Thermoelectric Power

[Biggkidd]

This is going to sound crazy but it looks like I can tune the thermostat with the pipe cap. I know it lifts about 245-255 without the cap. With the cap on just enough to stay put and still come apart easy it went up to about 315 and lifted so I pushed the cap down about a 1/4 inch and now it lifts about 290. I'm going to leave it there until I see how it acts once installed. I can still probably push it down close to another 1/2 inch if needed. I'm guessing this is working do to it cooling with more or less copper exposed or more or less cooling area taking heat away through the cap and pipe.

 

[Biggkidd]

It's obviously been far to long since I've done any metal working shop projects. Today was mostly a bust on account of nothing wanted to work. Air hose ends frozen (not cold) compressor & generator didn't want to run. Plasma cutter had dirt dobber's nests in the fittings and one of the airlines on it was cracked. Just not my day to accomplish anything I guess. Plus had a no delivery delivery in other words the post office web said it was delivered but it wasn't in the box. To top it all off my back is forked!!!!!!!!

I was cussing a blue streak when full dark hit because after f-ing around all day I had finally gotten to make a couple cuts and was starting to make a little progress. I have got to do something about making a shop space with light and heat! If I had such a place I'd still be busy right now intense pain or not.

 

[Biggkidd]

Guys I'm caught between I do and I don't. On one hand I want to build a smaller prototype. On the other hand I just want to build the unit I plan to use. What would you do? Remember I only have so much energy and even less money. One plus side to a prototype would be a smaller more "portable" unit. In other words 3 or 4 men could get a prototype in the back of a pickup truck. The unit I am planning to use might be a bit heavy for my tractor to pick up much less 3 or 4 guys and it'd take a stout 1 ton truck to haul it!

 

[Neb]

I would vote profit of concept.

Ben

 

[Biggkidd]

I would vote profit of concept.

Ben

Yeah that's my thinking too. But double work and money, well maybe not double but you get what I'm saying. I guess I really should since I will also be using an entirely new rocket stove design. Even though the two designs, full size versus prototype are similar in principal they are also quite a bit different from each other. Plus they are both a world away from standard rocket stove design.

This is starting to remind me of when I built my first REAL racing engine. I had previously built several hot engines 400hp was nothing new but I was getting pretty extravagant at the time, early 90's. Even the speed shop I'd been dealing with for years didn't want to order my requested parts in because the numbers didn't work out on paper. They didn't want to place a $6500 order and then for me to bad mouth them saying their junk didn't work. Well I finally got one of the oldtimers who worked there to back me up and they ordered the parts I asked for. When that SBC went over 650 ft lbs torque with 647hp at 6000 rpm suddenly they started stamping copies of my motor out like cookies from a cutter! They also begged me to let them run it up higher on the chassis dyno but I refused to budge past 6200 rpm. We know the dyno numbers were way low since the hp and torque curves hadn't crossed yet. We later found out the motor was making over 800hp at the tires in the higher rpm ranges by doing the math. Weight x speed x time to go 1/4 mile.

That engine saw over 10,000 RPM on several occasions for years after I built it.

 

[Biggkidd]

Well I decided to heed Ben's advice and build a smaller prototype unit first. So I set aside the parts I was working on yesterday and went on another hunt through my scrap trying to find things that required the least modification to make what I wanted. I settled on an old rusty camper frame for some box tube. It isn't sound enough to build any kind of structural stuff with but it should work okay for this. I got a large hunk maybe 15 feet all told cut out and started cutting it in to pieces. I'm only back now to refill my drink and put several tool batteries on to charge and get the one off the charger. I decided to follow the same basic design principals as I had decided on for the full size unit but the ratio's of the chambers are off. It'll still work fine I'm pretty sure but it won't be a true prototype since it's not going to be a scaled version with an apples to apples comparison. It does however fit within the general specs I was shooting for. It will also still be large enough to be useful just on a smaller scale.

 

[Neb]

Well I decided to heed Ben's advice and build a smaller prototype unit first. So I set aside the parts I was working on yesterday and went on another hunt through my scrap trying to find things that required the least modification to make what I wanted. I settled on an old rusty camper frame for some box tube. It isn't sound enough to build any kind of structural stuff with but it should work okay for this. I got a large hunk maybe 15 feet all told cut out and started cutting it in to pieces. I'm only back now to refill my drink and put several tool batteries on to charge and get the one off the charger. I decided to follow the same basic design principals as I had decided on for the full size unit but the ratio's of the chambers are off. It'll still work fine I'm pretty sure but it won't be a true prototype since it's not going to be a scaled version with an apples to apples comparison. It does however fit within the general specs I was shooting for. It will also still be large enough to be useful just on a smaller scale.

