Vertical slotted-tube diffuser

[ewdudley]

Here's one way of doing it.

Diffuser will be suspended into top of tank, hanging in nipple.

Crown of diffuser separated from steel by EPDM gasket for galvanic isolation.

Copper selected for being easy to work with.

Slots bent inward for Pall Ring effect.

--ewd

 

[Nofossil]

Interesting.... I'd love to see comparative data on the effectiveness of different diffuser designs at different flow rates.

 

[ewdudley]

Interesting.... I'd love to see comparative data on the effectiveness of different diffuser designs at different flow rates.

'Be careful what you wish for.'

(broken link removed)

What I took away from it:

Stratification is easy in the case of heat storage from boilers because the supply temperature is reasonably constant and the relative buoyancy across the thermocline is large. The hard cases are: solar heat storage where the supply temperature can vary a lot and it is very difficult to get the water to diffuse at the proper elevation; and chilled water storage, where although the supply temperature is constant, the difference in density between 32F and 60F water is only about 1/20th the difference in density between 90F and 170F water.

In the case of boiler hot water storage a reasonably fat horizontal port (1.5 inch) with reasonably slow water (1.0 ft / sec) hardly needs any diffusion hardware. Vertical ports could probably benefit from a diffuser but I got the impression that in the case of boiler hot water storage it's not something to get too worked up about.

The nicest easiest horizontal diffuser is a tube or an arrangement of tubes situated horizontally with a slot in the side. The nicest easiest vertical diffuser is a cup arrangement where the flow is directed back up to the top surface of the tank. [Note: This pertains only to the constant temperature injection case. Variable temperature injection requires more elaborate schemes, see post below.]

In my case I couldn't come up with a cup arrangement for a 1.5 inch port so I settled on the Pall Ring cylinder as nice enough and easy enough.

--ewd

 

[in hot water]

This site has some interesting concepts and devices for solar storage tanks. Solar harvest starts when the collector is 8-12 degrees abobe the tank senbsor, so a somewhat tight Δ T compared to a boiler powered system. Heat exchange and stratification is on area engineers are always looking to find improvements.

(broken link removed)

hr

 

[rkusek]

Here's one way of doing it.

Diffuser will be suspended into top of tank, hanging in nipple.

Crown of diffuser separated from steel by EPDM gasket for galvanic isolation.

Copper selected for being easy to work with.

Slots bent inward for Pall Ring effect.

--ewd

Are you using this EW? Since I plan on using just the existing 1 1/4" openings on top for my hot water entry I was thinking of how best to make a diffuser. Thought maybe a round metal disk just under 1 1/4" with 3 small "legs" welded to inside of nipple. This would at least deflect the water horizontally instead of it shooting down to bottom of tank. I would like to insert a long copper pipe with holes on top and capped at end but not sure the elbow of even a 1" copper tee would clear the 1 1/4" opening. Might go get some fittings to see if a 1" coupler could be welded to a 1 1/4" to 1" bushing. Might not even be possible.

 

[ewdudley]

Are you using this EW? Since I plan on using just the existing 1 1/4" openings on top for my hot water entry I was thinking of how best to make a diffuser. Thought maybe a round metal disk just under 1 1/4" with 3 small "legs" welded to inside of nipple. This would at least deflect the water horizontally instead of it shooting down to bottom of tank. I would like to insert a long copper pipe with holes on top and capped at end but not sure the elbow of even a 1" copper tee would clear the 1 1/4" opening. Might go get some fittings to see if a 1" coupler could be welded to a 1 1/4" to 1" bushing. Might not even be possible.

Yeah I put them in there but I doubt they're really necessary.

First I expect that at the beginning of the burn cycle the initial flow into the tanks is pretty slow as the boiler comes up to temp and as the house steals flow, so by the time the flow increases there's already a layer of hot water that will survive the turbulence. Second, if it's a full-pull burn chances are the mixed layer will become return water at the end of the burn and the whole tank will be good and hot before it's over. Third, if there's a fifty gallon layer of not so hot water just before storage is completely depleted, so what? Pull what heat you can out of it and get busy lighting another fire.

