Flow boiling over porous substrates

Contact Person: C. Argiropoulos [argiropoulosc@gmail.com]
 

The role of porous surfaces with regards to boiling enhancement has received recently serious attention. Porous surfaces change bubble dynamics over the traditionally hydrophilic boiling surfaces (because of their metallic nature) turning them to pseudo-hydrophobic (due to trapped vapour pockets from previous bubbles). Increasing the heat flux removal from novel boiling heat exchanging devices will promote development of cost – efficient and highly reliable thermal management in industrial processes. Despite the availability of several techniques to fabricate porous substrates to act as boiling surfaces, there are still difficulties and unresolved issues. Among them, the one that is a potential show-stopper is the manufacturing of such surfaces at large scale (mass production) in a reliable, reproducible and efficient way. Moreover, even if such surfaces can be eventually produced, replacement of the current boiling surfaces in industrial equipment with the new porous surfaces will require a substantial installation effort. To alleviate the above shortcomings it has been suggested to use woven metallic screens as structured porous surfaces that can simply be wrapped tightly around current metallic boiling surfaces. This is indeed the motivation for this project.

The project’s main task is the experimental validation of structured porous substrates as a boiling enhancing surface. As a result the following parameters will be studied:

  • Pore size (dictated by the mesh of the screen)
  • Substrate thickness (dictated by the wire thickness and the number of screen layers as it is shown)
  • Contact conditions with metallic surface (simply tight contact or permanently sintered)

A common porous material (woven screen) is being tested as boiling surface. The material’s structured porosity (uniform pore size distribution) advances new modelling approaches to flow boiling. Additionally, the role of wettability and fouling of the surface is explored.

Test Section: a) Heated block with fixed mesh, b) Assembled test section side view, c) Assembled test section detailed view

figuer-1

Copper woven metallic screens: a) M80 screen, b) M100 Screen, c) M150 screen, d) Experimental sintered screen, e) Two layer screen, f) Three layer screen

figuer-2

Advancing contact angle on smooth surface (left) and screen covered surface

figuer-3

Comparison between CFD computations and Infrared Thermography data of the boiling test section

figuer-4