REMINDER: Chen Fang Ph.D. Dissertation Defense Today, 1:30pm, MERL Rm.203

Department of Mechanical Engineering
University PhD Dissertation Defense

Impact of Surface Tension on Microchannel Two-Phase Flow

Chen Fang

Research Advisor: Professor Kenneth E. Goodson

Time: Monday August 31, 2009 @ 1:30 p.m. (Refreshments at 1:15 p.m.)
Location: MERL(Mechanical Engineering Research Lab) Conference Room (Rm. 203)

Abstract

Understanding the physics of microchannel two-phase flow is important for a broad variety of engineering problems. At microscale, small Bond number, Capillary number and Weber number indicate that the surface tension force dominates gravity, viscous force, and inertial force. In the confined space with complex geometry, i.e. porous media, the interaction between fluid phase and solid phase is of particular importance, and the surface hydrophobicity and contact angle hysteresis effect plays a significant role. In micro-devices involving phase change process, the inter-phase mass transfer coupled with the interfacial force further adds to the complexity of the problem, leading to many unique characteristics of the microchannel two-phase flow.

The first part of the work aims at developing a numerical model within the frame work of volume-of-fluid method to simulate the contact angle hysteresis effect governing the microchannel two-phase flow. The model is validated against two engineering problems, i.e. the sidewall water injection in the microchannel and the droplet detachment on a spinning plate. The comparison between model prediction and the experimental visualization shows that the new model accounting for the contact angle hysteresis effect can dramatically improve the simulation accuracy.

The second part of the talk is dedicated to the development and validation of the capillary force model used for simulating the multiphase flow in porous with controlled hydrophobicity. The model is then applied to the simulation of boiling flow in the vapor-venting microchannel, which enables the capillary-aided phase separation for heat removal capacity enhancement. The simulation replicates the capillary-induced vapor-venting process, and clearly shows that the vapor-venting microchannel can effectively suppress the channel clogging and dry-out.

The third part of the talk explores the impact of surface tension and channel hydrophobicity on the microchannel condensation. High speed imaging technique in conjunction with the interferometry is employed to study the flow pattern and construct the 3D liquid-vapor interface profile. The measured exotic interface shape is compared with the prediction of a compact model accounting for the capillary-assisted liquid transfer effect. The agreement clearly shows the dominant effect of the surface tension on the condensation flow in the microchannel.The influence of channel hydrophobicity on the heat transfer characteristic is also investigated.