Search

In this study, Graphene Ionanofluid (INF) was prepared and investigated in the temperature range of 30–60 °C for stability, pH, density, specific heat, viscosity, thermal, and electrical conductivity. These new fluids are produced by dispersing the Graphene NPs in ionic liquid (IL) 1-ethyl-3-methylimidazolium chloride [EMiM]Cl in the concentration range of 0.05–0.5 wt.%. The obtained data is compared to the classical models available in the literature. The pH of the INFs lies in the range of 8.2–9.0. The results reveal that the density, electrical and thermal conductivity (TC) of INF improves with concentration. At the same time, the viscosity of INF decreases with concentration. The minimum enhancement in thermal conductivity at 30 °C is about 4.9% at a concentration of 0.05 wt.%. The most significant thermal conductivity enhancement is 27.6%, achieved at 60 °C with a concentration of 0.5% by weight. Specific heat, thermal and electrical conductivity of INF increases as temperature rises, whereas viscosity and density decrease. Furthermore, the prepared INF has a lower viscosity than the base fluid. The new correlations are formulated to determine the viscosity and thermal conductivity of INF in the studied temperature and concentration range with R2 values of 0.98 and 0.96, respectively.

The dynamic coastal and marine waters are frequently polluted by metals that affect the biota. Metal concentrations in the biota, water and sediments of Ennore estuary were monitored spatially over two years to understand their potential impact and ecological risk. Variations in concentrations of chromium (Cr), copper (Cu), cadmium (Cd), lead (Pb) and nickel (Ni) were observed in water, sediment and marine organisms. The metal concentrations (μg/l) in the water were in the order of Ni (35) > Pb(16.9) > Cu(15.8) > Cr(12.5) > Cd(5.6) and sediment (μg/g) was Cr(390) > Pb(266) > Cu(162) > Ni(125) > Cd(7.6). Elevated metal levels in the ambient water and sediment tend to accumulate in the marine organisms. Average concentrations of Cr, Cu, Cd, Pb and Ni in fish Mugil cephalus measured as 4.6, 2.4, 2.21, 4.9 and 2.6 μg/g, 11.4, 22.1, 3.3, 8.9 and 6 μg/g in Crab Scylla serrata, 13, 20.8, 1.3, 7.9 and 4.8 μg/g in Oyster Crassostrea madrasensis and 18.8, 20.1, 1.0, 12 and 5.6 μg/g in polychaete Eunice spp. Distinct patterns of metal content in crab, oyster and polychaete (Cu > Cr > Pb > Ni > Cd) and in fish (Pb > Cr > Ni > Cu > Cd) are due to differences in their habitat and specific uptake and elimination capacity. Environmental quality indices (EQI) and Potential ecological risk index (PERI) were derived from the metal concentration in sediment. EQI evidenced that the Ennore estuary is highly contaminated by Cd and Pb from anthropogenic sources. PERI implied that the estuary is under considerable ecological risk from metals. Contamination and risk from metals are relatively higher during summer owing to the low influx of water and higher residential period. Metal concentrations are exceeding the guideline values in the ambient water, sediment and biota in Ennore estuary. It is concluded that long-term monitoring of metal distribution, bioaccumulation and risk assessment provides reliable data and valuable information for possible pollution management strategies in Ennore estuary.

An analytical method is proposed to estimate the ignition time of the fuel droplet injected in to the combustion chamber of an I.C. engine. The first phase of analysis related to the case of thermal conservation to raise its temperature up to the ignition temperature with non-vaporization from its spherical surface. The ignition temperature depends on the fuel characteristics like specific heat, density, vapor pressure, thermal conductivity, latent heat etc. Subsequently, the mass diffusion of the vapors is included in the investigation. The non –dimensional parameter Fourier number Fo is associated with mass diffusion of vapor from the spherical surface πm, the convective heat transfer πh and the thermal radiation πε from the compressed medium are observed to be the significant criteria in determining the ignition time. For a range of parameters analyzed the ignition time is observed to be a fraction of second. The results show that the term dimensionless radius R+ decreases with increase in Fourier number. Further a correlation is established between the non-dimensional numbers Fourier number and πm,πh, πε Tig+,R+ of the droplet to predict the ignition time is proposed based on the physical configuration of the droplet.

Nanofluids offer a significant advantage over conventional heat transfer fluids and consequently, they have attracted much attention in recent years. The engineered suspension of nano-sized particles in a base liquid alters the properties of these nanofluids. Many researchers have measured and modeled the thermal conductivity and viscosity of nanofluids. The estimation of forced convective heat transfer coefficients is done through experiments with either metal or nonmetal solid particles dispersed in water. Regression equations are developed for the determination of the thermal conductivity and viscosity of nanofluids. The parameters influencing the decrease in convection heat transfer, observed by certain investigators, is explained.

This paper presents a review of the studies undertaken on convection heat transfer with nanofluids. Initial studies were directed towards the determination of the properties of nanofluids, especially their thermal conductivity and viscosity. The studies indicate that thermal conductivity and viscosity increase with an increase in the concentration of the nanofluid. Experiments were conducted with different nanofluids, at various concentrations and temperature ranges, for the estimation of the heat transfer coefficient and friction factor for water-based nanofluids. All the studies confirmed enhancement of the heat transfer coefficient with an increase in concentration. The experimental ranges of temperature undertaken by the authors were different for different nanofluids. Certain studies with smaller particle sizes indicated an increase in heat transfer enhancements when compared with values obtained when using larger particle sizes. It is observed that the concentration of the nanofluid, the operating temperature, the particle size and shape, together with the material of the nanoparticle dispersed in the base liquid, have significant influence on the heat transfer coefficient. All the studies indicate a nominal increase in pressure drop.

