Answer:
T = 858.25 s
Explanation:
Given data:
Reheat stage for a 100-mm-thick steel plate ( 7830 kg/m3, c 550 J/kg K, k 48 W/m K),
initial uniform temperature ( Ti ) = 200 c
Final temperature = 550 c
convection coefficient = 250 w/m^2 k
products combustion temp = 800 c
calculate how long the plate should be left in the furnace ( to attain 550 c )
first calculate/determine the Fourier series Number ( Fo )

= 0.4167 = 
therefore Fo = 3.8264
Now determine how long the plate should be left in the furnace
Fo = 
k = 48
p = 7830
L = 0.1
Input the values into the relation and make t subject of the formula
hence t = 858.25 s
Ummm did you try to add or subtract and multiply or divide that can get your answer
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Solution:
Given that :
Volume flow is, 
So, 
Therefore, the equation of a single straight vessel is given by
......................(i)
So there are 100 similar parallel pipes of the same cross section. Therefore, the equation for the area is

or 
Now for parallel pipes
...........(ii)
Solving the equations (i) and (ii),




Therefore,

or 
Thus the answer is option A). 10