An automotive engine can be approximated asa 0.4-m-high, 0.60-m-wide, and 0.7-m-long rectangularblock. The bottom surface of the block is at a temperatureof 75°C and has an emissivity of 0.92. The ambient airis at 5°C, and the road surface is at 10°C. Determine therate of heat transfer from the bottom surface of the engineblock by convection and radiation as the car travels at avelocity of 60 km/h. Assume the flow to be turbulent over theentire surface because of the constant agitation of the engineblock. How will the heat transfer be affected when a 2-mmthickgunk (k = 3 W/m?K) has formed at the bottom surface asa result of the dirt and oil collected at that surface over time?Assume the metal temperature under the gunk still to be 75°C.

An automotive engine can be approximated as
a 0.4-m-high, 0.60-m-wide, and 0.7-m-long rectangular
block. The bottom surface of the block is at a temperature
of 75°C and has an emissivity of 0.92. The ambient air
is at 5°C, and the road surface is at 10°C. Determine the
rate of heat transfer from the bottom surface of the engine
block by convection and radiation as the car travels at a
velocity of 60 km/h. Assume the flow to be turbulent over the
entire surface because of the constant agitation of the engine
block. How will the heat transfer be affected when a 2-mmthick
gunk (k = 3 W/m?K) has formed at the bottom surface as
a result of the dirt and oil collected at that surface over time?
Assume the metal temperature under the gunk still to be 75°C.