Good!

We all learn things the first time we try something that helps the next time.

I used to tell software developers that lost code...

The good news is you will do a better job the second you do it.

Ben

 

[Biggkidd]

Good!

We all learn things the first time we try something that helps the next time.

I used to tell software developers that lost code...

The good news is you will do a better job the second you do it.

Ben

We shall see. Full on dark got here again, oh well today turned out a whole lot better than expected. It rained this morning and showered off and on all day. But after the main rain had passed I loaded up and went to feed the critters and stopped to work as long as I could on the project, which turned out to be the rest of the day. I did get a couple lite showers but I just kept on rocking. lol Man projects take longer when you first have to find and cut materials out of other items before you can use them. lol Just really glad I grab all the useful junk I run across! So far I've only managed to cut one piece to short. haha ha! So it looks like this unit is going to end up being about 12W x 18L x 26T. The rocket stove part is going to be smaller than any I've ever built. I'm trying to size it to try and keep as much of the heat inside as I can. It won't happen on this build but IDEALLY the exhaust gasses would never come out of the chimney more than 100 degrees hotter than the internal temperature of the working medium.

 

[Neb]

We shall see. Full on dark got here again, oh well today turned out a whole lot better than expected. It rained this morning and showered off and on all day. But after the main rain had passed I loaded up and went to feed the critters and stopped to work as long as I could on the project, which turned out to be the rest of the day. I did get a couple lite showers but I just kept on rocking. lol Man projects take longer when you first have to find and cut materials out of other items before you can use them. lol Just really glad I grab all the useful junk I run across! So far I've only managed to cut one piece to short. haha ha! So it looks like this unit is going to end up being about 12W x 18L x 26T. The rocket stove part is going to be smaller than any I've ever built. I'm trying to size it to try and keep as much of the heat inside as I can. It won't happen on this build but IDEALLY the exhaust gasses would never come out of the chimney more than 100 degrees hotter than the internal temperature of the working medium.

Succeed or fail I would love to see some images to help me/us follow along with your adventure.

Ben

 

[Biggkidd]

Succeed or fail I would love to see some images to help me/us follow along with your adventure.

Ben

I honestly do and don't want to post pictures. This is so radically different from any rocket stove design I've ever seen, I don't want to give anyone opportunity to sway me from my intended direction. Mostly I just don't want to hear that won't work you, can't do that, are you crazy, etc. If I fail I promise I will show and tell when I don't fail well I'll think about it . . . . lmao! The electrical part I will get pictures of as soon as I put it all together but again I'm still waiting on a few things. Once the entire project's all together I'll post pics of that too, might even do a video of the very first ever firing. Something tells me it's going to be a moment to remember.

 

[Neb]

I honestly do and don't want to post pictures. This is so radically different from any rocket stove design I've ever seen, I don't want to give anyone opportunity to sway me from my intended direction. Mostly I just don't want to hear that won't work you, can't do that, are you crazy, etc. If I fail I promise I will show and tell when I don't fail well I'll think about it . . . . lmao! The electrical part I will get pictures of as soon as I put it all together but again I'm still waiting on a few things. Once the entire project's all together I'll post pics of that too, might even do a video of the very first ever firing. Something tells me it's going to be a moment to remember.

Oh!
Oh!

A video. Yes please.

Ben

 

[Biggkidd]

Just want to point out the electronics will not be on it for the first few firings. I want to get a feel for how it operates, how long it holds heat, etc. in order to lessen the chance of burning the electronics. Plus I'll probably want to insulate it and put an outer cover over it. For me this will primarily be a power generator even though it'll also be capable of water and space heating as well as cooking.

 

[Biggkidd]

No progress today, didn't even lay eyes on the project. Worn out from yesterday coupled with the wind today was plenty to convince me to stay indoors as much as possible.

