How to calculate fuel required?

[SignalFailure]

Is there a rough and ready way to gauge how much methylated spirit is required to convert say 100ml of water to steam?

I know there's a formula (although I don't know what it is LOL) and that it will depend on the, er, 'calorific value' (?) of the particular spirit and probably a whole host of other variables. I could do it by trial and error I suppose but I'd prefer not to expend the time!

TIA

Paul

 

[Maryak]

Ethanol 29.8 Kj/g
Latent heat 2260 Kj/Kg

Temp diff 85 C

1Kg -85C 85 Kj/Kg

Total h 2345 Kj/Kg

Ethanol Req 7.87 g/100g

SG Ethanol 0.815

Ethanol Req 9.66 ml/100ml Water

At NTP i.e. No gauge pressure.

Near enough will be 1/10 of the amount of steam to be generated . I'm rusty at this so I hope others will confirm or deny.

Best Regards
Bob

 

[SignalFailure]

Bob, I followed all that except the first 10 lines or so ;D Maybe you or someone else could elaborate/explain?

 

[Maryak]

Ethanol 29.8 Kj/g - The Calorific value of the fuel.

Latent heat 2260 Kj/Kg - The amount of heat required to change the state of 1 Kg of water into steam at 100 deg C.

Temp diff 85 C - Assumes a starting temperature of 15 deg C

1Kg -85C 85 Kj/Kg - The heat required to take 1 kg of water from 15 C to 100 C

Total h 2345 Kj/Kg - The total heat required to take 1kg of water at 15 C to dry saturated steam at 100 C.

Ethanol Req 7.87 g/100g - The arithmetic result of the calorific value of the fuel and the total heat required.

SG Ethanol 0.815 - The specific gravity of ethanol

Ethanol Req 9.66 ml/100ml Water -the conversion from weight to volume of ethanol using the SG.

At NTP i.e. No gauge pressure. - At atmospheric pressure and temperature (1 atu abs and 15 C).

Paul,

My apologies for such a poor message :-[ looked like gobblydygook to me too and I wrote it. :'(

Best Regards
Bob

 

[SignalFailure]

That's better I think ;D Actually I wasn't far off understanding honest - it was just this 'Ethanol Req 7.87 g/100g ' that was confusing me! However, 10ml of fuel seems very little... maybe I should just shut up and try it? :big:

 

[tornitore45]

Paul, the answer you got assumes that all the heat generated by the fuel goes into the water and steam. In reality much heat will go to heat the boiler, and some more will go up the chimney.

I would guess a thermal efficiency no better than 50% and double the fuel prediction at least.

Mauro

 

[Maryak]

I would guess a thermal efficiency no better than 50% and double the fuel prediction at least.

Mauro,

Thank you for pointing out the glaring omission from my post :bow: :bow: and for bringing it back to the real world. ;D

I said I was rusty, perhaps I should amend that to almost corroded away. :-\

Best Regards
Bob

 

[SignalFailure]

Yup, I'd realised that all the heat wouldn't be going to the right place (if only!) but a theoretical value would at least give a starting point... thanks you both for the help :bow: