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[donkey131]

[h=3]Electrical Question? i have a revision question but not sure on how to work this out. Any help please?[/h] An electric furnace is used to melt a brass rod which has a mass of 500kg.
The furnace is rated at 200kW and it is fed from a 440V supply.
The initial temperature of the brass is 6°C and the melting point of brass is 910°C. There is no heat loss from the furnace and the specific heat capacity of brass is 0.39kJ/kg°C. Calculate:
(a) the time it takes to melt the brass;
(b) the furnace heater current.

not sure on how to do the above question any help please.

 

[MarkieSparkie]

Electrical Question? i have a revision question but not sure on how to work this out. Any help please?

An electric furnace is used to melt a brass rod which has a mass of 500kg.
The furnace is rated at 200kW and it is fed from a 440V supply.
The initial temperature of the brass is 6°C and the melting point of brass is 910°C. There is no heat loss from the furnace and the specific heat capacity of brass is 0.39kJ/kg°C. Calculate:
(a) the time it takes to melt the brass;
(b) the furnace heater current.

not sure on how to do the above question any help please.

Energy Q required to melt brass:
Q = mc(t2-t1) [J]
Q = 500kg x 0.39kj/kg°C (910 – 6°C) [kJ]
Q = 176280 kJ
Time t taken to melt brass:
P [W] = Q [J] / t
So:
t = Q / P
t = 176280kJ / 200kW
t = 881.4s
Current supplied to furnace:
P [W] = V [V] x I [A]
So:
I = P / V [A]
I = 200kW / 440V
I = 454.5A

 

[Inteificio]

I was going to give him a few hints, but totally spelling it out for him works too I guess ;-)

Donkey, that would have taken Markie a lot of effort, make sure you understand the process fully. If you need any clarification ask for more help.

Some students just skim a method if given the answer and learn nothing, don't be one of those students.

I should add the above is an adiabatic equation i.e. assumes no loss of energy to the environment. This means it will not be 100% correct, you need to correct for the efficiency of the system. That electricity will not 100% transfer to the copper, but also it will be heating the oven and the air surrounding it. The maths to do it properly is SIGNIFICANTLY more complex, so probably not required (2.5 maths a-levels and a math based degree subject and doing the real calc would still take me a few hours, the above to me would get change from a minute).

Slightly getting off track there, just understand the above is a simplification.

 

[Paul.M]

MarkieSparkie I'll give you a Thanks just for the amount of time and effort you put into that answer.

 

[Inteificio]

Don't forget my extra help paul ;-)

 

[donkey131]

Thank you Markie and Peter for your help and taking your time to help me, thats been a big help.
find it hard doing study revision at home and not knowing if im correct or not.
THANK YOU.