Kinnari Parekh

Experimental Investigation of Thermal Conductivity of magnetic nanofluids

Two different magnetic nanofluids comprising of magnetite and Mn-Zn ferrite particles were synthesized in light hydrocarbon oil using continuous chemical process. Powder XRD and TEM image show single phase spinel structure with size of 10 nm and 6.7 nm, respectively for magnetite and Mn-Zn ferrite. Thermal conductivity of nanofluids has been studied as a function of volume fraction under transverse magnetic field. Magnetite nanofluid shows 17% enhancements in thermal conductivity for 4.7% volume fraction while Mn-Zn ferrite shows 45% enhancement at 10% volume fraction. In presence of transverse magnetic field the magnetite nanofluids shows further enhancement from 17% to 30% while no change in thermal conductivity has been observed for Mn-Zn ferrite. These results are explained considering the dipolar coupling co-efficient which for magnetite particles favors chain structures.

Effect of carrier and particle concentration on ultrasound properties of magnetic nanofluids

Ultrasound wave propagation in nanofluids and its rheological behavior has been studied as a function of solid volume fraction, temperature and magnetic field for magnetic nanofluids synthesized in kerosene and transformer oil. Ultrasonic velocity decreases while viscosity increases with increasing volume fraction. The attenuation of ultrasonic wave is explained using dipolar coupling co-efficient which favors oligomer structures with increasing number density of particles. The structure formation increases further with increase in magnetic field which is prominent in transformer oil compared to kerosene. This difference can be due to the structural difference between these two carriers.

Ultrasonic propagation: A technique to reveal field induced structures in magnetic nanofluids

The paper reports the study of magnetic field induced structures in magnetic nanofluid investigated through ultrasonic wave propagation. Modified Tarapovs theory is used to study variation in velocity anisotropy with magnetic field. The types of field induced structures depend upon the chemical structure of the carrier in which magnetic nanoparticles are dispersed. Our study indicates formation of fractals and chain respectively, in transformer oil and kerosene based fluid. This difference is explained on the basis of particle-particle interaction and particle-medium interaction.

Maneuvering thermal conductivity of magnetic nanofluids by tunable magnetic fields

We report an experimental investigation of magnetic field dependent thermal conductivity of a transformer oil base magnetic fluid as a function of volume fractions. In the absence of magnetic field, thermal conductivity increases linearly with an increase in volume fraction, and magnitude of thermal conductivity thus obtained is lower than that predicted by Maxwells theory. This reveals the presence of clusters/oligomers in the system. On application of magnetic field, it exhibits a non-monotonous increase in thermal conductivity. The results are interpreted using the concept of a two-step homogenization method (which is based on differential effective medium theory). The results show a transformation of particle cluster configuration from long chain like prolate shape to the aggregated drop-like structure with increasing concentration as well as a magnetic field. The aggregated drop-like structure for concentrated system is supported by optical microscopic images. This shape change of clusters reduces t...

Magnetization dynamics in rare earth Gd3+ doped Mn0.5Zn0.5Fe2O4 magnetic fluid: Electron spin resonance study

The electron spin resonance (ESR) technique has been applied to study the spin dynamics in broad temperature range for rare earth doped Mn(0.5)Zn(0.5)Fe(1.9)Gd(0.1)O(4) (MZG5) magnetic fluid. Zero field cooled (ZFC) ESR spectra of MZG5 fluid exhibit an isotropic shift in the resonance field below 40 K, while the field cooled (FC) ESR spectra show a deviation from sin(2)θ behavior and an angle dependent hysteresis, this unambiguously points to the dominating unidirectional freezing of surface spins below 40 K. Above 60 K, the resonance field exhibits sin(2)θ behavior, indicating the uniaxial anisotropy contribution of core spin. This indicates that surface spin freezing temperature is around 40 K. The presence of surface spin freezing and the coupling between core and surface spins are further supported by cycle dependent FC ESR spectra measured at 20 K, which show the systematic increase in resonance field (H(res)) and intensity. The double peak behavior of blocking temperature distribution retrieved from ZFC-FC magnetization measurement is an additional corroboration of the existence of surface spin glass like layer.

Mechanism of acid corrosion inhibition using magnetic nanofluid

The inhibition effect of magnetic nanofluid on carbon steel in acid solutions was investigated using gravimetric, potentiodynamic and SEM measurement. The inhibition efficiency increases up to 95% and 75% for 51.7 mM concentration, respectively, in 1 M HCl and 1 M H2SO4 medium. The adsorption of nanoparticles to the steel surface forms a barrier between the metal and the aggressive environment, which is responsible for observed inhibition action. The adsorption of nanoparticles on steel surface is supported by the Langmuir and Freundlich adsorption isotherm and surface morphology scanned through SEM.

Ultrasonic Velocity and Rheological Measurement of Coolants

Rheology and ultrasonic velocity (at 2 MHz frequency) properties of Ethylene glycol (EG)-water mixed nano-coolants are studied at different temperatures. Variation in density and viscosity is found to be non-linear with increasing EG concentration. The viscosity of the mix system varies from 3.5 to 16.9 mPa.s. The results show that with increasing EG concentration in the system the ultrasonic velocity increases, reaches maximum and then decreases. The similar trend is observed for all the temperature under investigation. From these data, the adiabatic compressibility, mean free path and attenuation co-efficient have been calculated. The observed variation is explained considering the relative strength of hydrogen bond between EG and water.