Effect of water-based Al2O3 nanofluids on heat transfer and pressure drop in periodic mixed convection inside a square ventilated cavity

A numerical study of unsteady mixed convection flows through an alumina-water nanofluid in a square cavity with inlet and outlet ports due to incoming flow oscillation is performed. It is found that an oscillating velocity at the inlet port cased to creating a periodic variation in the fluid flow and temperature field in the cavity after a certain time duration. The influence of the nanoparticle on the flow and temperature fields has been plotted and discussed. The effect of the oscillation frequency is concealed in a dimensionless number which is the Strouhal number. It is observed that the heat transfer is enhanced for all the Strouhal and Richardson numbers investigated by adding the nanoparticle to the base fluid. It is also found that the performance of the nanoparticle on the enhancement of the heat transfer at higher Richardson numbers is less than that of lower Richardson numbers.     

Carbon nanofluids flow behavior in novel composites

Nanocomposite materials have broadened significantly to encompass a large variety of systems, made of distinctly dissimilar components and mixed at the nanometer scale. This rapidly expanding field is generating many exciting new advanced composites with promising properties. However, during the fabrication of nanocomposites, many problems could arise and remain as challenging tasks. One such problem is controlling of the nanofluid flow behavior around the microfiber perform as in case of Resin Transfer Molding (RTM) process because of the high resin viscosity and the low preform permeability. In this paper, a two-dimensional simulation model based on the Eulerian multiphase approach has been performed and solved to investigate and predict the flow characteristics of a carbon nanofluid around a staggered microfiber matrix. ‘The interactions between the microfiber walls and the interfacial nanofluid layers during the flow process have been also studied. Based on the predicted results an energy “imbalance” technique has been applied between the microfiber walls and the interfacial nanofluid layers allowing them the potential to flow more smoothly around the microfiber walls to prevent any potential sticking on the microfiber walls.     

Effects of nano-scale additives on the linear burning rate of nitromethane

This paper examines the effects of various nanoparticle additives on the combustion behavior of nitromethane, using a pressure-based method recently demonstrated by the authors to measure the linear burning rates of liquid monopropellants and heterogeneous mixtures with high precision. The linear burning rates of these mixtures were measured in a constant-volume system at chamber pressures ranging from 3 to 14 MPa, all without direct observation of the burning front. Nano-scale aluminum was used to increase the overall energy density of the mixture, fumed silica powder was used to increase the mixture thickness and encourage aluminum suspension, and nano-scale titania was also included based on its previous use as a burning rate modifier in solid propellants. The silica loading was varied from 1% to 3% by weight, aluminum was varied from 5% to 13.5% by weight, and titania was added at 1% by weight. The use of fumed silica yielded increased burning rates compared to those of neat nitromethane, and the pressure exponent of the burning rate curve shifted from lower to higher than the nitromethane baseline as more silica was added. This increased pressure sensitivity for mixtures containing 3% silica by weight was previously unobserved in similar studies by other groups and may be an effect of the higher specific surface area of the currently used silica. The subsequent addition of aluminum led to even faster burning rates and higher pressure exponents for all but one mixture. The addition of titania also led to elevated burning rates, with dramatically increased pressure sensitivity and rate inconsistency for chamber pressures above approximately 8 MPa but a decreased pressure sensitivity for the same mixture below 8 MPa. These changes in combustion behavior that accompanied titania were diminished by the presence of aluminum and completely negated in mixtures also containing fumed silica.     

Numerical investigation of fluid flow and heat transfer around a solid circular cylinder utilizing nanofluid

In this study, flow-field and heat transfer through a copper–water nanofluid around circular cylinder has been numerically investigated. Governing equations containing continuity, N–S equation and energy equation have been developed in polar coordinate system. The equations have been numerically solved using a finite volume method over a staggered grid system. SIMPLE algorithm has been applied for solving the pressure linked equations. Reynolds and Peclet numbers (based on the cylinder diameter and the velocity of free stream) are within the range of 1 to 40. Furthermore, volume fraction of nanoparticles (φ) varies within the range of 0 to 0.05. Effective thermal conductivity and effective viscosity of nanofluid have been estimated by Hamilton–Crosser and Brinkman models, respectively. The effect of volume fraction of nanoparticles on the fluid flow and heat transfer characteristics are investigated. It is found that the vorticity, pressure coefficient, recirculation length are increased by the addition of nanoparticles into clear fluid. Moreover, the local and mean Nusselt numbers are enhanced due to adding nanoparticles into base fluid.     

Numerical investigations of flow and heat transfer enhancement in a corrugated channel using nanofluid

In this paper, heat transfer and pressure drop characteristics of copper–water nanofluid flow through isothermally heated corrugated channel are numerically studied. A numerical simulation is carried out by solving the governing continuity, momentum and energy equations for laminar flow in curvilinear coordinates using the Finite Difference (FD) approach. The investigation covers Reynolds number and nanoparticle volume fraction in the ranges of 100–1000 and 0–0.05 respectively. The effects of using the nanofluid on the heat transfer and pressure drop inside the channel are investigated. It is found that the heat transfer enhancement increases with increase in the volume fraction of the nanoparticle and Reynolds number, while there is slight increase in pressure drop. Comparisons of the present results with those available in literature are presented and discussed.     

