Which of the following is true of elliptical galaxies?
A) They usually have significant, ongoing star formation.
B) They usually contain abundant clouds of cool gas and dust.
C) They are usually bluish in color.
D) They are the most common type of galaxy in the central regions of galaxy clusters.
D) They are the most common type of galaxy in the central regions of galaxy clusters.
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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 astronomical object is the most important source for determining the age of our Solar System?
a. lunar rocks b. Earth core samples c. meteorites d. meteors e. asteroids
Rapid change of a magnetic field induces
A) a magnetic field of greater magnitude. B) a magnetic field of the same magnitude. C) an electric field.
What is the number of molecules of O2 consumed if you combust one mole of CH4 according to the following balanced equation?
CH4 + 2 O2 ? CO2 + 2 H2O A) 1 molecule B) 2 molecules C) 6.022 × 1023 molecules D) 1.204 × 024 molecules E) 1 g of molecules