 

[Biggkidd]

Got back out this afternoon and got 5 more pieces cut and four more marked up ready to cut for the project. Here soon I need a warm windless day to attempt to weld all these internal parts together. Once that’s done I can start working on the case or shell or whatever you want to call the outer part. haha Still not sure I like this new shrunken redesign but we shall see what it has to teach me.
@Neb Need a little help here I can't figure out which is the better medium to put inside granite gravel or sand I need to know which one holds more heat and moves it the easiest, any way you can figure that out for me? I think maybe I've been seeing to many numbers. lol I was also considering using both sand and gravel, letting the sand fill all the small spaces between the gravel.

 

[Biggkidd]

Uhhh ah I'd still like hear what Ben or anyone who knows more than I do has to say. To me it looks like both of them are fairly close in both heat holding and heat moving capabilities so I'm leaning toward using sand to fill in between the gravel unless someone has a good reason I shouldn't.

 

[Neb]

Uhhh ah I'd still like hear what Ben or anyone who knows more than I do has to say. To me it looks like both of them are fairly close in both heat holding and heat moving capabilities so I'm leaning toward using sand to fill in between the gravel unless someone has a good reason I shouldn't.

Look up the"heat capacity" of the options you have. Water has one of the highest.

Sorry but its movie night dor us.

Ben

 

[Biggkidd]

Yes but that's not necessarily a good thing in this case besides without pressure the boiling point is far to low. Depending on if my lifting method for the module plate works then I'll be able to run sand or gravel up to 5-600f easy and have much more time between firings. Otherwise I'll only be able to heat to about 250-275f MAX and have to fire the generator more often. Water doesn't get hot enough for long enough to produce the output I'm looking for. Plus I really don't want to go to the trouble to try and make every weld water tight. I can not weld anything like I could back when my hands were steady and my eyes could see!

 

[Biggkidd]

Sometimes being lucky is better than being good. Case in point when I ordered aluminum plate to mount all my modules on I ordered 6061 aluminum not knowing at the time that is one of the best alloys to use for heat sinks and thermal transfer.

Rain day today has me stopped from being out working on this project. What a bummer!

 

[Neb]

Yes but that's not necessarily a good thing in this case besides without pressure the boiling point is far to low. Depending on if my lifting method for the module plate works then I'll be able to run sand or gravel up to 5-600f easy and have much more time between firings. Otherwise I'll only be able to heat to about 250-275f MAX and have to fire the generator more often. Water doesn't get hot enough for long enough to produce the output I'm looking for. Plus I really don't want to go to the trouble to try and make every weld water tight. I can not weld anything like I could back when my hands were steady and my eyes could see!

Heat capacity is a property of materials that describes the amount of heat energy per unit mass is required to raise the temp by one degree.

Materials with higher heat capacity store more heat energy.

https://www.google.com/search?q=hea...KABAbABD8gBCMABAQ&sclient=mobile-gws-wiz-serp
https://www.google.com/search?q=hea...pgBAKABAcgBEcABAQ&sclient=mobile-gws-wiz-serp
Ben

 

[Biggkidd]

Not exactly sure what your trying to say here. From what I see sand is 1.3-1.6 and gravel is 1.4-1.6 so pretty darn close to the same. Which is why I was thinking filling between the gravel with sand would be wise. Since it would fill all the voids with more heat holding capacity. What am I missing here?

ETA: my thermostat lifter seems to be breaking contact a little below 290f which is pretty darn good I think. Question is how will it being mounted in the 1/4 in thick aluminum plate affect that.

 

[UrbanHunter]

I hate to complicate this but you are dealing with 2 properties, heat capacity as @Neb so clearly described the ability to absorb heat. But you are also dealing with thermal conductivity which is the ability to carry heat through the material. Fine grain sand can absorb a lot of heat but because of it being an assembly of loose grains it is not a good conductor. The sand close to the stove will get very hot and hold that heat, it will take a long time for that heat to travel more than a few inches.

 

[Neb]

Not exactly sure what your trying to say here. From what I see sand is 1.3-1.6 and gravel is 1.4-1.6 so pretty darn close to the same. Which is why I was thinking filling between the gravel with sand would be wise. Since it would fill all the voids with more heat holding capacity. What am I missing here?

Yup

Filling the voids would increase the total mass and thereby the heat storage capacity.

