The passenger compartment of a minivan traveling at 60 mph can be modeled as a 3.2-ft-high, 6-ft-wide, and 11-ftlong rectangular box whose walls have an insulating value of R-3 (i.e., a wall thickness-to-thermal conductivity ratio of 3 h?ft2?°F/Btu). The interior of a minivan is maintained at an average temperature of 70°F during a trip at night while the outside air temperature is 90°F. The average heat transfer coefficient on the interior surfaces of the van is 1.2 Btu/h?ft2?°F. The air flow over the exterior surfaces can be assumed to be turbulent because of the intense vibrations involved, and the heat transfer coefficient on the front and back surfaces can be taken to be equal to that on the top surface. Disregarding any heat gain or loss by radiation, determine the rate of heat transfer from the ambient air to the van. Assume the air flow to be entirely turbulent because of the intense vibrations involved. Use a film temperature of 80°F for evaluations of air properties at 1 atm.
The passenger compartment of a minivan traveling
at 60 mph can be modeled as a 3.2-ft-high, 6-ft-wide, and 11-ftlong
rectangular box whose walls have an insulating value of
R-3 (i.e., a wall thickness-to-thermal conductivity ratio of
3 h?ft2?°F/Btu). The interior of a minivan is maintained at an
average temperature of 70°F during a trip at night while the
outside air temperature is 90°F.
The average heat transfer coefficient on the interior surfaces
of the van is 1.2 Btu/h?ft2?°F. The air flow over the
exterior surfaces can be assumed to be turbulent because of
the intense vibrations involved, and the heat transfer coefficient
on the front and back surfaces can be taken to be equal
to that on the top surface. Disregarding any heat gain or loss
by radiation, determine the rate of heat transfer from the
ambient air to the van. Assume the air flow to be entirely turbulent
because of the intense vibrations involved. Use a film
temperature of 80°F for evaluations of air properties at 1 atm.
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