The term Nanofluids was first coined by Sir Stephen Choi in 1995 at Argonne National Laboratory, U.S.A. Since the discovery, nanofluid have been explored as heat transfer fluids. Nanofluids increased the thermal conductivity of existing coolants (Water, Ethylene glycol) by a magnitude of hundred times which made them attractive for miniaturization of electronic devices. From 1995 till 2008 nanofluid research was focused on enhancing the thermal conductivity of the base fluid by various parameters like shape of nanoparticle, volume fraction of base fluid and material of base fluid and composition of nanoparticle. A lot of theoretical models have been evolved in an attempt to explain the basic mechanism of heat transfer in a nanofluid. Research has been with respect to viscosity, stability, thermal conductivity and convective heat transfer coefficients of nanofluids. From 2008 nanofluids have been investigated for their electrical properties and reported as electrical conductivity enhancers for base fluid. The latest trend in nanofluid is towards optical properties of nanofluid for direct absorption solar collectors.

Natural Circulation Loop (NCL) which is also called as a thermosyphon system is the heat transfer loop which uses no pump or external device to drive the loop fluid. In the present paper, a comparative study on thermal characteristics of two loop fluids viz. water and Al2O3/water nanofluid is made. Experiments are conducted on in-house designed test rig. Thermo-hydraulic behaviour of loop fluid is presented. Two parameters such as heat input, nanofluid concentration are varied in order to study their individual and combined effects. It is concluded that Al2O3/water nanofluid as loop fluid results in higher mass flow rates as compared to the water. Different derived quantities such as Nusselt number and Grashof number are calculated. Quantitative comparison is made between water and Al2O3/water nanofluid. Time to reach steady state is reduced by 22 % using Al2O3/water nanofluid as loop fluid when compared with water. Mass flow rate and Grashof number of the Al2O3/water nanofluid based NCL are enhanced by 6. 75% and 26% respectively, when compared with water-based NCL at 1000W heat input. At the heater, the temperature gradient is reduced by 30. 2% due to the improved thermal and transport properties of Al2O3/water nanofluid when compared with water at 1000 W heat input. As particle concentration increases from 1% to 5%, Nusselt number increases from 10. 1 to 20. 1, for the heat input of 1000W.

This paper was aimed to address the modeling of effective thermal conductivity and viscosity of carbon structured nanofluids. Response surface methodology, D_optimal design (DOD) was employed to assess the main and interactive effects of temperature (T) and weight percentage (wt %) to model effective thermal conductivity and viscosity of multi wall and single wall carbon nanotube, CVD and RGO Graphene and nanoporous Graphene sheet. The second-order polynomial regression model was proposed for effective thermal conductivity and viscosity as a function of relevant investigated parameters. Effective thermal conductivity and viscosity of nanofluids measured using an accurate transient short hot wire system and a viscometer, respectively. nanofluids was prepared using two-step method and showed a desirable stability. In general, Graphene nanosheets have more effective thermal conductivity and viscosity compared to carbon nanotube because of variation in shape and likely size.

Numerous techniques in designing zones happen at high temperature and functions under high temperature are in a way that involves non-linear radiation. In weakly conducting fluids, however, the currents induced by an external magnetic field alone are too small, and an external electric field must be applied to achieve an efficient flow control. Gailitis and Lielausis, devised Riga plate to generate a crossed electric and magnetic fields which can produce a wall parallel Lorentz force in order to control the fluid flow. It acts as an efficient agent to reduce the skin friction. So, in this paper, we start the numerical investigation on the threedimensional flow of nanofluids with the inclusion of non-linear radiation past a Riga plate. To this end, the numerical investigation is conducted on the three-dimensional flow of nanofluids with the inclusion of nonlinear radiation past a Riga plate. Water (H2O) and Sodium Alginate (NaC6H9O7) are the base fluids, whereas Magnetite (Fe3O4) and Aluminium oxide (Al2O3) are the nanoparticles. The mathematical formulation for Sodium Alginate base fluid is separated through the Casson model. Suitable transformations on governing partial differential equations yield strong non-linear ordinary differential equations. Numerical solutions for the renewed system are constructed by fourth-order Runge-Kutta method with shooting technique. Various deductions for flow and heat transfer attributes are sketched and discussed for various physical parameters. Furthermore, the similarities with existing results were found for the physical quantities of interest. It was discovered, that the temperature ratio parameter and the radiation parameter enhance the rate of heat transport. Moreover, the NaC6H9O7-Al2O3 nanofluid improves the heat transfer rate. Likewise, H2O-Fe3O4 nanofluid stimulates the local skin friction coefficients.

