Pool boiling characteristics of nano-fluids

The growth of a vapor bubble in a superheated liquid is controlled by three factors: the inertia of the liquid, the surface tension, and the vapor pressure. As the bubble grows, evaporation takes place at the bubble boundary, and the temperature and vapor pressure in the bubble are thereby decreased. The heat inflow requirement of evaporation, however, depends on the rate of bubble growth, so that the dynamic problem is linked with a heat diffusion problem. Since the heat diffusion problem has been solved, a quantitative formulation of the dynamic problem can be given. A solution for the radius of the vapor bubble as a function of time is obtained which is valid for sufficiently large radius. This asymptotic solution covers the range of physical interest since the radius at which it becomes valid is near the lower limit of experimental observation. It shows the strong effect of heat diffusion on the rate of bubble growth. Comparison of the predicted radius‐time behavior is made with experimental observations in superheated water, and very good agreement is found.

The growth of vapor bubbles in superheated liquids. report no. 26-6

Review of nanofluids for heat transfer applications

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Principles Of Enhanced Heat Transfer

Experimental study and modeling of an Organic Rankine Cycle using scroll expander

The debate on inculcating effective design engineering learning – its fundamental conceptualization, application of theoretical constructs to model physical devices/systems, and development of tools for solving unstructured problems – and associated critical thinking has primarily focused on curricula issues. Little effort has been made to understand the cognitive underpinning of students that lends to success in this direction. This paper presents the findings of a transverse study to assess learning styles of undergraduate mechanical engineering students and their perceptions about design engineering. Survey results from a batch of sophomores and seniors are analyzed to ascertain: (i) aspects of learning styles that are conducive to design comprehension, and (ii) perceptions about design engineering that aid or impede such learning.Copyright © 2006 by ASME

Influence of Interconnect-Channel Shape on Heat and Mass Transfer in Anode-Supported Planar Solid Oxide Fuel Cells


 To predict liquid-gas two-phase flow, accurate tracking of the evolving liquid-gas interface is required. Volume-of-Fluid (VoF) method has been used for computationally modeling such flows where a single set of governing equations are solved for both phases along with an advection equation for the volume fraction. Properties in each cell are determined by a linear weighted average of the properties of the two fluids based on the phase fraction. While the method predicts water-air flows well, the predictions tend to deviate significantly from experiments for liquids with high viscosity. A new property averaging technique is proposed, which is shown to provide accurate results for high viscosity liquids. Computational predictions using open source VoF solver interFoam and the proposed method are compared with experimental data for multiple two-phase applications. Four different problems, viz., suspended drop, jet breakup, drop impact on thin films, and on liquid pools, are considered to extensively validate the new method. Data for aqueous solutions of propylene and ethylene glycol are used to cover a range of surface tension (72 - 36 mN/m) and viscosities (1 - 40 mPa.s). For all cases, the modified VoF solver is observed to perform significantly better than original VoF method. It reduces spurious currents in simulations of drop suspended in air. For the cases of drop impacting on a pool and during drop generation from liquid jets, the time progression of the surface tension governed dynamics is improved from the slower estimate of interFoam solver.

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New Property Averaging Scheme for Volume of Fluid Method for Two-Phase Flows with Large Viscosity Ratios

A droplet impinging on a solid substrate can result in liquid spreading, recoil, column formation/breakup, partial or complete rebound, or splash. These outcomes are governed by liquid density, viscosity, and surface tension along with surface wettability and roughness. This chapter discusses the recent developments in modeling Newtonian drop spread-recoil dynamics on a solid surface and provides a review of post-impact drop–surface interactions for aqueous surfactant and polymeric solutions. In aqueous solutions, surfactant molecules diffuse toward interfaces and are adsorbed there. As a result, the liquid–gas interfacial tension changes with surface age and the equilibrium tension is a function of surfactant concentration. The timescale of droplet deformation is often comparable to the timescale of surface tension relaxation of surfactant solutions which affects the surface deformation, spread-recoil oscillations, and column breakup. Furthermore, physisorption of surfactant molecules on the substrate alters its wettability and affects the spread-recoil phenomena. Aqueous polymeric solutions exhibit non-Newtonian viscous behavior, where their apparent viscosity is a function of the shear rate. The complex interplay between dynamic changes in interfacial properties and liquid deformation produces drop spread-recoil dynamics that is vastly different from their pure, Newtonian counterparts. Over last two decades, high-speed videography, computational simulations, and analytical modeling have provided useful understanding of droplet impact phenomena that unfolds over timescales of milliseconds or less for these complex fluids. Current understanding of the effect of dynamic changes in interfacial properties on the outcomes of droplet impact is presented in this chapter.

Raj M. Manglik

Papers

Influence of Interconnect-Channel Shape on Heat and Mass Transfer in Anode-Supported Planar Solid Oxide Fuel Cells

New Property Averaging Scheme for Volume of Fluid Method for Two-Phase Flows with Large Viscosity Ratios

Drop Impact Dynamics of Newtonian and Non-Newtonian Liquids