Entropy: What is the change in entropy of the lead when 2.0 kg of molten lead at its melting point temperature solidifies? For lead: LV = 207 kcal/kg at 1744°C, LF = 5.9 kcal/kg at 328°C.
Fill in the blank(s) with the appropriate word(s).
-0.020 kcal/K
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A counterflow regenerator is used in a gas turbine power plant to preheat the air before it enters the combustor. The air leaves the compressor at a temperature of 350°C. Exhaust gas leaves the turbine at 700°C. The mass flow rates of air and gas are 5 kg/s. Take the cp of air and gas to be equal to 1.05 kJ/(kg K). Determine the required heat transfer area as a function of the regenerator effectiveness, if the overall heat transfer coefficient is 75 W/(m2 K).
GIVEN
• Counterflow air-to-gas heat exchanger
• Entering temperatures
? Ta,in = 350°C
? Tg,in = 700°C
• Mass flow rates: m a= 5 kg/s
• Specific heats: cpa = cpg = 1.05 kJ/(kg K) = 1050 J/(kg K)
• Overall heat transfer coefficient (U) = 75 W/(m2 K)
FIND
• The heat transfer area (A) as a function of the effectiveness (e)
SKETCH
The force of gravity between two objects:
A) increases with the masses of the bodies, but decreases with their separations. B) increases with the masses of the bodies, but decreases with the square of the distances between them. C) increases with the square of their masses, but decreases with the cube of their periods of orbit about the Sun. D) depends on the density, not the mass of the bodies. E) depends on the temperature, density, and size of the bodies.
What is the Big Bang?
A) An enormous explosion that organized all matter in the universe. B) The creation of matter and the universe. C) The creation of the primeval fireball. D) An explosion that spewed matter all over the universe. E) The event that started the expansion of the universe.
Each second, the burning Sun's mass
A) decreases. B) increases. C) remains unchanged.