Author Topic: tube in shell heat exchanger  (Read 23786 times)

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imt

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tube in shell heat exchanger
« on: June 06, 2006, 02:47:33 PM »
A little help wanted. I've been playing with heat exchangers and have settled on a tube in shell variation. Essentilaly, its a 3/4" convoluted surface tube inside a 1" shell. all components are copper. I use it in a counter flow configuration with the solar collector loop traversing the inside tube and the storage tank loop circulationg between the tube and shell. Its 48" in total length with two pumps; an elsid for the collector loop and an .33 hp Grundfus for the tank loop.


OK, here's my question....


What should I expect for temp difference between the collector loop input and the tank loop output? My collector loop routinly reaches 140 + F. The tank loop almost always reaches between 8 and 10 degrees F less than this. Its plently of hot water for our household needs. I just don't know what to expect here.


More info - single collector with 18 sq ft area, tank is converted Sears 65 us gal electric (just can't beat that price!). all collector loop piping is 1/2" with a loop total (both ways) of 156'.


Pix available if it will help you help me.


imt

« Last Edit: June 06, 2006, 02:47:33 PM by (unknown) »

halfcrazy

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Re: tube in shell heat exchanger
« Reply #1 on: June 06, 2006, 09:39:16 AM »
i would say ifyou are within 10 degrees you are about as efficient as you are going to get with a homeade heat exchanger.
« Last Edit: June 06, 2006, 09:39:16 AM by halfcrazy »

Slingshot

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Re: tube in shell heat exchanger
« Reply #2 on: June 06, 2006, 09:58:58 AM »
Did you build the exchanger yourself?  How did you make the "tube within a tube", particularly the terminations?  is there a readily-available fitting for this?  Did you produce the "convoluted surface" yourself?


I guess I'd like to see the pictures for general interest, even though I probably can't be of help.

« Last Edit: June 06, 2006, 09:58:58 AM by Slingshot »

wdyasq

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Re: tube in shell heat exchanger
« Reply #3 on: June 06, 2006, 11:08:20 AM »
Without a bit of other information it is hard to determine if you have reached the best you can with your setup. Your "collector hot to tank" and "hottest tank" should be on the same end. If not, the most hot collector water will be stripped of its' energy before it gets where it is needed.


Other points to consider are the heat isn't "lost" that doesn't go into the tank.  It goes back to the collector and doesn't need to gather that heat. Of course, your collector "Delta" is not as great and your heat rejection from the collector is higher. I have never seen the need to  put a pump on the potable water end. If the tube in shell collector is vertical and you pull cold off the bottom (usually by replacing the drain with a "T") the water normally will thermosyphen.  Slowing the collector water sometimes increases water temperature.


In short, there are many variables that must be considered if one cares to get "Scientific". On the other hand are not only five fingers, except for Zubbly, but also a usable device that provides hot water with little expense.


Ron

« Last Edit: June 06, 2006, 11:08:20 AM by wdyasq »
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imt

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Re: tube in shell heat exchanger
« Reply #4 on: June 06, 2006, 11:31:04 AM »
OK, some pix follow....


the heat exchanger was built for hardware store components. I used two flexible 3/4" water heater hookup pipe (copper)for the tube, 1" copper pipe for the shell, and standard fittings for the ends. Connecting the two peices to make the inner tube was the hardest part. I liked the 3/4" inner tube because I think it slows down the flow of the solar heated water somewhat and provides more contact time. The space between the convoluted (rumpled) surface and the shell inner wall is less than 1/16". This provides lots of surface area. The convoluted surface provides for turbulance. Everything I've read says these are all good things. All sweats are silver solder.


If 10 degrees F is good for a homemade exchanger, what would a commercial exchanger be able to give me? Anyone have a quad-rod they could give me temp readings off of?













« Last Edit: June 06, 2006, 11:31:04 AM by imt »

wind pirate

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Re: tube in shell heat exchanger
« Reply #5 on: June 06, 2006, 12:29:30 PM »
This type of heat exchanger has been used in the homebrewing area for years to cool boiled wort to fermentation temperature. There is a simple setup of "tube in tube" construction that can be made. Using 10-12' of a 5/8" garden hose - clamp 2 copper T's in the ends so that you have one outlet going straight, and one outlet at 90'. Solder a 1/2 x 3/8" swage connector to each of the straight outlets on the T. Take a length of 3/8 flexible copper and run it through the fittings, down the length of the hose, and out the other fitting. Tighten the swagelock fittings to secure the inner tubing. That becomes your inlet and outlet for the solar panel. The 90' fitting on the T is used to circulate the water from the tank around the inner core of copper tube. Just make sure that the direction of flow is reversed from the solar panel (counterflow).


For a commercial (and better) solution - look at this link to get more ideas.


http://morebeer.com/product.html?product_id=19533


Actually, at 12' of tubing, this could be very effective as a heat exchanger.


Wind Pirate

« Last Edit: June 06, 2006, 12:29:30 PM by wind pirate »

stevesteve

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Re: tube in shell heat exchanger
« Reply #6 on: June 06, 2006, 03:36:00 PM »
Hi John,


Here is my prototype. It is a single tube in tube unit but I have not had a chance to test it yet. I was going to run several together depending on efficiency.


Here is a kit of parts:





I have soldered up each end (OK I'm no plumber!)





and the whole thing slips into an insulating jacket





I have used 22mm and 15mm pipe (24mm ish to 1"?). I have since found that I can get a 22mm/15mm/15mm 'T' fitting that I can use to replace the 22mm/15mm/22mm and reducer that I used in combination.

