heat physics

Re: heat physics

PostBy: joeq On: Fri Jan 24, 2014 7:38 pm

Man, I think I've created a monster! :lol: So much to read, and every response has something interesting .
One that is sticking in my mind, is from Lee. You stated that if 2 identical stoves had the exact same conditions, (-.04 draft) one with a baro and one with a fully closed MPD, they'ld both be emitting the same amount/volume of gases. I'm not understanding. I do understand the closed MPD still allows air to pass, but with such a restriction, how could it possibly be equal? In volume? Unless you tell me the garden hose theory, where when you cover the end with your thumb, the water goes further in distance. (Pressure and velocity vary inversely... Bernoulli s theory, I think).
I kinda can relate to Kevins analogy of the potato in the tail pipe. I know a clogged converter will kill power, but not sure of the heating of the exhaust tho. Never experienced that. but if this is true, it would put a notch in the cane for the closed MPD theory.
I do know after the last few days of "cold", I can get the stove to 500* by blocking the baro opening, and putting the MPD at a 45* angle. My draft goes to -.06, and I've also opened my primary air damper a notch. Trying to hone in on the perfect combo.
Someone asked me a few pages back, (sorry, I forgot who), "why don't you just adjust your baro from -.04 to -.06?" Because of the setting on the weight of this "WC Frittos(?)" baro is very sensitive to movement, and it's finally set perfectly to -.04, which is where it runs good for long burns on low heat, I don't want to mess with it, if I can help it. It's just easier to block it, when more heat is needed. If I had a bigger stove, I probably wouldn't be asking all this. But hey!, it gives us something to chat about. Right? Would you rather be outside, shoveling snow? Cleaning your garage? Doing homework? ;)
joeq
 
Hand Fed Coal Stove: Surdiac Gotha 513
Stove/Furnace Make: Oil fired
Stove/Furnace Model: Thermopride

Re: heat physics

PostBy: Lightning On: Fri Jan 24, 2014 8:06 pm

joeq wrote:You stated that if 2 identical stoves had the exact same conditions, (-.04 draft) one with a baro and one with a fully closed MPD, they'ld both be emitting the same amount/volume of gases. I'm not understanding. I do understand the closed MPD still allows air to pass, but with such a restriction, how could it possibly be equal? In volume?
This example is for a relatively air tight stove. Focus on how much air is coming thru the primary combustion air opening for minute. For a higher volume of flue gases to exit the stove, what would need to happen at the primary air opening? Answer, more air would need to come thru it. Then ask yourself, how can more air volume come thru the primary air opening? Only two ways.. We can open it more OR we can increase the negative pressure in the fire box.. What I'm getting at is that the volume of gases leaving the stove are dictated by the volume of air that is entering the stove. The volume of air that's entering the stove is dictated by the stove's negative pressure. They are all tied together, so it doesn't matter what device you use to maintain the -.04 in the firebox. :D

joeq wrote:Would you rather be outside, shoveling snow? Cleaning your garage? Doing homework?
No way!!
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut Size / White Ash

Re: heat physics

PostBy: KLook On: Fri Jan 24, 2014 8:34 pm

If you wanted more heat and the baro is set for the correct draft, all you had to do is open the damn MPD all the way up and increase the AIR in! More air means more oxidation of the carbon and more heat! Yes, your flue temp may rise some, but you can't get something for nothing! As a percentage of heat loss, up the chimney, it is probably not different then the lower setting.

Kevin

What do you think us boiler guys do??? We push more coal and turn up the air. We dont mess with our baro's or MPD's! And first of all we push more coal before we turn up the air.
KLook
 
Stoker Coal Boiler: Harman VF 3000
Coal Size/Type: rice, bagged, Blaschak
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Re: heat physics

PostBy: joeq On: Fri Jan 24, 2014 11:49 pm

Lightning wrote: What I'm getting at is that the volume of gases leaving the stove are dictated by the volume of air that is entering the stove. The volume of air that's entering the stove is dictated by the stove's negative pressure. They are all tied together, so it doesn't matter what device you use to maintain the -.04 in the firebox. :D


You are persistent Lee. :) But you aren't answering the question. Your explanation above is correct when talking about looking for increased volume. What I'm asking is if both stoves have the same primary air opening, and both are up to temp with a strong flow maintaining an -.04 draft, and then on one stove, you "slam" the MPD shut, wouldn't it have to slowdown and restrict the airflow from that stove? Strictly speaking "volume" of heated air.

