When playing pool or billiards, the paths of the two balls after a collision are at approximately right angles to one another. This is due to:
A. The fact that momentum is conserved
B. The fact that kinetic energy is conserved
C. The fact that both momentum and kinetic energy are conserved
C. The fact that both momentum and kinetic energy are conserved
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A mercury-in-glass thermometer at 40°C (OD = 1 cm) is inserted through duct wall into a 3 m/s air stream at 66°C. This can be modelled as cylinder in cross-flow, as shown in figure. Estimate the heat transfer coefficient between the air and the thermometer.
GIVEN
• Thermometer in an air stream
• Thermometer temperature (Ts) = 40°C
• Thermometer outside diameter (D) = 1 cm = 0.01 m
• Air velocity (V) = 3 m/s
• Air temperature (Tb) = 66°C
FIND
• The heat transfer coefficient ch
ASSUMPTIONS
• Steady state
• Turbulence in the free stream approaching the thermometer is low
• Effect of the duct walls in negligible
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 28, for dry air at the bulk temperature of 66°C
Thermal conductivity (k) = 0.0282 W/(m K) Kinematic viscosity (?) = 20*10-6 m2/s Prandtl number (Pr) = 0.71 At the thermometer surface temperature of 40°C, the Prandtl number (Prs) = 0.71
Hot water is used to heat air in a double pipe heat exchanger as shown in the following sketch. If the heat transfer coefficients on the water side and on the air side are 550 W/(m2K) and 55 W/(m2 K), respectively, calculate the overall heat transfer coefficient based on the outer diameter. The heat exchanger pipe is 5 cm, schedule 40 steel (k = 54 W/m K), with water inside.
GIVEN
• A double pipe heat exchanger with water in inner tube and air in the annulus
• Heat transfer coefficients
? Water side ih = 550 W/(m2 K)
? Air side oh = 55 W/(m2 K)
• Inner pipe: 5 cm, schedule 40 steel
• Pipe thermal conductivity (k) = 54 W/(m K)
FIND
• The overall heat transfer coefficient based on the outer diameter (Uo). ASSUMPTIONS
• Uniform heat transfer coefficients
SKETCH
PROPERTIES AND CONSTANTS
for 5 cm, schedule 40 pipe
? Outside diameter (Do) = 2.375 in = 6.033 cm=0.0603 m
? Wall thickness (t) = 0.154 in=0.39 cm=0.0039 m
What would happen if a rocket were launched into space with a speed greater than Earth's escape velocity?
A) It would travel away from Earth into the solar system. B) It would fall back to the Earth. C) It would enter into orbit around the Earth. D) It would reach the orbit of the Moon, but could go no farther. E) It is not possible to reach speeds that high.
The existence of asteroids is supporting evidence of the solar nebula hypothesis, in that ________.
A. the gaps in the asteroid belt are created by the same process that creates gaps in Saturn's rings B. the asteroids are probably fragments of a shattered planet C. asteroids in the inner Solar System are small and rocky, while those in the outer Solar System are larger and have atmospheres D. inner belt asteroids are richer in silicate and iron materials and contain fewer carbon-rich materials