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Old 11-03-2018, 02:30 PM   #1
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Engine Room Intake Mist Eliminator/Demister

Ahoy,

Is anyone using a mist eliminator or demister on their engine room air intake(s)?

I am considering purchasing 2 for our air intakes aboard IRENE. I hope to benefit in the long-term by keeping more salt out of the boat, perhaps benefitting all things mechanical/electrical that salt does not help. Certainly they will help keep the ER cleaner, and reduce corrosion on the metal.

I have not worked aboard nor operated a boat with these installed. I see them on mostly commercial applications, as small as 45'. I am in the process of seeking quotes now.

All thoughts, advice, guidance, and snarky comments appreciated.

Thank you!
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Old 11-03-2018, 02:37 PM   #2
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Greetings,
Mr. I. I've never heard of such an animal. Any links to demystify my learning gap?
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Old 11-03-2018, 02:49 PM   #3
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Are you getting ER mist from the outside? Ours like many boats have the air intakes inboard or well elevated to minimize if not negate outside moisture entering the ER air intakes. I thought Nordhavns had a very good design for mist control. Those I've been on do.
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Old 11-03-2018, 03:34 PM   #4
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Thanks Gents.

Here are a couple of links to products:

Marine Demisting Louvers and Closures | Cooley Equipment Sales

Mist Eliminator Centrifugal Separator Moisture Droplet Separator Mesh Pad

https://deltatsystems.com/moisture-eliminators/

And here is a picture of the existing intake...
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Old 11-03-2018, 04:39 PM   #5
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Some demisters have vertical fins that are cooled by evaporative cooling and the incoming air hits the fins, moisture condenses on the fins and drips off into the drip tray and the drier air goes on into the engine room. The air goes through a box that collects much of the liquid water from spray or rain and routes the water back into the ocean.
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Old 11-03-2018, 04:53 PM   #6
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Sunchaser,

Sorry I neglected to answer your question.

I am getting some dust or salt in the engine room. It is not a lot or troubling, but we use the boat a lot and it is there. We have two axial blowers that draw air IN to the space, so we are moving a lot of air. The intake vents are in the cockpit, where there is some mist present due to the wake. It becomes visible in the cockpit and on the aft windows. All this at 7 knots!
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Old 11-03-2018, 07:33 PM   #7
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Mainships use a mist eliminator and is a frequent discussion looking for replacements.
Here is a link to one of those discussions in the Marlow - Mainship owners forum
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Old 11-03-2018, 08:40 PM   #8
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Thanks Bacchus. Looking at the .pdf in post #15 of the linked thread, I think it looks more like a louvered vent than a mist eliminator. Am I missing something? I am just scratching the surface here...
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Old 11-04-2018, 04:20 AM   #9
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Quote:
Originally Posted by IRENE View Post
Thanks Bacchus. Looking at the .pdf in post #15 of the linked thread, I think it looks more like a louvered vent than a mist eliminator. Am I missing something? I am just scratching the surface here...
It is a louvered vent as many mist eliminators are. If you google must eliminator or go to some of the manufacturers mentioned you will find the louvers are a special design... usually not just flat blades.
Mist eliminators frequently have curved blades with projections or reverse curves / barbs along the path.
I believe the mist impacts various surfaces, collects and condenses or coalesces on the surfaces and runs down the blade and out of the housing or frame.
The above describes what MS installed... although I agree the one shown in one of the posts appears to be flat blades. I don't belueve that was original... maybe closest replacement they could find to fit openning?
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Old 11-04-2018, 04:23 AM   #10
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Greetings,
Mr. I. I've never heard of such an animal. Any links to demystify my learning gap?
RTF
Google is / can be your friend... just try " mist eliminator" and you should find some explanations and pics.
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Old 11-04-2018, 06:50 AM   #11
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Many boats use fiberglass air filter media as a de-mist element. Never shopped for such, but they are available. A coalescing process, so there does need to be a drain below.
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Old 11-04-2018, 09:13 AM   #12
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Vane Type Mist Eliminators

Just got back to laptop to post some demister info...
The following is the type Mainship used on many of their late model trawlers - not sure about early years.

MS used vane type mist eliminators and at least w/ mine the vanes are vertical and collected mist drains to the bottom of the housing / frame where the bottom slopes towards the exterior to drain the liquid.

For more (than you ever wanted to know) re mist eliminators - see the
Chem E Visual Encyclopedia

VANE DEMISTERS
Vane or chevron demisters are made up of a number of parallel plates which have a number of bends in them. The vapor stream is forced to move back and forth along the path between the plates and while doing so the inertia of any entrained droplets causes them to impinge on the faces of the plates at which point they coalesce and fall back down the plate. Vane demisters are recommended for dirty service conditions where mesh demisters could block, vane demisters also have a higher comparable operating velocity than mesh demisters and are suited for higher velocity work.
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Old 11-04-2018, 09:45 AM   #13
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Possibly your N's air intake location is suffering from the station wagon effect. I've heard some builders comment on intake vent location and external vacuum effects.

Many types of side hull demisters and intake designs are utilized for avoiding actual ocean spray. The Ns do not have these low down side hull intake locations. Sounds like your situation is very different and coupled with a high fan induced intake phenomena.

What is your operating ER temperature with the fans off? Many vessels do not have intake fans operating when engines running, not needed. The excess heat from dry stack may be the primary reason for intake fans needed, maybe not necessary all the time in the PNW. I only run my fans when doing ER stuff shortly after a day's run and the big air pumps (engines) shut down.

Have you contacted PAE to see if they have a preferred solution for your specific model?
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Old 11-04-2018, 10:02 AM   #14
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Sunchaser,

I have not contacted PAE to discuss mist or the ER temperature delta.

I don't know the temperature with the fans off - I always use them. We usually have a 30-40 degree delta after some time at WOT.

Our boat is a dry stack boat, so we do make more ER heat. It is another topic, but I intend to add two axial fans to our stack vents to remove the air brought in by the intake vents. The installed ER exhaust fan ducting is not efficient, and the improvement is fairly streightforward. That should set us up well for the tropics/South Pacific.

Thanks for your counsel.
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