Seminars

Seminars are held on Tuesdays at 3:00 pm in 206 Thomas. Please e-mail comments, questions, and requests to be added to the seminar e-mail list to Maria Koeper.

April 22, 2008
Jacopo Buongiorno, MIT
Heat Transfer Enhancement in Nanofluids
Colloidal dispersions of nanoparticles are known as 'nanofluids'. Such engineered fluids offer the potential for enhancing transport phenomena, particularly heat transfer, while avoiding the drawbacks (i.e., erosion, settling, clogging) that hindered the use of particle-laden fluids in the past. At MIT we have been studying the heat transfer characteristics of nanofluids for the past 3½ years, with the goal of evaluating their benefits for and applicability to conventional and nuclear power systems. This presentation will survey the MIT research in this area with particular emphasis to nanofluid thermo-physical property determination, single-phase heat transfer measurements and interpretation, and boiling behavior, including, prominently, the Critical Heat Flux limit.

April 25, 2008 (Thesis Seminar)
Angel Ruiz Angulo, Caltech
2:00 pm
Surface Deformation in a Liquid Environment Resulting from Single Particle Collisions
Multiphase flows are fairly complex and they are usually studied as a bulk. The way we approach this problem is by looking at single particle interactions (particle-particle and particle-wall). This thesis presents experimental measurements of the approach and re- bound of a particle colliding with a "deformable" surface in a viscous liquid. The complex interaction between the fluid and the solid phases is coupled through the dynamics of the flow as well as the deformation process. Steel particles were used to impact different alu- minum alloy samples (Al−6061, Al−2024, and Al−7075) using different aqueous mixtures of glycerol and water as a viscous fluid. Normal coefficient of restitution and deformation parameters account for losses due to lubrication effect and inelasticity, identifying then, the dominant energy loss mechanism during the collision process. The experiments clearly show four different regimes depending on the impact Stokes number: lubrication effect and elastic deformation, lubrication effect and elastic-plastic deformation, elastic deformation with no hydrodynamic effects, and merely elastic-plastic deformation with negligible lubrication ef- fect. An analysis of the erosion of ductile materials during immersed collisions is presented. The size of the crater formed by the impact of a single particle against a ductile target can be estimated from theory, and these estimates agree well with experimental measurements.

April 29, 2008
Denis J. Phares, USC
Real-time Chemical Analysis of Aerosols: An Approach to Identifying Organic Compounds
Understanding how small particles in the atmosphere affect health and the environment requires knowledge of their chemical composition. Issues associated with bulk aerosol analysis, such as low temporal resolution, size biases, and chemical transformation after sampling, has led to the development of aerosol mass spectrometers that can determine the size and chemical composition of ambient aerosols in real-time. Some of these instruments have provided quantitative data concerning the content of various salts and metals present in the aerosol. However, identification of organic compounds is more difficult because of fragmentation that occurs during vaporization and ionization, and because of the complicated mass spectra that are generated from particles that contain mixtures of organics. This talk will focus on new developments in instrumentation aimed at addressing some of these issues.

May 13, 2008
Wendy Zhang, University of Chicago
Memory-encoding Shape Vibrations in a Disconnecting Air Bubble
Recent experiments have discovered that how an underwater air bubble disconnects is exquisitely sensitive to slight asymmetries in its neck shape. Here I show that the classic approach of modeling the disconnection as a 2D Rayleigh-Plesset collapse provides a simple explanation for this sensitivity. The cylindrically-symmetric inviscid collapse is Hamiltonian, thus naturally possessing a complete memory of the energy distribution initiating the disconnection. A linear stability analysis reveals the singularity dynamics controlling the final moments of the disconnection also has a precise memory of the azimuthal energy distribution. This memory is encoded by constant-amplitude vibrations in the cross-section shape of the bubble neck.  Finally I describe an effort to directly check the relevance of this mechanism. In an experiment by Keim and Nagel, a mode-2 vibration about the cylindrically-symmetric disconnection dynamics is excited by causing an air bubble to detach from a slot-shaped nozzle. A comparison finds good agreement between the measured vibration dynamics and the calculated dynamics.

May 20, 2008
Eric Lauga, UCSD

May 27, 2008
Shannon Browne (thesis defense)