klemen urbanija

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since Mar 31, 2015
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Recent posts by klemen urbanija

jessie franks wrote:Would it be feasible to char the wood under the glass instead of using the paint? Or would that be problematic?

When i was young we put a candle under the piece of glass to make it black - then we used it to look the solar eclipse - the sun was dark reddish in color... Darkened glass (soot on top) was really totally dark and matte.... I think that could work...
I would think that charring of the wood might add some additonal flour to a dehydrated food because charred wood is not soot only but also partially charred wood.... But if there is only soot layer it might be a better option...

1 month ago

Another feature for improvement is to add a 4-inch rocket mass heater under the ramp.  Maybe there can be an 8-inch thick mass under the ramp so you can heat the mass, but it doesn't heat the air too much.   And then when the fire is out, the mass is still something like 100 degrees and keeps pushing warm air through the system.   So in the fall when you have 12 hours of daylight and 12 hours of night, then you get 24 hours of drying time.

In our country i don't count on longer periods of sunny weather, especially not in foggy autumn days.
If i would build a drier of a larger size, i don't like the long burning of a 4-incher to get enough heat. Our local heritages used slow and dirty burning to heat large driers overnight or even longer - this i don't like either... Maybe there could be a solution with a small batchbox and a small bell with fat wall. I would make a bell with metal fins pointing from inside the mass towards the inside of the bell. This would make a larger and a more effective ISA that could store thermal energy quicker into the thickness of the bell's walls. Emitting that energy from the outer side towards the drier would be slow because of the fat cob walls...

Burn some kilos of wood in one batch and then walk away for a day would be really convenient... If only air inlets could be closed automatically ;-)

1 month ago

I just watched it and i would like to add something.

Ii tried one similar to hot aussie drier but it didn't perform well in my place -too much morning humidity, rainfall etc... But i remembered my research about updraft and downdraft driers...

The thing i found was interesting: the air with more humidity in it is lighter than the one with less humidity (relative humidity). The gas law from chemistry explains that because at the same pressure there can only be certain amount of molecules present in the same volume. Since the molecules of water vapour are lighter than average weight of molecules in the air, the drier air is denser (or heavier per volume unit).

https://www.omnicalculator.com/physics/air-density gives a simple calculation of air density:

few calculations:
at 50C and 20% density is 1,08 kg/m3
at 50C and 50% density is 1,07 kg/m3
at 50C and 70% density is 1,05 kg/m3
at 40C and 70% density is 1,10 kg/m3

The faster the airflow through the drier, the lesser is the cooling effect and the lesser is the humidifying effect - my conclusion would be that faster air flow saves it all, but it need some more solar gain surfaces to get that air faster to the appropriate temperature...

I would say that in this particular example there is not much of an information but maybe for the future projects it might come handy: humid air is lighter than dry air - contrary to obvious conclusion...

Thinking of it i can't help to think about rocket stoves with low temperature exhaust - now it looks like humidity in them helps to add upwards draft even if cooled to the temperature of the surrounding areas... But the CO2 highers the density of exhaust.

There is also an interesting point:
"Humid air containing water molecules as liquid - droplets - may be more dense than dry air or humid air containing water only as vapor.  "
I found that one here: https://www.engineeringtoolbox.com/molecular-mass-air-d_679.html

Pretty complex problems and with so many variables it is hard to walk safely on the edge -


1 month ago

Some years ago I was a shepherd on a mountain with milking cows and making cheese. I had an opportunity to be by the cheesemaker all the time and I did some cheese wheels then and later at home.

There have been some old wooden cheesemaking hoops and some new ones that were plastic. We were making cheese wheels 2 to 4kg in weight, up to 15 wheels per day.

Search for cheesemaking wooden hoop. Since you will work with smaller quantities go for the smallest ones. Here is a link for clarification.


Since it is simple to make you can DIY. The  wood used at our place  is maple, but ash would be a good choice too, IMO. The rope around the hoop is to tighten it to a desired size. You also need a cloth - the hoop is just for a desired shape...

Hope this helps,
2 months ago
1st Wofati microdoc

close 2nd skiddable structures.

3 months ago
You can make it round easily with bells (stratification chambers) instead of pipes for extracting heat.

One example is here:

It could be round like a cylinder or like a sphere or an egg. But some may be more difficult to build;-)
6 months ago
@hatten, do you have a link to those follow up videos? It seems like there has been some more info added...

As of video, it's a nice work...
There are oak shingles mentioned..but they seem to me like thin oak boards.. can anyone confirm this?
We make shingles by splitting spruce or larch. Boards are maid by sawing them. Shingles last much longer than boards ( larch can last up to 70 years but it really depends on local conditions)

Also, why burning method is not used on shingles? It would be a pain to burn them by hand but if one would make kind of "fire planer" that would be much easier...

Anyway, craftsmanship like this is great to watch..

9 months ago
Gosh, Donkey, that was fast!

Did you start writing reply prior to me writing the question ?!?

Thanks, much appreciated info!

11 months ago
Hi, Donkey.

I really like that one! But have some questions to understand the build better...

Do you have an approximate figure of effective inner surface area?

The front and back wall of the arch - you just filled it with bricks on side and then stuffed the gaps?

Did you use anything to compensate the outward force at the bottom of the arch? Or is it so steep that it doesn't matter?

Is the heat riser made from clay and perlite mix or is it something else? It looks to me like that you had some form inside but then you removed it...

How long is the firebox from the primary air gap to the last wall? How long firewood can you utilise?

Is there something that you would do differently if one says: "Please, make me something like that!"

What are the dimensions of the bricks that you are using?

Few years ago i did a casted 4" batchbox with p-channel. I had a feeling like that it is kinda too small of a sistem to work well. Maybe i should insulate around the 3cm casted firebox walls... Looking at your graphs it seems that yours is working well!

And i really like this kitchen utensil for the door! These doors  are the cherry on top! It looks like that the stove is saying to other heaters: "Look i can do it better with a casserole than you with a $$$ metal door!"

Thank you for sharing and i hope to hear more details about jamboree projects!

Best regards

11 months ago
My 139 page is empty, too. Appearance is the same as in above post. 140 page starts with "Within developing countries..."

Other wise it'sinteresting read...
1 year ago