DOI: 10.1615/ICHMT.2000.TherSieProcVol2TherSieProcVol1
ISBN Print: 978-961-6353-27-4
NUCLEATE POOL BOILING ON POROUS METALLIC COATINGS
RESUMO
Industrial demands for more efficient boilers and evaporators as well as economic incentives have spurred the development of methods to increase boiling heat transfer coefficients, critical heat fluxes and where it is desirable to obtain the highest heat flux by applying the smallest wall superheat. The goal may be to reduce the heat exchanger size or pumping power required for a specified heat duty and also to prevent excessive temperatures, or even system destruction, in systems where heat generation rates are fixed - for instance in nuclear fuel assemblies, or in the chemical reactors.
The boiling heat transfer can be intensified by increasing the number of active centers of vapour generation and also increasing the heat supply to vapour bubbles in the process of their growth. This can be obtained by creating different surface conditions such as micro- and macroroughness, finning, vibrorolling, tunnel-and-pore forming, and porous coatings (Bergles, 1988, Bolle, 1991).
There are many methods for fabrication porous coatings - for instance: wire mesh structures, metal-fibre porous coatings and the most popular produced by such methods as sintering or brazing of particles, electrolytic deposition, flame spraying or plasma spraying (Mitrovic, 1984, Danilova, 1990). The general object of these surface treatments is to provide nucleation sites which will be stable. Furthermore, these sites promote high rates of vaporization so that the wall superheat required for developed nucleate boiling is low compared to that required for boiling from surfaces with natural cavities.