Red-hot and blue-hot stars appear white to the eye because
A) the eye has difficulty seeing color at night.
B) they are too dim to fire the cones.
C) they are too dim to fire the rods.
D) they are overwhelmed by the blackness of the nighttime sky.
E) eye receptivity peaks in the yellow-green part of the spectrum.
Answer: B
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Replot the data points of Figure 5.9(b) on log-log paper and find an equation approximating the best correlation line. Compare your results with Figure 5.10. Then, suppose that steam at 1 atm and 100°C is flowing across a 5-cm-OD pipe at a velocity of 1 m/s. Using the data in Figure 5.10, estimate the Nusselt number, the heat transfer coefficient, and the rate of heat transfer per meter length of pipe if the pipe is at 200°C and compare with predictions from your correlation equation.
GIVEN
Figure 5.9(b) in text
Steam flowing across a pipe
Steam pressure = 1 atm
Steam temperature (Ts) = 100°C
Pipe outside diameter (D) = 5 cm = 0.05 m
Steam velocity (U?) = 1 m/s
Pipe temperature (Tp) = 200°C
FIND
(a) Replot Figure 5.9(b) on log-log paper and find an equation approximating the best correlation line
(b) Find the Nusselt number (Nu), the heat transfer coefficient (hc), and the rate of heat transfer per
unit length (q/L) using Figure 5.10
(c) Compare results with your correlated equation
ASSUMPTIONS
Steady state
Radiative heat transfer is negligible
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 35, for steam at 1 atm and 100°C
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A steel wire hangs from a high-altitude balloon. The steel has unit weight of 77 kN/m3 and yield stress of 280 MPa. The required factor of safety against yield is 2.0. The maximum permissible length of the wire is approximately:
(A) 1800 m (B) 2200 m (C) 2600 m (D) 3000 m
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