]
KLook wrote:If you wanted more heat and the baro is set for the correct draft, all you had to do is open the damn MPD all the way up and increase the AIR in!.
[/quote]

That's what I'm saying Kevin. When I open the MPD all the way, the draft doesn't increase with the baro unblocked, because it maintains the -.04. When I block the baro, and "then" open the MPD 100%, the draft will go up a few points, but it still doesn't increase stove temp much if any. "BUT", by closing the MPD down to about 45*, it seems to burn hotter. Especially now that my primary air is also opened more. tonite I've got it up to almost 600*. but it seems it won't hold it very long, if I don't riddle and rake a tad.
joeq
 
Hand Fed Coal Stove: Surdiac Gotha 513
Stove/Furnace Make: Oil fired
Stove/Furnace Model: Thermopride

Re: heat physics

PostBy: Lightning On: Sat Jan 25, 2014 4:31 am

joeq wrote:What I'm asking is if both stoves have the same primary air opening, and both are up to temp with a strong flow maintaining an -.04 draft, and then on one stove, you "slam" the MPD shut, wouldn't it have to slowdown and restrict the airflow from that stove? Strictly speaking "volume" of heated air.
Well yeah but then the mano reading will fall.. The same thing would happen if you prop open the baro door.. The mano reading would fall.. :? In both cases less volume will leave the stove...

joeq wrote:Especially now that my primary air is also opened more.
Here's why its burning hotter.. :D It's hard to keep conditions in the fire bed constant to compare one burn cycle to the next just because of variable ash clearing , coal sizing and possibly fines.
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut Size / White Ash

Re: heat physics

PostBy: J F Graham On: Sat Jan 25, 2014 11:10 am

Guys, Just wanted to chime in with my latest observations. Being such a long time wood burner, and this being my first season with coal, making the transition has been somewhat trying. somewhat like " teaching an old dog new tricks". But thanks to this web site I'm doing ok now. However, after many hours of observation, and especially today, I will be adding a baro. I have to admit
trying to control the draft with a MPD on days like today is virtually impossible. At least for me. With the main draft closed, the idle draft closed the MPD Closed the mano bounces from .03 to .12. Just from an economic standpoint it makes sense. Seems the older I get the tougher it is to accept change. Congrats " baro boys" you converted a MPD man. :D
J F Graham
 
Hand Fed Coal Boiler: harman sf 160
Coal Size/Type: nut
Other Heating: Pacific Energy woodstove

Re: heat physics

PostBy: KLook On: Sat Jan 25, 2014 11:16 am

Guys, Just wanted to chime in with my latest observations. Being such a long time wood burner, and this being my first season with coal, making the transition has been somewhat trying. somewhat like " teaching an old dog new tricks". But thanks to this web site I'm doing ok now. However, after many hours of observation, and especially today, I will be adding a baro. I have to admit
trying to control the draft with a MPD on days like today is virtually impossible. At least for me. With the main draft closed, the idle draft closed the MPD Closed the mano bounces from .03 to .12. Just from an economic standpoint it makes sense. Seems the older I get the tougher it is to accept change. Congrats " baro boys" you converted a MPD man. :D


And we have a winner!! :idea: :D Congrats on that and you will be very happy! Just sit back and let a simple genius invention make it work for you. :punk:

Kevin
KLook
 
Stoker Coal Boiler: Harman VF 3000
Coal Size/Type: rice, bagged, Blaschak
Stove/Furnace Make: Harman (Back In Maine)
Stove/Furnace Model: VF 3000

Re: heat physics

PostBy: joeq On: Sat Jan 25, 2014 12:20 pm

Lightning wrote: Well yeah but then the mano reading will fall.. The same thing would happen if you prop open the baro door.. The mano reading would fall.. :? In both cases less volume will leave the stove...