Palm oil is one of the vegetable oil, which is converted to biodiesel through a transesterification process using methanol as the catalyst. Palm oil biodiesel or palm methyl ester (PME) can be used in diesel engines without any modification, and can be blended with conventional diesel to produce different proportions of PME-diesel blend fuels. The physical properties of PME were evaluated experimentally and theoretically. The effect of using neat PME as fuel on engine performance and emissions was evaluated using a commercial four-cylinder four-stroke IDI diesel engine. The experimental results on an engine operated with PME exhibited higher brake specific fuel consumption in comparison with the conventional fuel. With respect to the in-cylinder pressure and heat release rate, these increased features by over 8.11% and 9.3% with PME compared to conventional diesel. The overall results show that PME surpassed the diesel combustion quality due to its psychochemical properties and higher oxygen content.

Experiments are undertaken to determine the efficiency of an evacuated tube solar collector using water-based Titanium Oxide (TiO2) nanofluid at the Pekan Campus (3˚32’ N, 103˚25’ E), Faculty of Mechanical Engineering, University Malaysia Pahang, for the conversion of solar thermal energy. Malaysia lies in the equatorial zone with an average daily solar insolation of more than 900 W/m², which can reach a maximum of 1200 W/m² for most of the year. Traditionally water is pumped through the collector at an optimum flow rate, for the extraction of solar thermal energy. If the outlet temperature of the water is high, further circulation of the water through the collector is useless. This is due to the low thermal conductivity of water of 0.6 W/m.K compared to metals which is many orders higher. Hence it is necessary to reduce the surface temperature either by pumping water at a higher flow rate or by enhancing the fluid’s properties by the dispersion of nanoparticles. Pumping water at higher flow rates is not advantageous as the overall efficiency of the system is lowered. Liquids in which nanosized particles of metal or their oxides are dispersed in a base liquid such as water are known as 'Nanofluids'. This results in higher values of thermal conductivity compared to the base liquid. The thermal conductivity increases with the concentration and temperature of the nanofluid. The increase in thermal conductivity with temperature is advantageous for application in collectors as the solar insolation varies throughout the day, with a minimum in the morning reaching a maximum at 2.00p.m and reducing thereafter. The efficiency of the collector estimated using a TiO2 nanofluid of 0.3% concentration is about 0.73, compared to water which is about 0.58. The efficiency is enhanced by 16.7% maximum with 30–50nm sized TiO2 nanoparticles dispersed in the water, compared to the system working solely with water. The flow rate is fixed at 2.7 liters per minute for both liquids.

Aerodynamic studies in the static components of a centrifugal compressor stage were conducted using the computational fluid dynamics solver FLUENT. For the simulation study, a typical centrifugal compressor stage geometry with a flow coefficient of 0.053 was chosen, The study is confined to the static components of the centrifugal compressor stage, i.e., the crossover bend (180° U-bend), a radial cascade of return channel vanes, and the exit ducting (90° L-turn). The aerodynamic performance is reported in terms of total pressure loss coefficient, static pressure recovery coefficient, return channel vane surface static pressure distribution, and stage exit swirl angle distribution. The simulated flow through the static components covered five different operating conditions of the actual centrifugal compressor stage: the design point with 100% flow rate, and the off-design operating conditions with 70%, 80%, 110%, and 120% flow rates. The standard k-ε model was used with standard wall functions to predict the turbulence. A minimum total pressure loss coefficient was observed near 80% flow rate when the average flow angle at the U-bend inlet was 24°. Better static pressure recovery was observed with 70%, 80%, and 100% flow rates. The swirl angle distribution at the stage exit was recognized as satisfactory.

The forced convection heat transfer coefficient and friction factor are determined for the flow of water and nanofluid in a vertical packed bed column. The analysis is undertaken in the laminar and transition Reynolds number range. The column is filled with spherical glass beads as the bed material. The heat transfer coefficients with Al2O3 nanofluid increased by 12% to 15% with the increase of volume concentration from 0.02% to 0.5% compared with water. The experimental values of axial temperature are in good agreement with the NTU-ε method proposed by Schumann’s model.

Experiments have been conducted to study the effect of mass flow rate on heat and mass transfer coefficients in a packed bed. It has been observed that an increase in mass flow rate of water increases the heat and mass transfer coefficients by 1.7–1.9 and 3.2–3.8 times, respectively, at 55–95 °C. The diffusion of oxygen from packed bed inlet water, obtained from experimental data, can be used to estimate the mass transfer coefficients. The theoretical equation available in literature is compared and satisfactory agreement has been observed. The increase in inlet water temperature decreases both the heat and mass transfer coefficients by 60% and 25%, respectively, because of the reduced driving force. The increase in oxygen concentration in inlet water has no significant effect on either heat or mass transfer coefficients.

L. Syam Sundar1 and K.V. Sharma2This paper reports experimental investigations of fully developed laminar convective heat transfer and friction factor characteristics of different volume concentrations of Al2O3 nanofluid in a plain tube, fitted with different twist ratios of twisted tape inserts. Experiments are conducted with water and nanofluid in the range of 700

A numerical analysis for the determination for turbulent characteristics of fluid flow and heat transfer have been developed by employing the eddy diffusivity equation of Van Driest. The properties of Silicon dioxide (SiO2) nanofluid with spherical particles in base liquid ethylene glycol (EG) -water (W) mixture of 60:40 ratio is employed for a wide range of concentrations and bulk temperature. A good agreement of the numerical results with the experimental data for properties and heat transfer is observed. A comparison of Copper oxide (CuO), Aluminum dioxide (Al2O3) and Silicon dioxide (SiO2) nanofluids revealed that SiO2 attain higher temperature gradients in comparison to CuO nanofluid at the same concentration and temperature.