A boy decides to place his glass marbles in an oven at 200C The diameter of the marbles is 15 mm After a while he takes them from the oven and places them in room air at 20C to cool The convection heat transfer coefficient is approximately 14 W m2 C Calculate the time the boy must wait until the ce...

A boy decides to place his glass marbles in an oven at 200C. The diameter of the

Question:

A boy decides to place his glass marbles in an oven at 200ºC. The diameter of the marbles is 15 mm. After a while he takes them from the oven and places them in room air at 20ºC to cool. The convection heat-transfer coefficient is approximately 14 W/m2 · ºC. Calculate the time the boy must wait until the center temperature of the marbles reaches 50ºC.