What do astronomers mean when they say that we are all "star stuff"?
A) that life would be impossible without energy from the Sun
B) that Earth formed at the same time as the Sun
C) that the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cores
D) that the Sun formed from the interstellar medium: the "stuff" between the stars
E) that the Universe contains billions of stars
C
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Molecular Vibration: For a diatomic quantum mechanical vibrator, the energy difference between adjacent quantum states
A. increases as the integer v increases. B. decreases as the integer v increases. C. is constant for all values of the integer v. D. varies randomly as the integer v increases.
We are not yet capable of detecting life on planets around other stars. But as our technology develops, our first real chance of detecting such life will probably come from
A) examining spectral lines from the atmospheres of distant planets. B) sending spacecraft to study the planets up close. C) examining high-resolution images of the planets made by orbiting telescopes. D) determining the orbital properties of the planets.
Mercury is to be evaporated at 317°C in a furnace. The mercury flows through a 25.4 mm BWG No. 18 gauge 304 stainless-steel tube, that is placed in the center of the furnace. The furnace cross section, perpendicular to the tube axis, is a square 20 cm by 20 cm. The furnace is made of brick having an emissivity of 0.85, and its walls maintained uniformly at 977°C. If the convection heat transfer coefficient on the inside of the tube is 2.8 kW/(m2 K) and the emittance of the outer surface of the tube is 0.60, calculate the rate of heat transfer per meter of tube, neglecting convection within the furnace.
GIVEN
Mercury flow through a tube in the center of a furnace
Mercury temperature (Tm) = 317°C = 590 K
Tube specification: 25.4 mm BWG no 18 gauge stainless steel
Furnace cross section is 20 cm x 20 cm = 0.2 m x 0.2 m
Furnace emissivity (Tube specification: 25.4 mm BWG no 18 gauge stainless steel
Furnace wall temperature (T2) = 977°C = 1250 K
Tube interior heat transfer coefficient (hci) = 2800 W/(m2 K)
Tube exterior emissivity (?1) = 0.602) = 0.85
FIND
The rate of heat transfer per meter of tube
ASSUMPTIONS
Steady state
Convection within the furnace is negligible
SKETCH
the Stephan-Boltzmann constant
for 25.4 mm 18 BWG tubes
Inside diameter (Di) = 22.9 mm= 0.0229 m
Outside diameter (Do) = 25.4 mm = 0.0254 m
for type 304 stainless steel,the thermal conductivity (ks) = 14.4 W/(m K)