You are right Lee, in that propping open the baro door, the draft will drop. But remember, on my installation, when the stove is clean and running fine, even with my MPD shut, ("AND NO BARO") my draft won't fall below -.06-.07. With the baro installed, (behind the MPD), it doesn't matter if the MPD is open or closed, the draft remains at the baro setting of -.04. Capiche? :)
I don't want you guys to get the wrong impression that I'm getting discouraged. I've learned alot from all your responses. Sometimes my replies may be misleading. Probably some of you have become bored and dropped out. Can't say I'ld blame you. I guess I'm a little hard headed. So because I'm simple minded, I'ld like to try something and just ask this question, and see if anyone can answer honestly and confidently, with a simple "true" or "false" answer. Here's the question.
"In a perfect world", where all outside variables remain "exactly" the same, 2 stoves "exactly" the same, connected to 2 chimneys, (same), both incorporating a baro and an MPD. Both stoves running and at normal temps. If one stove has its MPD suddenly closed, in a nominal amount of time, the stove temperature will rise, in this stove. True or false?
Now some of you will think, "Well you moron, why don't you just try it yourself?" I have tried, but can't come up with anything conclusive. Tough to keep all the variables from influencing the readings. Mostly the time factor, of the ash collecting thru the grates, but also the outside air changing. But when the stove is clean, the effect is inconsistent. Last nite, I did as someone recommended, and did move the weighted draft door adjustment, and brought it to -.05-06. Naturally the stove did get hotter, and this morning when I woke up, the stove was still running OK. Of course the hopper was a little less full, but that's to be expected. Anyway, still playing, and thanx for alls input. Joe
joeq
 
Hand Fed Coal Stove: Surdiac Gotha 513
Stove/Furnace Make: Oil fired
Stove/Furnace Model: Thermopride

Re: heat physics

PostBy: Lightning On: Sat Jan 25, 2014 12:36 pm

In a leaky unsealed stove maybe. In an air tight fire box that would be false. That's based on my observations and knowledge of what should happen when negative pressure in the fire box is reduced. Meaning weakened.
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut Size / White Ash

Re: heat physics

PostBy: Lightning On: Sat Jan 25, 2014 12:54 pm

I understand that at first glance it doesn't make sound reason. But when you look at the things you can't see, it will all come together my friend. :D
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut Size / White Ash

Re: heat physics

PostBy: KLook On: Sat Jan 25, 2014 1:32 pm

I believe I was the one that indicated you might see a small temporary spike in temps when you close the MPD down. Lighting has indicated that he has not observed this and he uses a IR temp gun to check for temperatures. I cannot see how a system that uses air for fuel can put out more heat when it is choked from either end. It is like coming up with a carburetor that gets 100mpg. :roll:
It seems there might be a momentary spike as the hot fuel bed cannot escape out the flue, but it must be only momentary or he would see it. As an old wood burner, I never thought the mpd was for keeping heat in but slowing the fire down and making it last and not overheating a chimney that might catch on fire. I know this flies in the face of good efficiency with wood as it needs to burn hot and fast. Hence, many old houses had bad chimney fires. Small fireboxes and long burn times don't mix well.
Kevin
KLook
 
Stoker Coal Boiler: Harman VF 3000
Coal Size/Type: rice, bagged, Blaschak
Stove/Furnace Make: Harman (Back In Maine)
Stove/Furnace Model: VF 3000

Re: heat physics

PostBy: joeq On: Sat Jan 25, 2014 6:00 pm

OK guys, I'm having a brain fart right now, and am going to say I can almost understand, looking at it from another perspective. If someone has already explained this previously, I apologize for not recognizing you.
In the above scenario, the burning coals are producing a certain amount of ...power, heat, pressure. Whatever we want to label it. If the combustion pressures are equal in both stoves, but one of the stoves shuts the MPD, yet the draft is remaining constant, (because of the baro), the exhaust will now try to "accelerate" through the smaller opening of the closed MPD because of the consistent pressure from the coal bed. Which "should " provide a stronger draft. However, the weighted baro door is adjusted to a preset flow, and in order to maintain that draft, the baro door will have to open more to reduce the excessive flow. Therefore, the "amount" of exhaust exiting the chimney pipe will be equal, it's just that the air needed to maintain the draft in the closed system, will be entering "also" from the baro door opening, rather than more from the open MPD.
It sounded good at 1st, but now as I read it, I think I'm backwards, in thinking the "accelerated" exhaust through the closed MPD will try and "open" the baro door. When I close the MPD, the baro door should close to compensate. (I'm so confused) :bang: I need Fred here to tell me I'm overthinking this, and to chill out.
At least we've got a temporary weather break here, as the temps "skyrocketed" up to 32*. So the little 513 is is breathing a little easier. I hear it won't be for long tho.
joeq
 
Hand Fed Coal Stove: Surdiac Gotha 513
Stove/Furnace Make: Oil fired
Stove/Furnace Model: Thermopride

Re: heat physics

PostBy: joeq On: Sat Jan 25, 2014 6:06 pm

KLook wrote: It is like coming up with a carburetor that gets 100mpg. :roll:


