Which of the speeds v listed below is the lowest speed where the probability of a gas molecule having that speed is negligible compared to that for v = vp (“negligible” meaning less than 1/100 of its value at v = vp ).
A. v ? 0.2 vp
B. v = 2 vp
C. v = 3 vp
D. v = 5 vp
D. v = 5 vp
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Consider a heat treatment process in which steel rods with a 10 cm diameter at an initial temperature of 600°C are inserted into an oil bath at 25°C. Assuming a convection coefficient of 400 W/(m2 K) between the oil and the rod, estimate how long it takes for the centerline of the rod to cool to 60°C. If the steel rod, which is 1 m long, is withdrawn from the bath at this point in the process, i.e., when the centerline temperature has reached 60°C, estimate the rate at which heat must be extracted from the oil to maintain its temperature constant during the process of treating 25 rods per hour.
GIVEN
• Heat treatment of steel rod inserted in oil bath
• Rod outside diameter = 0.1 m
• Initial temperature (T0) = 600°C
• Oil bath temperature (T?) = 25°C
• The average heat transfer coefficient ch = 400 W/(m2 K)
FIND
• Time it takes for centerline of the rod to cool to 600C.
• Rate at which heat must be extracted from oil to maintain its temperature constant during the process of treating 25 rods per hour.
ASSUMPTIONS
• Radial conduction only in billet
• Uniform and constant properties
SKETCH
The Sun appears to be red as it sets because:
1.Air absorbs red light less than other frequencies (i.e., acts like a red filter). 2.The sunlight has a red-shift when you're moving fastest away from it. 3.The Sun cools down to 5000 K each evening. 4.Light is refracted as it enters the atmosphere. 5.The Sun dies in a glorious fireball each evening and is reborn each morning. 6.None of the above.
If you are measuring the thickness of a strand of human hair, the most appropriate SI unit is the
A) kilometer. B) meter. C) centimeter. D) millimeter. E) micrometer.
When Saturn is at Equinox, its rings will
A) double the planet's brightness. B) appear face-on to the Earth. C) lie perpendicular to the plane of the ecliptic. D) contract closer to the planet's surface. E) lie in the plane of the ecliptic.