The observations of sunspots on the Sun and craters on the Moon by Galileo contradicted the commonly held belief that the universe was
A) spherical
B) unchanging
C) infinite
D) perfect
D
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For a system undergoing an isothermal expansion, the work done on the working fluid is:
A. May be either, depending on the temperature B. Positive C. Zero D. Negative
Which of these was NOT true about the limitations of Bohr's model?
a. The Bohr model failed to explain why electrons do not radiate. b. The Bohr model could not predict spectral lines for elements which have more than one electron in the outer shell. c. The Bohr model could not account for splitting of spectral lines. d. The Bohr model could not account for the basic periodic nature of the elements. e. The Bohr model could not explain why each shell held the number of electrons that it did.
A shell-and-tube heat exchanger with two tube passes and a single shell pass is used to heat water by condensing steam in the shell. The flow rate of the water is 15 kg/s and it is heated from 60 to 80°C. The steam condenses at 140°C and the overall heat transfer coefficient of the heat exchanger is 820 W/(m2 K). If there are 45 tubes with an OD of 2.75 cm, calculate the length of tubes required.
GIVEN
• Shell-and-tube heat exchanger with two tube passes and one shell pass
• Water in tubes, condensing steam in shell
• Water flow rate m w= 15 kg/s
• Water temperatures
? Tw,in = 60°C
? Tw,out = 80°C
• Steam temperature (Ts) = 140°C
• Overall heat transfer coefficient (U) = 820 W/(m2 K)
• Number of tubes (N) = 45
• Tube outside diameter (D) = 2.75 cm = 0.0275 m
FIND
• The length of tubes (L)
ASSUMPTIONS
• Counterflow
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water at the mean temperature of 70°C (cpw)= 4188 J/(kg K)
A physical pendulum is composed of a disc whose center of gravity is attached to a thin rod. The disc has a moment of inertia of 1?2 MR2. The mass of the disc is 500 gm and has a radius of 4.00 cm. The length of the rod is 50.0 cm. The period of the physical pendulum is
A. 1.24 sec. B. 1.42 sec. C. 1.74 sec. D. 1.90 sec. E. 2.25 sec.