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increased condensation/evaporation rates

increased condensation/evaporation rates

(OP)
I'm a materials guy who has made thousands of tons of stainless steel for pipe and tube. My question is, would there be value in a micro surface finish on heat exchanger surfaces (one that does alter dimensions or change traditional surface appearance; not a coating) which causes low surface energy, therefore hydropohobicity? It has been widely accepted that this would cause drop-wise condensation and nucleation sites for boiling with a many-fold increase in heat transfer rates, but I would like to hear what the real practioners in the field think.

Michael McGuire

RE: increased condensation/evaporation rates

Yes, if it won't deteriorate with age, or at least deteriorates less rapidly than competing coatings and such.

RE: increased condensation/evaporation rates

(OP)
On a well-selected stainless steel or titanium, there wouldn't be any deterioration.

Michael McGuire

RE: increased condensation/evaporation rates

I would say any pharma site that makes water for injection would definitely take a look at this efficiency gain but only if the surface roughness of any water contacting surface stayed at or below 25 Ra (micro inches) and if the surface can handle hot NaOH/CIP 200 solution cleaning.

RE: increased condensation/evaporation rates

Yes Mike, there is a lot of interest.
The OD of steam condenser tubes is one big application.
I have tested many coating that do this. The latest are CVD and appear quite durable, but application to long length tubing is a pain.
The question is would the surface texture survive the tube making process (forming, welding, sizing, annealing, straightening)?

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P.E. Metallurgy, Plymouth Tube

RE: increased condensation/evaporation rates

(OP)
Ed
Thanks for your observation. Perhaps we could discuss this. I think I can reach you through Plymouth Tube, yes?

Michael McGuire

RE: increased condensation/evaporation rates

I thought enhancement of heat transfer is effected by roughening up surface like adding grooves, rifling or fins to make flow turbulent instead of laminar. Why not make tubes for shell an tube heat transfer and do actual test.

RE: increased condensation/evaporation rates

(OP)
Well, that's exactly what I would like to do but we make steel, not heat exchangers. We need at least a tube making partner.
By the way, internal surface area enhancement IS helpful, as is making the flow turbulent (although it may be that already), but this effect is much larger, as much as a twenty-fold increase in cases of condensation, theoretically.

Michael McGuire

RE: increased condensation/evaporation rates

IF you can prevent the OD surface of a steam condenser tube from being covered with a film of water you will remove about 1/3 of the total resistance to hear transfer.
The problem with enhancements to the ID to generate turbulent cooling water flow is that they are generally not compatible with cleaning and NDT methods. Besides the OD film is the limiting heat transfer component.

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P.E. Metallurgy, Plymouth Tube

RE: increased condensation/evaporation rates

There used to be a single tube test rig that was used to establish the values in the HEI condenser spec.
Regrettably it does not exist any more, and back in the day it cost about $200k to build...
The other method is to heavily instrument an few tubes in a real condenser.
If it works then the cooling water exiting enhanced tubes should be hotter than the water leaving regular tubes.

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P.E. Metallurgy, Plymouth Tube

RE: increased condensation/evaporation rates

Google ASHRAE Technical Committee List to see which may assist you - Heat Transfer; Steam Equipment

RE: increased condensation/evaporation rates

It is common in AC systems to do this by adding oils to the system that serve to drive dropwise condensation instead of film forming.

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P.E. Metallurgy, Plymouth Tube

RE: increased condensation/evaporation rates

(OP)
While the low surface energy technology is real and very good, it doesn't appear that there is a welcome mat out for change in this industry. We'll just stick to non-soiling building exteriors.

Michael McGuire

RE: increased condensation/evaporation rates

Get an MBA on it, they're supposed to be good at market penetration and other such things, right?

RE: increased condensation/evaporation rates

The issue is risk.
And today very few utilities have enough technical people to even look at things like this.
While you would think that doing a trial with a few dozen tubes in a condenser at a small combined cycle plant would be easy, it turns out that there is no one to evaluate the potential, design the test, monitor the data, and write the report.
The ranks are very thin today.
Some of us keep plugging away.....

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P.E. Metallurgy, Plymouth Tube

RE: increased condensation/evaporation rates

Mike,

You might post a link to this post over in the Boiler & Pressure Vessel forum, there are some hx types in there that might have an interest, and I don't know how many cross over into this forum.

Ed, that is scary, but likely true. I know our local utilities contract most everything engineering-ish out to contractors/consultants...

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