How long to cool Steel down to -50C
How long to cool Steel down to -50C
(OP)
Hi
I have an application where i need to have a steel bar at -50C.
The steel is 420 Stainless Steel
The Freezer is set at -50
The dimensions of the bar are 134.8mm diameter x 470mm long
It will start at ambient temp 22C
Can anyone tell me how long i should leave it in the freezer for to ensure that the core of the bar is at the required temperature.
Thanks
I have an application where i need to have a steel bar at -50C.
The steel is 420 Stainless Steel
The Freezer is set at -50
The dimensions of the bar are 134.8mm diameter x 470mm long
It will start at ambient temp 22C
Can anyone tell me how long i should leave it in the freezer for to ensure that the core of the bar is at the required temperature.
Thanks





RE: How long to cool Steel down to -50C
Presumably, your freezer's cooling system actually goes below -50°C in order to maintain -50°C. So what happens if the bar gets below -50°C?
TTFN
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RE: How long to cool Steel down to -50C
I am not concerned if the steel is below -50C
Cheers
RE: How long to cool Steel down to -50C
dU/dt=Qr+Qc >m*Cp*dT/dt= e*s*As*F*(T1^4-TA^4)+Hc*As(T1-TA)
Get a book on HT for an explanation of each term. If there is a temperature gradient than the internal energy side will become a lot more complicated.
RE: How long to cool Steel down to -50C
corus
RE: How long to cool Steel down to -50C
RE: How long to cool Steel down to -50C
corus
RE: How long to cool Steel down to -50C
corus
RE: How long to cool Steel down to -50C
TTFN
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RE: How long to cool Steel down to -50C
corus
RE: How long to cool Steel down to -50C
Can you post the equations etc that you used, as i am going to have to do this calc with various different steels and different dimensioned parts so a step through would be a great help.
Thanks
RE: How long to cool Steel down to -50C
Function f(x)
'x is the temperature at time i
f = sig * eps * ((x - Tzero) ^ 4 - (Ta - Tzero) ^ 4)
f = -2. * f / (density * Cp * r)
End
then in the main section, the 4th order Runge Kutta scheme :
k(1) = delt * f(T)
k(2) = delt * f(T + k(1) * 0.5)
k(3) = delt * f(T + 0.5 * k(2))
k(4) = delt * f(T + k(3))
T(i+1) = T(i) + (k(1) + 2# * k(2) + 2# * k(3) + k(4)) / 6.
where delt is the time increment and T(i+1) is the temperature at time T(i) + delt
sig is the stefan boltzman number, eps is emissivity, Cp is specific heat, Ta is the ambient, Tzero is absolute zero.
The equation for f(x) is for a long bar. For any other section profile, or shape, the equation would have to be adapted based on Surface area/Volume
corus
RE: How long to cool Steel down to -50C
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: How long to cool Steel down to -50C
RE: How long to cool Steel down to -50C
corus