What indicates a better boil/evaporation rate, more steam, or more bubbles in the pan

[bcarpenter]

So this is my first year on a 2x3 Mason Evaporator. Tonight was also my second boil. I am still learning trying to find the happy mediums and what to look for as I boil.

My questions is, what visually indicates a better boil or greater evaporation rate, more steam, or more bubbles in the pan?

Tonight I could not help but notice that when I opened the door to re-load the evaporator, the amount of steam, increased to cover the whole pan, and was billowing off the sides of the pan in a thicker cloud than with the door closed. I have been running the evaporator with a single wall, 6" stack outside, with a 90 and (3) 2'-0" sections high and a rain cap. Temps tonight were in the mid to low 30's. I have been leaving the ash door cracked, but have not noticed differences in the steam with the ash door wide open or cracked?

If I leave the wood door open 3-4" the steam picks up and stays thick while the door is open, but the rapid bubbling slows and my stack temp 2'-0" up from the elbow joint reads approx 400F. When I close the wood loading door again and leave it shut the evaporator sounds like a throttle is ramping up and the rate water boils/bubbles significantly faster, but the amount of steam is less. Stack temp increases between 100-200F.

Hoping this is an easy answer, I am not sure I have the patience to try and gauge the evaporation rates of the two different methods just yet.

Thanks in advance.
Bill

[cpmaple]

Hello Bill,
I dont have an answer for your question but i do know that when i had a 2x3 i had a rain cover on it but after just a few boils i took it off and it was alot better. It seemed to hold the draft back to much. Hope this helps cpmaple

[happy thoughts]

I'd guess that you'll see a better evaporation rate with rapid bubbling because you've increased the surface area of the sap in your pan (the bubbles) and it means more excitable molecules that will reach a vapor state more quickly. Thick steam over your pans may actually decrease the evaporation rate as water vapor itself has pressure and that pressure affects the evaporation rate. I'd also guess that the steam formation you see may have to do with the temp of the sap in your pans decreasing so that water vapor is not being carried away as quickly as less energy is applied to your pans.

[Ausable]

Seeing steam is tricky. When it is cold out and you are doing a boil you will see steam coming out every nook and cranny of your sugar shack. Yet - when it warms up later in the season it is hard to see - yet it is still there. You are on the right track - pay attention to your temps - You want the heat under the pans - not - going up the stack to quickly. Play with the air and fuel and you will catch on to how your rig behaves under different conditions. One good way to check how efficient your rig is - is to track how many gallons per hour of sap you are boiling off - under different conditions. Main thing is - to have fun - and make some good maple. ---Mike---

[Dennis H.]

How fast the liquid level in the sight tube for the head tank drops!:)

[not_for_sale]

It's neither. When you see how water gets to boiling temperature you'll understand. The bottom of the pan is hotter and as such creates water vapor in bubbles. These bubbles rise in the water and through convection cool down and get smaller. As the boil progresses convection decreases the temperature gradient in the liquid and the bubbles become smaller. So lots of small bubbles indicate a good rate to go from 212 F liquid to 212 F steam.

Lots of big bubbles (violent boil) may not indicate a good evaporation rate in some cases. Just that you have a high temperature gradient.

There are some effects that reduce evaporation rate when you superheat the bottom of the pan.

Those effects become less dominant when you boil with minimal liquid covering the bottom of the pan. That is why people report it's better for the evap rate if you run the pans with low liquid level.

Visibility of that steam depends on the ambient temperature.

[happy thoughts]

Thanks NSF I actually understood that! :)

[325abn]

Yeah what Dennis H. said! :)

[TRAILGUY]

The hot the pans is what counts. I think one of the easy ways to get a better rate is defoamer and no bubbles the bubbles hold in the heat. It ups my rates by 25%

[not_for_sale]

Bubbles above the pan (foam) or bubbles in the pan (steam) are two different things.

[bcarpenter]

I may have to take a couple small videos next time I boil in the daylight, it was just odd how if I opened the wood door to load there was an instant change in the steam, which from the look of the steam itself I would have guessed more steam = more evaporation. When I close the door the amount of steam dies down, and the amount of bubbles (Not Foam) bubbling up from the bottom of the pan increases which would lead be to think its a stronger more rapid boil and therefore = more evaporation. I was just curious if I may be starving the fire and possibly need to provide more air or draft for the fire in the fire box to achieve the highest evaporation rate possible.

