An inductor has 1000 turns/m and an internal volume of 30 cm3 . What is its inductance?
a. 0.38 H
c. 3.8 mH
b. 38 mH
d. Insufficient information is given.
B
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A horizontal shell-and-tube heat exchanger is used to condense organic vapors. The organic vapors condense on the outside of the tubes, while water is used as the cooling medium on the inside of the tubes. The condenser tubes are 1.9-cm-O.D., 1.6-cm-ID copper tubes, 2.4 m in length. There are a total of 768 tubes. The water makes four passes through the exchanger. Test data obtained when the unit was first placed into service are as follows
Water rate = 3700 l/min
Inlet water temperature = 29°C
Outlet water temperature = 49°C
Organic-vapor condensation temperature = 118°C
After 3 months of operation, another test, made under the same conditions as the first (i.e., same water rate and inlet temperature and same condensation temperature) showed that the exit water temperature was 46°C.
(a) What is the tube-side-fluid (water) velocity?
(b) What is the effectiveness, e-NTU, of the exchanger at the time of the first and second test.
(c) Assuming no changes in either the inside transfer coefficient on the condensing
coefficient, negligible shell-side fouling, and no fouling at the time of the first test,
estimate the tube-side fouling coefficient at the time of the second test.
GIVEN
• A shell-and-tube exchanger, organic vapors condensing in shell, water in copper tubes
• Tube diameters
? Do = 1.9 cm = 0.019 m
? Di = 1.6 cm = 0.016 m
• Tube length (L) = 2.4 m
• Number of tubes (N) = 768
• Number of tube passes (Np) =4
• Water flow rate v w= 3700 1/min = 3.7 m3/min
• Water temperatures
? Tw,in = 29°C
? Tw,out = 49°C
• Organic vapor condensation temperature (Tc) = 118°C
• After 3 months: Tw,out = 46°C
FIND
(a) Water velocity (Vw)
(b) The effectiveness (e) at the time of both tests
(c) Fouling coefficient (1/Ri) at the time of the second test
ASSUMPTIONS
• No fouling at the time of the first test
• No change in the inside and outside heat transfer coefficients
• Negligible shell-side fouling
• Length given is the length of one tube - all four passes
SKETCH
PROPERTIES AND CONSTANTS
for water at 40°C
Density (?) = 992 kg/m3 Specific heat (cpw) = 4175 J/(kg K)
Thermal conductivity (k) = 0.633 W/(m K)
Kinematic viscosity (?) = 0.658 × 10–6 m2/s
Prandtl number (Pr) = 4.3
the thermal conductivity of copper (kc) = 392 W/(m K) at 127°C.
Which of the following explains why navigators prior to a few hundred years ago found it much more difficult to determine longitude than latitude?
A) Determining longitude requires an accurate clock, but latitude does not. B) Determining longitude requires mathematical techniques that were not known at the time. C) Determining longitude requires much more precise measurements of angles in the sky than does latitude. D) Determining longitude requires accurate tables of the celestial coordinates of stars, while determining latitude does not.
Which of the following lists the outer planets in order of increasing mass?
A. Uranus, Neptune, Saturn, Jupiter B. Saturn, Jupiter, Uranus, Neptune C. Jupiter, Saturn, Uranus, Neptune D. Jupiter, Saturn, Neptune, Uranus
How many electrons does it take to fill the d subshell?
A) 10 B) 6 C) 14 D) 2 E) 4 F) 8