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Liquid to liquid heat exchanger idea

C

Chris W

Jan 1, 1970
0
In order to heat my water and still use the existing hot water heater, I
was thinking about building my own liquid to liquid heat exchanger.
Since there would be antifreeze in the solar collector, I need some way
to make sure it will never contaminate the water in the hot water tank.
So I came up with this design, tell me what you think.

http://www.thewishzone.com/cdw/HeatExchanger/

--
Chris W

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E

Ecnerwal

Jan 1, 1970
0
Seems like it would work, though I doubt it would work as well as the
commercial double-wall heat exchangers - simply difficult to
home-fabricate that sort of thing with similar efficiency, and lost
efficiency makes your system work less effectively. In any case, use of
non-toxic antifreeze is a good idea, though some jurisdictions require
both non-toxic antifreeze and a double-wall heat exchanger.
 
L

LCT Paintball

Jan 1, 1970
0
In order to heat my water and still use the existing hot water heater, I
was thinking about building my own liquid to liquid heat exchanger. Since
there would be antifreeze in the solar collector, I need some way to make
sure it will never contaminate the water in the hot water tank. So I came
up with this design, tell me what you think.

http://www.thewishzone.com/cdw/HeatExchanger/

--


For efficient transfer of heat, you need surface area. While your idea would
work, the dead air space acts as an insulator.
 
T

Tom Miller

Jan 1, 1970
0
Chris W said:
In order to heat my water and still use the existing hot water heater, I
was thinking about building my own liquid to liquid heat exchanger.
Since there would be antifreeze in the solar collector, I need some way
to make sure it will never contaminate the water in the hot water tank.
So I came up with this design, tell me what you think.

http://www.thewishzone.com/cdw/HeatExchanger/

I doubt if it would be practical as the air gap between the heat exchange
surfaces will have so low a conductivity as to be useless.
I suggest that you make a conventional tube-in -tube heat exchanger and use
propylene glycol as an anti-freeze (not ethylene glycol, its poisonous). Any
leak will show up as sweet taste in the heated water. Simply marking the
level in the header tank will show if there is a leak anywhere in the
system.
 
C

Chris W

Jan 1, 1970
0
Tom said:
I doubt if it would be practical as the air gap between the heat exchange
surfaces will have so low a conductivity as to be useless.
Did you not see the copper "fingers" that give an easy path for the heat
to conduct from the center to inner tube in the cross section view?


--
Chris W

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
One stop wish list for any gift,
from anywhere, for any occasion!
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Y

YouGoFirst

Jan 1, 1970
0
In order to heat my water and still use the existing hot water heater, I
was thinking about building my own liquid to liquid heat exchanger. Since
there would be antifreeze in the solar collector, I need some way to make
sure it will never contaminate the water in the hot water tank. So I came
up with this design, tell me what you think.

http://www.thewishzone.com/cdw/HeatExchanger/

You may also want to consider looking into a cross flow, countercurrent heat
exchanger. I once built a heat exchanger using some copper pipe and a
bucket. For my purposes I was trying to cool a water mixture down. The
system used a 5 gallon bucket for its shell and copper pipe inside. The
system worked quite well. If you use a single piece of pipe to go through
your system, and grossly overside the pipe you will help prevent leaks due
to pressure buildup. Also, if you use a large pipe and can reduce the flow
rate through the heat exchanger, that will also help improve the efficiency.
 
S

SQLit

Jan 1, 1970
0
------snipped================

Did you not see the copper "fingers" that give an easy path for the heat
to conduct from the center to inner tube in the cross section view?


The fingers are a joke and would be hugely labor intensive to install.
Simple is better.
Have you considered mineral oil? Anything that uses water will eventually
need maintenance.
Our flat plate exchangers need to be torn down once a year to keep them at
optimal condition. They are aluminum alloy and are water to water medium. We
spend a million a month on water treatment. Starting out with distilled
water.
 
N

News

Jan 1, 1970
0
DJ said:
Well, you're certainly reinventing the wheel here ;-).

But, that said, my suggestion would be to mount the heat exchanger
vertically, with your drain holes pointing upward. Then fill the cavity
with non-toxic oil or something similar,

Low viscosity car engine oil? Cheap enough and everywhere.
 
M

Michael

Jan 1, 1970
0
Low viscosity car engine oil? Cheap enough and everywhere.On the other hand, it fails the "non-toxic" criteria rather spectacularly
 
W

wmbjk

Jan 1, 1970
0
Yes, always.

Nick

Caution: extreme thread drift - I am suddenly reminded of claims by
some that if you drive fast enough on washboard roads, you'll only hit
the high spots. :) Oddly enough, the same people claim that driving
fast worsens the washboard, when by their own logic it should be
wearing down the high spots...

