Heat Transfer in a bar of steel 9

[Qshake]

Hello MEs.

I'm a long time member who usually stays in my own backyard - over in the structures area. But I have a situation where a relatively quick calculation (I hope) is appreciated from those of you with course work in heat transfer.

I have a 10' mild steel rod that at one free end is heated by a typical oxy-acetylene torch for say a period of 5 minutes. Let's say that the temperature for the 5 minute period is about 700 degrees F. Say the bar has an area of 1 square inch. How far along the bar's length will the heat travel?

Many thanks.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[zekeman]

racookpe197,

Excellent. Nice to see some empirical data and it looks almost like the analytic solution.

For the fun of it, I tried to compare the steady state solution, which I did for the infinite bar,
( since 10 feet acts virtually as "infinite") with the empirical

I get

T-T0=(Tm-T0)*exp-[sqrt(hp/Ka)x]
h=3 BTU/hr-ft^2-F
p/a=4/1/12=48-ft^-1 for the square bar
K=20 BTU/hr-ft-F
Tm =750
T0=70

hp/Ka=7.2
sqrt(hp/Ka)=2.68

Evaluating
at x=2"=1/6'
T-T0=(750-70)exp(-2.68/6)=434
T=504

at x= 6"
exp(-2.68*.5)=.261
T-T0=.261*680=178
T=248

at x=1ft
exp(-2.68*1)=0.068
T-T0=.068*680=47
T=117

BTW, the time constant for this system is 1/nu=1/2.4= .4 hrs = 24 minutes (obtained from the transient solution)

 

[racookpe1978]

Thank you for the calc's.