Calculate boiling rate of water

  • #26
50
4
Do you know any specific way to determine its coefficient?
 
  • #27
50
4
While the method of taking the energy produced in an hour and dividing I by the latent heat of vaporization makes sense in some ways it also seems odd because it also means that if the boiling point and pressure were raised that the boiling rate would increase despite the fact that the temperature needs to boil the water are only met instead of exceeded by 30°C. I don't know if I explained that well but that's what I'm hung up on.
 
  • #28
russ_watters
Mentor
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Do you know any specific way to determine its coefficient?
No. I took a course in heat transfer, but didn't do very well; It is very complicated mathematically, since it is fluid dynamics mixed with thermodynamics. What I took away from it is that experimentation is better than trying to figure it out with math.
While the method of taking the energy produced in an hour and dividing I by the latent heat of vaporization makes sense in some ways it also seems odd because it also means that if the boiling point and pressure were raised that the boiling rate would increase despite the fact that the temperature needs to boil the water are only met instead of exceeded by 30°C. I don't know if I explained that well but that's what I'm hung up on.
The enthalpy of vaporization is slightly higher, but remember, you also had to heat the water to raise the temperature. The total energy is - I think - exactly the same. What's missing from that picture is the effective generation of the heat: the compost has a certain optimum operating temperature I'm sure, and if it overheats it probably dies (I'm assuming it is a biological process, not a chemical process...).
 
  • #29
Nidum
Science Advisor
Gold Member
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Why do you want to do this anyway ?

Even under the most optimistic conditions all that could be produced would be a very small quantity of sub atmospheric pressure steam .

Note also that you would need to have an external energy input to produce the vacuum needed to allow the water to boil at such low temperature .
 
Last edited:
  • #30
50
4
Yeah the maximum temperature is somewhere around 60°C
 
  • #31
50
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Well I was just interested in using compost as a way to produce steam and yes I know I would have to use a pump to reduce the pressure in the chamber initially
 
  • #32
50
4
I know I would need an energy source to produce the initial vacum and just curiosity I suppose, I'd like to know
 
  • #33
russ_watters
Mentor
19,932
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I know I would need an energy source to produce the initial vacum and just curiosity I suppose, I'd like to know
Depending on what you are doing with the steam, you may or may not need the vacuum continuously maintained:

-If you want to use this to purify water, you'll need to continuously suck away the condensed water.
-If you want to heat a house, it can naturally circulate via convection.
 
  • #34
17
0
I'm not planning on purifying it so hopefully I'll only need to produce the vacuum once and keep the system closed also as a side note I've found something intriguing. Compost Power Jean Pain Mound Project Summer 2011 by anenergyoptomist on YouTube, his mound of mulch is 40 meters cubed and with the density of mulch at around 600 lbs per cubic meters is around one ton. Instead of 1000 btu/h his mound is producing 17,000 btu/h according to his measurements so in the end it looks like if I really want to figure this out I'll have to just get to it and test it
 
  • #35
russ_watters
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That's 12 tons...
 
  • #36
Nidum
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(1) How do you propose to make use of any steam which is generated ?

(2) Have you looked at other possible ways of extracting energy from the composting process ?
 
  • #37
17
0
Oh woops, it's 24,000 but I didn't process that extra 0 on the end and thought it was only 2,400 and actually yes I have thought of another way to get energy from this process but it's much simpler so I think I'll just try testing it out first and see how it goes
 

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