Light from Proxima Centauri takes _____ to reach Earth
A) 2 years
B) 4.2 years
C) 6 years
D) 8.4 years
B
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Calculate the average heat transfer coefficient for film-type condensation of water at pressures of 10 kPa and 101 kPa for (a) a vertical surface 1.5-m-high (b) the outside surface of a 1.5-cm-OD vertical tube 1.5-m-long (c) the outside surface of a 1.6-cm-OD horizontal tube 1.5-m-long and (d) a 10-tube vertical bank of 1.6-cm-OD horizontal tubes 1.5-m-long. In all cases, assume that the vapor velocity is negligible and that the surface temperatures are constant at 11°C below saturation temperature.
GIVEN
? Film condensation of water
FIND
The average heat transfer coefficient at pressure of 10 kPa and 101 kPa for
(a) A vertical surface of height (H) = 1.5 m
(b) The outside surface of a vertical tube Outside diameter (D) = 1.6 cm = 0.016 m
Height (H) = 1.5 m
(c) The outside surface of a horizontal tube Outside diameter (D) = 1.6 cm = 0.016m
Length (L) = 1.5 m
(d) A 10 tube vertical bank of horizontal tubes Outside diameter (D) = 1.6 cm
Length (L) = 1.5 m
ASSUMPTIONS
? Steady state
? Vapor velocity is negligible
? Surface temperatures (Ts) are constant at 11°C below saturation temperature
? Film thickness is much smaller than the pipe diameter
? Laminar condensate flow
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 13, the saturation temperatures for water at
101 kPa (Tsv1) = 100°C, therefore Ts = Tsv – 11°C = 89°C
10 kPa (Tsv2) = 45.3°C, therefore, Ts = 34.3°C
The film temperatures, as given in Section 9.4.1 are
Tfilm1 = Ts + 0.25 (Tsv – Ts) = 89°C + 0.25 (11°C) = 91.8°C
Tfilm2 = 34.3°C+ 0.25 (11°C) = 37.1°C
From Appendix 2, Table 13, for water at the film temperatures
Refer to the graph. The velocity of this object at the start of the motion is
A. negative. B. positive. C. zero (it is not moving). D. It is not possible to tell from the graph
A light ray bends when it goes from one medium to another because of __________
Fill in the blank(s) with correct word
A nuclear reaction, which gives off a total of 1.2 × 10^17 J of energy, expends how much mass in the process? (c = 3.00 × 10^8 m/s)
a. 0.1 kg b. 1.3 kg c. 4.0 kg d. 13.3 kg e. 7.5 kg