Quad Castile Experiment Revisited

[tjnamtiw]

A while back I had a thread that outlined my efforts and those of some of you guys in trying to wring more heat out of our Quadrafire Castiles, Sante Fe's, and 1200's. For a background on what we did and the results > https://www.hearth.com/talk/threads/64123/

Skidozer emailed me that he had found some of the turbulator material and offered me some pieces already cut to length with a cross piece on it to keep it from going down in the heat exchanger tubes if I would experiment with them. Of course, being the tinkerer that I am, I accepted. Today I got around to running another experiment in four parts. First of all, I removed my springs from the tubes and set my running conditions, which were a medium feed rate and high convection blower speed. The blower speed stays on high no matter what the feed rate now that I did the B-Mod modification. I have the feed rate adjusted so that the flame is just barely, on average, coming out of the burn pot. Sometimes there is very little flame and other times it may reach up to a max of about 4". I'm mainly heating a 400 sq ft family room with this one so I don't need a lot of heat.

I let the stove reach steady state and took temperature readings in the CENTER of each tube. I also used a Dwyer wind velocity meter to measure air exit speed. This second part is rather sketchy and not all that scientific but better than nothing as long as I can duplicate the instrument's position in front of each tube. In some instances with the turbulators in place, it was difficult to get a good reading so I went for the highest reading I could get. The turbulators also probably swirled the air making it more difficult to measure but the swirling is what we want to gather more heat.

Next I put just the turbulators in all 10 holes, let it get to steady state and measured again. Then I put the springs in place in tubes 2-9 (only have 8 of them) and measured. Finally I put the turbulators and springs together into the tubes. From the attached chart you can see the resulting temperatures and speeds. You can see that the springs increased the speed quite a bit probably due to some restriction as well as the buffeting/swirling they impart to the airflow. You can also see that the addition of the turbulators SIGNIFICANTLY increased the output temperature while not causing any real increase in air speed, which to me means more heat is being extracted. I am also attaching pictures of the turbulators and both the springs and turbulators installed. Enjoy! I'm enjoying the heat. By the time I was done with all the swapping, the room was at 78 degrees!

 

[DexterDay]

WOW.. You get more wind spped to further push the air and a higher convection temp.. I kept visiting your last thread when it was "fresh" and was wondering what the outcome was gonna be. I get by on Low heat, High fan on my 1200. But if there was a way i could back my feed plate down even more, that would be awesome.. Good job and Congrats on that Modification.. I want me some tubulators now! < jealous >

 

[tjnamtiw]

Thanks. More wind speed MIGHT just mean that the line is restricted somewhat but there was a definite improvement in heat output with the turbulators. The things I didn't check yet were the exhaust temperature with and without the inserts and, as someone suggested in another thread, the current draw on the convection fan with and without. In the first experiments, my exhaust temp went down indicating that more heat was being extracted by the heat exchanger. I suspect that there should be even more of a dramatic decrease in exhaust temp meaning higher efficiency. I hope so.

I wish I had some way to actually measure the CFM out of each tube.

 

[Countryboymo]

I wish I could come up with some turbulators. They would have to make a huge difference. If someone gets them available I am interested just shoot me a price. I can do the welding if needed.

 

[tjnamtiw]

I found this source but have no idea what costs would be. (broken link removed to http://www.fuelefficiencyllc.com/products/lit_TwistedTapeAngularTurbulators.pdf)

If you were doing it without the springs, you would (in most cases ) need 1" width tape. Getting one inch flat stock, clamping on end in a vise, and twisting the other end with pliers or a jig with a handle would also be possible.

 

[Czech]

Wow, excellent work. I love this stuff. Thanks for doing the homework t, I was hoping you were busy at it. Now that the data supports the mod, I'm off to look for some flat stock. Rather than the cross pieces, do you think a precise measure would end up with one long enough to hit the bend in the back of the tubes and hold it in place? What's the twist on those, looks around 1 in 12" or so? Thanks again for sharing.

 

[tjnamtiw]

Wow, excellent work. I love this stuff. Thanks for doing the homework t, I was hoping you were busy at it. Now that the data supports the mod, I'm off to look for some flat stock. Rather than the cross pieces, do you think a precise measure would end up with one long enough to hit the bend in the back of the tubes and hold it in place? What's the twist on those, looks around 1 in 12" or so? Thanks again for sharing.

Hey Czech,

There is no turn in my tubes. The go straight back to a vertical wall. There's a small gap between the wall and the end of the tube. I was looking at it last night and shaking my head. There is NOTHING streamlined about the flow path You'll have to put some kind of stop at the end like skidozer did for me.

It looks like about 1 turn in 2 3/4" and they are 10 1/2" long. They are 1/16" flat stock, which might be a little tough to twist. Since they are there to promote swirling rather than direct heat transfer, I wouldn't see why around 20 gauge or even 24 wouldn't work just as well.

