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%.

Liquid Flow Characteristics inside Impeller Rotational Region of an Unbaffled Vessel Agitated with an Unsteadily Angularly Oscillating Impeller

Characteristics of the liquid flow were studied in the impeller region for an unbaffied vessel agitated with an angularly oscillating impeller whose rotation proceeds while periodically reversing its direction at the set angle, namely, rotating unsteadily with sinusoidal variation of the set amplitude. Measurement of the velocity of the liquid flow was performed, abreast of that of the torque of the shaft attached with the impeller. A disk turbine impeller with six flat blades was used in angular oscillation mode at the different amplitudes. The power characteristics were analyzed with the power number during one cycle of the angular oscillation consisting of a process for the impeller to stop and to reverse and that to rotate with a certain acceleration-deceleration in a uniform orientation. The power number in the process for the impeller to rotate exhibited slightly lower values compared with that of the identical design of impeller used in unidirectional rotation mode in a fully baffled vessel, being higher values in its process to stop and to reverse. Under such an operating condition in the amplitude, a time series of images was analyzed by particle tracking velocimetry （PTV） to characterize the fluctuation components of the velocities of the circumferential and radial flows inside the impeller rotational region. The impeller in its rotation process produced flows having a relatively large turbulence, independent of the amplitude condition. For the radial flow relating to the discharge flow, which contributes to transport of the turbulence throughout the vessel, operation at higher amplitude was clarified to be successful.

Numerical Simulation of the Whole Three-Dimensional Flow in a Stirred Tank with Anisotropic Algebraic Stress Model

In accordance to the anisotropic feature of turbulent flow, ananisotropic algebraic stress model is adopted to predict theturbulent flow field and turbulent characteristics generated by aRushton disc turbine with the improved inner-outer iterativeprocedure. The predicted turbulent flow is compared with experimentaldata and the simulation by the standard k-ε turbulence model. Theanisotropic algebraic stress model is found to give better predictionthan the standard k-ε turbulence model. The predicted turbulent flowfield is in accordance to experimental data and the trend of theturbulence intensity can be effectively reflected in the simulation.

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.

Investigation of Phase Inversion of Liquid-Liquid Dispersions in Agitated Vessels

In this paper we report results from on-going theoretical and experimental studies carried out jointly at Imperial College London and University College London. Laser-induced fluorescence （LIF） is used to investigate liquid-liquid phase inversion experimentally and to observe in detail phenomena that accompany the inversion process, such as secondary dispersions and drop coalescence and breakup. Theoretically, a two-region model together with a criterion based on a dynamic balance between drop coalescence and breakup is employed to predict phase inversion. The concept of a radial distribution function for hard spheres was also utilized in order to better model the interaction of drops at high dispersed phase holdup, The modeling work is capable of predicting the existence of ambivalent ranges which are in good agreement with experimental observations.