The mug shown in the figure is full to the rim with hot water at 90 ◦C. The mug’s wall is 5 mm in thickness and has a thermal conductivity of 0.15W/m K. The vessel is in atmospheric air with a...

The mug shown in the figure is full to the rim with hot water at 90 ◦C. The mug’s wall is 5 mm in thickness and has a thermal conductivity of 0.15W/m K. The vessel is in atmospheric air with a temperature of 20 ◦C.

(a) Calculate the total rate of heat loss from the mug to air, assuming that the air is quiescent.

(b) Repeat part (a), this time assuming that a breeze causes air to flow across the mug at a velocity of U_∞
= 10 cm/s.

For simplicity, neglect heat loss from the bottom of the mug and neglect the effect of evaporation at the free surface of water.