 

[Czech]

And here I was thinking the tubes angled down all this time? So it's just open wall down to the fans? So the turbs are not snug, wonder if they were if you'd get some transfer too. Either way the data shows a significant change that I don't think can be ignored, the only other varible is if it is related to an actual volume issue air wise, not velocity. I know they are related, smaller faster and bigger slower can equal the same volume as you already know (the Weatherby principle!). Just thinking out loud here. One other big area that these stoves miss out on is the gap on the sides between the housing and the firebox, some serious heat there that could be moved better. I've putzed with a couple PC fans with good results (I think anyway, never measured), if I could figure a way to wire these to the other fan circuit that'd be good (AC vs. DC?). I'll play with some stock maybe this weekend, thinking a vice and 2-3 foot jig should do it for the twist! Thanks again for the work and sharing.

 

[tjnamtiw]

You're more than welcome, Czech. Yea, there has got to be a lot of wasted heat on the sides of the heat box. When I put my inspection scope down there in holes 1 and 10, I can see a small opening but I'm not sure if that is from the double side walls and if it is, is it being fed some air from the fans? Don't know.... They sure didn't put much thought into the whole heat exchange thing. That back vertical wall could be crimped or corrugated to present more surface area at the very least.

 

[skidozer]

Nice Job I wonder if some temp measurements around the room would be usefull. Like in the corners of the room.
I noticed my room was warmer directly across from stove now.

I should ask the guru at work about them touching the walls of the tubes. But I remember when I built the project the turbulators were used in they were not tight to walls. I would think they would help heat transfer anyway as the industrial heat exchanger I built was all CFD computer model analyzed by the PE at work.

We weekly wind tunnel test all of our heat transfer surface but I cant give any info on that.

 

[tjnamtiw]

Wow, that sounds like interesting work! I'm sure glad you gave me that set and there's no doubt in my mind and my measurements that they really improved the heat transfer when combined with the springs. I measured the exhaust stack temps with some skepticism since the flame goes up and down quite a bit. I tried to hit it with the same flame conditions but it's tough. I saw a 15 to 20 degree DROP in stack temperature! 140 versus 120-5. The max with nothing was 170 and with everything 150. That sure points to better efficiency. I noticed that even on medium feed, it is not staying on very long. I am going to go down to low feed on it. The Sante Fe has to heat the rest of the house and has a harder job so I may move the turbulators over there. With the grill in front of the tubes, I'm not sure they will clear it. May have to space it out some but don't tell the 'Boss'.....

 

[Turbo-Quad]

I just have a thought and I'm just thinking out loud here .....if you are putting things in the tubes could that be restricting air flow? If it is restricting air flow then wouldn't that make the air that is making it through hotter since it is moving across the tubes slower? In other words isn't it the same as building a bigger flame and turning the fan down low? Again I'm just thinking out loud here and not trying to discredit what you are doing, just looking at it from a different angle.

 

[skidozer]

No not really. You are mixing the air up so it is dispersing through out the room better.
The extra surrface area of the turbulator is giving better heat transfer to put more hot air out to the room.
I would say its more like turning the fan up because you are putting more hot air into the room.
I have not used any extra fuel.

When you add a heat exchanger to a coal fired power plant boiler it saves 32 rail car loads of coal per day and the lower stack output temp helps with emmision outputs.

 

[checkthisout]

Out of curiosity, does your stove automatically adjust the combustion blower speed up and down based on certain passive inputs such as temperature sensors on the heat exchanger or in the exhaust?

 

[tjnamtiw]

Out of curiosity, does your stove automatically adjust the combustion blower speed up and down based on certain passive inputs such as temperature sensors on the heat exchanger or in the exhaust?

No, these stoves aren't that sophisticated. They are designed to have 3 different combustion and convection blower speeds for the three heat settings. That's it as far as technology goes! In my case, I have changed mine so that I always have the convection blower on high.

To turbo-quad, Skidozer is the expert in heat exchangers and I've been the guinea pig for testing things. As to the air flow slowing down with restriction in the tubes, actually with the same blower speed and a smaller tube (effective), the air flow speeds UP. Think of trying to force the same amount of air through a smaller hole like closing down on the nozzle of your garden hose. The stream gets faster. So for the speed to go up AND the temperature to go up indicates that we are getting more heat out of the stove. That is confirmed by seeing the flue temperature go down 15-20 degrees.

The springs and the turbulators do two things. The springs, because they fit tightly in the tubes, transfer heat from the tubes and present more surface area to the airstream. Also they help to break up the laminar flow of the air which always leaves a stagnant layer of air next to the tube wall which acts as an insulator. The turbulators, with or without the springs get the air spiraling and breaking up the laminar flow. Together they appear to be a match made in heaven.