Wayne
 
M

Michael

Jan 1, 1970
0
To some degree you're both correct, but....

It's important to distinguish between heat transfer RATE (which generally
increases with flow speed) and the total amount of heat transfer (which is a
function of both rate and residence time), which does not necessarily
increase with increased flow speeds.
 
Fact is, when heating up something with a heat exchanger, there are
alot of secondary concerns that effect the heating rate. And a faster
flowrate isn't the best way to warm up a fluid...

Raising a fluid velocity ALWAYS increases heat transfer.

Nick
 
D

daestrom

Jan 1, 1970
0
Raising a fluid velocity ALWAYS increases heat transfer.

This is true. BUT, increasing the flow rate will usually *reduce* the
outlet temperature of the liquid you're heating. These two statements are
not contradictory once you consider that heat transfer rate is equal to mass
flow rate times specific heat capacity times the temperature rise.

Q = mdot*Cp*(Tout - Tin)

Increasing the mdot, while reducing the (Tout - Tin) can still result in a
rise in Q.

If the fluid is being recirculated to a holding tank, then then only concern
with increasing flow rates is the increase in pumping power needed and
possibly flow-induced vibration.

But if its a once-through, or open-loop system, increasing the flow rate
will reduce the outlet temperature for the 'once-through' fluid and may drop
it below the desired range.

So, it depends on the exact application, and whether the heat-exchanger's
outlet temperature is paramount or maximizing the BTU/hr rate to a
recirculating fluid is the main concern.

daestrom
 
D

daestrom

Jan 1, 1970
0
wmbjk said:
Caution: extreme thread drift - I am suddenly reminded of claims by
some that if you drive fast enough on washboard roads, you'll only hit
the high spots. :) Oddly enough, the same people claim that driving
fast worsens the washboard, when by their own logic it should be
wearing down the high spots...

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
 
G

Gordon Richmond

Jan 1, 1970
0
Interesting diversion.

No question in my mind that washboard has a periodicity to it, and
that, with some vehicles, you can null it out by driving at the
"right" speed. I noticed that driving an old VW Beetle on gravel roads
a lot. But I don't drive that fast anymore. :>)

Washboard seems to show up first on hills, and around my home, where
the gravel starts at the end of the pavement. My own theory is that
the periodicity of the washboard is in fact caused by vehicle
suspensions breaking traction, with a resulting periodic axle hop.
This creates high and low spots in the road surface, which in turn
induces more axle hop in succeeding vehicles. A positive feedback
mechanism, if you will.

Now, when I encounter washboard, I just slow down. Why beat the heck
out my vehicle, its contents, and myself?

Gordon Richmond
 
C

Cosmopolite

Jan 1, 1970
0
Gordon said:
Interesting diversion.

No question in my mind that washboard has a periodicity to it, and
that, with some vehicles, you can null it out by driving at the
"right" speed. I noticed that driving an old VW Beetle on gravel roads
a lot. But I don't drive that fast anymore. :>)

You probably noticed that rear engine, rear wheel drive is the
smoothest ride on gravel.
 
R

Rick Frazier

Jan 1, 1970
0
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
 
W

wmbjk

Jan 1, 1970
0
Interesting diversion.

No question in my mind that washboard has a periodicity to it, and
that, with some vehicles, you can null it out by driving at the
"right" speed. I noticed that driving an old VW Beetle on gravel roads
a lot. But I don't drive that fast anymore. :>)

Washboard seems to show up first on hills, and around my home, where
the gravel starts at the end of the pavement. My own theory is that
the periodicity of the washboard is in fact caused by vehicle
suspensions breaking traction, with a resulting periodic axle hop.
This creates high and low spots in the road surface, which in turn
induces more axle hop in succeeding vehicles. A positive feedback
mechanism, if you will.

I agree. On a freshly graded level road, the washboard shows up first
on either side of cattleguards where there's more braking and
accelerating. I've also noticed that even on the 10% grade on my own
personal road, I can go for months driving fast in a car without
creating washboard, but if a dually pickup for instance makes a single
trip up the hill, the washboard is started immediately wherever the
material is loose enough.
Now, when I encounter washboard, I just slow down. Why beat the heck
out my vehicle, its contents, and myself?

On some vehicles there just doesn't seem to be any speed that can
improve the situation. I drove a moving van once 10 miles on the
proverbial bad road. Even crawling speed didn't help. I tell people to
drive at whatever speed they get the smoothest ride. The worse the
ride, the more they're enhancing the washboard. Reducing tire pressure
can help a lot. What I find is that the older people are, the more
they enjoy blaming young whippersnappers for the problem, even if
Grandpa's turtle speed on his own driveway earned him the worst
washboard in the neighborhood. ;-)

Wayne
 
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