Liquid to liquid heat exchanger idea

And there seems to be certain speeds where the wheel's seem to 'resonate' and act more like they're 'floating' than really following the ups/downs in the roads.

(or maybe I just need some new shocks ;-)

daestrom

Chris:

This may seem too simple, but if you just make the concentric tubes, with the clean water on one side, pressurized at house pressure (say, 50psi) and the solar water (or antifreeze) at a much lower pressure (10psi or less, depending on the head that results from the difference of the collector height and the storage tank/exchanger height), you shouldn't have to ever worry about getting clean water contaminated with solar water... Of course, if you are a worry wart, you can use a non-poisonous anti-freeze and tint the solar water with food coloring (massive amounts, say red?) and you'd be able to detect a leak without any problems at all. Of course, if you have any significant leak of the clean system into the solar system, it's going to blow the collectors anyway, as most of them aren't rated for anything near house pressures.

Simpler is typically better. Less maintenance, and often better heat transfer.

Good Luck!

-_Rick

Chris W wrote:

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He would be right if the high velocity fluid were in unlimited supply. And you would be right if the high tremperature fluid were in limited supply - at which point, residency takes on value.

Try not to suppose that people who argue with you are arguing from authority - people with any background at all, make assumptions- some good, some bad

Brian Whatcott Altus OK

Ah, see, I wasn't making assumptions. I was relying on memory of times I was told "...your shift is over when tank three hits 40C..." ;-).

Faster flow was NOT better in that case ;-).

DJ

As long as the fluid remains the same temperature. Having a large cylinder with stored water at 80C will transfer that heat faster if at a high velocity and the heat exchanger can "take" and transfer the heat. Say a boiler on a low flow can deliver 80C on the flow pipe. If you increase the flow rate the temperature may be cooler at the flow pipe.

News is confused again:

Not if you increase the VELOCITY with the same volume flow rate.

Nick

Here's another idea. What if the tube the potable water was running through were so thick as to guarantee a crack was virtually impossible? Say a .75 ID and a 1.25 OD for a .25 wall. Obviously thicker is going to take longer to conduct the heat but 1/4" of solid copper is going to conduct heat a lot better than some thermal past or oil in the middle chamber. Of course there is the problem of finding a tube like that. I doubt you could buy one, you would probably have to get a machine shop to gun drill a solid copper rod. Then soldering would be fun with a copper tube that thick.

I think in our part of the country we have codes and safety standards. You may be willing to rig whatever you want, but when it comes to your family, guests and people that buy your house, codes win out.

.....and increase the burner rate. A burner can only transfer so much heat to the water. A boiler raises the temperature of water - the temp rise. Say it can give a 40C rise at n water velocity. If water entering the return pipe is 30C then 70C out the flow, but only if the velocity of the water is n. Have n x 2 and the flow may be far lower as the water doesn't stay in the boiler long enough to have its temperature risen. You can run your fingers through a bunsen burner flame and no problems (we have all done it), but keep your fingers there and see what happens. Also when the flow temp is lower the return temperature is cooler too, so a double whammy.

And meanwhile you can actually meet code, cheaper, with off-the-shelf double wall heat exchangers which are actually designed to do the job correctly, and efficiently.

That is true, but you can reach a point where your fluid is traveling so fast through the heat exchanger that there is little to no effect occuring.

Also, the point I intended was that if you want to achieve the greatest temperature differential with a water heating system, the fluid that is being heated should travel as slower so that it is able to receive sufficient heat to obtain a desired temperature.

This commercial heat exchanger would be of interest to many of us DIYers. Do you have any pointers to where you might find such a heat exchanger that fits in place of a standard electric hot water heating element?

-- Bert Menkveld

I generally think in terms of hot water heat exchangers like the quad rod.

go outside the tank and attach to fittings that are already on the tank. A heat exchanger as small as an electric element probably would not have enough surface area. Solar tanks by Rheem and others usually use a copper coil inside.

I took a quick look via a search engine for current examples - I found that hot water tanks with indirect loops built in for closed loop glycol solar panel heating (like I did) were easy to find, but they go for premium prices. I saw one or two home brew copper loops fitted in tanks, but that seems like a lot of trouble. I couldn't find a screw in fluid to fluid heat exchanger of the type I bought though. I suspect it was a steam heating heat exchanger screw-in, for a 50 gal tank. Asking a H&V supplier would be my first move, if I did it over...

Sorry

Brian Whatcott Altus OK

Maybe IM missing something but wouldn't the design be much simpler is you just used propylene Glycol? I believe it's food grade and won't hurt you.