Ben

 

[Biggkidd]

@Neb added to last

 

[Biggkidd]

I hate to complicate this but you are dealing with 2 properties, heat capacity as @Neb so clearly described the ability to absorb heat. But you are also dealing with thermal conductivity which is the ability to carry heat through the material. Fine grain sand can absorb a lot of heat but because of it being an assembly of loose grains it is not a good conductor. The sand close to the stove will get very hot and hold that heat, it will take a long time for that heat to travel more than a few inches.

That may be the beauty of the thing. The top heat transfer area where the modules will be will be in direct contact with the heated medium so transfer should be nearly instant, or am I thinking backwards?

 

[Biggkidd]

Sure wish I could actually have conversations with you guys. I have no formal education in any of the engineering fields but I always thought I understood the workings of things fairly well at least for a high school drop out.

 

[UrbanHunter]

https://www.ferralloy.com/post/what-is-sand-casting-and-why-is-it-used
Sand is a great material, when it is exposed to hot metal the sand at the surface will heat up quickly and then hold that heat allowing things to cool (solidify) slowly. I don't know how you are planning to use it in your application, if you are using it to hold the heat in around your rocket stove it will do a great job of that and it will help keep the stove walls hot long after the fire has gone out.

I have seen granite slabs added to the sides of stoves to absorb the heat and then release it into the room slowly. The solid granite has better thermal conduction properties and will eventually have a uniform temperature that can be released into the room-- HOT Stove>>II>Room,
The sand will not conduct heat through it's self well, it will act as an insulator -- HOT Stove>>I I: Room -- holding the heat in the stove. There will be a thermal gradient in the sand but the heat will not be transferred as fast.

Think of an earthen pizza oven walls... They are made so the inside heats up when fired, then releases the heat back into the cooking chamber over time, but the outside stay's relatively cool.

 

[Biggkidd]

Did I mention since this particular units primary objective is electrical power production the entire body except the module mounting area will be fully insulated?

What I'm hoping to achieve is a fast clean burning stove that will store high heat and release it as low heat to release power for 12-16 hours minimum. Of course longer would be nice. lol But I'd like to be able to fire this thing up once after the sun goes down and have it supply 200-300 watts all night long. That's why the mass holding and releasing as much heat as possible in the right direction is critical.

 

[Biggkidd]

Off topic

@UrbanHunter or @Neb have either of you had any experience with sterling engines? Throughout this project I keep running up on them and they also have peaked my interest. My main point of curiosity is why everyone seems stuck on using that large moving displacer? I can see so many better options with todays tools and materials.

 

[UrbanHunter]

Did I mention since this particular units primary objective is electrical power production the entire body except the module mounting area will be fully insulated?

What I'm hoping to achieve is a fast clean burning stove that will store high heat and release it as low heat to release power for 12-16 hours minimum. Of course longer would be nice. lol But I'd like to be able to fire this thing up once after the sun goes down and have it supply 200-300 watts all night long. That's why the mass holding and releasing as much heat as possible in the right direction is critical.

In that case if the sand is in contact with the metal walls of the stove, and the thermoelectric modules are in contact with the metal walls (no sand in between them), the sand will heat up as the stove is fired and release it back into the stove walls, the stove walls are metal (Great thermal conductor!), they will transfer that heat to the thermoelectric modules... and the inside of the stove.

 

[Biggkidd]

In that case if the sand is in contact with the metal walls of the stove, and the thermoelectric modules are in contact with the metal walls (no sand in between them), the sand will heat up as the stove is fired and release it back into the stove walls, the stove walls are metal (Great thermal conductor!), they will transfer that heat to the thermoelectric modules... and the inside of the stove.

That's the idea. Using rocket stove type burning for fast high heat storing it in the medium (sand and gravel) to be released slowly over time to power the modules.

This really isn't going to be a rocket stove though it will use many of the principals of one. This is going to be a stove type all it's own from what I can tell so far. In lord only knows how many hours of research I have yet to see anything close to my design. If I can pull off what I'm attempting the exhaust gasses will never be more than 100f higher than the internal temperature of the stove. Probably nothing but wishful thinking on my part. Obtaining 90% + heat transfer inside the unit isn't going to be easy.

In my 8 years running a rocket stove to heat our water I found the temperatures often went over 2000f judging from the whitish sunshine yellow the steel often got to. Seeing the metal go from cold and rusty to slightly glowing dull orange to bright red hot and then yellow to almost white hot in the space of 15-20 minutes always amazed me!