Convective Transport in Nanofluids

Boundary-layer flow of a nanofluid past a stretching sheet

Abstract: The problem of laminar fluid flow which results from the stretching of a flat surface in a nanofluid has been investigated numerically. This is the first paper on stretching sheet in nanofluids. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. A similarity solution is presented which depends on the Prandtl number Pr, Lewis number Le, Brownian motion number Nb and thermophoresis number Nt. The variation of the reduced Nusselt and reduced Sherwood numbers with Nb and Nt for various values of Pr and Le is presented in tabular and graphical forms. It was found that the reduced Nusselt number is a decreasing function of each dimensionless number, while the reduced Sherwood number is an increasing function of higher Pr and a decreasing function of lower Pr number for each Le, Nb and Nt numbers.

Natural convective boundary-layer flow of a nanofluid past a vertical plate

Abstract: The natural convective boundary-layer flow of a nanofluid past a vertical plate is studied analytically. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. A similarity solution is presented. This solution depends on a Lewis number Le, a buoyancy-ratio number Nr, a Brownian motion number Nb, and a thermophoresis number Nt. For various values of Pr and Le, the variation of the reduced Nusselt number with Nr, Nb and Nt is expressed by correlation formulas. It was found that the reduced Nusselt number is a decreasing function of each of Nr, Nb and Nt.

Boundary layer flow of a nanofluid past a stretching sheet with a convective boundary condition

Abstract: The boundary layer flow induced in a nanofluid due to a linearly stretching sheet is studied numerically. The transport equations include the effects of Brownian motion and thermophoresis. Unlike the commonly employed thermal conditions of constant temperature or constant heat flux, the present study uses a convective heating boundary condition. The solutions for the temperature and nanoparticle concentration distributions depend on five parameters, Prandtl number Pr, Lewis number Le, the Brownian motion parameter Nb, the thermophoresis parameter Nt, and convection Biot number Bi. Numerical results are presented both in tabular and graphical forms illustrating the effects of these parameters on thermal and concentration boundary layers. The thermal boundary layer thickens with a rise in the local temperature as the Brownian motion, thermophoresis, and convective heating each intensify. The effect of Lewis number on the temperature distribution is minimal. With the other parameters fixed, the local concentration of nanoparticles increases as the convection Biot number increases but decreases as the Lewis number increases. For fixed Pr, Le, and Bi, the reduced Nusselt number decreases but the reduced Sherwood number increases as the Brownian motion and thermophoresis effects become stronger.

Finite difference solution of mhd radiative boundary layer flow of a nanofluid past a stretching sheet

Abstract: Unsteady heat and mass flow of a nanofluid past a stretching sheet with thermal radiation in the presence of magnetic field is studied. To obtain non-similar equation, continuity, momentum, energy and concentration equations have been non-dimensionalised by usual transformation. The non-similar solutions are presented here which depends on the Magnetic parameter M respectively . The obtained equations have been solved by explicit finite difference method. The temperature and concentration profiles are discussed for the different values of the above parameters with different time steps.

A review of the applications of nanofluids in solar energy

Abstract: Utilizing nanofluids as an advanced kind of liquid mixture with a small concentration of nanometer-sized solid particles in suspension is a relatively new field, which is less than two decades old. The aim of this review paper is the investigation of the nanofluids’ applications in solar thermal engineering systems. The shortage of fossil fuels and environmental considerations motivated the researchers to use alternative energy sources such as solar energy. Therefore, it is essential to enhance the efficiency and performance of the solar thermal systems. Nearly all of the former works conducted on the applications of nanofluids in solar energy is regarding their applications in collectors and solar water heaters. Therefore, a major part of this review paper allocated to the effects of nanofluids on the performance of solar collectors and solar water heaters from the efficiency, economic and environmental considerations viewpoints. In addition, some reported works on the applications of nanofluids in thermal energy storage, solar cells, and solar stills are reviewed. Subsequently, some suggestions are made to use the nanofluids in different solar thermal systems such as photovoltaic/thermal systems, solar ponds, solar thermoelectric cells, and so on. Finally, the challenges of using nanofluids in solar energy devices are discussed.

Investigation on Convective Heat Transfer and Flow Features of Nanofluids

Abstract: Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids that are required in many industrial applications. In this paper we propose that an innovative new class of heat transfer fluids can be engineered by suspending metallic nanoparticles in conventional heat transfer fluids. The resulting {open_quotes}nanofluids{close_quotes} are expected to exhibit high thermal conductivities compared to those of currently used heat transfer fluids, and they represent the best hope for enhancement of heat transfer. The results of a theoretical study of the thermal conductivity of nanofluids with copper nanophase materials are presented, the potential benefits of the fluids are estimated, and it is shown that one of the benefits of nanofluids will be dramatic reductions in heat exchanger pumping power.

Anomalously increased effective thermal conductivities of ethylene glycol-based nanofluids containing copper nanoparticles

Abstract: It is shown that a “nanofluid” consisting of copper nanometer-sized particles dispersed in ethylene glycol has a much higher effective thermal conductivity than either pure ethylene glycol or ethylene glycol containing the same volume fraction of dispersed oxide nanoparticles. The effective thermal conductivity of ethylene glycol is shown to be increased by up to 40% for a nanofluid consisting of ethylene glycol containing approximately 0.3 vol % Cu nanoparticles of mean diameter <10 nm. The results are anomalous based on previous theoretical calculations that had predicted a strong effect of particle shape on effective nanofluid thermal conductivity, but no effect of either particle size or particle thermal conductivity.

The Viscosity of Concentrated Suspensions and Solutions

Abstract: An expression for the viscosity of solutions and suspensions of finite concentration is derived by considering the effect of the addition of one solute‐molecule to an existing solution, which is considered as a continuous medium.