Which of the following does not provide evidence that Mars once had abundant liquid water on its surface?
A) the presence of features that look like dried up river beds
B) the presence of what looks like sedimentary layers in some crater bottoms
C) the presence of very old craters that appear to have been eroded by rain
D) the presence of canali, discovered in the late 1800s by Giovanni Schiaparelli and mapped by Percival Lowell
D
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______________ are cool, with temperatures of about 100 K and densities of ten to a few hundreds of atoms per cubic centimeter
Fill in the blank(s) with correct word
A 6.0-kg object is suspended by a vertical string from the ceiling of an elevator which is accelerating upward at a rate of 1.8 m/s2. Determine the tension in the string
a. 11 N b. 70 N c. 48 N d. 59 N e. 62 N
Two engineers are having an argument about the efficiency of a tube-side multipass heat exchanger compared to a similar exchanger with a single tube-side pass. Smith claims that for a given number of tubes and rate of heat transfer, more area is required in a two-pass exchanger than in a one-pass, because the effective temperature difference is less. Jones, on the other hand, claims that because the tube-side velocity and hence coefficient is higher, less area is required in a two-pass exchanger. With the conditions given below, which engineer is correct? Which case would you recommend, or what changes in the exchanger would you recommend?
Exchanger specifications
– 200 tube passes total
– 1 in.-O.D copper tubes, 16 B.W.G.
Tube-side fluid
Water entering at 16°C, leaving at 28°C, with a rate of 225,000 kg/h.
Shell-side fluid
Mobiltherm 600, entering at 50°C, leaving at 33°C.
Shell side coefficient = 1700 W/(m2 K)
GIVEN
• Tube and shell heat exchanger - water in tubes, Mobiltherm 600 in shell
• Number of tube passes (Np) = 200
• Tubes are 1 in copper 16 B.W.G.
• Water flow rate m w= 225,000 kg/h = 62.5 kg/s
• Water temperatures
? Tw,in = 16°C
? Tw,out = 28°
• Mobiltherm temperatures
? Tm,in = 50°C
? Tm,out = 33°C
• Shell side heat transfer coefficient h o= 1700 W/(m2 K)
FIND
• Which required less transfer area: (a) single tube pass (b) Two tube passes?
ASSUMPTIONS
• Thermal resistance of copper tube wall is negligible
SKETCH
PROPERTIES AND CONSTANTS
for 1 in 16 B.W.G. tubes, the diameters are
Di = 0.870 in. = 0.0221 m
Do = 1.0 in. = 0.0254 m
for water at the average temperature of 22°C
Thermal conductivity (k) = 0.601 W/(m K)
Kinematic viscosity (?) = 0.957 × 10–6 m2/s
Prandtl number (Pr) = 6.6
Density (?) = 998 kg/m3
Specific heat (cpw) = 4180 J/(kg K)
the specific heat of Mobiltherm 600 at its average temperature of 42°C (cpm) = 1654 J/(kg K)
Length Contraction: How fast would a rocket ship have to move past Earth to contract to half of its proper length as observed by an Earth-based physicist?
Fill in the blank(s) with the appropriate word(s).