greenhouse effects can be reduced by using MWCNT-W nanofluid as working fluid in shell & tube heat exchanger system.

Effect of surface tension on SiO2 -methanol nanofluids

Surface tension, the cohesive energy of an interface dominated the transportation behaviour of the liquids play an important role in the heat transfer performance. A new class of heat transfer fluid denoting Nanofluids with impressive thermo-physical properties, proved its promising potentiality in the heat transfer performance. However, very few numbers of studies observed for the effect of nanoparticles on the surface tension of liquids, also noted controversial results. In the present study, SiO2 nanoparticles dispersed in methanol solution to investigate the effect of surface tension with the change of concentration and their sizes. The most common Du-Nouy ring method was used to measure the surface tension of methanol based nanofluids by an automatic surface tensiometer.The results denote that the surface tension of the nanofluids increases with increase in concentration. On the other hand, the results indicate that the surface tension decreases with the increase in temperatures. Besides, the surface tension of SiO2-methanol nanofluids enhances compared to pure methanol. All in all, the enhancement observed 1.7% to 8.9% of the variation of volume fractions (0.05 Vol % to 0.25 Vol %) and the temperature change of 25 °C to 50 °C.

Effect of Filler Size on Flexural Properties of Calcium Carbonate Derived from Clam Shell Filled with Unsaturated Polyester Composites

The effect of filler size to the flexural properties of the calcium carbonate (CaCO3) filled with unsaturated polyester (UP) composites have been experimentally investigated. The filler was derived from the shell of local clam known as Polymesoda bengalensis. The ground shells were graded into eight different sizes according to the sieve aperture size of which they could pass through. The sample with 4 wt% CaCO3 reinforced with UP was fabricated. Then, the flexural test was done according to the ASTM D790. The result shows that for micron size filler, the flexural modulus was improved as the powder was filled into the UP matrix composite and the maximum value achieved at 574.81 μm mean diameter filler size. However, the infusion of the micron size CaCO3 filler into the UP matrix decreases the flexural strength of the composites.

Influence of Nanoparticle Type, Size and Weight on Migration Properties of Nanorefrigerant

Refrigerant-based nanofluids are termed as nanorefrigerants, which are capable of improving the performance of refrigeration systems. Refrigerants act as coolants due to their low boiling temperature. Therefore, the condition of nanoparticles during this phase change needs to be clarified. In this paper the migration properties of nanoparticles during pool boiling of a nanorefrigerant have been experimentally studied. The effects of nanoparticle type, size and weight on the migration of nano-sized particles have been investigated. Al2O3 and TiO2 particles, each with two different average diameters, were used with R141b refrigerant as the base fluid. Experimental results show that migrated mass of nanoparticles increases with the increase of initial mass of nanoparticles and sizes of nanoparticles as well. However, migration of nanoparticles decreases with the increase of the density of nanoparticles. Hence, migration properties of nanoparticles have a notable relationship with the distribution of nano-sized particles.

Measurement of latent heat of vaporization of nanofluids using calorimetric technique

In this study, the nanofluids are prepared from metal oxide nanoparticles such as Al2O3 (13 and 50xa0nm), SiO2 (5xa0~xa015 and 10xa0~xa020xa0nm), and TiO2 (21xa0nm) dispersed in distilled water (DW) at different volume fractions (0.05, 0.1, 0.15, 0.2, and 0.25xa0Vol.%). A differential scanning calorimeter was used to measure the latent heat of vaporization (LHV) of prepared nanofluids. The effect of change in volume fractions, types, and sizes of nanoparticles was investigated in this study. The outcomes of the study found that LHV of nanofluids decreases with the increase in volume fractions. The highest 21.96xa0% reduction in LHV was observed in SiO2 (5xa0~xa015xa0nm)–DW nanofluids, whereas TiO2–DW nanofluids showed the lowest percentage about 12.38xa0% at 0.25xa0Vol.%. Similarly, LHV of Al2O3 (13 and 50xa0nm)–DW nanofluids and SiO2 (10xa0~xa020xa0nm)–DW nanofluids found to be decreased up to 16.73, 13.31, and 19.84xa0%, respectively. Moreover, the results of the study indicate that LHV of nanofluids increases with increasing the size of that nanoparticle.

Effect of Premixed Diesel Fuel on Partial HCCI Combustion Characteristics

This study investigated the effects of premixed diesel fuel on the auto-ignition characteristics in a light duty compression ignition engine. A partial homogeneous chargecompression ignition (HCCI) engine was modified from a single cylinder, four-stroke, direct injection compression ignition engine. The partial HCCI is achieved by injecting diesel fuel into the intake port of the engine, while maintaining diesel fuel injected in cylinder for combustion triggering. The auto-ignition of diesel fuel has been studied at various premixed ratios from 0 to 0.60, under engine speed of 1600 rpm and 20Nm load. The results for performance, emissions and combustion were compared with those achieved without premixed fuel. From the heat release rate (HRR) profile which was calculated from in-cylinder pressure, it is clearly observed that two-stage and three-stage ignition were occurred in some of the cases. Besides, the increases of premixed ratio to some extent have significantly reduced in NO emission.