The Moon and Mercury can be eliminated as hosts for life because:
A) they do not have an atmosphere and water would boil away into space.
B) they have water in the form of ice.
C) they only have traces of water vapor in their atmospheres.
D) they do not have solid surfaces.
A
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Two pulses are traveling towards each other at 10 cm/s on a long string at t = 0 s, as shown below
Which diagram below correctly shows the shape of the string at 0.5 s?
a.
Physics & Space Science
Consider a heat exchanger consisting of 12.5 mm OD copper tubes in a staggered arrangement with transverse spacing 25 mm, longitudinal spacing 30 mm, and 9 tubes in the longitudinal direction. Condensing steam at 150°C flows inside the tubes. The heat exchanger is used to heat a stream of air flowing at 5 m/s from 20°C to 32°C. What is the average heat transfer coefficient and pressure drop for the tube bank?
GIVEN
Staggered copper tube bank with condensing steam inside tubes and air flowing over the outside
Tube outside diameter (D) = 12.5 mm = 0.0125 m
Transverse spacing (ST) = 25 mm = 0.025 m
Longitudinal spacing (SL) = 30 mm = 0.03 m
Number of rows of tubes (N) = 9
Steam temperature (Ts) = 150°C
Air velocity (Us) = 5 m/s
Air temperature: Ta,in = 20°C Ta,out = 32°C
FIND
(a) The average heat transfer coefficient (hc)
(b) The pressure drop (?p)
ASSUMPTIONS
Steady state
Thermal resistance of the condensing steam and the copper tube is negligible. Therefore, the tube
surface temperature = Ts
SKETCH
PROPERTIES AND CONSTANTS
Density (?) = 1.157 kg/m3
Thermal conductivity (k) = 0.0251 W/(m K)
Kinematic viscosity (?) = 15.9 × 10–6 m2/s
Prandtl number (Pr) = 0.71
Specific heat (c) = 1012 J/(kg K)
At the tube temperature of 150°C: Prs = 0.71
Gauss's Law: The figure shows four Gaussian surfaces surrounding a distribution of charges.(a) Which Gaussian surfaces have an electric flux of +q/?o through them?(b) Which Gaussian surfaces have no electric flux through them?
What will be an ideal response?
Lens-Maker Formula: A double-convex thin lens has radii of curvature of magnitude 46 cm, and it is made of glass of index of refraction 1.60. What is the focal length of this lens?
A. infinite B. 38 cm C. -30 cm D. 18 cm E. -19 cm