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Birrofilo wrote: ↑Fri Apr 24, 2020 6:59 pm
On the other hand, the vertical boiler (or the slim boiler) will reach boiling temperature faster than the squatty boiler, given the same amount of energy, for reasons not totally clear to me but that probably have to do with the heat dissipation on the upper surface during ramping up (the larger the surface, the larger the dissipation).
That's why automatic kettles for beermaking tend to be slim, and that's why the "Jet Boiler" product for hijacking is slim, because it boils faster, coeteris paribus. Shape affects function.

LWTCS wrote: ↑Sat Apr 25, 2020 12:06 pm Sorry mate. You'll have to prove that.
As mentioned the shape more often has to do with available floor space, and safe working elevations,,,,,function.

Otherwise it's all about BTUs in.

Birrofilo wrote: ↑Sat Apr 25, 2020 10:35 pm

LWTCS wrote: ↑Sat Apr 25, 2020 12:06 pm Sorry mate. You'll have to prove that.
As mentioned the shape more often has to do with available floor space, and safe working elevations,,,,,function.

Otherwise it's all about BTUs in.

I understand your perplexity, which is also mine. Yet, empirically speaking, we know that the "jetboil" product is known in hijacking circles to actually boil fast in relation to the BTUs applied. And in beermaking circles slim kettles are thought to favour a more robust boiling.

This is vox populi and it could be certainly wrong.

Yet, it is not "all about BTUs" as you will easily experience, with any pot in your house, that water boils faster if you put a lid on the pot. The amount of heat which is dissipated through the upper face of the pot, especially when there is no lid, slows the ramping up.

This appears to me good indication that it's the heat which is dissipated from the top surface which slows the reaching of the boiling point. And if that is correct, then I think it is equally correct to think that the pot with the smaller top surface will reach boiling point faster, coeteris paribus.

As a side note, one might think that homeothermic animals will dissipate, in order to keep their basal temperature, a certain amount of energy (calories etc.) following a relation which depends from their weight and not from their shape. Supposing that man and elephant have the same basal temperature (which is probably not true, but for the sake of the argument it will become true for the moment) the energy consumed to maintain thermal equilibrium, given the same external temperature, can be thought as proportional to weight.

But this is not true. Large animals (elephants, whales, and in the past large dinosaurs) benefit from the "pachiderm effect": they dissipate through the surface of the body, and the surface of the body doesn't grow proportionally to the weight/volume (the sking grows according to a quadratic law, the volume grows according to a cubic law). So an elephant with the dimension of a man, or a dog, would dissipate more heat in order to maintain thermal equilibrium than what would be suggested by the proportion with the weight of the real elephant.

Given the same proportion of bones, fat, muscles etc. man would, by the same token, consume less energy if he was shaped like a perfect ball, because the relation surface/volume in the ball is smaller than in man.

The shape of a living being, or of a kettle, influences the way its heat is dissipated.

Animals dissipate heat through their entire body (more or less, see below) while a kettle over a stove dissipate heat mainly from their upper part.

It is also known that man dissipate most of the heat from his head. This is, maybe, the "kettle effect": heat mounts along the body (because heat tends to "travel upward") until it arrives to the head, where if finds an "exit".

Reducing the surface of the boiling water, of the upper face of the pot, reduces the "escape" for the heat.

You might also have noticed that it is easier to get cold if you fall asleep in bed with your clothes on. You need a blanket. You were thermally comfortable while standing or sitting, but remaining half an hour in horizontal position makes you get cold. That's because the "escape" surface, when you are horizontal, is larger.

I am not totally sure what I say is true, but I am quite confident it makes sense.

NZChris wrote: ↑Sat Apr 25, 2020 10:59 pm The following formula is used to calculate the kW of power needed for an element needed to heat a specific volume of water by a given temperature rise in 1 hour.

Volume in litres x 4 x temperature rise in degrees centigrade / 3412

Note that there is nothing in the equation to allow for the shape of the vessel.

The only effect the shape has is due to heat loss from the surface area available for the losses. So insulate it.

LWTCS wrote: ↑Sun Apr 26, 2020 3:37 am Here we go again.
There is so much here that is completely irrelevant. Putting a lid on a kitchen pot to increase heat up time has nothing to do with the shape. That has more to do with pressure.

"Reducing the surface of the boiling water, of the upper face of the pot, reduces the "escape" for the heat."

For the purposes of distilling spirits,,,,no.

As far as your animal analogy is concerned,,,really?

stillanoob wrote: ↑Wed Apr 29, 2020 12:12 pm Don't want to pour gas on the fire and I am not sure if this is relevant but...

If reducing a sauce on the stove, it will reduce more quickly in a wider pan with less depth of sauce. It will take longer in a smaller pot with greater depth of sauce. In both cases the same heat would be applied.

stillanoob wrote: ↑Wed Apr 29, 2020 12:12 pm Don't want to pour gas on the fire and I am not sure if this is relevant but...

If reducing a sauce on the stove, it will reduce more quickly in a wider pan with less depth of sauce. It will take longer in a smaller pot with greater depth of sauce. In both cases the same heat would be applied.

stillanoob wrote: ↑Wed Apr 29, 2020 2:41 pm Sure? Hell no. But it has been my experience, it was taught to me waaaay back when I was a cook in my youth. Quoting from Bon Appetit:

"The more surface area your sauce has to do its thing, the quicker it'll reduce. A large Dutch oven or wide sauté pan will yield the quickest results. Can you reduce in a small sauce pot? Of course. Just keep in mind: The deeper the pan's volume, the longer it'll take to condense and reduce."

For sure when reducing a sauce it makes a difference. Practical experience has confirmed that for me. Whether or not that applies to our current conversation I leave to others smarter than I. Which is just about anybody...