Three legs (or one even) on an upside-down table sounds better than what I did, quicker, easier, can't hurt.

An idea I played with was some kind of upside-down Piña Colada parasol with an EDPM disk that would deploy against springy wire that unfolded.

Cheers --ewd

 

[Pat53]

I made mine out of 1 1/4" black pipe welded on the inside of the 2" fitting that was welded on the tank. I put about 20 - 1/2" holes at 45 degree angles upward and a cap on the end with a 1/4" hole in it. The only place the hot water can really go is up. Can't wait to try it and see how well the stratification works.

 

[jebatty]

In the case of boiler hot water storage a reasonably fat horizontal port (1.5 inch) with reasonably slow water (1.0 ft / sec) hardly needs any diffusion hardware.

You can see the accuracy of this if you look at the chart I posted in Horizontal Tank - Stratification.

 

[sparke]

I just got my pressurized storage operational. There are no diffusers, the supply comes straight out of a top fitting and the return is a dip tube to the bottom of the tank on the opposite end. I am noticing some weird results. Unless my temp gauge at the top of the tank is wrong. The return water temps are higher then the temp at the top of the tank. For instance - if the tank reads 140* at the top, my return temp is 180*. The temp gauge for the return is in the piping, I don't have a temp gauge for the bottom of the tank. The 180* return temp makes no sense unless there is some type of current in the tank that somehow is created from the supply to the return. Is that even possible? This phenomenon did not happen until the whole tank warmed up from top to bottom. I did not have the tank insulated and could feel the sides of the tank getting warmer from top to bottom. Is it possible with no insulation the top of the tank was giving off the BTU's as soon as they were stored? I could not get the tank over 140* either without insulation. I am almost done insulating and hope to fire up again later today. It will be interesting to see the differences.

Oh btw, the flow is from the top down when charging and reverses when drawing from tank.

 

[rkusek]

I just got my pressurized storage operational. There are no diffusers, the supply comes straight out of a top fitting and the return is a dip tube to the bottom of the tank on the opposite end. I am noticing some weird results. Unless my temp gauge at the top of the tank is wrong. The return water temps are higher then the temp at the top of the tank. For instance - if the tank reads 140* at the top, my return temp is 180*. The temp gauge for the return is in the piping, I don't have a temp gauge for the bottom of the tank. The 180* return temp makes no sense unless there is some type of current in the tank that somehow is created from the supply to the return. Is that even possible? This phenomenon did not happen until the whole tank warmed up from top to bottom. I did not have the tank insulated and could feel the sides of the tank getting warmer from top to bottom. Is it possible with no insulation the top of the tank was giving off the BTU's as soon as they were stored? I could not get the tank over 140* either without insulation. I am almost done insulating and hope to fire up again later today. It will be interesting to see the differences.

Oh btw, the flow is from the top down when charging and reverses when drawing from tank.

Sounds like you're using the existing fittings. What size of openings do you have? My existing dip tubes are only 3/4". One of the 500 gal does not have a drain either. I was going to make a second dip tube on that one using an existing 1 inch opening on the top. What size black iron or copper did you run to connect with boiler? Obviously, larger openings and larger pipe will result in slower moving water and less turbulence. I don't plan on doing any welding on my tanks unless I have problems.

I'm looking at using the bottom 1 1/4" drain and 3/4" diptube for cool return on one tank and a top 1 1/4" and 1" for hot water entry. This will leave one 3/4" port for a sensor pipe. The other tank will have the 1" (new) and 3/4" existing dip tubes and a 1 1/4" hot water top entry. This will also leave me a 3/4" port for a sensor pipe. The second tank will probably see faster moving water but if I manifold them together and tee off evenly between the 2 tanks I'm hoping they see equal amounts of water. I should be able to put the pressure relief valve right inline on the hot water manifold. It may even be worth putting a valve to balance the flows the 2 tanks see since I should be able to get accurate temps from the sensors.

