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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