As a guide, prepare a similar table showing the order of magnitudes of the thermal resistances of a unit area for convection between a surface and various fluids.
GIVEN
• The order of magnitude of convective heat transfer coefficient ( h c)
FIND
• The order of magnitudes of the thermal resistance of a unit area (A Rc) SOLUTION
The thermal resistance for convection is defined by Equation as
The thermal resistance for convection is defined as
Therefore the thermal resistances of a unit area are simply the reciprocal of the convective heat
transfer coefficient
As an example, the first item in Table 1.4 is ‘air, free convection’ with a convective heat transfer
coefficient of 6–30 W/(m2 K). Therefore the order of magnitude of the thermal resistances of a unit
area for air, free convection is
The rest of the table can be calculated in a similar manner
You might also like to view...
Air is denser than water, which has implications for underwater divers
What will be an ideal response?
Torque: A flat circular wire loop of area 0.25 m2 carries a current of 5.0 A. This coil lies on a horizontal table with the current flowing in the counterclockwise direction when viewed from above. At this point, the earth's magnetic field is 1.2 × 10-5 T directed 60° below the horizontal. What is the magnitude of the torque that the earth's magnetic field exerts on this loop?
A. 2.5 × 10-6 N ? m B. 5.0 × 10-6 N ? m C. 7.5 × 10-6 N ? m D. 1.0 × 10-5 N ? m
Why is the greenhouse effect weaker on Mars than on Earth or Venus?
A. High water vapor clouds reduce the amount of sunlight that reaches the planet's surface. B. There is no carbon dioxide in Mars's atmosphere. C. Mars's atmosphere is much thinner than those of Venus and Earth. D. Fog and frost on the Martian surface reflect much of the Sun's energy.
Conservation of Momentum: A small car meshes with a large truck in a head-on collision. Which of the following statements concerning the magnitude of the momentum change during the collision is correct? (There could be more than one correct choice.)
A. The truck experiences the greater magnitude momentum change. B. The small car experiences the greater magnitude momentum change. C. The small car and the truck experience the same magnitude momentum change. D. The magnitude of the momentum change experienced by each one is inversely proportional to its mass. E. The magnitude of the momentum change experienced by each one is directly proportional to its mass.