IMECE2011-64091 ANOMALOUS RHEOLOGICAL BEHAVIOR OF COMPLEX FLUIDS (NANOFLUIDS)

ABSTRACT The rheological behavior of various complex fluids was explored in this experimental study. Nanofluids were obtained by mixing nanoparticles with various solvents. The solvents consisted of metal salt eutectics that melt at high temperatures (exceeding 200 °C) depending on the composition of the metal salts in the eutectics. The rheological behaviors of these high temperature solvents were measured as a function of temperature before and after mixing with different types of nanoparticles (chemical composition, size, shape and concentration). These nanofluids exhibited non-Newtonian behavior (shear thinning behavior) while some of the other nanofluids were surprisingly found to have Newtonian behavior. It was observed that high aspect ratio nanoparticles (e.g., stick shaped carbon nanotubes) were more likely to cause shear thinning behavior of the resulting nanofluids. INTRODUCTION Concentrating solar power (CSP) plants utilizes thermal energy from the sun to generate electricity by utilizing various thermodynamic cycles (e.g., Rankine cycle

Experimental measurements of thermal conductivity of alumina nanofluid synthesized in salt melt

Nanoparticles were synthesized in-situ using a simple one-step synthesis protocol from a cheap additive, mixed apriori in a high temperature salt melt (solar salt, NaNO3-KNO3). The thermal conductivity of the nanofluid was measured using a standardized concentric cylinder (annulus) test apparatus under steady-state conditions. The thermal conductivity of the salt melt was enhanced by 20∼ 25% due to generation of nanoparticles in-situ from the additive. The level of enhancement was found to be insensitive to temperature but significantly exceeded the predictions from models in the literature. Materials characterization (using electron microscopy) showed the formation of percolation networks by secondary nanostructures in the molten salt nanofluid samples (that were induced by the nanoparticles generated in-situ). The enhancement in the thermos-physical properties of the salt-melt nanofluids can be attributed to the formation of these secondary nanostructures (which form a third phase)

Nanofins: science and applications

Nanofins Science and Technology describes the heat transfer effectiveness of polymer coolants and their fundamental interactions with carbon nanotube coatings that act as nanofins. Heat transfer at micro/nano-scales has attracted significant attention in contemporary literature. This has been primarily driven by industrial requirements where significant decrease in the size of electronic devices/chips with concomitant enhancement in the heat flux have caused challenging needs for cooling of these platforms. With quantum effects kicking in, traditional cooling techniques need to be replaced with more effective technologies. A promising technique is to enhance heat transfer by surface texturing using nanoparticle coatings or engineered nanostructures. These nanostructures are termed as nanofins because they augment heat transfer by a combination of surface area enhancement as well as liquid-solid interactions at the molecular scale

Point-Mass Model for Nano-Patterning Using Dip-Pen Nanolithography (DPN)

Micro-cantilevers are frequently used as scanning probes and sensors in micro-electromechanical systems (MEMS). Usually micro-cantilever based sensors operate by detecting changes in cantilever vibration modes (e.g., bending or torsional vibration frequency) or surface stresses - when a target analyte is adsorbed on the surface. The catalyst for chemical reactions (i.e., for a specific analyte) can be deposited on micro-cantilevers by using Dip-Pen Nanolithography (DPN) technique. In this study, we simulate the vibration mode in nano-patterning processes by using a Point-Mass Model (or Lumped Parameter Model). The results from the simulations are used to derive the stability of writing and reading mode for a particular driving frequency during the DPN process. In addition, we analyze the sensitivity of the tip-sample interaction forces in fluid (ink solution) by utilizing the Derjaguin-Muller-Toporov (DMT) contact theory

Modeling and Simulation of Capillary Microfluidic Networks Based on Electrical Analogies,”

In this study we implemented the network simulation techniques using macromodels (lumped models) for capillary driven flows in microfluidic networks. The flow characteristics in a flow junction, such as meniscus stretching and bifurcation, were studied and their effects on filling time as well as pressure drop were explored for various network configurations. The results from the network simulator are validated numerically using computational fluid dynamics (CFD) simulations by employing the volume-of-fluids (VOF) method. The predictions by the network simulator for free-surface flows in different microfluidic networks were found to be in good agreement with the results obtained from the VOF simulations for filling time and meniscus position