Thermodynamics-question

2008-01-31 08:43:48

#1

stef10: Member; +173|6968|Denmark

ok, Im looking at some thermodynamics-question which I need to be sure about. Been over a semester since I had it so I cant remember

well, I need to warm some water up so it boils. Currently the water has a temp of 16 degress-ok, I know how much energi it needs.

1.8 kg of water times specificwarm(2.1 kj) times delta temp.

ok no problem. But all this energy needs to go through this pot of metal.

so my question is - is the energy the water receives the same as the pot receives but just going through?

and then another question is how much energy is required to get the water to boil when we loose 45% of energi-thats simple if you guys can verify the correct method above.

thx.

2008-01-31 08:52:31

#2

Locoloki: I got Mug 222 at Gritty's!!!!; +216|7125|Your moms bedroom

thermo 1 and 2 are the only classes i ever aced

well, the metal does have a heat coefficient, but if they didn't give it to you or specify what kind of pot it was, i would say it is negligible

not really sure what you mean by your second question

2008-01-31 08:55:47

#3

mtb0minime: minimember; +2,418|7140

I think you have it right.

Considering they didn't tell you anything about the pot, you shouldn't have to worry about it. Don't take this the wrong way, but I think you're over-thinking it

2008-01-31 08:56:22

#4

stef10: Member; +173|6968|Denmark

Locoloki wrote:
thermo 1 and 2 are the only classes i ever aced

well, the metal does have a heat coefficient, but if they didn't give it to you or specify what kind of pot it was, i would say it is negligible

not really sure what you mean by your second question

no, i know exactly which metal it is and what mass it has - but my question is the amount of KJ the water received is it the same amount as the pot received meaning its the same amount as the stove made if we dont take into consideration than any energy went to the surroundings?

im just using the rule Q-giving=Q-receiving.

the other question is how much energy do we need to give if 45% goes to the surroundings?

Last edited by stef10 (2008-01-31 08:58:09)

2008-01-31 08:58:28

#5

Locoloki: I got Mug 222 at Gritty's!!!!; +216|7125|Your moms bedroom

you have to add the energy needed to heat the pot to the end boiling point of your water energy

multiply your total energy by 55% if 45% is lost

so that your total energy when multiplied by .45 = the amount needed to boil the water

Last edited by Locoloki (2008-01-31 09:01:04)

2008-01-31 08:59:32

#6

mtb0minime: minimember; +2,418|7140

Ah, well now that you say you know the properties of the metal...

I'm pretty sure you're still over-thinking it. The heat from the surroundings and heat lost from the pot "cooling off" are negligible.

Locoloki wrote:
you have to add the energy needed to heat the pot to the end boiling point of your water energy

I think he's right. Just heat the pot up to 100 and bam, boiling water.

Wait you don't have to take into account altitude of the pot with respect to sea level and atmospheric pressure do you?

Last edited by mtb0minime (2008-01-31 09:00:48)

2008-01-31 09:03:10

#7

stef10: Member; +173|6968|Denmark

mtb0minime wrote:
Ah, well now that you say you know the properties of the metal...

I'm pretty sure you're still over-thinking it. The heat from the surroundings and heat lost from the pot "cooling off" are negligible.

Locoloki wrote:
you have to add the energy needed to heat the pot to the end boiling point of your water energy
I think he's right. Just heat the pot up to 100 and bam, boiling water.

Wait you don't have to take into account altitude of the pot with respect to sea level and atmospheric pressure do you?

no, because the water needs to more energy than the pot to be heated a temp up. Meaning the pot needs to gain 700 c and then give it to the water. but remember the pot always seem to cool down because its giving energy.

Last edited by stef10 (2008-01-31 09:04:00)

2008-01-31 09:03:26

#8

Locoloki: I got Mug 222 at Gritty's!!!!; +216|7125|Your moms bedroom

well, it has been about 6 years since thermo in college, i am a bit rusty

2008-01-31 09:05:42

#9

Locoloki: I got Mug 222 at Gritty's!!!!; +216|7125|Your moms bedroom

you have to remember, think big, like if its a really thick pot, or say made of led or cyramic, not a thin steel pot,

it does matter how much energy is needed

2008-01-31 09:07:43

#10

mtb0minime: minimember; +2,418|7140

stef10 wrote:
no, because the water needs to more energy than the pot to be heated a temp up. Meaning the pot needs to gain 700 c and then give it to the water. but remember the pot always seem to cool down because its giving energy.

heh well looks like you know it all yourself already, why are you asking us?

I think you're good to go, you seem to know what you're doing. I haven't had thermo since high school, and that was very basic at best. I will be taking it this summer, though, so can you wait 6 months and I'll get back to ya?

2008-01-31 09:12:55

#11

Locoloki: I got Mug 222 at Gritty's!!!!; +216|7125|Your moms bedroom

lol, and you know our professors over here in America love to fuck us up and give us problems with Celcius and Farenheight and cubic meters and gallons just to fuck with with our heads, do you guys have to learn it to different ways as well? fucking Joules to BTU's

2008-01-31 09:20:59

#12

Locoloki: I got Mug 222 at Gritty's!!!!; +216|7125|Your moms bedroom

heat the metal to 100 deg C, from 16 deg C, how much energy did you use?
heat the water to 100 deg C, from 16 deg C, how much energy did you use?
add the two energies together

now divide the combined energies by .45 and that is your total energy needed before 45% was lost

wait till you start doing horsepower problems with engines with diffent types of petrol in it!!!!!!!!!!, and how much water is needed to be pumped into a specific heat exchanger of certain metals to cool the engine... oh wait that was my thermo2 final

Last edited by Locoloki (2008-01-31 09:27:02)

2008-01-31 09:25:01

#13

max: Vela Incident; +1,652|7053|NYC / Hamburg

Locoloki wrote:
lol, and you know our professors over here in America love to fuck us up and give us problems with Celcius and Farenheight and cubic meters and gallons just to fuck with with our heads, do you guys have to learn it to different ways as well? fucking Joules to BTU's

we actually stick to s.i. units usually

_{once upon a midnight dreary, while i pron surfed, weak and weary, over many a strange and spurious site of ' hot xxx galore'. While i clicked my fav'rite bookmark, suddenly there came a warning, and my heart was filled with mourning, mourning for my dear amour, " 'Tis not possible!", i muttered, " give me back my free hardcore!"..... quoth the server, 404.}

2008-01-31 09:27:54

#14

Locoloki: I got Mug 222 at Gritty's!!!!; +216|7125|Your moms bedroom

max wrote:
Locoloki wrote:
lol, and you know our professors over here in America love to fuck us up and give us problems with Celcius and Farenheight and cubic meters and gallons just to fuck with with our heads, do you guys have to learn it to different ways as well? fucking Joules to BTU's
we actually stick to s.i. units usually

you lucky fuckers, sometimes on tests they would actually mix and match the units

2008-01-31 12:10:59

#15

mtb0minime: minimember; +2,418|7140

Seriously, America needs to get off its high horse and just use SI Units for the love of god. I hate having to remember ksi, MPa, ft-lbs, N, and all that shit and what goes with what.

2008-01-31 12:30:32

#16

stef10: Member; +173|6968|Denmark

thx. karma for all.

BF2S Forums Thermodynamics-question

Locoloki wrote:

Locoloki wrote:

mtb0minime wrote:

Locoloki wrote:

stef10 wrote:

Locoloki wrote:

max wrote:

Locoloki wrote:

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