Which of the following statements is true of open clusters?
A) They contain 105 to 106 stars in a region about 10 pc in diameter.
B) They have a transparent appearance.
C) They comprise stars that are crowded together.
D) They are spherical.
B
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Mercury at an inlet bulk temperature of 90°C flows through a 1.2-cm-ID tube at a flow rate of 4535 kg/h. This tube is part of a nuclear reactor in which heat can be generated uniformly at any desired rate by adjusting the neutron flux level. Determine the length of tube required to raise the bulk temperature of the mercury to 230°C without generating any mercury vapor, and determine the corresponding heat flux. The boiling point of mercury is 355°C.
GIVEN
• Mercury flow in a tube
• Inlet bulk temperature (Tb,in) = 90°C
• Inside tube diameter (D) = 1.2 cm = 0.012 m
• Flow rate (m ) = 4535 kg/h = 1.26 kg/s
• Outlet bulk temperature (Tb,out) = 230°C
• Boiling point of mercury = 355°C
FIND
(a) The length of tube (L) required to obtain Tb,out without generating mercury vapor
(b) The corresponding heat flux (q/A)
ASSUMPTIONS
• Steady state
• Fully developed flow
SKETCH
PROPERTIES AND CONSTANTS
for mercury at the average bulk temperature of 160°C
Density (?) = 13,240 kg/m3
Thermal conductivity (k) 11.66 W/(m K)
Absolute viscosity (?) = 11.16 × 10–4 (Ns)/m2
Prandtl number (Pr) = 0.0130
Specific heat (c) = 140.6 J/(kg K)
Voltage can also be called potential
Indicate whether the statement is true or false
Answer the following statement(s) true (T) or false (F)
1. The mass of the earth–moon system is somewhat less than the sum of the mass of the earth and the mass of the moon. 2. If the activity of a radioactive sample has decreased by a factor of 4 in time T, then T = 2t1/2.
Determine the mass flow rate of R-134a required for steady state of the cross-flow heat exchanger shown. Air at 30ºC enters at a rate of 3.6 kg/s and leaves at 10ºC. The refrigerant enters at -10ºC, leaves at 5ºC, and has a specific heat of 2.1 kJ/kg?K.
