How long does it take to get heat? (thermodynamics )

AI Thread Summary
The discussion centers on calculating the time required to heat water using coal in a steel container. Participants propose formulas, including cmwaterΔT=qmfuelt and Pt=mcΔt, to relate heat transfer to time, specific heat, and power. There is a debate about the consistency of units in the proposed equations and the need for accurate parameters, such as burn rate and heat transfer properties. The conversation highlights the complexities involved in heating calculations, emphasizing that uneven heating and energy content of the fuel significantly impact results. Overall, understanding the thermodynamic principles and accurate measurements is crucial for determining heating time.
lasha1
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Can anyone tell me the formula.
For example: How long does it take to boil 1kg 20°C water in steel container. With 1 kg of coal (or something). I want to understand the formula of time attitude to heat.:smile:
 
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I think it's the following formula:
cmwaterΔT=qmfuelt where t is time q is specific heat of fuel.
 
That would depend on the burn rate of the coal and the heat transfer properties of the steel container. Don't forget that the transfer rate will change as the water warms. I haven't looked it up, but you should also make sure that the coal contains enough energy to bring the water to a boil. Then you need to assume that the heating is so even that there is no boiling till all the water gets hot enough. Uneven heating changes everything.
 
Ok FastChecker. But with Joule lenz's law we can get the following formula: Pt=mcΔt where P is power of kettle and t is time that needed to get heat.
 
Your second post came as I was writing my reply and I never saw it. So you have equations that you are satisfied with. Good.
 
lasha1 said:
I think it's the following formula:
cmwaterΔT=qmfuelt where t is time q is specific heat of fuel.
This equation does not make sense. The units are not consistent. If q is indeed specific heat of fuel you need some temperature.
But is more likely you mean the caloric power of the fuel. In any case, time is not supposed to be there

lasha1 said:
Ok FastChecker. But with Joule lenz's law we can get the following formula: Pt=mcΔt where P is power of kettle and t is time that needed to get heat.
This equation is OK but you changed the OP problem. Originally you said that you use some coal to heat up that water. Now you seem to switch to some kettle. You cannot apply this to OP question without knowing all kind of details about the burning of coal and heat transfer.
 
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Yes. But I checked lenz's law:biggrin:. I understand it. Thank you.
 

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