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Old 07-04-2016, 00:59   #1
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Aluminium or brass for heat exchangers?

Greetings all

I want to design new heat exchangers. These will be mounted inside the engine bay with raw water pumped through one side and fresh water / antifreeze / glycol pumped through the other side.
I want to make them out of aluminium for weight saving but I'm worried about how long they will last. Brass / bronze would be best but the weight is putting me off.
Does anyone have similar exchangers made from ali and can tell me how long they've been in service? Any problems with accelerated corrosion?

Thanks in advance

Dave
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Old 07-04-2016, 02:26   #2
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Re: Aluminium or brass for heat exchangers?

I'd think that the salt water will eat the aluminum almost as fast as you can make them. As, for example, I've seen it eat holes in beer (cans) stored in the blige, in 3 days.

It's easy enough to save a bit of weight elsewhere. The list of ideas is endless. Besides, there are other options, metal wise, which are still plenty light. Albeit, not necessarily cheap.

What's the application exactly? Maybe we can help out with some ideas.
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Old 07-04-2016, 03:23   #3
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Re: Aluminium or brass for heat exchangers?

Hi Uncivilized,

I'm in the process of designing my dream boat.
Basically a solar powered catamaran with diesel electric backup.
Or should I say Diesel electric cat with solar backup

Anyway, I don't like the idea of keel coolers, just see them as a lot of maintenance. Want to bring the heat exchangers inside the boat.

So the idea is, have a main heat exchanger in each hull.
This heat exchanger will handle the cooling for generators, refrigeration, air-con.

Simple system where raw water is pumped from a through hull through the heat exchanger and back out to sea.
The internal heat exchange circuit will pass through the genset intercooler (Charge air cooler) first, then refrigeration, then air-con and lastly the diesel engine on the genset then back to the heat exchanger.

It ensures all equipment runs on a nice clean mixture of antifreeze and fresh water. Should vastly reduce maintenance, especially with things like air-con and refrigeration cooling circuits blocking up with algae and our little barnacle mates. Water pumps in various circuits will be lubricated and should last longer. There are a whole number of reasons I want to plumb the system this way.

There is only one nasty to be cleaned once a year. It's easy to get to. One thru-hull instead of many etc.

Reason I was thinking about aluminium is, the heat exchanger in each hull will be quite large. Was just wondering if there is an alloy that would survive salt water for any amount of time.
I agree it's probably a bad idea, was just wondering if there was anyone out there with a surprise that's working well?

Back to the cooling system idea, the only real disadvantage I can see over a traditional keel cooler is it will need one extra pump. I think that's a small price to pay for really clean, easy to maintain cooling on the other systems listed above.

Any thoughts anyone?

Regards :-)
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Old 07-04-2016, 04:28   #4
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Re: Aluminium or brass for heat exchangers?

This idea is far more problematic than a simple keel cooler.

However mani coolers on small engines are Alu/bronze. The tube bundle and end caps are bronze, the body is Alu. Seawater never touches the Alu.


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Old 07-04-2016, 04:43   #5
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Re: Aluminium or brass for heat exchangers?

Hi Sailmonkey,

Thanks for the input.
What makes you think my idea would be more problematic?
I'm really interested because I don't want to put a crap idea in to action.

Regards

Dave
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Old 07-04-2016, 04:44   #6
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Re: Aluminium or brass for heat exchangers?

You might be interested in this:
https://www.nickelinstitute.org/~/me...es_12002_.ashx
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Old 07-04-2016, 05:19   #7
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Re: Aluminium or brass for heat exchangers?

Wonderful Gord,

Thank you

You're a font of knowledge, what do you think of having a single loop cooling system that handles the heat exchange needs of the entire boat through one heat exchanger? Or one per hull anyway.

Dave
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Old 07-04-2016, 05:31   #8
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Re: Aluminium or brass for heat exchangers?

You likely know this. But anything which you build custom, especially if it involves custom made (one off) parts, will wind up costing you 10x vs. something off the shelf, which you can adapt for your purposes.

And barring seeing diagrams, & all of the associated numbers, etc. Even as an engineer, & a sailor with decades of experience, I can't offer up realistic/accurate feedback on such a setup.
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Old 07-04-2016, 06:04   #9
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Re: Aluminium or brass for heat exchangers?

