This problem will be compared to the problem of natural convection from the ground. a team of soil scientists are interested in finding out how much grasses contribute to heat transfer from the earth surface to the ambient air, thereby cooling down the surface temperature. they model that the grass blades act as fins. the ground temperature is 33 c, while the air above is 22 c. we estimate that the heat transfer coefficient h-1.0 w/m2-c (not the value in the other problem). the ground is horizontal and flat, of size 20 m by 20 m surrounded by a fence. the grass is 8.0 cm long, and we will apprpximate that each blade has a rectangular cross section 0.1 mm 1.0 mm, of uniform cross section. an approximate value of the conductivity k is 40% of water, or 0.24 w/m-c. there are about 50 blades of grass per cm2- 500.000/m2- 200 million on the whole plot of ground. what is the heat loss from the ground due to the grass acting as fins? .
a)-74 w b)-15,000 w c)-2,200 w d)-0.0322 e)-610w