Be sure to tell us your results with full insulation. I think I'm leaning toward the small round disk (inverted table) welded to inside of the nipples to set a couple inches down from the top of the tank.

 

[sparke]

I am using the 2.5" original openings in the tank that have been reduced to 1". The feed and return from the boiler is 1" as is the dip tube... I am insulating today so i will have new results soon.

 

[jebatty]

When I had my tank set up similarly (supply to top, return from diptube), I made an "L" fitting into the supply, so that hot water would flow horizontally along the top of the tank and away from the diptube return; thus the supply would not flow vertically into the tank. This resulted in good stratification.

 

[sparke]

Update: The temp gauge in the top of the tank is not accurate. Yesterday I charged the tank. The gauge read 170* but the return temps were over 200*. I stopped charging because the psi in the system were getting close to 30psi. (my expansion tank is on the small side. Amtrol -160- 46 gallon acceptance volume) This morning I decided to draw off the tank. I turned on a heating zone and went to check the tank. The top temp gauge was still reading 170* BUT I was very happy to see the actual supply temp coming out of the tank was 190*(temp gauge in supply piping). So my temp gauge (top tank) is either in a place where the water is cooler for some reason (on very end of tank by dip tube). I think the dip tube is causing the water in that vertical column to be cooler. Anyway the system seems to be working right. However if i get the chance, I will put in some diffusers or at least some 90* fittings as suggested. P.S. I edited this post and asked jebatty for some info which you will see below.

 

[sparke]

EDIT

 

[jebatty]

Jebatty - you said somewhere your tank is 20’ long? What diameter is it? It should be about 3’ if I am doing the math right…Also Jebatty can you link me to the thread that discusses what you used for temp readings? I think I remember you are using surface mounted thermocouples? What device shows the temp readings? Money is very tight for me this year so I need to figure out a way to get more accurate tank temps. For now I can charge based on return temps and psi.

3' diameter, correct. A couple of ways to go that are fairly "inexpensive." First, for monitoring only and not data logging, you can use digital panel meters. I use (broken link removed to http://cgi.ebay.com/Car-Meter-Thermometer-Digital-LED-Two-External-DS18B20-/350411107300?pt=LH_DefaultDomain_0&hash=item5196212be4), with two external sensors, and can set the meter to alternate between the two readings, or just set up to show one reading. For monitoring only, I have 7 of these, single temp reading only: 1/3 of the way down from top of tank, 2/3 of the way down, and bottom of tank; boiler supply; boiler return (after the Termovar), radiant supply, and radiant return. The meters come with sensors. Total cost of the 7 is about $85. I then also have a K-type panel meter to read the internal stack temp, about another $15.

Second, to monitor and data log, both done on a Win-PC computer, I use the (broken link removed to http://cgi.ebay.com/1-wire-miniLAN-thermometer-/320613214019?pt=LH_DefaultDomain_0&hash=item4aa6096743). The cost for this and 16 sensors is about $150. Additional wired sensors are about $6 each, which I recommend, because to buy the DS18B20's separately (which I have done), wire them up, time involved, etc., the pre-wired are a good price. You also can add more sensors as you may want to monitor/data log other points in your system.

Neither of the above control my system, they just monitor or monitor/log.

I think the key to good charging/stratification, as others have suggested, is large ports and slow flow, charge at top and return from bottom. I do both of these at one end of my tank, with both ports horizontal, top port outlet extends 18" into the tank, bottom port is flush with the tank, ports 6" down from top and 6" up from bottom (hard to weld in ports if they are closer to top or bottom due to curvature of the tank). As my prior posts show, stratification is excellent.

 

[sparke]

Woops, I didn't mean to delete both posts. However, I had made a mistake. When the temps were 140* it was because the system had switched over to the wood boiler. Because of the large thermal mass in the wood boiler the temps creep up to 180 or higher even after the fire has been out for 8 hours or more... My system switches over to utilize that heat and I happened to check the tank while it had switched over. Not realizing the system had switched over I though the tank reading was 140*. Luckily I realized it before I tore everything apart : )

jebatty thanks for the info!