Heat equation 2

[celticmad]

I am trying to work out the work a burner has to do to heat a 3kg ceramic mould to 1100 c.Does anyone know what equation or formula i should use.
Thanks in advance

 

[patprimmer]

If I remember my high school physics correctly, the heat required to heat an object is

Calories of heat required equals Specific Heat for the material times weight in grams times degrees C temperature rise.

This does not allow for heat losses in the process, which I am sure will be significant.

Also note, that heating something to as high as 1100 C might boil some volatiles or send the material through at least a second order transition, which will alter the heat requirement, in which case, you might also need the latent heats of vaporisation and fusion, as well as the data for the entropy in any second order changes. Please verify these comments, as it is about 40 years since I studied this, and all my books are burried in a cupboard, lost or on loat to who knows who

Regards
pat

 

[celticmad]

Thanks Pat
To be honest....i dont know ,this is something i've been asked to do in work as a favour ..but i'm as lost on this as anyone.What kind of formula is it or where would i get it.
Thermodynamics ?.
Thanks

 

[patprimmer]

Latent heat and specific heat are basic senior high school physics. second order changes of statr are tersiary level.

I looked up an old tersiary level physics book and it started with a presumption of knowlege about the above, so I can't help any more. It's really a question for the younger textbook wizzkids, just out with their new engineering degree, and all this fresh in their minds

Regards
pat

 

[coughdrop]

celticmad,
I think the best solution is to contact a burner manufacturer, for example NA-Stordy or Nu-Way. I have found both to be very helpful with application advice in years gone by.

http://www.stordy.co.uk

(part of North American Manufacturing Co.)
Cheers,
John.

 

[celticmad]

Thanks Lads
I've decided to take coughdrops advice and contact the manufacturer.If they dont know for sure who does !!!!
Thanks

 

[ddace]

the equation is

Q=m*Cp*(t2-t1)where

q=watts
m=mass(kg)
Cp=j/kg*k
tdiff= 1100 - t at begining of process

Cp for ceramics (if not a wew material) is verry near porcelain = 920 j/kg*K

 

[daubery]

Hi all,

The equation 'ddace' provided is for the Heat Input [J], not Power [W]. Power is the rate of doing work. The correct formula (average) is:

q' = m*Cp*(T,final-T,start)/(dt)

where: dt = Time taken for heating (sec).

This equation assumes a 'linear' heating rate, which is often not really attained because of thermal convection & radiation heat losses at higher temps.

Regards,

Des Aubery...
(adTherm Technology -

http://www.adtherm.com

- info@adtherm.com )

 

[ddace]

hi to you daubery

i am not insulted by your correction but it should only read that i ommited to mark mass(m) as kg/sec...

"administration kills engineering"

 

[daubery]

Hi 'ddace',

Not true, in this case, as the initial question was regarding heating of a stationary lump of material from an initial temp to a final temp.

The actual equation should read:

q' = d/dt (m*Cp*T,solid) [W, or J/s]

(the rate of thermal storage in the mass...

Your equation (with m') refers to calculations of a 'moving/flowing fluid' - hence 'mass-flow-rate [kg/s]'.

Regards,

Des Aubery...
(adTherm Technology -

http://www.adtherm.com

- info@adtherm.com )