g Steel plates (AISI 1010) of 4 cm thickness initially at a uniform temperature of 500 deg C are cooled by air at 50 deg C with a convection coefficient of 30 W-m2-K-1. Estimate the time it will take for their midplane temperature to reach 100 deg C.

Solution :

Characteristic length  = thickness / 2

                                    = 0.02 m

Thermal conductivity for steel is 42.5 W/m.K

                  = 0.014

Since the Biot number is less than 0.01, the lumped system analysis is applicable.

Where,

T = temperature after t time

= surrounding temperature

= initial temperature

t = time

We calculate B:

  = 0.000416

Thus,

t = 5281.78 second

  = 88.02 minutes

Thus the time taken for reaching 100 degree Celsius is 88.02 minutes.

the warning light flashes for a second or two when the engine starts. if it stays on, there's must be something wrong with the coolant. you should never dare to continue driving when the light is on. pull over as soon as possible and shut the engine off.

hope this is what you're talking about