Gayatri Paul

Thermo-physical property measurement of nano-gold dispersed water based nanofluids prepared by chemical precipitation technique

Nano-gold dispersed water based nanofluid has been prepared following the chemical reduction method. Crystallite size, particle size/shape/morphology, and purity of the nanoparticles have been characterized using X-ray diffraction, scanning and transmission electron microscopy and energy dispersion spectroscopy, respectively. The degree of thermal conductivity enhancement of the nanofluid (with respect to the base fluid) as a function of concentration and size of gold nanoparticle has been determined using the transient hot-wire technique. The degree of enhancement increases with increase in concentration and decrease in size of nanoparticles. The maximum enhancement recorded is approximately 48% at 0.00026 vol.% concentration and 21nm average particle size.

Concentration and size dependence of nano-silver dispersed water based nanofluids

Nanometric silver dispersed water based nanofluids have been prepared by a single-step chemical process. The crystallite/particle size, morphology and purity of nanoparticles were characterized using standard microscopic, diffraction and spectroscopic techniques. The thermal conductivity enhancement (with respect to the base fluid) has been determined as a function of concentration and size of silver particles using transient hot-wire technique. The accurate fitting of the experimental data of thermal conductivity enhancement with a theoretical model developed by Patel et al. predicts that high specific surface area of the particles, layering at the liquid-solid interface and Brownian motion may be responsible for enhancement.

Formation, growth, and eruption cycle of vapor domes beneath a liquid puddle during Leidenfrost phenomena

Vapor domes emerge, grow, and erupt in a liquid puddle resting over a surface heated above the Leidenfrost temperature. In this letter we report that multiple vapor domes form, resembling a square lattice as a result of Taylor instability. The finite lattice structure can be estimated by classical film boiling theory over an infinite flat surface. The balance between vapor generation and escape dictates the dynamics of growth and eruption of vapor domes, particularly the formation of micro-jets and ejection of micro-droplets during rupture. A theoretical model is proposed to predict the formation of vapor domes and its subsequent instability.

Rewetting of Vertical Pipes by Bottom Flooding Using Nanofluid as a Coolant

The present investigation reports the rewetting phenomenon by bottom flooding in vertical pipes using both water and nanofluid as coolant. The transient temperature response of rewetted surface indicates that rewetting takes place faster in nanofluids than in water. The effect of several parameters, including the coolant flow rate, distance from the inlet of fluid, concentration of nanoparticle loading on the rewetting characteristics, has been investigated. The rewetting velocity, for both water and nanofluid, is observed to depend strongly on the inlet coolant flow rate and initial wall temperature of the tube. The rewetting velocity is observed to follow the correlation for water proposed in an earlier work. Starting from the logic proposed in that previous report, the authors propose a correlation for predicting the rewetting velocity in nanofluids.

Maneuvering the chain agglomerates of colloidal superparamagnetic nanoparticles by tunable magnetic fields

Magneto-viscous effect (MVE) provides an unique control over the rheological properties of magnetic nanofluids (MNFs) by externally applied magnetic field. In this letter, we report the factors affecting the MVE of surfactant coated magnetite (mean size ∼11.5 nm) dispersed water based nanofluid. We investigate the dependence of viscosity on the magnetic sweep carried out by increasing and decreasing the field in several consecutive cycles. We observe that the viscosity is considerably affected by the time interval between consecutive applications of the external field. The degree of hysteresis (quantified by the area of the hysteresis curve) decreases with the increase in time interval and the number of cycles of magnetic sweep. We also observe the excellent reversible switching properties of viscosity for MNF under pulses of applied magnetic field. The gap between the plates of the rheometer exhibits a profound influence in controlling the magnitude of viscosity. The lower the gap, the higher is the visc...

Nanofluids including ceramic and other nanoparticles: Synthesis and thermal properties

This chapter reports the detailed study on the synthesis of nanofluids comprising very low concentrations of nanometric metallic or ceramic particles, rods, tubes, etc. The most common ways of preparing nanofluids are the one-step and two-step methods. While the one-step approach usually yields more stable nanofluids, the two-step method is more versatile as it provides the opportunity to disperse a wide variety of nanoparticles in different types of base fluids. However, the main focus of this chapter is on the thermal conductivity of nanofluids, which is the most researched aspect of nanofluids worldwide. An insight into the different parameters that influence the thermal conductivity of nanofluids is presented. In addition to experimental work, the theories used to try to analyze the cause of the anomalous increase in thermal conductivity are also presented.

Thermal Conductivity and Rheological Behaviour of Al-alloy Dispersed Ethylene Glycol Based Nanofluids

Al-alloy (Al-5 wt. Zn and Al-5 wt. Si) nanoparticle dispersed (0.01-2.00 vol. ) ethylene glycol based nanofluids are prepared by a two-step process. Prior to dispersing in ethylene glycol by magnetic stirring and ultrasonication the Al-alloy nanoparticles synthesized by mechanical alloying are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area diffraction (SAD), and energy dispersive spectroscopy (EDS) to analyze the identity, size, shape, and purity of the powder. A maximum thermal conductivity enhancement of 16 for Al-5 wt. Zn and 13 for Al-5 wt. Si dispersed nanofluids are observed at 0.1 vol. of nanoparticle concentrations. Rheological studies of nanofluids show interesting findings as the viscosity of both types of nanofluids are observed to exhibit values lower than that of base fluid at lower concentrations and higher at higher concentrations. Maximum enhancement of viscosity up to 180 for Al-5 wt. Si and 120 for Al-5 wt. Zn dispersed nanofluids are observed at 2.0 vol. concentration. Copyright © 2012 by ASTM International.