Currently, most of the mass of the matter of the universe is believed to consist of
A) baryonic matter, made up of protons and neutrons.
B) tachyonic matter, travelling only faster than the speed of light.
C) dark matter not made of protons and neutrons.
D) dark energy.
E) tiny but very numerous black holes.
C
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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
In a flat Universe the angles of a triangle add up to ________.
A. exactly 360 degrees B. less than 180 degrees C. exactly 180 degrees
Seyfert galaxies are ________.
A. isolated black holes emitting radio waves B. bright elliptical galaxies C. spiral galaxies whose nucleus is abnormally luminous D. small irregular galaxies E. None of these choices is correct.
Clovis wants to lose weight. Clotilde tells him that he will be thin enough for her if he travels past her at 0.600c. If the distance she sees from the front of his stomach to his back is then 24.0 cm, what distance in cm does she see when he is standing still?
a. 15.4 b. 19.2 c. 24.0 d. 30.0 e. 37.5