A review of nanofluid heat transfer and critical heat flux enhancement—Research gap to engineering application

As a novel strategy to improve heat transfer characteristics of fluids by the addition of solid particles with diameters below 100 nm, nanofluids exhibit unprecedented heat transfer properties and are being considered as potential working fluids to be used in high heat flux systems such as electronic cooling systems, solar collectors, heat pipes, and nuclear reactors. The present paper reviews the state-of-the-art nanofluid studies on such topics as thermo-physical properties, convective heat transfer performance, boiling heat transfer performance, and critical heat flux (CHF) enhancement. It is indicated that the current experimental data of nanofluids thermal properties are neither sufficient nor reliable for engineering applications. Some inconsistent or contradictory results related to thermo-physical properties, convective heat transfer performance, boiling heat transfer performance, and CHF enhancement of nanofluids are found in data published in the literature. No comprehensive theory explains the energy transfer processes in nanofluids. To bridge the research gaps for nanofluids' engineering application, the urgent work are suggested as follows. (1) Nanofluid stability under both quiescent and flow conditions should be evaluated carefully; (2) A nanofluid database of thermo-physical properties, including detailed characterization of nanoparticle sizes, distribution, and additives or stabilizers (if used), should be established, in a worldwide cooperation of researchers; (3) More experimental and numerical studies on the interaction of suspended nanoparticles and boundary layers should be performed to uncover the mechanism behind convective heat transfer enhancement by nanofluids; (4) Bubble dynamics of boiling nanofluids should be investigated experimentally and numerically, together with surface tension effects, by considering the influences of nanoparticles and additives if used, to identify the exact contributions of solid surface modifications and suspended nanoparticles to CHF enhancement in boiling heat transfer. Once we acquire such details about the above key issues, we will gain more confidence in conducting application studies of nanofluids in different areas with more efficiency.     

Thermal instability of rotating nanofluid layer

In the present paper we have considered thermal instability of rotating nanofluids heated from below. Linear stability analysis has been made to investigate analytically the effect of rotation. The more important effect of Brownian motion and thermophoresis has been included in the model of nanofluid. Galerkin method is used to obtain the analytical expression for both non-oscillatory and oscillatory cases, when boundaries surfaces are free–free. The influence of various nanofluids parameters and rotation on the onset of convection has been analysed. It has been shown that the rotation has a stabilizing effect depending upon the values of various nanofluid parameters. The critical Rayleigh number for the onset of instability is determined numerically and results are depicted graphically. The necessary and sufficient conditions for the existence of over stability are also obtained.     

Modeling of conjugated heat transfer in a thick walled enclosure filled with nanofluid

The objective of this paper is to investigate the conjugated heat transfer in a thick walled cavity filled with copper-water nanofluid. The analysis uses a two-dimensional rectangular enclosure under conjugated convective-conductive heat transfer conditions and considers a range of Rayleigh numbers. The enclosure was subjected to a constant and uniform heat flux at the left thick wall generating a natural convection flow. The thicknesses of the other boundaries are assumed to be zero. The right wall is kept at a low constant temperature while the horizontal walls are assumed to be adiabatic. A moveable divider is located at the bottom wall of the cavity. The governing equations are derived based on the conceptual model in the Cartesian coordinate system. The study has been carried out for the Rayleigh number in the range of 10⁵ ≤ Ra ≤ 10⁸, and for the solid volume fraction at 0 ≤ ? ≤ 0.05. Results are presented in the form of streamlines, isotherms, average Nusselt number and input heat absorption by the nanofluid. The effects of solid volume fraction of nanofluids, the location of the divider and also the value of the ambient convective heat transfer coefficient on the hydrodynamic and thermal characteristics of flow have been analyzed. An increase in the average Nusselt number was found with the solid concentration for the whole range of Rayleigh number. In addition, results show that the position of the divider and the ambient convective heat transfer coefficient have a considerable effect on the heat transfer enhancement.     

Enhancement of heat transfer using CuO/water nanofluid and twisted tape with alternate axis

Heat transfer, friction and thermal performance characteristics of CuO/water nanofluid have been experimentally investigated. The nanofluid was employed in a circular tube equipped with modified twisted tape with alternate axis (TA). The concentration of nanofluid was varied from 0.3 to 0.7% by volume while the twisted ratio (y/W) of TA was kept constant at 3. The experiments were performed in laminar regime (Reynolds number spanned 830 ≤ Re ≤ 1990). The uses of nanofluid together with typical twisted tape (TT), TA alone and TT alone were also examined. To evaluate heat transfer enhancement and the increase of friction factor, the Nusselt number and friction factor of the base fluid in the plain tube were employed as reference data. The obtained results reveal that Nusselt number increases with increasing Reynolds number and nanofluid concentration. By the individual uses of TA and TT, Nusselt numbers increase up to 12.8 and 7.2 times of the plain tube, respectively. The simultaneous use of nanofluid and TA improves Nusselt number up to 13.8 times of the plain tube. Over the range investigated, the maximum thermal performance factor of 5.53 is found with the simultaneous employment of the CuO/water nanofluid at 0.7% volume and the TA at Reynolds number of 1990. In addition, the empirical correlations for heat transfer coefficient, friction factor and thermal performance factor are also developed and reported.