A 400-? resistor and an inductor are connected in parallel across a 300-Hz source. If the amplitude of the current in the resistor is equal to that in the inductor, what is the value of the inductance?
a. 0.212 H b. 0.666 H
c. 1.33 × 10^–6 H d. 0.333 H
a
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When viscous dissipation is appreciable, the conservation of energy [Eq. 5.6] must take into account the rate at which mechanical energy is irreversibly converted to thermal energy due to viscous effects in the fluid. This gives rise to an additional term, Ø , on the right-hand side, the viscous dissipation where
Apply the resulting equation to laminar flow between two infinite parallel plates, with
the upper plate moving at a velocity U. Assuming constant physical properties [p, cp, k,
?], obtain expressions for the velocity and temperature distributions. Compare the
solutions with the dissipation term included with the results when dissipation is
neglected. Find the plate velocity required to produce a 1 K temperature rise in
nominally 40°C air relative to the case where dissipation is neglected.
GIVEN
Laminar flow between two infinite parallel plates
Upper plate moves at a velocity U?
The viscous dissipation term given above must be used in the conservation of energy equation
FIND
(a) Expression for velocity and temperature distributions
(b) Compare these to solutions without the dissipation term
(c) Plate velocity that gives a 1 K rise in 40°C air relative to the case without the dissipation term
ASSUMPTIONS
Steady state
Constant physical properties
The plates are at constant temperatures, T1, T2
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 28, for dry air at 40°C
Thermal conductivity (k) = 0.0265 W/(m K)
Absolute viscosity (?) = 19.1 x 10–6 N s/m2
In your office, you have a rolling chair and a rolling filing cabinet. The chair weighs 10 pounds, and the filing cabinet weighs 50 pounds (it's partly full). If you push both of them away with about the same strength
A. the chair will accelerate about 5 times as much as the cabinet. B. the cabinet will accelerate about 25 times as much as the chair. C. the chair will accelerate about 25 times as much as the cabinet. D. the cabinet will accelerate about 5 times as much as the chair. E. both will accelerate about the same.
A thick-walled metal pipe of length 20 cm has an inside diameter of 2.0 cm and an outside diameter of 2.4 cm. What is the total surface area of the pipe, counting the ends?
What will be an ideal response?
A fully charged parallel-plate capacitor remains connected to a battery while you slide a dielectric between the plates. What happens to the value of C?
1.It increases. 2.It decreases. 3.It stays the same.