2200w Elec Element

[Supra-Jim]

Looking a building an electric urn my emerging AG rig.

Does anyone have any experience with times for a 2200W element to heat approx 40 ltrs of water to around 75degC.

I did study thermo years ago, but have forgotten alot of it, so if anyone knows the formula's for calculating this off hand, that would be even better.

Cheers

SJ

 

[jonocarroll]

Yaaay! Physics!

For the formula you want, just skip to the end. For those who want to know...

Assuming that your vessel doesn't absorb much heat (not a great assumption). You are adding heat at the rate of 2200 Joules/second (Watts) or 132000 Joules/minute. This is the power;

P = delta_Q / delta_t = 2200 Watts

delta_Q = heat added
delta_t = time taken

To heat a substance, you need to add heat according to

delta_Q = m c delta_T

m = mass of substance to be heated
c = specific heat capacity
delta_T = change in temperature

For water, c = 4181 Joules/Kilogram/*C

Rearranging gives the equation you want...

delta_t = m c delta_T / 132000

or

delta_t = m delta_T / 31.57 = time taken to raise m kilograms of water by delta_T *C (in minutes).

For example, 40L of water from 50*C to 75*C (delta_T = 25*C) will take

delta_t = 40*25/31.57 = 32 minutes.

YMMV depending on many factors, but that will be ballpark accurate.

Cheers. :icon_cheers:

 

[Supra-Jim]

I think google may have helped me answer my own question. Using this link:

http://www.heateflex.com/html/techtools/TT3.html

for 40 litres (10.5gal) time is 70minutes

for 30 litres (8 gal) times is 52 minutes

Has anyone had any experience to confirm or dispute this?

:icon_cheers: SJ

 

[Supra-Jim]

Thanks Quantum, a quick check on the calculator confirms.

:icon_cheers: SJ

 

[jonocarroll]

I think google may have helped me answer my own question. Using this link:

Picture says it all...

 

[Tony M]

1 watthour = 860 calorie so work from there.
As an aside, if you can run 3600W (15A) you will be glad.

 

[Supra-Jim]

Picture is good, but it is also good to get the theory/equation behind the calculator. Thanks again.

SJ

 

[jonocarroll]

1 watthour = 860 calorie so work from there.

Uhh... Okay.

Perhaps;

1. Watthours (?)
2. calories
3. ???
4. Profit!

As an aside, if you can run 3600W (15A) you will be glad.

Sub in 3600W in my calculations and you drop down to 20 mins. I just guess it depends on how much you want to spend on that extra 10 mins.

 

[raven19]

Insulation (or lack there of) of the kettle will also have an effect due to amont of heat loss.

I do like being able to use Physics for something useful though!

 

[jonocarroll]

Plenty of places to go wrong;

Insulation of HLT (heat loss)
Evaporation
Pressure inside HLT (lid vs. no lid)
Heat absorbed by the HLT itself
Actual specific heat capacity of the water
Specific heat capacity of HLT (combined with insulation and heat absorbed really)
Accuracy of the power rating of the heater

and of course how accurately you measure the mass of water and start temperature.

You should be pretty good to within 20% though I'd reckon. If not - just wait longer.

 

[sav]

I have 2400 in my HLT about 30 to 40min will get you there,I also use imersion element to get me there quicker