An analysis is made for the effect of throughflow on the onset of convection in a rectangular box under the assumption that total flux (sum of diffusive, thermophoretic, and convective) is zero on the boundaries. A linear stability analysis and Galerkin weighted residual method are used to obtain the Rayleigh number and stability curves for the onset of convection. Three dominating combination of parameters are extracted from the nondimensional analysis. All rescaled parameters promote the convection. Aspect ratios, throughflow, and nanoparticles play an important role in the formulation of cell distribution and development of convection. Oscillatory convection is possible for permissible range of nanofluid parameters. It is also found that the size of a cellular mode is altered by throughflow and nanoparticles.

Liquid paraffin can be used as a coolant fluid in electronic and cutting devices due to its suitable capabilities such as electrical insulating, high heat capacity, chemical, and thermal stability, and high boiling point. In this study, the dynamic viscosity of paraffin containing the alumina nanoparticles has been examined experimentally. The nano􀏔 luids with different composition of alumina (0, 1, 2, and 3%) with the diameter of 20 nm were prepared by two‐ step method and tested by professional Brookfield rheometer in the temperature range of 20 oC to 60 oC and the shear rates of 12 s‐ 1 up to 200 s‐ 1. Experimental results indicated that the nano‐ lubricant behaves as Newtonian 􀏔 luid in the volume fraction of 0 and 1% only at the temperatures of 50 and 60 oC. While it behaves as non‐ Newtonian 􀏔 luid in the volume fraction of 2 and 3% for all measured temperatures. The results showed that the power law model represents the best curve fitting of the experimental data. Therefore, the coefficient values of power‐ law model including, consistency index and flow index were reported. Finally, an equation of relative viscosity based on the volume fraction and temperature of the combination was proposed by applying the curve fit technique on the experimental data.

Purpose: In this paper, we present a mathematical model for Marangoni convection boundary layer flow with radiation and different types of nanoparticles, namely, Cu, Al2O3, and TiO2 in a water-based fluid.Method: The governing equations in the form of partial differential equations have been reduced to a set of ordinary differential equations by applying suitable similarity transformations, which is then solved numerically using the shooting method.Results: Numerical results are obtained for the surface-temperature gradient or the heat transfer rate as well as the temperature profiles for some values of the governing parameters, namely, the nanoparticle volume fraction φ, the constant exponent b, and thermal radiation parameter Nr.Conclusion: The results indicate that the heat transfer rate at the surface decreases as the thermal radiation parameter Nr increases.

In this study, two-dimensional pulsating unsteady flow of nanofluid through a rectangular channel with isothermal walls is investigated numerically. The finite volume approach with a staggered grid arrangement is employed to discretize the governing momentum and energy equations. The set of resultant algebraic equations is solved simultaneously using SIMPLE algorithm to obtain the velocity and pressure distribution within the channel. The results are obtained for different pulse parameters, which are Strouhal number (frequency of pulsation), Amplitude of pulsation, Reynolds number and volume fraction of nanoparticles. The results show that increasing the amplitude of pulsation has no effect on cycle period of pulsation, while it can raise the Nusselt number. The analysis also reveals that increasing the Strouhal number reduces the cycle period of pulsation significantly, while its effect on the rate of heat transfer is not more appreciable. Furthermore, it is found that the heat transfer increases, as the volume fraction of nanoparticles and Reynolds number increase. It can also be seen that the maximum value of relative Nusselt number for silver nanoparticles is more than other studied nanoparticles.

This work is an experimental study of the temperature and volume fraction effects, which provides a new model for the nanofluid viscosity of MWCNTs-EG. The MWCNT viscosity with a diameter between 1 and 2 nm in EG is calculated at 30 to 60 °C and the volume fractions of 0.025 to 0.3 using a viscometer. The type of viscometer is Brookfield, and its model is DV-I Prime. It was observed that the viscosity decreased, while the temperature increased, and at high volume fractions of the nanofluids, it showed non-Newtonian properties. Since no study has yet been carried out on this nanofluid, it is for the first time that a new equation about viscosity is obtained. The Einstein and Bachelor models are compared with the empirical relationships, and also to observe the similarities, a new Newtonian formula is offered.