Hey Kevin, what if we pulled the 4 cyl. out of a Vega, mounted it on a 75lb go-cart frame, and idled it downhill for a hundred miles. Do you think that Rochester Monojet could idle it's way through a mere gallon of gas? :)
joeq
 
Hand Fed Coal Stove: Surdiac Gotha 513
Stove/Furnace Make: Oil fired
Stove/Furnace Model: Thermopride

Re: heat physics

PostBy: Lightning On: Sat Jan 25, 2014 8:27 pm

I really want to help you understand this partner but I'm having trouble sorting out your scenario a little plus I've had 3 vodka and 7's, 1 beer and 2 lime a ritas.. :shots: So lets dissect this mess hahaha..

joeq wrote:In the above scenario, the burning coals are producing a certain amount of ...power, heat, pressure. Whatever we want to label it.
Lets label it heat.

joeq wrote:If the combustion pressures are equal in both stoves, but one of the stoves shuts the MPD, yet the draft is remaining constant, (because of the baro),
So there is a baro AND MPD on the second stove?? :? And why would the draft remain constant, you mean the negative pressure will remain constant? I don't see how it could.. That would imply the MPD is doing nothing.. Its gotta do something..

joeq wrote:consistent pressure from the coal bed.
The chimney causes the negative pressure, not the coal bed.. The coal bed makes the heat, the chimney causes negative pressure to form from the heat rising out the chimney.. :)

joeq wrote:When I close the MPD, the baro door should close to compensate. (I'm so confused)
You have the baro after the MPD correct? Heres the dilemma.. Too many things going on at once :lol: Look at it this way... the baro is limiting the draft strength of the chimney, then the MPD is restricting it further to attain the -.04 you like to keep.. I have mine set up the other way but this is considered a reckless arrangement since having a blockage (MPD) above the baro could (in theory) promote flue gases to leak out the baro under the right conditions.. Truth is, during times of excessive draft, I'll tweak my MPD so the baro will do its job better.. I don't recommend this arrangement though.. It's potentially dangerous I guess. I only use the MPD when I need to. The better arrangement is an over sized baro which I plan to do for next year.


It's 14 degreees outside and windy, me and wife and her girl friend are gonna go get in the outdoor hot tub now.. :woot:

Coal heated hot tub, that is hahahhaha
Last edited by Lightning on Sat Jan 25, 2014 10:18 pm, edited 1 time in total.
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut Size / White Ash

Re: heat physics

PostBy: Hambden Bob On: Sat Jan 25, 2014 10:12 pm

joeq wrote:Figured this title would bring in all the Sheldon Cooper fans. (Big bang theory).
Was curious about the theory or opinions on this. Concerning draft and/or rising heat out of our stoves. The more air flowing through the coal bed, usually dictates the intensity of the fire. More air equals more heat. (Providing enuff fuel to support it). Air in usually also requires air out. I've been skooled here that, if we close down our MPD, then more heat will be retained into the stove. (Makes sense to me). However, if closing the MPD slows down the draft, then the stove can't produce the required amount of heat to build the fire. I'm wondering about which phenomenon has a larger potential for heat output. Close down the MPD, to retain heat, but lose the higher draft, or open the MPD for a higher draft, but send the hot air up the chimney? Which is the preferable method? :gee:


Well,being I'm a Combination of an Aspiring Alzheimers' Patient/Concentration Deprivation Candidate,and just a General Mental Trainwreck,Look Out,here's my take..... The Fuel dictates the Flow Method of Control. The Stove Design and Total Thermal Mass available to radiate outward allows the heat produced to leave the unit,thereby getting the most productive heat output from the stove without sending heat up the flue. Baseburners come to mind.Keep in mind that the MPD and Baro are tools of Flow Control. Their Complimentary Tools are your Combustion Air Inlet Controls. If the Stove has been constructed and maintained as an Air Tight,Theoretically those Control Tools are the only way to conduct flow. So the preferable method is no single method is ultimately correct. Sorry to do it to you,but the MPD has carried the day forever. It went as far as it could. It seems to me that the Baro was developed to compensate for Windy,Gusty Days trying to suck or draft the Living Daylights out of the Stove and its Fuel Supply. The Stove lacked the ability to Control Combustion Air due to the Higher Vacuum trying to pull through the Stove.....I love definite situations,but this one seems to be an Eternal Grey Area. In closing,I'm so full of crap that my eyes are brown! :bang:
Hambden Bob
 
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