Can a star become a red giant more than once?
A) yes, before and after the helium flash
B) no, the planetary nebula blows off all the outer shells completely
C) yes, before and after the Type II supernova event
D) no, or we would see them as the majority of naked-eye stars
E) no, it will lose so much mass as to cross the Chandrasekhar Limit
A
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Water entering a shell-and-tube heat exchanger at 35°C is to be heated to 75°C by an oil. The oil enters at 110°C and leaves at 75°C. The heat exchanger is arranged for counterflow with the water making one shell pass and the oil two tube passes. If the water flow rate is 68 kg per minute and the overall heat transfer coefficient is estimated from Table 10.1 to be 320 W/(m2 K), calculate the required heat exchanger area.
GIVEN
• One shell pass, two tube passes counterflow heat exchanger with water in shell, oil in tube
• Water temperatures Tw,in = 35°C Tw,out = 75°C
• Oil temperatures To,in = 110°C Tw,out = 75°C
• Water flow rate m n= 68 kg/min = 1.133 kg/s
• Overall heat transfer coefficient (U) = 320 W/(m2 K)
FIND
• The required area (A)
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water at the average temperature of 55°C (cpw)= 4180 J/(kg K)
Which of the following is an important starting assumption in models of galaxy formation?
A) Some regions in the universe start out denser than others. B) Galaxies form first, then black holes. C) All galaxies start out as spiral galaxies. D) Black holes form first, seeding the formation of galaxies.
Which of the curves in the figure best shows the speed of an object falling from rest without air friction?
A. A B. B C. C
The segment of wire (total length including portions of incoming and outgoing wire = 6R) is formed into the shape shown and carries a current I. What is the magnitude of the resulting magnetic field at the point P?
a.
