Kirchhoff's Rules: A multiloop circuit is shown in the figure, but some quantities are not labeled. Find the current I1 if the batteries are ideal. (It is not necessary to solve the entire circuit.)
A. 0 A
B. +0.2 A
C. +0.4 A
D. -0.2 A
E. -0.4 A
Answer: B
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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)
A golf ball moving forward with 1 unit of momentum strikes and bounces backward off a heavy bowling ball that is initially at rest and free to move. The bowling ball is set in motion with a momentum of
A) less than 1 unit. B) more than 1 unit. C) 1 unit. D) not enough information
When you tune a radio to a certain station, you match the frequency of the internal electrical circuit to the frequency of that radio station, which illustrates
A) forced vibrations. B) resonance. C) beats. D) reverberation. E) wave interference.
Gluons
a. are carriers of the color force b. posses color charge c. can interact with each other via the color force d. can form glueballs e. all of the above