My plan is to build a prototype solar water panel and then run a couple of pumps with some hose and monitor temps in/out for both circuits. It will, of course, run with counterflow to get as much transfer as possible.

« Last Edit: June 06, 2006, 03:36:00 PM by stevesteve »

ghurd

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Re: tube in shell heat exchanger
« Reply #7 on: June 06, 2006, 03:45:25 PM »
"I was going to run several together", as in series?

G-
« Last Edit: June 06, 2006, 03:45:25 PM by ghurd »
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stevesteve

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Re: tube in shell heat exchanger
« Reply #8 on: June 06, 2006, 04:09:20 PM »
Well the clearence between the two pipes is limited so if the flow was to restricted I was thinking that a couple could run in parallel. On the other hand if the heat transfer is not very effective I could run a couple in series.
« Last Edit: June 06, 2006, 04:09:20 PM by stevesteve »

RP

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Re: tube in shell heat exchanger
« Reply #9 on: June 07, 2006, 09:24:51 PM »
Remember you have a finite quantity of heat available to transfer through the heat exchanger.  I suspect your potable (tank) flow rate is higher than your collector flow rate.  


Think about an extreme condition where your collector pump was delivering 140F water at 1 gallon/minute and your tank side pump was pushing 50F water at 100 gallons/minute.  In these extreme conditions there would be no way to get the tank water to rise anywhere near the collector temperature.


You're actuallly doing pretty good as it is but if you want to raise the temperature of the tank water to 140F, try throttling down the flow on that side or increasing the flow on the collector pump.

« Last Edit: June 07, 2006, 09:24:51 PM by RP »

imt

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Re: tube in shell heat exchanger
« Reply #10 on: June 08, 2006, 08:06:03 AM »
Sounds sound. The Grundfos pump (on the tank side) has a small screw valve on the input side for just this purpose. I'll start "playing" with it today. I Appreciate all the input her (small pun intended ;~)
« Last Edit: June 08, 2006, 08:06:03 AM by imt »

imt

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Re: tube in shell heat exchanger
« Reply #11 on: June 08, 2006, 08:11:05 AM »
Steve, I used a very similar design. My first attemp was just solid straight pipe in pipe. I was diappointed with the results. Being only 4' in length, it didn't seem to transfer a lot of heat. The convoluted tube (inner pipe) made a BIG difference.


Question for all - any insights into whick flow to run thru wich side of the exchanger? I'm running collector through the tube and tank through the shell. I choose this for two reasons; it fit better plumbing wise and I think that having the hotter fluid inside limits radiant loss. Any and all feedback is eagerly sought.

« Last Edit: June 08, 2006, 08:11:05 AM by imt »

Slingshot

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Re: tube in shell heat exchanger
« Reply #12 on: June 09, 2006, 10:26:36 AM »
Did you just dimple the inner pipe with a hammer to get the "convoluted" surface?
« Last Edit: June 09, 2006, 10:26:36 AM by Slingshot »

kanhoward

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Re: tube in shell heat exchanger
« Reply #13 on: June 20, 2006, 07:59:56 AM »
Hi,


Does anyone know who manufactures the Quad-Rod? I'd like to import some into the EU and can't find their details.


Thanks,


Nigel.

« Last Edit: June 20, 2006, 07:59:56 AM by kanhoward »

dpowell

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Re: tube in shell heat exchanger
« Reply #14 on: May 19, 2008, 07:57:19 PM »
Here is another homemade tube-in-tube exchanger.  I used the 3/4in hot water tank supply line as mentioned above.  1.5 in pipe surrounds because I needed to made space for large hex fittings on the inner tube.  Total cost ended up being about $200 because I had to buy 10 ft of the 1.5 in pipe.


Inside Tube:




Outside Tube:




Assembly:




All together:




Pressure Test:




On tank:  I just relied on natural circulation on the tank side of the heat exchanger.  The system is mounted to a trailer so I can transport the system to the actual location were it will be installed.  Insulation will be added later.



« Last Edit: May 19, 2008, 07:57:19 PM by dpowell »

bigswag

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Re: tube in shell heat exchanger
« Reply #15 on: June 09, 2010, 06:07:53 PM »
dpowell - that 1" to 3/4" reducer in your picture of the outer shell....is that a special slip coupling reducer? I can't find anyone around my parts who sells reducing Ts or straight reducers without the dimples to allow the inner pipe to run through. Plumbers Supply didn't have any. I would rather not mess around with filing down the dimples on my reducer or T if somebody makes copper fittings without dimples.....seems like it would be a simple thing for somebody to make....any ideas where to buy?

Thanks in advance - Mike




huntedheads

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Re: tube in shell heat exchanger
« Reply #16 on: June 28, 2010, 05:49:48 AM »
To get the 1/2" pipe into the 3/4" fittings bore it with a 5/8" bit, the fit is perfect. Here's a pic of mine. It's four rods without the second pump. The exchanger is thermal siphon and it's been running about 2 years now. The return temp varies with the input temp AND the lower tank temp! but at 120 degrees in i get a 10 degree drop on the return temp. The supply and return lines are 1" dropping to 3/4" at the first T's then to 1/2" at the second ones. I have tried adjusting flow rates but seems that all that happens is collector temp goes up, heat loss from collector to exchanger go up, and flow rate in exchanger go down.

huntedheads

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Re: tube in shell heat exchanger
« Reply #17 on: July 02, 2010, 05:27:13 AM »
Here is a pic without the insulation so it's a lot easier to see. This is the bottom of the exchanger the 1" pipe going away is the pipe going to the port where the lower heating element was.