Steel plates are manufactured in a rectangular shape with a length of 0.5 m, a width of 0.2 m, and a thickness of 20 mm. The plates are heat treated to a temperature of 300°C and left to cool under natural convection in ambient air at 20°C. As a thermal engineer you want to minimize the time it takes for the plates to cool down to a safe temperature.

a. How should the plates be oriented while cooling?
b. When oriented in this way, how long will it take for the plates to reach 50°C?
c. Your boss tells you that this cooling time is too long, and it needs to be decreased by a factor of ten. You decide to hang the plates vertically (long side pointed up/down) and blow air parallel over the plates using a fan. What is the minimum air speed that is required to meet this goal?
d. At what air speeds will conduction through the steel begin to play a relevant role in the overall cooling time of the plate?
e. Your boss says that the air speeds from (C) and (d) are both too large and cannot be generated with the fans your company has. Can you reduce the required air speed while achieving the same cooling time? How?