how long will it take to heat 5ltrs of glycerol?

Question

how long will it take to heat 5 ltrs of glycerol with a 1200 watt hot plate to 100ºC given the thermal conductivity @ 20ºC is 0.29 W/mk? please help

Answer 1

You're heating it from 20 to 100, an 80 degree C (or K) change.
The heat capacity of glycerol is 3.073 x 10^6 J/(degree K m^3) according to
http://www.hukseflux.com/thermal%20conductivity/thermal.htm.

So the amount of heat that has to be delivered is
3.073 x 10^6 J/(degree K m^3) * 5 liters*(.001m^3/liter)*80 degrees K = 1.229 x 10^6 Joules.
The hot plate delivers 1200 W or 1200 Joules / sec. So
1.229 x 10^6 Joules / (1200 Joules / sec ) = 1024 seconds. That's the length of time it takes for the hotplate to deliver the amount of heat the glycerol needs to reach 100 degrees.

Now I can't see what to do with the thermal conductivity. If you had a broad hotplate and a broad pan for the glycerol, the glycerol could be only perhaps 3 centimeters deep. Conductivity wouldn't be much of a concern. But if you had a tall container so the heat had to be conducted up a 200 cm tall column of glycerol, the rate of heat conduction would be much more of a factor. I think the question is flawed.

Answer 2

brother it takes 4.765 mins or may be convert into sec thats the answer brother.......