S0 galaxies have spiral arms, but little to no gas and dust. This is believed to happen because ____
a. their gas has been cannibalized by other galaxies
b. they have had bursts of star formation during major collision the gas and dust formed new stars
c. starburst events have used up all of the gas and dust in the disk
d. gas and dust have been stripped from the galaxies as they pass through hot, intergalactic gas
e. tidal interactions have forced the gas into the central bulge
d
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The second step in the precipitation-hardening process is to _________the alloy to maintain a uniform distribution of atoms in the grains at low temperature.
Fill in the blank(s) with the appropriate word(s).
The Earth remains in orbit about the Sun, rather than falling in to the Sun, because
1.it is outside of the gravitational influence of the Sun. 2.the net force on the Earth is zero. 3.although the Earth is constantly being pulled toward the Sun, it is always moving with a velocity component perpendicular to the direction that it is being pulled. 4.none of these apply.
Consider a heat exchanger consisting of 12.5 mm OD copper tubes in a staggered arrangement with transverse spacing 25 mm, longitudinal spacing 30 mm, and 9 tubes in the longitudinal direction. Condensing steam at 150°C flows inside the tubes. The heat exchanger is used to heat a stream of air flowing at 5 m/s from 20°C to 32°C. What is the average heat transfer coefficient and pressure drop for the tube bank?
GIVEN
Staggered copper tube bank with condensing steam inside tubes and air flowing over the outside
Tube outside diameter (D) = 12.5 mm = 0.0125 m
Transverse spacing (ST) = 25 mm = 0.025 m
Longitudinal spacing (SL) = 30 mm = 0.03 m
Number of rows of tubes (N) = 9
Steam temperature (Ts) = 150°C
Air velocity (Us) = 5 m/s
Air temperature: Ta,in = 20°C Ta,out = 32°C
FIND
(a) The average heat transfer coefficient (hc)
(b) The pressure drop (?p)
ASSUMPTIONS
Steady state
Thermal resistance of the condensing steam and the copper tube is negligible. Therefore, the tube
surface temperature = Ts
SKETCH
PROPERTIES AND CONSTANTS
Density (?) = 1.157 kg/m3
Thermal conductivity (k) = 0.0251 W/(m K)
Kinematic viscosity (?) = 15.9 × 10–6 m2/s
Prandtl number (Pr) = 0.71
Specific heat (c) = 1012 J/(kg K)
At the tube temperature of 150°C: Prs = 0.71
star Arcturus is a red giant that is easily visible in the night sky. Based on models of stellar evolution, what is happening to Arcturus as this stage of its life?
A) It is increasing in size, and hydrogen fusion reactions are occurring in a shell around the core. B) It is stable in its size, and hydrogen fusion reactions are occurring in its core. C) It is decreasing in size, and hydrogen fusion reactions are occurring in its core. D) It is increasing in size, and hydrogen fusion reactions are occurring in its core. E) It is decreasing in size, and hydrogen fusion reactions are occurring in a shell around the core. F) It is stable in its size, and hydrogen fusion reactions are occurring in a shell around the core.