At what frequency should a 200-turn, flat coil of cross sectional area of 300 cm2 be rotated in a uniform 30-mT magnetic field to have a maximum value of the induced emf equal to 8.0 V?
a. 7.5 Hz
b. 7.1 Hz
c. 8.0 Hz
d. 8.4 Hz
e. 16 Hz
b
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An air-to-water compact heat exchanger is to be designed to serve as an intercooler for a 3.7 MW gas turbine plant. The exchanger is to meet the following heat transfer and pressure drop performance specifications
Air-side Operating Conditions
The exchanger is to have a cross-flow configuration with both fluids unmixed. The heat
exchanger surface proposed for the exchanger consists of flattened tubes with continuous
aluminum fins specified as a 11.32– 0.737 – SR surface in Ref. 10. The heat exchanger is
shown schematically below.
The measured heat transfer and friction characteristic for this exchanger surface are
shown in the graph below
Geometrical details for the proposed surface are
The design should specify the core size, the air flow frontal area, and the flow length. The
water velocity inside the tubes is 1.34 m/s. See Problem 10.53 for the calculation of the
water side heat transfer coefficient.
Note: (i) the free-flow area is defined such that the mass velocity, G, is the air mass flow
rate per unit free flow area, (ii) the core pressure drop is given by ?p = fG2L/2?rh where
L is the length of the core in the air flow direction, (iii) the fin length, Lf, is defined such
that Lf = 2A/P where A is the fin cross-sectional area for heat conduction and P is the
effective fin perimeter.
GIVEN
? Air-to-Water Intercooler with the geometry and requirements specified above
? From Problem 10.53: Water side convective heat transfer coefficient (hc,H2O) = 7580 W/(m2 K)
FIND
(a) The air flow frontal area (Aair)
(b) The flow length (L)
(c) The core size
ASSUMPTIONS
? Steady state
? Entrance effects are negligible
? Flow acceleration effects are negligible
? Negligible fouling resistance
? Negligible variation in thermal resistance
? The thermal resistance of the tube wall is negligible
PROPERTIES AND CONSTANTS
From Appendix 2, Table 28, for air at the mean temperature of 77°C
From Appendix 2, Table 13, for water at 20°C, c = 4182 J/(kg K)
From Appendix 2, Table 12, the thermal conductivity of aluminum at 320 K (ka) = 238 W/(m K)
According to Wein's Law, if the surface temperature is increased by a factor of 2, its peak wavelength will:
A) increase by a factor of 2. B) decrease by a factor of 2. C) increase by a factor of 4. D) decrease by a factor of 4. E) not change; Wein's law has nothing to do with peak wavelength.
Despite varying masses, all spiral galaxies look essentially the same
Indicate whether the statement is true or false
A graph of x vs. t is linear, and intercepts the vertical axis at -15m and the horizontal axis at 5s. What is the value of x corresponding to t=3s?
A. 6m B. 26m C. -26m D. -9m E. 9m F. -6m