Cooling rate of some very hot steel
Cooling rate of some very hot steel
(OP)
I have a somewhat rectangle of .75 in x .75 in x 2 in. piece of low-carbon steel (1069) starting at 2250 F going to 1800 F set alone to cool off in 65 F air and need to find an approx. time between temps. I'm assuming no radiation, no forced convection, the grip holder is not affecting it and have standard conduction formula (q=hA(T-Ta). Think I can assume lumped capacitance? I'm thinking the convection coefficient will have to be up there because of how hot the steel is. Also assuming heat is leaving in all directions equally because of how small the thing is. I found a value of 45000 W/m^2*K but that seems to high and 10 seems to low. Thanks





RE: Cooling rate of some very hot steel
RE: Cooling rate of some very hot steel
RE: Cooling rate of some very hot steel
Your value of conductivity seems low as normally the value is about 50 W/m K. You'll also need density (7850 kg/m^3) and specific heat, about 500 J/kg C, if I remember.
corus
http://www.corusresearch.com
RE: Cooling rate of some very hot steel
RE: Cooling rate of some very hot steel
Natural convection coefficient is usually expressed in terms of A(T-Ta)^0.333 where A is a constant dependent upon the orientation of the surface. Including it in your calculation shouldn't be a problem if you're going to make the sum total of the two as a function of temperature.
You may find exact solutions have already been made for the case of radiation alone, however, as I think all you're solving is pcdT/dt=Ae(Tk^4-Tak^4). Remember Tk in the radiation part of the equation is in degrees K.
corus
http://www.corusresearch.com
RE: Cooling rate of some very hot steel
I analysed the problem using the limited data provided by you, using an FE software and I found after 90 seconds the whole mass coming to below the temperature you mentioned 1800 deg F (982 deg C).In this case both radiation and natural convection is taken.
Due to very high temperature the radiation effct is a major one and natural convection heat tranfer is insignificant. In that analysis if consider only the radiation heat transfer, the time required to cool the mass below 1800 deg F is roughly 110 seconds only.
Thermal conductivity value you mentioned is alright. Mr Corus has mentioned around 50 W/m K, but that value is for around 20 deg C and at higher temperatures the value is coming down.
I am having the complete analysis results. If you want please drop mail to me.
KMP
kmpillai@hotmail.com
RE: Cooling rate of some very hot steel
Have fun in the new job!
Jack
Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering
www.KleinfeldTechnical.com