Answer:

Step-by-step explanation:
Given that;
Thermal diffusivity

Thermal conductivity

Heat transfer coefficient h = ( we are to assume the imposed surface temperature ) = 20 W/m².K
Initial temperature = 150 ° C = (150+273) K = 423 K
Then coolant temperature with which the casting is exposed to = 20° C = (20+273)K = 293 K
Time = 40 seconds
Length = 20mm = 0.02 m
The objective is to determine the temperature at the surface at a depth of 20 mm after 40 seconds.


Bi == 0.02



For a wall at 0.2 Bi


Therefore;










