Introduction

Background

Objectives


Test facility

Measurement techniques


Disintegration regimes

Secondary atomization within the various boiling regimes

Boiling morphology at liquid-solid interface

Heat transfer and droplet dynamics on surface enhanced surfaces






 

 
Dynamics of impacting droplets

micro nano engineering
   

  Measurement techniques

  • Visualization: characterization of droplet morphology (e.g. spreading diameter, crown height and diameters, crown angles) and size and number of large secondary droplets (with diameters between 40mm and few millimetres) are evaluated from post processing of the images recorded using high speed cameras.

  • Phase Doppler interferometry: is used to determine size and velocity distributions of small secondary droplets (with diameters from 5mm up to 250mm).

  • Temperature acquisition: thermocouples type K are used to monitor the temperature of the targets. Micro-thermocouples of fast response are embedded in the surfaces at the impact region, to acquire the temperature variation during droplet impaction.

    Combination of these techniques allows to fully characterize the fluid dynamic and heat transfer processes occurring during droplet/surface interactions. Combination of image analysis with phase Doppler measurements provides the characterization of secondary dropletsí sizes and velocities, over the full range of diameters observed within all the boiling regimes.



    Characterization of the target surfaces
    The nature of the target surfaces is associated with the wettability, quantified as the contact angle and with the topography. Contact angle measurements are performed at the Structural Chemistry Center of the Department of Chemical Engineering at IST. The topography is characterized with a mechanical profilemeter at the Institute of Materials and Surfaces Science and Engineering at IST and with an optical profilemeter at the Laser Surface Processing Laboratory of the Faculty of Sciences of the University of Lisbon.