Quote:
Originally Posted by UNCIVILIZED View Post
You likely know this. But anything which you build custom, especially if it involves custom made (one off) parts, will wind up costing you 10x vs. something off the shelf, which you can adapt for your purposes.


And barring seeing diagrams, & all of the associated numbers, etc. Even as an engineer, & a sailor with decades of experience, I can't offer up realistic/accurate feedback on such a setup.
To the first part...
Very true, usually...But I manufacture heat exchangers and sell non ferrous metals for a living so in my case, manufacturing my own heat exchangers will be very cost effective. My draw back is I live very far away from the sea. So, although I have many years experience with heat exchange, none of it involves seawater. It's annoying being able to make something but not knowing how all of a sudden

And the second part...
Understood, but for now I'm really only asking if the concept sounds plausible. Why would running the boats cooling requirements in a single closed loop be a bad idea? Surely if I run everything on nice clean glycol mix and there is only one interface between seawater and coolant, that makes sense? Less thruhulls, no blocking of various pumps and plumbing with critters and algae, one seacock and strainer per hull. one heat exchanger to maintain, the others in the loop just won't need maintenance, or very little anyway. Any arguments as to why this would be a bad idea?

Dave
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Old 07-04-2016, 06:12   #10
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Re: Aluminium or brass for heat exchangers?

Quote:
Originally Posted by Dave-Zim View Post
Greetings all

I want to design new heat exchangers. These will be mounted inside the engine bay with raw water pumped through one side and fresh water / antifreeze / glycol pumped through the other side.
I want to make them out of aluminium for weight saving but I'm worried about how long they will last. Brass / bronze would be best but the weight is putting me off.
Does anyone have similar exchangers made from ali and can tell me how long they've been in service? Any problems with accelerated corrosion?

Thanks in advance

Dave
Absolutely no to aluminum or brass for a heat exchanger exposed to raw water. No problems on the fresh water glycol side.

Why the concern on weight? What is the application.

Bronze, not brass, or cupro nickel is ideal. Other nickel based materials are also available. Their are some design considerations that make domestic or automotive heat exchanger best practice not sufficient for marine use.

Peter Smith, the Rocna Anchor inventor has published online about the design and build of his high latitude aluminum yacht.

See www.petersmith.net.nz/about/kiwiroa.php

He describes how he feeds all raw water demands from a single thru hull into an interior tank (custom sea chest).

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Old 07-04-2016, 06:12   #11
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Re: Aluminium or brass for heat exchangers?

Take a big earth moving machine for example,
One big radiator cools the water which is then pumped around the whole machine through various coolers. It cools the engine oil, transmission and hydraulics all in various oil coolers in a closed loop.
Why not the same on a boat?

Would like to hear if anyone thinks this a bad idea and more importantly, why?
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Old 07-04-2016, 06:15   #12
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Re: Aluminium or brass for heat exchangers?

Heat exchangers are already available and more common than keel coolers.
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Old 07-04-2016, 06:18   #13
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Re: Aluminium or brass for heat exchangers?

Quote:
Originally Posted by leftbrainstuff View Post
Absolutely no to aluminum or brass for a heat exchanger exposed to raw water.

Why the concern on weight? What is the application.

Bronze, not brass, or cupro nickel is ideal.

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Hi Leftbrainstuff,

Accepted on the no ali or brass. Was just wondering if someone knew something different.

The concern on weight is, I want to build a (predominantly) solar powered boat. Weight in all boats is an issue but more so with solar as they aren't known for being sporty. So I'm following the philosophy of, if it can be made lighter, then it should be.

Thanks for the advice on the cupro nickel. Will research.

Dave
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Old 07-04-2016, 07:18   #14
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Re: Aluminium or brass for heat exchangers?

I suggest buying a commercially made heat exchanger made for a boat. It will be less expensive and it's already been engineered.
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Old 07-04-2016, 08:29   #15
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Re: Aluminium or brass for heat exchangers?

All sounds a bit like the gramme saving road bikers desperate to strip every last milligramme off their bike but forget the fact they weigh 100kilos.

Yes shaving weight will improve the performance of any vehicle but, unless you are planning on sailing an AC60 foiling catamaran, seriously are you going to notice the difference?

I'd go with the best metal for the job and think about where you can save the kilos or pounds rather than the ounces or microgrammes. 1 less meter of anchor chain will save you a couple of kilos for example.

Don't forget to KISS (Keep It Simple Stoopid)

Just my 2p worth

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