Experimental and CFD Heat Transfer Studies of Al2Oa-Water Nanofluid in a Coiled Agitated Vessel Equipped with Propeller

This paper presents the heat transfer characteristics of A1203-water nanofluid in a coiled agitated vessel with propeller agitator. The experimental study was conducted using 0.10%, 0.20% and 0.30% volume concentra tion of A1203-water nanofluids. The results showed considerable enhancement of convective heat transfer using the nanofluids. The empirical correlations developed for Nusselt number in terms of Reynolds number, Prandtl number, viscosity ratio and volume concentration fit with the experimental data within ±10%. The heat transfer characteris tics were also simulated using computational fluid dynamics using FLUENT software with the standard ke model and multiple reference frame were adopted. The computational fluid dynamics （CFD） predicted Nusselt number agrees well with the experimental value and the discrepancy is found to be less than ＋8%.

Experimental Study of the Effect ofWater Salinity on the Parameters of an Equilibrium Droplet Cluster Levitating over aWater Layer

New experimental results,which are important for the potential use of small levitating droplets as biochemical microreactors,are reported.It is shown that the combination of infrared heating and reduced evaporation of saline water under the droplet cluster is sufficient to produce equilibriumsaltwater droplets over a wide temperature range.The resulting universal dependence of droplet size on temperature simplifies the choice of optimal conditions for generating stable droplet clusters with droplets of the desired size.A physical analysis of the experimental results on the equilibrium size of saltwater droplets makes it possible to separate the effects related to the salinity of the water layer under the droplet cluster from the effects related to the reduction of water evaporation from the water droplets.This is expected to be important for further studies of heat transfer and diffusion in layers of evaporating solutions and condensed droplets.

HEAT TRANSFER OF TiO_2/WATER NANOFLUID IN A COILED AGITA-TED VESSEL WITH PROPELLER

An attempt is made to investigate heat transfer enhancement using nanofluid in a coiled agitated vessel fitted with propeller agitator. The heat transfer coefficient in coiled agitated vessel for water and TiO2/water nanofluid of 3 different volume concentrations （0.10%, 0.20% and 0.30%） are estimated and compared. The heat transfer coefficient for nanofluid is found to be higher than that for water and also found to increase with increasing volume concentrations. The enhancement in the convective heat transfer using nanofluid is found to be a maximum of 17.59%. Empirical correlations are separately formed for water and TiO2/water nanofluid as well as found to fit the experimental data within ±5% for water and within ±10% for nanofluid.

Effect of Geometry of Filler Particles on the Effective Thermal Conductivity of Two-Phase Systems

The present paper deals with the effect of geometry of filler particles on the effective thermal conductivity for polymer composites. In the earlier models, less emphasis has been given on the shape of filler particles. In this paper, expressions for effective thermal conductivity has been derived using the law of minimal thermal resistance and equal law of the specific equivalent thermal conductivity for three different shapes i.e. spherical, elliptical and hexagonal of filler particles respectively. Calculated values of effective thermal conductivity for various samples using the derived expressions then compared with experimental data available and other models developed in the literature. The results calculated are in good agreement with the earlier experimental data and the deviation, is least in our expressions showing the success of the model.

Numerically simulated behavior of radiative Fe_(3)O_(4) and multi-walled carbon nanotube hybrid nanoparticle flow in presence of Lorentz force

Free convection in hybrid nanomaterial-saturated permeable media is crucial in various engineering applications.The present study aims to investigate the free convection of an aqueous-based hybrid nanomaterial through a zone under the combined effect of the Lorentz force and radiation.The natural convection of the hybrid nanomaterial is modeled by implementing a control volume finite element method(CVFEM)-based code,whereas Darcy assumptions are used to model the porosity terms in the momentum buoyancy equation involving the average Nusselt number Nu_(ave),flow streamlines,and isotherm profiles.A formula for estimating Nu_(ave) is proposed.The results show that the magnetic force retards the flow,and the fluid tends to attract the magnetic field source.Nu_(ave) is directly correlated with the Rayleigh number and radiation;however,it is indirectly dependent on the Hartmann number.Conduction is the dominant mode at larger Darcy and Hartmann numbers.

Study of Multilayer Flow Insulation Utilizing Open-Cellular Porous Plates

To improve the performance of the single layer flow insulation system utilizing open-cellular porous plate, the multilayer porous gas enthalpy-radiation converter is proposed and investigated experimentally and theoretically. Two open-cellular porous materials with different porosity pore per inch and surface reflectivity have been examined. Each porous plate has the same thickness of a half of the single layer one. Both porous materials are not combined continuously but divided by free space. For the prediction model, two energy equations of the fluid and solid phases are employed, in which the convective heat transfer between both phases is described based on the empirical volumetric heat transfer coefficient. In addition, the radiative transfer equations are resolved by Pj approximation. When an equivalent blackbody radiation temperature of the radiation coming from the upstream region exceeds inlet gas temperature, use of a high reflective porous plate on the upstream side and a low reflective porous plate on the downstream side is quite effective to increase gas temperature drop across the converter. the multilayer porous converter should be made of pure scattering and porous layer, respectively. In order to obtain maximum gas temperature drop in that case, pure absorbing porous plate as the upstream and downstream

Modeling of rotational supercavitating evaporator and the geometrical characteristics of supercavity within

In this paper,a rotational supercavitating evaporator(RSCE)was at first modeled by means of theoretical analysis approach.The geometrical characteristics of supercavity in the modeled RSCE were then studied through numerical simulations.The current research objectives consist in determination of shape of the supercavitator(which in the plane of rotation generates supercavity occupying the most volume between blades),and location of the area suitable for steam extraction by revealing the inner structure of supercavity.Analytical analysis was performed by solving empirical equations for the shape of RSCE,through which an evaluation of two-dimensional relative position of supercavity trailing edge for different shapes of the supercavitator has been realized.Numerical simulation was then carried out,by numerically solving the unsteady Navier-Stokes equations in their conservation form coupled with the Rayleigh-Plesset cavitation and Shear-Stress Transport turbulence models,for verification of the results obtained from empirical equations.Despite unreliable assumption of applicability of empirical equations we have confirmed similarity of the supercavity shapes obtained by both methods for the same RSCE.Therefore,the shape of supercavitator calculated by using empirical equations is acceptable,which provides a simple but reliable approach for design of RSCE.The inner structure of supercavity obtained by numerical simulation has indicated position and parameters for steam extraction openings for further numerical and experimental studies on the performance of RSCE.Practical application of steam or gas extraction is suggested for solving of some problems associated with cavitating pumping of cryogenic liquid.