A spiral galaxy is the result of the collision and merger of galaxies that leave moderate to large amounts of gas in the system.
Answer the following statement true (T) or false (F)
True
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A quantity that is measured in ohms is
a. voltage b. current c. resistance d. electric field e. critical temperature
An engineer is designing a heating system that consists of multiple tubes placed in a duct carrying the air supply for a building. She decides to perform preliminary tests with a single copper tube, 2-cm-O.D., carrying condensing steam at 100°C. The air velocity in the duct is 5 m/s and its temperature is 20°C. The tube is placed normal to the flow, but it may be advantageous to place the tube at an angle to the air flow and thus increase the heat transfer surface area. It the duct width is 1 m, predict the outcome of the planned tests and estimate how the angle ? will affect the rate of heat transfer. Are there limits?
GIVEN
• A copper tube carrying condensed steam in an air duct
• Tube outside diameter (D) = 2 cm = 0.02 m
• Steam temperature (Ts) = 100°C
• Air velocity (U?) = 5 m/s
• Air temperature (T?) = 20°C
• Duct width (w) = 1 m
FIND
• Is it more advantageous to have the tubes normal to the air flow or at some angle to the air flow?
ASSUMPTIONS
• Steady state
• Air velocity in the duct is uniform
• Thermal resistance due to steam condensing is negligible
• Thermal resistance of the tube wall is negligible
SKETCH
PROPERTIES AND CONSTANTS
Thermal conductivity (k) = 0.0251 W/(m K) Kinematic viscosity
(?) = 15.7 × 10–6 m2/s Prandtl number (Pr) = 0.71
When Earth was young, its atmosphere had no free ____
a. nitrogen b. oxygen c. helium d. carbon dioxide e. water vapor
You observe two helium balloons floating next to each other at the ends of strings secured to a table. The facing surfaces of the balloons are separated by 1-2 cm. You blow through the opening between the balloons. What happens to the balloons?
1.They move toward each other. 2.They move away from each other. 3.They are unaffected.