 

[Turbo-Quad]

Now that you put it that way it makes sense to me. That's a nice gain.

 

[tjnamtiw]

Now that you put it that way it makes sense to me. That's a nice gain.

Great You're next

 

[checkthisout]

Out of curiosity, does your stove automatically adjust the combustion blower speed up and down based on certain passive inputs such as temperature sensors on the heat exchanger or in the exhaust?

No, these stoves aren't that sophisticated. They are designed to have 3 different combustion and convection blower speeds for the three heat settings. That's it as far as technology goes! In my case, I have changed mine so that I always have the convection blower on high.

To turbo-quad, Skidozer is the expert in heat exchangers and I've been the guinea pig for testing things. As to the air flow slowing down with restriction in the tubes, actually with the same blower speed and a smaller tube (effective), the air flow speeds UP. Think of trying to force the same amount of air through a smaller hole like closing down on the nozzle of your garden hose. The stream gets faster. So for the speed to go up AND the temperature to go up indicates that we are getting more heat out of the stove. That is confirmed by seeing the flue temperature go down 15-20 degrees.

The springs and the turbulators do two things. The springs, because they fit tightly in the tubes, transfer heat from the tubes and present more surface area to the airstream. Also they help to break up the laminar flow of the air which always leaves a stagnant layer of air next to the tube wall which acts as an insulator. The turbulators, with or without the springs get the air spiraling and breaking up the laminar flow. Together they appear to be a match made in heaven.

If heat transfer is more efficient, airflow should always speed up.

 

[tjnamtiw]

If heat transfer is more efficient, airflow should always speed up.

I'm not totally sure what you mean but it's kind of a chicken/egg dilemma. If you speed up airflow, you induce turbulent flow and get better heat transfer. If you have good efficient heat transfer, then you want to move that hot air out so new, cooler air can be introduced for more heat transfer. In blow molding, we always had a rule of thumb that you got the best uniform heat transfer if you had a delta-T of 3 degrees across the mold. You designed/adjusted the flow rate to achieve that.

I forgot to add in my other post that one other 'plus' for the slight restriction in the tubes was that more air was forced to flow through the outer tubes where, before, very little air flowed and there was little contribution to the overall heat transfer.

 

[Czech]

Now that you put it that way it makes sense to me. That's a nice gain.

Great You're next

I wanted to be next darn it! My stove area looks like Jay's from this weekend, been testing pellets and have jars full of ash all over. Toss in some springs and stuff and all will be perfect. All those posts about installing in a basement, and no one ever mentions "because I'm a mad scientist and have stuff all over" to the list to justify having the stove downstairs rather than in the livingroom.

 

[SmokeyTheBear]

Now that you put it that way it makes sense to me. That's a nice gain.

Great You're next

I wanted to be next darn it! My stove area looks like Jay's from this weekend, been testing pellets and have jars full of ash all over. Toss in some springs and stuff and all will be perfect. All those posts about installing in a basement, and no one ever mentions "because I'm a mad scientist and have stuff all over" to the list to justify having the stove downstairs rather than in the livingroom.

Step right up Czech,

Your assignment should you choose to accept it is to install a larger convection blower on your stove. I understand that the cooler you can keep that side of the heat exchanger the more heat you can extract from the fire.

Now let's not go overboard and find a 3000 CFM blower because likely your stove would toss its electrical cookies trying to run that thing.

Remember doing modifications likely voids your warranty and invalidates all certifications.

I have an ulterior motive here so best I disclose it now, I'm going to be replacing my convection with a larger flow one before the season ends. So I need a lab rat to test the theory.

Then another person can pull everything together in sort of an ultimate test.

 

[tjnamtiw]

I saw a used air boat on Craig's List. Take the motor/fan off of that and you'll have all the air flow you need! Just exhaust that 427 outside!

 

[SmokeyTheBear]

I saw a used air boat on Craig's List. Take the motor/fan off of that and you'll have all the air flow you need! Just exhaust that 427 outside!

Ah, thank you for locating my next snowblower engine and the combustion fan for Jackson Labs new pellet boiler.

 

[Czech]

You guys help with the electrical part of it, I'm in. I want to channel that air flow around the sides too. If you're nice, I'll tell you how I modified the door and airwash so I can use standard 3/4" gasket rather the $60 tadpole. Warranty, dough nee no stinkin warranty!

 

[SmokeyTheBear]

You guys help with the electrical part of it, I'm in. I want to channel that air flow around the sides too. If you're nice, I'll tell you how I modified the door and airwash so I can use standard 3/4" gasket rather the $60 tadpole. Warranty, dough nee no stinkin warranty!

Damn, I thought we hid your grinders.