I hopefully will be able to set-up a feed tank this weekend which is marked so that I may have a more accurate measure of how much liquid I go through in an hour. I just have not had the time to set that up or try and be mindful with all of the new things to watch being in my second year.

Thanks for the feedback, its amazing how there are no hard and fast rules in this hobby.


It's neither. When you see how water gets to boiling temperature you'll understand. The bottom of the pan is hotter and as such creates water vapor in bubbles. These bubbles rise in the water and through convection cool down and get smaller. As the boil progresses convection decreases the temperature gradient in the liquid and the bubbles become smaller. So lots of small bubbles indicate a good rate to go from 212 F liquid to 212 F steam.

Lots of big bubbles (violent boil) may not indicate a good evaporation rate in some cases. Just that you have a high temperature gradient.

There are some effects that reduce evaporation rate when you superheat the bottom of the pan.

Those effects become less dominant when you boil with minimal liquid covering the bottom of the pan. That is why people report it's better for the evap rate if you run the pans with low liquid level.

Visibility of that steam depends on the ambient temperature.

[miner1]

I've got a 2X3 and this is my first year too. Do anything you can to maximize draft. Get you stack temp up, 300 seems low to me. Get rid of the rain cap. I had a rain cap and had low stack temp and excessive amouts of fly ash. I find I get better GPH when the stack temp is 400+ deg. I also ground the slots bigger in the ash grate to let the ash clear better and allow better air flow. The combined area of the ash slots compared to the 6 inch stack was 10 in2 less before grinding the slots out. Are you batch boiling or keeping the sugar in the pan betten boils? I batched the first boil, and my second boil is still in the pan till tonight when I fire it up again. Looking for others to let me know what works best for them.

[bcarpenter]

I did one batch two weeks ago taking 35 gallons down to 5-6 gallons of sweet and finishing in the house due to colder weather. My trees have been slow (north side, and little sun), but finally over the last 4-5 days I have accumulated close to 30 gallons, so I figured I needed to boil last night to get the stockpile down. I only brought it down to 8 gallons before I needed to wind things down. I am emptying my pans when I am done because I boil outside and plan to reload the sweet and run sap as I collect it for the next boil.

As far as stack temps, I can run/get the stack temp between 500-600F, which is the towards the high end of the "best" range on my magnetic stack thermometer I just wasn't sure if that was giving me the best boil or if I was just putting too much heat up the stack instead of on the pan. Like you said I am also concerned about getting enough air/draft to the fire box, because of the variance I noticed by opening the fire box door last night and how much it appeared to impact the boil. I may just try your suggestion and take the cap off or adding another 2' section of stack which I have at the house the next time I boil.

Hopefully with all the advice/suggestions coming in, I can narrow in on doing the right things out of the gate instead of having to experiment with trial and error.
Thanks
Bill


I've got a 2X3 and this is my first year too. Do anything you can to maximize draft. Get you stack temp up, 300 seems low to me. Get rid of the rain cap. I had a rain cap and had low stack temp and excessive amouts of fly ash. I find I get better GPH when the stack temp is 400+ deg. I also ground the slots bigger in the ash grate to let the ash clear better and allow better air flow. The combined area of the ash slots compared to the 6 inch stack was 10 in2 less before grinding the slots out. Are you batch boiling or keeping the sugar in the pan betten boils? I batched the first boil, and my second boil is still in the pan till tonight when I fire it up again. Looking for others to let me know what works best for them.

[loggerhead]

First year boiler, and I have noticed the exact same thing. There are a few things going on. 1) the "steam" that we see is actually condensation. Before you open the doors, you don't see the steam as well: it does not condensate as much, but it's there, as much of it if not more. The increase in condensation (not steam) is due to something else but I don't know what. Have you noticed how you can see your breath near a bbq grill (i.e., more condensation near an open fire)? I suspect it's the same process, whatever it is.
2) when you open the door, you let cool air in, so the boiling slows down or stops.

[bcarpenter]

A picture or rather a video can be worth a thousand words so I updated a couple videos of each scenario to my blog http://billcarpenter4.wordpress.com/

Anyone notice anything different after viewing both videos taken on he same day within 10 minutes of each other?

[aws]

I would go with the more steam option, as the weather conditions are remaining pretty much constant between trying the two options they shouldn't be a significant variable. We boil on a 2x3 flat pan and always leave our door cracked. Most of the time we have so much steam we cant even see inside the pan. We use a sight glass from a boiler and a depth gauge to monitor depth. Interesting conversation.

