Heat exchanger question

[Markhunter1097]

Why would the heat exchanger only scale up on one side, am I only using half of it?

[billknny]

What you are looking at there is not "scale" in the way a chemical engineer would usually think of it, but residue from the corroding zinc, which I see installed in that half of the exchanger.

"Scale" would be lining the inside of the tubes, not the the end of exchanger.

[Markhunter1097]

Thx billknny, that is the obvious answer, don’t know why I didn’t think of that!!So I figure I can just clean out the tube ends as the old zinc residue as it doesn’t go all the way thru the tubes?

[Gary Mc]

Also I suspect that the flow is in on the dirty side and around and then out on the other side. Hence more fouling on the primary side?

[RaymondR]

Originally Posted by Gary Mc

Also I suspect that the flow is in on the dirty side and around and then out on the other side. Hence more fouling on the primary side?

Yep, some heat exchangers are built that way. There appears to be two types of deposit, the white on the outer housing and the black stuff trying to plug the tubes.

[DougR]

The deposits you see are salts which have dropped out of the salt water....

As you probably know when an engine is salt water cooled it is necessary to use a thermostat with an opening temp. of about 140 degrees or lower. This is because higher temps cause the salt to precipitate from the water and it will plug the cooling system.

In this case, you have cool sea water entering the heat exchanger and the 190 degree hot antifreeze is just on the other side of a thin wall of copper. This immediately raises the local seawater temp above the precipitation point and the salt drops out and coats the inner surface of the housing.

My old 4-108 heat exchanger had the zinc on the downstream/ outlet side of the HE, but it still collected salt on the upstream side where the sea water hit the hot antifreeze.

DougR

[a64pilot]

Originally Posted by Markhunter1097

Attachment 191705

Why would the heat exchanger only scale up on one side, am I only using half of it?

I believe that may be the “hot” side, I believe the water flows over one side around the end and back to the other side, the water is hotter on the second pass of course. I believe it precipitates out in hot water.

I’ve been told it’s not salt, it’s actually calcium carbonate, which makes sense to me for three reasons, first acid removes it quickly and I don’t think it would salt, and secondly salt is very soluble in water, so hot water will dissolve salt fast, and this stuff doesn’t dissolve in water.
Then it doesn’t taste like salt either, but I used it think it was salt too, cause it sure looks like it doesn’t it.

[Sailor647]

We removed the zinc in our heat exchanger for this very reason. Since we have other zincs connected to the engine, we really didn't need it anyway.

[chouliha]

Not sure why you would remove your heat exchanger zincs. Have you priced new heat exchangers?

[Compass790]

Originally Posted by a64pilot

I believe that may be the “hot” side, I believe the water flows over one side around the end and back to the other side, the water is hotter on the second pass of course. I believe it precipitates out in hot water.

I’ve been told it’s not salt, it’s actually calcium carbonate, which makes sense to me for three reasons, first acid removes it quickly and I don’t think it would salt, and secondly salt is very soluble in water, so hot water will dissolve salt fast, and this stuff doesn’t dissolve in water.
Then it doesn’t taste like salt either, but I used it think it was salt too, cause it sure looks like it doesn’t it.

Yea I agree with this. It's definitely not sodium chloride anyway as that, as you pointed out ,dissolves easily.

[RaymondR]

They build them this way so that the outlet and the inlet can come out of the same end. Helps for access and simplifies the piping runs.

There are numerous minerals dissolved in sea water which will precipitate out in the right conditions including calcium and magnesium.

The reason the anode is in the heat exchanger is that this provides a short current path for the impressed current which is preventing corrosion. You should not rely on the protection of more distant anodes particularly if the exchanger is piped to the engine with hoses.

It's easy to make tube cleaners out of old SS wire.

[a64pilot]

Often a good cleaner is a a properly sized rifle cleaning brush with its cleaning rod