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surface texture

surface texture

(OP)
Does anyone know of a surface texture which can be obtained for stainless steel to increase heat transfer in condensing heat exchangers?

Michael McGuire

RE: surface texture

What fluid is being condensed?
Which side (cooling liquid side) or condensing side needs the special (or axtra) heat transfer coefficient?

What chances of contamination or biological growth on either side?

RE: surface texture

In steam condensing? No. You can extend the surface via fins or some such thing, but if the surface is wet then the boundary layer film will still be there and that limits the heat transfer.
What you need is a hydrosocpic surface so that instead of wetting you get drop wise condensation.
There has been a lot of research and testing in this area. In systems other than steam it is done with additives in the working fluid. There has not been a surface treatment/coating that has yet shown that will hold up long term in a live steam environment.

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P.E. Metallurgy, Plymouth Tube

RE: surface texture

Yes, that hydroscopic surface treastment is what I was thinking of, but all that i have heard of have "lowered" the actual heat transfer coefficient in real life by increasing the biological scum and growth rates of the system.

RE: surface texture

Such a coating needs to be combined with more aggressive water treatment and higher cooling water flow velocities.
Considering that in a steam condenser roughly 30% of the total resistance to heat transfer is related to the water film on the steam side, this becomes the absolute upper limit of heat transfer improvement. Realistically if you capture 75% of this, and increase the flow also it should be possible to see a 20% overall improvement. This has not been demonstrated on an industrial scale. After that durability is the next big question.

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P.E. Metallurgy, Plymouth Tube

RE: surface texture

As usual, EdStainless is spot on.....

Virtually all of the steam surface condensers in thermal power plants have bare (non-finned) tubes.

There have been extensive studies by EPRI and others exploring finned and other enhanced surface HXs.

You can be sure that if anyone is intensely interested in wringing the last bit of performance from a steam surface condenser , it is the electric utility industry

Bare tubes are the best

For the design of steam condensing HXs, I suggest you become familiar with the HEI standards ....... and go with a fabricator who has done many of these......

MJCronin
Sr. Process Engineer

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