Max Heat input to a metal

[Sycorax]

I have a heater which gives out 1500 Watts at full output.

I have a block of metal say SS which I am trying to heat. I am trying to figure out the max temperature it will reach when the heater is used.

Formula: Q=m*cp* (T(final)-T(initial))
Tinitial=25C, C(specific heat)= 0.5KJ/kg-K, m=15 kg, q=1500Watts*time, T final?

Substituting all I get,

Tfinal=27 C in 10 sec.

In 500 sec, Tfinal is 125C.

I am a bit confused. I am trying to figure whats the max temperature the block can reach with that heater. This formula shows there is a linear increase of temperature with time and goes to infinity. Obviously thats not possible. It will reach a max temperature and plateau. What am I doing wrong?

( assume ideal conditions -no heat loss etc..)

Please help.

 

[desertfox]

Hi

Look at the specific heat capacity its in kJ, I think you need to put it in J's so multiply it by a 1000.

desertfox

 

[IRstuff]

Your model is too simplistic. Ask yourself how the heater doesn't run away, all by itself? Is it not heating up the room? You must consider conservation of energy, and heat balance. There is obviously some mechanism by which the heater reaches some steady state temperature.

And, therein lies your answer. The maximum temperature of your SS block cannot be any higher than the maximum temperature of the heater by itself.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[Compositepro]

The max temperature occurs when the heat loss to the environment equals the heat input. If there is no heat loss there is no limit.

 

[chicopee]

We assume that specific heat is constant as the temperature of the SS block increases, however, this may not be the case, so I would suggest that you research that function and than proceed to do a steady state heat transfer evaluation involving convective and radiative heat losses to the environment for a given heat input.

 

[Compositepro]

Common guys, heat capacity is irrelevant to how hot an object will get. It is only important to how quickly it heats-up. It is possible that the question was very poorly stated.

 

[AWloo]

You need to determine what modes of heat loss from the block to the environment. Is the air still, if so you will need natural convection relations to determine the heat transfer coefficient. Is conduction possible? Once you determine where heat is lost, you can do an energy balance from the heater to the surroundings determining the Tfinal.

Your analysis did not include any heat loss, that is why your block continued to raise in temperature.

 

[chicopee]

Also where is the heat coming from? Is it an internal or external heat source?