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Post by shilo on Feb 8, 2018 14:22:13 GMT -8
linkwhat will be the difference between this bell walls? the blue is insulation
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Post by Jura on Feb 8, 2018 23:38:58 GMT -8
linkwhat will be the difference between this bell walls? the blue is insulation IMHO (in case of stoves not, a house walls). In the 4th case (I count from the left ) the only difference will be in wavelength/emissivity of the external surface material. And in this case the stove will be cooling down most slowly. In the 3rd case you may achieve a higher value of chimney loss as the insulation stands for a hindrance to the heat exchange process.(obstruction to heat absorption by the wall). The 2nd case will allow to absorb heat energy faster than the first. (higher mass of the wall will allow the heat to dissipate in a bigger volume so the internal surface of the wall will reach higher temp later than in the first case. And as temperature difference and gas speed is a main driving force of the heat exchange process so theoretically the heat exchange process will be more efficient in that case)
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Post by esbjornaneer on Feb 10, 2018 1:07:45 GMT -8
Please would you clarify which is the inside of the bell wall in your explaination Jura.
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Post by Jura on Feb 10, 2018 1:31:25 GMT -8
Please would you clarify which is the inside of the bell wall in your explaination Jura . The left side
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Post by Vortex on Feb 10, 2018 4:42:01 GMT -8
In the 3rd case you may achieve a higher value of chimney loss as the insulation stands for a hindrance to the heat exchange process.(obstruction to heat absorption by the wall). Doesn't insulation anywhere in a bell wall increase the chimney losses, as the heat has more time to escape through the chimney?
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Post by Jura on Feb 10, 2018 5:24:33 GMT -8
In the 3rd case you may achieve a higher value of chimney loss as the insulation stands for a hindrance to the heat exchange process.(obstruction to heat absorption by the wall). Doesn't insulation anywhere in a bell wall increase the chimney losses, as the heat has more time to escape through the chimney? Well .. right I thought it was clear so just indicated the most obvious case of it. As you know I'm going to build one double skin stove with insulation. But in my case the plancha will be the main heat emitter.
With an insulated bell the energy gain of insulating it would have to be accumulated either by the increased ISA or using some heat exchanger... IMO. The OP Shilo did not provide us with many details...
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Post by shilo on Feb 11, 2018 1:10:32 GMT -8
"The OP Shilo did not provide us with many details..." there is no one specific project i refer to. it is a theoretical discussion for improve the understanding.
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Post by shilo on Feb 11, 2018 1:14:29 GMT -8
obviously, the main dilemma is between the 2 left sketches. the the other are here to make the discussion more clear.
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Post by Jura on Feb 11, 2018 8:33:40 GMT -8
obviously, the main dilemma is between the 2 left sketches. the the other are here to make the discussion more clear. As we are said the heat transfer mechanism in case of periodical stoves undergoes the law of exponential decay.The time after which a system reaches equilibrium temperature depends on the temperatures difference which in case of periodically working stove is not constant (as the stove wall temperature decreases in time). It causes the process to be described not by a linear function but an exponential one Results of real life processes following that law are my obtained by means lumped capacitance modelBut this law's assumption is that temperature remains relatively uniform through the volume of the conducting body i.e what is the Biot number of our stove. So here we come to the question if we may assume that our insulation will be a perfect one so we deal with a passive stove (sounds a bit oxymoronic :-), doesn't it? ) need to estimate the exponential temperature growth of the accumulating mass) or we can assume heat transfer outwards is allowed in some (what?) extent. In our case we need to of course apply the caveat that the accumulating mass has enough heat capacity to accumulate all the energy obtained from the combustion process but not higher as then we would lose the driving force of the stack effect.
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Post by esbjornaneer on Feb 13, 2018 0:10:09 GMT -8
I hope I have understood correctly that the reason for having a double skin is that the inner skin is likely to crack and the outer skin is what serves as the gas proof shell. I can then understand that there needs to be a space between the inner, more expanding skin, and the outer less expanding shell/skin, to prevent the outer to crack. To keep the space between uniform and not get it filled with 'mortar' it makes sense to put something that can be compressed in it. Is it because of insulation fitting the above criteria that it is used or is there another the reason for it being insulative? Surely if we wanted longer heat release we would add more mass in the walls instead, i.e. the insulation is not there to hold the heat in the stove.
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Post by Jura on Feb 13, 2018 2:58:07 GMT -8
Is it because of insulation fitting the above criteria that it is used or is there another the reason for it being insulative? Surely if we wanted longer heat release we would add more mass in the walls instead, i.e. the insulation is not there to hold the heat in the stove. You got the reasons right. But there is one more reason in a specific case when we want the stove not to emit the energy outwards. it occurs when we want to garner the heat it with an heat exchanger placed inside of stove and transfer & store it in an accumulative buffer for a future usage elsewhere.
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Post by esbjornaneer on Feb 13, 2018 4:58:21 GMT -8
I don't understand why another stove is not built in the other location to heat in those situations.
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Post by Jura on Feb 13, 2018 6:15:12 GMT -8
well ... there is one only disadvantage of the stove heating. It heats only its surroundings. While places behind walls (other rooms) do not get enough heat. I'm a big fun of buffer tank system as it may be loaded with energy inputs from many different sources: solar, heat pump, electrical heaters, kitchen stoves, even a composting pile or a cold fusion reactor once its available And the heat can be distributed equally and accordingly to your needs. Next advantage of it is when you leave home for longer, there is a danger your water installation gets frozen. With a buffer tank with electrical immersion heaters.. you may go out without thinking of it. And just a simple pleasure of returning to a warm home from a skiing weekend.. priceless. I'm probably soon going to build a vortex cooking stove with a heat exchanger that will be loading such a buffer. I'll start a new thread for this project.
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