[Flat Lander Sugaring]

your stack temp drops when you open the doors because your drawing in cold air across the top of the fire and essentially cooling it. Its not like air coming in from underneath through the hot burning wood. only keep doors open very short periods of time load quick and carefull. take rain cap off put some AUF to it.

[bowhunter]

I have a Leader 1/2 pint and this is also my first year. The pan is 24 inches by 33 inch flat pan. I have done 14 boils and I started slow. The unit was rated for 5 gph, but I was only averaging 3 1/2 over an 8 hour boil.

1. A good boil is when you have good bubbling over the entire pan. With lots of relatively small bubbles. You can track your sap and pan inventory and monitor your boil rate over several hours.
2. The wood needs to be split small so that you maximize the wood surface area. Dry wood is better, but not absolutely necessary. I got some very good results with wild cherry cut in January, but it was split almost as small as kindling. You want a brush fire in arch.
3. I added 3 ft to my stack. You have six feet if I counted correctly. I'm up to 12 feet on a 3 ft pan. I can boil sap out of the pan with this set up without a blower.
4. I had a gap between the grate and the door that allowed air to by-pass the grate. I laid some 1/2 brick to fill that gap and that improved the distribution of heat under the pan as evidenced by a good distribution of boiling. It forced all the combustion air through the grate and up through the burning wood instead of allowing it to pass above the wood under the pan and out the stack.
5. Use the ash door to control airflow into the arch.

Don't be afraid to experiment a little until you find the combination that works best for your set up, just don't let the pan go dry.

[MarkL]

Two questions:

1. What is AUF? Googling it brings a lot of interesting results, and I'm pretty sure it does not refer to "African Unification Front" or "Australian Underwater Federation."

2. Please expand on the fly-ash + chimney cap relationship. Is fly-ash the tiny, nearly weightless and floating specks of black that drift back into my shack and get in my pan? I hate that stuff! Are you suggesting that if I take off the cap that stuff will float away better...or not be created at all?

I am adding 3' to my stack tonight, and taking off the cap to see if this both improves the draft, and subsequently the boil, and if it affects the fly ash. At least the ash will be higher up and maybe get carried away before getting sucked back into the shack.

Thanks,

MarkL

[happy thoughts]

auf= air under fire

Can't help with the cap problem. I boil outside on a block arch and like the cap because it keeps rain out of the stack which I'm thinking will help it last longer and keep the fire box drier. We remove the pipe after sugar season. I also think it keeps sparks down so I don't burn down the neighborhood:).

[bcarpenter]

Let me know how the extra 3' works out. I have one more 2' section of stove pipe that I have in my garage that I can add to my stack when I put the snap-lock seam together. Because it was a royal PITA for the stove pipe I purchased to join the seam, I stopped at 3 sections when I ran out of patience.


Two questions:

1. What is AUF? Googling it brings a lot of interesting results, and I'm pretty sure it does not refer to "African Unification Front" or "Australian Underwater Federation."

2. Please expand on the fly-ash + chimney cap relationship. Is fly-ash the tiny, nearly weightless and floating specks of black that drift back into my shack and get in my pan? I hate that stuff! Are you suggesting that if I take off the cap that stuff will float away better...or not be created at all?

I am adding 3' to my stack tonight, and taking off the cap to see if this both improves the draft, and subsequently the boil, and if it affects the fly ash. At least the ash will be higher up and maybe get carried away before getting sucked back into the shack.

Thanks,

MarkL

[eustis22]

"Because it was a royal PITA for the stove pipe I purchased to join the seam, I stopped at 3 sections when I ran out of patience."

Brother, I feel your pain....everyone could use an extra 2 feet

[MarkL]

My neighbor has a tool I can borrow to bend in those f-ing corrugated sections of galvy stove pipe. Otherwise I'd be chucking them to the curb. I highly recommend buying or borrowing that tool!

[kiteflyingeek]

MarkL,

I've been reading this forum pretty steady for the last three months or so and because of that, I can answer one of your questions:

AUF is Air Under Fire -- where air is blown,well, under the fire to make sure there is enough oxygen there. It allows the fire to burn extremely hot and get a very fast boil going.

The other "air" option is AOF (Air Over Fire). This is running some tubes into the firebox and creating nozzles so more oxygen is added to help burn the gases before they run out the chimney.

Both Air systems have their place but I'm about at the end of my knowledge on the subject ;).

I hope that helps.

--andrew