In a series RLC circuit a capacitor will be dominant at lower frequencies
Indicate whether the statement is true or false
TRUE
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The greenhouse effect occurs because carbon dioxide in the atmosphere absorbs __________ radiation
Fill in the blank(s) with correct word
A proton has an initial velocity to the south but is observed to curve upward as the result of a magnetic field. This magnetic field must have a component
A) upward. B) to the east. C) to the west. D) downward. E) to the north.
Uranus was discovered by accident, and mistaken for a comet at first
Indicate whether the statement is true or false
Exhaust gases from a power plant are used to preheat air in a cross-flow heat exchanger. The exhaust gases enter the heat exchanger at 450°C and leave at 200°C. The air enters the heat exchanger at 70°C, leaves at 250°C, and has a mass flow rate of 10 kg/s. Assume the properties of the exhaust gases can be approximated by those of air. The overall heat transfer coefficient of the heat exchanger is 154 W/(m2 K). Calculate the heat exchanger surface area required if (a) the air is unmixed and the exhaust gases are mixed and (b) both fluids are unmixed.
GIVEN
• Cross-flow heat exchanger – exhaust gas to air
• Exhaust temperatures
? Te,in = 450°C
? Te,out = 200°C
• Air temperatures
? Ta,in = 70°C
? Ta,out = 250°C
• Air flow rate m a= 10 kg/s
• Overall heat transfer coefficient (U) = 154 W/(m2 K)
FIND
The heat exchanger surface area (A) if
(a) Air is unmixed, exhaust is mixed
(b) Both are unmixed
ASSUMPTIONS
• The properties of the exhaust gases can be approximated by those of air
• The air is in the tube
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of air at the mean temperature of 160°C (cpa)