A spherical ball of lead (density 11.3 g/cm3 ) is placed in a tub of mercury (density 13.6 g/cm3 ). Which answer best describes the result?
A) The lead ball will float with about 17% of its volume above the surface of the mercury.
B) The lead ball will float with about 83% of its volume above the surface of the mercury.
C) The lead will sink to the bottom of the mercury.
D) The lead ball will float with its top exactly even with the surface of the mercury.
A
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Water flowing in a long aluminum tube is to be heated by air flowing perpendicular to the exterior of the tube. The ID of the tube is 1.85 cm and its OD is 2.3 cm. The mass flow rate of the water through the tube is 0.65 kg/s and the temperature of the water in the tube averages 30°C. The free stream velocity and ambient temperature of the air are 10 m/s and 120°C, respectively. Estimate the overall heat transfer coefficient for the heat exchanger using appropriate correlations from previous chapters. State all your assumptions.
GIVEN
• Air flowing perpendicular to the exterior of an aluminum tube with water flowing within the tube
• Tube diameters
? Inside (Di) = 1.85 cm = 0.0185 m
? Outside (Do) = 2.3 cm = 0.023 m
• Mass flow rate of water (mw) = 0.65 kg/s
• Average temperature of the water (Tw) = 30°C
• Air free stream velocity (Va) = 10 m/s
• Air temperature (Ta) = 120°C FIND
• The overall heat transfer coefficient (U)
ASSUMPTIONS
• Steady state
• The variation of the Prandtl number of air with temperature is negligible
• The aluminum is pure
SKETCH
PROPERTIES AND CONSTANTS
thermal conductivity of aluminum (kal) = 238 W/(m K) at 75°C
for water at 30°C
Density (?w) = 996 kg/m3 Thermal conductivity (kw) = 0.615 W/(m K)
Absolute viscosity (?w) = 792 × 10–6 (Ns)/m2
Prandtl number (Prw) = 5.4
for dry air at 120°C
Thermal conductivity (ka) = 0.0320 W/(m K)
Kinematic viscosity (?) = 26.0 × 10–6 m2/s
Prandtl number (Pr) = 0.71
A puck moves on a horizontal air table. It is attached to a string that passes through a hole in the center of the table
As the puck rotates about the hole, the string is pulled downward very slowly and shortens the radius of rotation, so the puck gradually spirals in towards the center. What happens to the puck's angular speed?
The majority of earthquakes occur where
A) lithospheric plates meet. B) the asthenosphere touches the lithosphere. C) the land surface is made of unconsolidated sediments. D) narrow zones of land touch.
A firecracker breaks up into two pieces, one of which has a mass of 200 g and flies off along the +x-axis with a speed of 82.0 m/s. The second piece has a mass of 300 g and flies off along the +y-axis with a speed of 45.0 m/s
What is the total momentum of the two pieces? A) 361 kg ? m/s at 56.3° from the +x-axis B) 93.5 kg ? m/s at 28.8° from the +x-axis C) 21.2 kg ? m/s at 39.5° from the +x-axis D) 361 kg ? m/s at 0.983° from the +x-axis E) 21.2 kg ? m/s at 56.3° from the +x-axis